A system for dynamic shape measurements during laser processing

A laser-based 3D profilometry system is described which demonstrates high resolution, dynamic surface height measurements in hostile conditions. The system has been designed specifically to measure distortions under the conditions of high stray light and mechanical disturbances typical of laser forming (the bending of surfaces by thermally induced distortion) and welding. In our technique a CCD camera records images of the workpiece surface, onto which structured light is projected from an interferometer. A height map is generated from each image recorded in a sequence, allowing the dynamics of shape modification to be captured, quantified and studied. The system is capable of height resolutions of the order of 10µm over 60 x 60mm areas and is presently finding routine use in the in-process study of laser forming. We present the first examples of time-resolved shape measurements during laser forming, which demonstrate the transient and asymmetric nature of shape formation in this process. We hope that such measurements, combined with a process model, will further our understanding of the process to the extent necessary to implement it for practical applications.