1

Babylon University / Materials Engineering College

Ceramic Engineering Department

First Class ( First course 2015-2016)

Subject: Manufacturing(1) Sattar Alfatlawi

Introduction

Manufacturing processes can be divided into two groups, primary manufacturing

processes and secondary manufacturing processes. Primary processes provide the raw

materials or the basic shape and size to the work as casting, forming, powder metallurgy, etc.

Secondary manufacturing processes are aims to obtain desired product with final shape and

size with exact dimension of surface characteristics, as materials removal processes, powder

technology, etc. All of the products mentioned are made by various processes that we call

manufacturing as Casting or Moulding, Machining or Cutting, Forming or Deforming,

Assembly.

Figure 1 Relation between the Human and Machine

2

Materials removal processes can be divided into two groups (conventional and non-

conventional machining processes) for example of conventional processes are Turning,

Boring, Milling, etc. Non-conventional machining are Abrasive Jet Machining (AJM), Water-

Jet Machining (WJM), Ultrasonic Machining (USM), Chemical Machining (CM),

Electrochemical Machining (ECM), etc.

Production processes they are mechanical or chemical steps used to create any products,

generally involves the use of raw materials, machinery and human power to create a final

products. In addition to the process for shaping of raw materials, finishing operations are used

to obtain the final quality desired. These operation include: Cleaning, Painting, Buffing,

Plating, Polishing, Deburring, Heat treatment etc.

Manufacturing is the process of converting raw materials into products. It consist of the

design of the product and the selection of raw materials so the sequence of processes to the

product will be manufactured. It is the backbone of any industrialised country and the

mpo n o m n n onom y o n y l l o m n n y

is directly related to its economic health. Generally, the higher the level of manufacturing

activity in a country is the higher the standard of living of its people.

3

Measuring & Marking out& Hand Tools

Measurement a method of determining quantity, capacity, or dimension, and it is values

made meaningful by quantifying into specific units. Measurements act as labels which make

those values more useful in terms of details. . Several systems of measurement exist, each one

comprising units whose amounts have been arbitrarily set and agreed upon by specific groups,

but International System is accepted all over the world as the standard system for use in

science. Measuring are taken from a baseline or datum surface. A lot of tasks require two

datum surfaces at right angles to each other. Smoothing off will turn a rough, newly-sawn

edge into a datum surface.

To create a datum surface on wood, a plane is used.

To create a datum surface on metal and plastics, a flat file or hand file is used.

A steel rule or straight edge is used to check that a surface is flat, and a try square is used to

check a surface is at right angles to another surface

Marking out or layout is the process of transferring a design or pattern to a work piece, as

the first step in the manufacturing process. Or transfer of shapes and lines onto the material,

as guides for cutting, bending or shaping them. Accurate marking out is essential if the

different parts of the product are to fit together properly. It is performed in many industries or

hobbies although in the repetition industries the machine's initial setup is designed to remove

the need to mark out every individual piece.

Measuring Tools

Calipers are the very simple tools

used together with a steel rule for

the measurement or comparison

of linear dimensions. An

experienced worker can achieve

+/-0.05mm in the measurement.

Calipers are classified into two

types: -

Outside Calipers

Outside calipers (figure 2) are

used for measuring external

Figure 2. Outside Calipers

4

dimensions such as the length,

diameter, or even the thickness

of a solid.

Inside Calipers

Inside calipers (figure 3) are used

for measuring internal

dimensions such as the diameter

of a hole, or the width of a slot

etc

.

Figure 3. Inside Calipers

Vernier Calipers

Vernier Calipers (figure 4) are

more precise tools capable for

measuring external dimensions,

internal dimensions, and depths.

Besides the two pairs of

measuring jaws and the depth

gauge, its main features also

include a main scale and a

vernier scale.

Figure 4. Vernier Calipers

The resolution of a vernier scale is determined by the difference on the distance of one

division on the main scale and one division on the vernier. For example: A vernier scale of

length 49mm is divided into 50 equal divisions. That means one division on the vernier

represents 49/50=0.98 mm while one division on the main scale represents 1mm. Then, the

resolution of the vernier is 1mm - 0.98mm = 0.02mm

Vernier Height Gauge

A vernier height gauge (figure 5) is used for

measuring height of an object or for marking lines

onto an object of given distance from a datum base.

Figure 5. Vernier Height Gauge

5

Micrometer

A micrometer is a more precise measuring instrument than the vernier calipers. The accuracy

is come from the fine thread on the screw spindle. The ratchet prevents excess force from

being applied. Generally, the screw spindle has a pitch of 0.5mm. The thimble is divided into

50 equal divisions.

Common types of micrometers used in the workshops are: -

Outside Micrometer

An outside micrometer (figure 6) is used for

measuring external dimensions. The work to be

measured is placed between the anvil and the tip

of the spindle.

Figure 6. Outside Micrometer

Inside Micrometer

This is similar in structure to an outside

micrometer and is used for measuring internal

dimensions as shown in figure 7.

Figure 7. Inside Micrometer

Depth Micrometer

A depth micrometer (figure 8) is used for

measuring the depth of a hole, slot and keyway

etc. A complete set of depth micrometer is

equipped with spindles of different lengths,

which can be interchanged to suit different

measuring ranges.

Figure 8. Depth Micrometer

6

Engineer's Protractor

Engineer's protractor (figure 9) is a general

purpose tool used for the measuring / checking

of angles e.g. the angle of drill head, angle of

cutting tool, and even for the marking out of

angles on a component part.

Figure 9. Engineer's Protractor

Combination Set

Combination set (figure 10) is a set of equipment combining the functions of protractor,

engineer square, steel rule, Centre finder, level rule, and scriber.

Figure 10. Combination Set

Dial Indicator

The principle of dial indicator (dial gauge) is that the

linear mechanical movement of the stylus is magnified

and transferred to the rotation of pointer as shown in

figure 11. The accuracy of dial indicator can be up to

0.001mm. It is usually used for calibration of machine.

Figure 11. Dial Indicator

7

Marking Out Tools

Marking out is the preliminary work of providing guidance lines and centres before cutting

and machining. The lines are in 3-D and full-scale. The workpiece can then be cut or

machined to the required shapes and sizes. The common tools used for marking out are as

follow:

Scriber

A scriber (figure 12) is used for scratching lines

onto the workpiece. It is made of hardened tool

steel.

Figure 12. Scriber

Engineer's Square

Engineer's square (figure 13) is made of

hardened tool steel. It is used for checking the

straightness and the squareness of a workpiece. It

can also be used for marking perpendicular lines

onto a workpiece.

Figure13. Engineer's Square

Spring Dividers

Spring dividers (figure 14) are made of hardened

tool steel. The legs are used for scribing arcs or

circles onto a workpiece.

