Weld Penetration Control Research Articles

Weld penetration control system design and testing

The design, implementation, and testing of a feedback control system for regulating gas tungsten arc weld (GTAW) penetration are presented in this study. The derivation of reduced-order transfer function models representing the welding heat flow is also discussed. The control problem was cast in a robust design setting, and an H∞ controller was designed for regulating weld penetration. The H∞ control theory could quantify the trade-off between performance and robustness and achieve both good performance and robustness. The feedback control system, which used infrared temperature measurements, was implemented and tested. The dynamic and steady-state responses of the system to step input changes as well as unmodeled base metal width variations were studied by simulation and experimentally. The experimental results were similar to the simulation predictions. The controller was able to provide regulation to achieve full penetration for GTAW and was also robust to control weld penetration during perturbations in base metal width.

Dynamic Estimation of Full Penetration Using Geometry of Adjacent Weld Pools

Control of weld penetration is currently one of the most important and crucial research issues in the area of welding. The weld pool can provide accurate and instantaneous information about the weld penetration, however, the establishment and confirmation of the correlation between weld pool and weld penetration require numerous accurate measurements and suitable geometrical modeling of weld pool. A normalized model is proposed to characterize the weld pool two-dimensionally. More than 6,000 weld pools are measured from experiments using a developed real-time weld pool sensing system. A data analysis shows that the weld penetration is correlated with the weld pool which is specified by the three characteristic parameters proposed in the study. However, the correlation is nonlinear. To approximate the complicated nonlinearity, neural networks are used. Comparative modeling trails show that the weld penetration can be more accurately calculated if the adjacent weld pools are also used. This implies that the correlation between the weld penetration and weld pool is dynamic. Hence, an on-line nonlinear dynamic estimation system is developed to estimate the weld penetration.

Real-Time Sensing of Sag Geometry During GTA Welding

Seam tracking and weld penetration control are two fundamental issues in automated welding. Although the seam tracking technique has matured, the latter still remains a unique unsolved problem. It was found that the full penetration status during GTA welding can be determined with sufficient accuracy using the sag depression. To achieve a new full penetration sensing technique, a structured-light 3D vision system is developed to extract the sag geometry behind the pool. The laser stripe, which is the intersection of the structured-light and weldment, is thinned and then used to acquire the sag geometry. To reduce possible control delay, a small distance is selected between the pool rear and laser stripe. An adaptive dynamic search for rapid thinning of the stripe and the maximum principle of slope difference for unbiased recognition of sag border were proposed to develop an effective real-time image processing algorithm for sag geometry acquisition. Experiments have shown that the proposed sensor and image algorithm can provide reliable feedback information of sag geometry for the full penetration control system.

Computerized radiographic weld penetration control with feedback on weld pool depression : Guu, A.C.; Rokhlin, S.I. Materials Evaluation, Vol. 47, No. 10, pp. 1204–1210 (Oct. 1989)

Welding pool depression depends on plasma pressure and heat input to the pool and therefore is related to weld penetration. On the basis of information on pool depression received from radiographic images in real time during welding, the possibility of using automated weld penetration control to maintain the required weld penetration has been studied. The experimental system developed includes an arc welding unit, a welding manipulator, a real-time x-ray system, an image processing unit, and a system controller. By analyzing the radiographic information together with metallographs of the appropriate weld cross section, the depth of the liquid metal in the pool has been determined at different levels of current and weld penetration.

Weld penetration control with radiographic feedback on weld pool depression : Guu, A.C.; Rokhlin, S.I. Review of Progress in Quantitative Nondestructive Evaluation, Brunswick, Maine (United States), 23–28 Jul. 1989. Vol. 9B, pp. 1973–1980. Edited by D.O. Thompson and D.E. Chimenti. Plenum Press (1990)

Weld penetration control with radiographic feedback on weld pool depression : Guu, A.C.; Rokhlin, S.I. Review of Progress in Quantitative Nondestructive Evaluation, Brunswick, Maine (United States), 23–28 Jul. 1989. Vol. 9B, pp. 1973–1980. Edited by D.O. Thompson and D.E. Chimenti. Plenum Press (1990)

Closed-loop process control of weld penetration using real-time radiography : Rokhlin, S.1.; Cho, K.; Guu, A.C. Materials Evaluation, Vol. 47, No. 3, pp. 363–369 (Mar. 1989)

