Conventional Welding Processes Research Articles

Method for high accuracy measurements of energy coupling and melting efficiency under welding conditions

The demands on production processes vastly increased in the last decade. Besides the fulfillment of the fabrication task, a process has to be energy efficient and resource saving to be in line for mass production. For the evaluation of competing technologies or for the optimization of a process regarding these requests, the knowledge about the specific process efficiency is crucial. However, the value strongly depends on the chosen process parameters and the environmental conditions, wherefore documented values in the literature are inapplicable. Hence, an experimental determination for each individual case is inevitable. Existing methods for the estimation of the process efficiency are either inaccurate or time and cost intensive. Therefore, a new method for determining process efficiencies for almost arbitrary materials and process conditions is presented. The method is based on process observation using thermographic imaging and a subsequent adjusted numerical computation of temperature fields. The result of the numerical calculation in combination with the evaluation of the weld seam cross section is the value for the energy coupling efficiency, melting efficiency as well as the overall thermal efficiency. The features of the proposed method are evaluated with a Design of Experiments approach. The technique is applied to a conventional laser and plasma welding process as well as to laser-assisted plasma arc welding. In comparison to the individual processes, the laser-assisted plasma arc welding shows a more than doubled overall thermal efficiency, which can be ascribed to a drastic increase in melting efficiency and a moderate increase in energy coupling efficiency.

Influence of advanced laser-arc hybrid welding and conventional MIG process on microstructure, mechanical properties and corrosion resistance of dissimilar joints

The purpose of this paper is to study the technological potential advantages and quality of dissimilar metal (austenitic stainless steel and ferritic stainless steel) joint welded by advanced laser-arc hybrid process and compared it with a conventional metal inert gas welding process on key grounds like weld geometry, structure-property co-relationship, in order to encourage its industrial recommendation for this dissimilar metal combination. The characterization was accomplished by using an optical microscopy, scanning electron microscopy and energy dispersive spectrometer. Results indicated the full depth of penetration in both the processes; however, narrower weld bead and absence of heat affected zone achieved with laser-arc hybrid welding. Equiaxed dendritic microstructure comprised of massive acicular ferrite was observed in laser-arc hybrid welding, while, in case of metal inert gas welding process, cellular dendritic microstructure and type-II boundary was examined. Laser-arc hybrid welding showed higher hardness, higher tensile strength and low impact energy due to rapid cooling rate. Magnetic induction method (ferritoscope) revealed higher ferrite content in the laser-arc hybrid welding process. The modified strauss test revealed intergranular corrosion in the ferritic base metal.

Comprehensive optimization of friction stir weld parameters of lap joint AA1100 plates using artificial neural networks and modified NSGA-II

Friction stir welding (FSW) process overcomes many difficulties arising in conventional fusion welding processes of aluminum alloys. The current paper presents a comprehensive investigation on the effects of rotational speed, traverse speed, tool tilt angle and tool pin profile on the longitudinal force, axial force, maximum temperature, tensile strength, percent elongation, grain size, micro-hardness of welded zone and welded zone thickness of AA1100 aluminum alloy sheets. Design of experiments (DOE) was applied using the Taguchi approach and subsequently, effects of the input parameter on process outputs were investigated using analysis of variance (ANOVA). A perceptron neural network model was developed to find a correlation between the inputs and outputs. Multi-objective optimization using modified NSGA-II was implemented followed by NIP and TOPSIS approaches to propose optimum points for each of the square, pentagon, hexagon, and circular pin profiles. Results indicate that the optimization process can reach horizontal and vertical forces as low as 1452 N and 2913 N, respectively and a grain size as low as 2 μm. This results in hardness values of up to 57.2 and tensile strength, elongation and joint thickness of 2126 N, 5.9% and 3.7 mm, respectively. The maximum operating temperature can also reach a sufficiently high value of 374 °C to provide adequate material flow.

Multi-objective Optimization of Friction Welding Process Parameters using Grey Relational Analysis for Joining Aluminium Metal Matrix Composite

