SURFACE INTEGRITY IN FINISH HARD TURNING OF GEARS

摘要

In manufacturing of highly loaded parts, e.g. gears, the physical and technological material properties are of major importance on its functional behaviour. During finish hard turning, the integrity of the generated surfaces is influenced due to the thermomechanical material removal mechanisms. This paper has pointed out the interest in finish hard turning, regarding its capacities to produce a low surface roughness (Ra < 0.2 mu m) during a long cutting time and also to induce residual compressive stresses, when machining with low feed rates and low cutting speed. It has also been underlined that the feed rate is the major parameter that influences the surface roughness and that the cutting speed is the major parameter that influences the residual stresses level. Furthermore, the paper has shown that applications of hard turning can have some restrictions, especially because of the generated surface topography (a screw) and the apparition of material side flow with very low feed rates or with worn tools. An other restriction in the use of hard turning is the influence of the flank wear which shifts the residual stresses towards tension and also tends to induce white layers. In hard turning operations, residual stresses level and white layers are the main criteria for changing of inserts (far before roughness or accuracies-to-size), although these parameters are very difficult to follow in a production plant. A solution to minimize these restrictions could be to associate an abrasive process (as lapping), which is supposed to delete the screw topography and the presence of material side flow, and, at the same time, it should shift the residual stresses level towards compression, as described by Rech~(15).