METAL CASTING & METAL FORMING...Metal Casting is one of the oldest materials shaping methods known. Casting means pouring molten metal into a mould with a cavity of the shape to be

Elements of Mechanical Engineering Unit 2

Er. S.Rajesh, B.Tech (ME) and M.Tech (MD), Asst. Prof., Vignan`s Lara, Vadlamudi 1

METAL CASTING & METAL FORMING

Syllabus:

Metal Casting: Steps involved in making casting, Advantages and Applications, Patterns and

Pattern making.

Metal Forming: Forging-operations, Rolling and Extrusion principles.

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METAL CASTING

Introduction

Metal Casting is one of the oldest materials shaping methods known. Casting means

pouring molten metal into a mould with a cavity of the shape to be made, and allowing it to

solidify. When solidified, the desired metal object is taken out from the mould either by breaking

the mould or taking the mould apart. The solidified object is called the casting.

By this process, complex parts can be given strength and rigidity than any other

manufacturing process. The mould, into which the metal is poured, is made of some heat resisting

material. Sand is most often used as it resists the high temperature of the molten metal. Permanent

moulds of metal can also be used to cast products.

Fig: Metal Cast parts

Advantages:

The metal casting process is extensively used in manufacturing because of its many advantages.

1. Intricate (complex) shapes can be made by this process. As a result, many other operations,

such as machining, forging, and welding, can be minimized or eliminated.

2. Size is not a limitation (Big size components are can be made).

3. It is possible to cast practically any material that is ferrous or non-ferrous.

4. As the metal can be placed exactly where it is required, large saving in weight and wastage

can be achieved.

5. The necessary tools required for casting moulds are very simple and inexpensive.

6. Good surface finish can be achieved by casting.



Limitations

1. The strength and toughness of casting are usually inferior to forging.

2. Dimensional accuracy and surface finish of the castings made by sand casting processes are a

limitation to this technique.

3. The metal casting process is a labour need process.

CASTING PROCESS:

1.

2.

Casting Process

Steps in Making Sand Castings

There are six basic steps in making sand castings:

1. Pattern making

2. Core making

3. Moulding

4. Melting and pouring

5. Cleaning

1. Pattern making

The pattern is a physical model of the casting used to make the mould. The mould is made by

packing some readily formed aggregate material, such as moulding sand, around the pattern.



When the pattern is withdrawn, its imprint provides the mould cavity, which is ultimately filled

with metal to become the casting. If the casting is to be hollow, as in the case of pipe fittings,

additional patterns, referred to as cores and are used to form these cavities.

2. Core making

Cores are forms, usually made of sand, which are placed into a mould cavity to form the

interior surfaces of castings. Thus the void space between the core and mould-cavity surface is

what eventually becomes the casting.

3. Moulding

Moulding consists of all operations necessary to prepare a mould for receiving molten metal.

Moulding usually involves placing a moulding aggregate around a pattern held with a supporting

frame, withdrawing the pattern to leave the mould cavity, setting the cores in the mould cavity and

finishing and closing the mould.

4. Melting and Pouring

The preparation of molten metal for casting is referred to simply as melting. Melting is usually

done in a specifically designated area of the foundry, and the molten metal is transferred to the

pouring area where the moulds are filled.

5. Cleaning

Cleaning refers to all operations necessary to the removal of sand, scale, and excess metal

from the casting. Burned-on sand and scale are removed to improve the surface appearance of the

casting. Excess metal, in the form of fins, wires, parting line fins, and gates, is removed.

Inspection of the casting for defects and general quality is performed

CASTING TERMS:

Flask: A metal or wood frame, without fixed top or bottom, in which the mould is formed.

Depending upon the position of the flask in the moulding structure, it is referred to by various

names such as drag – lower moulding flask, cope – upper moulding flask, cheek –

intermediate moulding flask used in three piece moulding.

Pattern: It is the replica of the final object to be made. The mould cavity is made with the

help of pattern.

Parting line: This is the dividing line between the two moulding flasks that makes up the

mould.

