FORGING PROCESS

When a sufficient load(force) is applied to a metal, it will cause the material to change shape. This change in shape is called deformation.

There are 2 (Two) types of deformation1.Elastic Deformation2.Plastic Deformation

A temporary shape change that is self-reversing after the force is removed, so that the object returns to its original shape, is called elastic deformation.

This type of deformation involves stretching of the bonds, but the atoms do not slip past each other.

When the force is sufficient to permanently deform the metal, it is called plastic deformation.

Plastic deformation involves the breaking of a limited number of atomic bonds by the movement of dislocations.

Forging is defined as the

controlled plastic deformation

of metal into predetermined

shapes by applying pressure

or impact blows, or

combination of both.

A forged component has the ability to withstand higher load during service. A forged components can be produced to close tolerance. It reduces the machining time, material and labor considerably. It increase the strength and toughness of the metals by producing directional

grains. It refines the structure of the metal and thus renders it more dense. The internal defects like segregation, cracks and porosity are eliminated.

WHY FORGING ? ? ?

TEMPERATURE

COLD FORGING

WARM FORGING

HOT FORGING

THIXO FORGING

EXTRUSION

COINING

DIE

OPEN DIE FORGING

IMPRESSION / CLOSED DIE

FORGING

UPSET FORGING

ROLLING

PUNCHING

PEARCING

BLANKING

HEADING

MACHINE

HAMMER FORGING

PRESS FORGING

RING ROLLING

ORBITAL FORGING

Cold forging refers to working metal at room temperature.

The cold forging process was developed in Germany just before the end of World War II. It was used to produce artillery shells and other ordinance items for the war.

RAW MATERIAL

HEAT TREATME

NT

SURFACE TREATME

NT

COLD FORGING

Receipt, Inspection & Billet cutting etc

Annealing to remove strain hardening to set the desired mechanical properties to normalize the microstructureSurface treatment to remove dust & oil cleaning by acids and

degreasers Pre-Coating - Phosphating Soaps – Sodium / Calcium stearates

Single or multi stage forgingSecondary Forming – Thread rolling / Machining

COLD FORGING

EXTRUSION

COINING

ROLLING

PUNCHING

PEARCING

BLANKING

HEADING

FORWARD EXTRUSIONBACKWARD EXTRUSION

Extrusion is the process of squeezing metal in a closed cavity through a tool, known as a die using either a

mechanical or hydraulic press.

Forward Extrusion Forward extrusion reduces slug diameter and increases its length to produce parts such as stepped shafts and cylinders.

Backward ExtrusionIn backward extrusion, the steel flows back and around the descending punch to form cup-shaped pieces.

This process is used to produce coins, medallions and other similar products on flat stock with relief features. Very fine detail can be reproduced.

Coining is the squeezing of metal while it is confined in a closed set of dies.

• The first blow combines coning with

shank extrusion.

• Coning is a partial head upset.

• The second blow finishes the head

shape.

1-Die/2-punch method in producing headed fasteners.

Piercing and blanking are essentially the same process, involving the stamping of shapes out of sheet metal or metal strip.

In piercing a shaped hole is made in the metal, Whereas in blanking a shape is stamped out of the metal and

then used.

Better accuracy, Closer tolerances, Better surface finish.

Strain hardening increases strength and hardness.

Grain flow during deformation can cause desirable

directional properties in product.

An ideal method for increasing hardness of those metals which do not respond to the heat treatment.

A cold forging can generally achieve tolerance of ±0.005”.

• Cold forging improves the finished

part’s grain structure by making it

conform to the flow of the design.

• The machined diagram shows how

the grain structure is weakened by

cutting operations.

Higher forces and power required for deformation. Surfaces of starting work must be free of scale and

dirt. Ductility and strain hardening limit the amount of

forming that can be done.

Metal must be annealed and pre-coated before

further deformation can be accomplished.

In other cases, metal is simply not ductile enough to

be cold worked.

Microscopic structure of a

crystal.

Purple is sodium ion

Green is chlorine ion

Arrangement of atoms is called the crystal structure

• Close packed directions are face diagonals.

FACE CENTERED CUBIC STRUCTURE (FCC)

BODY CENTERED CUBIC STRUCTURE (BCC)

• Close packed directions are cube diagonals.

The change in the crystal structure of a substance that takes

place upon heating or cooling, without a changing the chemistry

of metals.

The minimum temperature at which destroyed grains

of a crystal structure are replaced by the new strain

free grains.

Recrystallization is usually accompanied by a

1.Reduction in the strength.

2.Reduction in hardness of a material.

3.Simultaneous increase in the ductility.

Above the recrystallization temperature the kinetic energy of atoms increases and therefore they are able to attach themselves to the newly formed nuclei which in turn begin to grow into crystals. This process continues until all the distorted crystals have been transformed.

