Finite-Element Modeling of Manual Metal Ac Welding (MMAW) Pocess Ali. Moaefadeh Abstact Manual Metal Ac Welding is a pocess whee an ac is stuck between a flux-coated consumables electode and the wok piece. The ac and the weld pool ae both shielded by gases geneated by the flux coating of the electode. In this pape, the Manual Metal Ac Welding is studied and Cabon Steel tempeatue field is gained in this pocess. The themal effect of Manual Metal Ac that specially depends on the electical ac, electode type and tempeatue field of it in wokpiece, is the main key of analysis and optimiation of this pocess, fom which the main goal of this pape has been defined. Numeical simulation of welding pocess in SIMPELC method and by ANSYS softwae fo gaining the tempeatue field of cabon steel, the effect of paamete vaiation on tempeatue field and pocess optimiation fo diffeent cases of electode done. Keywods Finite-Element, MMAW, FSI, SIMPLEC, ANSYS Tempeatue Field and Cabon Steel M I. INTRODUCTION anual Metal Ac Welding is a pocess whee an ac is stuck between a flux-coated consumables electode and the wok piece. The ac and the weld pool ae both shielded by gases geneated by the flux coating of the electode. Be cetain that you ae weaing suitable potective clothing, gloves etc. and that you ae woking in a non-haadous aea. If necessay, efe again to the SAFE PRACTICES section of this manual. Manual Metal Ac Welding (MMAW) Pocess shows in Fig.1. Connect the Wok Clamp to the wok piece. Place the desied electode in the Electode Holde. Tun on the powe switch located on the ea panel. Wait appox 5 seconds as the unit goes though its initiation sequence. Pess the Weld Mode button until the Stick Mode LED is lit. The Induo 145 keeps the last mode used in memoy, so this step is only necessay when using a diffeent mode to that used last. Select an appopiate welding cuent fo the electode diamete by setting the knob on the machine font panel. WIA AUSTARC electodes will give the best esults. To stike the ac, dag the end of the electode along the wok piece as if stiking a match. As the ac initiates, lift the electode slightly away, aiming to establish an ac length of appoximately 3mm. As the electode end is consumed, feed the electode into the ac in ode to maintain ac length. As a geneal ule, the ac should be held as shot as possible while still giving stable bun off and good weld appeaance. An ac which is too long cause an unwieldy flow of metal with a ough weld appeaance and educed penetation. An ac too shot leads to a naow weld deposit and stuttey ac chaacteistics, and the electode is liable to feee onto the wok piece. As the solidified weld deposit foms, move the end of the electode s lowly along the weld path, aiming to maintain a pool of molten weld metal behind the ac. Deceasing this ate of tavel will esult in a wide weld deposit, and similaly inceasing it will naow the weld deposit. Always fill the cate which tends to fom at the end of a weld deposit, by pausing momentaily befoe withdawing the electode to beak the ac. Unfilled cates ae a point of weakness, and can lead to weld cacking. F. A. Young Reseaches Club, Mahshah Banch, Islamic Aad Univesity, Mahshah, Ian E-mail: a_moaefadeh@yahoo.com a.moaefadeh@mahshahiau.ac.i Tel: +989123450936 Fig. 1 (a). Manual Metal Ac Welding (MMAW) Pocess [ISSN: 2045-7057] www.ijmse.og 1
Mass continuity equation: 1 ( ρυ ) = 0 (1) Radial momentum consevation equation: 1 2 ( ρυ υ ) = ρ 1 υ j Bθ + (2η ) + υ υ υ ( η + η ) 2η 2 (2) Axial momentum consevation equation: Fig.1 (b). Manual Metal Ac Welding Basic Equipment 1 2 ( ρυ υ ) = ρ υ + j Bθ + (2η ) + (3) 1 υ υ ( η + η ). II. GOVERNING EQUATIONS In the common diect cuent electode positive (DCEP) connection, the electode is the anode and the wokpiece is the cathode. A Manual Metal ac is stuck between the electode and the wokpiece. The electode is continuously fed downwad and melts at the tip by the high tempeatue ac. Doplets ae then detached fom the electode and tansfeed to the wokpiece. The computational domain includes an anode one (electode), an ac one, and a cathode one (wokpiece). The anode and cathode sheaths have been omitted and teated as special bounday conditions fo computational simplifications. Assuming the ac is in local themal equilibium (LTE) and the plasma flow is lamina and incompessible, the diffeential equations govening the ac, the electode, detached doplet, and the wokpiece can be put into a single set. The diffeential equations govening the consevations of mass, momentum, and enegy based on continuum fomulation given by Chiang and Tsai ae modified and