Parameters and Stiffness Optimization of a Five-axis Parallel Machining Unit
Large complex components are characterized by large size,complex structure and several local machining features.To meet the high-precise machining requirements of such components,the in-situ machining mode of"wide-range positioning+localized five-axis high-precise machining"was proposed,and a mobile hybrid machining robot of"automatic guided vehicle+high-stiffness positioning unit+high-precision five-axis parallel machining unit"has been developed.The core unit of this equipment is the five-axis parallel machining unit,which has a significant impact on the machining performance of the whole equipment.To further improve the motion/force transmission performance and stiffness of the five-axis parallel machining unit,the hierarchical optimization of structural and dimensional parameters based on the motion/force transmission performance evaluation method and the structural optimization oriented to improve the stiffness performance are carried out.The hierarchical optimization method of multiple parameters is proposed,and the optimization of multiple structural and dimensional parameters is realized,so that the motion/force transmission performance is improved by 48.37％compared with that before parameter optimization.The stiffness model of the five-axis parallel machining unit is established by the virtual joint method and the finite element method.The influence of the stiffness of each part on the stiffness of the five-axis parallel machining unit is revealed,and the base frame is identified as the stiffness weak link of the five-axis parallel machining unit.A stiffness step-by-step optimization method based on the stiffness contribution rate is established to optimize the structure of the base frame,so that the stiffness of the five-axis parallel machining unit is improved by 63.83％,and the stiffness-to-mass ratio is improved by 52.06％.Based on the above optimization results,a five-axis parallel machining unit with better motion/force transmission performance and stiffness performance is designed,which lays the foundation for the development of a new generation of mobile machining equipment with better machining performance.
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