Tridimensional Laser Engraving of Industrial Injection Moulds for Fresnel Surface Generation

We developed a method for generating a three-dimensional surface by laser ablation of successive layers of a hard steel substrate using a Q-switched Nd:YAG laser marking system driven by a scanning head. This development included the creation of a computational method to obtain level curves and for the generation of a suitable filling of these curves with the laser system. The level curves were then imported to proper file formats utilizing the laser’s graphic program that also allowed the development of optimal laser processing parameters to do the engraving. The input process was a grayscale bitmap representing a surface, with the value of each pixel (a value between 0 and 255) corresponding to the depth of the surface in the position (x,y) of the pixel. This numerical process allowed the generation of surfaces utilizing programs like MATLAB by direct micromachining the substrate, once a grayscale bitmap output is obtained. An optical polishing with an ultra-sound device was applied after the laser ablation to reduce the rugosity of the surface that resulted in surfaces with specular reflection. This method was used in the production of a Fresnel lens array mould with spatial filtering for passive infrared motion sensors with satisfactory results