內藏式馬達工具機主軸頭之溫度分布與熱變形分析

Analysis of Temperature Distribution and Thermal Deformation of Spindle Head of a Built-in Motor Machine Tool

本研究以數值計算探討一內藏式馬達的工具機主軸在運轉時可能對加工精度造成影響的主軸頭熱變形問題。考慮馬達的輸出功率分別為37、25、與22 kW，功率因子為80％，轉速7500 rpm，以及馬達的輸出功率分別為22與15 kW，功率因子為75％，轉速1500 rpm，冷卻油（VG32）在設計的螺旋形流道以流率40與20 L／min的流動情形下，模擬主軸心軸與周邊結構件的溫度分布與熱變形量分布，從而計算主軸心軸鼻端產生最大的熱變位。對於主軸頭主要散熱的冷卻流道，本研究也以計算流體力學（CFD）探討其流場結構，以揭示其熱傳增強機制。計算結果顯示，內藏式馬達與軸承運轉時產生的熱對主軸溫升與熱變形量均有不可忽略的影響。在馬達輸出功率37 kW且冷卻油流率降至20 L／min時，主軸最大變形量可達243.5μm，最高溫達89.6℃，顯示穩定加工的溫度控制或是動態加工的熱變位補償都很重要。

This study uses numerical calculations to investigate the thermal deformation problem of a spindle head, which may affect machining accuracy when the machine tool spindle of a built-in motor is running. Assuming motors output powers of 37, 25, and 22 kW, a power factor of 80%, speed of 7500 rpm or motor output powers of 22 and 15 kW, power factor of 75%, speed of 1500 rpm, and cooling oil (VG32) flow rate of 40 and 20 L/min, the temperature distribution and thermal deformation distribution of the spindle and its surrounding structural parts were simulated. The maximum thermal displacement of the spindle tip was calculated from the results. The VG32 coolant flow was responsible for major heat removal from the spindle head. A computational fluid dynamics study was performed to reveal flow structures and heat transfer enhancement mechanisms in the coolant channel. The computational results show that the heat generated in a built-in motor and bearings during operation has a non-negligible influence on the temperature increase and thermal deformation of the spindle. When the motor output power was 37 kW and the coolant flow rate was reduced to 20 L/min, maximum deformation of the spindle reached 243.5 μm and highest temperature reached 89.6 °C, which indicates that it is essential to control the temperature during steady machining and the thermal displacement compensation during dynamic machining.