Surface cleaning of 34CrMo4 steel pipes by using pulsed fibre laser

This paper deals with the laser cleaning of 34CrMo(4) steel pipes to be adopted before the electrical upsetting process. The cleaning aims to decrease the pipes' roughness and the coupled electrical resistance with copper inserts to achieve lower wear and obtain an overall better electrical contact between the pipe and the copper inserts. Compared to a traditional process (shot blasting), the results showed that the laser cleaning treatment leads to a lower pipe roughness and a lowered wear of the copper inserts. The first experimental tests were conducted by using a 30-W Q-switched Yb:YAG fibre laser with different cleaning parameters such as scan speed, pulse frequency, and hatch distance to identify a workability range. Successively, a three-level full factorial plan was developed, and results were analysed through the analysis of variance (ANOVA) to understand which parameters were significant during the cleaning process. Also, the cleaned samples were compared to shot-blasted ones to evaluate the percentage improvements in terms of surface roughness, wear resistance, and coupled electrical resistance. In the third phase, a pre-industrialisation analysis was performed by adopting higher laser power sources (50-100 W) to reduce the cleaning time and define a possible industrial setup. It was found that with the laser cleaning treatment the surface quality increases (about 10 times lower Ra and Rz compared to shot blasting), with a decrease of the wear of about 22%. Moreover, the laser cleaning treatment improves the electric contact resistance and reduces the initial variability compared to the as-rolled sample.