Unit Length Of Weld Research Articles

Heat affected zone evolution in fine grained aluminum alloys during laser welding: Phase-field simulation and analytical investigation

One of the biggest challenges in the welding of strengthened alloys by grain refinement is the grain growth phenomenon in the heat-affected zone (HAZ), which would result in the degradation of mechanical properties. The goal of this study is to comprehend the HAZ evolution in the fine-grained aluminum alloy during laser welding as a low heat input process. Spot laser welding of fined grain 1050 aluminum alloy revealed that grain growth and HAZ formation occurred in samples with 4 µm grain size, but no grain growth occurred outside of the fusion line (FL) in larger grain samples. The microstructure of HAZ was simulated using the numerical phase-field technique. The numerical model's findings demonstrated that a critical grain size (Dcr) for the base metal can be established, above which grain growth would not occur outside FL. To predict grain size distribution outside FL, an analytical model was also used. According to both models, as grain size increases, the HAZ width decreases, and above a critical grain size, no HAZ will form outside of FL. In spot welding, Dcr was independent of power density but for continuous welding processes, Dcr has a direct relationship with heat input per unit length of weld. Moreover, HAZ grain growth mainly occurred in heating step for both types of processes.

Determination of LME sensitivity of zinc-coated steels based on the programmable deformation cracking test

The current work presents a new test method to evaluate liquid metal embrittlement (LME) susceptibility of zinc-coated steels in arc processes under application-oriented conditions. The procedure is based on the programmable deformation cracking test (PVR test). The PVR test is a variation of a controlled tensile test for hot cracking investigations in arc welding processes. Two dual-phase steels (DP600, DP980) and five transformation-induced plasticity steels (TRIP690, TRIP700, TRIP700, TRIP1100, TRIP1200) were used. The investigations showed that comparable thermo-mechanical loading conditions can be guaranteed for materials of different sheet thicknesses in the PVR test through a targeted adjustment of the heat input per unit length of weld. Furthermore, it was shown that the critical deformation rate {v}_{cr} (used for assessing hot cracking susceptibility) may also be used to assess the LME susceptibility of a particular steel. Furthermore, another LME susceptibility parameter, the relative reduction in load-bearing ability DeltaSigma could be derived, which may be used to understand how LME cracking affects materials’ mechanical and fracture properties.

Wire-Based Additive Manufacturing of Stainless Steel Components

Three different wire-fed additive manufacturing (AM) processes were employed to evaluate differences between laser, arc, and electron beam heat sources used for high-deposition-rate AM on the order of 1 kg/h. Optimum weld and build parameters were developed independently to match the characteristics of each heat source using 308L stainless steel welding wire as the feedstock. Laser-wire AM was made with the lowest energy per unit length of weld and had the best control of the melt pool and surface finish. Wire arc-based AM had an intermediate energy per unit length of weld of approximately 5× that of the laser process, while electron beam wire AM had the highest energy per unit length of weld at approximately 10× that of the laser process. Analysis of the parts that were built included evaluation of mechanical properties and microstructures, and these properties are discussed with respect to the difference in input energy and cooling rates. Results show that all three processes build parts with properties that exceed those of annealed 304L wrought stainless steel. How-ever, significant differences exist between the processes, and the results presented here can be used to help select the best wire-fed process for a given high-deposition-rate application.

Thermal Modeling Based on the Energy per Unit Length of Weld in Friction Stir Welding

Thermal Modeling Based on the Energy per Unit Length of Weld in Friction Stir Welding

Friction stir welding of 25%SiC/2124Al composite with optimal mechanical properties and minimal tool wear

ABSTRACTIn this research, 8-mm-thick plates of 25%SiC/2124Al composite have been joined successfully by using an un-threaded WC–Co tool which showed minimal tool wear. Decreasing the rotational and advancing speeds is a key factor to obtain successful joints. Defect-free welds, and a joint efficiency (100UTSjoint/UTSBaseMaterial) of up to 97%, can be achieved if a high forge force, Fz, (above some 15 kN) is reached. Proportionality between the torque, M, and Fz is observed. High Fz values, and corresponding M, lead to high values of the total energy per unit length of weld, Htot, supplied by the tool to the workpiece. It is proposed that most of this energy is spent in plastic deformation of the high strength composite.

