Pulsed MIG Welding Process Research Articles

MECHANICAL AND METALLURGICAL CHARACTERISATION OF DOUBLE PULSE MIG WELDED IN 617- SS 304 H

ABSTRACT This work attempts to study the mechanical and metallurgical properties of dissimilar welded IN (Inconel) 617-SS (Stainless steel) 304 H plates. Welding was carried out using the Double Pulse MIG Welding Process (DP-MIG) with two different heat inputs, namely 412 J/mm and 452 J/mm. The presence of chromium-rich carbides Cr23C6 helped in strengthening the weld. The tensile strength of the weld made at 452 J/mm was 22% more than that of the weld made at 412 J/mm. Similarly, the weld hardness at 452 J/mm was 8% greater than the weld strength at 412 J/mm. The impact strength did not change significantly with respect to the heat input. Weld made at lower heat input (412 J/mm) had a lack of sidewall fusion. Lower frequency and amplitude contributed to poor heat distribution, leading to a lack of sidewall fusion.

Investigations of heat source models in transient thermal simulation of pulsed MIG welding of AA6061-T6 thin sheet

The automobile and aviation industries are exhaustively working on weight reduction by replacing steel with aluminium alloy. However, joining the aluminium alloy body panel is remain a big challenge because of the inherent properties of aluminium. The dynamic behaviour of arc plasma in the pulsed MIG welding process is a multifaceted heat mass transfer phenomenon involving chemical, electro-magnetic, and fluid dynamics. Numerical simulation using FEA techniques are greatly helpful in understanding responses of weld bead and material behaviour. Simultaneously it reduces time and cost consuming experimental trial and error approach. The approximation of the welding arc heat source is paramount for precise prediction in the welding process simulation model. The article focuses on the comparison, suitability and effects of various moving heat source models by developing the transient thermal simulation of pulsed MIG welding of 1mm thick AA6061-T6 sheet in ANSYS workbench. Moving heat source models were developed as ANSYS APDL command subroutine. It is observed that for 1mm thin sheets Gaussian surface heat source model is also valid. The difference in temperature field is not prominent in comparison with Goldak’s double ellipsoidal heat source model.

Progress in the arc plasma temperature measurement and its finite element analysis in pulsed MIG welding process

The article focuses on the state of the art review of progress in the arc plasma temperature measurement, a lesser-explored area of pulsed metal inert gas welding because of technological and economic constraints. However, investigation of the arc plasma temperature is paramount for precise prediction in welding process simulation models. The dynamic behavior of arc plasma in the pulsed MIG welding process is a multifaceted heat mass transfer phenomenon involving chemical, electro-magnetic, and fluid dynamics. In the pulsed MIG welding process thermal, mechanical, and electrical phenomenon co-exists and results in the formation of all four states of matter in a very small fusion sphere. The paper throws light on the latest investigations on the importance of precise measurement of arc plasma temperature, techniques used for measurement of the arc plasma, and challenges associated with pulsed MIG welding. Moreover, unanswered characteristics of the welding fusion sphere with future directions are discussed in the challenges section. It will serve as a guide to researchers and industry for developing better insight for performing pulsed MIG welding, developing accurate numerical models of pulsed MIG welding, and will also provide sufficient base to focus on thrust area of pulsed MIG welding.

Practical Investigation of FSS (AISI 430) Weldments Welded by Pulse MIG Welding Process

