TWI Industrial Member Report Summary 701/2000
G Verhaeghe and G B Melton
Arc welding is considered to be a 'special process' for quality assurance purposes, because the process is difficult to set up and welding procedures must be pre-qualified to comply with most fabrication standards. Where there is a quality or safety requirement, weld process monitoring has become essential to ensure the integrity of the welded joint. Various monitoring systems have been designed over the years for that purpose. The simplest practical approach is the continuous measurement of the arc, such as arc current, voltage and wire feed speed in order to monitor the welding performance. Such systems can be PC based, using high data acquisition rates and generating average process data. Only through the advent of bigger and faster PCs has it become possible to process more complex signals, increasingly used in processes such as square wave AC TIG, pulsed MIG and surface tension transfer® (STT) welding for example. Such a PC based arc monitor, the Fast AMV, was developed in a previous TWI project and used in the work described in this report.
Current research is focused on the development of monitors, which not only record the transient arc data, but also provide one or more analysis tools capable of distinguishing acceptable from defective welds, ie identifying for instance, where lack of fusion has occurred over a length of weld. This numerical indication of the process performance (based on analysis of the transient data) is expected to yield information on process stability, parameter optimisation and weld integrity/quality. This report describes the work carried out at TWI on the analysis of transient data when TIG welding thin sheet aluminium: an alternative signal analysis approach is described, as well as the use of a commercially available analysis tool to that end. The analysis of MIG welding trials on thin sheet aluminium is also reported.
- To investigate the use of a PC based arc monitor to detect the occurrence of arc irregularities that can be related to loss of gas shielding or weld contamination when TIG welding thin sheet aluminium using the AC TIG and pulsed MIG processes.