Moulding sand: Sand, which binds strongly without losing its permeability to air or gases. It

is a mixture of silica sand, clay, and moisture in appropriate proportions.

Facing sand: The small amount of carbonaceous material sprinkled on the inner surface of the

mould cavity to give a better surface finish to the castings.

Core: A separate part of the mould, made of sand and generally baked, which is used to create

openings and various shaped cavities in the castings.

Pouring basin: A small funnel shaped cavity at the top of the mould into which the molten

metal is poured.



Sprue: The passage through which the molten metal, from the pouring basin, reaches the

mould cavity. In many cases it controls the flow of metal into the mould.

Runner: The channel through which the molten metal is carried from the sprue to the gate.

Gate: A channel through which the molten metal enters the mould cavity.

Chaplets: Chaplets are used to support the cores inside the mould cavity to take care of its

own weight and overcome the metallostatic force.

Riser: A column of molten metal placed in the mould to feed the castings as it shrinks and

solidifies. Also known as “feed head”.

Vent: Small opening in the mould to facilitate escape of air and gases.

PATTERN:

Pattern is the replica or full size model of casting to be made. It gives its shape to the

mould cavity where the molten metal solidifies to the desired form and size. Pattern should be

simple in design for ease of manufacture and enable to draw easily from sand.

Pattern Making:

The pattern maker, before making patterns should study the blue print. The following

factors should be considered while making a pattern.

Type of metal to be cast.

Number of casting required to be produced

Method of moulding and

Pattern allowance

The sequence of operations involved in pattern making are:

1. Pattern Layout

2. Shaping the pattern

Pattern Layout: The production of the blue print to a full size scale on suitable board (layout

board) is called lay-out of a pattern. Pattern maker must be able to make full size layout drawings

from the information contained in blue-print.

Shaping of Pattern: After completing the layout, the next step is the shaping of the pieces that

are to be used for the making pattern.

Types of Patterns:

The type of pattern used depends upon the design of casting, complexity of shape, the number of

casting required, moulding process, surface finish and accuracy.

1. Single piece pattern

2. Split pattern

3. Match piece pattern

4. Gated pattern

5. Loose piece pattern

6. Cope and Drag Pattern



Pattern Allowances:

To produce the casting of the desired size and shape, its pattern must be provided with the

following allowances.

1. Shrinkage allowances

2. Machining or finishing allowances

3. Taper or draft allowances

4. Shake allowances

5. Distortion allowances

FORGING

Forging is the operation where the metal is heated and then force is applied to manipulate

the metal in such a way that the required final shape is obtained. It is hot-working operation. This

is the oldest of the metal-working process known to mankind since the copper age.

Because of forging the grain flow in the part will be fine. Fine grain structure will

improves the good strength and high toughness against load of the part. Forging grain flow is

better than casting and machining.

Fig: A part made by three different procedures, showing grain flow (a) casting (b) machining (c)

forging

Forging Operations:

Two types of forging operations are there in order to arrive at the final object configuration. They

are as follows:

(i) Drawing out operation

(ii) Upsetting operation



Drawing out:

This is the operation in which the metal gets elongated with a reduction in the cross-

sectional area. For this purpose, the force is to be applied in a direction, perpendicular to the

length axis.

Fig. Stages in Drawing out operation in forging

Upsetting:

This is applied to increase the cross-sectional area of the stock at the expense of its length

to achieve the upsetting, force is applied in a direction parallel to the axis.

Stages in forging:



ROLLING

Cold working is metal forming performed at room temperature.

Advantages: better accuracy, better surface finish, high strength and hardness of the part, no

heating is required.

Disadvantages: higher forces and power, limitations to the amount of forming, additional

annealing for some material is required, and some material are not capable of cold working.

Hot working involves deformation of preheated material at temperatures above the re-

crystallization temperature.

Advantages: big amount of forming is possible, lower forces and power are required, forming of

materials with low ductility, no work hardening and therefore, no additional annealing is required.

Disadvantages: lower accuracy and surface finish, higher production cost, and shorter tool life.

Rolling: Compressive deformation process in which the thickness of a plate is reduced by

squeezing it through two rotating cylindrical rolls.



