STRETCH FORMING

Traditional double action drawing permits a controlled amount of the blank to draw into cavity. In the stretch forming technique, the blank is clamped so tightly all around that it can not draw in. Rather, it is stretched over the punch or lower die and set by the upper die. A lower blank holding-ring is mounted on a nitrogen pressure pad. It maintains a high load (about 100 tons) against the blank and upper ring while traversing downward with the upper ring. It thus prevents the blank from slipping between the draw beads. As shown in Fig. 5.8, the upper blanking ring drops to the lower holding ring, and locks the perimeter of the blank in the draw bead. Thereafter, the ring lower together to a dwell position, stretching the blank over the lower die. At this point, the upper die descends, completing the operation. Stretch forming is being used for automotive panels providing advantages such as 15 to 20% smaller blank size, and elimination of turnover operation after the draw. The better quality results from the uniform stretch over the blank’s entire surface. For example, in conventional stamping of a hood, stretching occurs in the corners but very little, if at all, in the centre area. During stretch forming, measurable deformation occurs over the entire surface.

10

Sheetmetal Forming - Stretch Forming

Stretch forming is a very accurate and

precise method for forming metal shapes,

economically. The level of precision is so

high that even intricate multi-components

and snap-together curtainwall components

can be formed without loss of section

properties or original design function.

Stretch forming capabilities include

portions of circles, ellipses, parabolas and

arched shapes. These shapes can be formed

with straight leg sections at one or both

ends of the curve. This eliminates several

conventional fabrication steps and welding.

The stretch forming process involves stretch forming a metal piece over a male

stretch form block (STFB) using a pneumatic and hydraulic stretch press. Stretch

forming is widely used in producing automotive body panels. Unlike deep

drawing, the sheet is gripped by a blank holder to prevent it from being drawn into

the die. It is important that the sheet can deform by elongation and uniform

thinning.

The variety of shapes and cross sections that can be stretch formed is almost

unlimited. Window systems, skylights, store fronts, signs, flashings, curtainwalls,

walkway enclosures, and hand railings can be accurately and precisely formed to

the desired profiles. Close and consistent tolerances, no surface marring, no

distortion or ripples, and no surface misalignment of complex profiles are

important benefits inherent in stretch forming. A smooth and even surface results

from the stretch forming process.

This process is ideally suited for the manufacture of large parts made from

aluminum, but does just as well with stainless steel and commercially pure

titanium. It is quick, efficient, and has a high degree of repeatability.

Stretch Forming: • Elongation control for unparalleled accuracy and consistency • Bend precision and consistency is excellent with high to medium per–bend cost • Non-symmetric profiles are readily formed without twist • Maximum bend radius is unlimited

• Can bend, twist and lift simultaneously • Minimal surface distortion and traffic marking • Maximum diameter 180° bend at full tonnage = 70” • Minimum diameter 180° bend at full tonnage = 15” • 300” part length capability • Tooling typically is higher than other forming/bending methods • Arms can swing only to 180° • Minimum bend radius is generally 2-3 times greater than other forming/bending methods • Bend radius cannot be modified without additional tooling charge

The bending, shaping, and forming of aluminum is best accomplished with input from our engineers during the design phase of your projects. Alexandria Extrusion Company offers an in-depth aluminum extrusion seminar at your site where we can educate designers and engineers

about aluminum extrusion designing options, alloys and cost drivers. If you have questions or need assistance with your designs, please contact

your sales specialist.

SHEET METAL STAMPING IN AUTOMOTIVE INDUSTRY

STEEL PANELS IN CAR BODY STRUCTURE Ever increasing competition in automotive industry demands productivity improvements and unit cost reduction. The manufacturing engineers and production managers of car body panels are changing their strategy of operation. The days of ‘a simple washer to a very complicated fender, all in plant stamping facility’, are gone. In-house manufacturing facilities preferably produce only limited number of major car panels, Fig. 5.1.

Fig. 5.1 Major Panels of Car Body An automotive plant today produces some 40~50 critical panels per model of car in-house, that require some 100~150 dies.. Criteria for taking decision about the panels to be manufactured in-house vary from company to company. Very lately, the stamping plant of the automobile manufacturers includes the types of panels as given below in-house: 1. External (skin) panels, such as fenders, bonnet, decklid, roof, side panels, doors, etc. Some of these are two panels in a set as left hand and right hand 2. Internal mating panels, such as bonnet inner, decklid inner or door inner deciding subassembly quality

3. Dimensionally critical inner panels that are complicated either because of their complex shape or severe draw condition, such as, floor pans, dash panel, etc. Automanufacturers prefer to procure the medium and small size panels from vendors depending on the availability (nearer facilities are preferred) and their capability to meet demanded specifications. Some are even farming out the major subassemblies such as doors to specialised vendors. Trends are for farming out as much as possible.

MATERIALS FOR BODY PANELS Materials for car body panels require certain specific characteristics to meet the industry’s challenges: rationalisation of specifications for leaner inventory, improved formability for reduced rejection rate and better quality. Higher Strength Low Alloy (HSLA) steels of thinner gauges, are getting preference for weight reduction and the resulting better fuel economy. Other quality characteristics under demand are higher yield stress (strength), toughness, fatigue strength, improved dent resistance as well as corrosion resistance in materials used for body panels for improved durability and reliability. To obtain consistent quality of autobody skin panels without failures during stamping, the formability/ductility specifications of strip steels are the basic requirements. The numerical values of the strain hardening exponent (n-value), the plastic anisotropy (r-value), and the forming limit diagrams for the sheet steels provide the index of formability of the panels. Strain hardening to some extent improves the dent resistance. Strain gradients in pressings are not to be unduly severe causing splitting and other related problems. To maintain the shape after the forming operation, minimal ‘spring back’ and high ‘shape fixability’ are also essential. As the panels are welded to shape the body structure with various arc/resistance welding operations, the weldabilty of the materials in use is very important. Finally, the specific roughness levels (textures) of the steel used for skin panels must be consistent and reproducible. It will be essential for the good adhesion of the various combinations of primers and paints used on autobody pressings to obtain high quality paint finishes (clarity of image and gloss). Most of the steels used in automotive application are aluminium-killed steels of about 0.7 to 0.9 mm thickness. For inner automotive parts, drawing quality steels, such as SPCD (JIS G 3141), A619 (ASTM), CR3 (BS1449), and Sr13 (DIN 1623), while for outer panels requiring deep drawing such as fenders, hoods, oil pans, etc. Non-aging extra deep drawing steels such as SPCEN (JIS G 3141), A620 (ASTM), CR1 (Bs 1449), and St 14 (DIN 1623), are used. Aluminium-killed steels show little or no stretcher strains for a period of time sufficient to eliminate the need for roller-leveling. Thinner High Strength Low Alloy (HSLA) steels are being increasingly used for certain autobody components including skin panels. It must combine its high strength with a good level of formability, as a strength increase is always accompanied by a fall in formability. The

improved bake hardening steels used specially for the external panels possesses sufficiently high formability and provides an increase in strength after the paint baking. A consequence of strength increase obtained during paint baking, is the improved dent resistance of the surface. Difficult autobody pressings of complex geometry have necessitated the use of steel grades with lower strengths too. Vacuum degassed microalloyed steels containing Ti and/or Nb additions are classed as Interstitial-free steels (IF-steels). IF-steels are being used with advantages of extremely high value of maximum drawing ratio, and the absence of the straining effect for difficult-to-form panels. Fig. 5.2 shows panels of High Strength Low Alloy steel, and Table 1 provides a list of special steels for different automobile panels.

Table 5.1 Special Steels for Different Automotive Panels

Steels for Auto Panels

Yield Strength, N/m2

Application conditions

4

A. High Strength Steels REPHOSPHORISED STEELS with additions of P upto 0.08 %

220~260 Autobody structural parts- door, roof, trunklid, hood, pillar outer, rear floor, etc.

GRAIN REFINED STEELS appropriate alloy additions which forms typically NbCN, TiC

300~400 Formability relatively modest, so used for components with relatively less demanding forming

DUAL PHASE STEELS appropriate alloy additions (Mn, Mo, Cr, V) and processing

400~500 High strength, with good formability. Suitable for door, roof, trunklid, hoods, etc.

BAKE HARDENING STEEL

200~250 Slightly stronger, but 40N/m2 strength increase after baking. Suitable for doors, fenders, hoods, pillars.

B. Low Strength Ultra-soft Steel INTERSTITIAL FREE STEEL Ti and/or Nb additions combined with interstitial C and N to form stable TiC, TiN or NbCN precipitates

130~150 For difficult autobody panels of complex geometry. Suitable for automobile outer panels, oil pan, high roof panel, etc.

Laser textured steels, and new coatings such as nickel zinc are ensuring better paint finish and corrosion resistance respectively. Galvanised steel panels that provide better corrosion resistance are used to the extent of about 40% or more in a modern car body. Surface texture and coating provided by steel manufacturers demand stricter quality assurance at stamping stage. Dents and damage caused in stamping requiring repair by grinding or any surface deteriorating methods, may take away the basic advantages of special texturing. Fig. 5.3 shows the typical panels manufactured out of galvanised steels. An intensive research and development are going on for alternate materials, manufacturing processes and stamping tools for sheet-metal components with the main objectives of cutting down the weight and unit cost of the vehicle. Simultaneously, the steel content of the car is falling with the use of aluminium and new materials, such as plastics. Aluminium may provide the most sought after solution to reduce the weight of the vehicles. A reduction of 30% in weight is achievable if the same strength, stiffness, and stability of the component are to be realised by substituting steel with aluminium. Possibility of significant reduction in die cost will be another advantage with aluminium. However, problems related to strength, serviceability, manufacturability, and above all the cost, require effective solutions before the acceptance of aluminium as a substitute to steel for body panels. Plastics for bumpers,

Fig. 5.2 High Strength Low Alloy Steel Panels in a Car Body Fig. 5.3 Galvanised Steel Panels in a Car Body

facia, radiator grilles and even fuel tanks have become almost universally acceptable. Other applications will be commercially possible in years ahead.

Plasma coating of engine block cylinder bores...

Situation

Weight savings in the automotive industry can result in lower fuel

consumption and therefore reduced pollution. Constructive design

measures as well as the right material choice for the engine

blocks create a lighter and cheaper solution in the building of

engines. Less friction and high wear resistance on the cylinder

bore surfaces are required.

The solution

The solution is based on an optimum material selection between

the piston rings and cylinder bores. In a continous process, the

engine blocks are grit blasted, cleaned and plasma sprayed. The

plasma sprayed coatings are thin (140-200 microns), uniform (±

10% of the nominal coating thickness) and smooth (Ra = 8-12

microns). The system is designed for a prototype series and can

spray up to 200 inline four-cylinder engine

blocks per day.

Customer benefits

The plasma coating of the cylinder bores is

able to replace the pressing, shrinking,

casting-in of cylinder sleeves or the use of

expensive, nickel containing galvanic

plating processes. By replacing sleeves the

wall thickness between the individual bores

of the engine blocks can be made much

thinner. This results in a more compact construction, considerable

weight savings and lower production costs of engine blocks.

The potential for lower friction values (compared to cast iron) and

for excellent wear properties of the plasma coating result in the

required life time of the engine blocks.

In some cases the plasma coating is able to replace a galvanic

process, which results in an environmentaly friendly solution

because nickel based materials are no longer being used.

Depending on the coating, finishing costs of the plasma sprayed

coating may be lower because the coating can be honed faster,

and with less wear to the honing tools.