Ferritic stainless steels are iron-chromium alloys having chromium content usually in the range of 10.5–27%. In these steels the predominant metallurgical phase present is ferrite. These steels are Fe-Cr-C alloys with sufficient chromium or chromium plus other ferrite stabilizer, such as aluminium, niobium, molybdenum, titanium, used to inhibit the formation of austenite phase on heating. Ferritic stainless steel (FSS) is generally considered to have poor weldability when compared to austenitic stainless steel (ASS) but has recently drawn greater attention owing to their lower costs and better resistance to stress corrosion resistance than austenitic stainless steel. Ferritic stainless steels have been widely used in vessels, vehicles, household appliances, kitchen equipments and building decoration because of its excellent stress corrosion and spot corrosion resistance addition to good strength. Because it does not contain nickel, it is a cheaper alternative of austenitic stainless steel. In this work weldments of FSS welded by pulse MIG welding using argon as a shielding gas were investigated. The austenitic stainless steel (ER309L) and ferritic stainless steel (ER430) electrode wires were used to prepare the weldments. To obtain a good welded joint the welding process parameters were experimentally optimised. The microstructures and mechanical properties of the prepared weldments were investigated. In the weldment welded by austenitic stainless steel electrode wire dendritic austenitic phase was observed in the weld metal zone. In heat affected zone intragranular carbide precipitation and grain boundary martensite were observed. In case of weldments welded by ferritic stainless steel electrode wire coarse grains were formed in weld metal zone and heat affected zone. Grain boundary martensite, ferrite and intragranular carbide precipitation were found in weld metal zone and heat affected zone. Impact strength of the weldments welded by austenitic stainless steel electrode wire was found higher due to formation of austenite phase in the weld metal zone. Impact strength of the weldments welded by ferritic stainless steel electrode wire was found very low due to formation of coarse grain and martensite in the weld metal zone. The ultimate tensile strength and percentage elongation of the weldments welded by austenitic stainless steel electrode wire were found higher than the weldments welded by ferritic stainless steel electrode wire. Hence weldments of ferritic stainless steel having superior mechanical properties will be obtained by using austenitic stainless steel electrode wire. During the tensile test the specimens were broken outside the welded joint (in base metal) which confirms the good quality of the joints

Arc Length Control of Pulsed MIG Welding Based on Two Dimensional Fuzzy Control

In the process of the pulse MIG power supply welding, the arc length will change dynamically due to various environmental disturbances. Therefore, how to realize the real-time control of the arc length is the key to the stability of the pulse MIG welding process, and it is also an important guarantee of the welding quality. In this paper, the three voltage loop control methods of no arc length control, one-dimensional fuzzy control and two-dimensional fuzzy control are compared through matlab simulation. The simulation results show that the arc length control scheme of welding power supply based on two-dimensional fuzzy control can achieve better dynamic response when the stepwise mutation occurs in the arc length.

Modeling and Control of Pulsed Double-electrode MIG Welding Process

Pulsed double-electrode metal inert gas welding is a new kind of low heat input welding method. With different connection, parts of welding current bypassed and it controlled the base metal current and melting current separately. With free-flight metal transfer process, it could weld dissimilar metals. Aiming at the unstability of coupling arc in pulsed double-electrode metal inert gas welding process, a dynamic mathematic model has been built to truly describe and simulate the welding process with equivalent simplification, linearization and iterative solution. Then a control scheme is put forward and simulated, which changes the wire feed speed to adjust the main arc length, and further to control the stability of the coupling arc. Also the welding experiments with control scheme are carried based rapid prototyping system. Simulations proved the effectiveness of control scheme. And with controlling, the welding experiment is more stable and a good Al-Fe joint is acquired.

Study and Investigations on Process Parameters for Bead Geometry during Cladding by Pulsed MIG Welding Process

Bead geometry is a very important factor in achieving and studying the properties of the weld cladding in fusion welding process. This paper addresses minimization of depth of penetration and predicting the behavior of the cladded bead parameters during cladding of AISI 317L stainless steel electrode of 1.2mm diameter over low carbon structural steel (ASTM A105/ IS: 2062), by using Pulsed Metal Inert Gas welding process through response surface methodology. The input process parameters for present analysis are welding current (I), welding speed (S) and nozzle-to-plate distance (N) respectively. Experiments were conducted as per central composite design techniques, models were developed from the collection of data, and the measured responses are viz., depth of penetration, height of reinforcement and bead width. From the ANOVA it was found that welding speed and nozzle-to-plate distance is the dominant parameter in deciding the depth of penetration of the weld bead at the lower level. It is also found that the height of reinforcement reduces with increase in the welding speed.

