Thermal error reduction in CNC lathe with epoxy granite bed using thermo-structural optimization

Thermal error is one of the most influential parameters in precision and ultra-precision machine tool design. In recent decades, machine tool structures made of polymer concrete such as steel-reinforced epoxy granite (SREG) have gained popularity due to their superior damping properties, substantial stiffness and good thermal stability to variations in environmental changes. On account of the significant variation in the thermal properties of steel and epoxy granite, the thermal error in a lathe with an SREG bed is found to be 1.6 times that in a lathe with cast iron bed at 20 °C ambient conditions. This paper presents a novel method of reducing the thermal error in the CNC lathe with an SREG bed using a genetic algorithm (GA)-based multi-objective optimization. The proposed thermo-structural optimization is an efficient design model for the SREG bed to enhance heat transfer by maximizing convection area as an objective and required stiffness as one of the constraints. For all analyses, a validated numerical method was adopted. Thermo-mechanical analysis by simulations reveals that a 32% reduction in thermal error can be achieved with the optimized SREG bed. Experimental modal analysis (EMA) on the optimized bed (SREG-2) shows that the dynamic properties have not deteriorated compared to the results of the existing SREG-1 bed.