CVD diamond coated cemented carbide cutting tools

The development of CVD diamond coated cutting tools has faced several challenges since the commencement of the low pressure synthesis of diamond coatings from a vapor mixture of hydrogen and a carbon containing gas based on the original work by Derjaguin and Fedoseev. The reason for the fairly slow progress can be attributed to a number of problems. For example, obtaining a satisfactory and consistent adhesion between the diamond coating and the substrate has proven to be difficult. Further, the problems faced in expanding any of the existing CVD diamond laboratory processes into a large scale production technique have also turned out to be greater than exprected. The recent development of a scaled-up process with a high current density plasma beam will be described. This new CVD diamond process, the high current DC-arc process (HCDCA), which is based on a high current DC discharge are with a long discharge column, has been successful and high quality diamond coated cemented carbide inserts can be manufactured with good reproducibility and large productivity. Diamond coated tools are compared with both PCD tools and uncoated carbide tools. The main advantage compared to PCD tools are the possibilities of using multiple edges per tool insert and advanced chip breaker technology. Compared to an uncoated carbide tool, the CVD diamond coated insert shows, in addition to a much larger abrasive wear resistance, less built-up edge and a lower cutting forces resulting in a much improved surface finish to the workpiece material. Several results from field tests at end user machine shops in the turning of Al-Si alloys, particularly in wheel turning, are presented. In the tests diamond coated carbide inserts perform typically 3-5 times better than uncoated tools but peak values of 10-20 times improvement can be obtained. An example of machining of Cu is reported where the diamond coated tool is found to outperform a PCD tool.