MANUFACTURING PROCESSES Prepared by SREEJITH K. SREEJITH K.APMEJEC

MANUFACTURING PROCESSES

Prepared by

SREEJITH K.

APME

JEC

Basics of Mechanical Engineering (SK/APME)

Overview Forging

Welding

Rolling

Extrusion

Casting

FORGING


Forging is defined as the controlled plastic deformation of metal at elevated temperature into a predetermined shape or size by operations like hammering, bending and pressing etc.

These operations can be carried out by using hand hammers, power hammers, drop hammers or by forging machines.

When the shape of the metal is changed at an elevated temperature (above recrystallisation temperature) it is called hot forging, while the change of shape of the metal is happening at room temperature by the application of large compressive force it is called cold forging.

Forging is usually employed for those components which require high strength and resistance to shock or vibrations.

The major components produced by forging are nails, bolts, spanners, connecting rods, turbine shafts, crane hooks etc.

Methods of Forging

Important forging methods are; Smith Forging:- Oldest type of forging method. It is carried out by

striking the heated part repeatedly until it takes on the desired shape & size. It is mainly used for small scale production.

Drop Forging:- In drop forging the metal is heated and under the impact of a ram/hammer, the heated metal which is very malleable will fills the die cavity. Excess metal (flash) is trimmed off. This process can be used for mass production.

Hot Press Forging:- It is very similar to drop forging, but in this case we supply a steady pressure by means of a hydraulic press instead of an impact force. It is also a mass production process.


Smith Forging

Drop Forging

Drop Forging

Forging Operations (UQ-April 2012)

Important forging operations are; Upsetting:-It is a process of increasing the cross section

area of a metal bar at the expense of the length of the bar by heating it and hammering it axially.


Drawing:- It is the process of reducing the cross section of a metal bar by increasing its length.


Bending:- It is an operation by which bars and rods are bent to form hooks, rings etc.

Cutting:- Metal is heated to a higher temperature (850 to 900ºC) and is then cut by chiselling.

Punching:- Punching is done to produce a hole. A punch is forced through a heated metal job to get a hole.

Forge Welding:- It is the process of joining two metallic surfaces without using filler materials by heating the surfaces to a higher temperature, pressing them together and joining them by hammering


punch is forced into the annealed steel.

Hobbing:- It is used to form an impressions or patterns in annealed steel. The desired pattern is machined into the punch and the punch is forced into the annealed steel.


Swaging:- It is an operation in which required cross section shape is obtained, in this process the workpiece is held between the top and bottom swages and is hammered. Each swage will have the half of the shape to be produced on the job.

Drifting:- It is the process of increasing the diameter of the punched hole.



Drifting


Types of Forging

Open -Die Forging:- Open-forging typically involves placing a solid cylindrical workpiece between two flat dies and reducing its height by compressing it. This operation is also known as upsetting.


Open -Die Forging



Closed–Die Forging:- It is also called as Impression-Die Forging. In closed-die forging, the metal is placed in a die (lower) resembling a mould, which is attached to the anvil.

A ram is attached to the other die (upper) which will falls and strikes the top of the work piece. The metal work piece is heated and placed on the lower die while the ram falls down forcing the metal to fill the die cavity.

Excess metal (flash) is trimmed off.


Closed-Die Forging


Closed-Die Forging


Net Shape Forging:- Traditional forging results in wastage of material in the form of material flash and subsequent machining operations.

Net shape forging process minimizes the waste by making precision dies, producing parts with very little draft angle (less than 1º).

WELDING


Welding is the process of joining two metals by the application of heat. It is permanent way of fastening metals.

Heat for welding the metals is most often obtained from gas flame, friction , electric arc etc.


Types of Welding

Solid State Welding:- It does not involve the melting of the materials being joined but it is heated to a welding temperature before the joining. Examples:- Hot Forge Welding, Friction Welding.

Liquid State Welding (Fusion Welding):-The metal being joined is actually melted and the union is produced on subsequent solidification. Examples:- Arc Welding , Gas Welding


Shielded Metal Arc Welding (SMAW):-

One of the simplest welding process & mostly widely used welding process in industries.

In this an electric arc is generated by touching the tip of a coated electrode to the workpiece and then withdrawing it quickly to a distance sufficient to maintain the electric arc.

The heat generated will melts a portion of the electrode tip, its coating and the base metal in the intermediate area of the arc.


The electrode coating deoxidizes and provides a shielding gas in the weld area to protect it from the oxygen in the environment.

