Analysis on structure strength and rigidity for CNC lathe of a simultaneous turning with multiple cutting-tool

• Main Authors: Sheng-Fong Huang, 黃聖峰
• Other Authors: Shen-Yung Lin
• Format: Others
• Language: zh-TW
• Published: 2016
• Online Access: http://ndltd.ncl.edu.tw/handle/77wxa8

碩士 === 國立虎尾科技大學 === 機械與電腦輔助工程系碩士班 === 104 === Because domestic and foreign machinery manufacturing industry is facing fierce competition, development of complex, simultaneous machining with multiple cutting-tool and intelligent machine tools has become a new trend in the global machine tool development in recent years. Simultaneous processing technique could be overlapped such that machining time of parts may be reduced and the production efficiency can be enhanced consequently. However, due to design space limitation and cost consideration, the turret is usually replaced by a multiple cutting-tool post for a small and simultaneous turning machine. Therefore, it is hard to cover the structure rigidity and fluent movement of feeding mechanism in this multiple cutting-tool post structure in order to satisfy the requirement of dynamic rigidity under the maximum elongation of a simultaneous turning with multiple cutting-tool. In this paper, the machining quality of a simultaneous turning can be enhanced through the improvement both of the structure static and dynamic rigidities. First, for analysis reality, a turning experiment was carried out and the cutting forces were obtained as a boundary condition for stress and strain FEM analysis model. Next, the numerical and experimental modal analyses are performed for a CNC lathe of a simultaneous turning with multiple cutting-tool, and the natural frequency, damping ratio and mode shape of the structure are investigated consequently. At last, according to the above analyses in static and dynamic rigidities, the width of tool shank is widened to enhance the structure static rigidity based on a cantilever beam-deflection theory. Moreover, with reference to a column structure in the C-type machine-tool, increasing the supporting area at lower-half portion of the spindle, lowering the weight of structure and adding some reinforcement ribs at the same time to improve the dynamic rigidity. With the modification of tool shank width in consideration of cost factor, the FEM analysis results show that the maximum total displacement, maximum equivalent stress and strain are decreased about 26%, 38%, and 35%, respectively, in contrast to the dynamic rigidity is not improved significantly. In the final design improvement version, both the static and dynamic rigidities may be improved effectively, the maximum total displacement, maximum effective stress and strain are decreased about 30%, 38% and 35%, respectively. Under the maximum rotational speed of 5000rpm (83Hz) in this CNC lathe, the corresponding natural frequencies of the first-mode to third-mode were increased about 11%, 14% and 2%, respectively.