Efficient thermal error prediction in a machine tool using finite element analysis

Abstract

Thermally induced errors have a major significance on the positional accuracy of a machine tool. Heat generated during the machining process produces thermal gradients that flow through the machine structure causing linear and nonlinear thermal expansions and distortions of associated complex discrete structures, producing deformations that adversely affect structural stability. The heat passes through structural linkages and mechanical joints where interfacial parameters such as the roughness and form of the contacting surfaces affect the thermal resistance and thus the heat transfer coefficients. This paper presents a novel offline technique using finite element analysis (FEA) to simulate the effects of the major internal heat sources such as bearings, motors and belt drives of a small vertical milling machine (VMC) and the effects of ambient temperature pockets that build up during the machine operation. Simplified models of the machine have been created offline using FEA software and evaluated experimental results applied for offline thermal behaviour simulation of the full machine structure. The FEA simulated results are in close agreement with the experimental results ranging from 65% to 90% for a variety of testing regimes and revealed a maximum error range of 70 µm reduced to less than 10 µm.

Thermal compensation for large volume metrology and structures

“…However, it is often not clear how the relevant values should be set. It has been suggested that extensive preliminary experimentation is required with a FEA model in order to ensure good understanding and specification of parameters [13]. In practice, the possibility of undertaking extensive preliminary work may not exist.…”

Accuracy Enhancement with Processing Error Prediction and Compensation of a CNC Flame Cutting Machine Used in Spatial Surface Operating Conditions

“…Because of the inadequacy of in-situ sensing technology for thermal deformation measurement in the high-temperature state of the flame-cutting process, this section presents the FEA testing procedures [15] to obtain off-line data of thermal deformation and temperature-field variation under varied working conditions. Taking the 1/12 circumferential configuration of a straight-cutting task as the specified application example, a brief description of the setup steps of the FEA simulation in ANASY is as follows:…”

“…Appling temperature and displacement boundary conditions. The model in Figure 3 under research has three major temperature constraints [15]: (a) contact resistance within the 151 combined surfaces is set to . The displacement boundary condition is that the interfaces of the workpiece are in completed constraint state.…”

The role of measurement and modelling of machine tools in improving product quality

“…Parametric [16], FEA [17] and "black box" [18,19] approaches are often used to solve various problems. To obtain robust levels of accuracy in the models, significant effort can be required which in the case of black box models is in training, while for FEA it is in the determination of a variety of boundary conditions.…”