Temporally or spatially unstable thermal conditions in the course of geometric intermediate and final inspections lead to transient or inhomogeneous thermoelastic changes in the geometry of the workpieces to be inspected. This results in non-negligible measurement deviations, especially when measuring large workpieces with narrow tolerances, e.g. turbine components or gear parts.
The state of the art regarding the characteristic-specific determination of systematic measurement deviations due to thermoelastic workpiece behavior is very limited. It mainly comprises the one-dimensional linear scaling of thermal expansion or the use of calibrated workpieces assuming a steady, homogeneous temperature distribution. However, this is not sufficient for a characteristic-specific determination and correction of corresponding systematic measurement deviations if a transient and/or inhomogeneous temperature distribution is expected. This results in a high share of unknown systematic measurement deviations that have to be estimated conservatively and considered within the overall measurement uncertainty.
Modelling thermoelastic states of objects with the help of more complex models, e.g. based on the finite element method, is common in production research to simulate the behavior of machines or workpieces in manufacturing or assembly processes. The latter also holds for the investigation of measurement systems like coordinate measurement machines under certain operating conditions. Nevertheless, such approaches are not established yet concerning the thermoelastic behavior of workpieces during geometric inspection.
Thermoelastic deformations due to transient or inhomogeneous temperature distributions are generally expected to be a significant or even major contribution to the measurement uncertainty when inspecting large workpieces. Although, so far there is no comprehensive systematic study of which thermal conditions and other characteristic properties lead to critical effects for certain workpiece geometries and materials.
The model-based and experimental investigation of the transient thermoelastic behavior of large workpieces in typical measurement environments is part of the current research needs in production metrology. This work focusses on this problem and finally provides a solution approach for a more accurate determination of workpiece temperature-related measurement deviations and uncertainties.