Figure14. Spring Dividers

Punch

There are two types of punch namely

the Centre Punch and the Dot Punch. A

dot punch has a point angle of 60¢X and

it is used for making of small dots on

the reference line. The centre punch has

Figure 15. Punch

8

a point angle of 90¢X as shown in

figure 14 and it is used for making a

large indent on a workpiece for drilling.

Both punches are made of hardened tool

steel.

Surface Plate

Surface plate (figure 16) is made of

malleable cast iron. It has been

machined and scraped to a high degree

of flatness. The flat surface is being

used as a datum surface for marking out

and for measuring purposes. If it can

stand on the floor, it is called surface

table.

Figure 16. Surface Plate

Angle Plate

An angle plate (figure17) are used for supporting

or setting up work vertically, and are provided

with holes and slots through which securing

bolts can be located. It is made of cast iron and

ground to a high degree of accuracy.

Figure 17. Angle Plate

9

Vee Block

Vee blocks (figure 18) usually in a couple are

made of cast iron or steel in case-hardening. They

are generally used for holding circular workpiece

for marking out or machining.

Figure 18. Vee Block

Hand Tools

Bench Vice

A bench vice (figure 19) is the device for holding the

workpiece where most hand processes to be carried

out. The body of the vice is made of cast iron while

the two clamping jaws are made of hardened tool

steel. Some bench vice has a swivel base, which can

set the workpiece at an angle to the table. The vice

height should be correct ergonomically. Vice clamps,

made of copper are fitted over the vice jaws when

holding finished work to avoid damage to the finish

surfaces.

Care of Vices

a. Do not direct impact the vice body by the

hammer.

b. Light hammering can be done on and only on

the anvil of the vice.

c. To avoid over clamping, the handle of the

vice should be tightened by hand only

Figure19. Bench Vice

Files

Files are the most important hand tools used for the removal of materials. They are made of

hardened high carbon steel with a soft 'tang'. to which a handle can be fixed. Files are

categorised as follows:-

Length - measured from the shoulder to the tip.

Shape - the cross-sectional profile.

11

Grade - the spacing and pitch of the teeth.

Cut - the patterns of cutting edge.

Figure 20. File

Save Edge

There are no cutting edges on one side of the hand file. The purposes for the save edge is to

avoid the worker damage the work, when he is filing a shoulder position. Shape of Files

1. Hand File - The common file used for

roughing and finishing. It is a rectangular in

section and parallel in width. It has double cut

teeth on two faces, single cut teeth on one

edge, and one save edge.

Figure 20a. Hand File

2. Flat File - It is similar to a hand file

rectangular in section, tapered slightly in

width and thickness towards the tip. It has

Double Cut teeth on two faces and Single Cut

teeth on two sides.

Figure 20b. Flat File

3. Half-round File - The section is a chord of a

circle with its taper towards the tip. It is used

for forming radii, grooves, etc. and the flat

side is used for finishing flat surfaces.

Figure 20c. Half-round File

4. Round File - This is of round section

tapering toward the end. It is used for

enlarging holes, producing internal round

corners. Usually double cut in the larger sizes,

and single cut for the smaller sizes.

Figure 20d. Round File

11

5. Square File - This is square in section, with

tapered towards the tip, and usually double cut

on all four faces. It is used for filing

rectangular slots or grooves.

Figure 20e. Square File

6. Three Square File - It is also known as

triangular file. This is a triangular in section,

with tapered towards the tip with double cut

on both faces. It is used for filing corners or

angles less than 90°

Figure 20f. Three Square File

12

Casting Processes

The casting process involves pouring of liquid material (molten article) into a mold cavity

of the desired shape and allowing it to solidify to obtain the final casting. The flow of molten

metal into the mold cavity depends on several factors like minimum section thickness of the

part, number of corners, non-uniform cross-section of the cast, and so on. Important

considerations in casting operations are as follows;

1. The flow of the molten article into the mold cavity.

2. The solidification and cooling of the molten article in the mold.

3. The effect of the type of mold material.

Figure 21 Casting Process

Casting is most often used for making complex shapes that will be difficult or uneconomical

to make by other methods. The molten metal is poured into the mold, this mold made of some

heat resisting material. Sand is most often used as it resists the high temperature of the molten

metal. Permanent molds of metal can also be used to cast products.

13

Casting methods

The major classifications of casting are according to mold materials, molding processes,

and methods of feeding the mold with the molten metal, this classification involves three types

are;

1. Expendable mold casting, in this type the molds are made of sand, plaster, ceramics, and

similar materials. These are generally mixed with various binders, or bonding agents. These

materials are refractories, they are capable of resistance the high temperatures of molten

metals .After the casting has solidified, the mold in these processes is broken till remove the

product. Expendable mold casting processes are suitable for very complex shape parts and

materials with high melting point temperature. However, the rate of production is often

limited by the time to make mold rather than the casting itself. The major expendable mold

processes are; sand-mold casting, shell- mold casting, expendable-pattern casting, plaster-

mold casting, ceramic-mold casting, vacuum casting etc.

2. Permanent mold casting, the mold is made of metals that maintain their strength at high

temperatures. They are used repeating and can be easily removed and the mold used for the

next casting. Metal molds are batter heat conductors than expendable non- metallic molds, the

solidifying casting is subjected to a higher rate of cooling, which effect of the microstructure

and grain size of casting. The permanent-mold casting such as; slash casting, pressure

casting, die casting, centrifugal casting, squeeze casting, etc.

3. Composite mold casting, which are made of two or more different materials, such as sand,

graphite, and metal, to combining the advantages of each material. They are used in various

casting processes to improve mold strength, control the cooling rates, and optimize the

overall economics of the processes.

14

Sand Casting

Sand casting is widely used because this process is simple, and almost any material can be

cast, no limit to size, shape or weight, low tooling cost. The basic steps of sand casting

process are:

1- Selection suitable sand to create sand mold and to control on quality of casting.

2- Put pattern from wood or metal in sand to create mold cavity.

3- Do small hammering on the sand to make stability of the pattern.

4- Remove the pattern.

5- Fill the mold cavity with molten metal.

6- Allow the molten article to cool.

7- break the sand mold and remove the casting product.

The sand casting process is usually economical for small batch size production, but with

small limitations, some finishing required, small coarse finish, wide tolerances.

The quality of the sand casting depends on the quality and uniformity of green sand

material that is used for making the mold. Figure (22) schematically show a two of parts of

sand mold, also referred to as a cope and drag sand mold. The molten metal is poured through

the pouring cup and it fills the mold cavity after passing through down sprue, runner and gate.

The core refers to loose piece which are placed inside the mold cavity to create internal holes

or open section. The riser is used as a container or reservoir to excess molten metal that

facilities additional filling of mold cavity to compensate for volumetric shrinkage during

solidification. Sand castings process provides several advantages. It can be employed for all

types of metal. The tooling cost is low and can be used to cast very complex shapes. However

sand castings offer poor dimensional accuracy and surface finish.

