1. General

1.1 Machining behaviour

The characteristics of polymers that have a direct or indirect influence on machining operations are as follows:

• modulus of elasticity and hardness: plastics are very flexible compared to steels (moduli of between 1,000 and 20,000 MPa) and much less hard, which means, for example, that special clamping precautions must be taken to avoid deforming the part or marking its surface;

• internal stresses: plastic parts often contain internal stresses after molding, due in particular to the shrinkage of the material as it passes from the liquid to the solid state. Machining often alters the distribution of these stresses. Precautions must therefore be taken to avoid the build-up of stresses...