SENSOR FOR AUTOMATED WELD BEAD PENETRATION CONTROL

A backface penetration control system has been developed for DC pulsed tungsten inert gas (TIG) welding. The system is based on a binary vision system built around the BBC microcomputer. The system utilizes a coherent optical bundle to transmit the images of the backface bead to a b/w vidicon camera. The penetration control system regulates the bead size by controlling the pulse duration of the TIG process. Comparisons are made between the required and actual bead sizes in real time, the arc current being returned to the background level when the required penetration is reached. The system has been tested extensively on type 304 stainless steel, using various plate thicknesses for both bead on plate and butt weld tests. The system has also been tested on tapered plates from 0.5 mm to 4 mm. The backface penetration control system performs well over the complete range of tested plate thicknesses, in addition to the tapered plate tests. The image of the weld bead does not necessarily have to be in the centre of the screen to produce good welds; as long as the whole bead appears within the field of view of the lens, the bead size may be controlled. This allows the system to be easily set up and operated.