Acclimatisation time of precise workpieces for quality inspection

During manufacturing precise parts are machined under shop floor conditions. For quality inspections these parts are brought into a measuring chamber. The research presented is a simulation study investigating the acclimatisation time of a machine tool bed brought from one functional room into another. The work deals with effects of thermal memory from any previous environment as explained in the thermal effects diagram of Bryan [1]. For the study a machine tool bed is either made of cast iron or polymer concrete. The boundary conditions required for the computations, for example the convective heat transfer coefficients, are derived from computational fluid dynamics (CFD) of the conditions in the air conditioned measuring chamber. The air temperature in the measuring chamber is controlled to 20 °C. Finite element method (FEM) is used to compute the temperature distribution over time and the thermally induced deformation of the bed. The deformations due to the temperature distribution of functional surfaces of the bed are evaluated as a function of time. Evaluation criteria are, for example, the flatness deviation of the guideways. The study shows that the time to reach a temperature distribution of the part, appropriate for evaluation of manufacturing errors, strongly depends on the material of the part and the boundary conditions, like the air stream velocity in the measuring chamber. It is shown that a storage time of more than one week in the measuring chamber is necessary to inspect geometrical features with small tolerances. The described combination of several computation methods can be transferred to any type of part. Simulation, Measurement, Precise Workpieces