employed in this study. The deivation of the equations can be found in The idea of continuum fomulation is to eliminate the need of explicitly tacking the solidifying o melting inteface, and theefoe the established convesation equations is valid fo both solid and liquid phases[2]. The diffeential Equations (1) (4) ae solved iteatively by the SIMPLEC numeical pocedue: Enegy consevation equation: 1 ( ρυ h) + ( ρυ h) = 1 k h k h ( ) + ( ) + c c j E p + j E R, p In the solution of Equation (1) (4), special attention needs to be put on the enegy effects on the electode suface. At the cathode suface, additional enegy flux tems should be included in Eq. (4) because of themionic cooling due to the mission of electons, ion heating, and adiation cooling [2]. III. NUMERICAL SIMULATION Finite-Element techniques: 1-Finite elements modeling, types and popeties fo model diffeent pats. 2- The definition of mateial popeties 3- paamete definition 4- Loading 5- Bounday and initial value definition (4) [ISSN: 2045-7057] www.ijmse.og 2
IV. ARC-ELECTRODE MODEL The tungsten cathode, ac plasma and anode ae descibed in a fame of cylindical coodinate with axial symmety aound the ac axis. The calculation domain is shown in Fig. 2. The diamete of the tungsten cathode is 3.2mm with a 60 conical tip. The anode is a wate-cooled stainless steel. The ac cuent is set to be 150 A. A, He o mixtue of them is intoduced fom the uppe bounday of the calculation domain. The flow is assumed to be lamina, and the ac plasma is assumed to be unde local themodynamic equilibium (LTE). step. Second, an iteative pocedue is used to solve fo the advanced time pessue and velocity fields that satisfy Eq. (1) to within a convegence citeion at the new time. Thid, the enegy equation Eq. (4) is solved. Fig.2. shows A typical sequences of tempeatue, electical potential, and pessue distibutions on the symmetic plane fo an axisymmetic stationay ac. Fo the ac domain, a fully implicit fomulation is used fo the time-dependent tems, and the combined convection diffusion coefficients ae evaluated using an upwind scheme. The SIMPLEC algoithm is applied to solve the momentum and continuity Equations (1) (4) to obtain the velocity field. At each time step, the cuent continuity equation Eq. (4) is solved fist, based on the updated paametes. The new distibutions of cuent density and electomagnetic foce ae then calculated fo the momentum and enegy equations. The momentum equations and the mass continuity equation ae then solved in the iteation pocess to obtain pessue and velocity. The enegy equation is solved to get the new tempeatue distibution. Next, the tempeatue-dependent paametes ae updated, and the pogam goes back to the fist step to calculate the cuent continuity equation. This pocess is epeated fo each time step until the convegence citeia ae satisfied [2]. VI. RESULTS AND DISCUSSION Conclusions fo fluid tempeatue field cabon steel tempeatue field, completely shown in Fig.3. a) b) Fig. 2. Ac-electode model [8] V. NUMERICAL CONSIDERATIONS Fo the metal domain, the method developed by Toey et al. was used to solve p, u, v, and T. This method is Euleian and allows fo an abitay numbe of segments of fee suface with any easonable shape. The basic pocedue fo advancing the solution though one time step, Dt, consists of thee steps. Fist, explicit appoximations to the momentum Equations (2) (4) ae used to find povisional values of the new time velocities at the beginning of the time Fig.3. Conclusions fo tempeatue field: a) tempeatue field, b) Cabon steel tempeatue field [ISSN: 2045-7057] www.ijmse.og 3
A peson acting as Fie Watche must be standing by with suitable fie extinguishing equipment duing and fo some time afte welding o cutting if Combustibles (including building constuction) ae within 10 metes. Combustibles ae futhe than 10 metes but can be ignited by spaks. Openings (concealed o visible) in floos o walls within 10 metes may expose combustibles to spaks. Combustibles adjacent to walls, ceilings, oofs, o metal patitions can be ignited b adiant o conducted heat. Afte wok is done, check that aea is fee of spaks, glowing embes, and flames. Any tank o dum which has contained combustibles can poduce flammable vapous when heated. Such a containe must neve be welded on o cut, unless it has fist been cleaned as descibed in AS.1674-1974, the S.A.A. Cutting and Welding Safety Code. This includes a thoough steam o caustic cleaning (o a solvent o wate washing, depending on the combustible's solubility), followed by puging and ineting with nitogen o cabon dioxide, and using potective equipment as ecommended in