A weld forms after the molten metal solidifies in the weld area

The electrode coating deoxidizes and provides a shielding gas in the weld area to protect it from the oxygen in the environment.



Schematic illustration of Shielded Metal Arc Welding (SMAW)



Oxy- Fuel Gas Welding (OFW)

Uses a fuel gas, [acetylene (C2H2) or hydrogen (H2)] combined with oxygen to produce a flame, as the source of the heat required to melt the metals at the joint.

The most common gas welding process uses acetylene, the process is known as Oxy-acetylene gas welding (OAW).

The heat generated is a result of the combustion of acetylene gas (C2H2) in a mixture with O2, with a pair of chemical reaction.

C2H2+ O2 2CO + H2 +Heat

The temperature of the flame can reach 3575K


Flame Types

At a ratio of 1:1 (O2: C2H2) the flame is considered to be neutral. It is used for welding mild steel, copper, aluminium etc. Its approximate temperature is about 3260ºC.


With a grater O2 supply the flame can be harmful and oxidizes the metal called oxidising flame. O2 : C2H2 (1.5:1).It is used for welding copper based metals like brass, bronze and zinc based metals etc. Its approximate temperature is about 3482ºC.


If the oxygen is insufficient for the full combustion the flame is known as carburizing flame or reducing flame. O2 : C2H2 (0.85:1). It is used for welding high carbon steel, alloy steel etc. its approximate temperature is about 3038ºC.


Schematic illustration of Oxy Fuel Gas Welding (OFW)



ROLLING


Rolling is the process of reducing the thickness or changing the cross section of a long workpiece by the compressive force applied through a set of rolls.

The basic rolling operations are called flat rolling or simple rolling, where the rolled products are flat plate or sheet.

Rolling is usually carried at elevated temperature about 1200ºC (above recrystallisation temperature) called hot rolling. In cold rolling metal is fed to the rolls when it is below the recrystallisation temperature.


The major components produced by rolling are bars, plates, sheets, rails, channels etc.

The rolling process basically consists of compressing and squeezing a metal piece between two rolls rotating in opposite directions. It is the method of forming metal into desired shapes by plastic deformation as the metal passes between the rolls.


Rolling Mill

The arrangement of rolls for a rolling operations constitute a rolling mill.

The rolling mills are classified on the basis of the number of rolls and their arrangement. They are; Two high rolling mill (2 roll process) Three high rolling mill (3 roll process) Four high rolling mill Cluster mill


2 Roll Process (Two High Rolling Mill) [University Question-May 2010]

It consist of two rollers rotating in the same speed but in opposite directions. As the metal passes through the rolls, its thickness will get reduced and the length will increase.

Mostly the lower roll be fixed in position and upper roll can be moved to adjust the space between the rolls.




3 Roll Process (Three High Rolling Mill) [University Question-May 2011]

It consist of three rolls positioned one over the other. The upper and the lower rolls rotate in the same direction, while the middle roll rotates in the opposite direction.

The metal is rolled between the two lower rollers in one pass and then rolled between the two upper rollers in the second pass. The process is continued till the final shape is obtained.


In this process the middle roll is kept fixed and the upper and lower rolls are moved to adjust the roll gap.

This process is widely used for rolling structural shapes like channels, angles etc.




Four High Rolling Mill

It consists of four rolls, two of which are working rolls and the other two are back up rolls.

Back up rolls are used to provide rigid support to prevent the bending and the deflection of the working roll under rolling load.



Cluster Rolling Mill It consists of a pair of working rolls of very small diameter

supported by back up rolls on either side.



EXTRUSION


Extrusion is a process used to create objects of fixed, cross-sectional profile. In this process the material is pushed or drawn through a die of the desired cross-section.

Extrusion is a process of simply forcing a billet through a shaped die to produce a continuous length of constant cross section similar to the die profile. The dies may be round or of various other shapes.


Typical parts made by extrusion are railing for sliding doors, window frames, aluminium ladders, tubing etc.

Extrusions that are carried out at room temperature are called cold extrusion and those carried out at an elevated temperature above recrystallisation temperature are called hot extrusion.


Types of Extrusion

Direct Extrusion:- Direct extrusion, also known as forward extrusion, is the most common extrusion process. In this process the ram will push the billet through a stationary die.

The extrusion will take place on the same direction of the movement of the ram




Indirect Extrusion:- Indirect extrusion is also called backward extrusion. Here the die is not stationary and moves with respect to the container.

