Ito - Thermal deformation in machine tools

Thermal Deformation in Machine Tools

About the Editor

Yoshimi Ito, Dr.-Eng., C Eng., FIET, is Professor Emeritus at the Tokyo Institute of Technology, immediate past vice president of the Engineering Academy of Japan, and past president of the Japan Society of Mechanical Engineers, Tokyo. The author of numerous engineering research papers and books, he is currently involved in the establishment of the Indian Institute of Information Technology, Design & Manufacturing, Jabalpur, India.

Edited by Yoshimi Ito

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Within a machine tool context, there are two crucial technological issues. One is thermal deformation and the other is chatter. Since the 1940s, these two technological subjects have been primary concerns in both production and utilization of technologies for machine tools. We have endeavored to establish the effective remedies for the reduction of thermal deformation and suppression of chatter vibration from both academic research and practical applications. To our regret, even now the remedies available are not totally satisfactory. In other words, while thermal deformation and chatter are very old problems, they still present new technological challenges.

The root cause of difficulties lies in the holistic or synergistic influences of various factors in problems of thermal behavior and chatter. We must solve these problems from the viewpoint of the machine-tool-work system while considering the individual problem of the machine tool, the cutting tool, and the work; whereas, in modular design and lightweighted structural design, the objective is the machine tool itself. Nevertheless, the better functionality and performance of a machine tool itself, the easier it is to establish effective remedies to reduce thermal deformation and suppress chatter.

Importantly, the fundamentals of thermal deformation are transparent considerably relative to those of chatter vibration. For example, thermal elongation is as commonly reported as it has always been and dominant in discussions of thermal deformation. (Academic research has so far concentrated on thermal contact resistance.) In contrast, a considerable number of factors that influence thermal behavior of a machine-tool-work system exist; e.g., heat dissipation capacity from the surface of the structural body component and from the rotating chuck. These factors play very complicated and mutually tangled roles in determining the thermal behavior of a system. As a result, we have not been able to establish perfectly effective remedies, although we can apply a large number of remedies for reducing thermal deformation in practice.

It is desirable in an effective remedy that thermal behavior of a machine-tool-work system, or at least the machine tool itself, be estimated in the design stage. To meet such a desire, there are two crucial subjects to estimate authentically the thermal behavior of the machine tool: (1) dynamic and thermal boundary conditions of the machine tool and (2) heat dissipation capacity from the machine tool to the surrounding environment. Obviously, these two are important target subjects for academia, although corresponding research has not been active.

More specifically, there is a two-pronged perspective in considering the thermal behavior of a machine tool:

1. Design principle for lightweighted structural body component; e.g., realization of a lightweighted structure by using a structural material with a smaller thermal expansion coefficient.

2. The NC machine tool benefits, on one hand, to reduce thermal deformation using compensation technology, but on the other hand, deteriorates the thermal characteristics of the machine tool by, for example, increasing heat sources.