Aluminium metal matrix composites has gained importance in recent time because of its improved mechanical and metallurgical properties. The welding of aluminium metal matrix composites using conventional welding process has got many demerits so in order to overcome them a solid state welding process is to be employed. To achieve a good strength weld in the aluminium metal matrix composite bars an efficient and most preferred technique is friction welding. In this work the aluminium metal matrix composite AA7075 + 10 % vol SiC-T6 is selected and friction welded. The combination of friction welding process parameters such as spindle speed, friction pressure, upset pressure and burn-off- length for joining the AA7075 + 10 % vol SiCP-T6 metal matrix composite bars are selected by Taguchi’s design of experiment. The optimum friction welding parameters were determined for achieving improved ultimate tensile strength and the hardness using grey relational analysis. A combined grey relational grade is found from the determined grey relational coefficient of the output responses and the optimum friction welding process parameters were obtained as spindle speed – 1200 rpm, friction pressure – 100 MPa, upset pressure – 250 MPa, Burn-off-Length – 2 mm. Analysis of variance (ANOVA) performed shows that the friction pressure is the most significant friction welding parameter that influences the both the ultimate tensile strength and hardness of friction welded AA7075 + 10 % volSiCP-T6 joints. The fractured surface under microstructure study also revealed good compliance with the grey relational grade result. DOI: http://dx.doi.org/10.5755/j01.ms.24.2.17725

Microstructural features of friction stir welded dissimilar Aluminium alloys AA2219-AA7475

High strength, good corrosion resistance, light weight make aluminium alloys a material of choice in many industrial sectors like aerospace, marine etc. Problems associated with welding of these alloys by fusion welding processes restricted their use in various industries. Friction stir welding (FSW), a clean solid-state joining process, easily overcomes various difficulties encountered during conventional fusion welding processes. In the present work, the effect of rotational speed (710 rpm, 900 rpm and 1120 rpm) on micro-hardness distribution and microstructure of FSWed dissimilar aluminium alloy joints were analyzed. Plates of AA7475-T761 and AA2219-O having thickness of 2.5 mm were welded by fixing AA7475 on retreating side (RS) and AA2219 on advancing side (AS). Welded joints were characterized by Vickers micro-hardness testing, scanning electron microscopy (SEM) and optical microscopy (OM). Results revealed that rotational speed significantly affects the micro-hardness due to increase in grain size, coarsening and dissolution of strengthening precipitates and re-precipitation. Higher micro-hardness values were observed in stir zone due to grain refinement and re-precipitation. Minimum micro-hardness value was observed at the TMAZ/HAZ of advancing side due to thermal softening.

Thermo-Mechanical Analysis of Activated Tungsten Inert Gas Welding (A-TIG) of Type 316LN Stainless Steel Thin Plates

Abstract In the present study, thermo-mechanical behavior of 316LN stainless steel thin plates during activated tungsten inert gas (A-TIG) welding was investigated using SYSWELD®. A-TIG welding was carried out with more reduced heat input for fabricating 3-mm-thick 316LN stainless steel plates than that of the conventional TIG welding process. Induced transient temperature during welding was measured using a K-type thermocouple. A pulse-echo ultrasonic test was carried out using a 2-MHz probe employing critically refracted longitudinal waves for measuring residual stresses across the weld joint. A digital height gauge was used to quantify the distortion caused during welding. There was a good agreement between the predicted and measured thermal cycles, residual stresses, and distortion. The concentrated heat intensity of A-TIG welding induced higher surface temperature in the weld center, produced a narrow weld bead, and exhibited a sharp temperature gradient at the weld/base metal interface. Peak residual stress and distortion of the A-TIG weld joint were found to be less than that of the TIG weld joint.

A Comparison Between Half Bead Tempering and Conventional Welding Process on Properties of 9Cr–1Mo Steel

In the present study, shielded metal arc welding with three types of electrodes such as E-NiCrFe3, E309L, and E8015 along with three different welding techniques was utilized to investigate the elimination of post-weld heat treatment (PWHT). Variations in average HAZ width and evaluating ductility, hardness, and microstructural changes in the weld metal and heat-affected zone were investigated. It was found that PWHT can be ignored by applying half bead tempering technique due to HAZ tempering of the previous bead by the heat input of subsequent runs. The best combination of ultimate tensile strength and ductility was achieved by utilizing Ni-based electrode.

Establishing the Dependence of Output Parameters Depending on Local Process Conditions for Friction Stir Welding of Pure Copper Plates

Welding copper and its alloys is usually difficult to achieve by conventional fusion welding processes because of high thermal diffusivity of the copper, which is at least 10 times higher than most steel alloys, in addition to this, there are the well-known disadvantages of conventional fusion welding represented by necessity of using alloying elements, a shielding gas and a clean surface. To overcome these inconveniences, Friction Stir Welding (FSW), a solid state joining process that relies on frictional heating and plastic deformation, is being explored as a feasible welding process. In order to achieve an increased welding speed and a reduction in tool wear, this process is assisted by another one (TIG) which generates and adds heat to the process. The research includes two experiments for the FSW process and one experiment for tungsten inert gas assisted FSW process. The process parameters that varied were the rotational speed of the tool [rpm] and the welding speed [mm/min] while the compressive force remained constant. The purpose of this paper is to correlate the evolution of temperature, tensile strength, elongation and microscopic aspect with the linear position on the joint (local process parameters) for each experimental case and then make comparisons between them, and to identify and present the set of process parameters that has the best mechanical properties for this material.

