NDTnet 1998 Aug, Vol.3 No.8

Abstract

Welding today is an inseparable part of industries, plants and components. Present day welding science and technology has laid emphasis on the development of intelligent welding systems and processes. Intelligent welding (IW), combines welding equipment with intelligent sensing and control through smart sensors, knowledge of human experts, and artificial intelligence.. This technology if effectively implemented results in products with improved quality, reduced scatter in properties and cuts down in energy requirements. Different control methods such as use of dynamic circuit resistance, have been used to achieve good weld quality. The latest trend in IW involves the use of nondestructive evaluation (NDE) sensors. In this paper, the authors establish the feasibility on the use of thermal imaging and acoustic emission for monitoring resistance spot welding and end cap welding. While both these techniques give information about the inhomogeneities within a material, they are complementary to each other. The AE signals generated during spot welding and end capwelding were recorded using PZT transducers having resonant frequency of 175 kHz and 150 kHz respectively. Thermal images were captured using the Thermovision 870 scanner and recordedon a modified video thermal recorder.

Trial spot welds on carbon steel plates of thickness 1.6 mm have been created using different welding parameters (current and welding time) resulting in good and bad welds. End cap welding iswidely used for welding of nuclear fuel elements. A number of Zircaloy -2 fuel elements with diameter of about 17 mm were welded with imperfections such as end squareness, improper penetration, tube bending, ovality of tubes, graphite impurities etc. Analysis of the AE signals in both the cases indicated that good spot welds and end cap have a higher AE activity as compared to the bad welds. In the case of thermography, analysis of the nugget diameters in case of spot welds indicated that the radius of the nugget is unequal for the bad welds as compared to the good ones. In the case of end cap welds, good welds indicated thermal pattern with uniform isothermal width while the thermal image of the welds with imperfections has a nonuniform isothermal width. Hot spotswere also observed in the thermal image of welds in which sparking occurred due to the presence of tube imperfections.

Abstract Source:
Book of Abstracts, 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN: 87-986898-0-00

Full-Text Source:
Proceedings of the 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN:

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