FEATURED ARTICLE Laser Weld Process Monitoring: Seeing the Unseeable BY CHRISTOPHER M. GALBRAITH AND PAUL J.L. WEBSTER


The economic case for using lasers in industrial welding applications is no longer in question. Industrial lasers provide massive leverage in the form of an unmatched combination of speed, precision, robustness and—increasingly—accessibility. In serial production they can provide time and cost savings, and enable more efficient product designs. The price per kilowatt of laser power has dropped steeply in recent years, and in combination with a growing market and increasing number of players supplying laser solutions, this has led to increasing commoditization of laser sources and systems. In the quest to gain an edge over the competition, many system integrators and manufacturers are shifting their focus to increasingly sophisticated sensing techniques in order to wring more performance and higher quality out of their laser processes.


Controls and checks are of course an integral part of any production chain. The cost of out-of-spec parts reaching the hands of end users can be incalculable, and may be more than monetary where safety-critical components are involved. Many excellent quality assurance measures applicable to laser welding have existed for decades. The gamut of checks that can be applied to ensure a weld result is good reaches upstream


to production of the feedstock and downstream to a point where the weld may be part of a complex and expensive sub- assembly. What checks give the best return on investment for a manufacturer? This is a tough question to answer generally, but recent weld process monitoring advances have recently opened new opportunities for automated quality assurance and active control—improving laser weld quality and increasing certainty in the results.


Laser welding checks can be loosely sorted into three subsets: pre-process, in-process and post-process. For now, we’ll use ‘in- process’ checks to refer to any automated measures deployed during the welding process (while the laser is on) but not necessarily measuring the process itself (where the laser hits the metal).


Pre-process checks include steps taken at any stage prior to welding to ensure welds turn out in-spec. Tight control of feedstock and supplier processes are employed to enforce adherence to material standards, but such approaches classically have rapidly diminishing returns on investment and may be outside of a given organization’s power to control. The


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LIATODAY FOCUS: SCIENCE & RESEARCH SEPTEMBER/OCTOBER 2016


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