A New Precise Temperature Controlling Method for Machine Tool Structures

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In recent years, a high machining accuracy have been demanded from machine tools. But it is very difficult to keep a high accuracy during machining. One of the causes for the machining errors is the thermal deformation of machine tools, especially, the thermal deformation in unsteady-state conditions.Then, two heat sources are considered as the cause of thermal deformations of machine tool in unsteady-state conditions. They are as follows :(1) Inner heat sources : Such as bearings, motors and so on. The heat generation in them varies with the variation of the spindle speed.(2) Outer heat sources : The room temperature variation in a machine shop and thermal radiation from the walls of the machine shop and the other machine.In this study, two new methods are thought out to prevent the thermal deformation in unsteady-state conditions caused by the inner heat sources and outer heat sources.In the first method, forced cooling is adopted to take away the heat generated at the inner heat sou … More rce which passes through the structure. This cooling is carried out locally around the structure and the temperature of the coolant is not kept constant at 20 ^ﾟC, but varied according to the inner heat generation. This controlling method has been applied to a main spindle structure which may be considered to have a inner heat source. A hollow cylinder is considered as the model of the structure which supports a main spindle through bearings at which heat is generated.In the second method, the outer surface of the structure is thermally isolated to have little influence of the variable outer heat sources. In this isolating method, two sheets of thermal insulator are attached on the outer surface of the structure and the temperature controlled air is flowed between them. This isolating method has been applied to a column of a machine tool.In this study, the following conclusions are obtained.(1) The temperature rise or the thermal deformation of this cylinder controlled with this inner cooling method is very small and the time constant is very short.(2) In this isolating method, the temperature of the structure will be kept constant at 20^ﾟC if the heat caused by inner source is perfectly taken away by the inner cooling. Less