- 學位論文
工具機熱平衡結構設計與分析
Design and Analysis for Machine Tool Structure by Heat Balance Concept
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，而近年來即時線上熱補償系統技術的成熟，雖提升了傳動定位精度，但無法精確掌握非線性的熱變形。本文針對立式切削加工機在運作中產生的熱源，進行熱對稱結構及冷卻抑制的設計，達到機台熱平衡的狀態，減少熱變形對加工精度的影響，並提升機台結構熱穩定性。 首先針對工具機頭座、軸承座及導螺桿等主要發生熱變形單元進行熱探討，以瞭解熱源對結構的影響性。接著導入熱對稱、阻隔及冷卻等特性，進行工具機結構熱平衡設計，應用熱傳理論和運用主軸跑合實驗所測得之熱溫升數據當作邊界條件，利用有限元素法進行上述主單元之熱變形模擬分析並據以反覆修正其結構幾何尺寸。同時試著調變控制熱傳導方向與熱接觸傳導面積大小，使結構溫度分佈達到熱對稱設計，特別著重於底座結構板及肋尺寸與排列方式之設計，維持機台結構足夠的剛性。最後針對完成設計的整體機台分析其熱傳情況及溫度場，檢視工具機結構此改良設計之熱變形行為。並施加作用力於結構分析其剛性、強度、模態。同時分析此機械力與熱結構耦合作用下，瞭解此熱對稱結構設計的剛性及熱穩定性。結果顯示結構變形位移量主要來自於熱變形，此熱對稱的結構設計所呈現的變形量皆為對稱性變形，且適當的冷卻抑制，有效降低熱變形量的產生，維持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 real-time online technology for 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 nonlinear thermal deformation of the structure thoroughly. This study focuses on the heat source generation in a vertical machining center during operation and tries to perform a structure design of heat symmetry and thermal suppression via cooling. 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, a thermal study is performed on some major parts in a machine tool including headstock, bearing housing and ball screw, which the thermal deformation is easily to occur within them. The effect of heat source on these structure deformations is also investigated. Using the concepts of heat symmetry, isolation and cooling characteristics to conduct a structure design fulfilling a heat balance requirement for machine tool. The temperature data measured from the spindle run-in test is utilized as the boundary conditions which are combined with heat conduction theory for finite element analyses on those major parts just mentioned above. Based on the analysis results, the geometrical dimensions of those major parts in a machine tool are modified repeatedly and the base part including plate and rib dimension arrangements in this design are specially emphasized to keep a sufficient structural rigidity. It tries to change and control the heat conduction direction and contact area, which results in a symmetrical temperature distribution state based on a design concept of heat symmetry, and the influence of uneven thermal deformation will be greatly reduced. Finally, heat conduction and temperature distribution simulation are performed on this entire machine tool structure just designed completely and to investigate the thermal deformation behavior after this improvement design. In addition, a mechanical force is applied on this structure to investigate its rigidity, strength, modal shape. The rigidity and thermal stability are also investigated for this design structure with heat symmetry under the coupling action between both the mechanical and thermal loads. The results show that the deformation of a machine tool structure is mainly contributed from the thermal deformation. The design structure with heat symmetry exhibits a symmetrical deformation in thermal displacement which may also be reduced effectively by an appropriate cooling suppression strategy. The position stability and accuracy for each center point in the structures can thus be kept and the design machine tool structure fulfills the heat balance demand in industry.