Bulk Forming Processes

Bulk Forming Processes:

Bulk refers to workparts with low surface area to volume ratio.

• Bulk Forming uses heavy machine to apply three dimensional stresses.

There are 4 basic operations used for bulk deformation:

1. Rolling
2. Forging 
3. Extrusion
4. Wire & Bar Drawing

1. Rolling:

Deformation process in which work thickness is reduced by compressive forces exerted by two opposite rolls.

Variations in rolling are described ahead:

A. Types of Rolling Based on Workpiece Geometry:

I. Flat Rolling:

It is used to reduce thickness of a rectangular cross-section.

II. Shape Rolling:

It is used to deform workpiece into contoured cross-section.

B. Types of Rolling Based on Work Temperature:

I. Hot Rolling:

The material is heated to a uniform elevated temperature to achieve significant deformation.

• Parts are free from residual stresses.

II. Cold Rolling:

Hot materials (like plates or sheets) are further flatten by cold rolling to prepare them for metal operations at room temperature.

• It further strengthen material.

C. Thread Rolling:

It us a cold rolling process used to form threads on cylindrical parts by rolling them between two dies.

D. Ring Rolling:

It is used to reduce the wall thickness and increase the diameter of a ring.

E. Gear Rolling:

It is a cold working process used to produce gears.

2. Forging:

Manufacturing processes that induce plastic deformation through localized compressive forces applied through two opposing dies.

Varations in forging are:

A. Types of Forging Based on Work Temperature:

I. Hot or Warm Forging:

Deformation is done at high temperatures but it reduces strength and increases ductility of work metal.

II. Cold Forging:

It increases the strength of material results from strain hardening of work metal.

B. Types of Forging Based on Shape of Dies:

There different types of forging but we dicuss some of them:

I. Open-Die Drop-Hammer Forging:

The metal is heated to a specific temperature by furnace or electrical indunction then work is compressed between two flat dies.

• Only for large objects or for small number of parts.
• If no friction between work and die surfaces then homogeneous deformation.
• The opposition to flow of work metal due to friction between die and work is called Barreling Effect.

Open die drop hammer forging are further classifies as:

• Fullering   ⇔   performed to reduce the cross-section  by dies with convex surfaces.
• Edging   ⇔   performed to reduce the cross-section  by dies with concave surfaces.
• Cogging   ⇔   used to reduce cross-section  and increse length. Also called Incremental Forging.

II. Impression-Die Drop-Hammer Forging:

The work peice is deformed between two die halves which carry impressions of Desired final shape.

III. Swaging (or Rotary Swaging or Radial Forging):

It uses rotating dies which hammer the work peice to reduce the diameter to create a tapered section.

3. Extrusion:

Compression forming process in which the work metal is forced to flow through a die opening to produce a desired cross-sectional shape.

There are two types of extrusions:

A. Direct Extrusion (or Forward or Hot or Continuous Extrusion):

A hot working process in which final material move in the same direction as that of the force applied is called Direct Extrusion.

• Significant friction is present between work and die surfaces.
• Length of final material is not limited.

B. Indirect Extrusion (or Backward or Reverse or Cold or Discrete Extrusion):

A cold working process in which final material move in the direction opposite to that of force applied is called Indirect Extrusion.

• Frictional effects are not that significant as used to be in Direct Extrusion.
• Length of material is limited.

4. Wire & Bar Drawing:

Wire Drawing is defined as:

It us used to reduce the diameter of wire having stock diameter less than 9mm.

Bar Drawing is defined as:

It is used to reduce the diameter of bars or rod having stock diameter greater than 9mm.

Reference:

• University Notes 
• Book Fundamental of Modern Manufacturing 6th Edition by Mikell P. Groover
• Videos from youtube and Google 
• Images from google images