Development of Mathematical Model for Prediction of Convexity Index in Cladding by Pulsed MIG Welding Process

Pulsed metal inert gas welding (PMIGW) process is more effective for cladding. The input process parameters for present analysis are welding current (I), welding speed (S) and nozzle-to-plate distance (N) respectively. By using response surface methodology technique the experiments were conducted as per central composite design techniques. The measured response is convexity index and models were developed from the collection of data and checked for their adequacy. Analysis of variances was used to analysis the input process parameters. The direct effect and interactive effect of the process parameters on the convexity index is significant and cannot be neglected it is represented graphically.

Effect of Laser Power on Stability of Laser-Twin-Wire Hybrid Welding Process

Based on the chaos theory and related algorithm, largest Lyapunov analysis of current of laser-twin-wire pulse MIG welding process are performed from the point of view of nonlinear time sequence. Largest Lyapunov exponent (LLE) of characteristic current under different laser power were calculated, meanwhile synchronous high-speed photography was adopted to observe arc shape and droplet transfer. The results indicate that arc shape and the force state of droplets changes as a result of interactions between laser plasma and arc plasma. Addition of low power laser intensifies the interplay of two arcs, which decreases the stability of welding process. When laser power reaches to a certain extent, a stable cathod spot and a conductive channel are obtained for arcs. Stable welding process and small welding spatter are acquired.

Effect of Laser Beam on Double Wire Pulsed MIG Welding Process

Based on the coupling of laser beam and double arcs, a novel process was investigated. This research set up the laser-double wire pulsed MIG hybrid welding system. Meanwhile the current and voltage sensors were used to detect welding current and arc voltage wave-form and high-speed videography system was used to observe the metal transfer process and arc behavior. The three signals were acquired synchronously. The results showed that the synergic action of the three different heat sources leads to a change in metal transfer mode. It was revealed that the metal transfer mode was two droplets per pulse in laser-double wire hybrid welding process while one droplet per pulse in double wire welding process with the same certain experiment parameters. And we also discovered that the arcs were attracted strongly by the laser beam.

Weld Width Control System for Pulsed MIG Welding of Aluminum Alloy

Due to strong heat accumulation and low surface tension of aluminum alloy, weld width will become wider, even subsidence in pulsed MIG welding process of aluminum alloy at constant parameters. A variable double-pulse method for weld width control is proposed. Weld width control is realized by changing double-pulse duty cycle that is the ratio of high-energy pulse time in a double-pulse cycle to adjust heat input based on the vision sensing for weld width. A rapid prototyping control system is built on the basis of vision sensing and xPC Target real-time environment. Then variable double-pulse MIG welding process test is done and proves the feasibility of the control scheme. On this basis, weld width control test in pulsed MIG welding of aluminum alloy is carried out and obtains a good weld with beautiful formation and uniform weld width. The results show that weld width control can be realized well with the variable double-pulse method in pulsed MIG welding of aluminum alloy.

Double-variable Decoupling Control for Pulse MIG Welding Process of Aluminum Alloy

In view of the key problems such as small match range of welding parameters,strong coupling effect among parameters,unstable welding process and poor weld formation in pulsed MIG welding process,a double-variable decoupling control method is proposed.The weld pool width and wire extension signals are both fed back through vision sensing.On the one hand,weld pool width control is realized by changing double-pulse duty cycle to adjust heat input,on the other hand,wire extension is controlled simultaneously by changing wire feed speed.So the weld formation is improved by control and the stability of welding process is ensured at the same time.A self-tuning fuzzy PID controller is designed and a rapid prototyping control platform is developed for pulsed MIG welding of aluminum alloy by using real-time target environment based on xPC.On this basis,double-variable decoupling control test is carried out by adopting compensation decoupling method and weld beads with uniform pool width and good formation are obtained.The results show that the double-variable decoupling control method can realize the control of pulsed MIG welding process of aluminum alloy and obtain good weld formation on the basis of stable welding process.

