Characterising the machining of biomedical grade polymers

Abstract

The manufacture of polymer components for biomedical applications is an area which has received much attention from polymer scientists, with high levels of wear resistance achieved, but relatively little research has been done into the machining operations required to manufacture the complex geometries used in total joint replacement. Traditional metal cutting theories have been shown to be insufficient for analysis of polymer machining, as polymers exhibit viscoelastic behaviour, and unique chip formation mechanisms. This paper details an experimental investigation into the effect of tooling and machining parameters on the cutting forces, surface roughness and chip formation in Ultra High Molecular Weight Polyethylene, a common material used in biomedical applications. This research quantifies the relative importance of each parameter, the chip formation mechanisms and resulting surface roughness for the given machining parameters, and provides new insight into applied research on the machining of polymers.

Machining of biocompatible materials — Recent advances

“…When the temperature is above Tg, the cutting process is affected mainly by the cutting parameters, tool geometry and sharpness. According to Aldwell et al [5], due to polymers' viscoelastic behaviour, the effective DOC is always smaller than nominal value because of instantaneous elastic recovers and over time expansion from viscous relaxation (see Fig. 27).…”

“…Uniquely, when cutting processes are applied to polymers, the workpiece surface quality is dependent on the specific material properties such as the glass transition temperature (Tg), the melt temperature (Tm), the molecular weight (MW), the viscosity, and the relaxation rate [27]. Thus, the polymers present special characteristics when machining when compared with metals [5,151]:…”

“…28). The chip morphology mainly manifests as continuous and discontinuous types and transitions from flow, shear to crack type due to the viscoelastic behaviour of the polymer (see in Table 4) [5,99]. Chip management when machining of polymers is also a challenge, as the continuous chips tend to wrap around workpieces and tools, and sometimes interfere with the cutting operation itself.…”

Toolpath and machining parameters optimisation of the cavities of a knee prosthesis tibial insert

“…The UHMWPE, due to its properties, 11–13 is the material used since the late 1960s and is still today the “golden standard” polymer used in the manufacture of the patellar component and tibial insert, 14 whether in fixed or mobile bearing designs. 15,16…”

“…23 However, there is limited information on the effect of machining parameters on UHMWPE tribological properties. 13,21,23–26 This paper focuses on machining process variables, and, more precisely, on the main outcome factor, roughness.…”