Wear Behaviour of Silicon Nitride Tools as a Function of Their Specific Properties

Abstract

The present investigation compares wear behavior of oxide ceramics with nonoxide ceramics based on silicon nitride. The latter's most important properties are mechanical and thermal which give them their particular advantage. Transfer rupture strength and fracture toughness (K 1c ) are higher than that of either white or composite ceramic. The combination of High thermal stability, high hardness, high thermal conductivity and low thermal expansion coefficient, results in the higher thermal shock resistance. The specific mechanical and thermal properties result in a much lower sensitivity to temperature change and the improved performance in interrupted cut at high cutting speeds and high feeds. Different types of silicon nitride compositions are discussed in connection with their manufacturing processes and properties. Products made from silicon powder with subsequent nitriding and sintering are compared to products from silicon nitride powder produced by hot pressing. The special cutting edge configuration is investigated with relation to the cutting forces, the specific cutting force and the wear behavior of silicon nitride inserts. Results of force measurements show that with higher cutting speeds, higher feeds and larger depth of cut, the specific cutting force is decreased. Tool life tests in milling and turning showed that silicon nitride as a cutting tool material is advantageous when machining nodular cast iron. Comparison with a friction test showed that the formation of a glass phase at high temperature developed during cutting may explain the wear mechanism.