Shielding Gas Flow Rate Research Articles

Numerical simulation of droplet shapes in laser-MIG hybrid welding

A three-dimensional finite element model based on minimum energy principle is developed to simulate the droplet transfer process in laser-MIG hybrid welding. The energy manifestations of all forces that determine droplet shapes are considered in this model, and the model has been used to predict droplet shapes. Offset of droplet centroid and critical additional axial acceleration are adopted to characterize the stability of droplet transfer. The calculated droplet shapes and offset of droplet centroid agree well with experimental results. It is found that increasing laser power or decreasing welding current would destabilize droplet transfer. Additional mechanical forces contribute to stable droplet transfer, and the positive effects of increased shielding gas flow rate on the stability of welding processes are subsequently verified.

Influence of MIG Welding Process Parameters on Tensile Properties of Mild Steel.

Metal Inert Gas welding (MIG) is a widely used welding method for mild steel (low carbon steel) in industry due to its high weld quality, good penetration and comparatively low investment. It is an arc welding process wherein coalescence is produced by heating the job with an electrical arc struck between a filler rod and the job. A Shielding gas (argon, carbon dioxide) is used to avoid atmospheric contamination of the molten weld pool. A filler material is added for joining the work piece by MIG welding. Many researchers investigated on different welding process parameters on mechanical & microstructural characteristics. Some researchers used the welding speed, welding current welding voltage, number of welding passes & work peace thickness for stainless steel, naval grade steel & aluminum. But the shielding gas flow rate & gas mixture also important factor which affects mechanical properties of mild steel. For this study, process parameters such as welding current, gas flow rate and gas combination used in the range 170-210A, 13-17 Lit/min & 0-100 % of CO2 respectively. The material used E-250 grade mild steel with 12 mm thickness. The effect of the welding parameter is investigated by designing the experiments using central composite matrix. Using the data generated by the experimentation, an empirical relation is obtained for tensile strength. The optimum value of tensile strength 356 N/mm 2 is observed at 190A welding current, 15 Lit/min gas flow rate & 50% CO2+50% Argon gas combination. Index Terms —Co2 Welding, v-butt Welds, welding current, gas flow rate, Gas combination, Tensile strength.

The Influence of Shielding Gas Flow Rate on the Transfer Frequency of Electrode Metals Drops

Chemical composition of weld metal and properties of a joint weld are dominated by the processes occurring in the drop of molten electrode metal and in metal of the weld pool. Under certain conditions in consumable electrode welding with jet gas shielding the drop of electrode metal is influenced significantly both by main forces and the force of gas-dynamic impact of the shielding gas jet. The results of research have revealed that changing rate of shielding gas flow on the nozzle section influences the processes taking place in the welding area. There are changes in the transfer frequency of electrode metal drops and chemical composition of weld metal.

Effects of shielding gas control: welded joint properties in GMAW process optimization

One function of shielding gases used in welding processes, such as hydrogen (H2), oxygen (O2), carbon dioxide (CO2), nitrogen (N2), helium (He), argon (Ar) and their mixtures, is protection of the weld pool against harmful contamination that could generate defects. In addition to this primary function, shielding gases significantly affect the shape of the weld, weld geometry, seam appearance, metallurgical and mechanical properties, welding speed, metal transfer, arc stability or beam and fume emissions. The shielding gas is thus a key factor in determining weld joint properties and welding process efficiency. As welding processes have become enhanced and welding research has advanced, different combinations of shielding gas mixtures have become available under a wide variety of trademarks, each claiming to offer the best efficiency. The shielding gas flow rate in GMAW welding is usually set according to empirical experiment. The flow generally remains unchanged throughout the entire welding process and is set at maximum values of the welding parameters so that there is sufficient gas cover. This setting means, however, that unnecessarily large quantities of shielding gas may be consumed in other phases of the welding process. In view of constantly increasing prices and shortfalls in helium supply, there is a need to optimize the use of shielding gas. Consequently, an ability to closely monitor the shielding gas blend and reduce waste can provide valuable cost savings. This paper examines the effects of shielding gas mixtures and their components, presents a cross-comparison of shielding effects in fusion welding and suggests guidelines for adaptive controllability of shielding gas in advanced adaptive fusion welding. The study reviews scientific case studies and experiments from the point of view of the effect of the shielding gas on the process efficiency and process outcome. The study considers shielding gases for welding of both ferrous metals (i.e. carbon steels, stainless steels, high-strength steels) and non-ferrous metals (i.e. aluminium and its alloys, nickel and its alloys and copper and its alloys). Appropriate choice of shielding gas and use of an optimum flow rate results in better quality in terms of increased productivity, reduced gas consumption and improved weld geometry properties, microstructure and mechanical properties. Although some blends can be used effectively in many different processes, other blends appear process-dependent; they produce far poorer results when utilized in non-appropriate processes. Particle image velocimetry (PIV) and Schlieren techniques can be used for visual sensing of gas flow during fusing welding. Moreover, an adaptive alternative gas supply can improve welding performance and weld quality and reduce harmful fume emission.

