SURFACE ROUGHNESS OPTIMIZATION IN MILLING OPERATION OF POLYURETHANE BLOCK

Abstract

The polyurethane block also known as PB is widely used in the automotive industry to manufacture checking fixtures (CF's). This material has high machinability and a low hardness that ranges from 3 7 to 84 at the shore D hardness value. Acquiring the desired surface roughness for this material has always been a challenge for the manufacturing industry due to its high porosity, especially when it comes to machining of complex shapes. This study focuses on the optimization of the milling parameters for a radial profile on a CF for a car seat belt bracket. DoE is used to investigate the effect of the milling parameters on the PB. Five variables namely Feed rate, Depth of cut, Spindle speed, Step over and Plunge rate are considered for this experiment. Surface roughness tester is used to evaluate the surface finish whereas the composition of the PB is determined by Scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM-EDX). Through the preliminary experiment phase of this study, it is found that the surface roughness of the PB is severely affected when machined under a water based cooling medium instead of a dry condition. The most common chemical elements found in the Necuron 651 are carbon, silicon, oxygen and sodium. In addition to these, traces of other chemical elements were also detected but in negligible amount in all 16 work pieces. The step over was found to be the most significant milling parameter that influenced the surface quality of the PB. Finally, a set of optimized parameters is proposed to machine complex geometries of surfaces on PB (Necuron 651) that serves as a base material for manufacturing checking fixtures.