Assessment of controlled short-circuiting application in filling passes with MIG/MAG double-wire process

In this work, a technical–economic assessment of the double-wire MIG/MAG welding process was carried out for flat-position welding of filler passes, employing controlled short-circuiting (CSC) operating mode in the trailing wire, as a way of improving control of the molten pool and reducing splashes. The assessment was based on a comparative study between the conventional double-wire MIG/MAG technique (using pulsed current in both wires) and a combination of pulsed current in the leading wire and CSC in the trailing wire. The following were kept constant: the values of average current for each wire, the volume of material deposited per unit length of weld, the type and size of the bevel and the wire, the composition of the shielding gas and the CTWD. The surface finish and geometry of the weld beads, deposition rate and deposition efficiency and the maximum welding speeds resulting from the use of each technique were assessed. The results show that the use of the CSC mode in the trailing arc increases the production capacity of the process slightly, leads to less splashing, improves the finish of the bead, produces smaller fusion zone and smaller HAZ and yet maintains a similar operational envelope (with respect to the range of useful welding speeds), which are positive factors. On the other hand, as a disadvantage, the use of CSC led to beads that are more convex and have less penetration.

Profiling stainless steel welding processes to reduce fume emissions, hexavalent chromium emissions and operating costs in the workplace

ABSTRACTNine gas metal arc welding (GMAW) processes for stainless steel were assessed for fume generation rates, fume generation rates per g of electrode consumed, and emission rates for hexavalent chromium (Cr6+). Elemental manganese, nickel, chromium, iron emissions per unit length of weld, and labor plus consumables costs were similarly measured. Flux-cored arc welding and shielded metal arc (SMAW) processes were also studied. The objective was to identify the best welding processes for reducing workplace exposures, and estimate costs for all processes. Using a conical chamber, fumes were collected, weighed, recovered, and analyzed by inductively coupled atomic emission spectroscopy for metals, and by ion chromatography for Cr6+. GMAW processes used were Surface Tension Transfer, Regulated Metal Deposition, Cold Metal Transfer, short-circuit, axial spray, and pulsed spray modes. Flux-cored welding used gas shielding; SMAW used E308 rods. Costs were estimated as dollars per m length of a ¼ in (6.3 mm) thick horizontal butt weld; equipment costs were estimated as ratios of new equipment costs to a 250 ampere capacity SMAW welding machine. Results indicate a broad range of fume emission factors for the processes studied. Fume emission rates per g of electrode were lowest for GMAW processes such as pulsed-spray mode (0.2 mg/g), and highest for SMAW (8 mg fume/g electrode). Emission rates of Cr6+ ranged from 50–7800 µg/min, and Cr6+ generation rates per g electrode ranged from 1–270 µg/g. Elemental Cr generation rates spanned 13–330 µg/g. Manganese emission rates ranged from 50–300 µg/g. Nickel emission rates ranged from 4–140 µg/g.Labor and consumables costs ranged from $3.15 (GMAW pulsed spray) to $7.40 (SMAW) per meter of finished weld, and were measured or estimated for all 11 processes tested. Equipment costs for some processes may be as much as five times the cost of a typical SMAW welding machine.The results show that all of the GMAW processes in this study can substantially reduce fume, Cr6+, manganese and costs relative to SMAW, the most commonly used welding process, and several have exceptional capabilities for reducing emissions.

Metallurgical Characteristics on PGMA Welding of Dissimilar 304 Austenitic Stainless Steel and HSLA Steel

Welding of dissimilar metal between austenitic stainless steel (γ-SS) and, high strength low-alloy (HSLA) steel are widely used in high-temperature applications in power station and petrochemical plants. Fusion welding is one of the most widely used methods for joining of dissimilar metal. Therefore, continuous efforts are made to apply this method for joining of dissimilar metal of various combinations and despite many difficulties encountered. These difficulties include problems associated with microstructure of the weld metal and heat-affected zone (HAZ). Considering the lack of such knowledge some understanding in this regard has been presented in reference to dissimilar Austenitic stainless steel (γ-SS) and high strength low alloy (HSLA) steel under controlled pulsed current GMAW. This paper focus on effect of grain size, microstructure and the width of the heat affected zone by pulsed current gas metal arc welding (PGMAW) of dissimilar γ-SS and HSLA steel. The observations show that in PGMA welds, the decrease in grain size at heat affected zone and lower HAZ Width in both HSLA steel and γ-SS especially with the lowering of summarized influence of pulse parameters factor () at similar heat input per unit length of weld (Ω) has been observed.