Optimization of bead geometry for duplex stainless steel GTA welds using the Taguchi approach

AbstractSingle pass, autogenous flat butt welds were made on 6 mm thick duplex stainless steel (2205) plates using gas tungsten arc welding (GTAW) process. Four of the welding process parameters, i. e., arc current, welding speed, shielding gas flow rate and arc gap, were varied each at four levels and welding trials were conducted as per an L16 orthogonal array derived using the Taguchi methodology. Bead geometry parameters, depth of penetration and aspect ratio (width-to-depth ratio) were measured on polished and etched samples using microstructural image analysis. Tabulated results were subjected to analysis of variance and effects of each parameter on bead geometry were calculated. It has been found that welding current and welding speed are the dominant parameters determining the bead geometry. Gas flow rate also plays a key role in influencing the aspect ratio of the welds. Equations have been presented to predict depth of penetration and aspect ratio of the weld.

Investigation of the relationship between arc-anode attachment mode and anode temperature for nickel nanoparticle production by a DC arc discharge

Multiple and constricted arc-anode attachment modes were observed in helium arc discharge to prepare nickel nanoparticles. The electron overheating instability resulted in the formation of multiple attachment modes. The effects of hydrogen concentration and shield gas flow rate on the characteristics of nickel nanoparticles were investigated. The evaporation rate of anode material contributed to forming different arc-anode attachments. The surface temperature of the electrode was measured during the arc discharge by two-color pyrometry combined with a high-speed camera which employs appropriate band-pass filters. The relationship between the arc-anode attachment mode and the temperature behavior of the anode surface was investigated by using two synchronized high-speed cameras. The waveform of anode jet area variation with time follows that of the highest temperature variation of anode surface with time. The fluctuation of the highest anode temperature increased when the arc anode attachment changed from multiple into constricted mode. The highest temperature fluctuation and stability of the arc contributed to nanoparticle size distribution. Nickel nanoparticles with large productivity and narrow size distribution were obtained when shield gas was employed by controlling the residence time of nanoparticle growth. The formation mechanism of different arc-anode attachment modes was explained.

STS316L 강관의 수평자세 용접을 위한 GTAW 용접조건의 최적화

In this study, it was tried to analyze the effects of welding parameters on the weld penetration and aspect ratio when a STS316L pipe was welded in a horizontal position by GTAW. Experiments were systematically designed using a L18 orthogonal array, and the effects of welding parameters were statistically analyzed by ANOVA(Analysis of Variance). The shielding gas type has the largest effect on both the penetration and aspect ratio. The welding current type and shielding gas flow rate have a little effect on the penetration, whereas the electrode tip angle has a little effect on the aspect ratio. When welded at a selected welding condition, which is composed of He shielding gas, pulse current of 300/45 A, electrode tip angle of 90o, and shielding gas flow rate of 30 l/min, the estimated interval at least 95 % confidence was 1.99 ± 0.18 mm for the penetration and 0.31 ± 0.04 for the aspect ratio. From the confirmation experiments, the average penetration and aspect ratio were well agreed with the estimation as 1.96 mm and 0.30, respectively. Additionally, the effects of the welding speed and welding current on the penetration and aspect ratio were experimented and analyzed by linear regression. The penetration was linearly increased with the decrease of the welding speed and with the increase of the welding current, but the aspect ratio showed a tendency to a little decrease with the increase of both the welding speed and current.