15

Figure 22 Schematic of sand molding

Moulding Sand

Composition

The main components of any moulding sand are:

(a) Silica sand (SiO2) 80.8%

(b) Alumina (Al2O3) 14.9%

(c) Iron oxide (Fe2O3) 1.3%

(d) Combined water 2.5%

(e) Other inert materials 1.5%

Properties of Moulding Sand

The moulding sand should possess the following properties:

1. Porosity or permeability: It is that property of sand which permits the steam and other

gases to pass through the sand mould. When hot molten metal is poured into the sand mould,

it evolves a great amount of other gases while coming in contact with the moist sand. If these

gases do not escape completely through the mould, the casting will contain gas holes and

pores. Thus, the sand from which the mould is made must be porous or permeable. The

porosity of sand depends upon its grain size, grain shape, and moisture and clay contents in

the moulding sand. The quality of sand has directly affects to the porosity of the mould. If the

sand is too fine, its porosity will be low.

16

2. Plasticity: It is very important to made a mold, that property of sand due to which it flows

to all portions of the moulding box and taken a predetermined shape under hammering

pressure and keep this shape when the pressure is removed. The sand must have sufficient

plasticity to produce a good mould. The plasticity is increased by adding water and clay to

sand.

3. Adhesiveness: It is the property of sand due to which it adheres to the sides of the

moulding box. Good sand must have sufficient adhesiveness so that heavy sand masses can be

successfully held in moulding box without any danger of its falling out when the box is

removed.

4. Cohesiveness: It is that property of sand due to which the sand grains stick together during

ramming. It may be defined as the strength of the moulding sand. It is of the following three

types,

(a) Green strength: The green sand, after water has mixed to it, must have suitable strength

and plasticity for making of mould. The green strength depends upon the grain shape and size,

amount and type of clay and the moisture content.

(b) Dry strength: When the molten metal is poured, the sand adjacent to the hot metal

quickly loses water content as steam. The dry sand must have the strength to resist of erosion

and also the pressure of the molten metal, otherwise the mould may increase.

(c) Hot strength: After the moisture has evaporated, the sand may be required to possess

strength at high temperature, above 100°c. If the sand does not possess hot strength, the

pressure of the liquid metal bearing against the mould walls may cause mould enlargement or

if metal is still flowing, it may cause erosion, cracks or breakage.

5. Refractoriness: It is that property of the sand which enables it to resist high temperature of

the molten metal without breaking or fusing. The higher pouring temperature, such as those

for ferrous alloys, requires great refractoriness of the sand. The degree of refractoriness

depends upon the quartz contents, and the shape and grain size of the particles.

6. Flowability: It is the property of sand due to which it behaves like a fluid so that, when

rammed, it flows to all portions of a mould and distributes the ramming pressure equally.

Generally, sand particles resist moving around corners. In general, flowability increases with

decrease in green strength and decrease in grain size. It also varies with moisture content.

17

Die casting

The die casting or pressure die casting may be defined as that casting which uses the

permanent mould and used pressure to molten metal is introduced into it. The casting

produced by die casting method require very little machining. The dies are usually made in

two parts which must be locked securely before molten metal is forced into then under high

pressures of 7 to 700 MPa. The pressure may be obtained by the application of compressed air

or by hydraulically operated piston. The ferrous alloys are not yet commercially die-casted

because of their high pouring temperature.

Typical parts made through die casting are motors, appliance components, hand tools, and

toys. There are two types of die casting machines; hot chamber and cold chamber.

1. Hot Chamber

The hot chamber die casting machine of the submerged type is shown in Fig 23. The molten

metal is forced in the die cavity at pressures from 7 to 14 MPa. The pressure may be obtained

by the application of compressed air or by a hydraulically operated plunger.

Fig.23 Hot Chamber of Die Casting (hydraulically plunger)

In the first method, the goose neck is lowered to filling of the molten metal. It is then raised

and connected to the die neck. A suitable mechanism is provided to raise and lower the goose

neck. The compressed air at a pressure of about 2.5 to 5 MPa is now injected into the goose

neck to force the molten metal into the die. In the second method, the plunger acts inside a

cylinder formed at the end of the goose neck, which is immersed in a pot of molten metal. A

port is provided near the top of the cylinder to allow the entry of the molten metal. The

18

downward stroke of the plunger pushes the molten metal through the goose neck into the die.

The hot chamber die casting machine is used for casting zinc, tin, lead and other low melting

alloys.

2. Cold Chamber

In cold chamber die casting machine, the melting unit is usually separate and molten metal

is transferred to injection mechanism by ladle. The pressure on the casting metal in cold

chamber die casting machine may vary from 21 to 210MPa and in some cases may reach

700MPa. The greater pressures are required for semi-molten alloys to compensate for reduced

fluidity resulting from low pouring temperatures. This process is used for casting aluminum,

magnesium, copper base alloys and other high melting alloys. The cold chamber die-casting

machine, as shown in Fig. 24 consists of

Fig.24 Cold Chamber of Die Casting

a pressure chamber of cylindrical shape fitted with a piston that is usually operated by

hydraulic pressure. A measured quantity of molten metal is brought in a ladle form the

melting pot to a chamber and forced into the closed die sections by applying hydraulic

pressure upon the piston. The cycle is completed in the following four steps:

1. The metal is loaded in the chamber.

2. The plunger forces the metal into the die cavity.

3. After the metal solidifies, the die is opened.

19

4. The casting, together with the slag of the excess metal is ejected- form the die.

Advantages

1. The rapid and economical production of large quantities of identical parts can be achieved.

2. The parts having smooth surfaces and close dimensional tolerances may be produced, very

little machining is required.

3. The parts having thin and complex shapes can be casted accurately and easily.

4. The die casting requires less floor area than is required by other casting processes.

5. The castings produced by die-casting process are less defective.

6. The rapid cooling rate produced high strength and quality in many alloys.

7. The die is used more than once and life for longer periods. For example, the life of a die for

zinc base casting is up to one million castings, for copper base alloys up to 75,000 castings,

and for aluminum base alloys up to 50,000 castings.

Disadvantages

1. The cost of equipment and die is high.

2. There is a limited range of non-ferrous alloys which can be used for die castings.

3. The die castings are limited in size.

4. It requires special skill in maintenance.

21

Centrifugal casting

In centrifugal casting process, the molten metal poured at the centre of a rotating mold or

die. Because of the centrifugal force, the lighter impurities are crowded towards the centre of

the mold. For producing a hollow part, the axis of rotation is placed at the centre of the

desired casting. The speed of rotation is maintained high so as to produce a centripetal

acceleration of the order of 60g to 75g. The centrifuge action segregates the less dense non-

metallic inclusions near to the centre of rotation that can be removed by machining a thin

layer. No cores are therefore required in casting of hollow parts although solid parts can also

be cast by this process.

The centrifugal casting is very suitable for axisymmetric parts. Very high strength of the

casting can be obtained. Since the molten metal is fed by the centrifugal action, the feeding is

simple. Both horizontal and vertical centrifugal castings are widely used in the industry.

