Fluid Flow Behaviour under Different Gases and Flow Rate during Gas Metal Arc Welding

Gas metal arc welding (GMAW) is a highly efficient and fast process for fabricating high quality weld. High quality welds are fabricated by proper selection of consumable includes gas and filler metals. The optimum flow rate of gas will ensure the proper quality of weld. In this project, a fluid flow behavior of different flow rate is modeled and the change quality will be studied. KeywordsHydraulic diameter, Gas flow rate, Pipeflow, Reynolds number I. I.INTRODUCTION Gas metal arc welding (GMAW) is a highly efficient and fast process for fabricating high quality welds. High quality welds are fabricated by proper selection of consumable includes gas and filler metals. The optimum flow rate of gas will ensure the proper quality of weld. In this project, a fluid flow behavior of different flow rate is modeled and the change quality will be studied. The arc is established between the workpiece and a continuously fed wire anode. It is a welding process where an electrode wire is continuously fed from an automatic wire feeder through a conduit and welding gun to the base metal, where a weld pool is created. GMA welding is used as a semi-automatic or automatic arc welding process in many applications. In this process the arc is burning between a continuously fed and consumable wire electrode and the workpiece. The shielding gas undertakes a lot of tasks, for example the cooling of the torch, the definition of the arc properties or the protection of the melt from oxidation. If a welder is controlling the direction of travel and travel speed the process is considered semi-automatic [1]. The process is fully automated when a machine controls direction of travel and travel speed; such is in the case of robotics. The plasma flow and the arc attachment at the wire have an important influence on the droplet formation and the heat transfer. Conversely, the droplet geometry, surface temperatures and vaporization affect the fluid flow and the heat transfer inside the arc. A comprehensive understanding of the welding process and the physical effects involved are necessary to reduce the number of experimental parameter studies required and to advance the development of welding techniques and equipment. 1.1. SHIELDING GASES At high temperature, all metals commonly used for fabrication will oxidize in the presence of the atmosphere. Every welding process provides shielding from the atmosphere by some method. When welding steels we want to exclude oxygen, nitrogen, and moisture from the area above the molten puddle. In the Oxy-fuel process, the weld pool is shielded from the atmosphere by the combustion by-products of carbon monoxide (CO) and carbon dioxide (CO2) [1]. If air is aspirated into the shielding gas line through a leak, nitrogen and moisture will also contaminate the shielding gas. Nitrogen, while very soluble in the puddle at high temperatures, will cause porosity as it escapes during cooling of the weld bead. Metallic and argon ions transfer the positive charge across the arc. If air is aspirated into the shielding gas line through a leak, nitrogen and moisture will also contaminate the shielding gas [2]. Oxygen is obtained from direct additions of oxygen or from CO2. II. EXPERIMENTAL SETUP An analytical model for estimation of fluid flow behaviour in various sizes of gas metal arc welding torch nozzle under different shielding gas and inlet Gas Flow Rate (GFR) has been worked out. The variation in fluid flow behavior with a change in gas flow rate and shielding gas has been satisfactorily analyzed. To verify the model, surface appearance of weld deposit has been studied under different GFR at a given shielding gas during weld bead on plate deposition on plain low carbon steel [4]. The theoretical model may provide wider opportunity to design the different GMAW torch nozzle for welding of various plate thicknesses and groove design. RESEARCH ARTICLE OPEN ACCESS Jaison Peter et al. Int. Journal of Engineering Research and Application www.ijera.com Vol. 3, Issue 5, Sep-Oct 2013, pp.52-55 www.ijera.com 53 | P a g e (1).Inlet velocity Fig 2.1. Various components of torch nozzle 2.1. CO2 AS SHIELDING GAS-30 lpm Carbon dioxide is composed of 72% oxygen and 29% carbon. It is the least expensive shielding gas to purchase for welding plain carbon steel [5]. Fig 2.1.1 Contour showing 5.5 m/s velocity Vi = GFR A1 = 0.001166 = 41.25 m/s 0.00002826 GFR at 50 lpm =30/60000 = 0.000833m/s and A1 is 28.26mm 2 = 0.00002826m 2 For a given GFR and torch nozzle outlet area of 10 lpm and 254mm 2 respectively, typical estimation of fluid flow in the GMAW torch nozzle is as given below. Where, the torch nozzle inlet area and shielding gas considered as 24.61mm 2 and 100% CO2 respectively (2). Outlet torch nozzle velocity Vo = A1*V1 = 0.00002826*41.25= 4.59 m/s A2 0.000254 (3). The perimeter (P) P = 3.14*[D + d] = 3.14*[38+18] = 0.175m (4). Hydraulic diameter DH = 4*A2 = 4*0.000254 = 0.0058 m P 0.17 (5). Reynolds