Conventional Welding Processes Research Articles

Aluminothermic welding modeling of heavy haul rails using the element birth and death technique

The aluminothermic welding process (ATW) of rail tracks is the most used in the field due to its low cost, execution time, and light equipment. In recent years, some experimental and numerical models have been developed to study ATW. The accuracy of the models is still being demonstrated. In this work, a new three-dimensional thermoelastoplastic numerical model of the ATW process is proposed. This model uses the Element Birth and Death (EBD) technique with Ansys® software to accurately simulate filling the pouring region with filler metal. The thermal and mechanical phenomena of all stages of a conventional rail track welding process were considered, as well as the effects of the material’s phase transformations during the process. First, the validation was carried out with experimental and numerical data from studies available in the literature for UIC60 rails. Then, the validated model was applied in the simulation of welding a TR68-type rail and an unprecedented analysis of the residual stresses resulting from this type of rail was performed. The ATW process could then be simulated using significantly fewer elements than the numerical models available in the literature and proved to be applicable for the study of the ATW process of railway tracks.

Microstructures and mechanical properties of non-thinning and penetrating friction stir welded 2219-T6 aluminum alloy

The aim of this paper is to offer a novel friction stir welding technique to achieve non-thinning and lack of kissing bond welds with excellent mechanical properties. In the conventional friction stir welding (CFSW) process, a certain size spindle tilting angle and a shoulder plunge depth were applied in order to obtain high-quality welds. However, what was the reason for the thinning phenomenon of weld and thus the weakening of weld bearing capacity? The reduction of spindle tilting angle and shoulder plunge depth was likely to cause the welding tool not being able to reach the weld root, and thus, it was engendered for the kissing bond or the absence of complete penetration. In the present study, a novel welding tool with large size shoulder and Archimedes spiral groove was designed in order to achieve non-thinning and lack of kissing bond welds. The microstructures and mechanical properties of the joints obtained by the non-thinning and penetrating friction stir welding (NTPFSW) and the penetrating friction stir welding (PFSW) had been analyzed in detail. Compared with PFSW, NTPFSW had a narrow shoulder-affected zone. The thickness of NTPFSW joint is 0.1 mm thicker than that of BM and 0.22 mm thicker than that of PFSW joint. The stir zones (SZ) obtained by the PFSW and NTPFSW were both composed of fine equiaxed grains. The grains in the upper part of NTPFSW joint were larger in size, and the number of precipitates (θ’ phase) was less. NTPFSW completely eliminated the weld thinning phenomenon, and the tensile properties were 365 Mpa, which is 2% higher than that of PFSW.

Improvements in the Microstructure and Mechanical Properties of Aluminium Alloys Using Ultrasonic-Assisted Laser Welding

Welding high-strength aluminium alloys is generally a delicate operation due to the degradation of mechanical properties in the thermally affected zone (TAZ) and the presence of porosities in the molten metal. Furthermore, aluminium alloys contain compounds that solidify before the rest of the base alloy, therefore acting as stress concentration points that lead to the phenomenon of hot cracking. This paper investigates the process of applying ultrasonic vibrations to the molten pool aluminium alloy AA6082 to improve both its microstructure and mechanical properties. We analysed conventional and ultrasonic-assisted laser welding processes to assess the sonication effect in the ultrasonic band 20–40 kHz. Destructive and nondestructive tests were used to compare ultrasonically processed samples to baseline samples. We achieved a 26% increase in the tensile and weld yield strengths of laser welds in the aluminium plates via the power ultrasonic irradiation of the welds under optimum ultrasonic variable values during welding. It is estimated that the ultrasound intensity in the weld melt, using a maximum power of 160 W from a pair of 28 kHz transducers, was 35.5 W/cm2 as a spatial average and 142 W/cm2 at the antinodes. Cavitation activity was significant and sometimes a main contributor to the achieved improvements in weld quality.

Aspects Regarding Welding of DD13 Steel by Applying the FSW Process and some Processes Derived from it

Due to its characteristics, DD13 steel is recommended for various applications in the automotive field (including in the manufacture of components for car bodies). The paper presents solutions proposed by ISIM Timisoara for welding of DD13 steel, as alternative solutions to conventional welding processes. One solution that has proven to be viable for joining DD13 steel is the friction stir welding process (FSW). In terms of the quality of the welded joints obtained by applying the classic FSW welding process, these welds were excellent. In an attempt to obtain other benefits, mainly related to the efficiency of the welding process, ISIM Timisoara has developed research programs for the study and application of other methods based on the FSW process principle, namely: - hybrid friction stir welding ultrasonic assisted FSW-US; - friction stir welding in inert gas environment FSW – IG. The important effects due to the application of these methods are: improving (as appropriate) the degree of plasticization of the materials to be joined and increasing the degree of mixing of the materials as result of ultrasonic assistance of the FSW welding process; improvement of the welding process by reducing the pressing forces of the tool during welding, with an effect on increasing the service life of welding tool; respectively improving the aspect of the weld and some mechanical characteristics of the welded joints (at tensile tests, respectively static bending test). The obtained results showed that the two methods derived from the classical FSW welding process, can be used in industrial applications, with important benefits.

