The gastungstenarcweldingprocess uses the heat produced by an arc between a nonconsumable tungsten electrode and the base metal. The molten weld metal, heated weld zone, and nonconsumable electrode are shielded from the atmosphere by an inert shielding gas that is supplied through the torch. An electric arc is produced by an electric current passing through an ionized gas. In this process, the inert gas atoms are ionized by losing electrons and leaving a positive charge. The positive gas ions then flow from the positive pole to the negative pole and the electrons flow from the negative pole to the positive pole of the arc. The intense heat developed by the arc melts the base metal and filler metal (if used) to make the weld. As the weld pool cools, coalescence occurs and the parts are joined. The occurrence of spatter or smoke is minimized. The resulting weld is smooth and uniform and requires minimum finishing. Filler metal is not added when thinner materials, edge joints, or flange joints are welded. This is known at autogenous welding. For thicker materials an external filler or “cold” filler rod is generally used. The filler metal in gastungstenarcwelding is not transferred across the arc but is melted by it.
In GTAW welding, the arc is struck between the work piece and a tungsten electrode, which remains unmelted. The argon shielding gas, which protects both the hottungsten electrode and the molten weld puddle, is brought in through a nozzle or gas cup which surrounds the electrode. This process used to be called TIG (Tungsten Inert Gas). For both stainless and nickel alloys the current used is DCSP, direct current straight polarity (Durgutlu, 2004). The work is electrically positive and the tungsten electrode is the negative electrical pole. The electrode is usually thoriated tungsten, that is, tungsten metal added to improve the emissivity of electrons.
nickel, and zinc oxides. Fumes contain silicates and fluorides generated from the electrode-coating emissions. Gases generated by welding include carbon monoxide, nitrogen oxide, and ozone. lower welding fumes concentration are observed in TIG welding ranging between 45 and 77 µg/m3.Fumes are solid particles formed by condensation from the gas state. These particles react with air when they are vaporized . Welding fumes particle are, categorized into the ultrafine and fine particle ranges . The particles in this size range are of the respirable fraction. These particle sizes especially affect the lower respiratory tract including the bronchioles and alveoli .There is three modes of particle size distribution for aerosols produced while welding. The first captures Fumes less than 1 micrometer made up of oxidized metal vapors are the smallest. These particles are transported in the atmosphere by diffusion and other processes. The next mode includes spherical particles usually between 6 to 13 micrometers that have been solidified from the hot metal that is not oxidized . Reduction of welding fumes can be achieved by use of ventilator, fume hood, exhausts, and use of Abstract: The TIG welding processes are accompanied by some of toxic aero-disperse particles which can affect the lungs and respiratory system of welders. This paper has examined Various process parameters affecting electrode melting rate and safe welding fumes in TIG welding. The response surface methodology has been applied to model, examine and explain the influence of current, voltage and gas flow rate on electrode melting rate and fume concentration. Several statistical tools such as box cox plot, cooks distance and surface plots were employed to check for significance, compatibility and strength of the model. The model developed possessed a very high goodness of fit of about 95% determination strength explaining that critical control of gas flow rate is of great importance to reduce the electrode melting rate as well as the fume concentration in TIG welding.
mm Φ shielded by argon gas is used to strike the arc with base metal. Filler rods (31.5 mm Φ) of Aluminium alloy 5183 are recommend for welding of this alloy for getting maximum strength and elongation. The chemical compo- sition of base metal and filler rod are tabulated in Table 1. Sample plates of size 300 × 150 × 5 mm were prepared by milling and EDM wire-cut machines. Welding of the samples was carried out on Automatic Pulse GTAW Tri- ton 220 V AC/DC. In order to remove oil, moisture and oxide layer from base metal, they were thoroughly wire brushed, cleaned with acetone and preheated at 150˚C in the oven. The quality of weld is based on the process parameters, such as pulse current in the range of 150 - 210 A, base current in the range of 75 - 135 A, pulse fre- quency in the range of 50 - 150 Hz, pulse-on-time in the range of 30% - 90% and percentage of He in Ar + He mixtures in a range of 10% - 50%.
GTAW process is the most common operation used for joining two similar or dissimilar metallic pieces with or without heating the material or by applying the pressure or using the filler wire for increasing productivity with less time and cost constraint. A shielding gas is used like Argon, Helium, Nitrogen, etc. to avoid atmospheric contamination of the molten weld pool (as shown in fig. 2). Filler wire may be added depending upon the type of weld required and weld geometry. The arc is struck either by touching the electrode with a tungsten piece or using a high frequency current. In the first method, arc is initially struck on a scrap tungsten piece and then broken by increasing the arc length. This procedure is repeated twice or thrice which warms up the tungsten electrode. The arc is then struck between the pre-cleaned work-piece. This method avoids breakage of electrode tip, work-piece contamination and loss of tungsten from electrode. In the second method, a high frequency current is superimposed on the welding current. The welding torch is brought closer to the job. When electrode tip reaches at 2 to 3 mm distance, a spark jumps across the air gap between the electrode and the work-piece. Hence, arc is established. During welding, shielding gas is allowed to impinge on the solidifying weld pool for a few seconds even after the arc is extinguished. This avoids atmospheric contamination of the weld. The welding torch inclined at angles of 70-80˚ with the flat work-piece and commonly a leftward technique is used.
