Effect of coating roughness on performance of small CVD diamond coated tools

Small milling tools for dental application were diamond coated by means of Hot Filament CVD (HFCVD). Different thicknesses were obtained by using different diamond deposition times (3 and 12h) and seeding conditions. The surface roughness was measured for coated and uncoated mills and milling tests were performed to measure the cutting forces. A ceramic material and a polymeric matrix composite (PMC) were used as workpiece materials. The highest cutting forces were measured for the coated tool with the highest thickness of the diamond coating. Probably, roughness increase and non-optimal edge profiles affect the tool behavior during cutting. As a consequence, tool failure was observed in the case of milling of ceramic by means of the coated tool with the highest coating thickness. The coated tool with a lower thickness of the diamond coating showed an optimal behavior under cutting, above all in the case of PMC milling.