Pulsed Welding Research Articles

Evolutionary Algorithm to Optimize Process Parameters of Al/Steel Magnetic Pulse Welding

The Magnetic Pulse Welding (MPW) process uses only electromagnetic force to create a solid-state metallurgical bond between a working coil and outer workpiece. The electromagnetic force drives the outer tube to collide with the inner rod, resulting in successful bonding. However, due to the dissimilarity of the MPW joint, only a portion of the interface forms a metallurgical bond, which affects the quality of the joint. Therefore, the purpose of this study is to analyze the effects of process parameters on joint quality through experimental work using RSM. Furthermore, an optimization algorithm is utilized to optimize the process parameters used in magnetic pulse welding. A1070 aluminum and S45C carbon steel were used as the materials, while peak current, gap between working coil and outer tube, and frequency were chosen as the process parameters for MPW. The welding conditions are determined through experimental design. After welding, the maximum load and weld length are measured to analyze the effect of the process parameters, and a prediction model is developed. Specifically, to achieve a high-quality joint, the process parameters are optimized using the Imperialist Competitive Algorithm (ICA) and Genetic Algorithm (GA). The results reveal that the peak current is a significant parameter, and the developed prediction model exhibits high accuracy. Furthermore, the ICA algorithm proves very effective in determining the process parameters for achieving a high-quality Al/Steel MPW joint.

Pulsed gas metal arc additive manufacturing of low-carbon steel: Microstructure observations and mechanical properties

Gas metal arc additive manufacturing (GMA-AM), also known as wire arc additive manufacturing (WAAM), uses an electric arc to melt a wire electrode and deposit objects layer by layer. This study focuses on creating single-pass wall structures using a low-carbon steel wire (ER70S-6) and examining the relationship between pulse frequency and weld geometry, microstructure, and mechanical properties. Microscopic observations showed a typical columnar microstructure with three distinct regions: acicular ferrite, bainite, and allotriomorphic ferrite in the first and last layers, while the mid-region exhibited homogenous polygonal ferrite grains with some pearlite at the grain boundaries. The tensile test results demonstrated a dependency of strength on the applied pulse frequency, with the highest strength (i.e., the ultimate tensile strength of 522 MPa and yield strength of 375 MPa with ductility of ∼52%) achieved in parts processed at a frequency of 100 Hz. Vickers microhardness values revealed uniform hardness in the middle region, consistent with the microstructure observation. Analyzing thermal cycles, coupled with microstructure analysis and continuous cooling transition diagrams, provided insight into how phase and microstructure evolution occurred in low-carbon low-alloy steels processed through PGMA-AM.

High-Strength Dissimilar Welds Between a NiTi Shape Memory Alloy and Titanium Obtained by Intermixing Niobium Using Pulsed Laser Beam Welding

Joining of NiTi shape memory alloys with commercially pure titanium (Ti) is of great interest for manifold industrial applications. However, dissimilar fusion welding of these materials is associated with the formation of extremely brittle intermetallic compounds, e.g., Ti2Ni and TiNi3, which drastically limit the mechanical properties of NiTi/Ti joints. The present investigation seeks to improve both chemical compatibility and mechanical performance through intermixing of a niobium foil as filler material into a NiTi/Nb/Ti butt-joint configuration by means of pulsed laser beam welding. Different pulse durations are applied to tailor intermixing and evaluate the deviating chemical compositions of the weld metal. It is demonstrated that intermixing of niobium significantly increases the weldability of the material combination NiTi/Ti compared to autogenous welding. However, the proportion of intermixed filler material exerts a substantial impact on the microstructural evolution and mechanical properties. Ultimate tensile strengths of up to 679 MPa with fracture occurring in the titanium base metal at an elongation at break of 18.7 pct is obtained by a reduction of the pulse duration, which represents a major improvement over previous studies focusing on fusion welding of NiTi to titanium and its alloys.