Experimental study of porosity reduction in high deposition-rate Laser Material Deposition

Abstract For several years, the interest in Additive Manufacturing (AM) is continuously expanding, owing to the paradigm shift that new production processes, such as Laser Material Deposition (LMD), provide over conventional manufacturing technologies. With LMD, three-dimensional, complex components out of a wide range of materials can be manufactured consecutively layer-by-layer. Despite the technological advantages of the LMD process, currently achieved deposition-rates of approx. 0.5 kg/h for Inconel 718 (IN 718) remain a major concern in regards to processing times and economic feasibility. Moreover, processing conditions need to be chosen carefully or else material defects can be systematically formed either at the interface separating two adjacent clad layers, at the bonding zone or within the bulk of the layer. In this respect, the effects of powder humidity, laser power, nominal powder particle size, powder morphology and shielding gas flow rate on the porosity in laser deposited single tracks at an increased deposition-rate of approx. 2 kg/h was investigated through experiments. Based on experimental results, several approaches of reducing porosity in high deposition-rate LMD are proposed in this paper.

Effect of process parameters on toughness and metallurgical behaviour during uniaxial automatic gas metal arc welding of austenitic stainless steel AISI 316

Gas metal arc welding (GMAW) is extensively used for joining of different graded steels as well as aluminium and other nonferrous materials. GMAW offers clean welding with low defects without using flux and suitable for different positional welding. In the present work, a fabricated automatic movement setup is used for GMAW to study the influences of four different process parameters during joining of austenitic stainless steel AISI 316 using AISI 304 (ER304) filler wire. With this setup, welding is carried out maintaining a constant contact tube-to-workpiece (CTW) distance and uniform heat input. Experimental results and subsequent analysis show that the toughness is most significantly influenced by voltage followed by welding speed, gas flow rate, and current. Toughness reduces with the increase in shielding gas flow rate and welding speed as austenite and traces of retained delta ferrite may be present due to high solidification rate. Metallurgical observations by X-ray diffraction (XRD) and scanning electron microscopy indicate that solidification mode is mainly characterized by formation of fully austenite or austenite and ferrite at cell and dendritic boundaries. XRD results revealed that higher toughness is observed due to minimum formation of carbides.

Effect of shielding gas parameters on weld metal thermal properties in gas metal arc welding

This study considered the effect of shielding gas parameters (composition, supply method and flow rate) on the post-weld thermal properties (thermal expansion, specific heat capacity, thermal diffusivity and thermal conductivity) of the weld metal in gas metal arc welding. This is of importance as the thermal properties influence the temperature distribution and therefore the residual stresses and distortion present within the final structure. Due to the lack of accurate thermal data, computational modelling techniques (such as FEA and CFD) used for modelling the welding process generally make assumptions regarding the material thermal properties, and it is often the case that the parent material thermal properties are extended to the weld metal, introducing errors to the simulation. It was determined that the weld metal posses considerably different thermal properties to the DH36 grade steel parent material and that the shielding gas parameters significantly alter key thermal properties of the solidified weld metal. A lower shielding gas flow rate exhibited beneficial properties including a lower thermal expansion and higher specific heat capacity and thermal conductivity than a higher shielding gas flow rate.

Multi Response Optimization of Tungsten Inert Gas (TIG) Welding of Al6063/15%Sicp Metal Matrix Composites

Material scientists and researchers in this area have been fulfilling the demand of the engineering sector since decades in synthesizing materials to attain the demanded properties to enhance efficiency and cost savings in the manufacturing sector Aluminium metal matrix composites (AMMCs) are becoming more popular as structural materials and joining them is therefore of paramount importance. Joining of advanced materials plays an increasingly important role in modern manufacturing industries. AMMCs have a unique combination of mechanical and physical properties, such as high specific strength, specific modulus of elasticity, low thermal expansion coefficient and good wear resistance; these are being widely used in aerospace engineering, automotive industry, electronic packaging, medical appliances, heat exchanger fins and other related industries. As these new materials become available it is necessary to define and optimize joining techniques, and a thorough understanding of process. The present work first deals with the fabrication of SiCp reinforced AMMCs (Al6063/15%SiCp) with Liquid Processing Technique, i.e. Stir casting method and later to seek for possibilities of successful joining with TIG process, for possible structural applications. The present study deals with an experimental study carried out in order to optimize the process parameters namely Frequency (Hz), Current (A), Shielding gas flow rate (l/m), Percentage time electrode positive (μs). The performance measures evaluated are namely Micro- hardness, (VHN) and Impact strength, (Joule), for Tig welding of Al6063/15%SiCp. The results have been analysed using Taguchis methodology. The optimal values of micro-hardness are A1B3C3D1 (frequency HF Hz, current 105 A, shielding gas flow rate 14 l/m, percentage time electrode positive 60 μs). The optimal values for impact strength are A2B1C1D3 (frequency LF Hz, current 85 A, shielding gas flow rate 10 l/m, percentage time electrode positive 70 μs).