Recent Developments and Research Progress on Friction Stir Welding of Titanium Alloys: An Overview

Titanium and its alloys are joined by various welding processes. However, Fusion welding of titanium alloys resulted solidification problems like porosity, segregation and columnar grains. The problems occurred in conventional welding processes can be resolved using a solid state welding i.e. friction stir welding. Aluminium and Magnesium alloys were welded by friction stir welding. However alloys used for high temperature applications such as titanium alloys and steels are arduous to weld using friction stir welding process because of tool limitations. Present paper summarises the studies on joining of Titanium alloys using friction stir welding with different tool materials. Selection of tool material and effect of welding conditions on mechanical and microstructure properties of weldments were also reported. Major advantage with friction stir welding is, we can control the welding temperature above or below β-transus temperature by optimizing the process parameters. Stir zone in below beta transus condition consists of bi-modal microstructure and microstructure in above β-transus condition has large prior β- grains and α/β laths present in the grain. Welding experiments conducted below β- transus condition has better mechanical properties than welding at above β-transus condition. Hardness and tensile properties of weldments are correlated with the stir zone microstructure.

Studies on microstructure, mechanical and pitting corrosion behaviour of similar and dissimilar stainless steel gas tungsten arc welds

In the present study, an attempt has been made to weld dissimilar alloys of 5mm thick plates i.e., austenitic stainless steel (316L) and duplex stainless steel (2205) and compared with that of similar welds. Welds are made with conventional gas tungsten arc welding (GTAW) process with two different filler wires namely i.e., 309L and 2209. Welds were characterized using optical microscopy to observe the microstructural changes and correlate with mechanical properties using hardness, tensile and impact testing. Potentio-dynamic polarization studies were carried out to observe the pitting corrosion behaviour in different regions of the welds. Results of the present study established that change in filler wire composition resulted in microstructural variation in all the welds with different morphology of ferrite and austenite. Welds made with 2209 filler showed plate like widmanstatten austenite (WA) nucleated at grain boundaries. Compared to similar stainless steel welds inferior mechanical properties was observed in dissimilar stainless steel welds. Pitting corrosion resistance is observed to be low for dissimilar stainless steel welds when compared to similar stainless steel welds. Overall study showed that similar duplex stainless steel welds having favorable microstructure and resulted in better mechanical properties and corrosion resistance. Relatively dissimilar stainless steel welds made with 309L filler obtained optimum combination of mechanical properties and pitting corrosion resistance when compared to 2209 filler and is recommended for industrial practice.

EFFECT OF WELDING PARAMETERS ON MECHANICAL PROPERTIES OF FRICTION STIR LAP WELDED JOINTS FOR SIMILAR ALUMINUM ALLOYS (AA1100-H112 & AA6061-T6)

Friction stir welding (FSW) is a solid state welding used for joining similar and dissimilar aluminum alloys which are hard to weld by conventional fusion welding processes. In this study friction stir lap welding (FSLW) Joints are made for similar aluminum alloys (AA1100 to AA1100) and(AA6061to AA6061) sheets of 3mm thickness and those alloys have low to medium strength and have difference in melting temperature and other physical properties.FSLW processes were carried out by conventional technique. The friction stir lap welding of similar aluminum alloys was carried out by varying the welding parameters, such as tool rotation speeds (1000, 1250 and 1600pm) and travel speeds (35, 75 and 100mm) and pin length of ( 5.4 mm) with using cylindrical threaded pin geometry or profile. Many tests and inspections were performed such as X-Ray radiographic and tensile shear test .Microhardness and microstructure observations by using optical and SEM were carried out at the best welding parameters. The above tests were used to evaluate the weld quality and joint efficiency under different welding parameters. The best welding parameters appeared in FSLW were 1250rpm and travel speed 100 mm/min. It was found that higher hardness value was (94.38HV) for 6061-T6 and 49HV for 1100-H112 in stir zone for both FSLW joints of AA6061-T6 and AA1100-H112 and that decrease toward the HAZ and base metals of AA1100 and AA6061.

