Form Grinding of Helical Gears: Effects of Disk Shaped Tools Plunging

Following the example of aerospace transmissions producers, nowadays, more and more industrial fields are interested in reducing transmission noise and vibration and in increasing operating life. This requires a precise understanding of the real transmission behavior since the first steps of the design process. The usual approach is to apply theoretical meshing loads and to compute web, rim and supporting structures deflections by one of the several available methods (i.e. Finite Element Method), in order to predict stresses and deformations. But these calculations usually neglect that deformations modify gear meshing conditions, and therefore also load conditions can be very different from the theoretical ones. In order to realize models that simulate the contact between the actual tooth surfaces, taking into account the actual gear meshing conditions, we first need to know the gear tooth flank microgeometry. Also the experimental development phase of gear pairs could take advantage from a theoretical prediction of gear tooth flank micro-geometry, in order to minimize the necessary trials to set up the grinding machine. In this paper, a method and a software to compute the actual micro-geometry of ground tooth flank surfaces of helical gears is presented. In particular the grinding process by means of disk shaped tools has been studied. The effects of the choice of various parameters (especially the angle between the gear and the tool axis) have been investigated. The effects of tool plunging during its motion along the gear face have also been considered in order to appreciate the undesired modifications of tooth transverse and normal sections, caused by the particular shape of the instantaneous contact lines between the grinding wheel and the gear tooth flank being ground. The introduction of a new component of the tool relative velocity with respect to the gear, in fact, modifies the meshing conditions between the gear and the tool. The modification of the tool axis orientation, during the grinding operation, reduces this undesired effect. As a result of these calculations, the exact theoretical surface for more realistic meshing simulation is available, and, furthermore, the run of some simulations can give some helpful hints to set up the grinding machine and to design the grinding wheel.