Tensile stress-strain analysis of resistance spot weld using non-linear FEM with experimental verification

This research presents an investigation on stress-strain behavior induced by resistance spot weld followed by tensile shear test. The spot weld is modeled according to standardized dimension for tensile test with main material properties of Cu as electrode and low carbon steel S235 as plates with 1mm thickness which include electric conductivity, resistivity and heat transfer coefficient for solid body as well as a contact interface. The FEM simulation is conducted using the process parameter of current between 6,000 A to 15,000 A, force at 5,000 N and different stages of time following the welding process and tensile test which is carried out after releasing both of the electrodes and material reaches the initial temperature with contact clamp velocity of 5mm/min. To ensure the glued elements between the plates, subroutine in MSC Marc/Mentat is used in the simulation with defined temperature. The outcome of simulation results will be verified with series of experiments. It is expected that simulation will give good agreement compared to experimental analysis within acceptable range of error.

Comparative HAZ softening analysis of three different automotive aluminium alloys by physical simulation

The development of high strength aluminium alloy has revolutionized the automotive industry with innovative manufacturing and technological process to provide high-performance components, weight reduction and also diversified the application field and design consideration for the automotive parts that work under severe conditions, but the selection of proper production parameters is most challenging task to get excellent results. Growing industrial demand of aluminium alloys led to the development of new welding technologies, processes and studies of various parameters effects for its intended purposes. The microstructural changes lead to loss of hardening and thereby mechanical strength in the HAZ welded joint even though the base materials are heat treatable and precipitation hardened. So, our goal is to analyse HAZ softening and analyse the sub-zones as a function of the parameter. In this paper, the influence of weld heat cycle on the heat-affected zone (HAZ) is physically simulated for Tungsten Inert Gas Welding (TIG) using Gleeble 3500 thermomechanical simulator for three different automotive aluminium alloy (AA5754-H22, AA6082-T6 & AA7075-T6) plate of 1 mm thickness. In order to simulate the sub-zones of the heat-affected zone, samples were heated to four different HAZ peak temperatures (550 °C, 440 °C, 380 °C and 280 °C), two linear heat input (100 J/mm and 200 J/mm) by the application of Rykalin 2D model. A series of experiments were performed to understand the behaviour, which make it possible to measure the objective data on the basis of the obtained image of the aluminium alloys tested with heat-affected zone tests in a Gleeble 3500 physical simulator. The main objective is to achieve the weldability of three different automotive aluminium alloys and their comparison based on the welding parameters like heat input. Further, the investigation of HAZ softening and microstructure of the specimens were tested and analysed using Vicker's hardness test and optical microscope respectively. The paper focuses on HAZ softening analysis of different grades of aluminium alloys for automotive application.

Experimental and simulation study of phase transformation in thermite welded railway steel heat-affected zone regions

Rail transportation has been an emerging and promising transportation method for economic development in Thailand and several countries. Thermite welding is one of the major welding and joining processes used to weld rail steel both during construction and maintenance. Unlike most welding processes in which heat is generated by electrical energy, thermite welding use heat generated during the chemical reactions between iron oxide and aluminum or other metallic compounds to create the weld. The amount of heat generated is thus depended on the composition and ratios of iron oxide, aluminum, as well as other metallic compounds mixed in the thermite powder. In addition, the size, shape, and material used for thermite mold could also play an important role in the heat transfer process during thermite welding of rail steel. In this research, SYSWELD software developed by ESI Group is used to perform thermal-mechanical-metallurgical welding simulation during thermite welding of rail steel. The current article presents that research methodology used to formulate the prediction of microstructure developed in the heat-affected zone regions of thermite welding of railway steel. It is noted that this work attempts to evaluate how preheat, heat generation during chemical reaction, and possible post-weld heat treatment could be performed to controlled the microstructure of pearlitic rail steel using SYSWELD software. The results of this on-going research will be used as the baseline for future development of structural integrity program for improving joining of rail steel such as the design and selection of welding processes and materials involved for rail construction, especially when appropriate grades and welding procedures of rail steels must be chosen and developed to withstand the actual loading conditions.

Hybrid laser arc welding: State of the art in technology

Hybrid laser arc welding is complex process where two heat sources act simultaneously in a common weld pool. The synergy effect of laser beam and electric arc offers several advantages over other individual technological processes, such as: higher welding speed, increased productivity, deeper penetration, better gap bridging ability, stable process, less heat input to the welding material, etc. However, the combination of two heat sources in a single welding process leads to large number of parameters that need to be synchronized and optimized in order to obtain a perfect weld. This paper presents the current state of hybrid laser arc welding in terms of its development, industrial application and scientific research. The introduction part contains a general overview of the hybrid laser arc welding process, its advantages and operating principles, and chronological development. In the second part, welding parameters that directly influence on the hybrid process have been discussed. The third part presents the performance and weld qualities achieved by hybrid welding process in accordance with previous research. In the final part, examples of industrial application and conclusions for further research and development related to hybrid laser arc welding are given.

