Manufacturing Process

•Product can be cast as one piece.

•Very heavy and bulky parts can be manufactured

•Metals difficult to be shaped by other

manufacturing processes may be cast (eg: Cast

Iron)

•Best for mass production

•Casting process is a labour intensive process

•Not possible for high melting point metals

•Dimensional accuracy, surface finish and the

amount of defects depends on the casting

process

• Pattern: An approximate duplicate of final casting

• Flask/Box: The rigid metal or a wooden frame that holds

the moulding material

• Cope: Top half of the moulding box

• Drag: Bottom half of the moulding box

• Core: A sand shape that is inserted into a mould to

produce internal features of a casting such as holes

• Riser: A vertical opening in the mould

• Act as a vent for gases

• Helps to confirm that the mould is completely filled

•Gating System: Channels used to deliver the

molten metal to the mould cavity

•Sprue: The vertical passage in the gating

system

•Runner: The horizontal channel of the gating

system

• Pouring Cup

• Sprue

• Sprue Base/Well

• Runner

• Gate

• Riser

• Wood: Inexpensive, Easily available, Light weight, easy to shape, Poor wear resistance, absorb moisture, less strength, not suitable for machine moulding.

• Metal: Aluminium: No corrosion, good strength, wear resistant, good surface finish, less cost, cannot withstand rough handing, soft metal. • Plastic: High surface finish, light weight, moisture resistant, good

strength, wear & corrosion resistant, easy to make, not suitable for machine moulding.

• Plaster: Intricate shapes can be made, good compressive strength,

• Single piece pattern • Split piece pattern • Cope & Drag pattern • Gated pattern

• Green Sand • Dry Sand • Core Sand

The size of the pattern is slightly larger than the

finished casting by an amount called ALLOWANCE.

• Shrinkage Allowance

• Machining or Finishing allowances

• Taper or Draft allowance

• Distortion allowance

The pattern must be made oversize to compensate for contraction of liquid metal on cooling. This addition to the dimension of the pattern is known as shrinkage allowance.

The pattern must be made oversize for machining purposes so that the required dimensions and surface finish can be achieved by removing material from the casting. This extra amount of dimensions provided in the pattern is known as Machining allowance.

When a pattern is removed from a mould, the

tendency to tear away the edges of the mould is greatly

reduced if the vertical surfaces of the pattern are

tapered inwards. The provision of taper on vertical

faces of the pattern is called DRAFT.

Distortion allowances are applied to casting of irregular

shapes that are distorted in cooling because of metal

shrinkage

Due to rapping of the pattern in the mould, the size of mould cavity increases slightly.

A shake or rapping allowances shall be given to pattern by making it smaller to compensate for rapping.

Bench moulding

Floor moulding

Pit moulding

Green Sand Moulding

Dry Sand Moulding

Porosity / Permeability: The property that allows passage of gases through the mould

Cohesiveness: Ability of the sand particles to stick together

Adhesiveness: Ability of a moulding sand to adhere (stick on) to the surfaces of moulding boxes.

Flowability: ability to flow into deeper sections of the pattern and all portions of moulding box

Collapsibility: Property of the sand that permits it to collapse (break) easily during its knockout from the casting

Refractoriness: ability of a moulding sand to withstand the heat of molten metal without fusion

Na

SiO

+ CO

 Na

CO

+ SiO

1. Hand Forging

• Versatile process • Time consuming

• Not suitable for mass production

2. Drop Forging

• The die is made in two halves, which contains the shape of the component to be produced, in the form of a cavity.

• Force for shaping the component is applied in a series of blow by using drop hammers.

3. Press Forging

• Force is applied using a hydraulic press. • Suitable for mass production

4. Machine Forging

• Forging machines are used for appling force. • Used when large force is required

• Used for mass production

IMPRESSION DIE FORGING

1. Upsetting (Jumping)

2. Drawing Down (Necking Down) 3. Setting Down 4. Bending 5. Welding 6. Cutting 7. Punching 8. Swaging

• Process of increasing the cross sectional area of a bar at any desired portion, at the expense of length of the bar.

• Process of reducing the cross section of a bar by increasing its length.

• An operation by which bars and rods are bent to form rings, hooks etc.

• It is carried out by keeping the bar over the round edge of an anvil and hammering.

• Process of joining two metallic surfaces without using filler materials. • The surfaces to be joined are heated to a temperature higher than

• Process of removing pieces of metal from a work piece by means of a chisel.

• Process in which a punch is forced through the work piece to produce a hole.

• The work piece is heated and supported on a block.

• Two swage block, top swage and bottom swage are used for swaging operation.

• The work piece is held between the top and bottom swages and is hammered.

• Process of increasing the diameter of a punched hole.

• A drift which has tapered end is made to pass through the punched hole to produce a finished hole of the required size.

Improves the mechanical properties

Forged parts can withstand heavy load conditions. Metals can be easily shaped.

Higher reliability for forged products. No material wastage during forging High rate of production

High tool cost

All metals cannot be forged. Some metals may develop crack by forging.

Limitation in size and shape.

Process of forming metals into desired shapes by passing the metal in between a pair of rolls.

The rolls squeeze the metal to reduce its cross section while increasing its length.

The process of rolling basically consists of passing metal between two rolls rotating in opposite directions at the same speed.

HOT ROLLING is the process in which metal is fed to the rolls after being heated above the recrystallization temperature.

TWO HIGH MILL THREE HIGH MILL FOUR HIGH MILL

• Consists of two heavy rolls placed exactly one over the other. • Mostly the lower roll will be fixed in position.

