Micromachining characterization of anisotropic pyrolytic carbon

Abstract

Engineered features on pyrolytic carbon (PyC) have been demonstrated as an approach to optimize flow haemodynamics of the bileaflet mechanical heart valve (BMHV). To realize passive flow control in a functional BMHV, micro/meso-scale engineered features are required to be machined on the PyC leaflet. Since PyC is very brittle and has a layered anisotropic structure, its machining characteristics are different from those of standard isotropic materials. The surface finish requirements in these implants are also very stringent. A comprehensive approach needs to be devised which can create three-dimensional features with desired surface quality and integrity. Very little work has been reported on machining/micromachining of PyC, so it is expected that the present study will create the manufacturing knowledge base to generate engineered surfaces in PyC bio-implants. A full factorial experimental design was used to investigate the effect of micromilling process parameters (spindle speed, feed rate, depth of cut, tool diameter) on the response variables. Experiments were conducted in the AB plane (parallel to the layers) and the C plane (normal to the layers) to capture the effect of anisotropy. The process responses studied were cutting forces, surface roughness, surface morphology, and chip morphology. The mean radial/tangential forces and the mean surface roughness values increased by approximately 140 per cent and 77 per cent, respectively, when the cutting plane was changed from AB to C.