Figure 25 schematically shows a set-up for horizontal centrifugal casting process. Figure 25

typically shows large pipes that are made using centrifugal casting process.

Figure 25 Centrifugal casting process

21

Features of centrifugal casting

Castings can be made in almost any length, thickness and diameter.

Different wall thicknesses can be produced from the same size of mold.

No need for cores.

Resistant to atmospheric corrosion, a typical situation with pipes.

Mechanical properties of centrifugal castings are excellent.

Only cylindrical shapes can be produced with this process.

Size limits are up to 3 m diameter and 15 m length.

Wall thickness range from 2.5 mm to 125 mm.

Tolerance limit: on the OD can be 2.5 mm on the ID can be 3.8 mm (0.15 in).

Surface finish ranges from 2.5 mm to 12.5 mm.

Inspections of Casting

Visual inspection

Visible defects that can be detected provide a means for discovering errors in the pattern

equipment or in the molding and casting process. Visual inspection may not suitable of the

detection of subsurface or internal defects.

Dimensional inspection

Dimensional inspection is one of the important discovering of casting. When precision

casting is required, we make some samples for inspection the tolerance, shape, size and also

measure the profile of the cast. This dimensional inspection of casting may be conducted by

various methods:

• S nd d m n n m n o h k h z o h

• Con o o h h k n o p o l , nd h p

• Coo d n m n nd M k n M h n

• Sp l x

X-Ray Radiography

In all the foundries the flaw detection test are performed in the casting where the defects are

not visible. This flaw detection test is usually performed for internal defects, surface defects

etc. These tests are valuable not only in detecting but even in locating the casting defects

present in the interior of the casting. Radiography is one of the important flaw detection for

casting. The radiation used in radiography testing is a higher energy (shorter wavelength)

version of the electromagnetic waves that we see as visible light. The radiation can come from

an X-ray generator or a radiation source.

22

Magnetic particle inspection

This test is used to detect the location of cracks that extend to the surface of iron or steel

castings, which are magnetic nature. The casting is first magnetized and then iron particles are

sprinkled all over the path of the magnetic field. The particles are moved to the direction of

the lines of force. A discontinuity in the casting causes the lines of the force to bypass the

discontinuity and to concentrate around of the defect.

Fluorescent dye-penetration test

This method is very simple and applied for all cast metals. It is applying a thin penetration

oil-base dye to the surface of the casting and allowing it to stand for some time so that the oil

passes into the cracks by means of capillary action. The oil is then completely wiped and

cleaned from the surface. To detect the defects, the casting is painted with a coat of powdered

and then viewed under ultraviolet light. The oil being fluorescent in nature, can be easily

detect under this light, and thus the defects are easily detected.

Ultrasonic Testing

Ultrasonic testing used for detecting internal voids in casting is based on the principle of

reflection of high frequency sound waves. If the surface under test contains some defect, the

high frequency sound waves when emitted through the section of the casting, will be reflected

from the surface of defect and return in a shorter period of time. The advantage this method of

testing over other methods is that the defect, even if in the interior, is not only detected and

located accurately, but its dimension can also be quickly measured without in any damaging

or destroying the casting.

Macroscopic examination

The macroscopic inspection is widely used as a test in steel production because it is provide

effective means of determining internal defects in the metal. Macroscopic examination may

detect one of the following conditions:

• C y ll n h o n y, d p nd n on ol d on

•Ch m l heterogeneity, depending on the impurities present or localized segregation

• M h n l h o n y, d p nd n on n n od d on h m l

Microscopic Examination

Microscopic examination can enable the study of the microstructure of the metal alloy,

composition, type and nature of any treatment given to it, and its mechanical properties. In the

case of cast metals, as steels, cast iron, malleable iron, microstructure examination is essential

23

to discovery of metallurgical structure and composition. Grain size and distribution, grain

boundary area can be observed by this procedure. Distribution of non-metallic inclusion can

also be found from this process of inspection.

.Casting Defects

Figure 26 schematically shows various defects that are arise or occur during casting,

especially sand casting processes, some of defects are indicated as follow.

Shrinkage

Shrinkage of molten metal as it solidifies is an important issue in casting. It can reduce the

5-10% volume of the cast. Gray cast iron expands upon solidification due to phase changes.

Need to design pattern and mold to compensate of this amount of volume decreasing is

important. Shrinkage defect can be reduced by good design the riser and pattern and molds.

Porosity

Porosity is a phenomenon that occurs in materials, especially castings, as change of state from

liquid to solid during the manufacturing process. Casting porosity which either effects the surface

finish or as a leak path for gases and liquids. The poring temperature should be maintained

properly to reduce porosity. Adequate flux of metal, controlling the amount of gas-producing and

materials in the molding, core making and sand mixes can help in minimizing this defect.

Hot tear

Hot tears are internal or external discontinuities or crack on the casting surface, caused by rapid

contraction directly after the metal solidified. They may be produced when the casting is poorly

designed and sudden sectional changes occur. Incorrect pouring temperature and improper

placement of gates and risers can also create hot tears. Method to prevent hot tears may improving

the casting design, achieving directional solidification and even rate of cooling, selecting proper

mold and materials to suit the cast metal, and controlling the mold hardness in relation to other

components of sand.

Scar

It is usually found on the flat casting surface. It is a shallow blow.

24

Figure 26 Schematic of various casting defects..

Blowhole

Blowholes are smooth round holes that are clearly on the surface of the casting. To prevent

blowholes, moisture content in sand must be well adjusted, sand of proper grain size should be

used, ramming should not be too hard and venting should be adequate.

Blister

This is a scar covered by the thin layers of the metal.

Dross

The lighter impurities are appearing on the top of the cast surface is called the dross. It can be

taken care of at the pouring stage by using items such as a strainer and a skim bob.

25

Dirt

Sometimes sand particles dropping out of the cope get embedded on the top surface of a casting.

When removed, these leave small angular holes is known as dirts.

Wash

It is a low projection on the drag surface of a casting commencing near the gate. It is caused by

the erosion of sand due to high velocity liquid metal. .

Shift

A shift results in a mismatch of the sections of a casting usually as a parting line. This defect

can be prevented by ensuring proper place of the pattern for die parts, molding boxes, and

checking of pattern locating pins before use.

Warped casting

Warping is an undesirable deformation in a casting which occurs during or after

solidification. Wrap edge occurs in large and flat sections especially. Wrap edge may also be

due to insufficient gating system that may not allow rapid pouring of metal or due to low

green strength of the sand mold or inadequate tolerance in the pattern / mold cavity.

Metal Penetration and Rough Surfaces

This defect appears as rough external surface of the casting. It may be caused when the

sand has too high permeability, large grain size, and low strength. Soft ramming may also

cause metal penetration.

Fin

A thin projection of metal, this not part of casting, is called a fin. Fins occur at the parting of the

mold or core sections. Molds and cores incorrectly assembled will cause the fin. Insufficient

weighing of the molds or improper clamping of flasks may again produce the fin defect.

