Optimizing the Pulsed Current Gas Tungsten Arc Welding Parameters

The selection of process parameter in the gas tungsten arc （GTA） welding of titanium alloy was presented for obtaining optimum grain size and hardness. Titanium alloy （Ti-6Al-4V） is one of the most important non-ferrous metals which offers great potential application in aerospace, biomedical and chemical industries, because of its low density （4.5 g/cm^3）, excellent corrosion resistance, high strength, attractive fracture behaviour and high melting point （1678℃）. The preferred welding process for titanium alloy is frequent GTA welding due to its comparatively easier applicability and better economy. In the case of single pass （GTA） welding of thinner section of this alloy, the pulsed current has been found beneficial due to its advantages over the conventional continuous current process. Many considerations come into the picture and one needs to carefully balance various pulse current parameters to reach an optimum combination. Four factors, five level, central composite, rotatable design matrix were used to optimize the required number of experimental conditions. Mathematical models were developed to predict the fusion zone grain size using analysis of variance （ANOVA） and regression analysis. The developed models were optimized using the traditional Hooke and Jeeve＇s algorithm. Experimental results were provided to illustrate the proposed approach.

Optimization of pulsed current gas tungsten arc welding process parameters to attain maximum tensile strength in AZ31B magnesium alloy

An empirical relationship to predict tensile strength of pulsed current gas tungsten arc welded AZ31B magnesium alloy was developed. Incorporating process parameters such as peak current, base current, pulse frequency and pulse on time were studied. The experiments were conducted based on a four-factor, five-level, central composite design matrix. The developed empirical relationship can be effectively used to predict the tensile strength of pulsed current gas tungsten arc welded AZ31B magnesium alloy joints at 95% confidence level. The results indicate that pulse frequency has the greatest influence on tensile strength, followed by peak current, pulse on time and base current.

Optimizing pulsed current gas tungsten arc welding parameters of AA6061 aluminium alloy using Hooke and Jeeves algorithm

Though the preferred welding process to weld aluminium alloy is frequently constant current gas tungsten arc welding (CCGTAW),it resulted in grain coarsening at the fusion zone and heat affected zone(HAZ).Hence,pulsed current gas tungsten arc welding(PCGTAW) was performed,to yield finer fusion zone grains,which leads to higher strength of AA6061 (Al-Mg-Si) aluminium alloy joints.In order to determine the most influential control factors which will yield minimum fusion zone grain size and maximum tensile strength of the joints,the traditional Hooke and Jeeves pattern search method was used.The experiments were carried out based on central composite design with 31 runs and an algorithm was developed to optimize the fusion zone grain size and the tensile strength of pulsed current gas tungsten arc welded AA6061 aluminium alloy joints.The results indicate that the peak current (Ip) and base current (IB) are the most significant parameters,to decide the fusion zone grain size and the tensile strength of the AA6061 aluminum alloy joints.

Effect of Pulsed Current TIG Welding Parameters on Pitting Corrosion Behaviour of AA6061 Aluminium Alloy

Medium strength aluminium alloy （Al-Mg-Si alloy） has gathered wide acceptance in the fabrication of light weight structures requiring a high strength-to weight ratio, such as transportable bridge girders, military vehicles, road tankers and railway transport systems. The preferred welding process for aluminium alloy is frequently TIG （tungsten inert gas） welding due to its comparatively easier applicability and better economy.In the case of single pass TIG welding of thinner section of this alloy, the pulsed current has been found beneficial due to its advantages over the conventional continuous current process. The use of pulsed current parameters has been found to improve the mechanical properties of the welds compared to those of continuous current welds of this alloy due to grain refinement occurring in the fusion zone. A mathematical model has been developed to predict pitting corrosion potential of pulsed current TIG welded AA6061 aluminium alloy.Factorial experimental design has been used to optimize the experimental conditions. Analysis of variance technique has been used to find out the significant pulsed current parameters. Regression analysis has been used to develop the model. Using the developed model pitting corrosion potential values have been estimated for different combinations of pulsed current parameters and the results are analyzed in detail.

Effect of pulsed current on temperature distribution,weld bead profiles and characteristics of gas tungsten arc welded aluminum alloy joints

Temperature distribution and weld bead profiles of constant current and pulsed current gas tungsten arc welded aluminium alloy joints were compared. The effects of pulsed current welding on tensile properties, hardness profiles, microstructural features and residual stress distribution of aluminium alloy joints were reported. The use of pulsed current technique is found to improve the tensile properties of the weld compared with continuous current welding due to grain refinement occurring in the fusion zone.

