Novel and efficient thermal error reduction strategy for machine tool performance improvement

The accuracy of a machine tool is affected by the heat generated during the machining process. Also, varying environmental conditions produce thermal gradients that flow through the machine structure. The heat passes through assembly joints and structural linkages in the machine where the roughness and form of the contacting surfaces affects the heat transfer coefficients. Measurement of the thermal behaviour and associated deformations in the structure is a time consuming procedure where machine downtime is a dominant issue. This paper discusses a novel offline technique using Finite Element Analysis (FEA) to simulate the thermal distribution and deformations during the spindle heating and cooling cycle in static conditions on a small Vertical Machining Centre (VMC) CNC machine. Detailed experimental testing of the temperature distribution in the machine and heat transfer work to obtain accurate values of the thermal contact resistance across the joints is reported. The obtained experimental results are evaluated and applied to the FEA software to obtain thermal distribution and associated deformations in a machine tool structure offline. The FEA simulated results are presented and are in close correlation with the obtained experimental results. FEA simulation enables efficient offline assessments of temperature distribution and displacements in the machine tool structures that result in a significant reduction in machine non-productive downtime while enabling characterisation under variable environmental conditions.