Simulation Study on Effect of Thermal Variation on Straightness for Precision Linear Feed System
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摘要: 由热效应引起的精密直线进给系统直线度变化会显著影响机床精度稳定性。针对这一问题，对精密直线进给系统直线度的热变效应进行了仿真研究。首先，利用有限元热-流-固耦合仿真技术建立进给系统温度特性仿真模型，并在此基础上构建了进给系统热变形特性仿真模型；然后，分析热变形仿真结果得出进给系统直线度误差热增量及其测试基准线热漂移量的预估模型；最后，通过实验验证了精密直线进给系统直线度热变化分析模型的准确性。研究表明：综合热源对精密直线进给系统直线度误差测试基准线的热漂移具有明显影响，但对直线度误差热增量影响相对较小；而造成直线度热变效应的主要因素是机床床身热变形引起的床身-导轨装配面热漂移。Abstract: The straightness variation in precision linear feed system caused by its thermal effect can significantly affect the accuracy stability of machine. For this problem, the effect of the thermal variation on the straightness in precision linear feed system is simulated. Firstly, the model for temperature simulation in feed system is established by using finite element thermal-fluid-solid coupling technology. Based on it, the simulation model for thermal deformation in feed system is established. Then, the simulation results of thermal deformation are analyzed to obtain estimation models for thermal increment of straightness error and thermal drift of its base line in the feed system. Finally, the accuracy of the s analysis model for traightness thermal variation in the precision linear feed system is verified by experiment. The results show that machine comprehensive thermal factor has obvious influence on the thermal drift of straightness error base line in the precision linear feed system, but has a relatively small influence on the thermal increment of straightness error. The main factor causing the effect of the thermal variation on the straightness is the thermal drift of bed-guide assembly surface caused by the thermal deformation of machine bed.
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表 1 直线进给系统结构物性参数
结构名称 材料名称 密度/(kg·m-3) 比热容/(J·(kg·℃)-1) 导热系数/(W·(m·℃)-1) 弹性模量/GPa 热膨胀系数C-1 泊松比 丝杠螺母副、轴承 GCr15 7 830 460 44 219 1.2×10-5 0.3 床身 HT300 7 300 510 45 143 1.12×10-5 0.27 导轨滑块副、工作台 45钢 7 890 450 48 209 1.17×10-5 0.269 冷却液 主轴油 851 1 851 0.144 - - - 
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表 2 直线进给系统热载荷修正结果与边界条件数值
边界条件/热载荷 加载位置 载荷大小 生热率修正结果/(W·m-3) 丝杠-螺母副/导轨-滑块副/前轴承/后轴承 540 134.9/198 407.8/510 582.5/430 356.2(工况1)
350 072.1/110 013.7/374 901.3/312 058.4(工况2)对流换热修正结果/(W·(m2·℃)-1) 丝杠外表面
工作台、螺母副、床身37.4(工况1)/23.6(工况2)
10.5/17.8/9.7接触热传导系数/(W·(m2·℃)-1) 螺母-滚珠及滚珠-丝杠接触面
滑块-滚柱及滚柱-导轨接触面6 681
7 458其他参数 冷却液流速/湍流强度/液力直径 0.472/7.1%/0.015
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表 3 不同进给速度下直线度误差热增量
运行时间/h 误差热增量/μm 进给速度18 m/min 进给速度9 m/min 1 1.34 0.85 2 1.61 1.06 3 1.75 1.10 4 1.82 1.17 5 1.84 1.18
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表 4 Y向直线度误差热增量结果验证
运行时间/h 仿真结果/μm 实验结果/μm 1 1.34 2.05 2 1.61 2.37 3 1.75 2.61 4 1.82 2.76 5 1.84 2.85
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表 5 直线度测试基准线端点热漂移量结果验证
运行时间/h -800端 0端 仿真结果/μm 实验结果/μm 仿真结果/μm 实验结果/μm 1 3.59 4.31 3.76 4.12 2 7.09 8.33 7.12 7.96 3 9.8 11.3 9.73 10.92 4 12.09 13.46 11.94 12.97 5 14.04 14.79 13.81 14.42
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