Joining of Steel to Aluminum Alloy by AC Pulse MIG Welding

This study evaluates the characteristics of welds resulting from joining dissimilar alloys, steel SPRC440 and aluminum alloy 6K21. The joint was obtained by means of AC pulse MIG welding, which alternates between direct current electrode positive (DCEP) and direct current electrode negative (DCEN), based on the EN ratio. In order to evaluate the AC pulse MIG welding for the dissimilar joining of steel SPRC440 to Aluminum alloy 6K21, the arc characteristics in relation with varying EN ratios were analyzed. The AC pulse MIG welding process showed good gap bridging ability. The joining quality of the dissimilar alloys was evaluated by the analyzing the intermetallic compound layer. [doi:10.2320/matertrans.M2009105]

Joint strength prediction in a pulsed MIG welding process using hybrid neuro ant colony-optimized model

In this work, a pulsed metal inert gas welding (PMIGW) process is modeled by using a hybrid soft computing technique. Ant colony optimization (ACO) and back-propagation neural network (BPNN) models are combined to predict the ultimate tensile strength of butt-welded joints. A large number of experiments have been conducted, and comparative study shows that the hybrid neuro ant colony-optimized model produces faster and also better weld-joint strength prediction than the conventional back propagation model.

交流および直流パルスミグ溶接のアーク安定化制御方法に関する研究

Changes in arc voltage do not always mean fluctuations of arc length in aluminium alloy welding because cathode fall voltage increases with the absence of oxide. In addition, with the absence of oxide cathode spots become concentrated and the current density near the cathode surface becomes high so that the potential gradient there increases. After the breaking of a short circuit at electrode positive polarity cathode spots are formed on the centre of weld pool surface where little oxide exists. As a result, arc voltage becomes abnormally high in spite of the short arc length. Moreover, when polarity is switched from electrode positive to electrode negative right after the detachment of a droplet, cathode spots are formed on the surface of remained melt metal at the wire tip where little oxide exists so that arc voltage also becomes abnormally high. The arc becomes unstable when those abnormal arc voltages are included in the feedback signal for arc length control. Therefore, a digital filter is developed to obtain correct arc length information by eliminating those abnormal arc voltages from the feedback arc voltage.The algorism of arc length control system is another important factor that affects arc stability. A new algorism is developed to monitor continually the feedback arc voltage of the present pulse cycle and to determine the right timing to terminate the base duration of the present pulse cycle. By using this algorism the average current and average voltage of every pulse cycle plot a line with a decreasing characteristic called pulse V-I characteristic. The inclination of the pulse V-I characteristic can be set freely and controlled accurately. Arc stability is improved by optimisation of the inclination in AC or DC pulsed MIG welding. Furthermore, low frequency modulated AC pulsed MIG welding process is developed by setting two pulse V-I characteristics and switching between them periodically at a low frequency.