AS.1674-1974. Wate-filling just below woking level may substitute fo ineting. Hollow castings o containes must be vented befoe welding o cutting. They can explode. Neve weld o cut whee the ai may contain flammable dust, gas, o liquid vapous. Exposed conductos o othe bae metal in the welding cicuit, o ungounded electically alive equipment can fatally shock a peson whose body becomes a conducto. Ensue that the machine is coectly connected and eathed. If unsue have machine installed by a qualified electician. On mobile o potable equipment, egulaly inspect condition of tailing powe leads and connecting plugs. Repai o eplace damaged leads. Fully insulated electode holdes should be used. Do not use holdes with potuding scews. Fully insulated lock-type connectos should be used to join welding cable lengths. Teminals and othe exposed pats of electical units should have insulated knobs o coves secued befoe opeation. The output fluid tempeatue field fom nole showing heat tansfe way between electical ac and electode and envionment, with elated tempeatues is completely dawn in Fig.4. Fo study the tempeatue vaiations in plasma axis and its heat tansfe to electode accoding to diagam (Fig.5), the tempeatue field of electical ac in its symmety axis with standoff is dawn. Fig.5. The tempeatue field of electical ac in its symmety axis by standoff. In this diagam, in each distance fom nole to wokpiece suface, the desied tempeatue can be deived. Themal conductivity vaiation and themal specific of cabon steel ae shown in Fig. 6 and Fig. 7. Fig.6. Themal conductivity of cabon steel Fig.7. Themal specific of cabon steel Fig.4. Electical ac tempeatue field [ISSN: 2045-7057] www.ijmse.og 4
VII. CONCLUSIONS Exposed conductos o othe bae metal in the welding cicuit, o ungounded electically alive equipment can fatally shock a peson whose body becomes a conducto. Ensue that the machine is coectly connected and eathed. If unsue have machine installed by a qualified electician. On mobile o potable equipment, egulaly inspect condition of tailing powe leads and connecting plugs. Repai o eplace damaged leads. Fully insulated electode holdes should be used. Do not use holdes with potuding scews. Fully insulated lock-type connectos should be used to join welding cable lengths. Teminals and othe exposed pats of electical units should have insulated knobs o coves secued befoe opeation. A 3D mathematical model fo the metal tansfe pocess in MMAW was fomulated in this aticle. A complete model descibing the MMAW welding pocess is developed, howeve, the computation of the tansient solution of the complete model was pohibitively time-consuming and beyond the capability of the cuent PCs. In ode to study the plasma ac inteaction with metal duing the metal tansfe pocess, some simplifications have been made. A case of an axisymmetic ac was studied fist using this 3D model fo the veification pupose. The numeical esults ageed well with the pevious two-dimensional studies. A case of a moving ac was then computed to demonstate the 3D capability of the model. The esults evealed that the time-invaiant Gaussian assumption fo the distibutions of the ac pessue, heat flux, and cuent density on the wokpiece suface did not epesent of the eal situation. The calculated distibutions fo the moving ac wee nonaxisymmetic and the peaks shifted to the ac moving diection. REFERENCES [1] S. Tashio, M. Tanak, L. Muph, and J. Lowke, "Pediction of enegy souce popeties of fee-buning ac" Welding Jounal, Mach 2008, pp. 23-29. [2] A. Moaefadeh, "Numeical simulation of tempeatue field by Plasma ac welding Pocess in stainless steel" IREMOS Jounal, Febuay 2010, pp.101-107. [3] A.Moaefadeh, Choosing Suitable shielding gas fo themal optimiation of GTAW pocess, IREME Jounal, Sep 2010. [4] E. Goman, New developments and application in plasma welding Welding Jounal, July 2004, pp. 547-556. [5] Y. Wang, and Q. Chen, "On-line quality monitoing in Plasma ac welding Jounal of Mateials Pocessing Technology, Januay 2005, pp. 270-274. [6] H. Kyselica, "High Fequency evesing ac switch fo plasma welding of Aluminum" Welding Jounal, May 2005, pp. 31-35. [7] G. Langfod, "Plasma keyhole ac welding of stuctual stainless steel joints" Welding Jounal,Feb2005, pp.102-113 [8] ANSYS Help system, Analysis Guide & Theoy Refeence Ve. 9.10. Ali Moaefadeh Young Reseaches Club, Mahshah Banch, Islamic Aad Univesity, Mahshah, Ian Faculty membe of Depatment of Mechanical Engineeing, Mahshah Banch, Islamic Aad Univesity, Mahshah, Ian E-mail: a_moaefadeh@yahoo.com a.moaefadeh@mahshahiau.ac.i Tel: +989123450936 [ISSN: 2045-7057] www.ijmse.og 5