A Study on the Surface Depression of the Molten Pool with Pulsed Welding

Transcription

1 A Study on the Suface Depession of the Molten Pool with Pulsed Welding The effect of the ac foce with pulsed ac welding was examined BY M. YANG, Z. YANG, B. CONG, AND B. QI ABSTRACT Ac foce was the main facto fo ac behavio duing the ac welding pocess, which had an effect on the molten pool. Ultahigh-fequency pulsed gas tungsten ac welding (UHFP-GTAW) ceated the lage ac foce and weld penetation with expeimental eseach. The ac foce caused suface depession that pushed the heat souce downwad to the bottom of the molten pool. As a esult, the fluid status and geomety of the molten pool wee changed. The suface depession was calculated with the esultant liquid-gas inteface. Zeo solutions of the balance functions wee obtained with appoaching cuves. The esults indicated an available condition with ac cuve assumption and an acute angle of the spheical cap wee known to be accuate. Ellipsoid assumption was discussed with a lage ac foce (80 khz) that guaanteed the angle of the spheical cap θ > 90 deg. The tansient simulation was caied out, and the esults indicated the suface depession impoved the penetation although low heat conductivity of titanium was seen. Futhemoe, double ciculation can be found in the molten pool that was caused by both electomagnetic foce and suface tension. The velocity demonstated the dominance of suface tension with a maximum up to 1.74 m/s. And it also poved the effect of counteclockwise ciculation on penetation by electomagnetic foce. KEYWORDS Ac Foce Suface Depession Pulsed Ac Welding Gas Tungsten Ac Welding (GTAW) Intoduction Ac foce is the main facto fo ac behavio duing the ac welding pocess, which is composed of electomagnetic and plasma jet foces (Ref. 1). The welding cuent has a huge effect on ac behavio, including the method of pulsed ac welding (Ref. ). With pulsed welding, the electomagnetic foce in ac plasma changed with pulse fequency. Radial and axial elements wee also both affected (Ref. 3). And adial foce was the key fo the significant ac constiction and stiffness. Simultaneously, the enegy density of ac plasma inceased, and a lage penetation was obtained with the pulsed ac welding pocess (Refs. 4, 5). The axial element was the one of two main compositions of ac foce with axial electomagnetic foce, which was known as the eason fo suface depession of the molten pool (Ref. 6). With the lage ac foce, the deepe penetation can be found with the pevious expeimental esults (Ref. 7). Fluid and geomety of the molten pool is impotant fo weld appeaance, micostuctue, and popeties (Refs. 8, 9). And the suface defomation is the key facto fo the fluid and solidification (Refs. 10 1). Lage depession on the suface is a benefit fo the molten pocess of base metal as moe diect heat input (Ref. 13). Meanwhile, the ac foce has a moe significant effect fo the liquid metal status (Ref. 14), which may also alte diving foces in the molten pool. As known peviously, suface tension, electomagnetic and plasma dag foces, plus buoyancy ae the diving influences fo the fluidity of the molten pool (Refs ), which ae diffeent with vaious mateials and suface defomation. As a esult, diffeent welding methods and mateials will cause diffeent suface depessions. The eason fo suface depession is ealized as composed foces, such as suface tension, gavity, ac foce, and pessue in liquid metal. And the depession happened in the inteface between ac plasma and molten metal, which made it to be complex. With a conventional welding pocess, the pevious esults (Ref. 13) indicated that the suface depession caused by ac foce was no moe than 5% h (h is the thickness of the base metal) that could be ignoed (aveage welding cuent I avg < 110 A). The eo of penetation was less than 5% M. YANG (yangmingxuan@buaa.edu.cn), Z. YANG, B. CONG, and B. QI ae with the Depatment of Mateials Pocessing, Beijing Univesity of Aeonautics and Astonautics, China. 31-s WELDING JOURNAL / AUGUST 014, VOL. 93

