An alternate approach to free-form surface fabrication

Abstract

Abstract Surface milling and grinding are widely used for the fabrication of free-form surfaces for molds and dies. The continuous demand for better product quality has led to demand in higher surface accuracy. Limiting factors are the positioning accuracy of the tool and the accuracy of the manufacturing process. Computer controlled optical surfacing (CCOS) has been developed mainly for the fabrication of spherical and aspherical optics. The surface is repeatedly measured and corrected using abrasives until the target accuracy is attained. In principle, sub-micron accuracy is achievable. The accuracy is limited by surface measurement, and not by the processing equipment. The current research investigates the adoption of CCOS for the fabrication of free-form steel surfaces. This paper reports on the development of a test bed and initial experiment results. The test bed is based on a six-axis RX robot as the motion platform with a spindle attached to the wrist of the robot. Surface measurement is carried out using a Talysurf surface profiler. Surface error correction is performed by abrasion of material from the surface. The amount of material to be removed is based on the measured surface error. Following a predetermined tool path, the feed rate along the tool path for surface correction is to be varied according to the required among of material to be removed locally. A free-form surface specimen of mold steel of about 40 mm × 40 mm across is used for the initial experiment. The surface is prepared by CNC surface machining with the initial maximum error over 50 μm. The positioning accuracy of the motion system is estimated to be no better than 0.1 mm. Through surface measurement and correction, the surface accuracy is significantly improved.