The Process Window for Reference Free Part Encapsulation

Abstract

Reference Free Part Encapsulation (RFPE) is an automatic, universal workholding process developed by the authors and by researchers at Berkeley. In RFPE, a block of filler material encapsulates the workpiece and provides a fixturing surface, and after each machining operation, the filler block is re-filled with material to restore it to a perfect block. The objective of this research is to compute the process parameter window for RFPE. We examine the effect of process parameters such as the injection temperature, the preheating temperature, the cooling rate and the pressure on the effectiveness of the process. We show that when the temperatures are too low, or if the mold is cooled too much or too rapidly, the newly added material does not weld properly to the original encapsulation. If the temperatures are too great, then the entire encapsulation is likely to melt and lose location. The injection pressure, meanwhile, affects the surface finish of the process, and therefore the accuracy. We develop models to understand the effects of these parameters on process performance and design experiments to verify these predictions. Using these techniques, we determine the acceptable parameter windows for the process.