Transformation sequence of Mg-Si precipitates towards a precipitation of Mn and Cr containing phase governed by the high strain-rate collision during magnetic pulse welding of Al-Mg-Si alloy

This paper investigates the transformation of Mg-Si precipitates formed at an interface of an Al-Mg-Si alloy joint, welded by the high strain-rate collision during magnetic pulse impact welding. The Transmission Electron Microscopy (TEM) and Energy dispersive X-Ray (EDX) analysis of the precipitates reveal a nucleation of circular shape AlFeMnSiCr precipitate (size of ∼100 nm) from the dissolution of the native β″ (needle-shaped) precipitate. The AlFeMnSiCr phase can also reach a size up to several microns and grows into diverse shapes (rod-shaped, polygonal-shaped, ovoid-shaped). Based on the microstructural characterizations and on observations available in the literature including relevant data of Lodgaard and Ryum, the transformation sequence due to the high-speed collision can be described as follows: β″-Mg-Si (needle-shaped) → β’-Mg2Si (rod-shaped) ‘u-phase’ → Al(MnCrFe)Si (round-shaped) → Al(MnCrFe)Si +(+: Cr; Cu and/or Ni, rod-shaped, polygonal-shaped, ovoid-shaped). The comparison of samples welded at three different impact conditions (low impact intensity, intermediate impact intensity, high impact intensity) shows that the area fraction of the precipitates decreases with the increase of the impact intensity. The identification of the crystal structure of these different precipitates, from the nucleation to the final complete formation of the precipitation, can further enrich the transformation sequence in this paper. The role of the high strain kinematics on the deformation of the Al lattice and on the diffusion rate of alloying elements is also a perspective that can further explain this new observation of precipitation during magnetic pulse welding.

Multi-layer additive manufacturing on nickel-based superalloy by optimization of pulsed mode process parameters of single-layer bead geometry

Recent advancements in the wire arc additive manufacturing (WAAM) process for nickel-based superalloys have had a substantial impact on metal additive manufacturing industries such as aerospace, energy, and construction. The input process parameters influence the WAAM part's dimensional accuracy, process stability, and other critical impacts. The quality of each weld layers in WAAM can be controlled by various process parameters. In this study, a single-layer bead was deposited from Hastelloy C-22 using the pulsed mode gas tungsten arc welding (PC-GTAW) process. The chosen input process parameters include pulse frequency (X1), peak current (X2), and pulse on time (X3). The design of experiments (DoE) statistical quality tool was used to optimize the parameters, and the response surface m`ethodology (RSM) technique was used to develop the design matrix. The experiments were conducted based on central composite design (CCD), and their resulting responses bead width (Y1), height (Y2), and depth of penetration (Y3) were evaluated using optical microscopy. The results of the geometrical analysis have revealed a significant correlation between the characteristics of the layer and the parameters of the process. The analysis of variance (ANOVA) method was employed to verify the validity of the actual and predicted models. The model was experimentally validated using the established optimal process parameters, and the mechanical and metallurgical performance was evaluated. The microstructure of the single-layer exhibits equiaxed, cellular, and columnar structures at various regions. The pulse mode process was found to effectively reduce elemental segregation, improve the microstructure, and enhance the mechanical properties of the weld layer. The multi-layer experiments were carried out using the optimal process parameters of a single layer. According to metallographic investigations, the multi-layer that has been deposited exhibits a lack of cracks and porosity. This study provides new insights into the stabilized properties necessary to achieve optimal process parameters and metallurgical characteristics in the robust wire arc additive manufacturing of Hastelloy C-22.

Building ultra-thin Inconel 718 sheet joints using low-frequency PLBW scheme: Weld bead quality, keyhole dynamics, and solidification characteristics

Low-frequency pulsed laser beam welding (PLBW) was employed in building 0.32 mm-thick Inconel 718 superalloy butt joints which are frequently applied in manufacturing high-temperature functional units in the aviation industry. Several process parameter combinations concerning peak laser power, welding speed, and pulse frequency were implemented to explore the macro morphology, microstructure, and mechanical properties of the welded joints. Examinations exhibit that the resulting weld beads possess high continuity at the surface with an overlap factor ranging from 0.58 to 0.73. The cross-sectional profile changes from a V-shape to an H-shape with increasing heat input. Finer grain structures composed of γ matrix and γ/Laves eutectic penetration are observed within the FZ center, as compared to that near the fusion line. Excellent performance is achieved in microhardness and tensile tests. Numerical simulation based on an integrated mathematic model reveals periodic keyhole and weld pool dynamics depending on the pulsing laser power. During a typical pulse interval, keyhole geometry collapses within a fraction of a millisecond, leading to a sharp cooling stage at ∼4 × 106 K/s, and then, the melt cools due to the thermal convection with a normal cooling rate of 105 K/s. The full growth of the adjacent weld spot results in the secondary melting zone (SMZ), wherein the columnar dendrites can be refined mainly due to the heterogeneous nucleation as compared to the primary melting zone (PMZ).