The coating

In cooperation with the customer, a molybdenum based material was developed and supplied by Sulzer Metco which fulfils the requested friction behaviour and wear properties. This results in a coating solution meeting the economics and performance goals set by the customer in this demanding industry. Method for Coating Combustion Engine Cylinders by Plasma Transferred Wire Arc Thermal Spray 1 Background The internal combustion engine generates power by igniting a combustible substance in a closed chamber, with the addition of an oxidizer, and harnessing the resulting expanding gases to push a piston and turn a crankshaft. The piston slides inside a carefully constructed cylinder, which serves as the combustion chamber. The piston is collared by several rings which provide a gas-tight seal

and lubricate the inner surface of the cylinder. Engine blocks have traditionally been made of gray cast-iron because of the ease of casting (due to absence of appreciable volume shrinkage), machinability, wear resistance, and vibrational damping. Recently, engine manufacturers have been going to aluminum to save weight. With aluminum cast engine blocks (now accounting for more than 60% of automotive engines), silicon is usually added to improve uidity during pouring and to increase hardness. The cylinder bore must withstand rapid temperature cycling, repeated shear loading, extreme pressure, and impingement of hot gases, all on the scale of fractions of a second. This demands extremely tight dimensional tolerances and superior wear resistance. For light metal engine blocks, this is traditionally achieved by manufacturing a separate cylinder sleeve, usually made of steel or gray iron. Cylinder liners generally come in two types, wet and dry, characterized by whether or not they directly contact the cylinder coolant. The sleeve can either be press-_t into the engine block or suspended in the cylinder block sand mold prior to pouring (Kuhn 4). Clearly, the melting temperature of the liner material must be well above that of the engine block alloy. 1.1 Sleeveless Cylinders In order to save weight and enhance heat transfer characteristics it is desirable to reduce the thickness of the cylinder lining. In an aluminum engine block, every extra millimeter of cast iron or steel lining adds to the overall weight and reduces fuel economy. Previous attempts at 1 MSE 121 Spring 2010 April 30, 2010 manufacturing a sleeveless cylinder using a nickel-based liner deposited onto an aluminum substrate were employed by BMW and Jaguar. The lining material, known as Nikasil R, has better wear

resistance than aluminum and replaces the heavy cast-iron lining. However, nickel is extremely vulnerable to in_ltration by sulfur. Sulfur readily di_uses down grain boundaries into the nickel matrix and forms brittle nickel sul_des which are extremely susceptible to wear. Sulfur present in low quality fuels led to disastrous wear, and Jaguar and BMW both replaced their Nikasil linings with steel or cast-iron (US Auto Parts). Nikasil continues to be used in smaller engines, or applications where fuel quality is not a concern (Wikipedia). Another approach is to cast the engine from a hypereutectic Al-Si alloy, having greater than 12.6 wt% Si (ASM Handbook). The presence of proeutectic silicon increases wear resistance and hardness while decreasing the thermal expansion coe_cient. However, hypereutectic alloys also su_er from low toughness and di_culty of casting (Jorstad). Addition of graphite increases hardness and wear resistance of Al-Si alloys, but also has a disastrous e_ect on toughness (Gibson, et al.). 1.2 Development of Ford's PTWA Cylinder Lining Process In the early 1990's, Ford began developing an alternative process for coating aluminum cylinders using a plasma spray technique. Ford's R&D team sought to address several problems with previous cylinder manufacturing techniques: _ Weight: Steel or cast-iron liners are signi_cantly denser than their aluminum housing. _ Manufacturing time: Vapor deposition techniques require 10-60 hours (McCune, et al. 3) _ Cost: Cast-in-place methods and oxy-fuel thermal spray coatings are tedious and expensive. _ Wear resistance: Machinable aluminum is too soft for aggressive environments _ Heat transfer: Since gray iron has low thermal conductivity compared to aluminum, a thinner lining is preferred to enhance heat extraction from the cylinder. Throughout the 1990's and early 2000's, Matthew Zaluzec, the chief investigator and Ford's manager

of Materials Science and Nanotechnology, made numerous re_nements to the process (Wojdyla). Through 1997, signi_cant energy was focused on controlling or eliminating oxide formation on both the substrate and the _nished lining (Zaluzec, et al.). From 1998-2001 the team perfected a few more implementation details, including a process to improve evenness, increase deposition rate by controlling gas ow, and protect other engine components during spraying. The re_ned process was used in the 2008 Nissan GT-R and the new 2011 Shelby Mustang GT500 (Goodwin). 2 MSE 121 Spring 2010 April 30, 2010 2 Detailed Description of the PTWA Process The process of applying a thermal spray coating is achieved in several steps. First, the as-cast cylinder surface is bored to a rough diameter. Second, the surface must be cleaned and uxed. Next, a Ni-5Al bonding coat is applied. Then, the surface is coated with a low-carbon steel with highly controlled quantities of FexO wustite using a plasma transferred wire arc process. The part is then inspected for defects and honed to its _nal shape. 2.1 Cleaning and Fluxing After the cylinders are bored to the approximate diameter, the surface is immersed in a 0.5 M potassium-uoride bath. The KF solution etches away the oxide layer and then reacts with the aluminum to form K3AlF6 and KAlF4. If present in a eutectic composition (approx. 45 molar % AlF3) the ux agent will melt well below metallic aluminum (Popoola et al. 8). An initial thermal spray coating of Ni-5Al is applied to the uxed surface to thermally activate the ux (melt the salt and dissolve surface oxides) and e_ect a metallurgical bond to the aluminum surface. Aluminum is readily soluble in nickel up to quantities of 10 wt% without forming intermetallic phases (ASM Handbook). Ford initially experimented with feeding a ux-cored wire of

similar composition as mentioned above directly into the plasma spray apparatus described below. They eventually abandoned this idea due to its cost and complexity. Several other roughing and preparation methods were compared by engineers at Flame-Spray and Ford including water-jet roughing, grit blasting, and laser roughing. Water-jet roughing was found to damage the aluminum substrate leaving surface pores even after coating. Grit blasting was abandoned due to concerns of industrial contamination (E. Lugscheider, et al. 5). (a) Comparison of bond strengths for di_erent surface preparations (b) Microstructural damage due to water-jet roughening Figure 1 3 MSE 121 Spring 2010 April 30, 2010 2.2 Application of Final Coat Once the ux and bonding agent have been applied, the _nal composite coating is applied via plasma transferred wire arc thermal spraying to a thickness of less than a milimeter. A 0.1 wt% C low carbon steel wire is continuously fed into the nozzle apparatus and deposited on the cylinder wall. Immediately after application, a thermal imaging camera inspects the temperature pro_le due to the heat of application of the plasam spray. The system looks for hot spots that may indicate a defect. 2.3 Post Processing and Finishing After coating, the bore is honed to its _nal size and _nish. First, a course grained honing stone is passed through, to remove any large deviations or rough patches. Next, "large" volume of the material is removed, exposing micorpores, enabling oil retention for lubrication (Schwenk, et al. 7). As sprayed, the typical thickness is in the range of 120-250 _m, which is reduced down to the _nal

thickness of 70-170 _m (Barbezat 50). Finally, a _nishing pass is completed by a _ne grained stone or a diamond tipped tool to the _nal _nished surface (Schwenk, et al. 7). The diamond honing can achieve a surface roughness of Ra less than 0.3 _m (Barbezat 49). 3 PTWA Apparatus Plasma spray techniques generally operate by striking an electric arc in an inert gas and then using the extreme temperature, high velocity plasma stream caused by the rapid expansion of the gas to atomize and accelerate a feedstock of some kind towards a target. The feedstock may be a powder or wire, and may even include uxing agents in the wire itself or mixed in with the powder. In Ford's patented PTWA process, an arc is _rst struck from a tungsten cathode (described in detail in US patent 6,559,407) to the copper nozzle, acting as the anode. The arc is maintained with a 100-120V DC power source supplying 60-100 amps, and then "transferred" to the wire feedstock, which is negatively biased to provide a conducting path for the arc. The wire is fed perpendicular to the direction of spraying. The ionizing gas is fed through radial ports in the cathode assembly to produce a vortex. A secondary high velocity gas with carefully controlled oxygen content is introduced just beyond where the plasma stream intersects the wire arc. 4 MSE 121 Spring 2010 April 30, 2010

4 Thermal Coat Microstructure The rotational velocity of the gas vortex described above was shown to have a strong e_ect on particle size, with higher velocities corresponding to a _ner mist (Kim, et al.). Presumably, this results in a _ner grain structure resulting in increased hardness. The _nal coat can be controlled to have porosity less than 2%. The characteristic "splat morphology" resulting from high-velocity impact of spherical globules is apparent in Figure 3 (a). Gas atomization of the advancing wire produces predictably spherical molten globules, for which the surface area to volume ratio can be readily predicted (Beddoes and Bibby 176). Additionally, the feasibility of predicting oxygen content in a plasma arc torch with secondary shielding gas

shroud using computational uid dynamics in a simpli_ed geometry was demonstrated by Jamais, et al. Under these conditions, the molten iron forms a surface layer of wustite, FexO mid-ight, with x ranging from 0.5 to 1.5, mid-ight. The oxygen content can be carefully controlled during deposition to obtain a composition gradient between 10% and 30% wustite, with an oxide-rich region below and an oxide-depleted, easily machinable layer at the top (Zaluzec, et al. 6). Wustite is almost 70% harder than the steel matrix it inhabits (Bobzin, et al. 5). Among traditional liner materials, hardness generally correlates positively with wear resistance. Among thermal spray coatings, on the other hand, oxide content may be a more signi_cant factor in wear resistance (Hart_eld-W• unsch and Tung 23). Although independent test results for wustite-rich surfaces is lacking, it has been found that the presence of Fe2O3 in plasma sprayed coatings greatly improves wear resistance (Kleyman, et al. 139). Wustite easily shears along the f001g plane (principle cube faces shown in Figure 3 (b)) and acts as a solid lubricant. 5 MSE 121 Spring 2010 April 30, 2010 (a) Cross section of cylinder lining showing aluminum sub- strate, steel matrix, and iron oxide (b) Cubic wustite crystal. Figure 3 5 Performance of PTWA lined engines Ford constructed a 32 vehicle eet to run at 9 di_erent North American locales (with varied driving and weather conditions) The eet accumulated well over 3 million total miles - including several vehicles driving over 250,000 miles. In the laboratory, Ford also conducted numerous dynamometer tests, including a 2000+ hour endurance test. After these millions of miles and thousands of hours of testing, the PTWA process proved to be a success and had measurable e_ects on engine

performance. At large, PTWA coated engines boast improved mileage, as well as reduced wear, weight, and cost compared to their cast-iron lined counterparts. As a consequence of the wustite acting as a solid lubricant, friction is greatly reduced | on average 6.8% below the values of traditional cast iron liners and 14.1% below cast-iron engines (Milliken). This aspect alone allows an overall 4% potential reduction of fuel expenditure (assuming 40% of mechanical power lost in piston/cylinder component and a thermodynamic e_ciency of 35%). Plasma spray lined engines measured half the amount of wear of iron linings in a 300 hour full power endurance test (Barbezat 141). The reduced wear can be contributed to several things. First, the presence of FeO increases the microhardness of the coating, which reduces friction by decreasing the amount of plastic deformation between contacting surfaces (Cook, et al.). Additionally, after subsequent machining, the smooth surface with microcavities (from the exposed 2% porosity) allows for oil retention providing excellent lubrication conditions (Barbezat 2031). The cost savings are equally attractive. The wire feedstock itself costs about $0.50 to $0.75 per pound (Cook, et al.). It is estimated that the process, on average, saves $.50 to $1.50 per bore for a cost of $2 to $4 USD when scaled to high production volumes (Barbezat 141). Due to the high deposition e_ciency (over 80%) and high feed rates, the entire process can be completed in under 6 MSE 121 Spring 2010 April 30, 2010 60 seconds making mass-production feasible via this process feasible. Automakers are targeting weight reduction as their main strategy to improve fuel economy. The reduced mass of the PTWA coatings o_ers a reduction in weight of 6 to 8 pounds (Wojdyla). In fact, coupled with the transition from a cast-iron engine block to aluminum, the 2011 GT500

reduced the engine weight by a total of 102 pounds, noticeably improving overall fuel economy. Due to the high energy and CO2 investment required to cast new engine blocks, recycling and reuse of old engine blocks is becoming increasingly attractive. As engine blocks have reduced in size (thus shrinking space between bores), oversize boring of original lining and subsequent re-lining is no longer a possibility. Without PTWA process, the majority of these engine blocks would be scrapped. However, remanufacturing engine blocks with the PTWA process allows for a 50%-80% total manufacturing energy saving as well as a 25-50% cost savings over re-manufacture (Schwenk, et al. 1-3) 6 Conclusions In 2009, the engineers who perfected the PTWA deposition technique received the National Inventor of the Year Award. In presenting the award, the Intellectual Property Owners Education Foundation cited the energy savings and possible environmental impact of the process. The process has already proven itself worthy through extensive testing and market adoption. Researchers at General Motors are investigating a similar process. Engineers from Flame-Spray Industries, Land Rover, Jaguar Cars, and Caterpillar presented a joint paper at the 2007 ASME Internal Combustion Engine conference touting the bene_ts of thermal spray coatings and urging exploration of further applications. It is almost certain that thermal spray coatings will become an industry standard in automotive applications in the very near future.

