Manufacturing

## 2.8 Casting our gearwheel

### 3 Forming

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# 3.1 Introduction

Forming processes involve shaping materials which are solid. As mentioned before, a simple example is moulding with Plasticene. However, metals can be moulded using forming processes as well, as long as their yield stress is not too high and enough force is used. One way to lower a metal's yield stress is to heat it up. So we can shape metals without melting them; think of the blacksmith working on a horseshoe, heated, but still solid.

However, we have identified a key quandary in forming that actually applies to materials processing in general. The properties you want from a material during processing often conflict with the material properties you require for the product in service. If you have decided that the best route to make something is to squeeze it into shape, then the properties that are required to make the product will clearly be different from the properties required when in use. For easy forming, a material needs to be soft, with a low flow (or yield) stress. These are not properties that are generally attractive or useful in finished products. More often, high strength is required; so some way must be found to make the forming of such products easier – often through the use of high temperatures (see Properties for processing – forming).

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