Showing papers on "Electric resistance welding published in 2013"

Failure mode of spot welds: interfacial versus pullout

Abstract: Spot welds produced via resistance welding have been widely used in the joining of sheet metal for autobodies since the 1950s. Every modern car contains over 2000 spot welds. Failure of the spot weld is therefore an important concern in relation to autobody durability and safety design. Spot welds can fail in two completely distinct modes, namely, nugget pullout failure and interfacial failure. In the present paper, it is first shown that the nugget pullout failure is caused by plastic collapse and the interfacial failure is governed by crack or fracture mechanics. These two failure mechanisms compete with each other and failure of a spot weld occurs when the fracture criterion for one of the mechanisms is satisfied first. Test data from available literature are used to validate the theoretical predictions. Recommendations are made for minimum weld nugget size for a given sheet metal thickness so that nugget pullout failure, the acceptable mode of failure in industry, is ensured.

Process and performance evaluation of ultrasonic, induction and resistance welding of advanced thermoplastic composites:

Abstract: The possibility of assembling through welding is one of the major features of thermoplastic composites and it positively contributes to their cost-effectiveness in manufacturing. This article prese...

Advanced gas metal arc welding processes

Abstract: There is an increased requirement in the automotive, food and medical equipment industries to weld heat-sensitive materials, such as thin sheets, coated thin plates, stainless steel, aluminium and mixed joints. Nevertheless, relevant innovations in arc welding are not widely known and seldom used to their maximum potential. In the area of gas metal arc welding welding processes, digitalisation has allowed integration of software into the power source, wire feeder and gas regulation. This paper reviews developments in the arc welding process, particularly the effect of the set-up of the welding process parameters on waveform deposition. It is found that good weldability, good mechanical joint properties and acceptable process efficiency can be obtained for thin sheets through advanced power source regulation, especially over short circuiting, controlled polarity and electrode wire motion. The findings presented in this paper are valuable for waveform and deposition prediction. The need is furthermore noted for an algorithm that integrates gas flow parameters and wire motion control, as well as a variable sensor on the tip of the electrode, permitting flexibility of control of the current and the voltage waveform.

Ultrasonic Welding of Aluminum Alloys to Fiber Reinforced Polymers

Abstract: To realize multi-material structures, e.g., out of light metals and fiber reinforced polymer (FRP) composites suitable joining methods are required. The ultrasonic metal welding technology was applied to produce high strength joints between different aluminum alloys and carbon fiber reinforced polymers (CFRPs) in the framework of research unit 524 of the German Research Foundation. The bonding mechanisms were characterized by light optical and scanning electron microscopy (SEM). The performed analysis have shown a bonding zone with an intensive contact between the metallic surface and the load bearing carbon fibers of the CFRP as a result of the ultrasonic welding process. Using precipitation hardening aluminum alloy AA2024 tensile shear strengths of up to 58 MPa could be achieved. In comparison to established joining techniques ultrasonic metal welding can be an interesting alternative to realize dissimilar joints for the automotive or aircraft industry.

Effect of welding energy on interface zone of Al–Cu ultrasonic welded joint

Abstract: Ultrasonic welding is attracting increasing attentions in joining of dissimilar materials. The effect of welding energy on joint strength, failure behaviour and microstructure of Al–Cu ultrasonic w...

Solid-state welding of aluminum to copper—case studies

Abstract: This paper describes procedures for the joining of aluminum with copper via solid-state welding. Welding of dissimilar materials in order to reach a high strength and durable joints is a reasonable and outstanding challenge for industrial and especially for automotive applications. Nowadays, wiring and electrical systems, as for example batteries, turn out to be main drivers for new developments in the field of dissimilar joining technologies. Joining of aluminum to copper through a melting process leads to brittle intermetallic compounds, which cause failure of the joint already during cool down. Solid-state welding technologies allow the welding below melting temperature, so that phenomena at the interface, which lead to the formation of intermetallics under different conditions, are of interest to the resulting joint properties. Not only mechanical properties, but electrical resistivity and heat conduction are strongly dependent on those effects. Diffusion welding is performed as a model welding procedure, while friction stir welding and hybrid friction diffusion bonding are investigated as technological welding processes in this paper.

Microstructural Characteristics of a Stainless Steel/Copper Dissimilar Joint Made by Laser Welding

Abstract: The microstructures and its formation mechanism of a stainless steel/copper dissimilar joint by laser welding were investigated. It was found that the two modes of joining, i.e., welding-brazing and fusion welding, depend on different processing parameters. In the welding-brazing mode, the interface between copper and the fusion zone has scraggy morphology because the molten pool is frozen by solid copper with high thermal conductivity. The interdiffusion of elements occurs in the neighborhood of the interface, which leads to the metallurgy bond of the mode. In the fusion welding mode, the liquid phase in the fusion zone undergoes not only primary but also secondary liquid separation due to the high cooling rate and high supercooling level of laser welding. Some microcracks generated in the fusion zone by thermal stress mismatch are healed by liquid copper filling.

