Influence of an Angular Hatching Exposure Strategy on the Surface Roughness During Picosecond Laser Ablation of Hard Materials

Innovative chip breakers for cutting tools made of very hard materials require laser ablation and demand a high quality regarding the manufactured surface. When processing materials such as polycrystalline cubic boron-nitride or tungsten carbide the surface roughness by laser ablation reaches Sa = 1,0-2,9 mm compared to Sa = 0,42 mm achieved by grinding. Therefore in the presented research the influence of the hatching exposure strategy on surface roughness during picosecond laser ablation of tungsten carbide is examined. The areal, layerwise ablation process is separated into its elements which are represented by intersection zones between single and multiple laser vectors. Thus two mechanisms of roughness formation are identified and described by model functions. Further the mechanisms are transferred to areal ablation in which surface roughness decreases due to improved hatching angles compared to a commonly used one of f= 0°/90°. With this approach the roughness is reduced by approximately factor 2,0-3,5 to Sa = 0,82 mm. In conclusion guidelines are derived which present favorable settings for high quality laser ablation processes.