EFFECTS OF CNC MILLING MACHINING PARAMETERS ON THE SURFACE ROUGHNESS OF UHMWPE BIOMATERIAL

Abstract

Ultra High Molecular Weight Poly Ethylene (UHMWPE) is a plastic biomaterial developed and had been used for decades in biomedical applications. This material is commonly produced with machining processes. One of those process is the milling operation. This method is needed alongside with the more common turning operation since there are many implant designs are not geometrically cylindrical. The milling process like any other machining techniques requires the operators to set certain machining parameter values to achieve specific objectives. One of these is the surface roughness of the materials. Rough machined surfaces were suspected to harbor more bacteria when the implant products made from UHMWPE are being used inside the human body. This study tested the influences of feed rate and depth of cut machining parameters on the UHMWPE surface roughness. The milling machining process with a SIEMENS CNC machine on the UHMWPE biomaterial was proved capable to produce better surface finish qualities. Four feed rate values between 0.2 mm/rev. to 0.025 mm/rev. and three depth of cuts from 0.2 mm down to 0.05 mm were evaluated. Third machining parameter, i.e. cutting speed was set constant at 150 m/minute. The tool is the high speed steel end milling. Achieved minimum surface roughness was found below 2 microns. A multiple regression model was developed to guide the machine tool operators to determine proper machining parameters. Statistical tests conducted and it can be concluded that feed rate is the most influential parameter. It must be set 0.05 mm/rev. or lower in the purpose to obtain higher quality surface finish.