Friction stud riveting (FSR) of thick high-strength aluminum alloy structure

7-series aluminum (Al) alloy is a promising material that can meet the ever-increasing lightweight demand for transportation tools. However, the assembly between Al alloy and steel components brings challenges to the existing stud pre-embedded technology. This study proposes a friction stud riveting (FSR) process to achieve high-performance and high-efficiency embedding of steel studs in Al alloy parts by shank undercut, grooves interlock, and intermetallic compounds bonding. The stud geometry and FSR process were first optimized by evaluating the macro morphology of the joints. Then, the microscopic characterizations were performed to understand the material flow behavior, plastic deformation, and microstructure evolution of the joint induced by the feeding and rotation of the stud. The results indicate that the transient thermo-mechanical coupled FSR process leads to a continuous transition of sliding, mixed sliding-sticking, and sticking contact conditions between the stud and the Al alloy, resulting in a thermo-mechanical affected zone (TMAZ) outside the stud and a trapped Al alloy (TAA) inside the stud with diverse dynamic recrystallization (DRX) states and microstructures. The rotation state evolution and temperature gradients of the material within the TAA create two DRX bands that dominate the fracture behavior of TAA under tensile and shear loads. The strengths of the optimized steel stud-thick Al FSR joints reach 101.3% and 118.5% of the 7A52 Al alloy base material in tensile and shear tests, respectively, which solves the problem of low joining strength between steel stud and Al alloy plate due to the brittle and thick intermetallic compounds layers in conventional stud welding processes.

Effect of the welding technique on mechanical properties and metallurgical characteristics of the naval grade high strength low alloy steel joints produced by SMAW and GMAW

Naval grade, high strength low alloy (HSLA) steel is designed especially for shipbuilding applications due to its high strength to weight ratio. The conventional fusion welding processes of shielded metal arc welding (SMAW) and gas metal arc welding (GMAW) are employed widely for structural applications. This work reports the influence of welding processes on mechanical properties and metallurgical characteristics of fusion welded DMR249A grade steel. The evaluating tensile, impact, microhardness properties were correlated with microstructures. The maximum recorded transverse tensile strength value of SMAW and GMAW joints were 558 MPa and 578 MPa. The lower microhardness had obtained in the subcritical heat-affected zone than other regions. The weld zone microstructure consists of fine, elongated, and columnar grain structures. From this investigation, it has been concluded that GMAW joints displayed marginally better properties than SMAW joints. But most weld failures has been observed in the subcritical heat-affected region; due to grain deformation and subsequent softening in the weldment.

Comparative Studies on Influence of Tool Geometry on Heat Generation in Friction Stir Welding Process

Friction Stir (FS) welding offers a number of advantages over the conventional fusion welding process, and it is used to join aluminum alloys that are difficult to weld by fusion welding processes. It has compatibility to any alloy composition, and produces the welded joints by eliminating the defects with improved mechanical properties. The weld quality is mainly influenced by the heat generated and material flow pattern that takes place during the friction stir welding process which depends on the above mentioned parameters. The mechanical and micro structural properties are highly influenced by the heat generation and material flow patterns. The tool geometry plays a vital role in the heat generation and material flow. The aim of the research is to study the influence of tool geometry on heat generation and temperature during friction stir welding process. A comparative study has been done based on the results obtained from numerical analysis and experimentation. It was found that the dissimilar FS welded joints fabricated using hexagonal tool pin profile generates optimum heat generation and temperature required for formation of quality weld irrespective of other process parameter.

Studies on Bending Properties of AA 6061-T6 Aluminium Alloy Joined By Friction Stir Welding

Presently for various engineering applications AA6061-T6 aluminum-magnesium alloys are widely preferred, which is due to its light weight and superior properties as compared to other aluminum alloys. The metal joining process is most complex in various industrial applications like automobile, aerospace, railway and marine. The Friction Stir Welding (FSW) of AA6061-T6 alloy has influenced substantial scientific and industrial importance, because it has a potential to transform the welded product with a good quality joint. In the present work AA6061-T6 alloy joined using FSW process. Observation has been made about material flow behavior and effect of process parameters on various mechanical properties and associated defects during FSW. From experimental results it can be concluded that FSW can be used to produce defect free welds, with better bending properties as compared to the welds produced by other conventional welding process.

