An Approach to Improve Machined Surface Finish in Micro Milling

Micro milling has been known to behave quite differently from conventional macro milling The effect of cutting speed on the machined surface roughness in micro milling of ductile materials was investigated in this paper. The micro flat end milling cutters of the diameters of 0 5 mm and 0.3 mm were taken to machine 6061 aluminum alloy and S20C low carbon steel. For comparison purpose, the cutter of the diameter of 10 mm was tested as well. It is found that the machined surface finish is closely related to the cutting speed. For a large size cutter, the roughness decreases with the increase of cutting speed as expected. But the decreasing trend is valid only up to a certain speed for the small diameter cutters. It is also noted that beyond this speed limit broken and powder type chips form easily. These chips will adhere to the machined surface and tool face and deteriorate machined surface as a result. Based on this finding, an approach by directing the cutting fluid to the cutting zone via high pressure air assistance is proposed. It is verified that the cutting force and its variation are greatly reduced, tool wear becomes less, and finish of the machined surface is significantly improved.