X80 spiral-welded pipeline steel from China is used for the experiments, and Table 1 shows its chemical composition (wt.%). The X80 pipeline steel used for welding in the experiment was cut into 500 mm×150 mm×18.4 mm samples via wire-cutting. The welding method was hot-wire TIG welding, ER70S-G weldingwire was adopted, and single-sided welding was processed. Fig. 1 shows the type of welding groove used in this study. The welding parameters are shown in Table 2. Before welding, the 30~50 mm widths on both sides of the groove were eliminated by using a grinding disc. After welding, the size of each metallographic sample acquired from the welding area was approximately 4 mm×10 mm×20 mm. The metallographic samples were corroded with 4% alcohol nitrate solutions after grinding and polishing. Then, the microstructures of different areas in the welded joints were observed with a Leica DM2500M series microscope.
Plasma transferred arcwelding can be defined as a gas- shielded arcweldingprocess where the coalescence of metals is achieved via the heat transferred by an arc that is created between a tungsten electrode and a work piece. The arc is constricted by a copper alloy nozzle orifice to form a highly collimated arc column.The plasma is formed through the ionization of a portion of the plasma (orifice) gas. The process can be operated with or without a filler wire addition. PTA is suitable for manual, semi or fully automatic operations using manipulators, positioners, oscillators and microprocessor controls. It can be used with Robots and adapted with CNC systems. It produces a very high quality deposit offering optimal protection with minimal dilution or deformation of the base material which are relatively low cost surfaces in the case of Hardfacing.
Mild steel encapsulation was then removed by machining. The slabs, after removal of mild steel skin, were hot rolled using flat roll at 900 °C to make 4 mm thick sheets. Rolling was carried out very slowly at 900 °C with 0.1 mm thickness reduction per pass. The rolling was done using small laboratory scale rolling mill with 10 cm roll diameter. The sheets were then vacuum annealed at 950 °C for 40 min to relieve the residual stresses. The alloy prepared in this way was characterized in terms of density, microstructure, hardness, and tensile properties.
At this point, when these localized parts of the weldment becomes brittle, and load is applied, it would not have sufficient strength to resist fracturing. In recent times, other welding processes have been introduced into the country, such as the gas metal arcwelding (GMAW) processgastungstenarcweldingprocess and submerged metal arcweldingprocess. These welding processes have been used for welding of both aluminum and steel products. GMAW is a weldingprocess that joins metals by heating the metal with an electric arc between a continuously fed consumable electrode wire and the workpiece. Kim et al., (1991) were of the opinion that GMAW is the most common method for arcwelding of steels and aluminum alloys. Screeraj et al., (2013) wrote that GMAW is a multi-objective and multifactor metal fabrication technique.
Welding is an important fabrication technique for stainless steels and various guidelines have been provided by Patterson and Fager, (1995), Davison (2000), Avesta Welding (2004) and Messer, et al, (2007) for the welding of duplex stainless steel. These guidelines provide insights into the techniques and precautions needed to weld these materials successfully. Davison (2000) affirmed that the Duplex Stainless Steel and the Alloy 2205 are generally considered weldable due to their low carbon content although their successful welding depends on many rules and precautions that must be followed to ensure that the welds maintain the wrought microstructure as much as possible and are free of defects. Problems are common during fabrication and eventually in service when the proper procedures are not followed. According to Lippold and Kotecki (2005), the problems often encountered in welding these steels are associated with improper control of the weld microstructure and related properties. Therefore the aim in welding the Duplex stainless Steel (DSS) is to achieve a weld metal and heat-affected zone (HAZ) that retain the corrosion resistance, strength, and toughness of the base metal. The design of welding procedures are for the welding to lead to a favorable phase balance after welding in the weld and Heat Affected Zone (HAZ) and to prevent the precipitation of detrimental intermetallic or nonmetallic phases. Maximum corrosion resistance and mechanical properties in a Duplex Stainless Steel (DSS) weldment are achieved when the phase balance of ferrite to austenite is 50:50 but this is in most cases difficult to achieve in practice. The difficulty could be traced to the many variables such as metal chemistry, welding processes, and thermal history of the steel but the study of Lippold and Kotecki, (2005) have shown that Duplex Stainless Steel (DSS) will have optimal corrosion resistance and mechanical properties when 35 to 60% ferrite content is maintained throughout the weldment. The microstructure and properties of the Heat Affected Zone (HAZ) which is altered by inducing intensive heat into the parent metal during welding is expected to have comparable corrosion resistance and impact toughness of the base material minimum requirements. The low heat input welding processes and high thermal conductivity of Duplex Stainless Steel (DSS) and Super Duplex Stainless Steel (SDSS) make them to exhibit a narrow-HAZ, in comparison to Austenitic Stainless Steel. Typically an austenitic-SS’s HAZ is shown to be in the order of 500 µm in width (approximately 20 grains) but a DSS HAZ is often as small as 50 µm in width (2 grains).