Joining by forming technologies: current solutions and future trends

The progressively more demanding needs of emissions and costs reduction in the transportation industry are pushing engineers towards the use of increasingly lightweight structures. This goal can be achieved only if dissimilar and/or new materials, including polymers and composites, are joined together to create complex structures. Conventional fusion welding processes have often been proven inadequate to this task because of the high heat input reducing the joint mechanical properties or even making the joining process impossible. Joining by forming technologies take advantage on the plastic deformation to create sound joints out of even very dissimilar materials. Over the last 25 years, several new processes, with increasing potential in effectively joining virtually every structural material, have been invented and developed. In the paper, a comprehensive overview of the most utilized joining by forming processes is given. For each process, an analysis of the current research trends and hot topics is provided, highlighting strengths and weaknesses for industrial applications.

Low-Cost Magnesium Alloy Sheet Component Development and Demonstration Project

<div class="section abstract"><div class="htmlview paragraph">Most of the applications of magnesium in lightweighting commercial cars and trucks are die castings rather than sheet metal, and automotive applications of magnesium sheet have typically been experimental or low-volume serial production. The overarching objective of this collaborative research project organized by the United States Automotive Materials Partnership (USAMP) was to develop new low-cost magnesium alloys, and demonstrate warm-stamping of magnesium sheet inner and outer door panels for a 2013 MY Ford Fusion at a fully accounted integrated component cost increase over conventional steel stamped components of no more than $2.50/lb. saved ($5.50/kg saved). The project demonstrated the computational design of new magnesium (Mg) alloys from atomistic levels, cast new experimental alloy ingots and explored thermomechanical rolling processes to produce thin Mg sheet of desired textures. A new commercial Mg alloy sheet material was sourced and pretreated with protective coil coatings, and its properties fully characterized. The Mg sheet was successfully warm-formed using novel lubricants into intermediate size benchmark parts and full-size automotive door inner and outer panels. The project also explored conventional welding processes for joining of Mg sheet, developed novel corrosion treatments for multi-metal assembly coatings, performed computer simulations of door panel forming using two new material cards based on crystal plasticity theory, and concluded with a door static and dynamic performance analysis. An overall cost driver and sensitivity assessment task compared the final cost penalty depending on the cost of the primary magnesium sheet.</div></div>

Effects of heat source configuration on the welding process and joint formation in ultra-high power laser-MAG hybrid welding

Ultra-high power laser-MAG hybrid welding technology provides an effective method for joining thick plates with high-quality and efficiency. Heat source configuration of laser and arc was verified to play a vital role in conventional hybrid welding process. In this paper, ultra-high power laser-MAG hybrid welding was utilized to weld 20 mm thick Q235 steel for clarifying the effect of heat source configuration on welding process and joint formation. By high-speed photography, welding process was systematically recorded including hybrid plasma morphology, droplet orientation-transfer and molten pool flow. Subsequently, the joint formation was further analyzed via dynamic behaviors of liquid column and keyhole. Results exhibited that a stable arc characteristic and smooth molten pool flow was formed under HM (ultra-high power laser and MAG-leading) mode. Besides, the enlarged and stabilized keyhole would inhibit the height of liquid column and formation of spatters. Finally, a sound weld joint without “ant-colony-like defect” joint formation and 15.82 mm penetration was produced in HM mode. This work provides an effective method and reference for realizing thick plate single pass weldments in the practical industry.

Optimization of CA-TIG welding parameters to predict and maximize tensile properties of super alloy 718 sheets for gas turbine applications

PurposeThe primary objective of this investigation is to optimize the constricted arc tungsten inert gas (CA-TIG) welding parameters specifically welding current (WC), arc constriction current (ACC), ACC frequency (ACCF) and CA traverse speed to maximize the tensile properties of thin Inconel 718 sheets (2 mm thick) using a statistical technique of response surface methodology and desirability function for gas turbine engine applications.Design/methodology/approachThe four factor – five level central composite design (4 × 5 – CCD) matrix pertaining to the minimum number of experiments was chosen in this investigation for designing the experimental matrix. The techniques of numerical and graphical optimization were used to find the optimal conditions of CA-TIG welding parameters.FindingsThe thin sheets of Inconel 718 (2 mm thick) can be welded successfully using CA-TIG welding process without any defects. The joints welded using optimized conditions of CA-TIG welding parameters showed maximum of 99.20%, 94.45% and 73.5% of base metal tensile strength, yield strength and elongation.Originality/valueThe joints made using optimized CA-TIG welding parameters disclosed 99.20% joint efficiency which is comparatively 20%–30% superior than conventional TIG welding process and comparable to costly electron beam welding and laser beam welding processes. The parametric mathematical equations were designed to predict the tensile properties of Inconel 718 joints accurately with a confidence level of 95% and less than 4.5% error. The mathematical relationships were also developed to predict the tensile properties of joints from the grain size (secondary dendritic arm spacing-SDAS) of fusion zone microstructure.

