Interferometrical measurement of concave half cylindric surfaces in industrial environment

Nowadays many automotive parts have form tolerances in the micron range and the whole surface must be acquired within short time. Usually interferometric methods are very suitable to achieve the necessary accuracy within short measurement time. Many of these parts have precise concave cylindric shape. For such parts we developed a special form measuring machine using a point measuring stylus having an air bearing spindle. This machine is using a short coherent stylus system which can measure on almost all non-transparent surfaces. Recently wear protection layers are increasingly applied to technical surfaces. For the measuring of such parts with semi-transparent layers we developed a shape measuring system using a wavelength in the visible range for which the layer is not transparent. The interferometer works with a high precision axicon mirror to adjust the measuring wave onto the inside cylindric surface. To measure the complete surface we implemented a cylindric stitching algorithm. To avoid residual errors caused by movement and vibration we use a special reference gauge. We present results and experience of application in the production.