Morphology investigation on direct current pulsed gas tungsten arc welded additive layer manufactured Ti6Al4V alloy

The effects of pulsed gas tungsten arc welding parameters on the morphology of additive layer manufactured Ti6Al4V has been investigated in this study. The peak/base current ratio and pulse frequency are found to have no significant effect on the refinement of prior beta grain size. However, it is found that the wire feed rate has a considerable effect on the prior beta grain refinement at a given heat input. This is due to the extra wire input being able to supply many heterogeneous nucleation sites and also results in a negative temperature gradient in the front of the liquidus which blocks the columnar growth and changes the columnar growth to equiaixal growth.     

Modeling of transport phenomena and solidification cracking in laser spot bead-on-plate welding of AA6063-T6 alloy. Part I—the mathematical model

In this work, the oscillating arc narrow gap all-position gas metal arc (GMA) welding process was developed to improve efficiency and quality in the welding of thick-walled pipes. The statistical models of narrow gap all-position GMA weld bead geometry were developed using response surface methodology (RSM) based on central composite design (CCD). The developed models were checked for their adequacy and significance by ANOVA, and the effects of wire feed rate, travel speed, dwell time, oscillating amplitude and welding position on weld bead dimension were studied. Finally, the optimal welding parameters at welding positions of 0° to 180° were obtained by numerical optimization using RSM.     

Effect of process parameters and mathematical model for the prediction of bead geometry in pulsed GMA welding

Pulsed gas metal arc welding is one of the most widely used processes in the industry. It offers spray metal transfer at low average currents, high metal deposition rate, versatility, less distortion, and the ability to be used in automated robotic welding systems. The weld bead plays an important role in determining the mechanical properties of the weld. Its geometric parameters, viz., width, reinforcement height, and penetration, are decided according to the welding process parameters, such as wire feed rate, welding speed, pulse current magnitude, frequency (cycle time), etc. Therefore, to produce good weld bead geometry, it is important to set the proper welding process parameters. In the present paper, mathematical models that correlate welding process parameters to weld bead geometry are developed with experimental investigation. Taguchi methods are applied to plan the experiments. Five process parameters, viz., wire feed rate, plate thickness, pulse frequency, pulse current magnitude, and travel speed, are selected to develop the models using multiple regression analysis. The models developed were checked for their adequacy. Results of confirmation experiments show that the models can predict the bead geometry with reasonable accuracy.     

脉冲旁路耦合电弧MIG焊的动态数学建模及过程控制

脉冲旁路耦合电弧熔化极惰性气体保护(Metal inert-gas, MIG)焊是一种新型的低热输入焊接方法,它通过特定的接法引入旁路电弧与主路电弧实现热、力的耦合,利用旁路电弧的分流作用,实现熔化母材热量与熔化焊丝热量的独立控制,从而在精确控制母材热输入的同时保证熔滴的自由过渡形式,可以实现铝-钢等异种金属的连接。为了理论分析不同焊接参数对焊接过程的影响,通过等效、线性化处理与迭代数值求解算法,建立可以正确描述焊接物理过程的动态数学解析模型;针对焊接过程中耦合电弧稳定性较差且直接影响焊接质量的问题,提出通过检测弧压波动的反馈信号、实时调节送丝速度、进而控制耦合电弧稳定性的闭环控制方案,并基于快速原型系统进行焊接过程控制仿真与试验。仿真结果表明,当焊接过程受到干扰后,采用闭环控制方案可以显著提高耦合电弧的稳定性;焊接试验证明了控制仿真的预测与分析,进行闭环控制后,焊接过程更加稳定同时得到了成形良好的铝-钢异种金属接头。     

基于周期平均值外特性的脉冲MIG焊弧长稳定性研究

通过对脉冲熔化极惰性气体保护(Metal inert gas,MIG)焊脉冲平均电流电压变化率的计算,提出脉冲周期平均值外特性曲线,并对弧焊电源脉冲周期平均值外特性曲线和电弧静态性曲线的动态稳定工作点进行详细分析,得出利用脉冲平均值外特性控制脉冲MIG焊的控制策略。同时运用双闭环控制实现了基于弧压反馈的I/I模式控制数字化弧焊电源,此电源能在送丝速度稳定情况下自适应弧长扰动变化,实现脉冲弧焊过程一脉一滴熔滴过渡。通过弧长阶跃试验表明,脉冲弧焊过程中焊丝熔化速度快速跟踪弧长变化,具有良好的弧长动态调节性能,保持弧长动态稳定,即焊接过程稳定,焊缝成形良好,同时验证了分析过程正确性和设计过程的可行性。     

Effect of pulsed current welding on mechanical properties of high strength aluminum alloy

