Surface Finish in Micro-drilling of PTFE

Abstract

Surface finish of engineering components pl ays a key role in their functionality, particularly where the size of the geometric feat ures 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 mo lds are used for production of silicone scaffolds requiring very large aspect ratios – typical exam ples being to produce pillars/columns of 300 micron diameter and 15 mm length. The surface fi nish of the holes machined in the PTFE becomes critical in order to facilitate extractio n of the silicone from th e mold without damage. A systematic approach is used to determine th e 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 a pplication are difficult due to the scale of the holes – conventional measuremen t 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.