number of given torch nozzle is Re = *Vo*DH = 1.8*3.28*0.0058 = 3500 0.000007 Fig 2.1.2 Effect of GFR on Re for CO2 It is observed that irrespective of shielding gas and outlet area, the increase of gas flow rate enhances the Re .it is also observed that in case of 100% CO2 shielding gas the GFR exceeds beyond 35lpm. 2.2. ARGON AS SHIELDING GAS-50 lpm Colorless, odorless, tasteless and nontoxic, argon (Ar) is a noble gas that comprises 0.93% of the earth's atmosphere. Argon can provide an inert and clean environment free from nitrogen and oxygen for annealing and rolling metals and alloys. In the casting industry, argon is used to flush porosity from molten metals to eliminate defects in castings[6]. (1). Inlet shielding gas flow velocity Vi= 0.000833 = 29.47 m/s 0.00002826 (2). Outlet torch nozzle velocity Vo= 0.00002826*29.47 = 3.28 m/s 0.000254 Fig2.2.1. Contour showing 9 m/s velocity Perimeter and Hydraulic diameter are similar to the case of CO2 (3). Reynolds number of given torch nozzle is Re 1.6*3.28*0.0058 = 1449.01 m/s 0.000021 Jaison Peter et al. Int. Journal of Engineering Research and Application www.ijera.com Vol. 3, Issue 5, Sep-Oct 2013, pp.52-55 www.ijera.com 54 | P a g e It is also observed that in case of 100% ARGON shielding gas the GFR exceeds beyond 70 lpm (irrespective of A2); the fluid flow behavior is turbulence flow. Thus, it is concluded that or effective gas shielding in GMAW process better to keep the GFR less than 70 lpm. Fig2.2.1 Effect of GFR on Re for Argon 2.3. 80 % ARGON AND 20 % CO2 AS SHIELDING GAS-50 lpm When two shielding gases are mixed, they may also be called dual blends or binary blends. There are many advantages for using a mixture of argon and carbon dioxide. By optimizing the amount of CO2 in the argon mixture, the fluidity of the weld puddle can be controlled to give good bead shape in a variety of welding positions. It allows for good control and speed when in flat, horizontal, or vertical welding positions (up or down). Because Argon/CO2 mixtures provide an arc that remains more stable when welding over light mill scale or residual oil, there is a significant reduction of the possibility of weld porosity occurring. Also, by increasing the percentage of CO2 in a mixture, there is a greater tendency to remove some material contamination in advance of the arc, which can improve overall weld quality, particularly when coated steels are used. (1). Inlet shielding gas flow velocity Vi = 0.000833 = 29.47 m/s 0.00002826 (2). Outlet torch nozzle velocity Vo = 0.00002826*29.47 = 3.28 m/s 0.000254 (5). Reynolds number of given torch nozzle is Re = 1.64*3.28*0.0058 = 1733.3 m/s Fig2.3.1. Contour showing 9 m/s velocity Perimeter and Hydraulic diameter are similar to the case of CO2 It is observed that in case of 80 % ARGON and 20 % CO2 shielding gas the GFR exceeds beyond 70 lpm (irrespective of A2); the fluid flow behavior is turbulence flow. Thus, it is concluded that or effective gas shielding in GMAW process better to keep the GFR less than 70 lpm. Fig2.3.1. Effect of GFR on Re for 80 %Argon and 20 % CO2 III. CONCLUSION In case of 100% CO2 shielding gas the GFR exceeds beyond 35 lpm (irrespective of A2); the fluid flow behavior is turbulence flow. Thus, it is concluded that or effective gas shielding in GMAW process better to keep the GFR less than 30 lpm. Whereas, in case of 100% Ar and 80% Ar + 20% CO2 shielding gas the turbulence flow may occur when the GFR exceeds beyond 90 lpm. In the plasma region, the kind of flow is open channel flow. For open channel, the laminar and turbulence flow exits when the Re is less than 500 and more than 2000 respectively. This is much lower than pipe flow[7]. Jaison Peter et al. Int. Journal of Engineering Research and Application www.ijera.com Vol. 3, Issue 5, Sep-Oct 2013, pp.52-55 www.ijera.com 55 | P a g e Fig2.2.1. Effect of GFR on Re for CO2, ARGON and 80 %Argon and 20 % CO2 The modeling and analysis carried out inthis work has been found effective in quantitativeunderstanding of the nature of the fluid flow and itsbehavior during GMA welding of low carbon steel.It is clearly identified that the variation in GFR andshielding gas significantly affects the nature offluid flow. REFERENCES[1] Lancaster., The Physics ofWelding,Pergamon Press, New York,USA.[2] Nosse J.R. Nozzle for Shielded ArcWelding Gun ,April 2001.[3] Cooper P., Godbole A. and Norrish J.,Modelling and simulation of gas flows inarc welding – Implications for shieldingefficiency and fume extraction, 2007.[4] Settles G.S., Schlieren & ShadowgraphTechniques, 2006.[5] Malin,V.Y., The state oft he art of NarrowGap welding, Part II, Welding Journal ,Vol.62(6),1983,pp.37-46.[6] Lainh, Pollack.,Narrow gap welding ofHY-100 plate using close loop adaptivefeedback, through the arc trackingtechnology, Welding journal,Vol.62(4),1985,pp38-44.[7] Fan,F.G and Kovacevic.R., A unifiedmodel of transport phenomenain gas metalarc welding including electrode arc plasma and molten metalpool, Journal of Physicsd:Applied physics, Vol.37,2004,pp2531-2544