2 Fig. 1 Schematic welding cuents. without suface depession duing simulation by stainless steel. Ultahigh-fequency pulsed gas tungsten ac welding (UHFP-GTAW) ceated a much lage ac foce that caused significant suface depession. With moe than 0 khz, the ac foce inceased by 00% at least, compaed with conventional gas tungsten ac welding (C-GTAW). The moe obvious suface defomation was made by the lage ac foce that had a huge impact on fluid status in the molten pool. With simulation by stainless steel, the ac foce was added in the axis of ac plasma unde plane assumption. The esults indicated that double ciculation existed in the molten pool with UHFP-GTAW. And such double ciculation was ecognized as the eason fo inceased penetation (Refs. 18 0). Also, fluidity and tempeatue distibution, espectively, wee impoved. The expeimental esults demonstated the lage ac foce and penetation can be found unde titanium alloys (Ti- 6Al-4V) with UHFP-GTAW. With the lage ac foce, the suface depession will exist, which may be still impotant fo weld penetation and geomety. In addition, titanium alloy was paamagnetic so that its magnetic pemeability μ m was substituted by μ 0. The pape poduced the study on suface depession by the ac foce duing UHFP- GTAW. The welding pocess was caied out fo suppoting expeimental esults. The depession height would be calculated that was the tansient status fo simulation. Suface tension, gavity, and liquid pessue wee known as the thee key factos fo mathematic calculation. The eason fo penetation was discussed with Ti-6Al-4V. The study will also analyze the fluid and tempeatue distibution with depession caused by ac foce. Expeimental Pocedue Welding Expeiments Ti-6Al-4V titanium alloy was the base metal with dimensions of mm. Unde UHFP-GTAW, the switch fequency is 0~80 khz with cuent upslope/downslope ate (di/dt) moe than 50 A/μs. The schematic welding cuents ae illustated in Fig. 1. In the figue, I b is Fig. Measuement appaatus fo the ac foce duing the welding pocess. the backgound cuent and I p is the pulsed cuent. The times of the backgound and pulsed cuents ae t b and t p, espectively; as a esult, the pulse cicle time is epesented as T = t b + t p and the fequency f = 1/T. The duty cycle of the pulse duation is deduced to be δ = t p /T. The paametes of the pulsed cuent ae shown in Table 1. The electode adius was 1. mm and made of % ceium and 98% tungsten. The distance between the electode and the wokpiece was 3 mm. Metallogaphic specimens wee pepaed using the etchant HF:HNO 3 :H O = 3:10:100. The micostuctue of the welds was captued by Olympus BX51M. Figue shows the measuement appaatus fo the ac foce duing the welding pocess. The data of ac foce tanspoted fom the senso to acquisition cad and then displayed by softwae with a changing cuve of the ac Table 1 Paametes of Welding Pocess fo Ti 6Al 4V Titanium Alloys Expeiment No. I b /A I p /A f/khz δ (%) Agon (99.99%) q c /(L min 1 ) Welding Speed v/(mm min 1 ) Toch Taile Back AUGUST 014 / WELDING JOURNAL 313-s

3 YANG SUPP AUGUST 014_Layout 1 7/14/14 5:01 PM Page 314 WELDING RESEARCH Fig. 3 A D model with suface depession fo simulation. istics of UHFP-GTAW would be epesented with vaious adiuses. Table Physical Popeties of Ti 6Al 4V Physical Popeties Value Liquidus tempeatue T1(K) Solidus tempeatue Ts(K) Liquid density ρ (kg/m3) Liquid viscosity μ (kg/ms) Solid phase effective themal conductivity ks (J/ms K) Liquid phase effective themal conductivity k1 (J/ms K) Solid phase specific heat capacity CPS (J/kg K) Liquid phase specific heat capacity CPS (J/kg K) Tempeatue coefficient of suface tension dγ /dt (N/mK) Themal expansion coefficient β (K 1) Magnetic pemeability μm (N/A) Magnetic pemeability of vacuum μ0 (N/A) Melting heat L (J/kg) Suface tension σ (mn/m) foce duing the welding pocess. The testles unde the wokpiece made the distance between the ac plasma and senso, which was helpful fo eliminating electomagnetic intefeence. The measued esults fo evey goup of paametes wee captued at least thee times. Calculation and Simulation Suface depession caused by the ac