Effects of pulse parameters on arc characteristics and weld penetration in hybrid pulse VP-GTAW of aluminum alloy

A novel ultrafast-convert hybrid pulse variable polarity gas tungsten arc welding process （HPVP-GTAW） is developed. High frequency pulse square-wave current which has a frequency of more than 20 kHz is exactly integrated in the positive polarity current duration. The effects of pulse current parameters on arc characteristics and weld penetration have been studied during the HPVP-GTAW process using Al-5. 8 Mg alloy plates. The arc characteristics studied by arc voltage and its profile, weld penetration noted by the ratio of weld depth to width have been found to be influenced significantly by the pulse current. The experimental results show that the HPVP-GTA W process can improve the arc profile predominantly and obtain the higher weld penetration with lower heat input. The observation may help in understanding the weld characteristics with respect to variation in the pulse current parameters which may be beneficial in using the novel HPVP-GTAW process to produce the better weld quality of aluminum alloy plates.

Modeling corrosion behavior of gas tungsten arc welded titanium alloy

The pitting corrosion characteristics of pulse TIG welded Ti-6Al-4V titanium alloy in marine environment were explained. Besides the rapid advance of titanium metallurgy, this is also due to the successful solution of problems associated with the development of titanium alloy welding. The preferred welding process of titanium alloy is frequently gas tungsten arc(GTA) welding due to its comparatively easier applicability and better economy. In the case of single pass GTA welding of thinner section of this alloy, the pulsed current has been found beneficial due to its advantages over the conventional continuous current process. The benefit of the process is utilized to obtain better quality titanium weldments. Four factors, five levels, central composite, rotatable design matrix are used to optimize the required number of experiments. The mathematical models have been developed by response surface method(RSM). The results reveal that the titanium alloy can form a protective scale in marine environment and is resistant to pitting corrosion. Experimental results are provided to illustrate the proposed approach.

Optimization of back bead geometry in the PMAG-TIG twin arc hybrid root welding process using grey based Taguchi method

This study investigated multi-response optimization of the pulse metal active gas-tungsten inert gas( PMAG-TIG) twin arc hybrid root welding process for an optimal parametric combination to yield favorable back bead geometry of welded joints using grey relational analysis and Taguchi method.Eighteen experimental runs based on an orthogonal array following the Taguchi method were performed to derive objective functions to be optimized within the experimental domain.The objective functions were selected in relation to parameters of PMAG-TIG twin arc root welding back bead geometry: back bead width to root reinforcement ratio and deposited metal height.The Taguchi approach was followed by grey relational analysis to solve the multi-response optimization problem.The significance of factors on overall quality characteristics of the weld joint was also evaluated quantitatively using analysis of variance.Optimal results were verified through additional experiments,and showed to feasibility of applying grey relation analysis in combination with Taguchi technique for continuous improvement of product quality in the manufacturing industry.

Effect of process parameters of pulsed current tungsten inert gas welding on weld pool geometry of titanium welds

The effects of pulsing current parameters on weld pool geometry namely front height, back height, front width and back width of pulse current gas tungsten arc welded （GTAW） titanium alloy was analysed. Four factors, five levels, central composite design were used to develop empirical relationships, incorporating pulsed current parameters and weld pool geometry.

Numerical simulation for pulsed laser-gas tungsten arc hybrid welding of magnesium alloy

Based on the extended application of COMSOL multiphysics, a novel dual heat source model for pulsed laser-gas tungsten arc （GTA） hybrid welding was established. This model successfully solved the problem of simulation inaccuracy caused by energy superposition effect between laser and arc due to their different physical characteristics. Numerical simulation for pulsed laser-GTA hybrid welding of magnesium alloy process was conducted, and the simulation indicated good agree- ments with the measured thermal cycle curve and the shape of weld beads. Effects of pulse laser parameters （laser-excited current, pulse duration, and pulse frequency） on the temperature field and weld pool morphology were investigated. The experimental and simulation results suggest that when the laser pulse energy keeps constant, welding efficiency of the hybrid heat source is increased by increasing laser current or decreasing pulse duration due to the increased ratio of the weld bead depth to width. With large laser currents, severe spatters tend to occur. For optimized welding process, the laser current should be controlled in the range of 150-175 A, the pulse duration should be longer than 1 ms, and the pulse frequency should be equal to or slightly greater than 20 Hz.