ICSP9 : SHOT PEENING SHOT PEENING OF GEAR COMPONENTS FOR THE AUTOMOTIVE INDUSTRY ABSTRACT Shot peening using blast wheels offers a high level of flexibility and process r especially for larger series and larger workpieces. This paper describes shot solutions for bevel gears and crown wheels for the automotive industry at BMW, Dingolfing. The significance of shot peening trials to determine the optimum solution is outlined and solutions found - satellite shot peening systems - are presented. The influence of a proper working dust removal plant and separation system on shot peening results are shown, importance and control of process reliability are outlined. SUBJECT INDEX 1) Shot peening with blast wheels 2) Automotive gear parts 3) The significance of blast trials 4) The machine concepts, automatic handling 5) Dust removal and separation system 6) Process reliability

SHOT PEENING USING BLAST WHEELS Shot peening by means of the air blasting method is generally known. In the current technology of surface treatment, shot peening with blast wheels has become widely accepted as a reliable and economic processing method. The fields of application are thus accordingly diverse. Blast wheel systems offer a high level of flexibility and process reliability and can be applied for controlled treatment of a wide range of workpieces, especially larger series and parts. Shot peening is principally suitable for parts which are subjected to bending or alternating torsional stress. 1 Throwing blade 2 Shot opening 3 Control cage 4 Accelerator (impeller)

APPLICATIONS SHOT PEENING GEAR PARTS FOR THE AUTOMOTIVE INDUSTRY Shot peening leads to significant improvements of the mechanical properties of workpieces and serves to extend the stress-load limit of components or permits design of lighter weight parts. At the Dingolfing plant near Munich, BMW is manufacturing all gear components for passenger cars and motorbikes. Production can be both - single and mixed product runs (parts for passenger cars and motor bikes). After hardening and annealing, all gear parts are shot peened to increase vibration strength and resistance against stress cracks and vibration crack corrosion. Requirements are to a certain extent complex: On one hand root and tooth flanks of the parts have to be shot peened, with other areas only requiring descaling or deburring. Following part families are processed: BEVEL GEARS Dimensions: min. height 160 mm; max. height 220 mm; max. unit weight 3.5 kg Requirements: Shot peening of the tooth flanks to 0.28 - 0.32 mm Almen A with a coverage of > 98 %, cleaning resp. removal of the cover paste on the thread without impairing the thread function; descaling the remaining parts. An excessive increase in hardness at the shaft must be prevented. For certain types of bevel gears, it is necessary to additionally ensure that the tip surface is not hardened, which means

that the tooth flanks also have to be shot peened whereas further areas and the untempered head parts, in particular the centre where the parts are clamped into position for concentricity measurements, must not be shot peened. CROWN WHEELS Dimensions: max. diameter 240 mm; max. height 42 mm; max. unit weight 4 kg Requirements: Shot peening of tooth flanks to 0.28 - 0.32 mrn Almen A with a coverage of > 98 % and descaling of the remaining parts. Further requirements and specifications for both part families are as follows:

Abrasive of the size S230 (hardness 46-52 HRC) is used for all parts.

Crown wheels have to he shot peened individually (d 2), pair-wise (fig. 31, or making special carrier facilities nece ary. Production status:

s are working in 3-shift oper

tion process. In this specific ng and shot peening. In the prime importance that tole44 ICSP9 : SHOT PEENING rances for Almen values are always complied with to guarantee running smoothness of the gear. If the programmed Almen values are under-run, excessive material is removed during lapping, and if the values are exceeded a reduced amount of material is removed. This would either lead to raised noise emission of the vehicle gearbox or result in an inhomogeneous tooth contact pattern. Running smoothness is evaluated in a special test whereby the tolerance zone is between 7 and 10 on a scale of 10 units. It is therefore essentially important to ensure that the given Almen values are observed explicitly.

THE RELEVANCE OF SHOT PEENING TRIALS To meet these requirements, extensive shot peening trials were performed on a laboratory machine using the customer's workpieces at the DlSA Test Centre in Schaffhausen I Switzerland. In these tests the aim was to determine the position of the blast wheel (angle) as well as blasting intensity, abrasive quantity and blasting time. The shot peening programmes were to be tailored to the specific production process required and the process reliability was to be guaranteed. The information derived from such tests indicates that this task can be optimally solved with a satellite shot peening system, Due to the test results the machine construction was adapted to the customer's requirements and thus to the specific applications. With SRS Shot Peening Systems, bevel gears and crown wheels, wheel hubs, gear shafis and similar components, as well as cup springs and clutch springs are shot peened in cycled rotary operation. In this case 45 speed-controlled satellites, integrated into an indexing tmrntable carry "Ehe wsrkpreces through the system in

AUTOMATIC HANDLING The excellent performance of the first two machines led BMW to investigate the possibility of using a third systems including automatic handling for large-series production runs (monocultures) in fully automatic operation in an autonomous manufacturing cell. In this application (fig 5) robots are responsible for automatic feeding and unloading. The profitability can be additionally enhanced considerably by reducing staff costs and increasing the output. The cell functions are: Fully automatic loading and unloading the workpiece pallets Shot peening Aligning Inductive starting (threaded pins) Grinding (front surfaces of thread) Ball callipers (for surveying the tooth gaps) Loading procedure: The robot gripper retrieves the workpiece from a pallet, grasping the bevel drive pinion by its shaft, and then swivels to place the component into a central position above the fixture on the satellite table. A further gripper device, activated by a pneumatic cylinder, descends vertically to secure the pinion by its toothed head. The robot then releases and retracts. The gripper subsequently lowers the workpiece into the fixture and then moves upwards, back to its original position. Unloading then takes place as follows: After the machine table has indexed one position, bringing a processed component into view, the gripper device moves downwards. It grasps the gear drive-pinion and raises it sufficiently for the robot to move in and secure the component. At this point, the gripper releases its grasp,

allowing the robot to withdraw the part from the table and place it in a further pallet. Figure 5: DlSA Satellite Shot Peening System integrated in manufacturing cell

46 ICSP9 : SHOT PEENING Cell solutions require clear interfaces and clearly defined processes to the following functions. The modularity and flexibility of the systems is a further key criterion allowing adaptations to be made at short notice if there is a change in process steps. Cell solutions also permit a drastically improved exploitation of the production area For all applications, the shot peening programs themselves are assigned to the respective part families, ensuring that the given parameters are used in operation

and that process reliability is guaranteed. The individual programs are activated via the appropriate settings at the operator's panel. DUST REMOVAL AND SHOT RECONDITIONING SYSTEM A dust separation system (we principally recommend our customers to use separate filters for each individual shot peening system) with a capacity of 5,000 Nm31h is incorporated, allowing the function of the pneumatic separator to be optimally adjusted by suction-cleaning the system. The separator fulfils the following functions: Separating and discharging scale and dust from the abrasive e Eliminating abrasive particles which are unfit for the shot peening operation As the life of the wear parts depends primarily on the degree of purity of the abrasive, the following is applicable: e The better the separator, the higher its profitability The purer the abrasive, the cleaner and more dust-free the workpieces will be. Besides the wear and tear issue, the abrasive consistency in distribution of grain abrasive size - in particular in shot peening - is the key criterion in terms of qualityoriented manufacturing. Losses in quality or insufficient shot peening results (surface hardening) can thus be excluded. New shot is automatically fed into the cycle via an electronically controlled replenisher. In shot peening process reliability is the dec e blasting intensity can Due is the fact that

t sizes and distribution) are defmed exactly, it 1s possible to adjust and examine the Almen intensity and APPLICATIONS 4 7 coverage. The process reliability is supervised in periodic intervals and must be guaranteed at all times.

CONCLUSION We would once again like to underline that the requirements in terms of a shot peening solution in comparison with the more familiar blast cleaning applications, e.g. for cleaning workpieces in foundries and in forges, are highly complicated. The machine manufacturer therefore plays a decisive role in designing the system and has to make available the appropriate know-how.

Shot Peen Forming

Material Temperature [°C (°F)]

Magnesium 350-450 (650-850)

Aluminium 350-500 (650-900)

Copper 600-1100 (1200-2000)

Steel 1200-1300 (2200–2400)

Titanium 700-1200 (1300-2100)

Nickel 1000-1200 (1900–2200)

Refractory alloys up to 2000 (4000)

Shot peen forming is a dieless process performed at room temperature, whereby small round steel shot impact the surface of the work piece. Every piece of shot acts as a tiny peening hammer, producing elastic stretching of the upper surface and local plastic deformation that manifests itself as a residual compressive stress. The combination of elastic stretching and compressive stress generation causes the material to develop a compound, convex curvature on the peened side.

The shot peen forming process is ideal for forming large panel shapes where the bend radii are reasonably large and without abrupt changes in contour. Shot peen forming is best suited for forming curvatures where radii are within the metal's elastic range. Although no dies are required for shot peen forming, for severe forming applications, stress peen fixtures are sometimes used. Shot peen forming is effective on all metals, even honeycomb skins and ISO grid panels.

Shot peen forming is often more effective in developing curvatures than rolling, stretching or twisting of metal. Saddle-back shapes also are achievable. Because it is a dieless process, shot peen forming reduces material allowance from trimming and eliminates costly development and manufacturing time to fabricate hard dies. The shot peen forming process also is flexible to design changes, which may occur after initial design. Metal Improvement Company can make curvature changes by adjusting the shot peen forming process.

Parts formed by shot peen forming exhibit increased resistance to flexural bending fatigue. Unlike most other forming methods, all surface stresses generated by shot peen forming are of a compressive nature. Although shot peen formed pieces usually require shot peening on one side only, the result causes both sides to have compressive stress. These compressive stresses serve to inhibit stress corrosion cracking and to improve fatigue resistance. Some work pieces should be shot peened all over prior to or after shot peen forming to further improve fatigue and stress corrosion cracking resistance.

Shot peening of parts that have been cold formed by other processes overcomes the harmful surface tensile stresses set up by these other forming processes.

Shot peening is a cold working process in which small spherical media called shot bombard the surface of a part. During the shot peening process, each piece of shot that strikes the material acts as a tiny peening hammer, imparting to the surface a small indentation or dimple. To create the dimple, the surface of the material must yield in tension. Below the surface, the material tries to restore its original shape, thereby producing below the dimple, a hemisphere of cold-worked material highly stressed in compression.

Nearly all fatigue and stress corrosion failures originate at the surface of a part, but cracks will not initiate or propagate in a compressively stressed zone. Because the overlapping dimples from shot peening create a uniform layer of compressive stress at metal surfaces, shot peening provides considerable increases in part life. Compressive stresses are beneficial in increasing resistance to fatigue failures, corrosion fatigue, stress corrosion cracking, hydrogen assisted cracking, fretting, galling and erosion caused by cavitation. The maximum compressive residual stress produced just below the surface of a part by shot peening is at least as great as one-half the yield strength of the material being shot peened.

In most modes of long-term failure, the common denominator is tensile stress. Tensile stresses attempt to stretch or pull the surface apart and may eventually lead to crack initiation. Because crack growth is slowed significantly in a compressive layer, increasing the depth of this layer increases crack resistance. Shot peening is the most economical and practical method of ensuring surface residual compressive stresses. For applications that require deeper residual compressive stresses than those provided by shot peening, Metal Improvement Company's laser peening process imparts a layer of beneficial compressive stress that is four times deeper than that attainable from conventional shot peening treatments.