Important Applications:

Steel Plants,

Raw stock production (sheets, tubes, Rods, etc.)

Screw manufacture



MACHINE TOOLS AND OPERATIONS

Syllabus:

Lathe: Lathe Classification, specifications and operations

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INTRODUCTION

Cutting tools Tools which are used to separate or remove material stock from the work piece are known

as cutting tools. E.g. hack saw blade, single point cutting tools, drill bit etc.

Machine tools Machine tools are the power tools or machines which enable the removal of excess stock

of material from the work piece. E.g. Lathe, drilling machine, milling machine etc.

LATHE

Lathe is a widely used machine tool for turning operations.

Lathe is usually used for removing material from the job which is rotated and a cutting tool is

fed in to the job to cause cutting action.

Lathe is generally used for machining cylindrical jobs.

WORKING PRINCIPLE OF A LATHE

The work piece is hold firmly in the work holding device called the chuck and is supported by

the dead center as shown in the figure.

The chuck is rotated at a particular speed by some mechanisms and the single point cutting

tool is moved against the rotating work piece to facilitate the removal of material. The tool

material will be harder than the work piece material.



PARTS OF LATHE:

LATHE OPERATIONS

1. Turning

Turning is a lathe operation in which the cutting tool removes metal from the outside

diameter of a work piece. In other words, reduction in the diameter of the work piece due to

cutting is called turning.

Depending upon the job requirement, the turning operations include:

Straight turning

Stepped turning

Taper turning

Contour turning.

The figure shows the principle of a metal cutting operation using a single point cutting tool on a

lathe. The work piece is supported between the two centres (live and dead centres i.e. between

headstock and tailstock) which permit the rotation of the workpiece.

A single point cutting tool is fed perpendicular to the axis of the workpiece to a known depth of

cut and is then moved parallel to the workpiece.

This method of machining operation in which the workpiece is reduced to the cylindrical section

of required diameter is called turning.

Turning is done to reduce the diameter of the work piece, usually to a specified dimension, and to

produce a smooth finish on the metal.



A taper may be defined as a uniform increase or decrease in the diameter of the workpiece.

Taper turning is an operation on a lathe to produce conical surface on the workpiece. It is done by

either two ways: 1. with the workpiece mounted coaxial with the axis of the lathe centres and

cutting tool being moved linearly inclined to the lathe centres, and 2. The workpiece is mounted at

inclined angle with the lathe centres and the cutting tool being moved parallel along the axis of the

lathe.

In the first case, taper turning can be done either by swiveling the compound rest or by using a

taper turning attachment. In the second case, taper turning is done by off setting the tailstock

2. Facing

Facing is defined as an operation performed on a lathe to produce either flat surface or

shoulder at the end of the workpiece.

In facing, the direction of feed given is perpendicular to the axis of the lathe. The workpiece is

held in the chuck and the facing tool is fed either from the end of the workpiece towards its

centre or vice versa.

Axial movement of the tool can be avoided by locking the carriage.

Roughing cuts can be given from any end of the workpiece, but finishing cuts should be given

only from the centre to the outer edge of the workpiece.

The facing tool used is of round edge. If the tool is pointed, it will not result in good surface

finish of cut.

3. Knurling

Knurling is defined as a lathe operation of producing serrated surfaces on the workpiece using

a special tool called knurling tool , which impresses its patterns on the workpiece surface.



A typical knurling tool is shown in the figure. It consists of one upper roller and one lower

roller on which the desired impression pattern is present.

The serration or impression pattern can be straight or diamond-shaped. The serrated surfaces

are produced for applications in which grip is required to hold the part.

The knurling tool is held in the tool post such that the upper and lower rollers of the knurling

tool touch the surface of the workpiece. Usually a low speed and low feed is used while

machining using a knurling tool.

4. Thread Cutting



METAL JOINING

Syllabus:

Metal Joining: Arc welding, resistance Welding, gas welding, brazing and soldering.