• Upper roll can be moved to adjust the space between the rolls. • Both rolls rotate at the same speed but in opposite direction. • Low production rate

• Consists of three rolls positioned one over the other.

• The upper and lower rolls rotate in the same direction, while the middle roll rotates in the opposite direction.

• The work piece is made to pass in one direction between the upper and the middle rolls in the first pass.

• Then between the middle and the lower rolls in the opposite direction during the second pass.

• The middle roll is kept fixed and the upper and lower rolls are moved to adjust the roll gap.

• Consists of four rolls, two are working rolls and the other two are back up rolls.

• Back up rolls are larger and are used for preventing the deflection of the working rolls.

• High production rate

• Consists of a pair of working rolls of very small diameter, supported by a number of back up rolls on either side.

• The joint area of the parts are heated to plastic state and forced together by external force.

• Eg: Forge welding, Resistance welding.

• The joint area of the parts are heated to fusion state (molten state), and a joint is formed as a result of solidification.

PRESSURE WELDING

Requires only heat and pressure. Joint area is heated to plastic state. Requires lower temperature.

Composition and structure is not much affected.

Does not requires filler metal.

FUSION WELDING

Requires only heat.

Joint area is heated to molten state. Requires higher temperature.

Composition and structure is affected.

• In this process, the work piece to be joined are held

together and a strong electric current of low voltage

(6 to 10 volts) and high amperage (60 to 4000

amperage) is passed through them.

• When the current passes through the metal, the high

resistance at the point of contact raises the

temperature at the junction.

SPOT WELDING

• Used for making lap welds in thin sheets • Sheets are held between metal electrodes

• Secondary current from transformer is passed between the electrodes, causing the metal temperature in contact spot to be rapidly raised to welding temperature.

• The weld at this contact spot is then completed by applying pressure by the electrodes itself.

• Work pieces of the same cross section are held in suitable clamps butting each other.

• The current is switched on and the contacting surface gets fused and joined by mechanical pressure.

• Similar to butt welding

• The ends of the work pieces to be welded are put together and the required current is passed through the work pieces.

• Sudden separation of the ends by a short distance produces an arc in the space between the work resulting very high heat.

• Similar to Spot welding

• The electrodes are disk shaped rollers

• The electrode roll over the sheet and a continuous weld is obtained.

• The current passing from wheel to wheel through the work pieces heats the parts to be joined and due to the pressure, the weld is formed.

• Also known as CONTINOUS SPOT WELD PROCESS. • Used for welding sheet metals, radiator, drums etc.

• Modification of Spot welding

• The current and pressure are localized at the weld section by the use of some projections on one or both pieces of the work.

• The flattening out of these projections under pressure results in good welds at all points of contact.

SPOT WELD

The source of heat in Arc welding is an electric arc. The electric arc develops when current flows across the air gap between the end of metal electrode and the work surface. This arc is strong stable electric discharge occurring in the air gap between an electrode and the work. The temperature of this arc is about 3600°C which can melt and fuse the metal very quickly to produce joint. The temperature of the arc at the centre is around 6500°C. Only 60 to 70% of the heat is utilized in arc welding to heatup and melt the metal. The remaining 40 to 30% is dissipated into surroundings.

The principle of arc welding is based upon the formation of an electric arc between a consumable electrode (bare or coated) and the base metal. The heat of the arc is concentrated at the point of welding; as a result, it melts the electrode and base metal. When the weld metal solidifies, the slag gets deposited on its surface as it is lighter than

•Non-Consumable electrodes

•Consumable electrodes

•Bare electrodes

Advantages of Arc Welding

•Faster than Gas welding

•Low cost

•Versatile process

•Suitable for wide range of ferrous and non

ferrous metals and their alloys

Disadvantages of Arc Welding

•Not suitable for thin sections

•Electrode replacement is necessary for long

joints

•Not suitable for welding large metal pieces

•Need to remove slag at the end of welding

• In Gas welding, the heat necessary for melting base metal and filler rod is obtained by gas flame.

• The composition of filler rod is same as that of the base metal.

• In Oxy-Acetylene welding, heat is produced by burning acetylene in the presence of oxygen at the tip of a nozzle which is fitted to a torch body.

• The temperature of the oxy-acetylene flame is 3250°C and is used to melt parent metal to form a weld pool.

• Oxidising Flame

• Neutral Flame

• Reducing Flame

Acetylene production:

• Water to Carbide method (high pressure system) • Carbide to Water method (low pressure system)

CaC

+ 2H

O = Ca (OH)

+ C

H

•High portability

•Less welding skills required

•Easy control of filler metal

•Equipment are low cost

•Maintenance cost is less

•Takes longer time to weld

•Oxygen & Acetylene are costlier

•Shielding provided by flame is not effective

•Flame

temperature

is

less

than

the

temperature of the arc

•Safety problems in handling and storage of

gases

• Fusion welding process

• Heat required is obtained by an exothermal chemical reaction

8Al + 3Fe₃O₄ = 9Fe + 4Al₂O₃

Aluminium

Iron Oxide Aluminium Oxide (Slag) Iron (Thermit)

• Soft Soldering: Tin & Lead, 320°C

• Hard Soldering: Copper & Zinc, 600°C

• Semi-Permanent joint

Soldering is the method of joining

two or more metal pieces by means

of a fusible alloy or metal called

solder, applied in a molten state.

• Alloy of Copper, Zinc & Tin

• Can withstand temperatures up to 800°C

ADVANTAGES

• Dissimilar metals can be joined • Quick process

• Parts having thin sections can be easily joined. • Less heat than fusion welding