Machining of elastomers.

Abstract

The research investigates the use of sharp tools, cryogenic cooling of workpiece, and induction heating of the tool for machining of elastomers. The chip formation, inverse heat transfer solution of induction heating, induction-heated tool for elastomer machining, forces in end milling of elastomers, and machined grooves and surfaces are studied. A classification system that identifies elastomer chips based on their size and morphology is described. A four-step examination procedure is developed to specify seven types of chips. Serrated chip formation with apparent adiabatic shear bands, possibly due to the low thermal conductivity of elastomer, is observed for one end milling condition. Another type of serrated chip is found with surface wavy marks due to the workpiece vibration. The explicit finite difference formulation of an inverse heat transfer model to calculate the induction heat flux is developed for a workpiece with low cross-section Biot number. Compared to measured temperatures, the accuracy and limitation of proposed method is demonstrated. Finite element analysis results validate the assumption to use the uniform temperature in a cross-section for the inverse heat transfer solution of induction heat flux. The induction heating is applied to raise the temperature of an end milling tool for machining of elastomers. Experiments and finite difference thermal modeling of the induction-heated tool for elastomer end milling are investigated. The thermal model of a stationary tool can be expanded to predict the temperature distribution of an induction-heated rotary tool within a specific spindle speed range. Experimental measurements validate that the thermal model can accurately predict tool tip peak temperature. The induction-heated tool and cryogenically cooled workpiece are investigated for elastomer end milling to generate desirable shape and surface roughness. At high cutting speed, smoke is generated and becomes an environmental hazard. At the low cutting speed, induction-heated tool demonstrates to be beneficial for the precision elastomer machining with better surface roughness and dimensional control. Frequency analysis of cutting forces shows that the low frequency vibration of soft elastomer workpiece is correlated to the surface machining mark generation. The correlation between the machined groove width and cutting force reveals the importance of the workpiece compliance to precision machining of elastomer. The use of both contact profilometer and non-contact confocal microscope to measure the roughness of machined elastomer surfaces is explored. The comparison of measurement results shows the advantages and limitations of both measurement methods.