Highly efficient fabrication of reentrant microchannels with micro serrated pin fins using a micro staggered multi-edge ball-end milling tool in a single process

Microchannels with micro pin fins and reentrant cavities can increase the heat dissipation area and enhance heat transfer, which are promising for high-performance microchannel heat sinks for heat dissipation of high-heat-flux devices. Nevertheless, their fabrication is time-consuming and cost-inefficient for conventional methods. To this aim, we in this study developed a novel micro staggered multi-edge ball end milling tool (SMBMT) to fabricate a unique type of reentrant microchannels with micro serrated pin fins (RMSPF) in a single process. The formation feasibility of the RMSPF was demonstrated, and they were of narrow exit slots with a width of 500 μm on the top, reentrant circular cavities with a diameter of 800 μm at the bottom, and micro serrated pin fins with a width of about 52 μm and a height of 35 μm on the wall surface of reentrant cavities. More microscale serrated pin fins with much smaller sizes than the micro cutting edges of the SMBMT were obtained due to the staggered arrangement and overlapping effect of the multiple micro cutting edges. A geometrical model of the SMBMT with discrete multiple cutting edges was developed by considering the structure of the RMSPF. The formation process mechanism of RMSPF and its chip formation process was investigated with both experiments and finite element (FE) simulations. Compared to conventional micro ball end milling tool (CBM) with continuous cutting edges, the SMBMT suppressed the burr formation inside reentrant microchannels and improved the surface quality, and reduced the cutting force by up to 53 %. The enhanced cutting performance of SMBMT can be attributed to that the multiple discrete cutting edges of SMBMT effectively decreased the contact area of tool-workpiece and the friction between cutting tool and chips. This study offered a highly efficient method to fabricate microchannels with surface microstructures in a single micromilling process, which provided valuable insights for the development of high-performance microchannel heat sinks in a wide range of application areas.