Finite element simulation was used to estimate temperature at the weld and heat affected zones during welding. Actual temperature during preheating was measured and compared with calculated data to verify the validity of the simulation. Figures 4a, 4b, and 4c show how temperatures and their gradients change with time during the preheating sequences. Although a specimen was initially heated to 150°C on a hot plate, its surface temperature dropped to nearly 100°C after transferring and fixturing a weldment onto a welding table at room temperature. Additional preheating with a GTAW torch was necessary to maintain temperature before welding. When the surface above the left thermocouple was heated five times along a line 30 mm from the weld, the average temperatures of all three thermocouples rose linearly during the preheating time (0-95 sec). The temperature gradients then reduced when the heating torch was off while moving to the right location (95-110 sec), after which the temperatures rose again when preheating twice at the right location (110-145 sec). Reasonable agreement was obtained between the measured temperatures and the resulting finite element data at three thermocouple locations (left, right, and below a weld).
Measurement of welding parameters and monitoring of electric arc stability was performed by acquisition of welding current and voltage with on-line monitoring system. Figure 1 shows block diagram of experimental setup. Surfacing was performed by automatic MAG weldingprocess with TPS 4000 power source (Fronius International GmbH, A). Tracking Vehicle FTV 4 connected to Control Unit FCU – 4 – RC remote control (both made by Fronius International GmbH, A) was used for the welding speed setup.
In GasTungstenArcWelding (GTAW) or the TIG welding, the gun used to weld is called welding torch. The TIG works by supplying electric arc between the tungsten electrode and the workpiece. The electric arc produced melts the two workpiece and combine them when the weld solidified. The tungsten electrode is hold by collet which works as adjuster for the in and out of the electrode. The gun also has a ceramic cup that used to direct the shielding gas. Finch (1997) defined that the TIG welding torch work by producing electric arc instead of flame that occurs between the tungsten and workpiece. A collect clamps the tungsten so it can be adjusted in and out of the torch. Due to the intense of heat, the ceramic cup is used to direct the shielding gas to the area of weld. Figure 2.7 shows the welding gun used in TIG.
Spray arc is required for thicker section than short arc. It is very suitable when a high deposition rate is needed and when deep penetration is required for welding of massive base materials that can tolerate high heat input. The large weld pool makes vertical or overhead position welding diffi- cult, especially in the case of plain carbon steel and stainless steels. For joining steels, the transition current can be varied more than when welding aluminium alloys. A spray arc can be used with almost all common alloys containing aluminium and also nickel alloys, copper alloys, stainless steels, magnesium, and carbon steels (Lyttle and Praxair 1990; Althouse et al. 2004; Robert and Messler 2004; Goecke 2005a, b; Jeffus and Bower 2010). Despite the advantages of conventional spray arc, odd arc instabilities and disordered metal transfer have restricted its adoption. In spray arc mode, the current and voltage are almost Table 4 Comparison of different welding arcs a
two for the define weld job. Welder performs the technique arbitrary or self-define. Generally they adopt the technique as per their past experience or the availability of equipment. So it is required to define the technique for the welding job and this identification of technique for the job should be based on mechanical properties, Appearance and weld quality. Austenite stainless steels 304L welded by either PAW or GTAW but comparative study was not performed yet. So it will be very important to investigation in the field of welding. An experiment on Welding of SS 304L material using the GasTungstenArcWelding and Plasma ArcWeldingprocess and analysis techniques used like Scanning Electron Microscopy (SEM), Micro and Macro Examination, Bend Test, Ultimate Tensile Test (UTS), Radiography etc. An investigation of the Weld penetration, HAZ elongation. To evaluate mechanical properties of material welded by GTAW and PAW. To study the effect of various process parameters like current, weld speed, gas flow rate on weld properties. Identify suitable process for various materials.
