- 學位論文
多刀同步CNC車床結構強度與剛性改善分析
Analysis on structure strength and rigidity for CNC lathe of a simultaneous turning with multiple cutting-tool
摘要
近年來由於國內外機械製造業面臨激烈競爭，開發複合化、多刀同步及智能化等工具機，已成為全球工具機發展的新趨勢。同步加工技術工序可以重疊因而縮減了加工時間，提高零件的生產效率。但以刀座取代刀塔作法之中小型機台因設計空間與成本較為受限，較難兼顧多刀座結構的剛性及機構運動的流暢度，以滿足同步車削車刀最大伸長量動剛性的需求。 本文結合結構靜態與動態剛性之改善以提升同步車削之切削性能。首先，為力求分析真實性，進行車削實驗擷取切削力，以作為應力應變有限元素分析模型的邊界條件。接著使用有限元素法對多刀同步CNC車床進行數值模態分析，同時進行實驗模態分析，以探討該車床結構的自然頻率、阻尼比與模態振型。最後，根據結構靜動態剛性的解析結果，依材料力學懸臂樑-撓曲原理增加刀具柄徑以改善靜態剛性，同時參考立式C型加工機立柱結構，針對主軸立柱增加其下半部支撐面積，並適當地予以結構輕量化及添加補強肋，以改善動態剛性。結果顯示，在成本因素考量下所進行的刀具柄徑設計變更方案，由有限元素分析結果得知，雖然動剛性並無明顯改善，但其靜剛性最大總位移量、最大等效應力及最大等效應變分別減少約26% 、約38% 及約35% 。於最終版改善案靜動剛性皆獲得有效的改善，最大總位移量、最大等效應力及最大等效應變分別減少約30% 、約38% 及約35% 。於機台最高轉速5000rpm(83Hz)以下所對應之自然頻率，第一階至第三階頻率分別提升約11% 、約14% 及約2% 。
並列摘要
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.
參考文獻
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