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Scaling-up freeform manufacturing: challenges and solutions

With optical technology and design advances, larger freeform optics are increasingly sought after by consumers for an expanding number of applications. Many techniques have been developed to meet the challenges of producing these nonrotationally symmetric optics, which cannot be fabricated via traditional manufacturing and metrology processes. In the past, methods were established to create smaller freeforms. With demands for more and larger freeforms, manufacturers must scale up existing processes. This paper will present some of the challenges and solutions of extending freeform polishing capabilities from approximately 150 mm diameter parts to a component of over 500 mm in diameter. In fabricating the 500 mm freeform, Optimax has addressed many of the manufacturing and metrology challenges using some proprietary techniques as well as some novel methods. Some of the approaches explored in this paper include acquisition of a substrate blank of sufficient dimensions, material handling logistics, polishing strategies, and metrology. Earlier freeform polishing projects at Optimax utilized a smaller pick-and-place style, 6-axis robotic arm. The route to design, build, and program a scaled-up polishing robotic arm is discussed. Considerations for polishing path planning and metrology are explained. In addition, deflectometry, a non-interferometric measurement method using fringe reflection and ray tracing, has been developed in parallel to help measure mid-spatial frequency error on a part surface faster and more safely than traditional methods, as it can be done in-situ.