High strength aluminum alloys (Al-Zn-Mg-Cu alloys) have gathered wide acceptance in the fabrication of lightweight structures requiring high strength-to-weight ratio, such as transportable bridge girders, military vehicles, road tankers and railway transport systems. The preferred welding processes of high strength aluminum alloy are frequently the gas tungsten arc welding (GTAW) process and the gas metal arc welding (GMAW) process due to their comparatively easy applicability and better economy. Weld fusion zones typically exhibit coarse columnar grains because of the prevailing thermal conditions during weld metal solidification. This often results in inferior weld mechanical properties and poor resistance to hot cracking. In this investigation, an attempt has been made to refine the fusion zone grains by applying a pulsed current welding technique. Rolled plates of 6 mm thickness were used as the base material for preparing single pass welded joints. A single ‘V’ butt joint configuration was prepared for joining the plates. The filler metal used for joining the plates was AA 5356 (Al-5Mg (wt%)) grade aluminum alloy. Four different welding techniques were used to fabricate the joints: (1) continuous current GTAW (CCGTAW), (2) pulsed current GTAW (PCGTAW), (3) continuous current GMAW (CCGMAW) and (4) pulsed current GMAW (PCGMAW). Argon (99.99% pure) was used as the shielding gas. Tensile properties of the welded joints were evaluated by conducting tensile tests using a 100 kN electro-mechanical controlled universal testing machine. Current pulsing leads to relatively finer and more equi-axed grain structure in GTA and GMA welds. In contrast, conventional continuous current welding resulted in predominantly columnar grain structures. Grain refinement is accompanied by an increase in tensile strength and tensile ductility.     

焊接电弧的控制系统

本文对工业中常用焊接电弧特别是MIG-MAG电弧的控制系统进行了理论分析,并对其中存在的问题进行了讨论。为了改善焊接电弧的行为,提高焊接质量,作者提出一种新的电弧控制法（QH-ARC法）。利用这种控制法,焊接电弧可以在任何类型的外界扰动下或送丝速度大范围快速变化时保持稳定的弧长和最佳的射流过度状态。因而用它可以作为进行程序焊接、脉冲送丝焊接、单旋钮控制的手段。利用这种控制法还可以对焊缝成型、溶深以及热输入量进行闭环控制。     

Feed rate of wire electrochemical machining using pulsed current

The effect of various parameters on the feed rate in electrochemical machining has been investigated. Parameters considered were velocity of the electrolyte flow, nozzle diameter, material, diameter and tension of the wire, pulse period and peak value of the applied voltage. On the assumption that the feed rate is limited by accumulation of generated sludge or gas, the feed rate equation and favourable pulse conditions were derived and verified experimentally. The rate was improved by applying a shorter pulse period than the ‘residential’ time of the electrolyte between electrodes. Above the critical pressure, at which the feed rate is a maximum, the adverse effects of wire vibration cannot be neglected. Measures proposed to prevent it were reduction of nozzle diameter and length of wire span, and increase in applied voltage and wire tension.     

An experimental investigation on machining parameters of AISI D2 steel using WEDM

The performance of the wire electrodischarge machining (WEDM) machining process largely depends upon the selection of the appropriate machining variables. Optimization is one of the techniques used in manufacturing sectors to arrive for the best manufacturing conditions, which are essential for industries toward manufacturing of quality products at lowest cost. As there are many process variables involved in the WEDM machining process, it is difficult to choose a proper combination of these process variables in order to maximize material removal rate and to minimize tool wear and surface roughness. The objective of the this work is to investigate the effects of process variables like pulse on time, pulse off time, peak current, servo voltage, and wire feed on material removal rate (MRR), surface roughness (SR), gap voltage, gap current, and cutting rate in the WEDM machining process. The experiment has been done using Taguchi’s orthogonal array L27 (3⁵). Each experiment was conducted under different conditions of input parameters and statistically evaluated the experimental data by analysis of variance (ANOVA) using MINITAB and Design Expert tools. The present work also aims to develop mathematical models for correlating the inter-relationships of various WEDM machining parameters and performance parameters of machining on AISI D2 steel material using response surface methodology (RSM).The significant machining parameters and the optimal combination levels of machining parameters associated with performance parameters were also drawn. The observed optimal process parameter settings based on composite desirability (61.4 %) are pulse on time 112.66 μs, pulse off time 45 μs, spark gap voltage 46.95 V, wire feed 2 mm/min, peak current of 99.99 A for achieving maximum MRR, gap current, gap voltage, cutting rate, and minimum SR; finally, the results were experimentally verified.     