Effect of input current modes on intermetallic layer and mechanical property of aluminum–steel lap joint obtained by gas metal arc welding

Abstract: This paper studies Al–steel lap joints resulted from direct-current pulsed gas metal arc welding (DPG) and alternate-current double-pulse gas metal arc welding (ADG). Base metals being welded are 1 mm thick 5052 Al alloy sheet and 1 mm thick galvanized mild steel sheet with filler metal being 1.2 mm 4047. Effect of the different welding processes on joint properties is studied through characterization of the steel/Al interphases and mechanical strength. It is found that the thickness of intermetallic compound layer composed of Fe2Al5, FeAl3and Fe3Al, and the diffusion of Fe element from steel to weld seam are dependent on the amount of welding heat input. Lap shear samples of Al–Fe joints resulted from the ADG process fractured at Al base metal or weld seam with average ultimate tensile strength (UTS) of 201 MPa. On the other hand, all lap shear samples of the joints resulted from DPG process fractured along the interphase between the Fe2Al5 sub-layer and the steel sheet with average UTS of 115 MPa. ADG process offers higher joint strength than that offered by DPG process due to thinner intermetallic compounds layer caused by the reduced heat input, illustrating that cyclic polarity switching and a secondary low frequency current pulse can effectively reduce the heat input in joining Fe–Al dissimilar materials, which means the ADG process is much more feasible for making robust Fe–Al lap joints.

Improving aluminum resistance spot welding in automotive structures

Abstract: The majority of automotive body shop welding consists of resistance spot welding (RSW) steel sheet due to its inherently low cost and high speed. With the introduction of aluminum, it is desirable ...

Understanding the process parameter interactions in multiple-pass ultra-narrow-gap laser welding of thick-section stainless steels

Abstract: In laser welding, typical welding penetration depths are in the order of 1–2 mm/kW laser power. The multipass laser welding technique, based on the narrow-gap approach, is an emerging welding technology that can be applied to thick-section welds by using relatively low laser power, but the process is more complicated since it is necessary to introduce filler wire to narrow-gap weld configurations. The aim of this work was to understand significant process parameters and their interactions in order to control the weld quality in ultra-narrow-gap (1.5 mm gap width) laser welding of AISI grade 316L stainless steel. A 1-kW IPG single-mode fiber laser was used for welding plates that were 5 to 20 mm in thickness using the multiple-pass narrow-gap approach. Design of experiments and statistical modelling techniques were employed to understand and optimise the processing parameters. The effects of laser power, wire feed rate, and welding speed on the weld homogeneity, integrity, bead shape, gap bridgability and surface oxidation were studied. The results were evaluated under different optimising constraints. The results show that the models developed in this work can effectively predict the responses within the factors domain.

Diode laser welding of high yield steel

Abstract: The following article describes results of investigations on influence of laser welding parameters on the weld shape, quality and mechanical properties of 2.5 mm thick butt joints of thermo-mechanically rolled, high yield strength steel for cold forming S420MC (according to EN 10149 - 3 and 060XLK according to ASTM) welded with high power diode laser HPDL ROFIN SINAR DL 020 with rectangular laser beam spot and 2.2 kW output power, and 808 nm wavelength. The investigations at the initial stage were focused on detailed analysis of influence of the basic laser welding parameters such as laser power and welding speed on the shape and quality of single bead produced during bead-on-plate welding. Then the optimal parameters were chosen for laser welding of 2.5 mm thick butt joints of the thermo-mechanically rolled, high yield strength steel sheets for cold forming S420MC. The test joints were prepared as single square groove and one-side laser welded without an additional material, at a flat position. Edges of steel sheets were melted in argon atmosphere by the laser beam focused on the top joint surface. The test welded joints were investigated by visual inspection, metallographic examinations, mechanical tests such as tensile tests and bending tests. It was found that the high power diode laser may be applied successfully for one-side welding of the S420MC steel butt joints. Additionally it was found that in the optimal range of laser welding parameters the high quality joint were produced.

FEM based prediction of phase transformations during Friction Stir Welding of Ti6Al4V titanium alloy

Abstract: Friction Stir Welding (FSW) is a solid state welding process patented in 1991 by TWI; initially adopted to weld aluminum alloys, it is now being successfully used also for high resistant materials. Welding of titanium alloys by traditional fusion welding techniques presents several difficulties due to high material reactivity with oxygen, hydrogen, and nitrogen with consequent embrittlement of the joint. In this way FSW represents a cost effective and high quality solution. The final mechanical properties of the joints are strictly connected to the microstructural evolutions, in terms of phase change, occurring during the process. In the paper a 3D FEM model of the FSW welding process, based on a thermo-mechanical fully coupled analysis, is presented. The model, tuned both for the thermo-mechanical analysis and the phase transformation through experimental data, is able to predict the phase volume fraction in the typical zones of the joints at the varying of the main process parameters. The obtained results permit to assess that the tuned FEM model of the FSW process can be utilized as an effective design tool.

