Machine tools are used to manufacture components with desired size, shape, and surface finish. The accuracy of machining is influenced by stiffness, structural damping, and long-term dimensional stability of the machine tool structures. Components machined using such machines exhibit more dimensional variations because of the excessive vibration during machining at higher speeds. Compared to conventional materials like cast iron, stone-based polymer composites such as epoxy granite have been found to provide improved damping characteristics, by seven to ten folds, due to which they are being considered for machine tool structures as alternate materials. The stiffness of structures made of epoxy granite can be enhanced by reinforcing with structural steel. The current work highlights the design and analysis of different steel reinforcements in the lathe bed made of the epoxy granite composite to achieve equivalent stiffness to that of cast iron bed for improved static and dynamic performances of the CNC lathe. A finite element model of the existing the cast iron bed was developed to evaluate the static (torsional rigidity) and dynamic characteristics (natural frequency) and the results were validated using the experimental results. Then finite element models of five different steel reinforcement designs of the epoxy granite bed were developed, and their static and dynamic behaviors were compared with the cast iron bed through numerical simulation using finite element analysis. The proposed design (Design-5) of the epoxy granite bed is found to have an improvement in dynamic characteristics by 4–10% with improved stiffness and offers a mass reduction of 22% compared to the cast iron bed, hence it can be used for the manufacture of the CNC lathe bed and other machine tool structures for enhanced performance.

The main requirements for machine tool structures are higher damping, stiffness, and dimensional stability and low thermal expansion coefficient. Compared with cast iron (CI), stone-based polymer composite provides improved damping characteristics, because of which it is being considered as an alternate material for machine tool structures in recent research. In this work, process parameters of epoxy granite (EG) composite were optimized using the technique for order preference by similarity to ideal solution (TOPSIS) method to obtain optimum strength characteristics. The effect of process parameters, namely curing time (A), aggregate mass fraction (B), aggregate size mix (C), curing temperature (D), and stirring speed (E) on static and dynamic characteristics of EG composite were investigated. An analysis of variance test was performed to identify the significant process parameters with a confidence level of 95 %. The predicted process parameters are verified through confirmatory tests, which showed an improved preference value of 0.0948. To obtain optimum strength properties, the recommended optimum process parameters are found to be A = 12 h, B = 0.8, C = aggregate size mix 1, D = 40°C, and E = 90 r/min. Experimental modal analysis also revealed that the damping factor of EG composite with aggregate mass fraction B = 0.8 is 10 times higher than that of CI. Morphological analysis of EG composite using a field emission scanning electron microscope showed that granite aggregates are uniformly distributed with better epoxy bonding characteristics.

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.

Polymer concrete or epoxy granite is becoming more popular for beds, bases, and other structures of precision machine tools, owing to its excellent damping characteristics. 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. This work aims to investigate the thermal behaviour of a computerized numerical control (CNC) lathe built with a novel dynamically enhanced SREG bed and compare its performance with the lathe with a cast iron bed. Experimental and numerical investigations have been carried out under cross-feed (CF) drive 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 cast iron (CI) bed at 20 ºC and 1.8 times at 40 ºC 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 the 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 behaviour of the lathe.