Pulsed current gas metal arc welding of P91 steels using metal cored wires

A detailed experimental study was undertaken to examine the suitability of pulsed current gas metal arc welding of 12mm thick P91 steels in groove joint configurations with metal cored filler wire. Both the single and multipass welds showed satisfactory bead morphology, tensile strength and toughness especially at higher groove angles of 60° and 75° for the selected range of welding current and speeds. The weld metal compositions showed considerably high presence of Ni, Mn and Si with little loss of other alloying elements. The weld properties were primarily affected by the heat input per unit length of weld and the groove angle. The maximum ultimate tensile strength and toughness of the welds were found to be around 845MPa and 125J, respectively, for a heat input of 1.38kJ/mm and a groove angle of 75°. The use of metal cored filler wires could enhance the welding speed by 20% and filler wire deposition rate by 42% compared to that with the solid wires. Overall, the present study showed that the pulsed current gas metal arc welding of medium to high thickness P91 steels using metal cored filler wires could provide higher deposition rate and welding speed, and enhanced weld bead properties in comparison to solid wires.

Computational analysis of the effect of welding parameters on energy consumption in GTA welding process

The electrical energy needed in welding processes is a major factor of energy consumption in manufacturing processes that use welds to fabricate structures. In the arc welding process an intense electrical arc is used as the heat source to melt locally metallic materials to join them once they solidify. Although the arc is focused at the joint, a large portion of energy is dissipated as heat through the base metals to the surroundings. In this paper it is shown that selecting the welding parameters appropriately, viz., the power supplied to the arc and the translation speed of the arc, can reduce the energy consumed per unit length of weld. The range of parameters examined was selected such that the vaporization of the molten metal was negligible. It is shown that increasing the arc power in conjunction with increasing the travel speed of the arc leads to reduced energy consumption per unit length of weld; this reduction in energy consumption is for equivalent welds, i.e., welds with identical geometric features.

Investigations of properties in hybrid welds at 40-mm sheet thickness

Laser gas metal arc hybrid welding (laser-GMA hybrid welding) offers capabilities for improving the economy of welding in comparison to conventional welding processes due to characteristics concerning material and seam design. Research into this process was restricted to a sheet thickness range of between 6 and 12 mm for steel. However, for steel, container, vehicle or ship engineering in particular, structures (components) with large wall thicknesses are of special interest. These structures are currently welded by using the submerged arc welding process, which requires a high input of energy, welding material and working time. The objective of this project was to determine the influence of the reduction of the weld volume and energy per unit length of weld on the formation of residual stresses and their effects on the fatigue strength of hybrid welded sheets with large wall thicknesses. As a result, better qualities with regard to fatigue strength and toughness have been achieved for hybrid welded joints in comparison to submerged arc-welded joints for wall thicknesses of 40 mm.

Coupled Field Analysis of a Gas Tungsten Arc Welded Butt Joint—Part II: Parametric Study

The process of welding has a direct influence on the integrity of the structural components and their mechanical response during service. Welding is an inherently multiphysics problem, encompassing a large array of physical phenomena—fluid flow in the weld pool, heat flow in the structure, microstructural evolution/phase transformations, thermal stress development, and distortion of the welded structure. The mathematical model to simulate the coupled fields of the welding process has been outlined in Part I of the present study. In Part I, the developed model have been validated with experimental results and the depth/width (D/W) predictions agree well. Part II documents the effects of welding parameters (welding current/speed, electrode gap, and electrode angle) on the weld D/W ratio, for both low (≤40 ppm) and high (≥150 ppm) surface active agent (oxygen) content. The parametric characterization of the weld D/W ratio is validated with published experimental data. They agree well. Results show that increasing the oxygen content beyond 150 ppm does not increase the weld D/W ratio. At high oxygen content of 150 ppm and under current variation, the weld D/W ratio increases and remains constant beyond 160 A. However, when the welding speed is varied, the weld D/W ratio decreases with increasing speed. Similarly, increasing the electrode gap under high oxygen content decreases the weld D/W ratio. The weld D/W ratio shows weak variation with electrode tip angle. The results from the present simulations have also been used to predict the modes of weld solidification. With increase in welding speed, finer dendritic microstructures are expected to be formed near the weld centerline. The variation of weld D/W with heat input per unit length of weld is also presented elaborately. The workpiece deformation and stress distributions are also highlighted. The present study shows the pertinence of coupled welding process simulation to delineate the underlying physical processes and thereby better predict the behavior of welded structures.