Adaptive Predictive Control of Backside Weld Width in Pulsed Gas Metal Arc Welding Using Electrical Characteristic Signals as Feedback

The control of backside weld width in pulsed gas metal arc welding (GMAW-P) is achieved with two electrical characteristic signals as feedback in the present work. The GMAW-P process is adjusted by changing the parameters of the base current period to provide the needed heat input, while the backside weld width is characterized during the amplitude-fixed peak current period. The two characteristic signals, i.e., the relative change in arc voltage and the average arc voltage during the peak current period, exhibit negative linear relationships with backside weld width and are employed as sensing signals. With these two characteristic signals as outputs, the backside weld width control system in GMAW-P is modeled and analyzed. The adaptive predictive controller is thus designed and validated in real-time control. This work provides an easily implemented way for weld geometry control in GMAW-P and thus has a practical meaning.

The role of asymmetric metal flow on weld formation and solidification characteristics during pulsed laser butt welding with assembly tolerance

In comparison to other laser-assisted welding techniques, the pulsed laser welding process (PLBW) provides cost-effectiveness and ease of operation while effectively connecting butt-assembled thin plates with manufacturing tolerances (both air gap and edge misalignment). A combination of numerical simulations and experimental studies was conducted to analyze the forming mechanism and solidification behavior of the weld. In this paper, a transient three-dimensional heat-flow-metallurgical model has been established for a PLBW process of mild steel plates with a thickness of 1.8 mm. The predicted weld pool profiles were consistent with the experimental findings. The finding suggested the molten metal, driven by surface tension and recoil pressure, successively generated liquid bridges on the rear and front sides of the pool. The two sheets were joined as the molten metal gradually solidified. The energy absorptivity was highly correlated with the weld pool and keyhole dynamics, and the laser energy absorbed by the metal was mainly transferred in the form of thermal convection. The kinematic features of the melt were observed by the liquid phase mass transfer rate and surface fluctuations. According to the Fourier analysis results, the molten pool oscillated at the characteristic frequency of the laser pulse frequency. The spatial and temporal distributions of solidification parameters aided in analyzing the solidification features within the pool. The asymmetric flow had a greater influence on the temperature gradient. These findings addressed the roles of PLBW on fluid flow, heat behaviors, and solidification parameters of welds with assembly tolerances, as well as the reasons for improved weld formation.

Reduction of the welding fume emission rate of gas-shielded cored wires by the MAG pulse welding process variant

The aim of the study is to reduce welding fume emissions from flux-cored wires using pulse technology. Low-alloyed cored wires of the rutile, basic, and metal powder types were selected for this purpose. The analyses were carried out on a DIN EN ISO 15011–1:2010 compliant test rig. In addition, high-speed recordings of the material transition mode and metallographic cross-sections were made to interpret the results. Using characteristic curves developed in pre-tests, the influence of pulse time, pulse frequency, and trigger current on the welding fume emission potential of the rutile cored wire was first determined. Short pulses, medium trigger current, and medium pulse frequency were found to have a positive influence on the emission rate.Finally, the welding fume emissions of the conventional characteristic are compared with the emission-optimized pulse characteristic. For all three filling types, emission reductions of up to 41% were found when using the pulse technology. When considering the ratio of fume generated to the mass of the weld metal produced, with the associated greatly reduced economy of the process, it became apparent that pulse welding is not suitable for welding cored wires without restrictions.In summary, the suitability of pulse GMAW technology for reducing welding fume emissions can also be confirmed for flux-cored wires.

Numerical and experimental investigation of metal droplet transfer during pulsed bypass-current plasma-GMAW hybrid arc welding

Numerical and experimental investigation of metal droplet transfer during pulsed bypass-current plasma-GMAW hybrid arc welding

Effect of preheating temperature on the defects in pulsed laser welding of sheet AZ31 magnesium alloy

To suppress the welding defects of thin sheet magnesium alloy by pulsed laser welding, AC-300 W pulsed laser welder is used to weld 1 mm magnesium alloy at different preheating temperatures, and the effect of preheating temperature on solidification cracks, pore and undercut are studied. Preheating temperature is set at 25 ℃, 100 ℃, 150 ℃, 200 ℃, 250 ℃, 300 ℃ and 350 ℃. Results show that preheating increases the peak temperature (1494.14 ℃ to 1785.86 ℃) and reduces the cooling rate (14489.33 ℃/s to 14282.11 ℃/s) of the molten pool, thereby reducing welding defect sensitivity. When preheated at 200 ℃, the solidification cracks and pores disappear, and the undercut depth reaches the minimum value of 0.04 mm.