Identification of Process Parameters in Electromagnetic Pulse Welding and Their Utilisation to Expand the Process Window

Impact welding, represented by the industrial processes explosion welding and electromagnetic pulse welding, offers unique advantages over conventional welding processes, especially fusion welding. The joint is produced during a high speed impact between two workpieces without additional heating or melting. Thus, even dissimilar metals can be joined. However, in contrast to fusion welding, the fundamentals are understood to a significantly lesser extent. In this publication, the effect of the density of the surrounding gaseous medium is investigated. The results show that a lower density results in a higher weld strength. At higher densities, a weld can even be inhibited completely. High speed images of the impact indicate that this is caused by the obstruction of the so-called jet due to the increased air resistance. In general, “jetting” describes the ejection of oxides, dirt and superficial material from the closing gap during the impact. It is presumed to be essential for the formation of the bond.

Investigation of Mechanical Properties of Friction Stir Welded pure Copper Plates

In conventional welding process, copper and copper alloys are difficult to welding because of high thermal conductivity and high melting point of copper. Due to high melting point, more amount of heat is required to weld the copper and due to high thermal conductivity, heat effected zone in the welded component increases so loses its mechanical and thermal properties. Friction stir welding is a new method that resoles the all above problems. Friction stir welding is a solid state joining process welding done at below the recrystallization temperature. The joint technique is a energy efficient, the environment friendly, easy and defect free welding process.Purpose of this study is to find out the optimum mechanical properties of the friction stir welding of copper. Present study entails an attempt has been made to study the effect of tool rotational speed, traversing speed and tool pin profiles (straight cylindrical profile) on FSP zone transformation in copper. For two different tool rotational speeds, two different traversing speeds, one tool pin profiles have been used to fabricate the joints. The formation of FSW of copper of fusion zone has been evaluated and correlated with base metal. Tensile strength, toughness, hardness and microstructure of the joint evaluated and Tensile strength correlated with weld zone hardness and microstructures. The joints fabricated using rotational speed of 910 rpm, a welding speed of 30mm/min, tool pin with square profile, tool shoulder diameter of 34mm, (Ds/Dp)=3 showed higher tensile strength compared to other joints at a constant load.The experimental results showed that the fracture locations of the joints are affected by FSW parameters, where copper joints are fractured in TMAZ and or in NZ/TMAZ interface on the retreating side of the welds and all fracture locations are nearer to the weld centres.

Mathematical Modeling of Process Parameters of Friction Stir Welded Aluminium Alloy Joints Using Central Composite Design

The structural application of aluminium alloy involves welding and joining, which are difficult to weld using conventional welding processes. In 1991 a solid state joining process named Friction Stir Welding was developed and this technique has attracted considerable interest from the aerospace and automotive industries, since it is able to produce defect free joints particularly for light metals i.e aluminum alloy and magnesium alloy. This process uses a non-consumable tool to generate frictional heat in the abutting surfaces. The welding parameters such as tool rotational speed, welding speed and tool shoulder diameter play a major role in deciding the weld quality. In this research work an attempt has been made to understand the effect of tool rotational speed, welding speed and tool shoulder diameter on friction stir welding of AA6061 aluminium alloy. Statistical tools such as design of experiments, analysis of variance, and regression analysis are used to develop the relationships. The mathematical model has been developed to predict mechanical properties of friction stir welded aluminium alloy joints at the 95% confidence level

Understanding the dissimilar friction stir welding through force and temperature evolution

Friction stir welding (FSW) is a promising technology to join aerospace grade aluminium alloys that are difficult to be welded by conventional fusion welding processes. Force and temperature measurement during FSW process plays a vital role in understanding the process, tool degradation analysis, predicting the tool life, mechanical properties and microstructure of the welded joints. In the present research work, an attempt has been made to investigate the effect of traverse speed on longitudinal force and temperature distribution during FSW of dissimilar aluminium alloys. Traverse speed, on which heat input depends, was varied from 160 mm/min to 250 mm/min keeping the other FSW parameters constant. It was observed that increase in the traverse speed resulted in the higher longitudinal force. Results revealed that highest longitudinal force of 971 N was observed at maximum traverse speed of 250 mm/min attributed to higher flow stresses resulting from low heat input and higher weld consolidation rate. Conversely, lower longitudinal force was observed at lower traverse speed as slow traversing of the tool resulted in high heat input leading to sufficient softening of the material being welded. HAZ peak temperature of 218 oC and 193 oC was detected at retreating side and advancing side respectively.