Shot peening also can induce the aerodynamic curvature in metallic wing skins used in advanced aircraft designs. Additional applications for shot peening include work hardening through cold work to improve wear characteristics, closing of porosity, improving resistance to intergranular corrosion, straightening of distorted parts, surface texturing and testing the bond strength of coatings.

Metal Improvement Company engineering specialists can help you best address the fatigue, forming and distortion correction challenges that manufacturers of fabricated metal parts face every day. Metal Improvement Company's shot peening facilities employ the latest state-of-the-art processing capabilities for shot peening

components of diverse shapes, sizes and materials under rigidly controlled conditions.

Metal Improvement facilities are capable of meeting most industry standard shot peening specifications, including:

AMS-S-13165

BAC-5730

PWA-6

RPS-428

AMS 2430

AMS 2432

J2441

MIL-S-

13165C

ABP 1-2028

MIL-P

81985(AS)

MIL-STD-852

P11TF3

EXTRUSION

Extrusion is a process used to create objects of a fixed cross-sectional profile. A material is

pushed or drawn through a die of the desired cross-section. The two main advantages of

this process over other manufacturing processes are its ability to create very complex cross-

sections and work materials that are brittle, because the material only encounters

compressive and shear stresses. It also forms finished parts with an excellent surface

finish.[1]

Extrusion may be continuous (theoretically producing indefinitely long material) or semi-

continuous (producing many pieces). The extrusion process can be done with the material

hot or cold.

Commonly extruded materials include metals, polymers, ceramics, concrete and foodstuffs.

Hollow cavities within extruded material cannot be produced using a simple flat extrusion

die, because there would be no way to support the center barrier of the die. Instead, the die

assumes the shape of a block with depth, beginning first with a shape profile that supports

the center section. The die shape then internally changes along its length into the final

shape, with the suspended center pieces supported from the back of the die.

Process

Extrusion of a round blank through a die.

The process begins by heating the stock material (for hot or warm extrusion). It is then

loaded into the container in the press. A dummy block is placed behind it where the ram

then presses on the material to push it out of the die. Afterward the extrusion is stretched in

order to straighten it. If better properties are required then it may be heat treated or cold

worked.[2]

The extrusion ratio is defined as the starting cross-sectional area divided by the cross-

sectional area of the final extrusion. One of the main advantages of the extrusion process is

that this ratio can be very large while still producing quality parts.

edit] Hot extrusion

Hot extrusion is a hot working process, which means it is done above the material's

recrystallization temperature to keep the material from work hardening and to make it

easier to push the material through the die. Most hot extrusions are done on horizontal

hydraulic presses that range from 230 to 11,000 metric tons (250 to 12,000 short tons).

Pressures range from 30 to 700 MPa (4,400 to 100,000 psi), therefore lubrication is

required, which can be oil or graphite for lower temperature extrusions, or glass powder for

higher temperature extrusions. The biggest disadvantage of this process is its cost for

machinery and its upkeep.[1]

[edit] Metal

Metals that are commonly extruded include:[9]

Aluminium is the most commonly extruded material. Aluminium can be hot

or cold extruded. If it is hot extruded it is heated to 575 to 1100 °F (300 to

600 °C). Examples of products include profiles for tracks, frames, rails,

mullions, and heat sinks.

Copper (1100 to 1825 °F (600 to 1000 °C)) pipe, wire, rods, bars, tubes, and

welding electrodes. Often more than 100 ksi (690 MPa) is required to

extrude copper.

Lead and tin (maximum 575 °F (300 °C)) pipes, wire, tubes, and cable

sheathing. Molten lead may also be used in place of billets on vertical

extrusion presses.

Magnesium (575 to 1100 °F (300 to 600 °C)) aircraft parts and nuclear

industry parts. Magnesium is about as extrudable as aluminum.

Zinc (400 to 650 °F (200 to 350 °C)) rods, bar, tubes, hardware components,

fitting, and handrails.

Steel (1825 to 2375 °F (1000 to 1300 °C)) rods and tracks. Usually plain

carbon steel is extruded, but alloy steel and stainless steel can also be

extruded.

Titanium (1100 to 1825 °F (600 to 1000 °C)) aircraft components including

seat tracks, engine rings, and other structural parts.

Magnesium and aluminium alloys usually have a 0.75 µm (30 μin) RMS or better

surface finish. Titanium and steel can achieve a 3 micrometres (120 μin) RMS.[1]

In 1950, Ugine Séjournet, of France, invented a process which uses glass as a

lubricant for extruding steel.[10]

The Ugine-Sejournet, or Sejournet, process is now

used for other materials that have melting temperatures higher than steel or that

require a narrow range of temperatures to extrude. The process starts by heating

the materials to the extruding temperature and then rolling it in glass powder. The

glass melts and forms a thin film, 20 to 30 mils (0.5 to 0.75 mm), in order to

separate it from chamber walls and allow it to act as a lubricant. A thick solid glass

ring that is 0.25 to 0.75 in (6 to 18 mm) thick is placed in the chamber on the die to

lubricate the extrusion as it is forced through the die. A second advantage of this

glass ring is its ability to insulate the heat of the billet from the die. The extrusion

will have a 1 mil thick layer of glass, which can be easily removed once it cools.[3]

Another breakthrough in lubrication is the use of phosphate coatings. With this

process, in conjunction with glass lubrication, steel can be cold extruded. The

phosphate coat absorbs the liquid glass to offer even better lubricating properties.[3]

[edit] Plastic

Sectional view of a plastic extruder showing the components

Main article: Plastics extrusion

Plastics extrusion commonly uses plastic chips or pellets, which are usually dried

in a hopper before going to the feed screw. The polymer resin is heated to molten

state by a combination of heating elements and shear heating from the extrusion

screw. The screw forces the resin through a die, forming the resin into the desired

shape. The extrudate is cooled and solidified as it is pulled through the die or water

tank. In some cases (such as fibre-reinforced tubes) the extrudate is pulled through

a very long die, in a process called pultrusion.

A multitude of polymers are used in the production of plastic tubing, pipes, rods,

rails, seals, and sheets or films.

[edit] Ceramic

Ceramic can also be formed into shapes via extrusion. Terracotta extrusion is used

to produce pipes. Many modern bricks are also manufactured using a brick

extrusion process.[11]

Extrusion is the process by which long straight metal parts can

be produced. The cross-sections that can be produced vary from solid round, rectangular, to L shapes, T shapes. Tubes and many other different types. Extrusion is done by squeezing metal in a closed cavity through a tool, known as a die using either a mechanical or hydraulic press.

Extrusion produces compressive and shear forces in the stock. No tensile is produced, which makes high deformation possible without tearing the metal. The cavity in which the raw material is

contained is lined with a wear resistant material. This can withstand the high radial loads that are created when the material is pushed the die.

Extrusions, often minimize the need for secondary machining, but are not of the same dimensional accuracy or surface finish as machined parts. Surface finish for steel is 3 µm; (125 µ in), and Aluminum and Magnesium is 0.8 µm (30 µ in). However, this process can produce a wide variety of cross-sections that are

hard to produce cost-effectively using other methods. Minimum thickness of steel is about 3 mm (0.120 in), whereas Aluminum and Magnesium is about 1mm (0.040 in). Minimum cross sections

are 250 mm2 (0.4 in2) for steel and less than that for Aluminum and Magnesium. Minimum corner and fillet radii are 0.4 mm (0.015 in) for Aluminum and Magnesium, and for steel, the minimum corner radius is 0.8mm(0.030 in) and 4 mm (0.120 in) fillet radius.

Cold Extrusion: Cold extrusion is the process done at room temperature or slightly elevated temperatures. This process can be used for most materials-subject to designing robust enough

tooling that can withstand the stresses created by extrusion. Examples of the metals that can be extruded are lead, tin, aluminum alloys, copper, titanium, molybdenum, vanadium, steel. Examples of parts that are cold extruded are collapsible tubes, aluminum cans, cylinders, gear blanks. The advantages of cold extrusion are:

• No oxidation takes place.

• Good mechanical properties due to severe cold working as long as the temperatures created are below the re-crystallization temperature.

• Good surface finish with the use of proper lubricants.

Hot Extrusion: Hot extrusion is done at fairly high temperatures, approximately 50 to 75 % of the melting point of the metal. The pressures can range from 35-700 MPa (5076 -

101,525 psi). Due to the high temperatures and pressures and its detrimental effect on the die life as well as other components, good lubrication is necessary. Oil and graphite work at lower

temperatures, whereas at higher temperatures glass powder is used.

Typical parts produced by extrusions are trim parts used in automotive and construction applications, window frame members, railings, aircraft structural parts Extrusion is the process by which long straight metal parts can be produced. The cross-sections that can be produced vary from solid round, rectangular, to L shapes, T shapes.

Tubes and many other different types. Extrusion is done by squeezing metal in a closed cavity through a tool, known as a die using either a mechanical or hydraulic press.

Extrusion produces compressive and shear forces in the stock. No tensile is produced, which makes high deformation possible without tearing the metal. The cavity in which the raw material is contained is lined with a wear resistant material. This can withstand the high radial loads

that are created when the material is pushed the die.

Extrusions, often minimize the need for secondary machining, but are not of the same dimensional accuracy or surface finish as machined parts. Surface finish for steel is 3 µm; (125 µ in), and Aluminum and Magnesium is 0.8 µm (30 µ in). However, this process can produce a wide variety of cross-sections that are hard to produce cost-effectively using other methods. Minimum thickness of

steel is about 3 mm (0.120 in), whereas Aluminum and Magnesium is about 1mm (0.040 in). Minimum cross sections are 250 mm2 (0.4 in2) for steel and less than that for Aluminum and Magnesium. Minimum corner and fillet radii are 0.4 mm (0.015 in) for Aluminum and Magnesium, and for steel, the minimum corner radius is 0.8mm(0.030 in) and 4 mm (0.120 in) fillet radius.

Cold Extrusion: Cold extrusion is the process done at room temperature or slightly elevated temperatures. This process can be used for most materials-subject to designing robust enough tooling that can withstand the stresses created by extrusion. Examples of the metals that can be extruded are lead, tin, aluminum alloys, copper, titanium, molybdenum, vanadium, steel. Examples of parts that are cold extruded are collapsible tubes, aluminum

cans, cylinders, gear blanks. The advantages of cold extrusion are:

• No oxidation takes place.

• Good mechanical properties due to severe cold working as long as the temperatures created are below the re-crystallization temperature.

• Good surface finish with the use of proper lubricants.

Hot Extrusion: Hot extrusion is done at fairly high temperatures, approximately 50 to 75 % of the melting point of the metal. The pressures can range from 35-700 MPa (5076 - 101,525 psi). Due to the high temperatures and pressures and its detrimental effect on the die life as well as other components, good lubrication is necessary. Oil and graphite work at lower temperatures, whereas at higher temperatures glass powder is used.

Typical parts produced by extrusions are trim parts used in automotive and construction applications, window frame

members, railings, aircraft structural parts

Extrusion press is a sophisticated machinery in the extrusion process that is available in a huge variety of sizes ranging from 400 tonnes to 1600 tonnes. From the common large extruded profiles to thin-wall extruded profiles, extrusion presses are geared to meet virtually any demand of the extrusion industry. Modern extrusion presses are equipped with all the latest technology and innovative features, for example the infinitely variable extrusion speeds, PLC control, reducing an operator's need etc. It is the press size that determines the size of an extrusion, and therefore the selection of a proper extrusion press is of critical importance in the extrusion process. discussed.

Aluminium Extrusion Press

To be in a position to understand an aluminium extrusion press completely and thoroughly, we need a basic understanding of what are the main parts of an extrusion press, what do they look like, what functions do they perform, etc. Going through the diagram below would be helpful in understanding the aluminium extrusion process step by step in detail.