Effect of process parameters on surface formation in laser welding of Al2O3 ceramic

The attainment of formability in ceramic welding presents an imposing quandary within the realm of the manufacturing industry. In this article, the laser welding of Al2O3 ceramics was carried out to compare and analyze the influence of laser power, welding speed, laser duty cycle, and other process parameters on the macroscopic morphology of the weld, weld cracking rate, and welded joint properties. The results show that Al2O3 ceramic welds have a greater tendency to cracking and that the laser power should be matched to the appropriate welding speed. When heat input increases, the weld cracking rate decreases and then increases. Ceramic welded joints with a weld cracking rate of less than 30 % and a bending strength of more than 4 MPa can be obtained when the heat input range is 17–20.5 J/mm for continuous laser welding or 20.5–24 J/mm for pulsed laser welding. In addition, under high heat input conditions, pulsed laser welding reduces the tendency for weld cracking compared to continuous laser.

Double pulse gas metal arc welding process parameter optimization and weld performance analysis based on response surface method

Double pulse gas metal arc welding (DP-GMAW) is a low-frequency modulated high-frequency pulse welding, which can fully stir the molten pool, and improve the forming and performance of the weld. In this study, a mathematical model was developed using the response surface method (RSM) with three main process parameters (welding current, peak-to-base ratio, welding speed) as input values with three key geometric characteristics parameters, and the mechanical properties of the resulting welds were investigated. The results showed that the parameter model developed in this study had less error and could optimize the process parameters better; the optimal process parameters (welding current, peak-to-base ratio, welding speed) were 160 A, 39.93%, and 83.11 cm min−1, respectively. The improved welding parameters result in better mechanical properties and better weld profile, and more stable welding process. As a result, this experiment provides a new perspective for process parameter optimization and mechanical properties research for weld manufacturing.

Optimization on the mechanical parameters and impact of welding parameters of pulsed TIG welding of Aluminium-Zinc-Magnesium alloy

As a function of pulsed Tungsten Inert Gas (TIG) weld processing factor, authors have studied the relationship between dilution and mechanical qualities including impact toughness, notch tensile strength, hardness in the as-welded condition. Welds made with a pulsed TIG torch have a minimum notch tensile strength and impact toughness than the base metal (BM) because of the grains of the inter-dendritic network formed during the welding process. Weldments made from heat-treatable (Al-Zn-Mg) Aluminium alloys have their process parameters for pulsed TIG welding optimized employing the Taguchi analysis to get the best possible mechanical qualities. Notch tensile strength is shown to be inversely proportional to impact toughness.

Effect mechanism of arc oscillation on microstructure and mechanical performance of SUS304 weld seams manufactured by local dry underwater double pulsed MIG welding

An innovative local dry underwater double pulsed MIG (LDU-DPMIG) technique was successfully applied to fabricate SUS304 weld seams, in which the stirring effect on the molten pool was realized via a double pulsed current waveform. The weld formation, phase morphology and distribution, grain structure characteristics, microhardness, and tensile properties of underwater weld seams were comprehensively analyzed in this study, especially the mechanism differences between local dry underwater single pulsed MIG (LDU-SPMIG) and LDU-DPMIG were revealed. The results demonstrated that the stirring effect caused by arc oscillation contributed to the enhancement of the molten pool fluidity during the solidification process, which effectively facilitated the smooth elements allocations between austenite and ferrite and the evolution of δ-ferrite phase structure from skeleton to lath. In addition, the grain structure in the DPMIG weld centre transformed from slender columnar dendrites to fine equiaxed dendrites. Due to the pronounced stirring effects in uniform composition distribution, ferrite morphology evolution, grain refinement, and increased twin activity, DPMIG weld seams exhibited an attractive enhancement in weld mechanical performances, with the optimal low frequency of 3 Hz, the average microhardness, ultimate tensile strength, and elongation enhanced by the highest 18.1%, 8.9%, and 16.3% compared with SPMIG weld seam. These results are expected to offer a novel approach to regulate and control the microstructure and mechanical performance of underwater weld seams and facilitate the application of LDU-DPMIG in ocean engineering equipment.

