Mathematical formulation and simulation of specular reflection based measurement system for gas tungsten arc weld pool surface

While penetration occurs underneath the workpiece, the raw information used to detect it during welding must be measurable to a sensor attached to the torch. Challenges are apparent because it is difficult to find such measurable raw information that fundamentally correlates with the phenomena occurring underneath. Additional challenges arise because the welding process is extremely complex such that analytically correlating any raw information to the underneath phenomena is practically impossible; therefore, handcrafted methods to propose features from raw information are human dependent and labor extensive. In this paper, the profile of the weld pool surface was proposed as the raw information. An innovative method was proposed to acquire it by projecting a single laser stripe on the weld pool surface transversely and intercepting its reflection from the mirror-like weld pool surface. To minimize human intervention, which can affect success, a deep-learning-based method was proposed to automatically recognize features from the single-stripe active vision images by fitting a convolutional neural network (CNN). To train the CNN, spot gas tungsten arc welding experiments were designed and conducted to collect the active vision images in pairs with their actual penetration states measured by a camera that views the backside surface of the workpiece. The CNN architecture was optimized by trying different hyperparameters, including kernel number, kernel size, and node number. The accuracy of the optimized model is about 98% and the cycle time in the personal computer is ~ 0.1 s, which fully meets the required engineering application.

Download Full-text

Sensing Free Surface of Arc Weld Pool Using Specular Reflection: Principle and Analysis

Proceedings of the Institution of Mechanical Engineers Part B Journal of Engineering Manufacture ◽

10.1243/pime_proc_1996_210_154_02 ◽

1996 ◽

Vol 210 (6) ◽

pp. 553-564 ◽

Cited By ~ 31

Author(s):

R Kovacevic ◽

Y M Zhang

Keyword(s):

Weld Pool ◽

Specular Reflection ◽

Three Dimensional ◽

Surface Shape ◽

Pool Surface ◽

Imaging Model ◽

Dimensional Shape ◽

Weld Pool Surface ◽

Welding Processes ◽

Three Dimensional Shape

The weld pool surface provides important information for understanding arc welding processes. In this study, a novel vision sensor is proposed to measure the three-dimensional shape of the free weld pool surface. A pulsed laser is projected on to the weld pool through a specific grid. Specular reflection from the pool surface is sensed using a high shutter speed camera. The three-dimensional weld pool surface shape is clearly shown by the specular reflection. To determine the shape of the pool surface, an image processing technology has been developed to extract the skeleton of the specular reflection from the acquired image. The imaging principle is analysed to determine the correlation between the reflection and the weld pool surface. If the weld pool surface is known, the corresponding specular reflection can be directly calculated using the imaging model which is derived based on the reflection law. However, no explicit models can be obtained to determine the weld pool surface using the reflection and sensor parameters. To solve this difficulty, an iterative algorithm is proposed. The weld pool surface can now be calculated in 1 second from the specular reflection of the weld pool surface. A higher calculation speed is currently being pursued.

Download Full-text

Real-Time Image Processing for Monitoring of Free Weld Pool Surface

Journal of Manufacturing Science and Engineering ◽

10.1115/1.2831091 ◽

1997 ◽

Vol 119 (2) ◽

pp. 161-169 ◽

Cited By ~ 77

Author(s):

R. Kovacevic ◽

Y. M. Zhang

Keyword(s):

Weld Pool ◽

Specular Reflection ◽

Welding Process ◽

Ccd Camera ◽

Weld Penetration ◽

Reflection Pattern ◽

Pool Surface ◽

Edge Points ◽

On Line ◽

Weld Pool Surface

The arc weld pool is always deformed by plasma jet. In a previous study, a novel sensing mechanism was proposed to sense the free weld pool surface. The specular reflection of pulsed laser stripes from the mirror-like pool surface was captured by a CCD camera. The distorted laser stripes clearly depicted the 3D shape of the free pool surface. To monitor and control the welding process, the on-line acquisition of the reflection pattern is required. In this work, the captured image is analyzed to identify the torch and electrode. The weld pool edges are then detected. Because of the interference of the torch and electrode, the acquired pool boundary may be incomplete. To acquire the complete pool boundary, models have been fitted using the edge points. Finally, the stripes reflected from the weld pool are detected. Currently, the reflection pattern and pool boundary are being related to the weld penetration and used to control the weld penetration.

Download Full-text

Study on Dynamic Development of Three-dimensional Weld Pool Surface in Stationary GTAW

High Temperature Materials and Processes ◽

10.1515/htmp-2016-0224 ◽

2018 ◽

Vol 37 (5) ◽

pp. 455-462 ◽

Cited By ~ 2

Author(s):

Jiankang Huang ◽

Jing He ◽

Xiaoying He ◽

Yu Shi ◽

Ding Fan

Keyword(s):

Weld Pool ◽

Specular Reflection ◽

Three Dimensional ◽

Welding Process ◽

Surface Shape ◽

Weld Penetration ◽

Dynamic Development ◽

Pool Surface ◽

Gtaw Process ◽

Weld Pool Surface

AbstractThe weld pool contains abundant information about the welding process. In particular, the type of the weld pool surface shape, i. e., convex or concave, is determined by the weld penetration. To detect it, an innovative laser-vision-based sensing method is employed to observe the weld pool surface of the gas tungsten arc welding (GTAW). A low-power laser dots pattern is projected onto the entire weld pool surface. Its reflection is intercepted by a screen and captured by a camera. Then the dynamic development process of the weld pool surface can be detected. By observing and analyzing, the change of the reflected laser dots reflection pattern, for shape of the weld pool surface shape, was found to closely correlate to the penetration of weld pool in the welding process. A mathematical model was proposed to correlate the incident ray, reflected ray, screen and surface of weld pool based on structured laser specular reflection. The dynamic variation of the weld pool surface and its corresponding dots laser pattern were simulated and analyzed. By combining the experimental data and the mathematical analysis, the results show that the pattern of the reflected laser dots pattern is closely correlated to the development of weld pool, such as the weld penetration. The concavity of the pool surface was found to increase rapidly after the surface shape was changed from convex to concave during the stationary GTAW process.

Download Full-text