Dynamic thermal tensioning for welding induced distortion control

Welding induced distortion is a major concern in industry. Many methods have been studied to control it. Among them, the in-process control methods, such as steady-state and transient thermal tensioning, have received more attention due to their low cost and flexibility. However, the existing thermal tensioning methods have been developed assuming nominal structural geometry and welding process conditions. They cannot compensate for production variations such as the initial geometry, fixture, and welding process errors.;In this study, a dynamic thermal tensioning method is developed. The new method employs a distortion feedback signal to determine the thermal tensioning parameters such that the preheating torches can be adjusted automatically in real time to minimize the welding induced distortion. Based on a box beam structure that is welded simultaneously with four plates, a finite element analysis model is developed to simulate the response of the welding and preheating process. The element birth and death procedure is applied to consider the relative sliding effects between the side plates. A decoupled thermal tensioning strategy is developed to control various types of welding induced distortions individually. In order to develop an automatic control system using the dynamic thermal tensioning method, the nonlinear time-varying response of the welding and preheating process is studied using the finite element simulation model. A linearized response model is then constructed based on the superposition principle. With the linearized process model, a threshold-based control algorithm is developed and implemented in production. The finite element simulation model is also used to identify a critical preheating temperature for buckling distortion control.;The dynamic thermal tensioning method developed in this research is proved to be successful. It is able to control the welding induced distortion caused by production variation, which the existing methods have not been able to handle. In addition, this research provides fundamental understanding of the thermal mechanical behaviors of large welded structures in the welding and preheating process through the finite element simulation.