Cold Shut

A cold shut is a defect in which a discontinuity is formed due to the imperfect fusion of two

streams of metal in the mold cavity. The reasons for cold shut may be too thin sections and wall

thickness, improper gating system, damaged patterns, slow and discontinuity pouring, poor

fluidity of metal caused by low pouring temperature, improper alloy composition, etc.

26

Materials joining methods

Two methods used to join of materials permanent and semi-permanent, Different materials

can be joined in many different ways depending on the joint needs to be permanent or semi-

permanent. They are (Welding, Brazing, Soldering, Riveting, Adhesives, Nuts and bolts and

washers, Knock-down fittings, Screws).

• P m n n : Th m o w ld n , b z n , old n nd dh bond n In h

processes a permanent joint between the parts is formed and cannot be separated easily, if

separate these parts are damage.

• S m -permanent: this type of joint is a method of joining that is designed to be permanent,

this term refer to nuts and bolts and washers, knock-down fittings; however, it can be

disassembled without damage the materials.

Welding

Welding is a material joining process in which two or more parts are assembled (joined

together) at their contacting surfaces by a suitable application of heat and/or pressure.

Sometimes parts are united together by application of pressure only without external heat. In

some welding process a filler material is added to facilitate united. Welding is used most

commonly with metallic parts but for plastics also it is used.

The main method of permanently joining metals is by welding. Two main types of welding

are conventional and nonconventional welding. There are many types of welding as MIG and

TIG, oxyacetylene welding, electric arc and spot and seam welding, all involve permanently

joining metals by the use of heat, causing the two main pieces of metal to become molten and

using a joining material to mix them before they solidify, forming a permanent, strong joint.

Riveting

Rivets are used to join two sheets or plates of metal together. There are four main types of

rivets: snap head, mushroom, pan head, countersunk, and the operation with join by rivets

including;

27

1. The rivet is placed into a tool called a dolly that is held in a vice.

2. The plates are then placed over the rivet.

3. The rivet set is then placed over the rivet and pressed down to ensure that there are no gaps

between the sheets/plates of metal.

4. The rivet set is tapped with a ball pein hammer. This closes any gaps and starts to form the

rivet joint.

The ball pein hammer is then reversed to form the head of the rivet. The final stage is using a

rivet snap to form a similar shaped dome on both sides of the joint.

Figure 27 Rivets are used to join

Adhesives

The main advantage of using an adhesive over other methods of joining, it is generally

invisible unlike other methods of joining and adhesives do not damage or change the

materials being joined, but it is not used to all materials.

Types of adhesives

Synthetic resin glue; Use to joining wood, it is a powder that is mixed with water to made a

thin paste, advantages of this type are; stronger than PVA, heat and water resistant,

economical, permanent, And disadvantages are; takes 4-6 hours to set, hard on tools.

PVA (Polyvinyl; use to Joining wood, it is a white liquid sold in various sizes of containers,

with advantages (strong and water resistant, sets quickly (2-3 hours), excess glue can be

removed by a damp cloth).

Contact (impact) adhesive; Use to joining different types of materials, e.g. plastic or metallic

strips to wood and other materials. Each surface is coated with the adhesive and left for 10-15

minutes until touch dry. With advantages are; Clean, quick, economical.

28

Epoxy resin; is the main example of this adhesive. It is used to form a rigid bond with most

unlike materials with exception of silicon rubber, polythene or thermoplastic. The resin and

hardener are mixed and spread over surfaces and left to set for 24 hours. Advantages are;

Good water resistance, insulation and gap filling properties. Disadvantages are expensive

because it needs to be spread over a larger area to be permanent, high coast prevents large-

scale work.

Other adhesives are;

• T n ol 12 nd n ol 70 o jo n n h mopl

• T n ol 53 o jo n n PVC

• R d poly y ne cements.

• Sp l DIY ll-purpose adhesives.

• Sp l nd l dh

• Do bl -sided tape.

• L x dh

• Ho -melt glue used in hot glue guns.

Nuts, bolts and washers

Nuts and bolts are used to hold two or more pieces of materials together in a semi-

permanent method of joining. Bolts tend to be made from high tensile steel and are threaded

(square or hexagonal threaded) for all or part of the length of the shaft. Nuts used with bolts

must have matching diameter and thread form. They come in various forms, from wing nuts

(made for easy removal by hand) to hexagonal nuts and special locking nuts that resist

coming loose. Types of washers: Washers are used to protect the surface when nuts are

tightened. They spread the load applied to the surface and prevent loosening that can be

caused by vibrations.

29

Conventional Welding

Welding processes usually divided into three main groups, solid state and liquid state

welding, but there are third type namely solid/liquid state. With three types the materials are

joined together with these methods cannot separate easily and achieved by pressure, pressure

and heat, or heat only.

Solid-state Welding Processes; In solid state welding such as friction welding, forge

welding, explosion welding, etc. The surfaces to be joined are brought into close proximity by

heating the surfaces without causing melting and applying normal pressure and providing

relative motion between the two surfaces, after stop the motion is applying high pressure

without heating. In these processes the materials remain in solid state and welding is achieved

through the application of heat and pressure, or high pressure only.

Liquid State (Fusion) Welding Processes; arc welding, resistance welding, oxy fuel gas

welding, etc. There are two inherent problems with fusion welding, effect of localized heating

and rapid cooling on the microstructure of the parent metals and effect of residual stresses

developed in the parent metals due to restrained expansion or contraction.

Solid / Liquid State Bonding; In this state low temperature joining methods are used when

the metal to be joined cannot withstand to high temperature, or complex sections are to be

joined, or dissimilar metals are to be joined, or weldability of material is poor. Also in these

methods, the gap between the metal pieces to be joined is filled with molten filler material

after heating the base metal. Melting point of filler material is much lower than base metals.

The bonding is not due to melting of parent metal.

Filler material is drawn into the gap between the metal pieces to be joined by capillary

action and the bond formation is started when the molten filler metal comes to contact with

the solid surface as in solid state welding. The nature of bond formed is much complex here,

there is some of inter-solubility between filler and base metals to produced resulting alloy.

This inter-diffusion at the base metal surface and resulting alloy has a strength which is very

close to that the base metal.

Also for a good joint strength the liquid filler metal; must flow into the gap between the

metal pieces to be joined and cover the entire surface area, without gaps or blow holes.

Usually to good bonding are doing the following:

– Clean base metal surfaces

31

– Maintain optimum gap.

– Heat the joining area above melting temperature of the filler material.

– Use fluxes for welding of base metal surfaces.

Welding which is the process of joining two components for the desired purpose, can be

defined as the process of joining two similar or dissimilar materials components with the

application of heat, with or without the application of pressure and with or without the use of

filler metal. Heat may be obtained by chemical reaction, electric arc, electrical resistance,

frictional heat, sound and light energy etc.