Joining and fabrication of metal matrix composites by friction stir welding/processing

Herein, friction stir welding (FSW) of metal matrix composites (MMCs) with different combinations of the reinforcement and the metal matrix is highlighted with a brief introduction into recent efforts that have been used to fabricate MMCs by FSW. As a solid state joining technique, FSW consumes significantly lower energy than conventional fusion welding processes. In addition to properly selecting the process parameters, the mechanical properties of the FSW joints of MMCs are closely related with the refinement and homogeneous distribution of reinforcements in the stir zone. The fatigue and fracture properties of MMCs may be enhanced or aggravated by FSW, depending on the combination of the reinforcement and the metal matrix. For FSW of MMCs, the selection of the tool material can also be a critical issue; the presence of hard reinforcements may increase the rate of tool wear. Macro-and microstructural phenomena for MMCs during FSW depend on the material flow due to plasticization and the behavior of the reinforcements. Even though FSW are generally expected to induce a homogeneous distribution of reinforcements in the stir zone (SZ), it can be difficult to obtain a homogeneous distribution of reinforcements in the SZ depending on the combination of the reinforcement and the metal matrix. The existence of reinforcements naturally affects the microstructure of the joint and can even induce the formation of intermetallics/complex phases in the joint. This review provides a general understanding of the joining or in-situ fabrication of MMCs using solid-state friction stirring.

Fatigue Life Extension of AA2024 Specimens and Integral Structures by Laser Shock Peening

The goal of the present study is to understand the effects of laser shock peening (LSP)-induced residual stresses on the fatigue crack propagation (FCP) behaviour of the commonly used aircraft aluminium alloy AA2024 in T3 heat treatment condition. LSP treatment was performed using a pulsed Nd:YAG laser on compact tensile C(T)50-specimens with a thickness of 2.0 mm. LSP-treated specimens reveal a significant retardation of the fatigue crack propagation. The fatigue crack retardation effect can be correlated with the compressive residual stresses introduced by LSP throughout the entire specimen thickness. A possible application of the LSP process on a component like panel with three welded stringers representing a part of a fuselage structure was performed as well. The skin-stringer AA2024-AA7050 Tjoints were realised through stationary shoulder friction stir welding (SSFSW), a variant of the conventional friction stir welding process. In this relatively new process, the shoulder does not rotate and therefore does not contribute to the heat generation. Consequently, a reduced and more homogeneous heat input leads to a less affected microstructure and better mechanical properties. The efficiency of the LSP process has been demonstrated resulting in an increase of 200 – 400% in fatigue lifetime.

A comparative study on creep behavior of AISI 409 ferritic stainless steel in as-received and as-welded condition (A-TIG and M-TIG)

Activating flux tungsten inert gas (A-TIG) welding process is an evolving welding process to increase the productivity of the conventional or multi-pass tungsten inert gas (M-TIG) welding process. The current work presents the characterization of the microstructure evolution during the creep exposure of Base metal, A-TIG and M-TIG weldments of AISI 409 ferritic stainless steel (FSS). The creep tests were performed at temperature of 600 °C and a stress of 50 MPa. Energy dispersive X-ray spectroscope (EDS) assisted field-emission scanning electron microscopy (FESEM), optical microscopy and microhardness testing were used to evaluate the samples after creep exposure. Creep tests were performed on round creep specimens. The M-TIG and A-TIG creep samples were get ruptured from the heat affected zone during creep test. The rupture time was found nearly equal for A-TIG and M-TIG weldments and maximum for base metal sample.

Analysis of mechanical properties on friction stir welded magnesium alloy by applying Taguchi Grey based approach

Friction stir welding (FSW) process avoids problems related to solidification formed during conventional fusion welding processes. To improve the mechanical strength, in this investigation the effect of tool rotational speed, welding speed and plunging depth with each three levels of magnesium alloy ZM21-weldments were analyzed using Taguchi grey relational analysis (GRA). The ultimate tensile strength, yield strength and percentage elongation were evaluated and obtained joint efficiency of 81%, 78% and 85% than that of base metal respectively. The micro hardness profile obtained on various cross-sectional regions of the welded zone indicates uniform distribution of grains at the nugget zone.

Friction stir welding of Aluminium matrix composites – A Review

Friction stir welding (FSW) is established as one of the prominent welding techniques to join aluminium matrix composites (AMCs). It is a solid state welding process, takes place well below the melting temperature of the material, eliminates the detrimental effects of conventional fusion welding process. Although the process is capable to join AMCs, challenges are still open that need to be fulfill to widen its applications. This paper gives the outline of the friction stir welding technique used to join AMCs. Effect of process variables on the microstructure and mechanical properties of the joints, behavior of reinforcing materials during welding, effect of tool profiles on the joint strength are discussed in detail. Few improvements and direction for future research are also proposed.