metal forming & shaping: lecture introduction

17-01-2013

Introduction to Metal Forming Processes

Definition of Metal Forming “Metal forming refers to shaping of metallic materials by

means of plastic deformation”. The term plastic deformation describes permanent shape

change, in contrast to elastic deformation.

An elastic deformation disappears when the load is

removed. Many industrial materials are shaped into useful

products by plastic deformation.

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Bulk Deformation and Sheet-Forming ProcessesA- Bulk Deformation Processes

These processes involve large amount of plastic

deformation. The cross-section of workpiece changes

without volume change. The ratio cross-section area/volume

is small.

For most operations, hot or warm working conditions are

preferred although some operations are carried out at room

temperature.

Bulk Deformation Processes includes a wide variety of

techniques, which make use of suitable force, pressure or

stresses, like compression, tension and shear or their

combination to cause a permanent deformation of the raw

material to impart required shape.

These processes are also known as mechanical working

processes and are mainly classified into two major categories

i.e., hot working processes Warm working and cold working

processes.

In these processes, no material is removed; however it is

deformed and displaced using suitable stresses like

compression, tension, and shear or combined stresses to

cause plastic deformation of the materials to produce required

shapes.

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Such processes lead to production of directly usable articles

which include kitchen utensils, rods, wires, rails, cold drink

bottle caps, collapsible tubes etc.

Some of the important metals forming processes are:

Hot working Processes(1) Forging, (2) Rolling, (3) Hot spinning, (4) Extrusion, (5) Hot

drawing

Cold working processes(1) Cold forging, (2) Cold rolling, (3) Cold heading, (4) Cold

drawing, (5) Wire drawing,(6) Stretch forming,

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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.

Warm working is metal forming at temperatures above the

room temperature but below the recrystallization one.

Advantages: lower forces and power, more complex part

shapes, no annealing is required.

Disadvantages: some investment in furnaces is needed.

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 is required, forming of materials with low ductility,

no work hardening and therefore, no additional annealing is

required.

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Disadvantages: lower accuracy and surface finish, higher

production cost, and shorter tool life.

Importance of Rolling Example:

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Forging Example:

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B- Sheet-Forming Processes In sheet metal working operations, the cross-section of

workpiece does not change—the material is only subjected to

shape changes. The ratio cross-section area/volume is very

high.

Sheet metal working operations are performed on thin (less

than 6 mm) sheets, strips or coils of metal by means of a set of

tools called punch and die on machine tools called stamping

presses. They are always performed as cold working

operations.

Sheet metal working processes such as piercing, punching,

lancing, notching, coining, squeezing, deep drawing, bending

etc.

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Characteristics of Metal FormingFollowing are some general characteristics of metal forming

processes:

The work piece is completely or partially subjected to plastic

deformation during the forming operation; that is, it is

plasticized.

The plastic deformation is most commonly large.

Little or no material is removed during the forming process.

The microstructure of the as-cast workpiece is broken down

by the plastic deformation. Therefore, the final component,

or product, made by metal forming usually will have better

mechanical properties than a similar product manufactured

by casting or machining.

During cold deformation, mechanical properties, such as the

yield strength and tensile strength, will increase because of

the accumulation of plastic strain in the material.

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Animation

Tensile Test (Stress-Strain Diagram)

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Fracture

Necking

Final

metal forming & shaping: lecture introduction

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