Diamond coated cutting tools

Abstract

The high current DC-arc technique (HCDCA) offers a new plasma CVD method for diamond coating of cutting tools. The technique enables coating of cutting tool inserts in a scale that is larger than demonstrated by any previously established method. The technique is based on the formation of a high current discharge arc column. The substrates to be coated are placed at a relatively large distance around the intense discharge column allowing simultaneous coating of numerous cutting tool inserts. The diamond is of high quality, well comparable with diamond produced using deposition techniques such as microwave or hot-filament assisted plasma CVD methods. A high degree of uniformity is obtained over the large area that is coated, both regarding coating growth rate, diamond quality and the adhesion of the coating to the carbide substrates. Coating of cutting tool inserts of essentially any style can be realized. Cutting tool inserts coated by the HCDCA method have been tested in different machining operations using workpiece materials ranging from Al-Si-alloys and metal matrix composites to fibre reinforced plastics. Tool life improvements from four to 10 times that of uncoated carbide tools are found for Al-Si machining. Cutting in plastics implies even larger improvement factors. Cases where the diamond coated tools compete with and even outperform polycrystalline diamond compact (PCD) tools are also presented. The expected performance of diamond coated cutting tools has been fulfilled to a large extent. Properties such as high wear resistance, less built-up edge formation and better surface finish are demonstrated in comparison with uncoated carbide tools. In comparison with PCD inserts, the advantage of the chipbreaker on the diamond coated tools is also shown.