Study on Self Compulsory Cooling for Reducing Thermal Deformation of Machine Tool.

Abstract

As higher precision machining is required, reducing thermal deformation of a machine tool becomes more important. Today, there are much study about the thermal deformation of machine tool ; a compulsory cooling of main spindle or ball screw, a feed back control of thermal expansion, an isolation of heat source and etc. However, it is necessary to used a cooling system, a controller of temperature and a sensor of temperature or heat flux for attaining these countermeasure. After all, many costs become necessary. Therefore, in this report, a self compulsory cooling for reducing thermal deformation was experimentally investigated. This method is the compulsory cooling using evaporation of water ; a cloth is bonded on a machine tool surface, water is supplied in the cloth by capillarity, then heat of the machine tool surface is removed by evaporation of water, and thermal deformation of the machine tool is finally reduced. The best suitable place on a machine tool for using this method is on the front surface of the head stock. Because this place has the strong inner heat source and is given strong wind by the spindle. When the spindle speed is higher and higher, the inner heat source is stronger, however the wind on the front surface of the head stock is also stronger and the surface is cooled down intensely with very large heat transfer coefficient. In the experiment, NC milling machine was used and thermal deformation of the machine with this countermeasure was investigated. It is concluded from the results that the proposed countermeasures are very cheap and effective in order to reduce thermal deformation.