Machinability of rapid tooling composite board

The recent introduction of particulate-filled polymer composite materials for rapid tooling applications has made CNC machining an attractive alternative to additive rapid prototyping processes. However, data on the machinability of this material is lacking. Understanding the effects of machining parameters on machinability is critical for identifying optimal processing conditions that maximize material removal rate, and minimize surface roughness and workpiece break-out. Flat end-milling experiments were conducted on an aluminum-filled epoxy composite material with feed per tooth (ft), surface speed (V) and depth of cut (d) as process variables. Three responses were measured to characterize machinability: machining forces, surface roughness and workpiece break-out at tool exit. The effect of machining parameters on the cutting forces and surface roughness followed trends similar to those of metals. The primary mode of material removal was by brittle fracture at high cutting speeds, although a ductile-to-brittle transition was detected at lower cutting speeds. The former observation helps to explain why rapid molds made from this material require less “benching” than conventional metal molds.