Mirror surface finishing of hardened stainless steel using spherical PCD tool

   At present, the surface precision requirements for mold and die parts are extremely high. Especially in the
precision mold and die cavity for ELD lenses, several mirror surfaces for automotive lens parts, and general
camera lenses that required a few tens or a single nano-level like a mirror-finished surface. This final process is difficult to achieve with the conventional cutting edge of ball-nose end mills. In addition, it is commonly performed for a very long time by manual polishing of the skilled worker after machining. To the problem, we purposed to develop a sintered polycrystalline diamond (PCD) tool with a simple spherical cutting part. This PCD tool is a novel method for the final process of the small molds and dies cavities with high precision. A distinctive feature of its cutting can achieve a mirror-finished surface by full automation on a CNC machining center. This study aims to clarify the basic machining characteristics and verify its effectiveness on the hardened stainless steel commercial STAVAX with the hardness of 54 HRC for small mold and die cavities. As a result, we can clarify the chip generation mechanism, finish surface accuracy, internal crystal structure state, and residual stress characteristic of this processing method. It also shows that the manual problems related to mirror finishing of the precision mold and die cavity can be solved under the actual mold manufacturing process by consecutive conditions.