The Laser Group
at Liverpool

K R Edwards, G Dearden, K G Watkins and S P Edwardson

 

Laser Group, Department of Engineering, The University of Liverpool, UK

 

Abstract: Laser peen forming has been carried out on 0.075mm thick steel samples, using relatively low power Q-switched Nd:YAG lasers at 1064nm, 532nm and 355nm wavelengths. The experiments have been carried out without the usually used tamping layer associated with laser peen forming, which would help to confine the shock wave and direct more of the energy produced by it into the material. An absorptive graphite coating was applied to increase coupling, so that the generation of plasma and shock waves was enhanced. The forming achieved was progressive, producing a bend angle of approximately 1 - 2 degrees per pass. The graphite coating was gradually removed with each pass, and as a result the laser forming effect was limited to the first 15 - 20 passes, after which there was little additional increase in cumulative bend angle.
The results from these experiments have been compared to samples formed using continuous wave laser thermal forming, with similar power settings. The results showed that laser peen forming could take place with a pulsed Nd:YAG laser, and that the laser peen formed samples do not have evidence of heat affected zones or changes to the bulk material, both seen with laser thermal forming. This indicates that the laser peen forming process is largely athermal, as there is very little heat input into the samples except for discoloration of the surface layer due to the plasma which generates the shockwaves.
Keywords: laser peen forming; laser induced shockwaves, micro forming, athermal

 

Download a copy of this paper