Ain Shams Production University Engineering Shams University Faculty of Engineering Design & Prod....

Ain Shams University Faculty of Engineering Design & Prod. Dept.

Production Engineering 1st Year Mechanical Dr. tayseer

Lecture Notes Metal Forging 1

Metal Forging [01] Definition: Forging is the process of shaping heated metal by the application of sudden blows or steady pressure to deform the material. A metal such steel can be shaped in cold state, but the application of heat lowers the yield point and makes the deformation easier.

Outline of forging operations:

[02] Grain Flow & Mechanical Properties Improvements:

Forging refines the grain structure and improves mechanical properties of the metal. With proper design, the grain flow can be oriented in the direction of principal stresses encountered in actual use. Grain flow is the direction of the pattern that the crystals take during plastic deformation. Mechanical properties (such as strength, ductility and toughness) are much better in a forging than in the base metal, which has, crystals randomly oriented.

Shearing Sawing Cutting off

Heating Trimming Machining Heat treatment Cleaning Open-die forging

Closed-die forging Coining Heading Others

Billet Furnaces Hammers Presses

& Forging Machines

Finishing Inspection




Directional Grain Flow Forging’s directional grain flow ensures high part strength with superior fatigue resistance, mechanical properties, and metallurgical soundness.

Superior Structural Integrity Forging eliminates internal voids and porosity, producing unmatched structural integrity. Costly internal rework and tooling wear, part rejections, and field failures are avoided.




[03] Open-die Forging: Open-die forging is the simplest forging process and can be classified to two main operations, upsetting and drawing out.

Upsetting is deforming the workpiece between two flat dies and reducing its height by compressing it. In open-die forging, the die surface may have simple cavities to produce relatively simple forging.

Drawing out (also called cogging) is an open-die forging process, in which the thickness of a bar is reduced by successive forging steps at certain intervals. Swaging: A tube or rod is forced inside a die and the diameter is reduced as the cylindrical object is fed. The die hammers the diameter and causes the metal to flow inward causing the outer diameter of the tube or the rod to take the shape of the die.

Swaging Process




Roll Forgings: In roll forging, a bar stock, round or flat is placed between die rollers which reduces the cross-section and increases the length to form parts such as axles, leaf springs etc. Roll forging using specially shaped rolls. Larger rolls cause greater lateral spread and less elongation because of the greater frictional difference in the arc of contact. The properties of roll-forged components are very satisfactory. In most cases, there is no flash and the fiber structure is very favorable and continuous in all sections. The rolls perform a certain amount of descaling, making the surface of the product smooth and free of scale pockets.




Rolled Ring Forging The production of seamless forged rings is often performed by a process called ring rolling on rolling mills. The process starts with a circular preform of metal that has been previously upset and pierced (using the open die forging process) to form a hollow "donut".

This donut is heated above the recrystallization temperature and placed over the idler or mandrel roll. This idler roll then moves under pressure toward a drive roll that continuously rotates to reduce the wall thickness, thereby increasing the diameters (I.D. and O.D.) of the resulting ring.

1- Starting stock cut to size by weight is first rounded, then upset to achieve structural integrity and directional grain flow.

2 Work piece is punched, then pierced to achieve starting "donut" shape needed for ring rolling process.

3- Completed preform ready for placement on ring mill for rolling.

4 Ring rolling process begins with the idler roll applying pressure to the preform against the drive roll.




5- Ring diameters are increased as the continuous pressure reduces the wall thickness. The axial rolls control the height of the ring as it is being rolled.

6- The process continues until the desired size is achieved.




[04] Closed Die Forging:

Closed-die Forging: In Closed-die forging the workpiece acquires the shape of the die cavities (impressions), while being forged between two shaped dies. During forging some of the material flows outwards and forms a flash. The flash has a significant role in the flow of material in closed-die forging. The thin flash cools rapidly and, with its frictional resistance, subjects the material in the die cavity to high pressures, thus encouraging the filling of the die cavity.

Closed-die forging is classified into two main types based on the used machine, the first is drop forging (Hammers), and the second is Press Forging (Presses).

Drop forge: The workpiece is created by hammering a piece of hot metal into an appropriately shaped die. The metal is heated and placed on the bottom part of a die. The top part of the die then drops onto the piece. The die may drop under gravity or be powered, but in all cases drop forging involves impact.