Performed at temperatures above room temperature,

below recrystallization temperature

HEATING AND COOLING OF

IRON

Temperature, C

BCC Stable

FCC Stable

914

1391

1536

shorter

longer!shorter!

longer

Tc 768 magnet falls off

BCC Stable

Liquid

heat up

cool down

WARM FORGING

BAND 550 0 C

950 0 C

Reduced tooling loads, as compared to cold forging.

Reduced press loads, as compared to cold forging.

Increased steel ductility.

Elimination of annealing prior to forging.

Favorable as-forged properties that can eliminate

heat

treatment.

Transmission Gears

Transmission Shafts

Hot forging is the plastic deformation of metal at a

temperature and strain rate such that recrystallization

occurs simultaneously with deformation, thus avoiding

strain hardening.

For this to occur, high work piece temperature (matching the metal's recrystallization temperature) must be attained throughout the process.

- Decrease in yield strength, therefore it is easier to work

and takes less energy (force).

- Increase in ductility.

- Elevated temperatures increase diffusion which can

remove or reduce chemical inhomogeneity.

- Pores may reduce in size or close completely during

deformation.

Lower dimensional accuracy due to thermal contraction & wrapping from uneven cooling.

Grain structure may vary through out the metal for various reasons.

Higher total energy required, which is the sum of The thermal energy needed to heat the work piece Energy to deform the metal

Work surface oxidation (scale) Thus, poorer surface finish

Shorter tool life Dies and rolls in bulk deformation

Two dies are brought together and the work piece

undergoes plastic deformation until its enlarged sides touch

the die side walls.

Some material begins to flow outside the die impression, forming flash.

Impression die forgings may be produced

on a horizontal forging machine (Up

setter) in a process referred to as

upsetting.

A work piece may be forged by a series of punch and die operations (or by several cavities in the same die) to gradually change its shape. 

Amount of energy is imparted by impulsive load,

Close tolerances are not much important

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

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

3. Completed pre-form ready for placement on ring mill for

rolling.

4. Ring rolling process begins with the idler roll applying pressure to the pre-form against the drive roll.

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

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

Forming Type Cold Warm Hot

Temperature 

Room 

550 - 950oC 950 - 1250oC

1020 - 1740oF 1740 - 2300oF

Accuracy High Good Low

Formability Restricted Good Good

Material Restricted Large variety Large variety

Energy Costs Low Moderate High

Surface Quality High Good Low

Tolerances Close Closer Low

Grain Structure Good Good Variable

Heat Treatments Few Few Necessary

Machining Least Less Necessary

Forged components are shaped either by a hammer or press.

Forging on the hammer is carried out in a succession of die impressions using

repeated blows.

The quality of the forging, and the economy and productivity of the hammer

process depend upon the tooling and the skill of the operator.

In a press, the stock is usually hit only once in each die impression, and the

design of each impression becomes more important while operator skill

is less critical.

In the most basic example of impression die forging, which accounts for the majority of forging production, two dies are brought together and the work piece undergoes plastic deformation until its enlarged sides touch the die side walls

Then, some material begins to flow outside the die impression, forming flash. The flash cools rapidly and presents increased resistance to deformation, effectively becoming a part of the tool. This builds pressure inside the bulk of the work piece, aiding material flow into unfilled impressions.

Impression die forging

Grain Structure

• Parts have good strength

• High toughness

• Forgings require additional heat treating

grain flow (a) casting (b) machining (c) forging

Forging Defects• Unfilled Section: In this some section of the die

cavity are not completely filled by the flowing metal.• Cold Shut: This appears as a small cracks at the

corners of the forging.• Scale Pits: This is seen as irregular depurations on

the surface of the forging. • Die Shift: This is caused by the miss alignment of

the die halve, making the two halve of the forging to be improper shape.

• Flakes: These are basically internal ruptures caused by the improper cooling of the large forging.

• Improper Grain Flow: This is caused by the improper design of the die, which makes the flow of the metal not flowing the final interred direction.

Forging Defects

Crack:Cracks are two types –

Surface Crack

Micro Crack

Reason –

Ingot Cracks

Improper Heating and Forging @ Low temperatures

Incorrect cooling of Alloy steel forgings

Incorrect Forging methods

Lap:Reason –

Due to folding of metal over itself during forging, laps are usually found where vertical and horizontal section intersect, when fillet radius is less.

Unfilling:Reason –

Inadequate Forging pressure

Chilled die or forge metal

Short supply of feed metal from either web or blocker

Inadequate Preform Design

Pitting:Depression on component surface due to scale imbedded during forging

Reason-Incomplete cleaning of dies & scales.

Dents:

Reason-Improper positioning of stock on the die.Hot forgings are thrown from place to place.

MismatchReason –Improper alignment of dies

Buckling:Reason-In upsetting forging. Subject to high compressive stress.

Thank You