Numerical simulation of welding distortion in thin plates

A three-dimensional model based on the finite-element method is developed to simulate the temperature field and stress distribution in the welding and heat-affected zones during fusion welding of thin plates. The governing equations are solved using the SYSWELD program commercial code. The model's predic- tions are tested and verified against the experiments. Angular distortion and longitudinal bending are meas- ured, the results are compared with those obtained from the mathematical model, and a relatively good agreement between them is found. The verified model is used to evaluate the effects of various parameters on the temperature and stress distributions in the welding and heat-affected zones of a thin austenitic stain- less steel plate. Introduction. Welding distortion and residual stress have remained major challenges in manufacturing. In the automotive industry, parts involving thin plates are commonly employed, and a lot of such parts are assembled by the arc welding process because of its high productivity. Due to the relatively small stiffness of the plates, significant welding distortion often occurs. To comprehensively understand the characteristics of welding deformation in a struc- ture composed of welded thin plates, it is necessary to carry out further fundamental investigations by means of both experimentation and numerical simulation. Extensive experimental efforts have been made to understand and control the welding distortions and residual stresses. In the last two decades, numerous results on using analytical and computational methods have also been re- ported to predict and quantify the effect of the distortion and residual stresses during the welding process. However, there is a very limited literature concerning the prediction and measurement of welding deformation in structures in- volving welded thin plates, especially for welded structures with plate or wall thickness below 3 mm. For a given con- figuration, the magnitude of those effects depends primarily on the specific thermal energy input of the welding process, that is, on the energy per unit length of weld. Therefore, significant reductions in distortion cannot be achieved without using the welding process with a smaller heat input, which is not always practicable. An accurate prediction of distortion is difficult even for simple welded structures, and all the more for fabrications where several such processes are applied consecutively. In previous works (1, 2), simulation of the welding process for a plate from CT3 steel with a thickness of 3 mm and a plate from austenitic stainless steel with a thickness of 1 mm was carried out. In (2), due to the restriction of the Ls-Dyna program in the removal of material history at high temperatures, the behavior of steel during welding was assumed to be fully plastic. However, many authors suggest that the behavior of metals during welding obeys the model of isotropic or kinematic hardening. Because of this, in the present work the isotropic hardening model is con- sidered. The simulation is accomplished by the SYSWELD program, which is a famous software in simulation of welding, and all the physical and mechanical properties of steel are taken from its library. As a first step towards simplification, the sequential computations for thermal-transient and thermo-elastic-plas- tic stages may be uncoupled without penalty, as suggested by various authors (3-7). In (8), a coupled transient thermal and structural analysis of the temperature distribution and deformation was carried out. The transient temperature field calculated at the first stage provides the input for the thermo-elastic-plastic stage. The outputs of the latter stage, in the form of the transverse angular deformation and contraction forces, provide, in turn, the input for the elastic finite-

Why power per unit length of weld does not characterize a weld?

A number of publications have characterized low-alloy steel welds by specifying the power per unit length. This paper uses a 3D numerical model to compute the transient temperature and evolution of the microstructure in six welds with the same weld power per unit length of weld but with different weld powers. The results show that the welds have large differences in their transient temperature field and the fields for phase fractions of gamma, martensite, bainite and ferrite–pearlite phases. Also the gamma phase grain size and hardness profiles are quite different. The reason for the differences is that with high welding speeds, the heat flows primarily in the two-dimensions that are normal to the weld path and cools more slowly near the weld pool than in welds made with low welding speeds where the heat flows in three-dimensions and cools more quickly. However, there is a region in the heat-affected zone farther from the weld pool where the time to cool is higher at lower powers and lower welding speeds. The longer times at higher temperatures causes more growth of gamma grain size. The larger gamma grain size reduces the density of nuclei for the austenite to ferrite transformation and thus more gamma can be present when the martensite start transformation is reached. At low weld powers, the hardened zone is wider, deeper and shorter but the maximum hardness is attained in the highest power welds in the coarse grained heat-affected zone that is primarily a martensite and bainite microstructure. This paper studies the extent to which the ratio of power per unit length of weld is not a unique descriptor of a weld.