Electric Arc Welding

Electric Arc Welding provides the heat required for melting the parent as well as filler

material. The workpiece and the electrode are connected to the power source and the arc is

started with touching the electrode to the workpiece and then withdrawing it to a short

distance (a few mm) from the workpiece. When the electrode and workpiece are in contact the

current is flows. The arc is generated by the electrons emitted form cathode and moving

towards anode and the arc changes electrical energy into heat and light.

Figure 28 Electric Arc Welding

About 70% of the heat emitted due to flux of electrons at anode raises the anode temperature

to high values (5,000 to 30,000oC). This heat melts the base metal as well as tip of the

electrode in the area surrounding the arc. A weld is formed when the mixture of molten base

and electrode metal solidifies in the weld area.

Both direct current (DC) and alternating currents (AC) are used in arc welding. AC

machines are less expensive to purchase and operate, but generally limited to welding of

31

ferrous metals. DC equipment can be used on all metals with good results and is generally

famous for better arc control. The used can be either non-consumable or consumable

electrodes. Consumable electrodes usually have a coating on its outer surface which on

melting emitted gases like hydrogen or carbon dioxide to form covering around the molten

pool.

The electrode also reacts to slag which is a liquid and lighter than the molten metal. The

slag therefore is rises and floating on the surface and by solidification forms a protective

covering over the hot metal. This also slows down the rate of cooling of the weld. The slag

layer can be removed by light chipping or small hammering on the slag cover. Electric arc

welding of this type is known as (Shielded Metal Arc Welding). More than 50% industrial arc

welding is done by this method.

For continuous arc welding operations, the consumables electrode is wire in the form of a

coil and the flux us fed into the welding zone, or the weld area is covered by an inert gas. In

Submerged Arc Welding the electrode is shielded by granular flux supplied from a source,

while is Gas Metal Arc Welding shielding of the area is provided by an inert gas such as

argon, helium, carbon dioxide , etc.

Arc Welding (GTAW) is also called as Tungsten Inert Gas (TIG) welding. It uses tungsten

alloy electrode and helium gas shield. Because of inert gas atmosphere tungsten is not

consumed. Filler materials are supplied by a separate rod or wire in this case.

Friction Welding

Friction welding is a solid-state joining process that produces coalescence in materials,

using the heat developed between surfaces through a combination of mechanically induced

rubbing motion and applied load. The resulting joint is of forged quality. Under normal

conditions, the faying surfaces do not melt. Filler metal, flux and shielding gas are not

required with this process. Friction welding is a type of forge welding, i.e. welding is done by

the application of pressure. Friction generates heat, if two surfaces are rubbed together,

enough heat can be generated and the temperature can be raised to the level where the parts

subjected to the friction may be fused together.

Types of friction welding

Linear friction welding.

Spin welding.

32

Rotary friction welding.

Inertia friction welding.

Friction stud welding.

Friction stir welding.

In conventional friction welding, relative rotation between a pair of workpieces is caused

while the work pieces are stuck together. Typically then once sufficient heat is built at the

interface between the workpieces, relative rotation is stopped and the workpieces are adhere

together under forging force which may be same as or greater than the original adhering force.

In this process the two surfaces to be welded are rotated relative to each other under light

normal pressure. When the interface temperature is produced due to frictional rubbing and

when it reaches the required welding temperature, sufficient normal pressure is applied and

maintained until the two pieces get welded, figure below is explain the process.

Figure 29 Friction welding

With friction welding can be saving cost, time, materials, and dissimilar materials can be

joined, a significant cost savings is possible because engineers can design parts that use

expensive materials only where is needed. Expensive forgings and castings can be replaced

with less expensive forgings welded to bar stock, tubes, plates and the like. Substantial time

savings are realized since the process is faster than more conventional methods of welding.

Even dissimilar metals or considered incompatible can be joined by friction welding, such

as aluminum to steel, copper to aluminum, titanium to copper and nickel alloys to steel. As a

rule, all metallic engineering materials which are forgeable can be friction welded, including

33

automotive valve alloys, maraging steel, tool steel, alloy steels. In addition, many castings,

powder metals and metal matrix composites are weldable.

Mechanism of friction welding

It is carried out by moving one component relative to the other along a common interface,

while applying a compressive force across the joint. The friction heating generated at the

interface softens both components, and when they become plasticised the interface material is

extruded out of the edges of the joint so that clean material from each component is left the

original interface. The relative motion is then stopped, and a higher final compressive force

may be applied before the joint is allowed to cool. The key to friction welding is that no

molten material is generated, the weld being formed in the solid state.

The principle of this process is the changing of mechanical energy into heat energy. One

component is rotated about its axis while the other component to be welded to it and does not

rotate but can be moved axially to make contact with the rotating component. At a point

fusion temperature is achieved then rotation is stopped and forging pressure is applied. Then

heat is generated due to friction and is concentrated and localized at the interface, grain

structure is refined by hot work. Then welding is done, but there will not occur the melting of

parent metal.

Advantages

1. Dissimilar metals are joined, even some considered incompatible or non-weldable.

2. The process is much faster than other welding techniques.

3. Friction welders are enough to join a wide range of part shapes, materials and sizes.

4. Join p p on n‟ l m h n n , w , nd n h d w ld bl

5. Resulting joints are of forged quality, with a 100% butt joint weld through the contact area.

6. The machine-controlled process eliminates human error, and weld quality is independent of

operator skill.

7 I ‟ olo lly l n, no obj on bl mok , m , o n d h n d o

be exhausted.

8. No consumables are required, flux, filler material, or shielding gases.

34

9. Power requirements are as low as 20% of that required of conventional welding processes.

10. Since there is no melting, no solidification defects occur, e.g. gas porosity, segregation or

slag inclusions.

Disadvantages

The disadvantage of friction welding are that not every configuration is feasible, that a

machine of sufficient power is needed and that for short runs the process may not be

economical. The friction welding process has some costs in tooling and set up that must be

taken into account when calculating the costs per weld. Also finishing operations may be

requested which sum up to the total cost.

Application of friction welding

Generally friction welding is used in most areas of life to join a wide range of parts, shapes,

materials, and weld sizes. Applications typically friction welded include aircraft and

aerospace components, cutting tools, agricultural machinery, automotive parts, oil field

pieces, military equipment, etc. These are some applications of friction welding.

1. Commercial

Many commercial parts are candidates for inertia welding due to the fact that the weld is

accomplished quickly and with minimum clean. The fact that the weld is at 100% strength, it

provides a stronger part than traditional welds. It uses in air cylinders, oil pipe and water pipe

fittings, bicycle parts, medical equipment, marine equipment, electrical equipment,

photographic and sound equipment, etc.

2. Aerospace

Full strength inertia welded parts are used in a wide range of aerospace applications. Such

as turbine wheels and shafts, pressure vessels, welding parts have been used in satellites,

telescope equipment, etc.

