TWI Industrial Member Report Summary 480/1993
By M A O'Key and M R Osborne
For consistent quality in laser processing - whether in welding, cutting, surface treatment etc - it is essential to maintain a reproducible power density profile, and spot size (if at the focus). It is also necessary to maintain the position of a focus with respect to the work surface within a well defined range related to the depth of focus. These aspects are not controlled by the laser power alone, but also by the beam modes. With the extensive choice of industrial lasers now commercially available, and the increasing diversity of applications in materials processing, the need for on-line monitoring of beams for characterisation and QA has never been more important. Thus the overall aim of this CRP programme is to determine the most suitable technique(s) to characterise adequately an on-line laser beam for given processes, using the minimum of data storage capacity. The three major industrial lasers covered in this project are CO2 with powers up to 10kW at 10.6µm, Nd:YAG up to 2kW at 1.06µm, and Excimers up to 300W at UV wavelengths. Particular emphasis is given to pulsed lasers and to poor quality (multimode) beam profiles where present methods of monitoring are frequently inadequate and no universally accepted standards exist.
This report, which introduces the problems of beam characterization, presents data on application-specific beam parameters, a survey of laser-user opinions on beam monitoring and commercially available beam monitoring systems. Experiments have been performed to assess the suitability of two devices, in particular, for online monitoring.