Microstructure and hardness of Al-Mg-Si weldments produced by pulse GTA welding

This paper describes the effects of pulsed TIG welding process parameters (pulse duration, peak current, and pulse frequency) on the microstructure and microhardness of Al-0.8%Mg-0.5%Si (6061) alloys. It was observed that pulse TIG welding produced finer grain structure of weld metal than conventional TIG welding (without arc pulsation). An increase in the pulse frequency has been found to refine the aluminium and eutectic grain structure of weld metal especially when welding is done using short pulse duration. Long pulse duration lowers the pulse frequency up to which refinement of constituents in weld metal takes place. Effect of the pulse frequency on the grain structure was found to be determined by pulse duration. For a given pulse frequency, long pulse duration produced a coarser structure than short pulse duration. An increase in the peak current coarsened the grain structure.     

Multisensor-based monitoring of weld deposition and plate distortion for various torch angles in pulsed MIG welding

Manufacturing companies often fail to maintain good weld quality due to poor arc stability and distortion after welding. Weld quality can be improved by reducing the transverse shrinkage and the angular distortion in butt welding. The welding deposition efficiency is also an important economic factor. In this work, various pulse voltage parameters have been varied along with welding torch angle in pulsed metal inert gas (P-MIG) welding. The experimental results revealed that the peak voltage is the dominant pulse voltage parameter. Various sensors were also used to monitor arc current, arc voltage, arc sound, and also weld temperature. A strong relationship between arc sound (as well as arc power) and transverse distortion (as well as metal deposition) was found to exist in P-MIG welding. The frequency domain features of welding arc sound were also extracted and correlated to the process characteristics.     

Seam gap bridging of laser based processes for the welding of aluminium sheets for industrial applications

Laser welding has a large potential for the production of tailor welded blanks in the automotive industry, due to the low heat input and deep penetration. However, due to the small laser spot and melt pool, laser-based welding processes in general have a low tolerance for seam gaps. In this paper, five laser-based welding techniques are compared for their gap bridging capabilities: single-spot laser welding, twin-spot laser welding, single-spot laser welding with cold wire feeding, twin-spot laser welding with cold wire feeding and laser/GMA hybrid welding. Welding experiments were performed on 1.1- and 2.1-mm-thick AA5182 aluminium sheets. The resulting welds were evaluated using visual inspection, cross sectional analysis with optical microscopy, tensile tests and Erichsen Cupping tests. The results show that the use of a filler wire is indispensable to increase the gap tolerance. A proper alignment of this wire with the laser spot(s) is crucial. With the single spot laser welding with cold wire feeding, a gap up to 0.6 mm could be bridged as opposed to a maximum allowable gap width of 0.2 mm for single-spot laser welding without filler wire. For 2.1-mm-thick sheets, the laser/GMA hybrid welding process can bridge even gaps up to 1.0 mm. Most welds had a high tensile strength. However, during Erichsen Cupping tests, the deformation of the welds is significantly lower as compared to the base material.     

Optimizing pulsed current parameters to minimize corrosion rate in gas tungsten arc welded titanium alloy

The preferred process for welding titanium alloy is frequently gas tungsten arc (GTA) welding due to its comparatively easier applicability and better economy. Weld fusion zones of this alloy typically exhibit coarse columnar grains and lead to inferior mechanical and metallurgical properties. In the case of single pass GTA welding of a thinner section of this alloy, the pulsed current has been found to be beneficial primarily due to grain refinement of the weld fusion zone over the conventional continuous current process. Fusion zone grain refinement is controlled by pulsed current parameters such as peak current, back ground current, pulse frequency and pulse-on-time. In this investigation, a mathematical model has been developed to predict corrosion rate of gas tungsten arc welded titanium alloy by incorporating pulsed current parameters. Four factors, five level, central composite, rotatable design matrix has been used to minimize the experimental conditions. A mathematical model has been developed by response surface method (RSM). The developed model has been optimized using genetic algorithm (GA) and contour plots to attain minimum corrosion rate in the weld fusion zone.     

Wire melting rate of alternating current gas metal arc welding

The wire melting phenomenon in alternating current gas metal arc welding (AC-GMAW) process should be carefully observed and analyzed since it is one of the most important representative characteristics of GMAW process. In this study, a new form of wire melting rate equation for AC-GMAW process is proposed based on energy conservation theory and arc physics. Using experimental data, the wire melting rate coefficients of AC-GMAW are obtained through nonlinear regression analysis. The wire melting rate is influenced not only by the current waveform, electrode polarity, and droplet size but also by the shape of the wire tip. That is, if the wire tip becomes more slender, arc heating has more influence on the wire melting. Using the wire melting rate proposed in this research, the uncertainty of calculating wire melting rate coefficients of AC-GMAW can be excluded comparing to existing method.     