Variants of TIG welding process for improvement of weld penetration depth - A review

This article deals with the various process modifications that occurred in the tungsten inert gas welding process over a decked of time. The conventional TIG welding process usually offers a shallow weld penetration (up to 5 mm). Due to this limited depth of penetration, the industrial applications of this process are very limited and used only for sheet metal working. This article focuses on the various modification that has been made in the conventional TIG welding process to improve the process capabilities. Mainly flux assisted TIG welding, pulse current TIG welding, keyhole TIG welding, multi-electrode TIG welding, TIP-TIG welding process, and their hypothesis responsible to improve the weld penetration were discussed. The effect of various process parameters of these process variants on weld penetration was also discussed. So, this article will help in strengthening the future research trend in TIG welding for enhancement of its industrial application and capability of the process.

A short review of the effect of plunge depth on friction stir welding of aluminium pipes

Since the start of welding, fusion welding has been the key contributor to welding materials. Due to the shortcomings of fusion welding, friction stir welding emerged as an alternative to fusion welding. Aluminum and magnesium which were considered un-weldable by conventional welding processes now can be easily welded by the friction stir welding technique. Much work has been done on friction stir welding of aluminum, magnesium, and copper plates. Various welding parameters like tool rotation rate, tool traverse speed, tilt angle, and tool geometry affect the texture and mechanical properties of FSW alloys. In addition to the above parameters plunge depth also greatly affects the welding characteristics and quality. The present work addresses a review of the current understanding of the effect of plunge depth on various facets of welding of aluminum pipes especially considering the role and effects of plunge depth as a parameter affecting welding characteristics.

Joining of titanium and stainless steel by using different welding processes: A review

In recent years, there is a huge demand in various industries on use of different material combination with contradictory properties for overall cost reduction and performance enhancement. As a result, use of advanced and hybrid welding techniques, development in conventional welding process etc. goes on hike to meet the expectation of dissimilar metal welding and their large-scale production. Particularly the joining of Titanium (Ti) and stainless-steel (SS) dissimilar metal couple is extensively employed for various industrial applications, i.e., nuclear, aviation, automobile, power generation and transmission, chemical industries etc. The main motivation of this combination offers superior corrosion resistance and high strength. The objective of the present study is to address the recent development on joining of Ti-SS metal couple combination by several welding processes, followed by their mechanical and metallurgical properties. It is also observed that the joining of such combination through the fusion welding process quite challenging to achieve desire properties, as the brittle intermetallics such as FeTi/Fe2Ti may formed during process. To overcome such issues, use of interlayer with low melting point than the base metal may proceed to some remarkable achievement.

Friction stir welding and friction stir spot welding of polymethyl methacrylate (PMMA) to other materials: A review

Polymers are widely used in packaging and automobile industries because of their desirable properties such as lightweight, transparency, strength to weight ratio, good hardness and stiffness, low water absorption, ultraviolet rays' protection. Keeping Polymethyl methacrylate (PMMA) polymer in focus, this review research is being done here to collect the literature available best of our knowledge on the joining of PMMA to PMMA/Polymers/ Metal alloys by Friction stir welding/ Friction stir spot welding (FSW/FSSW). Friction stir welding is a solid-state joining process in which the temperature remains below the material's melting temperature. This friction stir welding technique is widely applied on materials that are difficult to weld by fusion welding, such as aluminium alloys, titanium alloys, and polymers. Friction stir welding is an ecological weld method and environmentally friendly as it does not produce harmful radiation toxic gases, requires less energy, produces less waste than conventional fusion welding processes. It was found out that by applying Friction stir welding/ Friction stir spot welding technique, the Polymethyl methacrylate can be welded to itself, to polymers, and metal alloys. In this review, efforts are made to point out the optimum level of process parameters of FSW concluded by researchers in their studies of PMMA joining. For each study, its parameter range and the optimum value of process parameters are presented in the form of tables and graphs, and explanations and discussions are made to better understand welding Polymethyl methacrylate polymer by Friction stir welding process.

