Real-time monitoring and control of submerged arc welding process using point infrared sensor

Preset automated systems presently available for submerged arc welding systems lack the ability to compensate for perturbations that occur during the welding operation. To cope with perturbations and to prevent weld defects, a system capable of sensing the variations and modifying process parameters in real time is required. The present work was undertaken to study the feasibility of monitoring and controlling weld penetration variations in real-time for submerged arc welding process using a point infrared sensor. A simple theoretical thermal analysis showed that conditions which cause changes in weld penetration depth such as variations in plate thickness and butt joint gaps result in corresponding changes in thermal distribution. Such changes in thermal distribution were considered as an indicator of changes in weld penetration depth that could be used for monitoring and control of the welding process. Point infrared sensor was selected for monitoring the thermal distribution changes as it provided a simple, cheap, unobtrusive and non-contact, sensing method.; A monitoring system based on point infrared sensor was constructed. An unobtrusive torch attachment that held the infrared sensor close to the weld pool was fabricated. The torch attachment was also capable of holding the infrared sensor to plate distance constant. The infrared sensor was cooled using compressed air in order to maintain it at constant temperature. A virtual instrument weld process controller was created using the software LabVIEW. The weld machine power supply control system was modified to provide direct control of wire feed speed (welding current) and arc voltage from the computer. Infrared sensor signal obtained due to the thermal exchange between the plate being welded and the infrared sensor was acquired. The wire feed speed and arc voltage was automatically controlled to maintain the infrared sensor signal at a constant set point.; The infrared sensor monitoring and feedback control system was demonstrated on plates with constant thickness, plates with step change in thickness and butt joints with variable gaps. Changes in the plate thickness and joint gaps were used as process perturbations. Changes in the thermal distribution due to the process perturbations were recognized by the infrared sensor system. Sudden decrease in the plate thickness and increase in the butt joint gap caused the infrared sensor signal to increase due to the increase in heat input to the mass ratio. Use of automatic feedback control decreased the heat input corresponding to the increase in the infrared sensor signal and prevented burn through at the region of lowered plate thickness and at the region of wider gaps in butt joints.