Arc profile characteristics of Al alloy in double-pulsed GMAW

In order to study arc profile variation process with double-pulsed gas metal arc welding of aluminum alloy, a synchronous acquisition system and an analysis system have been established to acquire and analyze electrical signals and instantaneous images of arc profile. The results show that in double-pulse mode, the arc profile is matched with high-frequency pulse and thermal pulse. The droplet transfer mode always accompanies with high-frequency pulse cycle “one drop per pulse.” The arc profile variation and droplet transfer in thermal base are lower than that in thermal peak. The serial-type arc is easier to occur in thermal base stage. High current density distribution at the top and bottom of traveling droplet leads to dazzling region. The variation of wire extension is influenced by thermal pulse frequency. The variance of arc size in thermal base is higher than in thermal peak, which leads arc force to vary with thermal pulse frequency. The variation of the droplet transfer and arc force in double pulse can improve the weld pool mobility.     

高速旋转电弧传感器的数学模型

以气保护焊接系统的数学模型和HALMOY焊丝熔化模型为基础,对高速旋转电弧传感器进行数学建模。利用该数学模型模拟焊接电流、弧长和焊丝伸出长度随时间的变化规律。实际焊接试验显示,模拟焊接电流与实际焊接电流波形高度吻合,说明建立的数学模型是准确的。结果表明,高速旋转电弧焊接时,弧长的变化较焊丝伸出长度的变化更为显著。利用每个电弧旋转周期内左半周与右半周平均电流值的差,可以判断焊枪的偏差量及其方向,同时还可根据平均电流值的大小来检测角接终止点。所建立的模型对于高速旋转电弧传感系统的设计具有指导意义。     

Optimization of pulsed GTA welding process parameters for the welding of AISI 304L stainless steel sheets

Optimization of pulsed gas tungsten arc welding (pulsed GTAW) process parameters was carried out to obtain optimum weld bead geometry with full penetration in welding of stainless steel (304L) sheets of 3 mm thickness. Autogenuous welding with square butt joint was employed. Design of experiments based on central composite rotatable design was employed for the development of a mathematical model correlating the important controllable pulsed GTAW process parameters like pulse current (I _p), pulse current duration (T _p), and welding speed (S) with weld bead parameters such as penetration, bead width (W), aspect ratio (AR), and weld bead area of the weld. The developed models were checked for adequacy based on ANOVA analysis and accuracy of prediction by conducting a confirmation test. Weld bead parameters predicted by the models were found to confirm observed values with high accuracy. Using these models, the main and interaction effects of pulsed GTAW process parameters on weld bead parameters were studied and discussed. Optimization of pulsed GTAW process parameters was carried out to obtain optimum bead geometry using the developed models. A quasi-Newton numerical optimization technique was used to solve the optimization problem and the results of the optimization are presented.     

Prediction of metal deposition from arc sound and weld temperature signatures in pulsed MIG welding

The weld deposition efficiency is an important economic factor like productivity and weld quality in gas metal arc welding (GMAW). There is a strong relationship between arc sound signals and arc stability (or deposition efficiency) in GMAW. In this work, the variation of weld deposition efficiency with various pulse parameters in pulsed metal inert gas welding was investigated. The arc sound signal along with current and voltage signals were acquired and analyzed in time domain as well as in frequency domain. The sound signal kurtosis and arc power were found to be highly correlated with welding process stability. The weld deposition efficiency was also related to weld surface peak temperature. Finally, an attempt was made to correlate the sound time domain as well as frequency domain features of sound signal with the deposition efficiency. The variation of pulse shape with the duty factor also influenced the deposition efficiency as evidenced by in fast Fourier transform analysis.     

Effect of pulse current on thermal performance and deep drawing of SiCp/2024Al composite sheet

The effect of pulse current on heating performance and thermal deep drawing of SiCp/2024Al composite sheets was studied in this work. The high-intensity pulse current flows through the sheet and generates the tremendous Joule heat. The heating performance and temperature distribution were investigated to confirm process parameters. The temperature of specimen is up to around 673 K at a rate of 13.5 K/s under the current density of 21.7 A/mm². The stainless steel inserts make temperature difference reduced by 73.3 %. Moreover, the workpiece was successfully deep drawn and exhibited good surface quality. The dimensional accuracy achieved within ±0.2 mm.     

Genetic algorithm based optimization of the process parameters for gas metal arc welding of AISI 904 L stainless steel

The present study is focused on welding of super austenitic stainless steel sheet using gas metal arc welding process with AISI 904 L super austenitic stainless steel with solid wire of 1.2 mm diameter. Based on the Box — Behnken design technique, the experiments are carried out. The input parameters (gas flow rate, voltage, travel speed and wire feed rate) ranges are selected based on the filler wire thickness and base material thickness and the corresponding output variables such as bead width (BW), bead height (BH) and depth of penetration (DP) are measured using optical microscopy. Based on the experimental data, the mathematical models are developed as per regression analysis using Design Expert 7.1 software. An attempt is made to minimize the bead width and bead height and maximize the depth of penetration using genetic algorithm.