Thermal Issues in Machine Tools and Coordinate Measuring Machine Similarities and Differences

Thermal issues are relatively well developed and described in machine tools and their development is quite rapid in recent decades. This is related to increased awareness of the impact of thermal conditions on the accuracy and efficiency of their work and the increased requirements of users (up to 75% of the overall geometrical errors of machined workpieces can be induced by the effects of temperatures). There is a large stock of published research and case studies aimed at compensation and reduction of thermal error of machine tools. Branch of coordinate measuring machine (CMM) is strongly associated with the machine tool industry. There are a lot of convergence in approach to this theme in both subject groups. Both in the construction of machine tools and measuring machines as the key point of interest is the influence of various physical phenomena on the behavior of the executive point, in the case of measuring machines is the end of the measuring head, in the case of machine tools is a tool centre point (TCP). Considerable amount of research on the effects of thermal phenomena in the case of machine tools is carried out without taking into account the cutting forces, which also conforms research approach in both concerned areas. An important difference, however, is the fact that the compensation of thermal deformation in machine tools must be made immediately during work, if we want to improve the geometric parameters of the workpiece, which involves the introduction of some actuators, or correction of the trajectory in real time. While the result of work of the measurement machine are stored data that can be corrected or processed after the process of measuring and correction does not make any material actuator. Order of magnitude of precision in the case of machine tools and CMM is also different. Thermal phenomena associated with measuring machines are relatively well developed in the case of steady thermal state, and the uniform temperature gradient. Mathematical models are described, compensation systems have been developed. There are publications concerned with selected aspects of the measuring machine work, or selected components that generate heat inside or outside of the machine structure. However problem of modeling of the whole machine and studies of thermal effects, and timevarying or locally occurring phenomenon ,based on numerical methods is relatively poorly studied. This probably results from the fact that both numerical methods and hardware have developed enough to address this issue only in recent decades. Important here is the economic aspect (the cost of computing hardware and software), and the performance parameters, which allow the calculation of the real-time close to the real-time or made in acceptable period of time post factum.