考虑工件热变形的大型结构件误差建模与补偿

为减少大型结构件的加工误差,基于热特性分析建立了考虑工件热变形的综合误差模型及其补偿方法.分析光栅尺温度变化产生热变形的机理,并通过热流研究光栅尺局部的非线性温度变化规律,对龙门加工中心几何误差和热误差分别建模,并叠加生成复合误差模型.建立工件热变形与温度变化量之间的线性模型,并分析加工过程中复合误差与工件热变形之间的相互关系,建立考虑工件热变形的综合误差模型.利用数控系统外部机械原点偏移功能,应用自主研制的误差实时补偿系统,并依据考虑工件热变形的综合误差模型,实现对龙门加工中心的误差补偿.结果表明:只考虑机床误差时,复合误差模型有很高的预测精度,但并不能应用到有较大工件热变形的大型结构件加工中;而考虑工件热变形的综合误差模型在大型扭力臂的实际加工中效果良好,其加工定位精度至少提高了52%.

Modeling and compensation of machining errors for large structural parts considering thermal deformation

To decrease the machining error of large structural parts, a comprehensive error model considering thermal deformation was established based on thermal characteristics analysis, and the error compensation verification was carried out. The mechanism of thermal deformation caused by the temperature change of the grating scale was analyzed and the nonlinear temperature variation law of the grating scale was studied by heat flux. The geometric error and thermal error of gantry machining center were modeled separately and superimposed to generate a compound error model. A linear model between the thermal deformation and the temperature change of the workpiece and a comprehensive error model considering the thermal deformation were established. The relationship between the compound error and the thermal deformation of workpiece in the machining process was analyzed. The innovative real-time compensation system was applied by the external mechanical origin offset function of the CNC system, and the error compensation of the gantry machining center was realized. The results show that the compound error model has high prediction accuracy when the machine tool error is only considered, but it cannot be applied to the machining process of aerospace structures with large thermal deformation. The comprehensive error model has a good effect on the machining process of large torque arm, which increases machining positioning accuracy by at least 52%.