UBC Theses and Dissertations
Friction sawing of metals Ogunlade, Omojola
Most of the research done on the friction sawing of metals has been application oriented and the operating mechanism of friction sawing has not been fully investigated. Hence the present study was directed towards gaining a better understanding of friction sawing using analytic and experimental methods. The analytic method considered the heat partition at the interface and the temperature distribution in both the workpiece and the sawing disk. The cutting forces were measured experimentally by means of strain rings to which linear displacement transducers were fixed. From these measured forces, the friction force at the disk-workpiece interface was obtained and this was used to calculate the heat generated during the sawing operation. The experimental method attempted to measure the interface temperature and the temperature distribution in the workpiece. Four different metals, which gave a wide range of physical properties, were used in the experiments leaded brass, mild steel, TI steel and Ti-6Al-4V alloy. The heat partition between the sawing disk and a metal workpiece was obtained by matching the temperatures at the contact zone. This partition furnished a temperature distribution in the work-piece and disk when the total heat generated at the sliding contact was known. Using a PbS cell sensor and optic glass fibre transmission units, an attempt was made to measure the interface temperature. However, owing to the oblique cutting of the workpiece and the highly localized nature of friction sawing process, the instrumentation developed could not give an accurate measurement of the temperature. Nevertheless, this temperature measuring device would find good use in high temperature transient heat transfer studies. Thermocouples embedded at different distances from the cutting zone were used to measure the temperature distribution in the workpiece. The theoretical results agree well with these experimental measurements; the agreement being better at points which were at least the order of magnitude of the kerf width distance from the cutting zone. Metallographic examinations were done on the as-received materials, the kerf materials, and the cut edge materials. The heat treatment evidence from both mild steel and Tl steel indicated the kerf material and the cut edge material reached temperatures about 1600 deg F. This was in good agreement with the theoretical predictions. All the results obtained in this study indicated non-fusion cutting. For the leaded brass the friction sawing was similar to conventional machining whereby discrete particles of material were formed during sawing. For the steels, ductile fracture theory explained the cutting mechanism and for the titanium alloy, brittle fracture was observed at slow feed speeds and brittle plus some ductile fractures were observed at higher feed speeds.