Thermal investigations on CNC lathe fitted with dynamically enhanced steel reinforced epoxy granite bed

Abstract

Polymer concrete or epoxy granite is now becoming more popular for beds, bases, and other structures of precision machine tools, owing to its excellent damping characteristics. In order to realize the same static rigidity as that of the cast-iron structures, steel-reinforced epoxy granite (SREG) structures are being used. The vast differences in the thermal properties of steel and epoxy granite (EG) are likely to cause higher magnitudes of thermal error. The objective of this work is to investigate the thermal behavior of a CNC lathe built with an SREG bed and compare its performance with the lathe with cast iron bed. Experimental and numerical investigations have been carried out under cross feed drive (CF) idle running conditions to determine the TCP deformation. The results reveal that the thermal error in the CNC lathe with SREG bed is 1.68 times that of the lathe with CI bed at 20ºC and 1.8 times at 40ºC environmental temperature variation chamber (ETVC) conditions. It could be identified that the heat generated in the CF is conducted to the steel guideways embedded in the SREG bed, but further heat transfer to the EG portion of the bed is impeded and hence the heat accumulation that occurs in the guideways leads to higher magnitude of thermal error. The experimentally validated numerical model is used to extend the investigations to study the effect of the idle running of the longitudinal feed drive (LF), and combined cross and longitudinal feed drives, on the thermal behavior of the lathe.