3. Hydraulic

Inertia welding is used in hydraulic cylinders and valves, the cylinders can be completely

machined and the caps can be weld on afterwards providing for cost reductions. For irregular

shapes, the cylinder can be welded to a larger piece of material to reduce cost and machine

time. This process also used to the pistons and shaft weldments as well as side ports.

35

4. Automotive

In many automotive applications it is necessary to use different stress loads on various types

of materials. Such as in some cases the requirement of two types of metal on one part.

Applications include drive shafts, axles, front wheel drive shaft joints, wheels and rims,

certain camshaft and crankshaft applications.

5. Bi-metal

Applications range of bi-metal as electrical connectors, vacuum and pressure systems,

satellite heat pipes and pressure storage systems, turbine engine components, etc.

Brazing and Soldering

Both brazing and soldering are the metal joining processes in which parent metal does not

melt but only filler metal melts and filling the joint with capillary action. If the filler metal is

having melting temperature more than 450°C but lower than the melting temperature of

components then it is termed as process of brazing or hard soldering. However, if the melting

temperature of filler metal is lower than 450°C and also lower than the melting point of the

material of components then it is know as soldering or soft soldering.

During brazing or soldering flux is also used which performs the following functions:

• Dissolve oxides from the surfaces to be joined.

• Reduce surface tension of molten filler metal i.e. increasing its wetting action or

spreadability.

• Protect the surface from oxidation during joining operation.

The strength of brazed joint is higher than soldered joint but lower than welded joint.

How , n b w n w ld n nd b z n h no h p o m d „b z w ld n '

Brazing is used to join metals such as copper and steel. Brazing is similar to soldering but

uses much higher temperatures (870 – 880°C). The rod used to fuse the two pieces together is

called the brazing spelter and is composed of an alloy of copper, zinc, and tin. When the

correct temperature is reached, the spelter melts and fills the joint by capillary action. The

joint is allowed to cool and harden before the excess flux is removing .

36

Firure 30 Brazing Welding

Solder welding

The two main types of soldering are:

• H d old n

• So old n

The principle of the two types is the same; however, the lowest melting point in hard

soldering is 450°C, whereas in soft soldering the melting point is approximately 200°C. The

stages in the soldering process are:

1. Materials are cleaned and degreased. The surfaces of the two materials can be kept clean by

use of a flux.

2. The surfaces must fit together without gaps and must be held together securely while being

heated.

3. A heat source such as a blow torch is used to heat the materials around the joint to make

sure that both pieces are evenly heated. The solder filler rod is rested on the joint and as it

starts to melt, capillary action will allow the solder to run between the joint.

4. Once filled, the joint will be left to cool and hard end.

Soldering is very similar to brazing except that filler material is usually a lead-tin based

alloy which has much lower strength and melting temperature around 250°C. In this process

less alloying action between base metal and filler material as compared to brazing takes place

hence the strength of joint is lesser. It is carried out using electrical resistance heating, the

37

joint in soldering; (a) Flat lock seam (b) Bolted or riveted joint (c) Copper pipe fitting (d)

Crimping of cylindrical lap joint as shown in figure.

Figure 31 Soldering Welding

Soldering Methods

Various soldering methods are soldering with soldering irons, dip soldering, torch

soldering, oven soldering, resistance soldering, induction soldering, infra-red and ultrasonic

soldering. Soldering iron being used for manual soldering, consists of insulated handle and

end is fitted with copper tip which may be heated electrically or in coke or oil/gas fired

furnace. Solder is brought to molten state by touching it to the tip of the soldering iron so that

molten solder can spread to the joint surface.

Ultrasonic soldering uses ultrasonics i.e. high frequency vibrations which break the oxides

on the surface of workpieces and heat shall be generated due to rubbing between surfaces.

This heat melts the solder and fills the joint by capillary action.

38

Braze Welding

In braze welding capillary action plays no role but the filler metal which has liquids above

450 ° C but below the melting point of parent metal, fills the joint like welding without the

melting of edges of parent metal. During the operation, the edges of the parent metal may not

melt but melting temperature of filler metal is reached. When filler rod is brought in contact

with heated edges of parent metal, the filler rod starts melting, filling the joint. If edges

temperature falls down then again heat source is brought for melting filler rod. The molten

filler metal and parent metal edges produce adhesion on cooling resulting into strong braze

weld.

The braze welding filler material is normally brass with 60% Cu and remaining Zn with

small additions of tin, manganese and silicon. The small additions of elements improve the

deoxidizing and fluidity characteristics of filler metal.

Brazing methods;

Brazing methods (a) Torch and filler rods (b) Ring of filler metal at entrance of gap (c)

Foil of filler metal between flat part surfaces as shown in fig.

Figure 32 Brazing methods

39

Borax and boric acid are commonly used fluxes for brazing with copper base filler metals.

Many other commercial fluxes may be available in the form of paste or liquid solution leading

to ease of application and adherence to the surface in any position.

Flux Residue Treatment:

When brazing or soldering is completed then the flux residues are to be removed because

without removal the residues may lead to corrosion of assemblies. Brazing flux residues can

be removed by rinsing with hot water followed by drying. If the residue is sticky then it can

be removed by thermal shock i.e. heating and cooling. Sometimes steam jet may be applied

followed by wire brushing.

Soldering flux residues of rosin flux can be left on the surface of joint, however, activated

rosin flux and other flux residues require proper treatment. If rosin residues removal is

required then alcohol, acetone or carbon tetrachloride can be used. Organic flux residues are

soluble in hot water so double rising in warm water shall remove it. Residue removal of zinc

chloride base fluxes can be achieved by washing first in 2% hydrochloric acid mixed in hot

water followed by simple hot water rinsing.

Common Welding Defects

The defects in the weld can be defined as irregularities (non-homogeneous) in the weld

metal produced due to incorrect welding parameters or wrong welding procedures or wrong

combination of filler metal and parent metal. Defects may be on the surface or inside the weld

metal. Certain defects such as cracks cannot be tolerated but other defects may be acceptable

within permissible limits. Various welding defects can be classified into groups such as

cracks, porosity, solid inclusions, lack of fusion and inadequate penetration, imperfect shape

and various defects.

1. Cracks

Cracks may be of macro size and may appear in the weld metal or base metal or base metal

and weld metal boundary. Different types of cracks are longitudinal cracks, transverse cracks

or radiating/star cracks and cracks in the weld crater. Cracks occur when localized stresses

exceed the ultimate tensile strength of material. These stresses are developed due to shrinkage

during solidification of weld metal. Cracks may be developed due to poor ductility of base

41

metal, high sulpher and carbon contents, high arc travel speeds i.e. fast cooling rates, too

concave or convex weld bead and high hydrogen contents in the weld metal.