Analysis of Arc Physical Property of Pulsed Tungsten Inert Gas Welding Based on Fowler-Milne Method

Pulsed tungsten inert gas （TIG） welding is widely used in industry due to its superior properties, so the measurement of arc telnperature is important to analyse welding process. Arc image of spectral line in 794.8 nm is captured by high speed camera; both the Abel inversion and the Fowler-Milne method are used to calculate the temperature distribution of the pulsed TIG welding. Characteristic of transient variation in arc intensity and temperature is analyzed. When the change of current happens, intensity and temperature of arc jump as well, it costs several millisoconds. The flirther the axial position from the tungsten is, the greater the intensity jumps, and the smaller the temperature changes.

A novel ultrafast-convert hybrid pulse square-wave VP-GTAW process for aluminum alloys

A novel ultrafast-convert hybrid pulse square-wave variable polarity arc welding power source was developed. The variable polarity current which crossed zero with no dead time possessed the ultrafast converting speed and the series of ultrasonic pulse current were superimposed in the positive polarity current duration. A high-efficiency hybrid pulse variable polarity gas tungsten arc welding （HPVP-GTAW）process for aluminum alloys was achieved. With X-ray inspection, microstructure analysis, tensile tests and scanning electron microscopy （SEM） for fracture surface, the square butt welding cbaracteristics of 5A06, 2A14 and 2219 aluminum alloys were tested, respectively. Experimental results show that microstructure and mechanical properties of these aluminum alloy welded joints are influenced significantly by the introduction of ultrasonic pulse current. The weld quality is improved predominantly by the novel HPVP-GTA W process.

Effect of pulse frequency on hardness characteristics of Al-Cu alloy HPVP-GTAW joints

AA 2219-0 Al-Cu alloy single bead welds were obtained by hybrid ultrahigh frequency pulse variable polarity gas tungsten arc welding （HPVP-GTAW） process with pulse frequency varying from 25 kHz to 70 kHz. Weld hardness characteristics which mainly depicted by microhardness and its gradient were investigated systematically. The results show that pulse frequency has a great effect on the hardness characteristics. The weld zone microhardness and its gradient with different pulse frequency present an evident fluctuant trend. The fluctuation of gradient is slight, illustrating that the mierostructure is uniform with pulse frequcncy varied from 35 kHz to 60 kHz. The fusion zone microhardness and its gradient foUow the similar trends but fluetuate greatly. Maximum value of gradient appears around the fusion boundary due to the coarse and non- uniform microstrueture. The maximum gradient at 60 kHz is only 25.5 % of that at 45 kHz. According to the study, the best hardness characteristics are achieved at 60 kHz frequency.

Optimization of HPVP-GTAW aluminum alloy process parameters for Al-Mg welded joints

Optimization of hybrid ultrahigh frequency pulse variable polarity gas tungsten arc welding （HPVP-GTAW） process was carried out to obtain the optimum weld characteristics of 5AO6-HX4 aluminum-magnesium alloy sheets of 3 mm thickness. The square butt joints were produced by HPVP-GTA W process, the microstructure and mechanical properties were systematically investigated. It is observed that the process parameters influence the weld microstructure and mechanical properties significantly. Weld microstructure is mainly composed of grid a （A1） solid solution, with a large number of intermetallic （ Mg2Al3 ） precipitates distributed in the matrix. The amount of ~ （ Mg2Al3 ） precipitates has an obvious difference with different parameters. Compared with that of the base material, tensile strength of 5AO6-HX4 alloy welded joints has a certain reduction, as well as the elongation and reduction of area. The optimized welding process parameters for 5A06-HX4 alloy sheets are presented.

Improvement of Microstructure and Mechanical Behavior of Gas Tungsten Arc Weldments of Alloy C-276 by Current Pulsing

Superalloy C-276 is known to be prone to hot cracking during fusion welding by Gas Tungsten Arc method. Microsegregation occurring during cooling of fusion zone with consequent appearance of topologically close-packed phases P and IX has been held responsible for the observed hot cracking. The present work investigated the possibility of suppressing the microsegregation in weldments by resorting to current pulse. Weldments were made by continuous current gas tungsten arc welding and pulsed current gas tungsten arc welding using ERNiCrMo-4 filler wire. The weld joints were studied with respect to microstructure, microsegregation, and mechanical properties. Optical microscopy and scanning electron microscopy were employed to study the microstructure. Energy-Dispersive X-ray Spectroscopy was carried out to evaluate the extent of microsegregation. Tensile testing was carried out to determine the strength and ductility. The results show that the joints fabricated with pulsed current gave rise to narrower welds with practically no heat affected zone, a refined microstructure in the fusion zone, reduced microsegregation, and superior combination of mechanical properties.

