Influence of Drilling Parameters on Temperature and Hole Roundness in PTFE Machining

Abstract

This study examines the influence of drilling parameters and techniques on the machining performance of polytetrafluoroethylene (PTFE), a polymer known for its low friction, high chemical resistance, and thermal sensitivity. PTFE’s low thermal conductivity and high deformability often lead to dimensional inaccuracy, burr formation, and heat-induced defects during drilling. To address these challenges, the effects of spindle speed, feed rate, and drilling methods (straight, peck, and dwell) were investigated using an 8 mm HSS drill bit under controlled dry-machining conditions. Temperature distribution along the drilling path was monitored using dual K-type thermocouples positioned at entry and exit points, while an optical microscope was used to evaluate hole roundness.  This study presents an analysis and strategic optimization of drilling parameters for PTFE to resolve conflicting performance objectives between geometric accuracy and thermal stability. Using Signal-to-Noise ratio analysis, the most critical quality characteristic, hole roundness, was found to demand a high spindle speed to ensure stable cutting conditions. This requirement imposes a significant thermal penalty, as high spindle speed is simultaneously the least optimal setting for minimizing both Entry and Exit temperatures. The final process configuration addresses this trade-off by selecting parameters that maximize thermal mitigation: a high feed rate is chosen to reduce the time-in-cut and dissipate heat efficiently, and the Dwell technique is implemented. The Dwell technique is identified as the optimal thermal moderator, as it provides robust hole roundness while simultaneously maximizing the SN ratio to minimize the critical Exit Temperature. This strategic compromise effectively achieves the primary objective of superior geometric tolerance while preventing catastrophic material failure caused by thermal degradation at the hole exit.