Infrared Pyrometry-Guided Torch Motion in Scanned Thermal Joining Techniques

In thermal manufacturing methods, the motion of the concentrated heat source is usually scheduled off-line as dictated by the product geometry, thus leaving no control over its material structure and properties. To enable such a real-time regulation of thermal quality, the temperature field in the part must be controlled through the heat input distribution on its surface. In this article, this is implemented by power modulation and a scanning motion of the torch, guided by infrared sensing instrumentation on an in-process defined trajectory through the locations of highest thermal demand. The design of this distributed-parameter thermal control scheme is based on a numerical simulation model and a real-time thermal optimization algorithm. This sensory control system was implemented experimentally in scanned are welding, and its performance was compared to off-line, hardware-based thermal scanning of the source by a dedicated cam system. The resulting uniform temperature distribution in scan welding provides several material quality benefits, which make the regulation system applicable to other thermal processing techniques.