foce duing UHFP-GTAW was calculated with suface tension, gavity, and liquid pessue. The conditions of the computing pocess ae discussed in the esults section. The depessions with diffeent paametes wee the evidence fo simulation of the molten pool. Physical popeties of Ti-6Al-4V ae displayed in Table. The heat flux on evey bounday was zeo except fo suface depession. A -D model with suface depession was poduced fo tansient status unde the effect of ac foce that is illustated in Fig. 3. It would be caied out in the discussion section to exploe the accuacy with 80 khz. The quad elements with submap type wee used fo gid mesh. The calculation scale was 10.5 mm with 860 nodes, 75 quadilateal cells, and 5316 mixed inteio faces. The assumptions wee as follows: The liquid in the molten pool could be ecognized as viscous, incompessible, lamina fluid; Density vaiations follow the Boussinesq appoximation; The paametes of mateial ae independent of tempeatue except fo specific heat capacity, themal conductivity, viscosity, and suface tension coefficient. The heat input followed Gauss distibution that was epesented in Equation 1. As descibed in Ref. 3, thee is a mathematical coelation between the adius of ac plasma and pulsed fequency. Thus, the chaacte- 314-s WELDING JOURNAL / AUGUST 014, VOL. 93 Q = 3 η 30 UI exp Rac π Rac (1) Whee Q = heat input; η = efficiency; U = aveage ac voltage; I = aveage welding cuent; Rac = adius of ac plasma; and 0 = adius of andom position unde ac plasma. Diving foces, such as suface tension and buoyancy, wee known as the souce tem by the momentum equation of x/y diection. And intedenditic flow foce was egaded as the souce tem that was indicated by function y = f(fl), in which fl was epesented as Equation. The model follows the mass consevation equation, momentum consevation equation of the x/y diection, and the enegy consevation equation. The electomagnetic foce was the souce tem of momentum consevation in both x and y diections with Equation 3 that could be poduct fom the powe J B. The deivation of electomagnetic foce with -/3-D model has been studied by seveal scholas ove the yeas (Refs. 4, 5); thus, it is not povided in this pape. 0 T T s fl = T T l s l T < Ts Ts T Tl T > Tl ()

4 Fig. 4 Geomety of suface depession in the molten pool. Fig. 5 Spheical cap of the vitual sphee. Whee T s = solid phase tempeatue, T l = liquid phase tempeatue; f l = 1 in the liquid phase egion; 0 < f l < 1 in the solid-liquid egion; f l = 0 in the solid phase egion. 0 ( ) = μ I J B x exp 4 ac π R Rac x 1 exp( ) 1 ac R h 0 ( ) = 1 exp( ) 1 μ I (3) 4π y J B y ac h R h Whee R ac = goove adius of ac plasma; h = ac length; x = x coodinate; and y = y coodinate. The bounday of suface depession was the intefee between gas and liquid. The velocity of depession was diven by suface tension o Maangoni convection that could be deived with tempeatue coefficient dγ/dt. The heat flux distibution followed the heat input of welding. And the initial tempeatue of suface depession T 0 = 1700 K as the depession happened duing the melting pocess. Heat insulation was used at the othe boundaies; thus, heat flux at the axis and edge wee both φ / y = 0, and similaly, the suface and bottom wee φ/ x = 0. Results Calculation Pocess Duing the welding pocess, molten metal owned the fee suface Fig. 4. It was the inteface of liquid metal and ac plasma whee the foce balance happened. Ac cuve assumption was caied out fo volume appoximate calculation; thus, vitual adius R equaled the distance fom the cente O to the inteface. The mathematic coelation between angles and scales was epesented in Equation 4, fom which vitual adius R can be descibed with Equation 5. Whee R = vitual adius of vitual sphee; h = depth of suface depession; = adius of weld (half of width); θ = half angle of spheical cap; and α = half cone of spheical cap. θ h tan = tanθ= R h R h + = h (4) (5) Futhe, the suface depession of the molten pool can be ecognized as the spheical cap of the vitual sphee that is illustated in Fig. 5. The volume of the spheical