Closed-loop process control of weld penetration using real-time radiography : Rokhlin, S.1.; Cho, K.; Guu, A.C. Materials Evaluation, Vol. 47, No. 3, pp. 363–369 (Mar. 1989)

Dynamic Analysis and Identification of Gas Tungsten Arc Welding Process for Weld Penetration Control

In this study, gas tungsten arc welding is analyzed and modeled as a 2-input (welding current and arc length) 2-output (weld depression and width) multivariable process. Experiments under a number of typical welding conditions are performed to excite and identify the process characteristics and variations. It is observed that the model parameters vary in a large range with the experimental conditions. A real-time model frame with only a few parameters to be identified on-line is proposed. Based on the obtained models, the process characteristics in terms of inertia, delay, nonminimum phase, and coupling are given. These characteristics suggest an adaptive predictive decoupling control algorithm. By designing and implementing the suggested control algorithm with the real-time model, excellent results have been achieved for both simulation and practical control. This shows that the dynamic analysis and identification provide sufficient process information for design of the control system.

Machine Vision Recognition of Weld Pool in Gas Tungsten Arc Welding

The weld pool and its surrounding area can provide a human welder with sufficient visual information to control welding quality. Seam tracking error and pool geometry can be recognized by a skilled human welder and then utilized to adjust the welding parameters. However, for machine vision, accurate real-time recognition of weld pool geometry is a difficult task due to the high intensity arc light, even though seam tracking errors can be detected. A novel vision system is, therefore, used to acquire quality images against the arc. A real-time recognition algorithm is proposed to analyse the image and recognize the pool geometry based on the pattern recognition technique. Despite surface impurity and other influences, the pool geometry can always be recognized with sufficient accuracy in 150 ms under different welding conditions. To explore the potential application of machine vision in weld penetration control, experiments are conducted to show the correlation between pool geometry and weld penetration state. Thus, pool recognition also provides a possible technique for front-face sensing of the weld penetration.

Infrared sensing of full penetration state in gas tungsten arc welding

The objective of this study is to present an applicable top-side infrared sensing technique for the prospective closed-loop control of weld penetration in gas tungsten arc welding (GTAW). A model is developed to calculate the full penetration state, which is specified by the back-side bead width, from the sensed infrared images. To ensure the model validity in the prospective closed-loop control, the experiments, which generate the data for the model identification, are conducted under the experimental conditions that will be encountered during practical closed-loop control of the welding process. The heat transfer condition and electrode tip angle may vary during welding or from case to case. Also, the control variables which are used to adjust the weld process in order to reach the required weld penetration will also change. In many cases, the current can be employed as an on-line adjustable control variable because of the implementation ease, when the welding speed and arc length are maintained at the preset values. Thus, different currents, workpiece sizes, and electrode tip angles are arranged in the experiments to emulate the possible current adjustments, case to case heat transfer variations, and electrode wear. The infrared characteristics of the effects of these parameters are extracted to regress the full penetration state. Finally, the back-side weld width (the full penetration state) is calculated using the resultant model from the sensed infrared data.

Closed-Loop Control of Weld Penetration Using Front-Face Vision Sensing

Feedback control of weld penetration based on a front-face sensor is a challenging problem in the field of welding. A novel vision-based approach is proposed in this paper for full penetration control of the gas tungsten arc welding (GT AW). Owing to the relationship between the front-face weld geometry and back-face weld width (representation of the full penetration state), which has been reported earlier by the present authors, it is possible to use the front-face geometry as feedback of full penetration. Based on the dynamic modelling and the analysis of accepted adaptive control algorithms, an adaptive predictive decoupling controller is developed. Simulations and experiments under a variety of welding conditions have been conducted to verify the effectiveness of the proposed approach and controller.

Weld penetration control with radiographic feedback on weld pool depression

Weld penetration control with radiographic feedback on weld pool depression

Computerized radiographic weld penetration control with feedback on weld pool depression

Computerized radiographic weld penetration control with feedback on weld pool depression

Closed-loop process control of weld penetration using real-time radiography : Rokhlin, S.I.; Cho, K.; Guu, A.C. Materials Evaluation, Vol. 47, No. 3, pp. 363–369 (Mar. 1989)

Closed-loop process control of weld penetration using real-time radiography : Rokhlin, S.I.; Cho, K.; Guu, A.C. Materials Evaluation, Vol. 47, No. 3, pp. 363–369 (Mar. 1989)