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WELDING

Welding may be defined as the metallurgical joining of two metal pieces together to

produce essentially a single piece of metal. Welding is extensively used in the fabrication work in

which metal plates, rolled steel sections, casting of ferrous materials are joined together. It is also

used for repairing broken, worn out, or defective metal part.

Principle of welding

A welding is a metallurgical process in which the junction of the two parts to be joined are

heated and then fused together with or without the application of pressure to produce a continuity

of the homogenous material of the same composition and characteristics of the part which are

being joined.

Types of welding

Welding are classified in to two types

Pressure welding

Fusion welding

In Pressure welding the parts to be joined are heated only up to the plastic state and then

fused together by applying the external pressure.

Example: forge welding, resistance welding

In Fusion welding which also known as non-pressure is welding, joints of the two parts

are heated to the molten state and allowed to solidify.

Example: arc welding, gas welding.

ARC WELDING:

The arc welding operates under the principle that when two conductor of an electric circuit

are touched together temporarily and then instaneously separated slightly under sufficient voltage

in the circuit to maintain the flow of current to form an electric arc is formed.

Concentrated heat is produced throughout the length of the arc at a temperature of about

5000 to 6000°C in arc welding, usually the parts to be welded are wired as one pole of the circuit,

and the electrode held by the operator forms the other pole.

When the arc is produced, the intense heat quickly melts. The work piece metal which is

directly under the arc, forming a small molten metal of the electrode is carried over by the arc to

the molten metal pool of the work piece. The molten metal in the pool is agitated by the action of

the arc, thoroughly mixing the base and the filler metal.



A solid joint will be formed when the molten metal cools and solidifies. The flux coating

over the electrode produces an inert gaseous shield surrounding the arc and protects the molten

metal from oxidizing by coming in contact with atmosphere.

Fig. Arc Welding

Arc welding machine:

Both AC and DC are used for arc welding. For AC arc welding a step down transformer is

used. It receives AC supply between 200 to 440V and transforms it to required low voltage of 80

to 100V. A high current of 100 to 400A is suitable for arc welding.

In DC arc welding work piece is connected to positive pole of DC generator and the

electrode to the negative pole in order to melt greater mass of metal in the base metal, this setup is

called straight polarity When the heat required is less in the base metal then the polarity is

reversed Due to this option in DC arc welding it is possible to melt many metals In AC there is no

choice of polarity since the current changes every cycle.

Arc welding electrodes:

There are two types of electrodes that are used in arc welding

(A) Consumable electrodes

(B) Non- consumable electrodes

Consumable electrodes are the electrodes which also melts along with the work piece and

fill the joint Consumable electrodes could be either bare or coated. When bare electrodes are used

globules of the molten metal while passing from the electrodes absorb oxygen and nitrogen from

atmosphere Which gets trapped in the solidifying weld metal and thereby decreases the strength

of the joint Electrodes are made up of soft steel or alloy steel The coating consists of chalk, starch,

ferro-manganese and binding agents.

Coated electrode facilitates:

(a) Protection of molten metal from oxygen and nitrogen by providing a gaseous shield

around the arc

(b) To establish and maintain the arc throughout the welding

(c) The formation of the slag over the joint thus prevents from rapid cooling

(d) Addition of alloying element



When Non- consumable electrodes are used, an additional filler material is also required

Advantage in using this electrode is that amount of metal deposited can be controlled which is not

possible in other type of electrode.

RESISTANCE WELDING:

This type of welding employs the principles of both the pressure and fusion welding

methods. It consist of heating of the Parts to be welded are heated up to the plastic state and joined

by applying mechanical pressure. Heating is done by passage of heavy localized electric current,

the current flowing from one part of joint to other encounters a high resistance and temp increases.

This method is employed for fastening thin metal sheets and wires.

General welding procedure

1. Cleaning: The surfaces of the parts to be welded need to be thoroughly cleaned for removal

of dirt, oil, grease, etc.

2. Edge preparation: The process of preparing a contour at the edges of the pieces to be joined is

called as edge preparation. This involves beveling or grooving. The idea of doing this is to get

fusion or penetration through the entire thickness of the member.

