SIMULATION OF LIGHT DEFLECTION DUE TO AN INHOMOGENEOUS REFRACTIVE INDEX FIELD INDUCED BY A HOT MEASUREMENT OBJECT

Inline process control by 3d geometry measurement is an important part of the cost-effective production of high precision hybrid components. The characterisation of the topography of the joining zones of these so called Tailored Forming components directly after each process step yields advantages – such as early error detection and a rejection of deficient parts. Due to the heat transfer from the hot object’s surface to the ambient medium air, an inhomogeneous refractive index field is building up. A ray of light traversing such a field is deflected towards the more dense air layers. Optical triangulation techniques rely on a rectilinear projection of light on and reflection of the measurements object’s surface. A deviation from the linear path results in a loss of measurement accuracy. We present 2d-simulations of the light deflection of a laser spot on a hot, circular object’s surface by combining heat field simulations with classical ray tracing and extrapolating Ciddor’s equation for the refractive index of air. The results show that the amount of deflection depends on the ambient pressure, the triangulation angle and the measurement object’s temperature.