Friction stir welding of aluminium 7136-T76511 extrusions

This research programme evaluates the as welded properties of Al 7136-T76511 extrusions joined through friction stir welding (FSW). Microstructural characterisation and mechanical testing were performed on the baseline material and on panels friction stir welded at 250 and 350 rev min–1 (all other weld parameters held constant). Transmission electron microscopy revealed the microstructural features in each of the unique weld regions and demonstrated that the precipitate density and morphology in these regions correlates with the temperature profile produced by the FSW process. A thermal model of FSW is developed that utilises an energy based scaling factor to account for tool slip. The slip factor is derived from an empirical relationship between the ratio of the maximum welding temperature to the solidus temperature and energy per unit length of weld. The thermal model successfully predicts the maximum welding temperatures and profiles over a range of energy levels. The mechanical behaviour after welding is correlated to the temperature distribution predicted by the model and to the observed microstructural characteristics. As welded mechanical properties of the alloy trended positively with the energy per unit length of weld, i.e. the highest joint efficiency was achieved at the highest welding temperature.

A thermal model of friction stir welding in aluminum alloys

A thermal model of friction stir welding was developed that utilizes a new slip factor based on the energy per unit length of weld. The slip factor is derived from an empirical, linear relationship observed between the ratio of the maximum welding temperature to the solidus temperature and the welding energy. The thermal model successfully predicts the maximum welding temperature over a wide range of energy levels but under predicts the temperature for low energy levels for which heat from plastic deformation dominates. The thermal model supports the hypothesis that the relationship between the temperature ratio and energy level is characteristic of aluminum alloys that share similar thermal diffusivities. The thermal model can be used to generate characteristic temperature curves from which the maximum welding temperature in an alloy may be estimated if the thermal diffusivity, welding parameters and tool geometry are known.

A model for evaluation of laser welding efficiency and quality using an artificial neural network and fuzzy logic

For any welding process, efficiency and quality strongly depend on the energy input, which is the energy introduced per unit length of weld from a travelling heat source. The focused laser beam is one of the highest power density sources available to the welding industry today, which makes it possible to weld with very low energy input with respect to most of other welding processes. In this paper a number of stainless steel butt joints were produced by laser irradiation. The welding efficiencies were calculated as the melted volume-energy input ratio. Moreover, the weld crown and depth were measured in order to evaluate the joint quality. The collected data were interpolated and correlated to the process parameters using an artificial neural network. They were then clustered using a fuzzy C-means algorithm. During the training stage of the neural network algorithm, the design of experiment (DOE) technique was used for the selection of the optimized network parameters. In practice, using some artificial intelligence, a model was built to choose the most suitable laser welding process for producing high efficiency and good quality, and is now available for supporting design and research.

A simple model for multipass steel welds

A model has been developed which is capable of describing the thermal cycles occurring in multipass welds. The method involves a calculation of the size and shape of the single bead-on-plate weld. The isotherms beneath the weld centre-line are estimated using an analytical solution for the problem of heat-flow into a thick plate. The volume of metal deposited per unit length of weld, i.e. the reinforcement, is then assumed to adopt the shape of a spherical cap on the surface of the plate. For multipass welds, the model applies the heat-flow equations as each bead is deposited. The model has been calibrated for a 2 1 4 Cr1Mo multipass weld of a type commonly used for joining steam-pipes in a modern steam-generating power plant. The method has been used to investigate theoretically the effect of interpass temperature, welding current and Ac3 temperature on the fraction of weld microstructure which becomes reaustenitised during fabrication of the weldment. Where possible, the results are rationalised by comparison with experimental observations.