Desempenho de Ferramentas Reafiadas - Furação

Abstract

The present work evaluated the performance of step drills, new and after regrinding. The way of regrinding the drills after they reached the end of tool life criterion was also varied. The following variables were also considered: type of coatings (uncoated, TiAlN e AlCrN) and the routine of re-coating them after regrinding (no recoating, recoating over the previous coating and recoating after removing the previous coating). The output parameters considered for determining the machining performance were: tool wear rate, tool life, thrust force, torque, form desviors (roundness and cylindricity) and surface roughness (parameters Ra, Rz and Rt). All the results were compared to those obtained by a new tool (first time used). The tool life test were carried out at the shop floor of Fiat Powertrain Technologies - FPT in Betim MG. The regrinding processes were performed both at Fiat Powertrain Technology FPT and at OSG Sulamericana de Ferramentas Ltda in Bragança Paulista SP. The other tests were carried out at the Machining Teaching and Research Laboratory LEPU of Federal University of Uberlândia UFU. The results showed that in general the reground tools showed worse performance than the new tools. Among the TiAlN coated tools only those that have undergone the process of cleanness of the previous coating and then reground and recoated (with the same type of coating) showed results close to the new tools. It was found that the tools reground at OSG Sulamericana de Ferramentas Ltda showed performance slightly better than those reground at Fiat Powertrain Technologies PPT. The results also showed that even though a smaller number of holes has been machined, the uncoated drills presented higher wear rates than the coated tools. These tools also showed, practically in all tests, higher thrust force and torque, higher form desviors and worse surface roughness.