- 學位論文
四軸臥式加工機熱變形分析及改善設計之研究
Analysis and Improvement Design of Thermal Deformation for a Four-Axis Horizontal Machine-Tool
摘要
工具機在高速切削過程中結構溫升熱變形成為目前最須克服的難題，近年來即時線上熱補償系統技術的成熟，雖然提升了工件的加工精度，但仍無法確實掌握非線性的熱變形。本研究針對四軸臥式綜合加工機在高速運轉下，所產生的熱對頭座、導螺桿與軸承座結構熱變形的影響，進行熱對稱結構、熱阻絕與冷卻抑制的設計，期達到機台熱平衡的狀態，減少熱變形對加工精度的影響，並提升機台結構的熱穩定性。 本文首先以熱電偶與紅外線熱影像儀量測主軸系統與導螺桿在長時間運轉下重要部位之溫度，將所量測到之溫度作為數值分析之邊界條件。使用有限元素法針對頭座、導螺桿與軸承座進行數值熱傳分析，以求得這些部件之溫度場與熱變形。接著對頭座與軸承座進行熱阻絕與冷卻管路埋設之設計，根據數值熱傳分析之結果，不斷修正熱阻絕板/罩結構幾何尺寸與冷卻管路埋設位置，反覆進行數值熱傳分析，促使機台結構溫度分布達到平衡，降低熱變形的影響。再者，施加作用力於機台結構上，進行剛性及強度之數值模擬分析計算。最後進行結構之熱-機械負載耦合數值模擬分析，模擬工具機結構在實際加工狀況，觀察結構同時受到熱能與機械負載下之變形情形。結果顯示頭座、導螺桿與軸承座之整體位移量主要來自於熱變形。而熱對稱結構與熱阻絕之設計能有效阻絕熱的傳導，再搭配冷卻管路的埋設，能快速將熱能帶走，減少熱變形的產生，維持工具機結構中心位置的精度穩定性，達到熱平衡設計的結構需求。
並列摘要
Thermal deformation of the structure due to temperature rise in high-speed cutting process becomes a challenge that should be overcome at present for machine tools. In recent years, the technology of a real-time online thermal compensation system has been largely progressed. Although the positioning accuracy of a feed-drive system has been increased, but it still can not solve the issue of nonlinear thermal deformation of the structure. This project focuses on the study of thermal deformation within headstock, ball-screw and bearing in a four-axis horizontal machine-tool caused by heat source generation during high-speed operation. It tries to perform structure design of heat symmetry, heat isolation and cooling suppression. The goal is to achieve a heat balance structure, reduce the effect of thermal deformation on machining accuracy and promote the thermal stability of a machine tool structure. First of all, thermocouples and an infrared thermal imager were used to measure the temperature at some important locations of the spindle system and ball-screw after a long period of operation. The measured temperatures were used as the boundary conditions for numerical analysis. The heat transfer analysis was conducted for headstock, ball-screw and bearing by finite element method, and the temperature field and thermal deformation of these parts can thus be obtained. Then, heat isolation and cooling piping embedded design for headstock and bearing was conducted. The geometrical configuration and dimensions of this heat isolation structure and the setting location of the cooling pipes were modified constantly according to the analysis results from the repeated finite element simulation procedures. It is expected that the temperature distribution in a machine tool structure may reach equilibrium state and the impact of thermal deformation can be reduced. Additionally, a mechanical force was applied to this machine tool structure for numerical simulations of rigidity and strength. Finally, the numerical simulation analysis was performed to determine the deformation situation under the coupling action between both the mechanical and thermal loads. This analysis may reflect the machine tool structure under practical working conditions. The results show that the total displacement of headstock, ball-screw and bearing is mainly contributed from the thermal deformation. The structure design of heat symmetry and heat isolation can isolate the heat transfer effectively, and the accompanied cooling pipe system can remove the heat source quickly. The thermal deformation can thus be reduced. As a result, the stability and central positioning accuracy in each substructure can thus be maintained and the machine tool structure design fulfills the heat balance demand in industry.