Effect of post-weld tempering treatment on performance of DP600 spot welded joint

In order to meet the increasing requirements of the automotive industry for material strength grades and performance, the application of advanced highstrength steel automotive panels, represented by dual-phase steel, in lightweight vehicle bodies is increasing. Resistance spot welding is the main joining process for vehicle body manufacturing. How to improve the tensile strength and fatigue performance of dual-phase steel resistance spot welding joints is of great significance to the welding structure of the body. In this paper, resistance spot welding of cold rolled DP600 dual phase steel in the welding current range of 9000A-12000A was carried out. The effects of post-weld tempering treatment on microstructure, microhardness, shearing and fatigue of joints were compared. The results show that the microstructure transformation occurs in the weld nugget area after post-weld tempering, and the tempered martensite appears to reduce the microhardness of the weld nugget area; the nugget diameters, tensile-shear strength and failure energy are all higher than those without tempering treatment; tempering improves the fatigue strength of the spot joints, and regardless of whether the welded joints are tempered, cracks are all generated near the heat affected zone of the joint after fatigue test.

Dissimilar metal joining by ultrasonic welding

The dissimilar metal welding always challenges. The different alloys have different physical and mechanical properties. In the case of the electronic component of the car, it needs to establish a joint between dissimilar metals. The useful metals are for this application are copper and aluminium. Even that has good conductivity, corrosion resistance and formability. By fusion welding technologies these thin metal workpiece joining is not a simple technology. To use a solid state welding technology can be a suitable solution to establish a cohesion joint in case of this task. It well-known much suitable technologies, even that all of them has advantages and disadvantages. The choice of solid-state technology is the ultrasonic welding process. In the case of this process, we use pressure and high-frequency vibration for welding. Besides this process, the friction and vibration generated heat is lower than the metal melting temperature. The base of this technology is the ultrasound-assisted high-level formability. The optimization of this dissimilar joining technology parameters needs many pre-welding and testing process. In this work, we wanted to introduce this empirical optimization process.

Residual stress management: Recent advances in engineering methods for non-destructive measurement and beneficial redistribution of residual stresses

Welding is used widely in the automotive industry for joining a variety of structural components and parts. Of paramount importance in these structures are their engineering properties, such as fatigue life, distortions, dimensional stability and corrosion resistance that can be affected considerably by the presence of residual stresses (RS). The knowledge of RS and the ability to control their distribution in welded structures is critical when evaluating their fatigue life and preventing catastrophic failures. An engineering concept of residual stress management (RSM) has been developed that addresses all aspects of residual stresses in structural elements. RSM includes three major stages in stress management, i.e. RS determination, RS analysis and RS redistribution. Using this approach, stresses in structures and materials can be evaluated in each specific case either theoretically or experimentally and the performance and fatigue behavior of such structures optimized. This paper is built as an overview of the RSM concept and its application in the fields of non-destructive measurement of residual and applied stresses and in treatment of structures with residual stresses to achieve better performance and longer fatigue life. All three stages of the RSM concept will be discussed and for each of the stages practical engineering approach examples will be given. An example of a project in which the residual stress distribution in a filet welded joint was measured, analyzed and changed by post-weld treatment will be presented to demonstrate the effectiveness of the RSM approach. The advancements in the modern tools used in this project for non-destructive measurement of residual stresses using an ultrasonic computerized complex for residual stress measurement and the ultrasonic peening for redistribution of the residual stresses that allowed improving the quality of the welds and increasing their fatigue life will also be presented.

Effect of boron and manganese on hot crack resistance and toughness for flux cored arc weldments of 550 MPa grade tensile strength

The hot crack resistance and mechanical properties of flux cored arc (FCA) welds were investigated with three kinds of welding consumables having different boron (B) and manganese (Mn) contents for high strength carbon steel. The hot crack resistance measured from self-restraint testing strongly depended on the amount of B in the welding consumable. Welding consumable with higher B contents resulted in longer total crack length and an increased number of cracks. Boron was intensely detected near the grain boundary of the weld centerline by secondary ion mass spectrometry (SIMS) analysis, and precipitated with boron carbide (Fe23(C,B)6), as analyzed by transmission electron microscopy (TEM). This promoted hot crack propagation in the high strength carbon steel welds. However, removing B from the welding consumable decreased the low temperature toughness for root and face weld metal due to the growth of Ferrite Side Plate (FSP) in comparison with welding consumables having more B or Mn contents. The addition of Mn in the weld metal suppressed the formation of FSP and increased the low temperature toughness. Therefore, the minimization of B and the supplement of Mn successfully achieved hot crack resistance and low temperature toughness for high strength carbon steel welds of 550 MPa tensile strength.

Research on water-air plasma cutting process of carbon steel

The principle and equipment of water-air plasma cutting has been introduced in this paper. Especially, the function of water is not only to prevent the cutting pool from oxidizing in the form of a water curtain, but also to generate plasma in the center of arc. The Numerical Model of Low temperature Plasma has been eatablished with equation of energy, status, motion and chemical dynamic equation. Working process, mechanical properties and micro-structural features of 20 mm carbon steel processed by water-air plasma cutting and air plasma have been investigated, which choose the same parameters. The voice of plasma arc and dust of pool are being limited in the area of water curtain, so that the noise and dust of water air plasma cutting can be compared favorably with under-water plasma cutting. Lower temperature of water-air cutting plates is due to the fluent water taking off energy of metal pool during cutting. It is impossible to find oxide layer on the incisions surface of water-air plasma cutting, and the heat affected zone is so thin that welding can be carried out directly after cutting without any else process. So inclusion also can be avoided in the weld. But for air plasma cutting, lot of time is waste to remove oxide layer by mechanical polishing before welding. With the help of addition plasma arising from water, the water-air plasma arc becomes stronger, so smooth and high flatness cutting surface can be acquired. Compared with the technology of air plasma cutting, water-air plasma cutting has benefits of friendly working environment, higher quality incision and lower cost.