[edit] Hot extrusion

Hot extrusion is a hot working process, which means it is done above the material's

recrystallization temperature to keep the material from work hardening and to

make it easier to push the material through the die. Most hot extrusions are done on

horizontal hydraulic presses that range from 230 to 11,000 metric tons (250 to

12,000 short tons). Pressures range from 30 to 700 MPa (4,400 to 100,000 psi),

therefore lubrication is required, which can be oil or graphite for lower temperature

extrusions, or glass powder for higher temperature extrusions. The biggest

disadvantage of this process is its cost for machinery and its upkeep.[1]

Hot extrusion temperature for various metals[1]

Material Temperature [°C (°F)]

Magnesium 350-450 (650-850)

Aluminium 350-500 (650-900)

Copper 600-1100 (1200-2000)

Steel 1200-1300 (2200–2400)

Titanium 700-1200 (1300-2100)

Nickel 1000-1200 (1900–2200)

Refractory alloys up to 2000 (4000)

The extrusion process is generally economical when producing between several

kilograms (pounds) and many tons, depending on the material being extruded.

There is a crossover point where roll forming becomes more economical. For

instance, some steels become more economical to roll if producing more than

20,000 kg (50,000 lb).[2]

Aluminium hot extrusion die

Front side of a four family die. For reference, the die is 228 mm (9.0 in) in

diameter.

Close up of the shape cut into the die. Notice that the walls are drafted and

that the back wall thickness varies.

Back side of die. The wall thickness of the extrusion is 3 mm (0.12 in).

[edit] Cold extrusion

Cold extrusion is done at room temperature or near room temperature. The

advantages of this over hot extrusion are the lack of oxidation, higher strength due

to cold working, closer tolerances, good surface finish, and fast extrusion speeds if

the material is subject to hot shortness.[1]

Materials that are commonly cold extruded include: lead, tin, aluminum, copper,

zirconium, titanium, molybdenum, beryllium, vanadium, niobium, and steel.

Examples of products produced by this process are: collapsible tubes, fire

extinguisher cases, shock absorber cylinders, automotive pistons, and gear blanks.

[edit] Warm extrusion

Warm extrusion is done above room temperature, but below the recrystallization

temperature of the material the temperatures ranges from 800 to 1800 °F (424 to

975 °C). It is usually used to achieve the proper balance of required forces,

ductility and final extrusion properties.[3]

[edit] Equipment

A horizontal hydraulic press for hot aluminum extrusion (loose dies and scrap

visible in foreground)

There are many different variations of extrusion equipment. They vary by four

major characteristics:[1]

1. Movement of the extrusion with relation to the ram. If the die is held stationary and the ram moves towards it then its called "direct extrusion". If the ram is held stationary and the die moves towards the ram its called "indirect extrusion".

2. The position of the press, either vertical or horizontal. 3. The type of drive, either hydraulic or mechanical. 4. The type of load applied, either conventional (variable) or hydrostatic.

A single or twin screw auger, powered by an electric motor, or a ram, driven by

hydraulic pressure (often used for steel and titanium alloys), oil pressure (for

aluminum), or in other specialized processes such as rollers inside a perforated

drum for the production of many simultaneous streams of material.

Typical extrusion presses cost more than $100,000, whereas dies can cost up to

$2000.

[edit] Forming internal cavities

Two-piece aluminum extrusion die set (parts shown separated.) The male part (at

right) is for forming the internal cavity in the resulting round tube extrusion.

There are several methods for forming internal cavities in extrusions. One way is

to use a hollow billet and then use a fixed or floating mandrel. A fixed mandrel,

also known as a German type, means it is integrated into the dummy block and

stem. A floating mandrel, also known as a French type, floats in slots in the

dummy block and aligns itself in the die when extruding. If a solid billet is used as

the feed material then it must first be pierced by the mandrel before extruding

through the die. A special press is used in order to control the mandrel

independently from the ram.[1]

The solid billet could also be used with a spider die,

porthole die or bridge die. All of these types of dies incorporate the mandrel in the

die and have "legs" that hold the mandrel in place. During extrusion the metal

divides and flows around the legs, leaving weld lines in the final product.[4]

[edit] Direct extrusion

Plot of forces required by various extrusion processes.

Direct extrusion, also known as forward extrusion, is the most common extrusion

process. It works by placing the billet in a heavy walled container. The billet is

pushed through the die by a ram or screw. There is a reusable dummy block

between the ram and the billet to keep them separated. The major disadvantage of

this process is that the force required to extrude the billet is greater than that need

in the indirect extrusion process because of the frictional forces introduced by the

need for the billet to travel the entire length of the container. Because of this the

greatest force required is at the beginning of process and slowly decreases as the

billet is used up. At the end of the billet the force greatly increases because the

billet is thin and the material must flow radially to exit the die. The end of the billet

(called the butt end) is not used for this reason.[5]

[edit] Indirect extrusion

In indirect extrusion, also known as backwards extrusion, the billet and container

move together while the die is stationary. The die is held in place by a "stem"

which has to be longer than the container length. The maximum length of the

extrusion is ultimately dictated by the column strength of the stem. Because the

billet moves with the container the frictional forces are eliminated. This leads to

the following advantages:[6]

A 25 to 30% reduction of friction, which allows for extruding larger billets, increasing speed, and an increased ability to extrude smaller cross-sections

There is less of a tendency for extrusions to crack because there is no heat formed from friction

The container liner will last longer due to less wear The billet is used more uniformly so extrusion defects and coarse grained

peripherals zones are less likely.

The disadvantages are:[6]

Impurities and defects on the surface of the billet affect the surface of the extrusion. These defects ruin the piece if it needs to be anodized or the aesthetics are important. In order to get around this the billets may be wire brushed, machined or chemically cleaned before being used.

This process isn't as versatile as direct extrusions because the cross-sectional area is limited by the maximum size of the stem.

[edit] Hydrostatic extrusion

In the hydrostatic extrusion process the billet is completely surrounded by a

pressurized liquid, except where the billet contacts the die. This process can be

done hot, warm, or cold, however the temperature is limited by the stability of the

fluid used. The process must be carried out in a sealed cylinder to contain the

hydrostatic medium. The fluid can be pressurized two ways:[6]

1. Constant-rate extrusion: A ram or plunger is used to pressurize the fluid inside the container.

2. Constant-pressure extrusion: A pump is used, possibly with a pressure intensifier, to pressurize the fluid, which is then pumped to the container.

The advantages of this process include:[6]

No friction between the container and the billet reduces force requirements. This ultimately allows for faster speeds, higher reduction ratios, and lower billet temperatures.

Usually the ductility of the material increases when high pressures are applied.

An even flow of material. Large billets and large cross-sections can be extruded. No billet residue is left on the container walls.

The disadvantages are:[6]

The billets must be prepared by tapering one end to match the die entry angle. This is needed to form a seal at the beginning of the cycle. Usually the entire billet needs to be machined to remove any surface defects.

Containing the fluid under high pressures can be difficult.

Extrusion is the process by which long straight metal parts can be produced. The cross-sections that can be produced vary from solid round, rectangular, to L shapes, T shapes. Tubes and many other different types. Extrusion is done by squeezing metal in a closed cavity through a tool, known as a die using either a mechanical or hydraulic press.

Extrusion produces compressive and shear forces in the stock. No tensile is produced, which makes high deformation possible

without tearing the metal. The cavity in which the raw material is contained is lined with a wear resistant material. This can withstand the high radial loads that are created when the material is pushed the die.

Extrusions, often minimize the need for secondary machining, but are not of the same dimensional accuracy or surface finish as machined parts. Surface finish for steel is 3 µm; (125 µ in), and Aluminum and Magnesium is 0.8 µm (30 µ in). However, this

process can produce a wide variety of cross-sections that are hard to produce cost-effectively using other methods. Minimum thickness of steel is about 3 mm (0.120 in), whereas Aluminum

and Magnesium is about 1mm (0.040 in). Minimum cross sections are 250 mm2 (0.4 in2) for steel and less than that for Aluminum and Magnesium. Minimum corner and fillet radii are 0.4 mm (0.015 in) for Aluminum and Magnesium, and for steel, the minimum corner radius is 0.8mm(0.030 in) and 4 mm (0.120 in) fillet radius.

Cold Extrusion: Cold extrusion is the process done at room temperature or slightly elevated temperatures. This process can

be used for most materials-subject to designing robust enough tooling that can withstand the stresses created by extrusion. Examples of the metals that can be extruded are lead, tin, aluminum alloys, copper, titanium, molybdenum, vanadium, steel. Examples of parts that are cold extruded are collapsible tubes, aluminum cans, cylinders, gear blanks. The advantages of cold extrusion are:

• No oxidation takes place.

• Good mechanical properties due to severe cold working as long as the temperatures created are below the re-crystallization temperature.

• Good surface finish with the use of proper lubricants.

Hot Extrusion: Hot extrusion is done at fairly high temperatures, approximately 50 to 75 % of the melting point of

the metal. The pressures can range from 35-700 MPa (5076 - 101,525 psi). Due to the high temperatures and pressures and its detrimental effect on the die life as well as other components,

good lubrication is necessary. Oil and graphite work at lower temperatures, whereas at higher temperatures glass powder is used.

Typical parts produced by extrusions are trim parts used in automotive and construction applications, window frame members, railings, aircraft structural parts.

The Hydroforming Process

Hydroforming was developed in the late 1940's and early 1950's to provide a cost effective means to produce relatively small quantities of drawn parts or parts with asymmetrical or irregular contours that do not lend themselves to stamping. Virtually all metals capable of cold forming can be hydroformed, including aluminum, brass, carbon and stainless steel, copper, and high

strength alloys.

A hydroforming press operates like the upper or female die element. This consists of a pressurized forming chamber of oil, a rubber diaphragm and a wear pad. The lower or male die element, is replaced by a punch and ring. The punch is attached to a hydraulic piston, and the blank holder, or ring, which surrounds the punch.

The hydroforming process begins by placing a metal blank on the ring. The press is closed bringing the chamber of oil down on top of the blank. The forming chamber is pressurized with oil while

the punch is raised through the ring and into the the forming chamber. Since the female portion of this forming method is rubber, the blank is formed without the scratches associated with stamping.

The diaphragm supports the entire surface of the blank. It forms the blank around the rising punch, and the blank takes on the shape of the punch. When the hydroforming cycle is complete,

the pressure in the forming chamber is released and the punch is retracted from the finished part.

Hydroforming Advantages

Inexpensive tooling costs and reduced set-up time. Reduced development costs. Shock lines, draw marks, wrinkling, and tearing associated

with matched die forming are eliminated. Material thinout is minimized. Low Work-Hardening Multiple conventional draw operations can be replaced by one

cycle in a hydroforming press. Ideal for complex shapes and irregular contours.

Materials and blank thickness specifications can be optimized to achieve cost savings.

Manufacturing Costs: Hydroforming versus Deep Draw

Stamping

Tooling - With low volume runs, tooling is often the most important cost consideration. With hydroforming, a male die, or punch, and a blank holding ring are the only tools required as the

rubber diaphragm and pressurized forming chamber act as the female die. As a result, hydroforming tooling is typically 50% less expensive than matched die tooling. With hydroforming, most punches are made from cast iron as opposed to the hardened tool steels used for match die drawing punches. Finally, hydroforming tools are easily mounted and aligned, making set-ups fast and efficient.

Development Costs - Proto-typing is often a necessary step in the manufacturing process. Changes in material type or wall thickness specifications can typically be accommodated with hydroforming without creating a need for new tooling.

Reduced Press Time - Complex parts requiring multiple press cycles in matched die operations can be drawn in a single hydroforming cycle. Hydroforming presses frequently achieve reductions of 60-70% compared to 35-45% for conventional matched die presses.

Finishing Costs - Aerospace, medical and commercial cookware applications often demand parts with outstanding surface finishes. Unlike matched die metal forming, which can leave scratches and stretch lines, the flexible diaphragm utilized in hydroforming eliminates surface blemishes, reducing the need for costly finishing processes like buffing.

