Surface Finish in Micro-drilling of Ptfe

Surface finish of engineering components plays a key role in their functionality, particularly where the size of the geometric features of the component decreases. This paper reports on such an application – the drilling of micro-holes in PTFE during manufacture of molds for use in the bio-medical field. These molds are used for production of silicone scaffolds requiring very large aspect ratios – typical examples being to produce pillars/columns of 300 micron diameter and 15 mm length. The surface finish of the holes machined in the PTFE becomes critical in order to facilitate extraction of the silicone from the mold without damage. A systematic approach is used to determine the optimum combination of machining parameters with respect to this goal. Furthermore, a novel approach to surface quality estimation is proposed. Direct methods of surface quality assessment in this application are difficult due to the scale of the holes – conventional measurement methods are expensive, time-consuming and require destruction of the mold. In this work, the quality is inferred indirectly through measurement of the force required to extract the silicone from the mold. A simple apparatus to standardize the extraction procedure has been designed and built as part of this work.