The extrusion will take place on the opposite direction of the movement of the ram



Hydrostatic Extrusion (UQ-May 2011):-

In this process the container is filled with fluid that transmits the pressure to the billet which is then extruded through the die.

A ram or a pump is used to pressurize the fluid inside the container. There will be negligible friction along the container walls.



Benefits of Extrusion

Low tooling cost

Minimal wastage material

Most economical

Highly efficient process


CASTING


Casting is the process of producing metallic parts of desired shape and size by pouring molten metal into a mould having a cavity and then allowing the molten metal to solidify thereby taking the shape of the cavity.

The desired metal object (CASTING) is taken out from the mould after the solidification by either breaking the mould or taking the mould apart.


Casting is most often used for making complex shapes that would be otherwise difficult to make by other methods.

The mould, into which the molten metal is poured, is to be made of some heat resistant material.

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


Sand Casting


Important Nomenclatures

Mould :- A mould is a hollow block having a cavity inside that is filled with molten metal. The molten metal will eventually harden or sets inside the mould, adopting its shape.

Moulds are mainly classified into :- Expendable mould , Permanent mould.

Expendable mould (temporary, non re-usable):- are made of sand , ceramics etc.

Permanent mould (used repeatedly):- are made of metals like cast iron, steel, aluminum

Moulding :- It is the process of making a mould using a pattern

Pattern :-It is defined as the model of a casting, constructed in

such a way that it can be used to form an impression in the moulding sand. Types:- Solid pattern, Split Pattern, etc. Materials used for making pattern :- Wood, Metals (Cast iron, Brass etc), Plastic, Plaster of Paris, Wax etc.

Pattern Allowances :- They are provided to produce a casting of proper size and shape Types: - Shrinkage allowance, Draft allowance, Machining allowance etc.

Sprue:- Passage through which the molten metal flows downward


Runner:- Which carry the molten metal from sprue to the mould cavity.

Riser:- Which supply additional metal to the casting as it shrinks during solidification

Core:-Which are inserts made from sand. They are placed in the mould to form hollow regions in the castings.

Gas vent:- Permit the ejection of gas like CO2 or air entrapped in the mould.




Types of moulding sand

Green Sand:- It is a mixture of silica sand with 18 to 30 % clay and 6 to 8% water. The clay and water give bonding strength to green sand. A small amount of coal dust is mixed with green sand to prevent defects in casting. It is fine, soft, light and porous. They are used for making small and medium sized moulds.

Silica sand, Dry sand, Loam sand, Facing sand, Backing sand, Parting sand, Synthetic sand


Sand Casting (UQ MAY 2011)

Sand casting consists of placing a pattern (having the shape of the desired casting) in sand (usually Silica sand (SiO2) or green sand) to make an imprint, incorporating a gating system, filling the cavity with molten metal allowing the metal to cool until it solidifies, breaking away the sand mould and removing the casting.



Die Casting ( UQ APRIL 2012)

It is the process of producing castings using permanent moulds (die). Permanent mould is also called as die, made of cast iron, steel, aluminum etc. Gravity Die casting (Permanent Mould Casting) Pressure Die Casting Hot- Chamber Die Casting Cold-Chamber Die Casting


Gravity Die casting (Permanent Mould Casting)

Molten metal is prepared in a crucible furnace, poured by a ladle into an open steel mould, where it is allowed to cool and solidify.

Molten metal is poured into the mould under gravity only.

No external pressure is applied to force the liquid metal into the mould cavity.




Pressure Die casting

Molten metal is forced under high pressure into the mould.

The high pressure (70 to 5000 Kg/cm2) is obtained by compressed air or hydraulically.

The pressure is maintained during solidification.




Hot- Chamber Die Casting

In hot chamber die-casting, the metal is melted in a container (furnace) attached to the machine, and a piston is used to inject the liquid metal under high pressure into a die (furnace is integral part of machine).

As the molten metal possesses high temperature, less pressure (30 to 45 kg/cm2) is needed to force the metal into the die



Cold- Chamber Die Casting

Molten metal is prepared in crucible furnace and poured by ladle in to the die. (furnace is not an integral part of machine).

Molten metal is poured into the cold chamber die casting machine at low temperature as compared to that poured into hot chamber die casting machine.

Pressure is much higher (200 to 2000 kg/cm2) than those applied in hot-chamber die casting.


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MANUFACTURING PROCESSES Prepared by SREEJITH K. SREEJITH K.APMEJEC