Welding of titanium alloy by Disk laser

Abstract: The following article describes results of investigations on influence of laser welding parameters on the weld shape, quality and mechanical properties of 2.0 mm thick butt joints of titanium alloy Ti6Al4V (Grade 5 according to ASTM B265) welded with a new generation disk laser TRUMPF TRUDISK 3302, emitting at 1030 nm, with maximum output power 3300 W at circular laser beam spot, characterized by laser beam divergence 8.0 mm•mrad. The test butt joints of Ti6Al4V titanium alloy sheets were prepared as single square groove (I-type joint) and one-side laser welded without an additional material, at a flat position, using a specially designed system for shielding gas (purity 99.999%). The investigations at the initial stage were focused on detailed analysis of influence of the basic laser welding parameters such as laser power and welding speed on the shape and quality of single bead produced during bead-on-plate welding. Then the optimal parameters were chosen for laser welding of 2.0 mm thick butt joints of the titanium alloy Ti6Al4V. Edges of the titanium alloy sheets were melted in argon atmosphere by the laser beam focused on the top surface of butt joints. The test welded joints were investigated by visual inspection, metallographic examinations, hardness and micro-hardness measurements and mechanical tests such as tensile tests and bending tests. It was found that the welding mode is a keyhole welding and providing high quality of joints requires a special techniques and conditions of laser welding, as well as special gas shielding nozzles is required.

Double-sided fiber laser beam welding process of T-joints for aluminum aircraft fuselage panels: Filler wire melting behavior, process stability, and their effects on porosity defects

Abstract: Aluminum alloy T-joints for aircraft fuselage panels were fabricated by double-sided fiber laser beam welding with filler wire, and the influence of the wire feeding posture on the welding process stability was investigated. A CMOS high speed video system was used to observe the wire melting behavior and the weld pool dynamics in real time during the welding process by using a bandpass red laser with an emission wavelength of 808 nm as backlight source to illuminate the welding zone. The weld porosity defects were analyzed by X-ray radiography. The effects of wire feeding posture on the wire melting behavior, process stability, and porosity defects were investigated. The experimental results indicated that three distinct filler material transfer modes were identified under different wire feeding positions: liquid bridge transfer mode, droplet transfer mode, and spreading transfer mode. The liquid bridge transfer mode could guarantee a stable welding process, and result in the lowest porosity. Compared with wire feeding in the leading direction, the process was not stable and porosity increased when wire feeding in the trailing direction. Increased in the wire feeding angle was disadvantage for pores to escape from the weld molten pool, meanwhile, it made the welding process window smaller due to increasing the centering precision requirement for adjusting the filler wire.

Analysis and Comparison of Friction Stir Welding and Laser Assisted Friction Stir Welding of Aluminum Alloy.

Abstract: Friction Stir Welding (FSW) is a solid-state joining process; i.e., no melting occurs. The welding process is promoted by the rotation and translation of an axis-symmetric non-consumable tool along the weld centerline. Thus, the FSW process is performed at much lower temperatures than conventional fusion welding, nevertheless it has some disadvantages. Laser Assisted Friction Stir Welding (LAFSW) is a combination in which the FSW is the dominant welding process and the laser pre-heats the weld. In this work FSW and LAFSW tests were conducted on 6 mm thick 5754H111 aluminum alloy plates in butt joint configuration. LAFSW is studied firstly to demonstrate the weldability of aluminum alloy using that technique. Secondly, process parameters, such as laser power and temperature gradient are investigated in order to evaluate changes in microstructure, micro-hardness, residual stress, and tensile properties. Once the possibility to achieve sound weld using LAFSW is demonstrated, it will be possible to explore the benefits for tool wear, higher welding speeds, and lower clamping force.

Trends in Joining Dissimilar Metals by Welding

Abstract: The welding of dissimilar materials finds a wide variety of applications in the fields of industrial construction and manufacturing, where the characteristic features of the different materials are optimized for the desired application to result in cost effectiveness and value addition. Non-fusion welding methods such as solid state welding and high energy beam welding are more popular for welding dissimilar metal combinations, due to fewer complications, than fusion welding, which melts the base metal and forms brittle intermetallic compounds (IMCs) that may lead to failure. Various factors have to be considered when assessing the feasibility of welding dissimilar metals and producing a sound weld joint. This paper presents a broad classification of the most commonly used welding processes for dissimilar materials, discusses some of the commonly used welding processes with examples of some common material combinations, critical factors for good welding, and practical difficulties arising from the physical and chemical properties of materials. From the findings, it can be inferred that continuous improvement and research is still required in the field of dissimilar metal welding, particularly in the light of increasing demand for tailored material for modern engineering and industrial applications.