A Comparative Study on High-Temperature Oxidation Behavior, Microstructure Characterization, and Texture of UNS R30155 Superalloy Weldment Joint Using Pulsed Current and Constant Current Gas Tungsten Arc Welding

A Comparative Study on High-Temperature Oxidation Behavior, Microstructure Characterization, and Texture of UNS R30155 Superalloy Weldment Joint Using Pulsed Current and Constant Current Gas Tungsten Arc Welding

Miniaturized S-shaped flexible magnetic pulse welding coil design for engineering applications

Magnetic pulse welding (MPW) as a new solid-phase welding technology in the manufacturing field has vast application prospects. However, the application of MPW in engineering is severely limited by the large working area required for existing coils resulting in poor flexibility of the process. In this paper, a highly flexible, miniaturized S-shaped stereoscopic coil was proposed to reduce the working area required for the MPW process. The required working area was reduced to 32 × 30 mm. Numerical simulations were performed to determine the most suitable coil cross-section size. In addition, the feasibility of the coils was verified by welding AA5052 aluminum alloy and 316 L stainless steel through the new stereoscopic coils. Quasi-static tensile testing, laser microscopy, Scanning Electron Microscopy (SEM) and Energy Dispersive Spectrometer (EDS) were used to characterize the mechanical properties of the joints, weld interface morphology and element diffusion, respectively. It was revealed through simulation that the impact velocity of the new stereoscopic coil during MPW (342 m/s) was slightly higher than that of the conventional flat coil (327 m/s) at the same discharge energy. This indicated that the coil could achieve reliable welding. The AA5052-316 L joint welded by the new stereoscopic coil was demonstrated to be reliable by experiments. Furthermore, microscopic observation revealed that two effective bonding regions were formed at the interface. In addition, continuous interfacial waves and element diffusion were observed at the welding interface. Finally, the typical parts of AlFe double-cap beam structure were successfully welded by using a new stereoscopic coil. The coil is beneficial to broaden the application field of MPW.

Study on pulsed wave mode laser welding of Nb-Zr-C alloy and many-objective optimization using meta-heuristic techniques

Study on pulsed wave mode laser welding of Nb-Zr-C alloy and many-objective optimization using meta-heuristic techniques

Contact reactive brazing of TC4/304 stainless steel dissimilar metals by interrupted arc pulsed welding

The most challenging aspect of producing durable joints between titanium alloy and stainless steel (Ti/SS) is preventing the formation of brittle Ti–Fe intermetallic compounds, particularly the TiFe2 phase. In this paper, the interrupted pulsed arc welding (IPAW) was proposed to join TC4 and 304SS dissimilar metals. The joining mechanisms, microstructures and shear strength of the joints were investigated. The precise regulation of arc pulsed time in the millisecond range enabled the creation of a joint without the formation of the TiFe2 phase through contact reactive brazing. A Ti-rich reaction layer consisting of β-Ti and TiFe phases was formed in the brazing joint, and the shear strength of the joint reached 106.3 MPa. By increasing the arc pulsed current or time, the brazing joint was transformed into the fusion joint. The formation of two reaction layers was observed: Ti-rich phases (TiFe and β-Ti) near the TC4 and Fe-rich phases (TiFe2 and TiCr2) near the 304SS, which exhibited high brittleness. The presence of a high brittleness fusion zone resulted in immediate cracking post-welding.

Using the numerical simulation and artificial neural network (ANN) to evaluate temperature distribution in pulsed laser welding of different alloys

The temperature field during laser welding process plays an important role on determining the quality and quantity of the weld bead size, microstructure characterizations and mechanical properties of the welding interface in the thermal engineering applications. In this study, using the numerical simulation, the influence of pulse duration and frequency on the temperature distribution and velocity field in distinctive laser welding of stainless steel 420 (S.S 420)/stainless steel 304 (S.S 304), and Bohler 303 (B 303)/stainless steel 304 (S.S 304) was examined. The results of numerical modeling illustrated that shear stress of Marangoni and buoyancy force are the most curtail aspects in the formation of the flow of liquid metal. A novel artificial intelligence method is proposed to optimally predict the melting ratio, and maximum temperature of the materials. To this end, a combination of ANN and Particle Swarm Optimization (PSO) algorithms are employed. The PSO algorithm is used to optimize the architecture and training algorithm of the ANN, while the ANN is employed for the regression problem. Based on the results, a three-layer feed-forward architecture with sigmoid transfer functions having 17 and 8 neurons in the hidden layers combined with the scaled conjugate gradient backpropagation training scheme is recognized by the PSO as the optimal configuration. Application of optimal ANN to the regression problem results in an acceptable level of error for the training, validation, and test datasets. Finally, the optimized ANN can be utilized to anticipate the melting ratio and thereby the resultant temperature.