铝合金薄板焊接应力三维有限元模拟

采用热弹塑性有限元方法,对铝合金薄板脉冲TIG焊接接头的焊接应力进行了三维数值模拟,考虑材料性能随温度的变化,对焊接残余应力进行测量。结果表明,铝合金薄板中的焊接应力产生、发展很快,加热结束后不久应力便趋于稳定。热源前缘和两侧区域存在数值很高的纵向和横向动态压应力,焊缝中心的纵向残余拉应力低于母材的屈服强度,距焊缝中心10 mm处的最大纵向残余拉应力达到母材的屈服强度,并且拉应力区较宽,远离焊缝区域的纵向残余压应力数值较大,因此铝合金薄板焊接结构易发生动态和焊后失稳,横截面上纵向残余应力的数值模拟结果与实测结果基本一致。

超音频脉冲TIG焊电源拓扑及电弧焊适用性

研制出一台超音频直流脉冲TIG(Tungsten Inert Gas)焊电源,对该电源的拓扑结构及工作原理进行了介绍.与常规直流TIG焊电源相比,该电源可输出不同频率、均具有陡峭的上升、下降沿的脉冲电流,电流变化率大于50 A/μs.该电源的基值电流、峰值电流、脉冲电流频率、占空比等焊接工艺参数调节方便,使该电源不仅能够焊接薄板,而且能够适用于中厚板的焊接.通过对比常规直流TIG焊和超音频直流脉冲TIG焊焊接的1Cr18Ni9Ti奥氏体不锈钢焊缝的微观组织,发现采用超音频直流脉冲TIG焊工艺的焊缝粗晶区变窄,晶粒细化现象显著.试验结果表明:所研制的超音频脉冲TIG焊电源具有良好的弧焊适用性.

热输入对超薄443铁素体不锈钢组织性能的影响

针对443铁素体不锈钢焊接接头存在粗晶组织与性能脆化等问题进行研究,采用光学显微镜(OM)、扫描电子显微镜(SEM)分析了不同焊接方法焊后接头组织和性能的变化.采用钨极氩弧焊(TIG)、脉冲钨极氩弧焊(P-TIG)和脉冲激光焊(P-LBW)三种焊接方法进行焊接,分析了不同热输入对超薄443铁素体不锈钢焊接接头微观组织、拉伸性能和杯突性能的影响规律.结果表明,焊接热输入是影响该铁素体不锈钢焊接接头组织和性能的重要因素,采用脉冲焊接方法来细化组织可以有效提高焊接接头综合性能.

0Cr18Ni9Ti超音频脉冲TIG焊接头组织与性能

采用研制的基于新型IGBT拓扑电路的超音频直流脉冲TIG焊电源焊接0Cr18Ni9Ti奥氏体不锈钢,并与常规直流TIG焊获得的接头进行对比.分别对各接头进行X-射线探伤检测,接头的抗拉强度测试,焊缝金相显微组织与拉伸断口SEM照片观察对比.试验结果分析表明:采用超音频脉冲TIG焊工艺的焊接接头,随着脉冲电流频率提高,焊缝的粗晶区变窄,晶粒逐渐细化,且焊缝中心细小等轴晶所占区域扩大;与常规直流TIG焊相比,30 kHz的超音频直流脉冲TIG焊焊缝中心晶粒更细小,接头的抗拉强度与延伸率分别得到提高.

HPVP-GTAW电弧力及焊接质量分析

分别以3种不同材质铝合金平板材料为试验对象,研究分析了复合超高频脉冲方波变极性钨极氩弧焊接(HPVP-GTAW)过程中电弧力的变化及其对焊缝成形特征和接头力学性能的影响.结果表明,与常规变极性氩弧焊工艺相比,脉冲方波电流的加入使得HPVP-GTAW电弧力显著增加,同时焊缝熔透率大幅提高,接头力学性能得到明显改善和提高;保持脉冲电流幅值和占空比基本不变,在10～80 kHz范围内,脉冲电流频率对焊接过程产生了重要影响,频率为40 kHz时,HPVP-GTAW电弧力和焊缝熔透率均达到最大,分别约为常规变极性焊接电弧的1.9倍和1.7倍.