cap is epesented with Equation 6. The gavity of squeezed liquid can be deduced followed by Equation 6. V =πh R h 3 (6) The foce balance happened on the inteface of the liquid metal and ac plasma that is illustated in Fig. 6. The ac foce was the main component downwad in axis. On the othe side, the suface depession had caused some volume of liquid to be squeezed out. The feedback of such liquid metal would own evesed gavity opposite to the ac foce. The pessue of liquid had the same effect with gavity. And the suface tension made dag foce though the liquidus line, which was also upwad against the ac foce. Integating Equations 5 and 6, the function of esultant is epesented in Equation 7. Whee φ = half andom angle of the spheical cap. AUGUST 014 / WELDING JOURNAL 315-s

5 The depth of depession was calculated with the esultant, and the esults indicated that a lage ac foce caused deepe depession, which had been poved by the expeiments. Discussion Fig. 6 Foce balance on the inteface. f(h) = F G P S σsum = F ρgv ρgh S σ R ϕ sinϕ ϕ = F ρg πh R h 3 ρgh π σ R θ sinθ = F π ρgh ( h + 3 ) 6 h ρgh π 8σ actan 3 3 = π ρgh π ρg h 6 h 8σ actan + F (7) Whee F = ac foce; G = gavity of squeezed liquid metal; P = liquid pessue; S = suface aea; and σ sum = sum of suface tension on the liquidus line. The zeo solution of Equation 7 meant foce balance in the inteface. Table 3 Appoaching Results of Suface Depession The appoaching cuve was poduced fo the solution pocess, and the esults wee illustated in Fig. 7 and Table 3. With conventional GTAW, the suface depession was 0.11 mm, which was just about 4% of thickness (.5 mm). As a esult, the suface depession could be ignoed duing the conventional welding pocess that had been mentioned in the intoduction. Table 3 also displayed the coelation between the ac foce and suface depession. The esults demonstated that suface depession inceased with the ac foce, which had the same tend following by pulsed fequency. A lage ac foce with UHFP-GTAW caused the bigge depession h, which was a benefit fo lage weld penetation. Fom pevious wok, compaed with conventional GTAW, the weld width deceased by moe than 1% and by 35% with moe than 70 khz. Meanwhile, the depth and penetation ate inceased, espectively. Above all, ac foce with UHFP- GTAW had been enhanced that caused suface depession in the molten pool. Pulsed Fequency Ac Foce Weld Width Weld Depth Penetation Rate Suface Depession f/khz F/mN B/mm H/mm φ/% h/mm Fist of all, the calculation pocess in the esults section ignoed the effect of gas shea on the suface depession. Histoical eseach demonstated the effect of a highe cuent level (> 00 A) was significant on the plasma jet foce with a huge impact on the molten pool (Ref. 6). Howeve, the aveage cuent fo the study is less than 100 A. As a esult, compaed with suface tension, the dag foce of gas shea was not efeed in this study. Secondly, in the esults section, the discussion above was unde the condition of h R, which was available fo most of the nomal conditions. That indicated an angle of spheical cap was the acute angle. And h = R was the citical condition with Equation 8 that indicated citical depession was detemined by the ac foce. f(h) = F G P S σsum = F ρg πr ρg π h σ R π = F π ρg h π σ h (8) 3 The condition of h > R (angle of spheical cap θ > 90 deg) could be discussed with Fig. 8. Accoding to the pinciple of tiangle, thee should be such consevation as shown in Equation 9. That indicated the vitual adius R still followed Equation 5; thus, the condition of h > R can be witten as h >. Similaly, the function of foces and its fist deivative ae epesented in Equations 10 and 11, espectively. With calculation, f (h) < 0 can be gained, which poved Equation 10 was also a monotonic function. The adius in this study belonged to [1.3,.08], which demonstated the only one zeo solution h[0] fo it. This condition had been checked with a limited value that was the depession equaled thickness of base metal. The esults demonstated that f(.5) = > 0, which meant the zeo solu- 316-s WELDING JOURNAL / AUGUST 014, VOL. 93

