Laser Ablation of Primer During the Welding Process of Iron Plate for Shipbuilding Industry

Pre-construction Primer (PCP) is an epoxy resin charged with a zinc powder, applied at low thickness to minimize rusting of steel plates during storage and fabrication in shipbuilding industries. In this material, the zinc, in contact with the iron support, acts as a sacrificial anode protecting the surface from corrosion. However, this coating is problematic when the steel plate requires to be welded. In fact, the solid polymeric coating sublimates when exposed at the high temperatures due to the welding process, producing porosity in the welding bead. Different methods can be used to remove the primer before the welding: brushing, sand or ice blasting, waterjet, chemical solvent and laser cleaning. In this paper, laser cleaning tests were carried out by etching a 10x10 mm2 surface of primer coated steel plate, using a 30 W Q-Switched Yb:YAG fibre laser. The cleaning tests were carried out varying the scan speed, the pulse power and the distance between two consecutive beam travel (Step). From the treated surface analysis, the percentage of cleaned area was obtained and the process parameters were correlated to the percentage of cleaned area. The process window where laser cleaning could be successfully performed and the maximum process speed were individuate. Finally, observation about the energy consumption and the energy efficiency were reported.