• Fast and Mass production technique • Limited for smaller products

Hydraulic Press Forgings: Press forging use a slow squeezing action of a press, to transfer a great amount of compressive force to the workpiece. Unlike drop forging where multiple blows transfer the compressive energy to the product, press forging transfers the force uniformly to the bulk of the material.

• process takes longer time (few

Seconds) • Suitable for large weight forgings • Requires more energy • More control over metal flow • Uniform material properties • The quality of the pieces is better than




drop forging




Upset Forging

Upset Forgings: Upset forging increases cross-section by compressing the length, this is used in making heads on bolts and fasteners, valves and other similar parts.

Heading: Upset forging: also called heading, is a process by which the cross-sectional size of a bar is increased, either at an end or at some point along its length. It is done on specially designed upsetting machines, using closed dies to control size and shape. Typically, dies have several stations, and the parts are formed progressively by moving the parts from one die station or cavity to another until the forging is complete. The process is performed on machines called headers, which are usually highly automated, with production rates of hundreds of pieces per minute for small parts. Heading processes can be carried out cold, warm, or hot. And called Cold Heading or Hot Heading.

Coining:




Coining is a closed-die forging operation typically used in minting coins. The material is coined in a completely closed die cavity. The pressure required is as high as 6 times the strength of the material in order to produce fine details. The coining process is also used with forgings and other products to improve surface finish and impart the desired dimensional accuracy. The process is then called sizing.




[05] Manufacturing Characteristics & Workability Materials exhibit different manufacturing characteristics such as (Castability, workability, Machinability, heat-treat ability, Weld ability, formability, and other.). These characteristics quantify the compatibility between the different materials and the different manufacturing techniques. Workability: is defined as the degree of deformation that can be achieved in a particular metal working process without creating an undesirable condition such as (Cracking, lack of die filling, and poor surface finish). Workability and formability are the terms that are commonly used to refer to the ease with which metal can be shaped during bulk and sheet forming operations, respectively. In the broadest sense, workability and formability indices provide quantitative estimates of the strength properties of a metal and its resistance to failure. However, the ductility or failure resistance is usually of primary concern. The techniques used to estimate this property vary, depending on the class of forming operation. Note That: Ductility indicates the ability of metal or alloy to be deformed by tensile stresses such as wire drawing, while, malleability indicates the ability to be deformed by compressive stresses such as forging.

Forgeability:

Metal or Alloy

Approximate

Range of Forging Temperature[0C]

Aluminum alloys 400—550 Magnesium alloys 250-350 Copper alloys 600-900 Carbon and low-alloy steels 850—1150 Martensitic stainless steels 1100—1250 Austenitic stainless steels 11 00—1 250 Titanium alloys 700-950 Iron-base superalloys 1050-1180 Cobalt-base superalloys 1180—1 250 Tantalum alloys 1050-1350 Molybdenum alloys 1150—1350

Forgeability is generally defined as the capability of a material to undergo deformation without cracking. A number of tests have been developed to quantify forgeability, although none is accepted universally. A commonly used test is to upset a solid cylindrical specimen and observe any cracking on the barreled surfaces. The greater the deformation prior to cracking, the greater is the forgeability of the metal. Upsetting tests can be performed at various temperatures and deformation rates.

Nickel-base superalloys 1050—1 200




Tungsten alloys 1200-1300




[06] Forging Force:

Open-die Forging The forging force F required to carry out a open-die forging operation of a solid cylindrical workpiece can be estimated from the formula: F = Yπr2 [1+ (2µr/3h)] Where; Y= yield (flow) stress of the material at forging temperature. r = radius of the workpiece. h = height of the workpiece. µ = coefficient of friction

Closed –die Forging The forging force F required to carry out a closed-die forging operation can be estimated from the formula: F = k Y A Where; Y= yield (flow) stress of the material at forging temperature. A= The projected area of the forging included the flash K is a multiplying factor K = 3-5, for simple shapes without flash. K = 5-8, for simple shapes with flash. K = 8-12, for complex shapes with flash. [07] Economics of Forging:




A number of factors are involved in the cost of forgings, which can be summarized as: Labor cost, machinery cost, material cost, and material properties and shape complexity, which is directly reflected in form of tooling cost. The figure shows the relative costs of a small connecting rod made by various processes. Note that for large quantities forging is more economical and sand casting is the most economical process for quantities less than 20000 pieces.