6 YANG SUPP AUGUST 014_Layout 1 7/15/14 1:49 PM Page 317 WELDING RESEARCH Fig. 7 Solution cuve of the foce balance function. tion was out of effective egion. The assumption of h > R was not available. (h R ) = R (9) f ( h) = F G P S σ sum πr π(r h) = F ρg R R h 3 ρg π h σ R θ sin(π θ) π = F ρgh (h + 3 ) ρgπ 6 h h σ π+actan h 3π π = F ρg h3 ρg 6 h (10) h σ π+actan h 3π π f '(h) = ρgh ρg σ ( h ) ( + h ) (11) Futhemoe, with pulsed fequency f = 80 khz, suface depession equaled 1.63 mm > 1.33 mm (R[h80 khz]) that was in the egion of h > R. It was descibed above that the assumption of h > R was not available. That demonstated the ac cuve assumption was ineffective with 80 Fig. 8 Geomety with the condition of h > R. khz. An ellipsoid cap would be moe accuate unde the condition of the lage ac foce that was illustated in Fig. 9. With ellipsoid assumption, depession can be moe than the adius when the angle of the spheical cap was acute angle. As a esult, the ellipsoid molten pool geomety can be the eason fo lage depession with 80 khz. A suface depession with 80 khz was used fo the D model. The tansient status of the molten pool was discussed with the molten condition, fluid convection, and tempeatue distibution; those ae illustated with Fig. 10A C. An ellipsoid cap assumption was used. Figue 10B displays the fluid status duing the welding pocess. Compaed with simulated esults by stainless steel, double ciculation also exists with suface depession in the molten pool. The clockwise ciculation was diven by suface tension that was still the most impotant facto fo fluidity of the molten pool. The maximum velocity of it eached up to 1.74 m/s. On the othe side, counteclockwise ciculation was found nea the bottom of the suface depession. That was diven by electomagnetic foce as descibed in the expeimental pocedue section. Futhe, except fo the suface depession, the lage ac foce also caused a huge impact with 80 khz, which made the impulse to the liquid metal. And the impulse could push the fluid downwad to the bottom. Such impulse would follow the distibution with Fig. 9 Ellipsoid cap assumption of the suface depession. the oiginal line distibution epesented as F = Fpeak exp(-a ) fo the D model. As a esult, the maximum impact by ac foce happened nea the axis of the ac plasma that was meaningful fo the suface depession of the molten pool. As descibed befoe, vaious depessions wee ecognized as the impotant eason fo the distibution of counteclockwise ciculation that was diven by electomagnetic foce. Howeve, the aveage velocity of it was up to 0.5 m/s, which was much less than clockwise ciculation (1.74 m/s). This esult demonstated the AUGUST 013 / WELDING JOURNAL 317-s

7 Fig. 10 Tansient status of the molten pool (80 khz). A Molten pool; B fluid velocity vectos; C tempeatue distibution of the molten pool. dominance of suface tension about fluid velocity status. The tempeatue distibution of the molten pool is illustated in Fig. 10C, which indicates the spead speed of tempeatue was little as low themal conductivity. This esult also poved the significant gain gowth of titanium alloys that had been known in the eseach field (Refs. 3, 7, 8). Futhe, the downwad heat input made a high tempeatue at the bottom that was believed fo lage penetation. And it was the main effect of the ac foce on the suface depession of the molten pool. Figue 11 indicates the pessue contou of liquid metal. The maximum value (6.56 kpa) happened nea the edge of the weld that was also the edge of the suface tension diving aea. In contast, the pessue at the bottom of A B C Fig. 11 Total pessue distibution in the molten pool. the suface depession (1.91~4.57 kpa) was about half less than the edge. That demonstated the impotance of suface tension fo the fluidity of the molten pool, which had been poved with velocity peviously. And the pessues at the bottom and the edge of depession wee caused by the ac foce and suface tension, espectively. Simultaneously, significant pessue distibuted at the bottom of depession