Study of Surface Roughness on Milling Unfilled-polyetheretherketones Engineering Plastics

Polyetheretherketones (PEEK) have been increasingly employed as biomaterials for trauma, orthopedic, and spinal implants. These implants are commonly fabricated by extrusion and injection molding, and for this fact, additional machining operations are required. Surface roughness is a vital factor for medical implants since the cells of the surrounding tissue interact with the underlying substrate on the micro and nanometer scales. For some application, such as self-mating articulation cervical disc implants smooth surface finish is critical so as to minimize the contact friction and wear. The requirement for a fine surface roughness poses a major concern in machining of polymeric base materials due to its low thermal conductivity. Machining performance such as surface roughness is directly affected by the milling parameter and should be methodically analyzed. Thus, this paper aims to study the effect of milling parameter on surface roughness of PEEK plastic under dry machining condition. Response Surface Methodology (RSM) technique was used to evaluate the influence of milling parameter namely cutting speed, feed rate and depth of cut on machined surface. From the conducted study, based on the statistical analysis result it is found that feed rate is the main factor that influence the surface roughness followed by milling speed and depth of cut. In addition, optical observation on the machined surface indicated that the mechanisms of the surface finish obtained from machining of polymeric based composites are different from those obtained from machining of the metals. It shows that there is some form of polymeric softening taking place when the cutting speed exceeded a critical cutting speed.