3. Clamping: Next, the parts to be welded are clamped suitably through jigs and fixtures to that

there are no undesirable movements during welding.

4. Check for safety devices: safety devices like goggles and shield to protect the eyes, protective

clothing to prevent the sparks and flying globules of molten metal, safety shoes, gloves, apron

and other safety devices must be ensured.

5. The initial weld: Initial tack welds are done at opposite corner of the joints to secure the

pieces together. Any cracks at this stage must be chipped off as the presence of these cracks

causes residual stresses. The length and spacing of the tack weld varies with the thickness of

the metal and length of the joint.

6. Intermediate and final welding: The weld joint is formed through various weaving

movement. During the process, filler metal and a suitable flux are used. After the intermediate

run of welding, the final run is taken

7. Excess material removal: Extra material on the weld surface can be removed using tongs and

chipper. The final weld is now allowed to cool and finally cleaned.

GAS WELDING:

It is a fusion welding, in which a strong gas flame is used to raise the temperature of the

workpiece to melt them. As in the arc welding, a filler metal is used to fill the joint. The gases that

can be used for heating are

(i) Oxygen and acetylene

(ii) Oxygen and hydrogen.

Oxy-acetylene gas mixture is most commonly used in gas welding



Oxy-acetylene welding

When Right proportions of oxygen and acetylene are mixed in the welding torch and then

ignited. The flame produced is called as the oxy-acetylene flame. The temperature attained in this

welding is around 3200oC hence has an ability to melt all commercial metals.

Types of oxy-acetylene flames:

The types of flames depends on the gas ratio i.e., ratio of the parts of oxygen to the parts of

the acetylene. Depending on the gas ratio following flames are obtained

(i) Neutral flame

(ii) Oxidizing flame

(iii) Reducing flame (carburising flame)

(i) Neutral flame:

A neutral flame is obtained by supplying equal volume of oxygen and acetylene

It consists of a small whitish inner cone surrounded by sharply defined blue flame

Most of the gas welding is done using the neutral flame

(ii) Oxidizing flame:

This is obtained by supplying excess of acetylene in the gas ratio. It has 3 cones, an inner

white cone, surrounded by an intermediate whitish cone known as “intermediate flame feather”

and a bluish envelope flame. This flame is used for welding alloy steels, cast iron, aluminium.



(iii)Reducing flame:

This is obtained when there is excess of oxygen, gas ratio.

It appears to be similar to that of neutral flame but the inner white cone flame is shorter

than that of neutral flame

This flame is generally used in metal cutting rather than welding since weld metal gets

oxidized

Advantages of oxy-acetylene welding:

1. Most versatile process of welding with wide use in various manufacturing process

2. Low cost of the equipment and low cost of maintenance of the equipment

3. Because of separate heat source and filler metal the control can be exercised on the rate at

which the filler metal deposits.

4. The rate of heating and cooling is slow. This help in retaining the structural homogeneity.

5. The equipment is portable and multi-functional because, apart from gas welding, it can also be

used in torch brazing, braze welding, preheating and post heating.

Disadvantages:

1. Difficult to attain low cost target while joining heavy section.

2. Handling and storage of gases not an easy job.

3. It takes long time for the flame to heat up the metal piece than compared to the arc

welding.

4. Possible hazards due to explosion of gases.

SOLDERING:

Soldering is a method of uniting two thin metal pieces using a dissimilar metal or alloy by

the application of heat. The alloy of lead and tin is called soft solder, is used in varying

proposition for sheet metal work, plumbing work and electrical junctions. The melting temp of

the soft solder will be between 150̊ to 350̊ C. To clean the joint surfaces and to prevent oxidation a

suitable flux is used while soldering. Zinc chloride is the flux that is commonly used in soft

soldering. A soldering iron is used to apply the heat produced from the electrical source.

An alloy of copper, tin, and silver known as hard solder is used for stronger joint. The

soldering temp of hard solder ranges from 600̊ to 900̊ C

Method of soldering

(i) Cleaning of joining surfaces

(ii) Application of flux

(iii) Tinning of surface to be soldered

(iv) Heating



(v) Final clean-up

(i) Cleaning of joining surfaces: Firstly, the joining surface are cleaned mechanically to make

free from dust, oil scale,etc and ensure that the molten filler metal wets the surfaces.

