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Off-axis machining of NURBS freeform surfaces by fast tool servo assisted turning

: Brecher, C.; Merz, M.; Niehaus, F.; Winterschladen, M.; Lange, S.

Production Engineering. Research and development in Germany. Annals of the German Academic Society for Production Engineering 13 (2006), Nr.1, S.189-192
ISSN: 0944-6524
Fraunhofer IPT ()

In this paper a new approach for machining complex optical surfaces is presented. The illustrated off-axis machining allows for an efficient manufacturing of optical freeform surfaces by avoiding typical issues of conventional turning like artifacts in the surface center and highly varying cutting speeds. In that way the surface quality is increased as well as the production time is cut down significantly. In addition, a solution for the data pre-processing of the off-axis machining is demonstrated. In this case four single freeform surfaces described in the NURBS data format are combined automatically. An interpolation algorithm has to fill interjacent areas between the optical surfaces while those functional areas remain untouched. After generating the combined surface a simulation tool is used to analyze the machining process concerning restrictions caused by the cutting tool geometry the dynamics of the Fast Tool Servo. For the actual machining a clamping device has been designed to enable the precise placement of four work pieces. Reference surfaces permit an exact, repositioning on different machine tools for pre-machining the raw pieces. Due to the off-axis arrangement of four work pieces the process time for the final machining is reduced by 50% referring to single machining of the mirrors coming along with a very uniform surface finish. The machining results are very promising for future applications.