Improvement on uniformity of diamond coatings on PCB milling cutters with specific cutting edge structures

Abstract

Recently, specially-designed printed circuit board (PCB) milling cutters with specific cutting edge structures have been extensively applied. Hot filament chemical vapor deposition (HFCVD) diamond coatings uniformly deposited on cemented carbide (WC-Co) cutters can effectively improve their performance. To improve the coating uniformity, the complex cutters were precisely modeled and the temperature field generated by the HFCVD setup was simulated, using the finite volume method (FVM), taking spiral milling cutters as a reference for comparison. Temperature measurements revealed deviations between simulated and measured temperatures smaller than 4%, verifying the accuracy of the constructed model. Effects of some critical HFCVD setup parameters, including the filament height (Hf), the material and height of the sample holder (Ms and Hs), the material and dimensions of the heat insulating block (Mh, Hh and Ah), and the surface convection coefficient (h), were studied by the control variable method. Under the optimized conditions, the axial temperature deviation on cutting edges dropped from 193.3 °C to 64.3 °C for a PCB milling cutter, and from 53.3 °C to 29.6 °C for a spiral cutter, ensuring appropriate temperature ranges for fabricating high-quality diamond films. Besides, the two-dimensional plane temperature field and received radiation field of a cutter were both calculated by MATLAB. The results showed that heat conduction hindrance and heat convection reduction could effectively reduce energy consumption and improve the uniformity of substrate temperature. With the aim to study the specific cutting-edge structures, cross-sectional temperature distributions were further examined by presenting both simulations and numerical calculations. It was seen that the temperature distribution for PCB milling cutters was complicated, which was attributed to the densely-distributed cutting edges and long flute. Lastly, under the optimized HFCVD setup parameters, it was found that the grain size and thickness uniformity of diamond coatings, at different positions along the axial direction, were significantly improved, revealing the effectiveness of simulation as an optimization method.