Papers by Author: Guan Long Chen

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Authors: Xin Zhao, Xin Min Lai, Yan Song Zhang, Guan Long Chen, P.C Wang
Abstract: With the implementation of crash-toughened adhesives in automotive industry, adhesive bonding has become one effective joining technology instead of resistance spot welding especially for AHSS materials because of its better fatigue performance and greater flexibility. However, while chisel test has been widely used for resistance weld inspection, no practical inspection method is available for adhesive bond discrepancies identification. The inspection method we need for use in a high-volume, low-cost production environment should be fast, convenient, nondestructive, cost-effective, and able to effectively assure some minimum acceptable level of joint quality. The method we finally conducted was based on the weld-bonding process of different adhesive bonding joints by acquiring and analyzing the dynamic welding parameters’ signal curves such as the electrode displacement and dynamic resistance from different sensors installed onto the welding gun. Based on the integrated inspection system, lots of experiments and analysis showed that this inspection method is basically feasible, that is, it could identify different adhesive bond discrepancies qualitatively and accurately. Especially, the on-line inspection is conducted before the complete curing of joints in paint shop. If the inspection results are nonideal and some discrepancies are detected, the further repairing work is much easier and cost-effective. So the inspection method has a good potential especially applied in production line. The findings in this study provide the guidelines for using adhesive bonding AHSS materials in automotive industry.
Authors: Xin Zhao, P.C Wang, Yan Song Zhang, Guan Long Chen, Xin Min Lai
Abstract: Adhesive bonding technology has become one effective joining technology instead of the traditional spot-welding especially for AHSS materials. But Adhesive bond quality inspection method is limited to the mechanical performance tests such as tensile-shear test recently and it’s time-consuming and unpractical. So a reliable and practical method for on-line identifying different bond discrepancies and assessing the bond quality is necessary in industry. Based on the thermal expansion electrode displacement mechanism during weld-bonding process, the dynamic electrode displacement method could be applied for differentiating adhesive bond discrepancies effectively through acquiring and analyzing the dynamic electrode displacement signal curves during weld-bonding process from laser displacement sensors installed onto the welding gun. Lots of experiments and analysis showed that this method is basically feasible, that is, it could identify different adhesive bond discrepancies qualitatively and accurately. So it has a good potential especially applied in production line.
Authors: A.H. Luo, Guan Long Chen
Abstract: Projection welding is a variation of electric resistance welding with the dynamic changes of the flow paths for heat and electrical properties with changing temperature caused by the large plastic deformation with collapse of projection. The common standards of projection welding are AWS, IIW and Harris& Riley which have been established and in use for some time. All these standards have the slots located under the projection. However, the standard proposed in this paper researches on is a special one with the slots designed on the two sides of the projection. A comprehensive thermal-electrical-mechanical analysis was performed to quantitatively simulate the projection welding of the special standard by a coupled finite element method. The electrical, thermal and mechanical aspects of the projection welding processes such as the projection collapse mechanism, the nugget formation process and the effects of different electrode forces were discussed in this paper.
Authors: Xiao Yun Zhang, Yan Song Zhang, Guan Long Chen
Abstract: Dual-phase steel is a mixture of ferrite matrix and martensitic islands distributed at grain boundaries with the possible addition of bainite. Its formability, capacity to absorb crash energy, and ability to resist fatigue make it a desirable material for use in the automotive industry to enhance automobile’s strength and reduce its weight. However, the resistance spot weldability of dual-phase steel is sometimes limited by a propensity for weld metal failure due to the welding process. To improve its weldability, a servo gun spot welding system is introduced to control electrode force during the welding process. The paper take 1.5mm DP600 steels as an example, experimental data shows that by optimizing electrode force during welding process, the width of weld lobe can be enlarged from 0.9kA to 2.1kA and the weldability of dual phase steel is improved greatly.
Authors: Chang Ming Qian, Yan Song Zhang, Xiao Yun Zhang, Guan Long Chen
Abstract: In order to reduce vehicle weight and improve crash performance, dual-phase (DP) steels are increasingly used for lightweight auto-body. the high cooling rates in Resistance spot welding (RSW) process will make the nugget very brittle and result in interfacial fracture modes. In this study, a servo resistance welding system is firstly introduced to control process parameters during the welding process. The influences of different process parameters (weld current, weld time and electrode force) on the weld strength, nugget diameter, facture modes and weld indentation are analyzed. Finally, an on-line weld failure mode inspection method is proposed based on servo gun’s feedback characteristics.
Authors: Yong Bing Li, Xin Min Lai, Guan Long Chen
Abstract: Resistance spot welding process is strongly related to interfacial contact behaviors. The effects of thermal contact is rarely investigated so far and generally ignored in numerical models. In this work, a parametric FE model, which considers the variation of the surface roughness of the electrodes and workpieces, has been developed to investigate the effects of thermal contact on weld nugget formation. With the parametric model, four cases, e.g. ideal smooth surface, minimal roughness surface and maximum roughness surface for steel sheets and electrodes of as-received condition, and highly rough electrode surface, are investigated. Researches show that when the surface roughness of the electrodes exceeds some limit, the thermal contact conductance will substantially affect the weld nugget formation, therefore, must be considered in numerical models to precisely predict welding process.
Authors: Hong Qing Shen, Shu Hui Li, Guan Long Chen
Abstract: In this paper, the mechanism of surface low defect in sheet metal stamping is studied. Firstly, we simulate the forming procedure of a stamping component by Finite Element Method (FEM) to observe the growth of surface low defect. And then, we establish an analytical model and deduce the critical stress for local buckling. Finally, we take advantage of the critical stress to detect local buckling areas in the component. The FE simulation result shows that during springback the non-uniform displacement in the thickness direction forms surface low. Moreover, the detected local buckling area agrees with the experimental surface low area. This indicates that the essence of surface low phenomenon is panel’s local buckling under the residual compressive stress during springback.
Authors: Xin Min Lai, Xin Zhao, Yan Song Zhang, Guan Long Chen
Abstract: The current inspection methods of spot-weld quality are difficult to achieve an ideal result especially for the stick-weld defect which is one of the most important types of spot-weld defect in the automotive body. This paper thus developed one fast-identification method to identify the joint defects quickly and efficiently based on quantitative analyzing the echo characteristics of ultrasonic curves that could reflect the spot-welding joint defects. The echo-characteristic parameters were analyzed quantitatively through the decision-making bintree of defects and ART networks. After knowledge acquiring and information processing, a fast-identification expert system (FIES) was developed to identify the automotive body spot-weld defects, through collecting the standard ultrasonic curves and quantitatively analyzing. Finally, a series of experiments were conducted to verify the proposed methods and the results showed that FIES is credible and the identification rate can exceed 95% in total test samples.
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