Laboratory for Manufacturing and Sustainability

Micro-end-milling is emerging as an important fabrication process. Its benefits include the ability to fabricate micro and meso-scale parts out of a greater range of materials and with more varied geometry than is possible with lithography and etching. It also enables the creation of micro and meso-scale molds for injection molding. Factors affecting surface roughness have not been studied in depth for this process. A series of experiments has been conducted in order to begin to characterize the factors affecting surface roughness and determine the range of attainable surface roughness values for the micro-end-milling process. A 229 ?m diameter end mill was used to cut slots into aluminum (6061) samples. The machining factors studied were chip load (feed per tooth), cutting speed, and depth of cut. A two level factorial experiment was run, and it was determined that while chip load was the dominating factor, the interaction between chip load and cutting speed was also significant. Further experiments allowed the generation of a second order relationship between chip load and surface roughness. The model, which includes the effect of chip load, cutting speed, and the interaction between the two, predicted the surface roughness values with an accuracy of about +/- 10%. The surface roughness values ranged from 600 Å all the way to 3800 Å over the span of the studied parameters.

It has previously been shown that run-out creates a greater problem for the dimensional accuracy of parts created by a micro-end-milling process as compared to parts created by a traditional end-milling process (Lee, et al 2001). It appears that run-out also has a more significant effect on the surface quality of micro-end milled parts. The surface roughness traces reveal large peak to valley variations with a period of twice the chip load. This means that one of the two cutting edges on the tool creates a deeper cut than the other. Cutting marks from the non-dominant cutting edge are also visible on the surface roughness traces as small steps between the much larger marks from the dominant cutting edge. It is postulated that the effect is due to run-out, and that improving machine tool run-out will have a very significant effect on the surface quality of micro-end-milled features.