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.

Engineered features on pyrolytic carbon (PyC) have been demonstrated as an approach to improve the flow hemodynamics of the cardiovascular implants. In addition, it also finds application in thermonuclear components. These micro/meso scale engineered features are required to be machined onto the PyC leaflet. However, being a layered anisotropic material and brittle in nature, its machining characteristics differ from plastically deformable isotropic materials. Consequently, this study is aimed at creating a finite element model to understand the mechanics of material removal in the plane of transverse isotropy (horizontally stacked laminae) of PyC. A layered model approach has been used to capture the interlaminar shearing and brittle fracture during machining. A cohesive element layer has been used between the chip layer and the machined surface layer. The chip layer and workpiece are connected through a cohesive layer. The model predicts cutting forces and the chip length for different cutting conditions. The orthogonal cutting model has been validated against experimental data for different cutting conditions for cutting and thrust forces. Parametric studies have also been performed to understand effect of machining parameters on machining responses. This model also predicts chip lengths which have also been compared with the actual chip morphology obtained from microgrooving experiments. The prediction errors for cutting force and chip length are within 20% and 33%, respectively.