(ii) Application of flux: Then the joining surfaces are coated with a flux usually rosin or borax.

This cleans the surfaces chemically and helps the solder in making bond.

(iii) Tinning of surface to be soldered: before carrying out the soldering operation, the soldering

iron must be tinned. This is to remove a thin film of oxide that forms on the copper bit, which in

turns does not allow the job to be heated and thus it becomes difficult to solder. In tinning the

copper bit is heated and then rubbed with a file to clean it properly and then rotating with solder

using resin. This causes the formation of a thin film of solder over the copper bit. This whole

process is called tinning.

(iv) Heating: The soldering iron is then heated and flowing molten filler metals fills the joints

interface. Allow the soldered area to cool and then solidify thus making the joint.

(v) Final clean-up: After completing the soldering and joints are formed, clean it with steel wool

or solvent to remove left over flux. After this clean the soldering iron using a damp sponge

Advantages of soldering:

1. Low cost and easy to use

2. Soldered joints are easy to repair or do rework

3. The soldered joint can last for many year

4. Low energy is required to solder

5. An experienced person can exercise a high degree of control over the soldering process

Disadvantages of soldering:

1. Not suitable for heavy sections.

2. Temperature is limited.

3. Strength is limited.

BRAZING:

Brazing is the method of joining two similar or dissimilar metals using a special fusible

alloy. Joints formed by brazing are stronger than that of soldering. During the brazing, the base

metal of the two pieces to be joined is not melted. The filler metal must have ability to wet the

surfaces of the base metal to which it is applied. Some diffusion or alloying of the filler metal with

base metal takes place even though the base metal does not reach its melting temp. The materials

used in brazing are copper base and silver base alloy. These two can be classified under the name

spelters.

Method of brazing:

1. Cleaning the surface of the parts.

2. Application of flux at the place of joint.

3. Common borax and mixture of borax and boric acid is used as flux.



4. The joint and the filler material are heated by gas welding torch above the melting

temperature of the filler material.

5. It flows into the joint space and a solid joint is formed after cooling.

Advantages of Brazing

1. It is easy to learn.

2. It is possible to join virtually any dissimilar metals.

3. The bond line is very neat aesthetically.

4. Joint strength is strong enough for most non-heavy-duty type of application.

Disadvantages of Brazing

1. Brazed joints can be damaged under high temp.

2. Brazed joint require a high degree of cleanliness.

3. The joint colour is often different from that of the base metal.

DIFFERENCE BETWEEN BRAZING, SOLDERING AND WELDING:

S.No Brazing Soldering Welding

1. In brazing filler metal is

having the melting point

greater than 450oC.

Soldering using the filler

metal having the melting

point less than 450oC.

Welding using the filler

metal having the melting

point nearly equal to the base

metal.

2. Joints takes place due to

capillary action between the

base metal and the filler

metal.

Capillary action is also

present in soldering between

the base metal and filler

metal.

No capillary action is

present. Joint takes place due

to fusion.

3. Base metal does not melt. Base metal does not melt.

Base metal melts in welding.

4. Filler metal is having the

melting point less than the

base metal.

Filler metal is having the

melting point less than the

base metal.

In welding filler metal is not

having the melting point less

than the base metal.

5. Filler metal is uniformly

distributed because of

capillary action.

Filler metal is uniformly

distributed because of

capillary action.

Filler metal melts and gets

mixed with the base metal

6. Joints are stronger than

soldering but weaker than

welding.

Joints are weaker than

brazing.

Joints are stronger as

compared to brazing and

soldering.

7. It was uses filler metal

which contains copper and

zinc etc.

It uses the filler metal which

contains lead and tin.

It uses the filler metal mostly

having the same composition

as that of base metal.

Documents

METAL CASTING & METAL FORMING...Metal Casting is one of the oldest materials shaping methods known. Casting means pouring molten metal into a mould with a cavity of the shape to be