[08] Principles of Closed-die Forging: [1] Selection of parting line The three basic considerations involved in selection of parting line are: A) - Avoidance of deep impression B) - Avoidance of side thrust C) - Favorable grain flow [2] Shape & Dimensions Modifications: Fillet and corner radii: A corner is a convex arc, which joins two intersecting sides at an external angle of more than 1800. A fillet is a concave arc, which joins between two intersecting surfaces at an internal angle less than 1800.

Forging weight [Kg]

Filler radii [mm]

Corner radii [mm]

Machining allowances

[mm]

Length & width tolerances

Draft angles Mismatch allowances

0.1 1 1 0.8 0.5 1-2 1-2 1 2 1-3 1-3 2 5 2-4 2-3 2-3 10 3-6 3 3 20 4-6 3-4 3 50 7-12 4-7 3

0.003 inch per inch

= 0.003 mm per mm

Drop Forging: 70 external 100 internal Upsetting 30 external 50 internal

Up to 1 Kg 3 mm For each additional 3 Kg 0.05 mm

Draft angles: To enable ejection of part from the die. Tolerances and allowances: Includes: Machining allowance Mismatch allowance Shrinkage allowances Decarburization limits Die-Wear tolerances Length & width tolerances

[3] Forging Drawing: Engineering drawing of the product as finished after forging operation and flash trimming. By adding the shape modifications (Drafts, corner and fillet radii), and the new dimensions




and tolerances. Note that the outside contour of the product with thick lines, and the original product after machining with thin lines.

[4] Flash design: Flash thickness:

h F = 0.15 √ area of forging at parting line

Volume of flash V F= 0.75 [P + 4 (b + b1)] Where, P = perimeter of forging at parting line

Forging weight

[Kg]

Flash thickness

hf

h1 R

Where depth of impression is

Stamping by upsetting

Squeezing of simple shapes

Complicated shapes

20 mm 40 mm b b1 b b1 b b1 0.1 1 3 1 1.5 6 18 6 20 8 22 0.5 1.8 3.5 1 1.5 8 22 9 25 11 30 1 2.2 4 1.5 2.5 9 25 10 28 12 32 5 3.5 6 2 3 11 30 14 38 16 42 10 4.5 8 2.5 3.5 13 35 16 42 20 50 100 8 10 3 4 14 38 18 46 22 55

[5] Billet size calculation: W billet = W Forging + W Flash + W Cropping + W Scales W Cropping = 15% [W Forging + W Flash] W Scales = 2% [W Forging + W Flash]

[6] Sequence of operations:




[1] Swager swager of fuller (drawing out) [2] Edger (Distributing the stock) [3] Bender (Bending the stock) [4] Blocker (Forms the general shape) [5] Finisher (Bringing the forging to its final size and shape) [6] Cutoff (shearing off the tong hold)

How to estimate the Die Impresion [Edger] Shape?

1. Lay out a dimensioned drawing of the finish configuration, complete with flash.

2. Construct a baseline for area determination parallel to the centerline of the part.

3. Determine maximum and minimum cross-sectional areas perpendicular to the centerline of the part.

4. Plot these area values at proportional distances from the baseline.

5. Connect these points with a smooth curve (in instances where it is not clear how the curve would best show the changing cross-sectional areas, additional points should be plotted to assist in determining a smooth representative curve).

6. Above this curve, add the approximate area of the flash at each cross section, giving consideration to those sections where the flash should be widest. The flash will generally be of a constant thickness but will be widest at the narrower sections and smallest at the wider sections (the proportional allowance for flash is illustrated by the examples in Figure).

7. Convert the maximum and minimum area values to rounds or rectangular shapes having the same cross-sectional area.

[09] Forged Parts Comparative Analysis




Comparing with machined Parts: • Contoured grain flow yielding greater impact and directional strength • Cost savings in material and reduction of waste • Less machining and longer tool life

Comparing with Welded Parts:

• Single-piece design & Stronger parts due to the elimination of welds • Simplified production requirements & reduced labor. • Superior and consistent metallurgical properties

Comparing with Castings Parts:

• Directional grain flow and superior final part strength • Reduced process control and inspection requirements • Structural integrity and More predictable response to heat treating

Ain Shams Production University Engineering Shams University Faculty of Engineering Design & Prod....

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