HSC-CUTTING OF LIGHTWEIGHT ALLOYS WITH CVD-DIAMOND COATED TOOLS

摘要

CVD-diamond coatings on cemented carbide substrates have undergone significant developments in recent years. Former CVD-diamond coated tools failed in metal cutting applications due to severe flaking of the diamond layer. Thus, first industrial applications had been restricted to machining of graphite, fibre reinforced plastics and green compacts made of cemented carbide respectively of ceramics. The field of application is widened nowadays towards machining of non ferrous metallic materials like aluminium and magnesium alloys. Such lightweight materials will increasingly replace steel and iron based castings in automotive products. A rising demand for diamond tools suitable for HSC-cutting will consequently follow up. The challenge for the tool producing industry and for job coaters will be the further improvement of carbide substrates, the grinding and edge preparation, the surface/interface treatment prior to coating and the CVD-diamond coating process itself. Qualified feedback from cutting applications in industry and in laboratory is necessary for analysis of tool wear and improvement of CVD-diamond coated tools. CVD-diamond coatings are usually produced in a multiple step process chain. The substrate (either inserts or shaft tools) will be cleaned, etched and finally coated. Etching removes the cobalt binder from the rim zone of the carbide. This supports the diamond formation and the adhesion to the substrate. But the removal of the cobalt binder causes also a brittle tungsten carbide skeleton in the rim zone of the substrate which includes the sensitive cutting edge (Figure 1). Thus, only the choice of suitable cutting conditions with the aim to move the maximum load away from the sensitive cutting edge will allow for full exploitation of the high hardness and wear resistance of diamond coatings. Feed, depth of cut, cutting edge roundness after coating and roughness of the diamond surface are the factors to be considered for optimised tool life~1.