End Milling of Elastomers

Abstract

The purpose of this study is to identify mechanisms for effective elastomer machining using sharp, woodworking tools and cryogenic cooling. The development of an elastomer machining process could reduce cost and time spent in mold processing as an alternative approach. Thirteen tools of different sizes, tool geometries, materials, and milling configuration are used in this study. Fixture design is identified to be critical to elatomer machining due to material's elastic properties. The finite element method using ANSYS software is used to evaluate the stiffness of the workpiece when machined by different size end mills. The term effective stiffness is defined for the elastomer workpiece and found to increase with increasing tool size. Down milling configuration tools can effectively remove elastomer material at room temperature. Cryogenic cooling to -78.6 degrees C with solid carbon dioxide also improves the machined elastomer surface. A survey of the chip morphology is taken using Scanning Electron Microscopy (SEM). A system of classifying 7 types of chips based on size and morphology is developed. Serrated chip formation with apparent adiabatic shear bands is observed for one end milling test, possibly caused by the low thermal conductivity of elastomers. Other serrated chips exhibit wavy marks on the surface possibly due to vibration during machining. Milling forces were recorded and analyzed and show higher cutting forces for samples cut at the cryogenic condition. Cutting forces also reveal a correlation of the maximum uncut chip thickness with averaged peak cutting forces for different spindle speeds, which may have potential for modeling the elastomer machining process.