The present work deals with optimization of weldingprocess variables by using Metal inert gas welding.The aim of my work is to study the hardness that affect the welding joint of dissimilar metals. Stainless Steel 304 was welded to C-25 carbon steel using a metal inert gaswelding which also known as gas metal arc is welding with the help of filler wire of stainless steel and 0.8 mm diameter. Argon gas was used as shielding gas in this process. Dissimilar metals welding have great scope in advanced technology now a days owing to their high strenght, hardness, and corrosion resistance properties. The combination of midium carbon steel and austenitic stainless steel has got large number of application in industry such as tublar product, building and costruction, nuclear plant, and heat exchanger assembly etc. Due to the fact that low cost of C-25 carbon steel and corrosion resistance property of stainless steel. All these applications are require welding of the two which can perform the desired service requirement of the industry. In this experiment we got that the hardness depend on the variable parameter and wire feed rate is the main effective parameter.
The micro hardness associations midst the micro hardness of the base metal, the heat heart-rending region and the weld metal of all welded joint illustrations are as follows: weld metal > HAZ > base metal. During the course of GTAW welding in the magnesium alloys, the weld metal comprised of fine equiaxial grains owing to the extraordinary cooling rate, whereas grain coarsing created in the HAZ caused by the impact of the thermal cycling. The grains contains of the three zones were weld metal > base metal > HAZ. As the grain size begin small, So the measurement of the micro hardness becomes higher, demonstrating the Hall-Petch equation. Accordingly, The modification of the micro hardness contain an contrary relationship with the square root of the grain amount. Another note worthy issue is that in overall, the intensification of the hardness can be accredited to the grain modification and the consolidation influential of the brittle and hard, β- phase . Throughout the welding course, grain coarsening happened in both the HAZ and the FZ with an upsurge of the heat input. Hence forth, a higher micro hardness values were attain with lower heat inputs for alternative current specimens. In addition, it can be realized that with supplementary upsurge in the heat input, that the micro hardness of the FZ and HAZ improved to some extent. The reason being is that a moderately extraordinary heat input could result in more granular β-Mg17Al12 phase to form in the HAZ and FZ, which partly balances, the effective of the grain coarsening on the diminution of the micro hardness of the HAZ and FZ of the welded joint. The twins were An important factors for hardness and strength. For pulsed current, this period is not proper for using welding parameters. It is possible to say that likewise for pulsed current at higher welding parameters, the same result would take place as mentioned above.
Among all welding processes GTAW (GasTungstenArcWelding) or TIG (Tungsten Inert Gas) is appropriate candidate for industrial application due to its high delicate achievement qualities. The GTAW is thus a method of choice in industries as diverse as nuclear, aerospace, and pharmaceutical and food processing. Indeed beyond 3 mm it is necessary to perform edge preparation (chamfer) and adding filler material by multi pass welding -. This is due to low yielded arc centrifugal convection current which unfavorable for high penetration weld. Increasing number of pass of welds increase the risk of defects and heat affected zone increases making it slow and unproductive compared
Furthermore, by examining the effect of surface tension temperature gradient on the flow velocities, interesting observations on the magnitude of the forces associated with the weld pool could be revealed. At ∂γ ∂T ⁄ = 0, a very small negative (outward flow) velocity was usually induced, less than 2 cm/s in magnitude, reinforcing the theory that for GTAW process, surface tension forces would have the most profound impact; the outward flow direction suggests that buoyancy forces (outward flow) would outweigh electromagnetic force (inward flow), since these are the only two forces existing in this model. Moreover, the velocity magnitudes for positive gradients are much larger than when negative, this may be due to the fact that gravitational force would stimulate the inward flow, further speeding up the circulating flow initiated from the top surface.
thickness . The FSW sample was slightly more noble than BM, with a corrosion potential of approximately -650 mV at the end of experiment. The GTAW sample exhibited better corrosion resistance than the BM, SMAW, and FSW samples at the beginning of the experiment, especially in the first 10 min. However, the potential then rapidly decreased, and the final corrosion potential recorded was -700 mV, intermediate to the potentials of BM and SMAW. The fluctuation of the potential was observed over the whole surface, indicating the destruction and reformation of the protective oxide film. This phenomenon can be attributed to the intergranular corrosion or passivation and depassivation of pits frequently observed for aluminum alloys . The deeper examination of the corroded samples presented later in this work clarifies the type of corrosion. The corrosion potential of GTAWB was similar to that of GTAW at the beginning of the experiment but then decreased rapidly because of the attack of Cl - ions on the oxide film. However, the corrosion potential remained stable after 10 min, and no fluctuation was observed over the entire surface of the sample until the end of the experiment. The addition of borax pentahydrate powder during GTAW welding in the joint area made the corrosion potential more noble than that of the other welds tested. The oxide components of boron most likely served as a corrosion barrier, which merits further examination. The final corrosion potential registered for GTAWB was -400 mV, which is the noblest potential observed for any alloy. The most reactive E corr in saline solution was observed for the SMAW sample, being -750 mV at the