| As the requirement of aircraft performance develops, aircraft becomes lighter and the structure strength improves. During aircraft assembly, it is required to drill thousands of holes with high precision, high efficiency and high reliability on the accessories. However, as titanium alloy, Carbon fiber reinforced plastics (CFRP) are widely used in aircraft manufacturing. Some disadvantages such as high thrust force, tool wear as well as bad machining quality occur when drilling titanium alloy and composites, which have a negative influence in the intensity and fatigue life, conventional drilling has already not been suitable for aircraft manufacturing.As a new hole-making process, orbital drilling can enable heat extraction and efficient chip removal. Orbital drilling can also reduce thrust force as well as tool wear and improve machining quality. Furthermore, it’s possible for orbital drilling to make holes of different diameters with only one tool by adjusting eccentricity, which can maximize the productivity and cost-effectiveness. In this paper, some problems about orbital drilling of hard-to-cut materials are studied through mechanical modeling, finite element simulation and experiments.Firstly, the cutting mechanisms of orbital drilling are analyzed through kinematic simulation:Two different machining operations occur in orbital drilling; one is drilling by end cutting edges and the other one is the peripheral milling machined by its side cutting edges. By cutting force analysis for both end and side cutting edge, the overall instantaneous cutting forces acting on the whole tool in the three orthogonal directions are obtained through coordinate transformation and summation of all the teeth.The material constitutive equation of titanium alloy TC4DT model is achieved through static and high speed compression experiment. Finite element key techniques, such as the chip separation criteria, friction mode, heat conduction and adiabatic shear during cutting process have been implemented. On the basis, the finite element model of one blade cutting process of titanium alloy orbital drilling is developed for the first time. According to the cutting force simulated results and analytical model, the cutting force in orbital drilling can be predicted.Considering the practical processing condition in aircraft assembly field, one robot automatic orbital drilling system including orbital drilling end-effector and tool was established; In order to validate the finite element model, orbital drilling experiments under different condition was carried out, and a good agreement between simulations and experiment result is achieved, which proves the cutting force predicted model is correct. Meanwhile, the impact of cutting parameters on surface quality, exit burr and borehole diameters are discussed also.Finally, through the robotic automatic orbital drilling system, The orbital drilling parameters orthogonal experiment of CFRP was carried out based on this robot automatic orbital drilling system, and the impacts of spindle speed, feed per tooth, axial feed depth on cutting force were deeply analyzed; With the defects inspection results, we investigated the relationship between thrust force and hole exit defects, such as delamination and tear. At last, the optimal set of process parameters was obtained and it is verified that thrust force decreases more than26%and there are hardly tear and burr formation around the borehole, which indicates a better machining quality. |
PDF Full Text Request