The Study on Surface Roughness and Fatigue Life of Fastener Holes for 7075 Al Alloy

The aim of investigation is to analyze the effects of conventional drilling processes with multiple step and Winslow(one-step compound process) on the surface roughness and fatigue life of fastener holes drilled on 7075-7351 Al alloy for aircraft assembly. The Surface topography was tested and observed by using advanced detection devices. We found that the Ra value produced by multi-step drilling processes was about 2.4μm, and with more machining defects, large thermal distortion and low fatigue life. While Ra value caused by Winslow was about 0.93μm, and with smooth surface and strong fatigue resistance, and the thermal distortion was 68% lower than the former. According to the experiments, the empirical equation indicating the influence of feed rate and cutting speed on the surface roughness were presented by using regression method. Using Deform 3D numerical simulation method, the change laws of cutting temperature and thermal deformation under the different processes were discussed. And the effects of the surface roughness on fatigue life of the fastener hole were studied with the theory of fracture mechanics. The main factors affecting the surface roughness were burr, built-up-edge and scale-splinter. Reducing amount of feed and increasing the cutting speed properly were important ways to reduce surface roughness and increase fatigue life.