Mechanical and Microstructural Evaluation of AA6082-T61 Joints Produced by Ultrasonic Vibration Assisted Friction Stir Welding Process

Continuous improvement in the friction stir welding process (FSW) is still growing to improve the process capabilities and overcome certain drawbacks encountered in the process. Low welding speeds, high welding loads, and high torque needed are the main limitations of this process. Applying ultrasonic vibration is one of the versatile approaches that was proposed to tackle these issues. In this paper, a comparative study between the conventional friction stir welding process (CFSW) and the ultrasonic-assisted friction stir welding process (UAFSW) was conducted. The objective is to evaluate quantitively and qualitatively the influence of ultrasonic vibration waves on the weld surface quality, tensile strength, micro-hardness, microstructure, and weld formation of the joints. The results have demonstrated that ultrasonic vibration waves cause grain refinement action by 23.6% at the stirring zone (SZ) as well as its desirable role in enhancing the mechanical properties by a percentage up to 15% for ultimate tensile strength and eliminating weld defects, especially at high welding speed (120 mm/min). However, no profound effect was found for ultrasonic waves on the grain size in the thermomechanical affected zone (TMAZ) or the heat-affected zone (HAZ). A considerable reduction in the elongation % whether in CFSW or UAFSW compared to that of base metal was detected.

The Effect of Induction Heating Stress Remedies on piping reliability

To address the effect of Intergranular stress corrosion cracking (IGSCC) on the probability of a leak in BWR piping, we have introduced some changes to the model of IGSCC for the Probabilistic fracture mechanics PRAISE code. This semi-empirical model is based on experimental and field data compiled from several sources. Using probabilistic techniques, the model addresses various stress corrosion phenomena, including crack growth, crack initiation, and linking of multiple cracks. The model also considers the effect of residual stresses in addition to cyclic stresses resulting from normal plant operation. Residual stresses which are an inherent result of conventional welding processes have long been known to play an important role in the failure of structural components. Such stresses can have a beneficial or detrimental influence, depending primarily on whether they are tensile or compressive at the inside surface of the pipe. Residual stresses undoubtedly are influential in both the initiation and propagation of cracks. The purpose of this paper is to review the influence of residual stresses on the reliability of piping under IGSCC. A procedure such as induction heating stress improvement (IHSI) is a means of altering the residual stress pattern in a pipe. Examples of the use of this technique to the initiation and growth of stress corrosion cracks in pipes are presented for various pipe sizes and residual stress distributions. The effectiveness of IHSI as an eternal countermeasure for IGSCC depends upon the level of service stress as well as the crack size and its large benefit is immediately apparent.

Emission of scattered radiation from the process zone of welding processes using high-power diode lasers

Highly efficient manufacturing processes in which innovative technologies are continuously integrated are essential for a globally competitive European maritime industry. Promising optimization potential lies in the welding of thick sheet metal. The use of new high-power diode lasers with output powers of up to 60 kilowatts can replace conventional welding processes and significantly improve welding quality and efficiency. In addition to the welding process development with extremely high laser powers, ensuring laser safety is a major challenge for adequate employees’ protection. This work aims to investigate the spatial distribution of laser radiation backscattered from the laser process zone into the hemisphere above the sheet metal. The results of the scattered radiation measurements performed are used to estimate the amount of thermal energy introduced from the laser process zone into a possible protective shielding against the scattered radiation. The derived maximum temperatures finally allow a suitable dimensioning of the shielding.

Effect of heat input and heat treatment on the microstructure and toughness of pipeline girth friction welded API 5L X65 steel

High-strength low-alloy steels (HSLA) have been considered key materials for the petroleum industry for the construction of pipelines to move oil and gas for long distances. Conventional welding processes may produce important microstructural changes, which negatively impact the mechanical behavior of the pipeline material. Alternatively, pipeline girth friction welding is an excellent choice to lessen the detrimental effect on microstructure since it is a one-shot low heat input process. This work aims to optimize impact toughness – the most affected mechanical property - to qualify pipeline girth friction welded API 5L X65 steel joints according to the requirements of the DNV OS F101: 2013 international standard. The impact toughness optimization process relied on the evaluation of the welding parameters' effect on heat input and on post-weld heat treatment (PWHT). The results indicated that even though the single thermal cycle imposed lowered the size and fraction of martensite-austenite (M/A) constituent in the as-welded condition, impact toughness was notably reduced due to previously austenite grain growth and unfavorable crystallographic texture. However, at least part of the original base material's impact toughness can be restored by decreasing the heat input, although not sufficient to qualify the weld. Otherwise, PWHT led to grain size refinement and reduced crystallographic texture, which in turn improved impact toughness beyond the minimum level specified by the technical standard.