| Friction stir welding is a solid-state joining process based on the effect of mechanicalforce and friction heat, which has been widely used in the manufacturing of structured partsmade of alloys such as aluminium, copper, etc. Because the machine tools are subject to greatload during friction stir welding, using parallel structure is an effective method to improveload bearing capability and rigidity of machine tool.In the paper the combination of parallel structure and series structure is used, where themotion along the z axis and the rotation of A axis and C axis are applied to parallel spindlehead based on3-PRS parallel structure, and the motion of X axis and Y axis are applied to theworktable. Due to its characteristics of large working space and simple structure, the machinetool can complete5-axis motion conveniently. The research focuses on the parallel spindle,which includes kinematics analysis on3-PRS parallel structure, structure scheme design onparallel spindle and finite element analysis of principal parts.Firstly kinematics analysis on3-PRS parallel structure is completed. The kinematicsbasis of parallel structure is discussed, and the degree of freedom of3-PRS parallel structureare analyzed. Based on the analysis of the physical constraints subjecting to the structure,inversion computing formula is developed. The forces acting on the structure are studied, andthe relationship of external forces among the driving axis, the supporting bars and the movingplatform.Based on the kinematics analysis, the structure scheme design on parallel spindle isfinished. According to the characteristics of the acted forces and the requirements onmovement ranges, the constitute form of spherical pairs on parallel moving head are chosen.The pairs of all the branching of parallel moving head are analyzed, and the types of mainmechanical parts such as leadscrews, ways, and bearings are determined based on the forceanalysis.Finally, finite element analysis of main mechanical members of parallel spindle head isfinished. Three dimension modeling of mechanical structure of spindle head is accomplised.The static stiffness analysis of the whole structure is dealt with, and the effect of force actingon spindle on mechanism accuracy is studied. The strength analysis on main elements including the moving platform, universal joint bracket, universal joint, the supporting barsand external frame are analyzed. Frequency and model of vibration is determined based onmodal analysis. The fatigue life of concentrate-stressed components has been predicted. Theinfluence caused by variation of environment temperature to machining accuracy of parallelspindle head has been taken into consideration and the thermal-structure coupling analysis isconducted as well. |
PDF Full Text Request