交流パルスミグ溶接のワイヤ溶融現象およびビード形成現象に関する研究

Mechanisms of high melting coefficient and bead formation in welding aluminium-magnesium alloy with AC pulsed MIG welding process are investigated. In electrode negative polarity cathode spots clime up to the solid part of wire tip for the existence of oxide and arc root covers uniformly a large area on the surface of wire tip. This polarity prevents a droplet on wire tip from being overheated in part so that the heat transferred from arc plasma to wire tip is effectively used for wire melting. Moreover, as electrode negative ratio increases at a certain welding current, arc plasma transfers more heat to wire tip at the cost of reducing the heat transferred to base metal. As a result, wire melting coefficient becomes greater at a higher electrode negative ratio. Since the heat input to base metal is a sum of the heat transferred from arc plasma to base metal and the heat brought into weld pool by droplet transfer, it does not change obviously as electrode negative ratio changes drastically at a certain welding current. At a constant wire feed rate, heat input to base metal and penetration depth decrease as electrode negative ratio increases mainly due to the decrease of welding current. Besides, reinforcement becomes high and bead width becomes narrow as electrode negative ratio increases because of the lower heat input to base metal and reduction of heat content of droplets. Accordingly, AC pulsed MIG welding process can successfully solve the burn through problem in welding thin sheet joints and greatly improve the gap bridging ability. Moreover, thin sheet joints can be welded with high speed and small distortion.

交流パルスミグ溶接法によるＡｌ‐Ｍｇ合金の溶接ヒューム抑制機構に関する研究

Large amounts of welding fumes are produced in joining aluminium-magnesium alloys with DC pulsed MIG process. Welding fumes consist of magnesium oxide, aluminium oxide and pure aluminium. Magnesium element evaporates from both the surface and inside of droplets that are superheated. Evaporation inside of droplets produces magnesium bubbles, leading to violent explosions of droplets and emissions of magnesium vapour and liquid spatters. Part of magnesium vapour escaped from the shielded arc area is oxidised and then becomes super fine fume particulates that their shapes can not be recognized even with transmission electron microscope. Part of spatters ejected from the shielded arc area are partially or completely oxidised and then become fume particulates. In AC pulsed MIG welding the average heat content of droplets is low, and besides, the temperature distribution inside a droplet is deduced to be more uniform compared with that of DC pulsed MIG welding. In consequence, the evaporation of magnesium is restrained so that both frequency and violence of droplet explosions decrease clearly. AC pulsed MIG welding process can effectively control welding fumes at source in joining aluminium-magnesium alloys.

Inhibiting effect of low‐frequency pulsed MIG welding on blowhole generation in AI and its alloys (3rd report). Study of low‐frequency pulsed MIG welding

Summary Vibration of the weldpool is achieved in the low‐ frequency pulsed MIG welding process using a new current waveform for alternate switching of two unit pulse conditions. This paper describes an investigation of the beneficial effect of reducing blowholes, which often cause problems during MIG welding of A1 and its alloys, using the above process in 99.9%Ar‐0.1%H2 shielding gas. A switching frequency of the unit pulse conditions in the fs = 10–25 Hz range is shown to have a beneficial effect of reducing blowholes in various wire‐parent metal combinations, at various welding speeds, and in flat, vertical‐up, and horizontal positions. This process is also effective in reducing blowholes in Al cast alloys.

低周波パルスミグ溶接の研究（第３報） 低周波パルスミグ溶接法によるＡｌおよびその合金の溶接部に発生する気孔の抑制効果

Vibration of molten puddle is achieved with the low frequency pulsed MIG welding process of new current waveform to switch over two preset unit pulse conditions alternately.In this paper, beneficial effect of reducing the blowholes which often cause problems in MIG welding of Al and its alloy was investigated by using above mentioned process under 99.9%Ar-0.1%H2 shielding gas atmosphere.It was made clear that switching frequency of unit pulse conditions in the range of fs=10-25 Hz had beneficial effect of reducing blowholes on various wire-base metal combinations, welding speed and flat, vertical-up and horizontal positions.Moreover, this process was effective in reducing the blowholes for Al cast alloy.

Ａｌおよびその合金の低周波パルスミグ溶接法の開発 低周波パルスミグ溶接の研究 （第一報）

The low frequency pulsed MIG welding process of new current waveform control to switch over unit pulse conditions (pulse current, pulse duration) in the fixed cycle was developed and its effect were investigated for aluminium and its alloy.By using this new welding process, the bead appearance having clear ripple pattern, such as TIG welding bead can be obtained and the gap tolerance of lap and butt welding joint can be expanded.