Wear characteristics and cutting performance in micromilling reentrant microchannels with micro serrated pin fins with a micro staggered multi-edge ball-end milling tool

Reentrant microchannels with micro serrated pin fins (RMSPF) are promising for high-performance microchannel heat sinks for heat dissipation of high-heat-flux devices. They can be efficiently fabricated in a single micromilling process using a specially designed micro staggered multi-edge ball end milling tool (SMBMT). The tool wear is an inherent problem for the micromilling process, as the machining quality and efficiency of RMSPF are significantly affected by the tool wear progression. Nevertheless, the wear behaviors and mechanisms of the micromilling tool with discontinuous cutting edges has not been understood. To this aim, wear characteristics and cutting performance of the SMBMT in micromilling of RMSPF were investigated through experiments and finite element simulations in this study. Results revealed that the tool wear of SMBMT could be divided into three stages, i.e., initial, steady and severe wear stages. The cutting force and cutting temperature increased nonlinearly with tool wear. Adhesive wear and abrasive wear mainly occurred on the auxiliary forming face and the tool end face for the SMBMT, which was different from the common occurrence of tool wear on the flank face and cutting edges for conventional milling tools. Abrasive wear on the tool end face produced uniform circular wear lands. Progressive tool wear reduced the height of serrated pin fins by 33 %, and increased the surface roughness of the reentrant microchannels. Moreover, chip morphology transitioned from regular strips in the initial wear stage to irregular blocks in the severe wear stage. This study elucidated the wear characteristics and cutting performance of the micro staggered multi-edge ball end milling tool, which provided valuable insights into the design of the unique tool of SMBMT and fabrication of RMSPF for high-performance microchannel heat sinks.