Sharp attack

Most engineers will be aware of the problems of machining composites. Yet in the not-too-distant future composites will increasingly take the place of traditional materials, and even some of the more exotic alloys.

Composites provide distinctive manufacturing advantages thanks to properties such as high specific strengthto- weight ratios and/or stiffness, low electrical conductivity, transparency to radio emissions, corrosion resistance and good thermal stability. But they are easily damaged and can cause unbelievable degrees of tool wear without the appropriate coating technologies and geometries.

One example of this is de-lamination caused when a drilling force exceeds a threshold value at the entry and exit of a drill bit.

So tool sharpness is a must. An equally important quality is tool hardness, as the abrasive nature of most composites wears sharp tools quickly.

From humble beginnings — for instance pre-history mud bricks reinforced with straw — composites have become the major topic in materials technology today. Applications include aerospace, automotive, and prosthetics. Recently a number of man-made fibres have been developed for polymericmatrix composites.