Unit 20 Assignment 2 Deformation Processes for Metals & Polymers

UNIT 20: Engineering Primary Forming Processes

Assignment 2: Deformation Processes for Metals & Polymers

P4 Describe the deformation processes used to manufacture a metal-based component

Metal forming is the manufacturing process of reshaping metals while they are still in their solid state through mechanical deformation. The metal is worked on without adding r removing any material from it hence the mass remains constant throughout the whole process. Forming processes uses suitable forces such as compression, tension and sheer to cause plastic deformation on metals in order to produce desired shapes. The major deformation processes use to form metallic objects are:

• Rolling
• Extrusion
• Forging
• Presswork
• Metal spinning

Forming can be divided into two categories:

• Hot working
• Cold working

Hot working involves deformation of preheated materials at temperatures above their recrystallization temperatures. Cold working is metal forming done at room temperature. Cold working is divided into two classes. In the first class, cold working is used for the purpose of shaping the metal. In the second class, not only is it used to shaping, but also to strain, harden and strengthen the metal. Hot working serves the purpose of obtaining the expected shape and improving the physical properties of the material.

• Rolling

Rolling is a bulk deformation process in which metal is passed between two rollers, which exert compressive forces, reducing the thickness of the metal. Rolling is the most used deformation process since a large majority of all metal products produced are subject to undergo metal rolling at one point of their manufacture. Metal rolling is the most economical process when it comes to making of simple shapes in large quantities. This process is usually the first step in creating raw material forms such as sheets and structural shapes and rails. Rolling is further divided into two:

• Hot rolling
• Cold rolling

[pic 1]

Figure 1: Rolling

Hot rolling is done first on ingots or continuously cast slabs to change them from coarse-grained, brittle and porous structures to wrought structures with finer grain sizes and give them enhanced properties. The structures produced can either be a bloom (square) or a slab (rectangular). Hot rolled products are often pickled because the worked metal tends to oxidise leading to scaling. This might result in a poor finish and loss of accurate dimensions. Hot rolling allows large deformations of metal to be done with a low number of rolling cycles. When the metal is rolled, the broken up grains recrystallize and form an equal axis formation and prevent the metal from hardening. The high temperatures ensures that there is no residual stress accumulating in the material and also the material will not require annealing after it has been rolled.