Forming Operations

FORGING

COURESE- Smith forging, Drop forging, press forging & Machine forging, Description of Presses and hammers, forging defects. Forging die design.

What is Forging?

Grain Structure Comparison

• Parts have good strength• High toughness• Forgings require additional heat treating to improve its

mechanical properties

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

Why Forging is Necessary ?

Typical Forging Operationsa,b - To shape the ends of the bars to gather metals.

C- Fullering is used to reduce the cross –sectional area of a portion of the stock.

D- the reduction in cross section of the work with concurrent increase in length is called drawing.

e. If the drawing-down operation is carried out with a concave dies so as to produce a bar of smaller diameter is called swaging

• Is the simplest forging process• Sizes can very from very small parts to very large parts

Open-Die Forging

Open-Die Forging • Upsetting or flat-die forgingUpsetting or flat-die forging – a solid work piece is

placed between flat dies and is compressed• Defects Associated with Open Die forging• Barreling

– caused by frictional forces at the die-work piece interfaces– Can be minimized if a lubricant is used– Thermal effects caused by barreling can be minimized by using

heated dies

Impression-Die & Closed-Die Forging• The work piece acquires the shape of the die cavities while

being forged between the two shaped dies

Step-1 Step-2 Step-3

Impression-Die & Closed-Die Forging• The blank to be forged is prepared by:

– Cutting from a bar stock– Preformed blank– Casting– Preformed blank from prior forging

Impression-Die & Closed-Die Forging

Steps Involved in Close Die Forging• Fullering & edging are used to distribute the material

– Fullering – material is distributed away from an area– Edging – material is gathered into an area

• Blocking – rough shaping of the part

• Impression dies – give the part its final shape

Closed Die ForgingPurpose of Flash1. It acts as a safety valve to store the

excess metal in the closed die cavity.

2. The thin flash increases the flow resistance to the system , so that the pressure builds up to high to ensure that metal fills all recesses of the forging die cavity

Sectional view through closed –die forging

Typical Curve of Forging load vs Stroke for closed-die forging

Open Die Forging Closed Die Forging

Carried out between flat dies

For very simple shape

At low pressure

For large objects and small quantity

Preprocessor for close die forging

Carried out between two die halves

For complex shape

At high pressure

For mall objects and large quantity

Close dimensional tolerances

Typical Values of Velocity for different Forging Equipments

Energy Restricted machines

Stroke-restricted machines

Load restricted machines

High Energy rate forging - HERF

Total Energy supplied to the blow in a power drop hammer is given below

Classification of Forging and its Application

• Hand forging :- Hand forging is emplayed only to shapea small number of light forgings chiefly in repair shops.

• Hammer forgings :- Usually used for small item forging.

• Press forging :- Usually used for heavy item forging.

• Machine forging :- For medium sized and large articlesrequiring very heavy blows.

• Drop forging :- For mass production of identical parts.

Forging Defects

Internal Cracks