Optoelectronic device for non-invasive focal point measurement and control of the laser welding process

Although the laser welding process has many advantages over other techniques, especially for the welding of complex parts, it requires a precise focusing of the laser beam onto the workpiece to achieve the proper penetration over the entire weld seam. However, the unavoidable set-up tolerances and thermal distortion of the workpiece can result in focus errors that should be minimized. In this paper, an optoelectronic device for real-time measurement and control of the focal position is presented. It is based on the non-intrusive capture of the light emitted by the welding process by means of an optical fibre inside the laser head, and the estimation and correction of the focal error from the analysis of the light at two different spectral bands. The reported system has been optimized for use in a real environment: it is robust, compact, easy to operate and able to adjust itself to different welding conditions. Details of the design, figures of performance obtained from lab testing and results from recent field trials on complex aerospace parts are provided.