Hardmetals milling

The desired final carbon content of the WC powder depends on the further production mode of the hardmetal producer (mainly powder milling and sintering conditions), and varies between slightly understoichiometric to stoichiometric (6.13 wt%) to slightly overstoichiometric. 

For most WC powders (APS 0.5-4 pm), there also exists a close relationship between the APS of the WC powder and the average grain size (AGS) of the WC in the sintered hardmetal structure (as long as milling conditions in grade powder preparation and sintering conditions are kept constant). In this case, the APS of the WC powder is used as the main steering parameter for the hardmetal structure. This is shown schematically in Fig. 9.15. 

Although the above characterization in regard to physical and chemical properties seems to be quite rigid and complete, in some cases imexpected and unsatisfactory results may occur diuing the further hardmetal production. The reason for this behavior is based on still insufficient specification, because the carbon black quality, carburization temperature, as well as type and diuation of milling after carburization are not clearly defined, and can be changed by the supplier or may differ between diverse suppliers. 

The choice of the correct mill and milling conditions depends on the hardmetal grade produced, mainly on the WC grain size. Attritors are used today for most powder qualities (1-12 pm). They have become increasingly popular because of the significantly shorter milling times. Optimized ball mills are still preferred for submicron qualities, which are very sensitive to all types of heterogeneities. 

Coated hardmetal is the dominant tool material for indexable inserts and will remain so in the foreseeable future. More than 80% of all turning inserts and about 70% of milling... 

FIGURE 9.40. Hardmetal tools used in different machining operations (a) turning (b) slot milling (c) threading (d) drilling. By courtesy of Iscar Ltd., Israel. 

Transition metal carbide, nitride and carbonitride layers of the IVB group made by CVD (chemical vapor deposition) and PVD (physical vapor deposition) are produced in order to increase the service life of hardmetal tools [18,21,108] for cutting and milling operations. About 90% of cutting tools are coated. 

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