LASER BEAM

WELDING

[ PRINT ]

Laser welding is a high energy beam process and in this

regard is similar to electron beam. With that exception they are unlike

one another. The energy density of the laser is achieved by the

concentration of light waves not electrons. The laser output is not

electrical, does not require electrical continuity, is not influenced by

magnetism, is not limited to electrically conductive materials and in fact

can interact with any material whether it be metal, plastic, wood, ceramic,

etc. Finally its function does not require a vacuum nor are x-rays

produced.

The focal spot (thousandths of an inch in diameter) is targeted on the

weld joint surface or by focal length selection above or below it. At the

surface the enormous concentration of light energy is converted to

thermal energy. Surface melting occurs and progresses through the weld

joint by thermal conductance. For welding, beam energy is maintained

below the vaporization temperature of the weld joint material. For hole

drilling or cutting vaporization is required. Because weld joint penetration

is dependent on conducted heat the thickness of materials to be welded

is generally less than .080 inches if the ideal metallurgical and physical

characteristics of laser welding are to be realized. These benefits are

narrow welds, no distortion, minimal heat affected zones and excellent

metallurgical quality.

As with electron beam the intense, concentrated energy produces melting

and coalescence before a substantial heat affected zone can develop.

Because the welds are narrow and therefore are of correspondingly low

volume there is a minimal reservoir of heat for conductance into the

adjacent area. When materials to be welded are thick and particularly if

they have high thermal conductance (aluminum for example) this

important metallurgical advantage of minimal heat affected zone can be

detrimentally affected. It is claimed that since the source of energy is light

of a specific wavelength contaminants in the weld pool or on the facing

surfaces of the joint may be preferentially vaporized by their particular

light absorbing characteristics resulting in a kind of weld purification. The

excellent fatigue strength of laser welds is sometimes attributed to this

purifying phenomenon.

Energy

distribution across the beam is generated by the design of the resonant

cavity, including mirror curvatures or shape and their relative

arrangement. This combination results in photon oscillation within the

cavity producing specific output beam energy distributions or patterns.

These patterns are labeled transverse energy modes (TEM) and have

specific identifying numbers. We cannot within this seminar describe their

variety and effects. However, we will point out that the Gaussian mode

TEM 00 is often preferred for welding inasmuch as its peak energy is in

the center of the beam feathering off to its periphery. It might be likened

to a pointer. The symmetry and profile of the Gaussian Beam is

particularly suited for welding.

We have learned how light energy is amplified in the solid state laser

cavity and how the laser beam and its unique characteristics are formed.

It is important to note before proceeding that the function of all lasers

whether they be gas (carbon dioxide, helium neon, etc.) or other lasing

sources is based on the principle of the excitation of atoms by means of

intense light, electricity, electron beam, chemicals, etc., and the

spontaneous and stimulated emission of photons. Depending on the

lasing source, output frequencies differ widely and are capable of a great

number of applications. These range from welding to critical surgery,

resistance trimming, communication, etc.

As a clear demonstration of the effect of light wave

frequency, the beam of a neodymium YAG laser (l.06 micron wavelength)

will pass through quartz lenses, clear plastic or glass and other

transparent materials. However a carbon dioxide laser emitting a beam

with a wavelength of 10.6 microns will not pass through the quartz lens

etc. but rather will be absorbed by those materials resulting in their

destruction. Carbon dioxide lasers must achieve focusing either by

converging reflective optics or special salt based lens materials such as

zinc selenide.

We have discussed the role of the objective focusing lens and how it

concentrates the beam energy into a focal spot as small as .005 inches in

diameter or less. We have also reviewed how a laser weld is produced by

conducted heat and the excellent quality of the weld.

Because the energy density is so intense, in

fact second only to the electron beam, the laser is capable of vaporizing

metals such as tungsten or non-metallic materials such as ceramics. In

fact, in conductance welding, care must be taken to prevent this

vaporizing action. However, as with electron beam, lasers can produce

deep penetration welds by the keyholing technique. Laser keyholing is

limited to perhaps 3/4 to 1 1/2 inch thickness and for these depths a

multi-kilowatt laser, such as the carbon dioxide type, must be used.

We need to mention that although there are many laser types, the

Nd:YAG and carbon dioxide lasers (CO2) are most common in production

metal working. Carbon dioxide lasers utilize a combination of carbon

dioxide, the primary lasing source, helium and nitrogen. The gas mixture

circulates through a bank of electrodes, which is the energy source. The

output wavelength is 10.6 microns. Carbon dioxide lasers have been

developed with outputs exceeding 25 kilowatts. This high output of CO2

lasers is possible since they can be efficiently cooled. In contrast, cooling

the solid state YAG laser crystal is difficult and critical. Considerable

design attention is directed towards cooling, excitation lamps, their

reflectors, cavity shape, materials, plating of reflectors, lens anti-

reflection coatings, etc. This includes power supplies, which may be

designed for continuous or for a pulsing output. Pulse repetition rates

and pulse shaping are programmable.

We must now continue our initial discussion of the interaction of the laser

beam with metals. As stated, heat is generated by the conversion of light

energy. All metals reflect light to some degree, with gold and silver high

on the list and carbon steel low on the list. Gold, silver, copper, and

aluminum are therefore difficult to weld requiring intense energy usually

available from high energy peaking pulses or resorting to light absorbing

coatings such as graphite on the weld joint surfaces to reduce their

reflectivity. The 1.06 micron wavelength of the Nd:YAG laser is more

readily absorbed than the longer 10.6 micron wavelength of the CO

lasers, therefore, in this respect more suited for welding highly reflective

materials. However though metallic reflectivity is a factor, once melted,

the reflectivity essentially disappears at the curie temperature (about

1425 degree F). Therefore most metals are readily welded. The intense

energy of the beam quickly melts the surface, from which thermal

conductance progresses to achieve penetration.

Because the beam can be reflected from mirrored surfaces (reflective at

the laser wavelength) it follows that beam manipulation is almost

unlimited. It is this feature that makes marking or engraving lasers

possible. Holes can be drilled or cut as square, round, any geometric

pattern, size or dimensional proportions by mirror manipulation. Beam

energy can be tailored to produce strategic pulse profiles. Energy can be

continuous, or weld seams may be produced by overlapping individual

pulses which tend to reduce heat input by the brief cool cycle between

pulses, an advantage for producing welds in heat sensitive materials. A

third arrangement is a continuous output with pulsing action

superimposed by an acousto-optic (Q) switch located in the cavity. This

device is capable of generating pulse rates in the tens of thousands and

can increase cavity energy by interrupting the output thus causing a brief

period of gain or storage in the laser crystal. Considering that photon

oscillations within the cavity occur at the speed of light even a brief

interruption of the output is extremely effective for increasing the gain.

The manipulative ability of the laser establishes it as ideal for automation

and robotics. Fiber optics dramatically adds to this versatility. Utilizing

this capability, production assemblies on trays, fixtures or shuttles can be

conveyorized while the laser focusing optics, incorporating the necessary

axis of motion (x, y, z) including targeting and scanning, can track and

follow the weld joint. This flexibility combined with motion and parameter

programming is seemingly unlimited. Inert gas shielding of the weld is

usually incorporated coaxially with the laser. However, inert gas trailers,

underbead coverage and other strategic, and beneficial inert gas

applications are easily adopted. If necessary assemblies can be placed in

a vacuum chamber and the laser beam introduced through a quartz

window. The raw beam can be focused through optics within the

chamber or may be focused external to the chamber utilizing the

appropriate focal distance. Alternately fiber optics may be utilized and

routed through appropriate hardware in the chamber walls. The fiber

optics can be terminated with focusing optics internal to the chamber.

Many arrangements are possible.

The

disadvantages of lasers include its high capital cost, the need for clean

environment (to protect the optics), and the safety considerations. The

latter two are most often resolved by the installation of the laser in a laser

room. Warning signs, sounds and/or flashing lights are employed to

signal when the laser is on. An additional disadvantage is though

maintenance is generally minimal, laser operation requires training and

experience. Maintenance and machine operator personnel must become

aware of the subtleties that can influence the laser output. In this regard,

the laser is somewhat unlike the electron beam, which has with rather

positive switch controlled reactions.

We will next discuss how a laser beam is generated. It is necessary to

start with atoms. Depending on the particular element there may be one,

two or more electrons in single or multiple energy orbits circling the

nucleus of the atom. In their normal quiescent or ground state the orbits

are at discrete energy levels or distances from the nucleus that are

characteristic of the specific atom. All of the atoms of a given element

share this identical behavior.

Spontaneous Emission

The basis for laser action occurs when an atom (for this example,

neodymium) is excited by an external energy source. The absorbed

energy will cause the atom's electrons to move from their ground state to

one of the discrete and exact energy orbits, characteristic of the specific

atom. Therefore when these orbiting electrons return spontaneously to

their ground state, they release the energy difference as a photon. Since

all of the photons originate from electrons in the same energy orbit, they

have the same wavelength.

Stimulated Emission

Einstein theorized and proposed that a photon passing near an excited

electron of the same energy would cause the approached electron to

return to its ground state and in doing so release its photon of light. Two

identical photons would now exist. The two photons would travel as a

coherent pair and in the exact same direction. This phenomena would be

repeated over and over again as each of the triggered photons

approached other excited electrons in the same energy orbits. Groups of

photons, depending on the emanated direction of their original source.

When an external source of energy, whether it be intense light, chemical,

electrical, etc. is absorbed by the atom, its excited electrons will move to

a new energy orbit but only after they have absorbed a specific amount of

energy. They do not move half way or one and one-half times out but

rather to a discrete new energy orbit characteristic of the atom. An

analogy would be stepping from stone to stone across a stream. Too

short or too long a step will result in a soaking. There is no margin for

error. Another analogy is throwing a ball through a distant basket or loop.

It requires a specific amount of energy to succeed. Too little, too much

result in misses. This relationship between atoms, their electrons and

energy is an atomic law. Therefore, the orbiting electron must absorb a

specific energy value before they move to that very discrete and distinct

new orbit. The electrons of every atom of a specific element excited by a

common energy source contain the same energy inasmuch as they are in

the same energy orbit and will release this energy as photons when they

randomly drop back to their ground level, or normal state, an action

called spontaneous emission. The released photons, therefore contain the

same energy and, as a result, the same light wavelength.

Based on this fundamental atomic action a laser crystal (ground rod)

containing an element such as neodymium, which is capable of releasing

photons, when appropriately energized can become the basis for laser

activity. All of the neodymium (Nd) electrons in their identical energy

orbits will randomly return to their ground state, collectively releasing

enormous quantities of photons each containing the energy difference

between the excited orbit and the ground state. Their light wavelength is

equivalent to this energy. In the instance of neodymium, the light

wavelength is 1.06 microns. Other photon emitting elements can have

other wavelengths. It should be noted there are numerous elements

capable of emitting photons but many are ruled out for laser use because

of the difficulty in acquiring, their instability, etc. To return to the

foregoing, a neodymium: yttrium, aluminum garnet (Nd:YAG) solid state

laser consists of the element neodymium dispersed in the host yttrium

aluminum garnet (YAG) crystal.

Lets proceed to the next important phase of laser beam generation. In

fact, the term laser (light amplification by stimulated emission of

radiation) is the function we are about to discuss. As a matter of interest

this theory was postulated by A. Einstein contributing to the

development, design and fabrication of the first research lasers.

We have learned the atoms of certain elements when they absorb energy

move their electrons to a new and discrete orbiting energy level. On their

random, spontaneous return to their ground or quiescent state they emit

photons of light. We may think of the photons as particles. The photons

contain the energy difference between the excited and ground state

orbits. Their specific wavelength is a result of and proportional to this

energy.

The photons move in random spatial directions at the speed of light and

of a specific wavelength. However, Einstein postulated that when a

photon passes close to an excited electron of equal energy, it would

trigger the electron spontaneous emission of a photon. There would now

be two. Interestingly, the second photon as we now know will contain the

same energy, therefore wavelength as the first triggering photon. To

continue the phenomena the second triggered photon will travel in the

exact same spatial direction as the first. As these two paired photons

continue on they will trigger other electrons by stimulated emission

creating an enormous amplification of photons traveling in the exact

same direction dependent on their origin. Needless to say all of the

photons have the same light wavelength.

