Visual Online Monitoring of Pgmaw without a Lighting Unit

In this paper, a low cost, high performance and full PC-based sensor system for the pulsed gas metal arc welding (PGMAW) is described. It allows the visual online observation of all states of the welding process, including the material transition, and all welding situations without an additional lighting unit. Additionally, the synchronized measurement of the welding current and welding voltage signals during image recording and the extraction of characteristic parameters of the signals (average values, etc.) is possible. Furthermore, the system allows the visual analysis of the material transition images. The system can be used for the optimization and the analysis of the welding process using visual information of the material transition and electrical welding parameters. INTRODUCTION The pulsed gas metal arc welding process is an important component in many industrial and manufacturing operations. It is highly suited to a wide range of applications. This is because, modern welding supplies are equipped with microprocessor-based power sources with a high number of variable welding parameters. Due to the complex combination of chemical and physical processes that depends on a multitude of parameters, the extreme brightness of the welding arc plasma, the high number of different welding tasks, etc., the practice of welding is difficult. To consistently produce high quality weld, finding correct welding combinations often requires extensive series of experiments. One approach to control the quality of the welding process is to adjust the welding supply parameters like controlling the heat and mass input to the weld pool and, more specifically, the droplet properties. Typically, the droplets should be even and in uniform size and the material transition should be splashless. The visual observation of the material transition has been used extensively. Normally high speed cameras in combination with an optical laser are used. A further approach is the use of a digital CCD-camera with a shutter and external trigger input in combination with a high energy flashlight, e.g. described by Nordbruch and Gräser [1][2]. Due to the extreme brightness the approaches use the shadowgraphing technique, described by Allemand et. al. [3]. This technique increases the contrast in the arc zone and the limited dynamic of the cameras with respect to the lighting conditions becomes insignificant. However, high speed systems are mainly suitable to clarify any questions of interest in understanding the arc welding processes, e.g. to analyze the forces acting on the droplet. For monitoring and control in manufacturing they are unsuitable due to a set of disadvantages. The most important are: ► Due to the shadowgraphing technique, only the observation of some few weld situations, such as build-up welding, is possible. The observation of welding in positions of constraint, e.g. welding in corners with the associated effects on the welding process, is not possible. ► The assignment of the images to other information, as current or voltage, is difficult. ► Because the cameras continuously take images, no specific states can be observed. Additionally, the high resolution leads to redundant information and a time-consuming, computer-bound quantitative offline analysis. 1 University Bremen, Institute of Automation, Germany