Investigation on burr formation characteristics in micro milling of Ω-shaped reentrant microchannels

Reentrant microchannels show excellent heat dissipation capabilities and are promising for microchannel cooling systems in a variety of application areas. This study developed a micro milling method to fabricate a unique type of Ω-shaped reentrant microchannels in pure copper. The critical issues in micromilling, i.e., formations of side burr, entrance burr and exit burr in reentrant microchannels and their mechanisms, were comprehensively investigated with experiments and finite element (FE) simulations. It was found that side burrs in reentrant microchannels were mainly formed on the up-milling side, and some of them extended from the sidewall of circular cavity to the top exit slot. The restriction of top exit slot of reentrant microchannels played a significant role on the extrusion, squeezing and thrusting of deformed materials and chips, which contributed to the formation of side burrs. Moreover, the effects of spindle speed and feed rate on the side burr formation and their sizes were also explored. The side burr size firstly increased, reached the maximum, and then decreased with increasing spindle speed. Besides, it firstly increased, then decreased to be the minimum and finally increased with increasing feed rate. The ratio between the feed per tooth and cutting edge radius (fz/re), which combined both spindle speed and feed rate, is believed to be the critical factor for burr formation. The minimum uncut chip thickness seemed to be of 0.25 fold of the tool edge radius in micromilling reentrant microchannels. The fz/re of 0.42 with a spindle speed of 15,000 r/min and feed rate of 25 mm/min was suggested to be the optimal machining parameter to minimize the side burrs of reentrant microchannels.