Characteristics of the laser beam

Monochromatic

All of the photons which compose the beam are of the same energy and

therefore the same wavelength. If the laser beam was directed through an

optical prism it could not split up into the separate colors representing

the wavelengths of the optical spectrum.

Coherent

The light waves are in phase (in step).

Collimated

The laser beam does not diverge. It can be projected great distances

without significant spreading. For example, it is used for topographical

surveys where elevations miles away can be measured from a single,

central location. Collimation makes is possible for laser beams to target

satellites, etc. at great distance. Because of these three characteristics the

laser beam can be precisely focused to very small diameters, resulting in

an enormous increase in energy density.

From here we will proceed to understand how all of this activity i.e. the

triggered release of photons by stimulated emission and the cascading

effect resulting from the stimulating action of photons approaching other

excited electrons of equal energy become the basis of the laser. The

question now is how to harness, organize, control and concentrate the

spatial motion of photons into a controlled beam of light capable of being

projected without significant divergence, for miles and to contain a level

of concentrated energy capable of vaporizing such high temperature

materials as metals and ceramics.

The atoms of reodymium are a stable source of lasing action. The "YAG"

crystal which is grown as a boule is doped with the element neodymium.

This crystal is precisely ground to a rod configuration. When assembled in

a resonant cavity it becomes the basis for solid state laser action, emitting

a laser beam having a light wavelength of 1.06 microns.

The diagram shows a neodymium doped YAG crystal absorbing energy

from an intense light source resulting in the release of photons in random

spatial directions by the combined mechanism of spontaneous and

stimulated emission.

Next, another view of the crystal with mirrors added to each end to

produce a resonant cavity. By coincidence, the spatial direction of some of

the photon groups will cause them to travel along the longitudinal axis of

the cavity. The result is the impingement of these photons on the mirrors

located at the ends of the crystal from where they will be returned to the

crystal by reflection and will continue to stimulate the emission of other

photons. This activity creates an enormous amplification of photons

traveling back and forth between the mirrors, continually stimulating and

aligning their travel direction. One of the mirrors designated the front

mirror is deliberately designed to allow a controlled leakage or

transmission of light -up to 60%. This transmission is the raw laser beam.

The beam is pure light since it consists of a single wavelength

(monochromatic) and in addition is both coherent (in phase) and

collimated (low divergence).

The basic solid state neodymium "YAG" laser cavity consists of the

ND:YAG crystal, an energy source, a 100% reflective rear mirror and a

front or output mirror which is up to 60% light transmissive. The cavity

may also contain accessories such as shutters, apertures and electro

optical mechanisms.

A laser

beam is generated when photons traveling in a direction along the

longitudinal axis of the crystal are reflected and returned to the crystal by

the end mirrors where they continue to amplify the output through the

phenomena of stimulated emission. Since the front mirror is up to 60%

light transmissive a laser beam is emitted. This beam of light is

monochromatic, collimated and coherent. Because of these three

characteristics and resultant low divergence, the beam is capable of

traveling great distances with minimal energy loss.

These characteristics are extremely important. The ability to deliver this

pure beam of light through an optical system and project it for miles or to

focus it to so small a diameter its energy density can vaporize ceramics, is

dependent on these three characteristics. It is timely to mention there are

many lasers emitting pure light beams of different frequencies depending

on their atomic origin. Special applications require particular light

frequencies to be efficiently absorbed by the characteristics of the target

material. Eye surgery or measurement operations, etc. require different

light frequencies than those we commonly use for metal working. We

must not neglect to add the cavity and optical system just described

includes other items, apertures, collimators, safety shutters, beam

splitters, viewing optics etc. to fine tune and control the beam.

After leaving the cavity

through the partially transmissive front mirror, the beam continues

through a safety shutter followed by an up collimator. The latter, a kind of

reverse telescope, expands the beam, further improves the collimation

and prepares it for the final optics. After leaving the up collimator, the

beam proceeds to a turning or beam bending mirror where it is usually

directed vertically downward through the final, objective focusing lens.

Between the turning mirror and final lens, other accessories such as a

trepanning device may be introduced. Depending on the system the

beam, after leaving the up collimator, may enter a fiber optic coupler

rather than the hard optics just described. Fiber optics terminated by

focusing optics provide complete mobility of beam direction.

The final lens focuses and concentrates the raw laser beam into the

desired spot diameter. In addition, it establishes the focal distance

between the lens and workpiece and relative to this produces a specific

depth of field within which distance there are negligible changes in focal

spot diameter. Short or long focal distances have their corresponding

short or long depth of fields. In all of the foregoing arrangements there

are numerous variations; lens design, lens combinations, beam splitting,

trepanning heads, power sampling, apertures, up collimator ratios, etc.

intended to provide particular performance and control characteristics.

Powder injection mouldingBE

Plastic components have been produced by injection moldingAE for years. Therefore the complexity of the components have increased steadily. Through the development of special

processes, such as the multi-component injection molding, but also the micro-injection molding, completely new possibilities of plastics processing result are possible. In addition to plastics, since years the powder injection moulding of metallic and ceramic materials are now well established. With this procedure complex components can be made out of metal and ceramic far cheaper than by using other production possibilities. The powder injection molding is divided into four production

steps:

First, through a combination of plastic, wax and metal or ceramic powder a material is generated which can be processed by

injection moulding. This material is generally named - feedstock - . By custom machine and tool technology, this feedstock can be injected, similar to plastic injection molding. The moulded part is

so-called green part. The next step is the release of the plastic and wax component by the debindering process. The result is called brown part. The last step is the sintering of the brown part. In this process the individual particles are merged together, the brown part shrinks and becomes an compact component. This sintering shrink depends on the proportion of powder in the feedstock: normally between 20% and 30%. This final component has similar properties to the base material.

If you have further questions on the powder injection have a look at our other explanations. If you have specific project ideas please contact us. We will try to clarify your questions or give you an appropriate contact person to you.

Selectively reinforced squeeze cast pistons

Dr R Mahadevan and R Gopal

1. SQUEEZE CASTING

A process which is a combination of gravity die casting and

closed die forging. The technique in which metal solidifies

under pressure within closed die halves. The applied pressure

and the instantaneous contact of molten metal with the die

surface produces rapid heat transfer that yields a porous free

casting with mechanical properties approaching the wrought

product . Squeeze casting offers high metal yield, nil or

minimum gas or shrinkage porosity, excellent surface finish

and low operating costs.

Squeeze casting (also known as extrusion casting, squeeze

forming, liquid forging) was developed to produce high

quality components. In this process, pressure is applied on

the solidifying liquid metal. Due to the intimate contact

between the liquid metal and the mold and hence higher rate

of heat removal across the metal mold interface, premium

quality castings are obtained. The patent on this process

seems to be that of James Hollingrake in 1819 from

Manchester. The steps involved in this process are : (i)

pouring of metered quantity of liquid metal with adequate

super heat in to the die cavity, (ii) application of pressure on

the liquid metal and maintaining the same till the solidification

is complete and (iii) removal of the casting and preparation

of he die for the next cycle. These steps are illustrated

schematically

The process is basically divided into two types: direct and

indirect. What is shown is the direct process, where the

squeeze pressure is applied through the die-closing punch

itself, whereas in the indirect process, the squeeze pressure

is applied after closing of die, by a secondary ram

SPECIFIC FEATURES OF SQUEEZE CASTING OVER

CONVENTIONAL GRAVITY DIE CASTING:

a. Solidification under pressure enhances internal

soundness, thereby increasing the suitability potential

for critical applications.

b. Squeeze casting results in a high degree of refinement

in the structure of the alloy. Grain size reduction to the

extent of 50% of that of the conventionally gravity cast

alloy is usually possible finer microstructure.

c. In general, material formed by squeeze casting has a fine

equiaxed grain structure and exhibit higher toughness

than materials formed by gravity casting.

d. Absence of gas/shrinkage porosity.

e. Near net shape, high degree of surface finish and

dimensional accuracy.

68th WFC - World Foundry Congress

7th - 10th February, 2008, pp. 379-384

f. Significant improvement in mechanical properties due to

finer microstructure.

g. Faster cycle times.

h. In conjunction with high quality reusable dies and thin

die coatings, good dimensional reproducibility is

possible, matching that of pressure die casting.

i. In the absence of running or feeding system, a high

metal yield approaching 95% can be achieved because

all the metal poured into the die is used to form the

components.

j. Casting alloys as well as wrought alloys can be squeeze

cast to finished shapes; castability and fluidity of the

material are of little concern. Suitable for long freezing

alloys too.

k. Components of forging quality can be produced by

squeeze casting.

l. Fibre and particulate reinforcement can be incorporated

with advantage in squeeze casting.

m. Recycled scrap material can be used for components

which would conventionally require a more expensive

high quality primary alloy

Table lists mechanical properties squeeze cast Vs chill cast

and forging. The mechanical properties of squeeze cast

components are superior to that of conventional casting.

Chill Cast Squeeze cast

Alloy

UTS Elongation UTS Elongation

(MPa) (%) (MPa) (%)

LM5 230 10 250 14

LM18 150 6 187 13

LM 24 200 2 233

368(T6) 272

LM 25 310 (T6) 3 331(T6) 7

A 357 313(T6) 7 347(T6) 9

FORGING

A 6061 -

Forging 262 10% 292 10

Proceedings of 68th World Foundry Congress 380 7th-10th February 2008, Chennai, India Some of the Squeeze Cast components being made worldwide

are in the following table.

Piston Motor Support

Engine Block Disc Brake Caliper

Cylinder Head Turbo Charge Impeller

Connecting Rod Brake Drum

Brake Disk Brake Pedel

Wheel Track shoe

Pulley Piston Pin

Pull Arm socket Valve Rocker Arm

Track Hub Exhaust Manifold

Bushes Differential Clutch compartment

Flange Hub Cylinder Liner

Gear Housing Pinion Gear

3. ALUMINIUM MATRIX COMPOSITES

Composites are materials composed of more than one

constituent. One of the constituent is the metallic matrix and

the other a reinforcement. The matrix holds the reinforcement

together.

Aluminium matrix composite refer to a class of material where

aluminium is the metal matrix reinforced by materials like SiC,

Al2O3 ,TiC, TiB2, Graphite and certain other ceramics.

Apart from the reinforced material, the morphology of the

reinforcement too is of importance. The three major

morphologies are Continuous fiber, Chipped fiber or Whisker

and particulate. With further options like Reinforcement

Volume Fraction and reinforcement orientation and aluminium

alloy composition and heat treatment , a wide range of

materials and resultant properties are feasible.

The automotive piston components that are currently under

development using Aluminium matrix composites by various

automotive manufactures are listed below:

Reinforcement Component Manufacturer

SiC (particulate) Piston Dural, Martin

Marietta, Lanxide

Al2o3 (fibre) Piston Ring Toyota

Groove

Al2o3 (fibre) Piston Crown FM, JPL, Mahle and

others

SiC (particulate) Cylinder liner, FM

Pistons

Al2O3 – SiO2-C Cylinder liner Honda

The most widely used reinforcements in the case of aluminium

matrix composites for automotive applications have been

graphite and silicon carbide, both in the form of particulates

and fibers. The development that have taken place in the

recent years are

a. Aluminium-Graphite composites

Initially, cast Al/Gr (p) composites were developed through

liquid metallurgy route for automotive antifriction

applications. The primary advantages of this material were

less cost, easy machinability and improved damping capacity

which is essential for automotive applications. These

composites have been used to fabricate many automotive

components like pistons, liners and bushings using

permanent mould casting, squeeze casting, centrifugal casting

and pressure die casting.

The pistons of Al/Gr (p) composites tested in diesel engines

led to reduced wear of the pistons and rings, reduced loss

of frictional horsepower and freedom from seizure under

adverse lubrication conditions. The specific fuel consumption

is observed to have decreased. Similar results have been

obtained by using these pistons in gas-line engines.

