Laser Polishing

Abstract

A new approach to polish metallic freeform surfaces is polishing by means of laser radiation. In this technology a thin surface layer is molten and the surface tension leads to a material flow from the peaks to the valleys. No material is removed but reallocated while molten. As the typical processing time is 1 min/cm² laser polishing is up to 30 times faster than manual polishing. Reducing the roughness by laser polishing is achieved for several different materials such as hot work steels for the die and molding industries or titanium alloys for medical engineering. Enhancing the appearance of design surfaces is achieved by creating a dual-gloss effect by selective laser polishing (SLP). In comparison to conventional polishing processes laser polishing opens up the possibility of selective processing of small areas (< 0.1 mm²). A dual-gloss effect is based on a space-resolved change in surface roughness. In comparison to the initial surface the roughness of the laser polished surface is reduced significantly up to spatial wavelengths of 80 microns and therefore the gloss is raised considerably. The surface roughness is investigated by a spectral analysis which is achieved by a discrete convolution of the surface profile with a Gaussian loaded function. The surfaces roughness is split into discrete wavelength intervals and can be evaluated and optimized. Laser polishing is carried out by using a special tailored five-axis mechanical handling system, combined with a three axis laser scanning system and a fibre laser.