Effect of process parameters and tool shape on the machinability of a particulate filled-polymer composite material for rapid tooling

This paper presents the results of an experimental study on the effects of machining parameters (cutting speed, feed, depth of cut) and tool shape on chip formation, surface topography, resultant cutting force and surface rou ghness produced in flat and ball end milling of the Ren Shape-Express 2000 (TM) aluminum particulate filled-polymer composite material. This material is shown to exhibit a brittle-to-ductile transition in chip formation with decreasing cutting speed. The transition is explained by the strain-rate se nsitivity of the polymer matrix and is found to correlate well with a corre sponding change in the surface roughness. The absence of clear feed marks o n the milled surface explains why molds made from the composite material re quire less hand polishing than machined metal molds. The influence of cutti ng conditions and tool shape (flat end vs. ball-nose) on the cutting force, surface roughness, and workpiece break-out are discussed and relevant comp arisons with conventional metal and polymer machining are made.