FM reports that 4% graphite dispersed in Al-18Si alloy

improves its scuffing resistance by a factor of two. The

liners from these alloys have been evaluated by them in twostroke

and four-stroke engines in collaboration with Ferrari,

Hiro and Alfa Romeo. It has been observed that the power

generated improved by 10%. Also, negligible wear with no

friction marks or scuffing has been observed and power

ratings were found to be close to highest levels achievable.

b. Aluminum-Silicon Carbide composites

These composites show excellent specific strength, specific

modulus and wear resistance. The coefficient of thermal

expansion decreases linearly with increase in SiC content.

Dural has been manufacturing this material since 1986. These

materials are supplied in the form of ingots which can be

remelted and cast into desired components. Conventional

casting processes like sand casting, permanent mould

casting, investment casting and squeeze casting have been

used to make automotive

components. The automotive components that are

manufactured using these composites include pistons, brake

rotor, cylinder sleeves and drive shafts.

The Piston Division of Karl-Schmidt Unisia(Germany) have

introduced a squeeze-cast aluminium alloy ( HD-339-P) piston

reinforced with a 80% alumina-20%silica perform in the crown

and combustion bowl region for tractor-trailer diesel engines.

It is observed that high temperature (300o C – 400oC) yield

strength and stability were markedly increased in the critical

piston regions, increasing the thermal gradients generated

by high output diesel engines. Although the perform was

slightly heavier that the matrix alloy, overall weight penalty

was trivial because the perform was confined to a small

region (17% by volume).

Summing up, in automobile applications, the Aluminium Metal

Matrix composites offer the following benefits relative to the

conventional metal / alloys.

Weight saving.

Increased specific stiffness

Enhanced Wear resistance

Reduced Coefficient of Thermal Expansion.

Elevated temperature strength

Fatigue strength

Improved creep resistance

High surface durability.

Reduced emission

7th-10th February 2008, Chennai, India 381 Proceedings of 68th World Foundry Congress The salient features :

(i) Hydraulic Press , C/H frame type construction ( day

light – 1000 mm, pate size – 1000 x 500 mm)

(ii) Die locking cylinder (Capacity 200T , stroke – 300mm)

(iii) Top closing cylinder (Capacity 150T, stroke – 700 mm,

speed – 200 to 5m/s, variable)

(iv) Squeezing/Ejection Cylinder(Capacity 20T, , stroke –

150 mm, programmable pressure control)

4. DEVELOPMENT OF SQUEEZE CAST

PISTONS

IPL and IIT, Madras have worked together to develop

squeeze casting and an Aluminium Metal Matrix composite

piston.

SQUEEZE CASTING MACHINE

An indirect type squeeze casting machine (Fig) was designed

to fulfill the requirements to cast the composite piston.

Proceedings of 68th World Foundry Congress 382 7th-10th February 2008, Chennai, India (v) Options for manual and auto-cycle operations.

In auto-cycle of mode, the following sequence of operations

will take automatically (with operator intervention at step

No.2)

1. Die locking cylinder moves fast forward, slows down

after tripping limit switch, locks the die halves and

develops the set load ( max. 200T). The cylinder is

isolated using check valve.

2. Operator places the preform in the die cavity and

presses the button, which activates the auto ladle.

3. Auto ladle pours the desired quantity of metal.

4. Return motion of the ladle activates the die closing

cylinder.

5. Die closing cylinder moves fast forward, changes over

to slow speed after tripping limit switch, closes the die.

6. Squeezing cylinder ram, held in position with backpressure,

moves backward to accommodate the excess

metal, as the die closes in step 5.

7. Die closing cylinder develops the set load (max. 150 T)

and gets isolated using check valve.

8. Squeezing cylinder moves forward, develops the set

pressure ramp rates, as programmed in PLC.

9. The liquid metal solidifies under pressure for a specified

time, set on the panel. At the end, the squeeze pressure

is reduced to the back pressure level.

10. Dwell timer gives signal to the die closing cylinder to

retract in slow-fast motion to the set position.

11. Die locking cylinder retracts in slow-fast motion to the

set position.

12. Squeeze cylinder moves forward, ejecting the component

and the pressure is reduced to the back pressure level

at home position.

13. Component pick-up, die cleaning and coating done

manually

AUTO LADLE:

Pouring of metered quantity of liquid metal into the die

cavity is essential for castingthe near-net-shape components.

This necessitates the inclusion of auto-ladle in the system.

This is integrated with the squeeze casting machine.

Specifications:

Ladle range : 0.5 – 2.0 Kg

Arm traverse range : 1500 mm

Average cycle time : 15 Sec

Metering accuracy : +/- 2%

Control system : 2 axes servo DC, user control of cycle

speeds ( variable within a cycle) and

metering, detection of pouring

problem and return of molten metal to

crucible, motion controller interfaced

to a pendent with 2 line 16 char. LCD

display and key board, windows 95

based application software for

configuring and controlling the

system.

FURNACES:

Two furnaces, one for melting the alloy, viz., aluminium –

12% silicon alloy and the other for heating the composite

before placing into the die cavity.

Aluminium Melting furnace:

Electrical resistance heated Capacity : 300 Kg

Power rating : 72 KW

Max temp. : 10000C

Preform Preheating Furnace:

Double chamber construction +/- 180oC rotation

Electrical resistance heating Max. Temp : 10000C

MOBILE DEGASSING UNIT:

The MDU is used for in the removal of dissolved hydrogen

from the melt, before starting the casting operations.

Specification :

Gas flow rate: 0 – 10 lpm

Gas pressure : 2 bar

Sleeve speed range : 80 – 650 rpm

5. PRODUCT DEVELOPED

The diesel engine piston (Simpson Model No.S3/25) was

taken up for development. Presently this is made by

conventional process, viz gravity casting and is not

reinforced with fibers. The present design in use is an alfin

piston 88.9mm diameter and 100mm height made by gravity

die casting process

The intention was to make this piston by squeeze casting

process with Alumina-silicate fiber reinforcement in the top

ring groove area. The necessary die set, consisting of two

vertically split halves, top punch (the shape matching with

that of inside contour of piston) and the bottom pad was

designed and fabricate. The ceramic insert in the form of

ring, preheated to 5000C was placed on the bottom pad. The

die was locked with a locking force of 150T. The aluminium

– 12% Si melt with super heat of 7500C was poured in the

die cavity. The die was closed with the top punch (Load =

100T). Immediately after closing, the squeezing operation

started automatically according to the programmed sequence.

The maximum pressure applied was 75 MPa in 5 ramps and

the pressure was maintained for 60s. Initially the castings

were examined visually by cutting into several pieces

and subsequently the uncut castings were examined by

NDTs. The casting was heat treated to T6 condition and

machined to the exact dimensions.

7th-10th February 2008, Chennai, India 383 Proceedings of 68th World Foundry Congress Proceedings of 68th World Foundry Congress 384 7th-10th February 2008, Chennai, India In the present development, material system consisting of

Alumina –Silicate flake at 15% volume fraction

(Vf+15%) and eutectic Al-Si alloy forms the Metal Matrix

composite.

These MMC pistons are evaluated for physical and

mechanical properties like wear, density, fatigue strength,

tensile strength, hardness, microstructure etc.

EVALUATION OF MATERIAL PROPERTIES:

DENSITY :

The density indicates the quality of the castings produced.

The density of the squeeze cast base alloy and composites

were measured using Archimedes principle. These values are

given in Table. The Theoretical densities are obtained by rule

of mixtures. The density values of the matrix and the fibre are

assumed to be 2.71 and 2.6 gm/cc respectively. The results

indicate marginal decrease in composite density with

increasing fibre volume fraction. The measured densities are

greater than 99.5% of the theoretical density. This indicates

that the squeeze casting process produces denser castings

indicating minimal porosity and the infiltration is complete in

the case of composites.

TENSILE STRENGTH

Tensile strength tests were conducted on sample specimens

from MMC portion and unreinforced portion of squeeze cast

piston. Fiber reinforced portion shows higher tensile strength

at 290 N/mm2 against 260 N/mm2 recorded by unreinforced

portion.

MICROSTRUCTURE

The samples were taken from reinforced portion and unreinforced

portion of squeeze cast piston and the

microstructure was studied at 200X. In the reinforced area

uniform distribution of Alumina-Silicate fiber in the matrix of

Al-Si eutectics is seen. Polygonal primary silicon particles in

Al-Si eutectic matrix is observed in unreinforced region.

HARDNESS

Hardness of the reinforced area is found to be slightly lower

(104 BHN) when compared to un-reinforced area (128BHN).

It may be attributable to volume fraction as well as

solidification kinetics influenced by ceramic fiber.

7. ENGINE TESTING

A S3-24 Simpson diesel engine 88.9 x 127 mm 3 cylinder 2.4

litre naturally aspirated Direct Injection diesel engine was

assembled with the composite piston and dynamometer tested

at full load rated speed for a duration of 1000 hours after

running in. All performance parameters were measured

including power, fuel consumption, oil consumption, blowby

and smoke. Standard three ring pack was used in the test

for comparison, consisting of Top Ring: Inlaid chrome,

internally beveled, Barrel periphery comp., ring 2nd ring:

Internally stepped, taper periphery IP18, uncoated comp.,

ring 3rd ring: Chrome conformable oil ring

Wear : Wear tests were conducted on specimens of two

materials; fibre reinforced squeeze cast and Ni-resist cast

iron against standard top ring material in the conventional

pin-on-disc type wear testing machine. The tests were

conducted under similar conditions, viz, disc speed,

lubrication and duration. The results are given in table. It

may be seen that there is no wear in the case of composite

and there is a wear in the case of Ni-resist material. The

composite gains weight, 0.0080 gm, by removal of material

from the ring. On the other hand, the Ni-resist cast iron loses

weight, 0.0016 gm. In both cases, the ring material loses

weight.

Thermal Expansion : The measured values as functions of

temperature are given in the table.

CONCLUSION

1. An alternative process of squeeze casting using

selective reinforcement at the top groove and land area

provides a superior alternative to the conventional

method of gravity die-casting and forging.

2. Indirect squeeze casting machine designed and

developed as a collaborative project between IIT

Chennai and India Pistons has successfully been used

to produce such an alternative piston

3. This piston has been subjected to static and dynamic

tests to establish its superiority in terms of strength,

wear resistance and fatigue.

Centrifugal Casting: In centrifugal casting, a permanent mold is rotated about its axis at high speeds (300 to 3000 rpm) as the molten metal is poured. The molten metal is centrifugally thrown

towards the inside mold wall, where it solidifies after cooling. The casting is usually a fine grain casting with a very fine-grained outer diameter, which is resistant to atmospheric corrosion, a typical situation with pipes. The inside diameter has more impurities and inclusions, which can be machined away.

Only cylindrical shapes can be produced with this process. Size limits are upto 3 m (10 feet) diameter and 15 m (50 feet) length. Wall thickness can be 2.5 mm to 125 mm (0.1 - 5.0 in). The tolerances that can be held on the OD can be as good as 2.5 mm (0.1 in) and on the ID can be 3.8 mm (0.15 in). The surface finish ranges from 2.5 mm to 12.5 mm (0.1 - 0.5 in) rms.

Typical materials that can be cast with this process are iron, steel, stainless steels, and alloys of aluminum, copper and nickel.

Two materials can be cast by introducing a second material during the process. Typical parts made by this process are pipes, boilers, pressure vessels, flywheels, cylinder liners and other parts that are axi-symmetric.

Semi-Centrifugal Casting: The molds used can be permanent or expendable, can be stacked as necessary. The rotational speeds are lower than those used in centrifugal casting. The center axis of the part has inclusion defects as well as porosity

and thus is suitable only for parts where this can be machined away. This process is used for making wheels, nozzles and similar parts where the axis of the part is removed by subsequent machining.

Centrifuging: Centrifuging is used for forcing metal from a central axis of the equipment into individual mold cavities that are placed on the circumference. This provides a means of increasing the filling pressure within each mold and allows for

reproduction of intricate details. This method is often used for the pouring of investment casting pattern.