Figure 33 Types of Cracks in Welds

2. Porosity

Porosity results when the gases are remain in the solidifying weld metal. These gases are

generated from the flux or coating components of the electrode or shielding gases used during

welding or from absorbed moisture in the coating. Rust, dust, oil and grease on the surface of

work pieces or on electrodes are also source of gases during welding. Porosity may be easily

prevented if work pieces are properly cleaned from rust, dust, oil and grease. Porosity can also

be controlled if excessively high welding currents, faster welding speeds and long arc lengths

are avoided.

Figure 34 Forms of Porosities

41

3. Solid Inclusion

Solid inclusions may be in the form of slag or any other non-metallic material in the weld

metal as these may not able to float on the surface of the solidifying weld metal. During arc

welding flux either in the form of granules or coating after melting, reacts with the molten

weld metal removing oxides and other impurities in the form of slag and it floats on the

surface of weld metal due to its low density. However, if the molten weld metal has high

viscosity or too low temperature or cools rapidly then the slag may not be leaved from the

weld molten and may cause inclusion.

Slag inclusion can be prevented if proper groove is selected, all the slag from the previously

deposited bead is removed, too high or too low welding currents and long arcs are avoided.

Figure 35 Slag Inclusion in Weldments

4. Lack of Fusion

Lack of fusion is the failure to fuse together either the base metal and weld metal or

subsequent beads in multipass welding because of failure to raise the temperature of base

metal or previously deposited weld layer to melting point during welding. Lack of fusion can

be avoided by properly cleaning of surfaces to be welded, selecting proper current, proper

welding technique and correct size of electrode.

Figure 36 Types of Lack of Fusion

42

5. Imperfect Shape

Imperfect shape means the variation from the desired shape and size of the weld bead.

During undercutting a notch is formed either on one side of the weld bead or both sides in

which stresses tend to concentrate and it can result in the early failure of the joint. Main

reasons for undercutting are the excessive welding currents, long arc lengths and fast travel

speeds.

Underfilling may be due to low currents, fast travel speeds and small size of electrodes.

Overlap may occur due to low currents, longer arc lengths and slower welding speeds.

Figure 37 Various Imperfect Shapes of Welds

Excessive reinforcement is formed if high currents, low voltages, slow travel speeds and

large size electrodes are used. Excessive root penetration and sag occur if excessive high

currents and slow travel speeds are used for relatively thinner members. Distortion is caused

because of shrinkage occurring due to large heat input during welding.

43

Nonconventional welding (hybrid welding)

The aim of nonconventional welding is increasing of joining process efficiency. Welding is

today a key manufacturing process, present practically in all industrial sectors. One of the

principal directions for the progress of the welding is the development of hybrid welding

processes. These are created by combination of two conventional welding processes and

through effects of the advantages with respect to each individual welding process, first of all

an increase of the process stability and efficiency.

Hybrid welding processes combines two welding processes to improve or increasing of

joining process efficiency. The first hybrid welding process was the plasma – MIG welding

which represents a combination between plasma welding and shielded gas welding with

fusible electrode (MIG welding). At present over 20 hybrids welding processes are known,

the most important as the following:

- Laser arc hybrid welding which combines the laser welding with a TIG or MIG shielded gas

electric arc welding process;

- MIG welding combined with submerged arc welding.

- Resistance spot welding combined with brazing.

- Laser activated friction stir welding

- A-TIG welding (chemically activated TIG welding).

- Ultrasonically activated TIG welding.

PLASMA – MIG HYBRID WELDING

The plasma – MIG welding process is a combination between the plasma welding and the

MIG welding. The electric arc produced between a fusible electrode (wire) and the

component is situated in the hot ionized gas current of a plasma arc. The process principle is

illustrated in figure. Usually, the plasma arc is supplied in direct current direct polarity and

the MIG arc in direct current reversed polarity.

The MIG arc ignites in the interior of the plasma stream which assures a contraction effect.

Two operating modes are possible. In the case of a MIG current having a reduced value the

44

electric arc is narrow, this technological version can be used for thin plates high speed

welding or when welding thick plates at reduced welding speed. The second version uses a

high intensity MIG current. In this case the wire melting rate increases.

Figure 38 Principle of plasma – MIG hybrid

welding (1- MIG, 2 -Plasma)

There appears a rotation effect of the plasma arc which has as effect a rotation of the MIG

arc and a deposition of the melted metal with small drops on a higher radius action. The result

is a greater width of the weld and reduced penetration, recommended for the application of

hardfacing by welding. The plasma – MIG welding is achieved by high efficiency, the

deposition rate exceeds that corresponding to the two original processes (up to 25kg/h). This

process can lead to very good quality welded joints, too. The process is applied in fillet and

butt welding of relatively thick plates and in hardfacing by welding. A new welding version is

realized by combining the plasma welding and TIG welding, resulting in this way, plasma –

TIG welding. The welding root is deposited by plasma welding and the filling is performed by

cold wire TIG welding.

Laser – Electric Arc Hybrid Welding

The laser – electric arc hybrid welding is based on the overlapping, in a single melted pool,

of a laser radiation action and an electric arc (TIG or MIG) as shown in figure.

45

Figure 39 Laser – electric arc hybrid welding

Advantages of Hybrid Welding

The new process combines the advantages of the two welding processes, namely

productivity by energy concentration, high welding speed, deep penetration and reduced heat

influence on the material and as an effect the reduced level of deformation by welding,

specific characteristics of laser welding, with the toughness application by using a filler

material. So, the hybrid welding is applicable mostly for the series produ ction welding of

thicker materials considering greater tolerances to prepare components for the welding

operation.

The hybrid process eliminates the metallurgical problems specific to laser welding caused by

the too high speed cooling of welding. As compared with the laser welding the hybrid process

n mp o m n o h “ b o b b l y” o h l d on ollow n h p -

heating effect produced by the TIG arc.

As compared with the TIG welding, the hybrid laser – TIG welding:

- Increase of the anodic spot magnitude and stability of the electric arc under the effect of the

laser.

- Possibility to weld with a longer electric arc.

46

- Ignition without pulses of high voltage.

- Higher welding speed.

- Increase the weldable material thickness without groove preparation.

The melted metal volume in the case of hybrid laser – arc welding of aluminium is up to

80% higher than the sum of melted metal volumes obtained from the two welding processes

considered separately. The main industrial applications of the hybrid laser – electric arc

welding are: naval industry, automobile industry, as well the fabrication of special steel

pipelines having a difficult welding behaviour (ex. supermartensitic steels).

To improve welding efficiency, the laser-MAG welding process was developed, a version

which uses two MAG (Metal Active Gas) welding wires which melt in same time with the

high intensity electric arc. This version can be applied to weld pressure vessels and pipelines,

by the reduced melted metal volume and as a consequence, the more reduced level of

deformation by welding. The hybrid laser – plasma welding is possible, a version which is

used in rapid prototyping processes.

References

1-Serope. k.,2012, Manufacturing Eng. and Technology, India.

2-U.K.Singh, Manufacturing Processes,

3-R.S.Parmar, 2011, Welding Eng. And Technology, New Delhi.

4- Internet

47