Shifted Laser Surface Texturing (sLST) in Burst Regime

Abstract

High laser-scanning speed and high precision are two opposite parameters for effective laser surface texturing (LST). Application of a sequence of laser pulses (called burst) helps to increase the processing effectivennes and speed, but precision control of laser pulses arriving becomes a difficult task for micro-texturing. In this work, one possible solution for this dilemma is presented: a scan-ning strategy called shifted laser surface texturing (sLST) in burst regime. This burst sLST repre-sents an alternative method, where the inertia of galvanoscan mirrors becomes a useful factor at higher speeds. Physical principles of laser burst interaction with a material surface and resulting subsurface thermal-stress fields are discussed. Heat accumulation was calculated from a semi-planar model of temperature distribution from laser spots in the line of the burst. Residual subsurface temperature and pressure is called positive heat accumulation in the case of minimal output roughness of laser-scanned surfaces. Experimental application of the burst sLST was performed with a pico-second laser with a galvanoscan system. Results were evaluated by newly developed shape analysis of objects detected on contrast images of laser-processed stainless steel surfaces painted with high-emissivity paint. Deviation in sLST precision was determined from larger and smaller diameters of detected microobjects on the surface with LabIR coating. The roughness of depth structure in microobjects was controlled by a contact surface profiler and compared with the goal profile and positive heat accumulation distribution. The sLST method in burst regime enables a significant increase of processing speed while maintaining good precision of the produced texture.