Low frequency vibration assisted drilling of PC1000 polycarbonate

A challenge in drilling polymers is their very low melting point, especially when holes with a large length-to-diameter ratio are required. One opportunity to avoid chip accumulation is the use of low vibration assisted drilling. In the present work, the comprehensive knowledge acquired from the machining of metals is transferred to drilling of polycarbonate PC1000. The first research objective of this work was to evaluate if the kinematic models proposed in literature could predict the onset of discontinuous chip generation. To do so, a series of drilling tests were performed with a MITIS tool holder varying vibration amplitude and hole length. During the tests, thrust force and workpiece temperature were registered and, afterwards, hole diameter and surface roughness were measured. The results showed that a kinematic model can be useful to predict the onset of discontinuous chip generation. It was also concluded that surface roughness increases with vibration amplitude until the onset of chip breakage is reached. Furthermore, a correlation between temperature and surface roughness was detected. Regarding cutting forces, a relationship was observed between the thrust force signal amplitude and the amplitude vibration of the MITIS tool-holder. This correlation could be useful to calibrate other future designs of tool holders.