Analysis of weld seam uniformity through temperature distribution by spatially resolved detector elements in the wavelength range of 0.3μm to 5μm for the detection of structural changing heating and cooling processes

Abstract

Online process control systems often only detecting temperatures at a local area of the machining point and determining an integrated value. In order to determine the proper welding quality and the absence of defects, such as temperature induced stress cracks, it is necessary to do time and space resolved measurements before, during and after the production process. The system under development consists of a beam splitting unit which divides the electromagnetic radiation of the heated component on two different sensor types. For high temperatures, a sensor is used which is sensitive in the visible spectrum and has a dynamic range of 120dB.1Thus, very high intensity differences can be displayed and a direct analysis of the temperature profile of the weld spots is possible.2 A second sensor is operating in the wavelength range from 1 micron to 5 microns and allows the determination of temperatures from approximately 200°C.3 At the beginning of a welding process, the heat-up phase of the metal is critical to the resultant weld quality. If a defined temperature range exceeded too fast, the risk of cracking is significantly increased.4 During the welding process the thermal supervision of the central processing location is decisive for a high secure weld. In the border areas as well as in connection of the welding process especially cooling processes are crucial for the homogeneity of the results. In order to obtain sufficiently accurate resolution of the dynamic heating- and cooling-processes, the system can carry out up to 500 frames per second