Optimization and Prediction of Ultimate Tensile Strength in Metal Active Gas Welding.

We investigated the effect of welding parameters on ultimate tensile strength of structural steel, ST37-2, welded by Metal Active Gas welding. A fractional factorial design was used for determining the significance of six parameters: wire feed rate, welding voltage, welding speed, travel angle, tip-to-work distance, and shielded gas flow rate. A regression model to predict ultimate tensile strength was developed. Finally, we verified optimization of the process parameters experimentally. We achieved an optimum tensile strength (558 MPa) and wire feed rate, 19 m/min, had the greatest effect, followed by tip-to-work distance, 7 mm, welding speed, 200 mm/min, welding voltage, 30 V, and travel angle, 60°. Shield gas flow rate, 10 L/min, was slightly better but had little effect in the 10–20 L/min range. Tests showed that our regression model was able to predict the ultimate tensile strength within 4%.

Investigation on the effects of shielding gas on porosity in fiber laser welding of T-joint steels

Keyhole-induced porosity as one of the serious defects in deep-penetration laser welding, negatively affected the mechanical properties of welded structures. Keyhole laser welding is an effective method to fully penetrate the face and web plate for T-joint steel structures used in ship building and offshore platform. It is found that shielding gas parameters play an important role in laser welding process; different flow rates, blowing angle, and distance of shielding gas are considered to study the porosity number and distribution in order to make a systematic investigation on keyhole-induced porosity formation and its influencing factors. The result shows that appropriate shielding gas flow rate, blowing angel, and distance to molten pool could help to achieve less porosity for this T-joint. Also, a high-speed photography of 1,000 fps was applied to observe the plasma over the keyhole and fluid flow of molten pool to better understand the formation process of porosity.

Prediction of ferrite number in stainless steel gas tungsten arc welded plates using artificial neural networks

The quality of stainless steel weld is highly influenced by delta ferrite content expressed in terms of ferrite number. The quantity of delta ferrite content formed is controlled by the process parameters. This paper discusses the development of artificial neural network model for predicting the ferrite number in 202 grade stainless steel gas tungsten arc welded plates (GTAW). The process parameters chosen for study are welding gun angle, welding speed, plate length, welding current and shielding gas flow rate. The experiments were conducted based on design of experiments – fractional factorial with 125 runs. Using the experimental data, feed forward, back propagation neural models were developed and trained using Levenberg Marquardt algorithm. The training, learning, performance and transfer functions used are trainlm, learningdm, mean square error and tansig respectively. Five networks were developed with five neurons in the input layer, 1 neuron in the output layer and different nodes in the hidden layer. They are 5-3-1, 5-5-1, 5-10-1, 5-11-1 and 5-15-1. It was found that the artificial neural network (ANN) model based on network 5-5-1 predicted ferrite number more accurately than other networks. The prediction helps in identifying the recommended combination of process parameters to achieve a desired ferrite number in GTAW of stainless steel 202 grade plates.

Influence of plasma characteristics on nitrogen mixing into shielding gas in helium gas tungsten arc welding

The influence of welding condition on the mixing of atmospheric nitrogen into the arc plasma in helium gas tungsten arc welding was analysed by numerical simulations. In order to evaluate the effects of the convection flow and the diffusion on the nitrogen mixing phenomenon, the distributions of the Peclet number were used. Elongation of the electrode length has low impact on the decrease of shielding gas concentration because the convection flow becomes dominant in this area, which indicates higher Peclet numbers. Meanwhile, nitrogen diffusion increases in the plasma area with a temperature of about 10,000 K, so that elongation of the arc length leads to a remarkable decrease of shielding gas concentration. Additionally, the impact of convection flow increases in the arc centre area where high-velocity plasma jet exists, and the shielding gas concentration tends to rise owing to higher welding current in the condition of sufficient shielding gas flow rate.

