Investigations On Thermal Behavior of VMC Base Made Of Epoxy Granite

In a vertical machining centre (VMC) heat generation occurs due to the movement of the machine tool components. This heat generationand surrounding air temperature create temperature rise in the machine tool. Due tothe temperature rise, the tool centre point (TCP) displaces which leads to inaccuracy and loss of precision in machined components. VMC base is one of the major componentsof a machine tool contributing to TCP displacement. In VMC base, thermal deformation of the guideway is caused by heat generation of linear motion bearing, and thermal deformation of the feed drive system is caused by ball screw movement. Further, the ball bearing also contributes to TCP displacement. Epoxy granite is used as a replacement for conventional cast iron in VMC base due to its better dynamic characteristics. But the lower thermal conductivity of epoxy granite, makes the heat to concentrate in a localised region which creates structural deformation. The present work focuses on determination of heat generation due to the frictionof linear motion bearing and feed drive system, the corresponding temperature rise and deformation of the VMC base. A mathematical model based on transfer function is also developed to predict thermal errors.