Mirror Surface Finishing of Molds using Spherical PCD tool 3rd Report: Construction of Empirical Formula to Guarantee Dimensional Accuracy

We developed a new polycrystalline diamond (PCD) spherical rotary tool to achieve a mirror-finished surface on the small mold core and cavities with the surface roughness within ten nanometers Ra. In the case of the study on the mirror finishing with this PCD spherical rotary tool, we found that the actual cutting depth was about 2/5 less shallow than that the set depth of cut because this series of tools is generally small in diameter having a radius of 0.5 mm or less. In order to guarantee the dimensional accuracy of the cut surface, it is necessary to know the actual depth of cut. Therefore, we consider predicting this actual depth of cut from the processing conditions. we experimented on the set depth of cut and the actual depth of cut by changing the machining conditions within the practical range, and conducted a study aimed at constructing this empirical formula.　The experiment is performed on two different types of materials that are widely used for mold cavities, the hardened stainless steel AISI420 grade modified commercially called STAVAX and cemented carbide D3 grade to determine the correlation coefficients of these materials. As results, the empirical formula under actual machining conditions was confirmed that the actual depth cut and the experimental value were in a good agreement within ±0.2 µm. It was clarified that the proposed empirical formula is practical.