Investigation on the influence of various welding parameters on the arc thermal efficiency of the GTAW process by calorimetric method

Arc efficiency of Gas Tungsten Arc Welding (GTAW) was determined by calorimetric method. A water-cooled anode calorimeter was designed and manufactured to measure the arc thermal efficiency, which was determined as a function of current, arc length, polarity and gas flow rate for GTAW of mild steel. With Direct Current Electrode Negative (DCEN) polarity and 5 mm arc length, a thermal efficiency of 67±4% was obtained, which was independent of the welding current. With Direct Current Electrode Positive (DCEP) polarity and 5 mm arc length, arc thermal efficiency was determined as 52±4%. The experimental data show that the arc efficiency decreases from 67% to 58% and 51% as the arc length increases from 5 mm to 11 and 17.5 mm, respectively. The experimental results also show that the arc efficiency is not significantly affected by the shielding gas flow rate.

Artificial neural network optimisation of shielding gas flow rate in gas metal arc welding subjected to cross drafts when using alternating shielding gases

This study implemented an iterative experimental approach in order to determine the shielding gas flow required to produce high-quality welds in the gas metal arc welding process with alternating shielding gases when subjected to varying velocities of cross drafts, thus determining the transitional zone where the weld quality deteriorates as a function of cross-draft velocity. An artificial neural network was developed using the experimental data that would predict the weld quality based primarily on shielding gas composition, alternating frequency and flow rate and cross-draft velocity, but also incorporated other important input parameters, including voltage and current. A series of weld trials were conducted to validate and test the robustness of the model generated. It was found that the alternating shielding gas process does not provide the same level of resistance to the adverse effects of cross drafts as a conventional argon/carbon dioxide mixture. The use of such a prediction tool is of benefit to industry in that it allows the adoption of a more efficient shielding gas flow rate, while removing the uncertainty of the resultant weld quality.

Investigation of Mechanical Properties of Metal Inert Gas-Brazed TRIP800 Steel Joints Using Different Shielding Gas Flow Rate

In this study, TRIP 800 (transformation induced plasticity) steel plates having 1.5 mm thickness were joined by copper-based (CuAl8) wire in gas metal arc brazing technique. Specimens were prepared in joining forms as butt joint. Brazing operations were done with ve di erent shielding gas ow rates of 8, 10, 12, 14, and 16 L/min. CuAl8 wire composed mostly of copper serves as the ller metal. Having accomplished the brazing operations, tensile properties of joints were detected, and microand macrostructures of joints were investigated in order to see the joinability of TRIP 800 steel by gas metal arc brazing technique.

Effect of Laser Welding Parameters on Formation of NiTi Shape Memory Alloy Welds

In this work experimental trials of welding of NiTi flat plates with 2.0 mm thickness were conducted using a 4.5 kW continuous wave (CW) Nd:YAG laser. The influences of laser output power, welding speed, defocus amount and side-blow shielding gas flow rate on the morphology, welding depth and width, and quality of the welded seam were investigated. Meanwhile, the effects of heat input on the mechanical and functional properties of welded joints were studied. The results show that laser welding can take better formation in NiTi alloys. The matching curves with laser power and welding speed affecting different formation of welds were experimentally acquired, which can provide references for laser welding and engineering application of NiTi alloy. The heat input has obvious effects on the ultimate tensile strength (UTS) and shape memory behavior of the welded joints.

TIG클래딩 공정에 대한 품질 모니터링기법의 개발

Pipe inside clad welding is mainly used to the flow pipe of sub-sea or chemical plant. For the inside clad welding to the medium pipe with the diameter of about 12", TIG welding is frequently applied with filler metal. In this case, the clad welding has the very broad weld area over <TEX>$10m^2$</TEX>. And, the non-destructive test (NDT) such as ultrasonic test (UT) or radiographic testing (RT) should be conducted on the broad weld area, and it costs very high due to the time-consuming work. Therefore, the present study investigated the variation of arc voltage to develop the in-line quality monitoring system for the pipe inside TIG cladding. The 4 experimental parameters (current, arc length, wire feed position, and shield gas flow rate) varied to observe the change of arc voltage and to establish the model for the monitoring. The arc voltage was decreased when the wire was fed to the backward eccentric position(over 2mm), and the shield gas flow rate was insufficient under 10L/min. In the case of the backward eccentric position over 2mm, the bead appearance was not good and the dilution ratio was increased due to deep penetration. When the shield gas flow rate was lower than 10L/min, the bead surface was oxidized.