Cutting Tools

The introduction of new steel grades in combination with the ever-present demands for improved economies of production and higher production rates have illuminated the need to increase the knowledge of the tool wear mechanisms in high speed machining, see Figure 1. In the literature, three main tool wear mechanisms can be identified: i) adhesive wear due to the formation of adhesive junctions at the tool-work material interface, which results in material removal from the tool surface, ii) abrasive wear by the grooving action of hard second phase particles in the work material, and iii) solution wear by diffusion of tool material into the work material at elevated temperatures. In order to resist wear, a tool must thus have a high hardness, a high temperature strength and a high chemical inertness. It must also possess the high toughness necessary for a sufficient mechanical shock resistance. These properties are difficult to combine in a conventional tool material. However, by using surface coatings, the bulk tool material can be chosen mainly in order to provide the toughness, while the other demands are met by the coating.

Schematic drawing of a cutting operation. A chip is formed on top of the cutting tool during cutting. The cutting forces, temperatures are a complex and dynamic system and depends on the material to be cut, cutting speed, tool material etc.

Wear resistant coatings

In the late 1960's it was discovered that wear-resistant CVD (Chemical Vapour Deposition) coatings on cemented carbides could drastically increase tool life. Since then, a rapid development of CVD coatings (Fig. 2) and coating tech-nologies has taken place. Multilayer coatings of TiC, TiN, Ti(C,N), a-Al2O3 and k-Al2O3 have further increased tool life in high speed machining applications. The development of wear resistant CVD coatings has been on an advanced scientific level for many years, combining coating deposition technology and detailed coating characterisation with first-principles calculations.

A wide range of coated cutting tool inserts.