HCDCA diamond-coated cutting tools

Abstract

The high-current d.c.-arc technique (HCDCA) offers a new plasma CVD method for diamond coating of cutting tools. The technique enables coating of cutting tool inserts at a scale greater than that 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 from the intense discharge column allowing simultaneous coating of numerous cutting tool inserts. The diamond is of high quality, comparing well 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 coated area, regarding coating growth rate, diamond quality and the adhesion of the coating to the carbide substrates. Coating of cutting tool inserts of virtually any style can be realised. Cutting tool inserts coated by the HCDCA method have been tested under different machining operations using workpiece materials ranging from AlSi alloys and metal matrix composites to fibre-reinforced plastics. Tool life improvements of four to ten times over uncoated carbide tools were found for AlSi machining. Cutting plastics gave even larger improvements. 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. The advantage of the chip-breaker on the diamond-coated tools over PCD inserts is also shown.