Adaptive Interval Model Control For Depth Of Weld Penetration In Pulsed Gas Metal Arc Welding

Machine vision methods are extensively used to obtain the weld pool surface information which is considered containing sufficient information to determine the weld penetration, but these methods are not suitable for manufacturing facilities because of their complex system. This work aimed at the development of a simple yet innovative method to effectively derive the weld pool surface depth from arc electrical signals and relate it to the depth of weld penetration, and control the depth of weld penetration in real-time.A high speed camera based vision system is used to image the weld pool surface and calculate the weld pool surface depth during pulsed gas metal arc welding (GMAW-P). The weld pool surface depth measurement algorithm gets the maximum weld pool surface depth under the wire tip using the pinhole model of camera. It is simple and is accurate enough to apply in depth of weld penetration control. Welding parameters are designed to conduct series of GMAW-P experiments so that the weld pool surface depth can be related to the depth of weld penetration and the arc voltage which is easily measured in the manufacturing facilities.Analysis of GMAW-P process suggests that not only the welding current/voltage but also the wire feed speed (WFS ) and welding travel speed (TS ) affect the weld pool surface depth and weld penetration. The metal deposition is first controlled at a constant C which is equal to WFS / TS. Experiment results show that average change in weld pool surface depth during peak current period decreases while the depth of weld penetration increases. Taking WFS / TS as a factor into account, the depth of weld penetration is expressed as a linear function of the average change in weld pool surface depth during peak current period and WFS / TS.The average change in weld pool surface depth can be replaced by the change in arc voltage during peak current period to predict the depth of weld penetration because there is a relationship between the change in weld pool surface depth and the change in arc voltage. A model, which only uses voltage signals to determine the depth of weld penetration, is obtained with adequate accuracy. Since the arc voltage is one of the easiest measureable signals in the manufacturing facilities, the model confirmed in this study between the depth of weld penetration and the change in arc voltage during the peak current period provides a simple yet suitable method to monitor the depth of weld penetration for manufacturing applications.A constant depth of weld penetration can be achieved if the change in arc voltage during peak current period is controlled to a certain constant in GMAW-P process. Hence, a depth of weld penetration control system is established with the change in arc voltage during peak current period as the system output and base current time as the system input because it affects the change in arc voltage during peak current period in a smoother way than the base current amperage. As the depth of weld penetration control system has a large time delay of nondeterministic length, and is time-varying, a controller with adaptive interval model, which is based on the predictive control, is designed and welding experiment results show the effectiveness of the control algorithm.