Numerical simulation of tensile strength of upset welded joints with experimental verification Mohsen Hamedi a , Hamid Eisazadeh b, * , Mousa Esmailzadeh c a School of Mechanical Engineering, University of Tehran, North Kargar at Jalal-Exp Way, Tehran 1439957131, Iran b Department of Mechanical Engineering, Chabahar Maritime University, Chabahar, Sistan va Balochestan 9971756499, Iran c School of Mechanical Engineering, University of Tehran, Iran article info Article history: Received 3 September 2009 Accepted 4 December 2009 Available online 11 December 2009 Keywords: Numerical simulation Resistance welding Upset welding Tensile strength Post-weld heating time Post-weld heating current abstract Resistance upset welding (UW) is a widely used process for joining metal parts. In this process current, time and upsetting force are three parameters that affect the quality of welded products. This paper con- siders numerical simulation and experimental investigation of UW process parameters. The investigated parameters include heating and post-weld heating current and their corresponding duration as well as interference of the part features that form the joint. In this study, evaluation of tensile strength of the welded joint with variation of the process parameters is also reported. For numerical analysis, a two- dimensional axisymmetric model using a coupled electro-thermal finite element method is developed to study the thermal behavior of the welded joints. The results of this numerical simulation are used to determine the status of the weldment and therefore evaluate the quality of the weld at the joint. Both numerical and experimental results suggest an optimum set of welding parameters, i.e. time and electri- cal current that yields a maximum value for the tensile strength of the joint. Also the effects of post-weld heating time and current on the tensile strength are evaluated and show that these parameters have a remarkable effect on improving tensile strength of the weldment. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction Resistance upset welding is a solid-state welding process which involves the interaction of electrical, thermal, mechanical and met- allurgical phenomena. In this process, the joining surfaces are kept at a forced contact; followed by a high electric current passing through the workpieces. Due to contact resistance and joule heat- ing, a vast amount of heat is generated at the faying surfaces. Be- fore, during and after applying the electric current, force is applied to maintain the electric current continuity and to provide the pressure necessary to form the weld zone. The metal at the joint is heated to a temperature where re-crystallization can rap- idly occur across the heated surfaces. In this process, similar to other resistance welding processes, there is no requirement to any extraneous material such as filler material or shielding gasses [1]. The general configuration of parts and equipments in upset welding is shown in Fig. 1. Compared to typical fusion welding pro- cesses, the UW process has advantages such as speed, ease of con- trol, fewer defects, enhanced weld properties, simplicity of equipment and the ability to join difficult-to-weld materials. These qualities make UW an appropriate welding process to be utilized in various industrial settings; such as assembling automotive bodies, sealing of containers of high-level nuclear waste, joining steel materials, super alloy materials, aluminum alloys and parts made of dissimilar materials. In this study evaluation of tensile strength of an upset welded joint with variation of the process parameters is investigated through experiments and numerical simulation. 2. Literature review The first reported work on development of UW was the research done at NASA Lewis Research Center [2]. This project focused on magnetic resistance upset welding of stainless steel 304 plates with different thicknesses. Resistance welding of nuclear waste containers was another application of this technology which re- quired design of new equipment able to deliver currents of up to 400,000 A at 64,000 kgf. The same application was further reported in [3–5] where Kanne examined the properties of upset welded cylindrical and spherical components. He pointed out that advan- tages of UW, compared to fusion welding processes, include fewer defects and stronger welds with a faster and more reliable process. Cannell [4] used UW for welding canisters made of 304L stainless steel. Bezprozvannyi [6] at Paton Welding Institute reported upset 0261-3069/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.matdes.2009.12.011 * Corresponding author. Tel.: +98 21 88003318/9354; fax: +98 21 88003029. E-mail addresses: mhamedi@ut.ac.ir (M. Hamedi), heisazadeh@cmu.ac.ir, heisa- zadeh@gmail.com (H. Eisazadeh). Materials and Design 31 (2010) 2296–2304 Contents lists available at ScienceDirect Materials and Design journal homepage: www.elsevier.com/locate/matdes