TWI Frequently asked questions
by John Weston
Automation, a subset of machine welding, involves a high level of control. Referring to the diagram below may help with understanding the concepts involved.
With manual welding, placement of the welding process and control of the welding process lies solely with the welder.
Machine welding is considered to be the generic term covering situations where the welding activity is assisted by a mechanism. In this context, the term 'mechanised welding' is occasionally used, although this may lead to confusion with respect to the definitions set out below.
Where there remains a high level of manual involvement, the term 'mechanised' may be used. For example, in submerged-arc welding, mechanisms move the welding head relative to the work, feed the welding wire and often manage the flux control. The welding operator will control and set the parameters and usually guides the weld head as it is mechanically driven along the joint line.
In this scheme of definitions, 'automatic' welding refers to dedicated machines, whereas 'robotic' welding applies to those machines that can be programmed to perform several different tasks (often sequentially in the same cycle). When operated at their basic level, automatic machines or robots have piece-parts delivered to them with a high degree of consistency, especially in terms of dimensional tolerance. The result is that the operator can simply place the parts in the machine, press the start button and welding will be performed.
However, it is frequently the case that there is variation in the piece parts, or in the welding system, so that some adaptivity is required. To be adaptive, it is necessary for the system to first sense some measure of the variation that is occurring, so that control can ensure that appropriate corrective action is applied.
In the first instance, it may be necessary to find, or recognise the position of, the joint (so that welding can start at the correct point, for example). Next, it might be necessary to follow or track the joint. Both of these adaptive functions involve the physical relationship between the weld head and the joint-line.
It might also be necessary to perform weld recognition so that the welding process itself can be adapted to give control, for example, over variations in the joint preparation. One approach taken is to vary welding travel speed asthe volume of the weld joint changes.
The control systems outlined above operate as welding takes place. In contrast, longer-term control loops look at data after the event and then feed the information acquired back to the beginning of the operation, prior to restarting the process of welding the next unit. For example, studies can be made of the shape of the weld bead produced, or of the printouts of monitored welding parameters, as measures of process performance. If poor values are found then adjustments will be made to the welding machine with the aim of improving performance.
Remote viewing systems can also assist operator's control welding processes.
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