Experimental and numerical study on micro ball-end milling of pin fin-interconnected reentrant microchannels

Pin fin-interconnected reentrant microchannels (PFIRM) of microchannel heat sink cooling systems provide a promising solution for efficient heat dissipation of high heat flux devices. They feature interconnected Ω-shaped reentrant configurations in cross-section, with large circular cavities at the bottom and diamond pin fins at the top. In this paper, a micro ball-end milling process was proposed to fabricate PFIRM. The burr formation process and deformation mechanisms during the micromilling process of PFIRM were investigated with experiments and finite element (FE) simulations. Results revealed that the burrs were mainly formed under the vertex of diamond pin fins on both up-milling and down-milling sides. The burrs on the up-milling side were pushed by the tool neck to the left side of feed direction, whereas the burrs on the down-milling side were thrusted by the flank face to the right side of feed direction. Besides, two unique types of chips, i.e., swallowtail-shaped chips and half swallowtail-shaped chips, were found to be formed during the micro ball-end milling process. Moreover, the effects of spindle speed and feed rate on the machining accuracy and surface roughness of PFIRM were also explored. The machining accuracy and surface roughness firstly increased and then decreased with increasing spindle speed. As the feed rate increased, the machining accuracy decreased in general, and the surface roughness firstly decreased and then increased. The present study suggested that the spindle speed of 15000 r/min and feed rate of 20 mm/min was optimal to improve the surface quality and machining accuracy.