indicated the effect of the ac foce and also the impulse of ac plasma. In addition, the aea of liquid pessue was actually ac suface, and it was ecognized as plane instead in the esults section. The discussion below will check the availability of plane assumption. The aea of plane was witten as π, compaed with it, the aea of spheical cap was πrh. Similaly to Equation 7, the function of esultant is epesented as Equation 1. With the same appoaching analysis, the depessions of diffeent paametes can be obtained as 0.1, 0.3, 0.53, 0.67, and 1.54 mm, espectively. f(h) = F G P S σsum = F ρgv ρgh S σ R ϕ sinϕ ϕ = F ρg πh R h 3 ρgh πrh σ R θ sinθ = π ρgh π ρg h 8σ 6 h actan + F (1) Compaed with Table 3, the eo was less than 3.% duing 0 60 khz, and the maximum eo was less than 5.5% at 80 khz. That meant the diffeence between ac suface and plane assumption would be little when studying liquid pessue. That is also the eason fo using plane assumption in this eseach. Conclusion 1. The high-fequency pulsed ac welding pocess ceated the lage ac foce and penetation. The ac foce caused suface depession of the molten pool that pushed the heat souce downwad to the deep. As a esult, the fluid status and geomety of the molten pool would be changed.. The depession can be calculated with the esultant. Ac cuve assumption was used fo nomal conditions (0~60 khz), and the suface depession inceased with pulsed fequency. The conditions with acute angle of the spheical cap wee known to be accuate. With a lage ac foce (80 khz), the assumption was impoved to ellipsoid that condition guaanteed θ > 90 deg. 3. Ellipsoid assumption was used fo simulation with 80 khz. Suface depession impoved the penetation, although the low heat conductivity of titanium alloys, which was inconsistent with the expeimental esults. Double ciculation displayed in the molten pool was caused by electomagnetic foce and suface tension. The velocity demonstated the impotance of suface tension with a max of 1.74 m/s. Compaed with it, the velocity of ciculation by electomagnetic foce was up to 0.5 m/s that poved the effect on penetation. Acknowledgments This wok was suppoted by the National Natual Science Foundation of China unde gant No Fundamental eseach funds fo the Cental Univesities unde gant No. YWF-14-JXXY-008. The authos also acknowledge the Beijing Univesity of Aeonautics and Astonautics fo suppoting thei eseach wok. 318-s WELDING JOURNAL / AUGUST 014, VOL. 93

8 Refeences 1. Ando, K., and Hasegawa, M Welding ac phenomena. Beijing. China Machine Pess: 49, 50 (in Chinese).. Cook, G. E., El-deam, Hussam, and Eassa, E. H The effect of highfequency pulsing of a welding ac. IEEE Tansaction on Industy Applications 1A- 1(5): Yang, M., Qi, B., Cong, B., Liu, F., Yang, Z., and Chu, P. K Study on electomagnetic foce in ac plasma with UHFP-GTAW of Ti-6Al-4V. IEEE Tansactions on Plasma Science 41(9): Amin, M Pulse cuent paametes fo ac stability and contolled metal tansfe in ac welding. Metal Constuction (15): Zachaia, T., and David, S. A Weld pool development duing GTA and lase beam welding of type 304 stainless steel, Pat I Theoetical analysis. Welding Jounal 68(1): 499-s to 509-s. 6. Lin, M. L., and Eaga, T. W Influence of ac pessue on weld pool geomety. Welding Jounal 64(6): 16-s to 169-s. 7. Yang, Z., Qi, B., Cong, B., Yang, M., and Li, Y Effect of pulse fequency on weld appeaance behavio by TC4 titanium alloys. Tansactions of the China Welding Institute 34(1): Pado, E., and Weckman, D. C Pediction of weld pool and einfocement dimensions of GMA welds using a finite-element model. Metallugical and Mateials Tansactions B 6(0): Sundaesan, S., Janaki, D., et al Micostuctual efinement of weld fusion zones in α - β titanium alloys using pulsed cuent welding. Mateial Science and Engineeing, A-Stuctue 6: Wu, C. S Numeical simulation of TIG weld pool behavio unde the action of pulsed cuent. Acta Metallugica Sinica 34(4): Cao, Z. N., and Wu, C. S Mathematical modeling of TIG molten pool with full penetation. Tansactions of the China Welding Institution 17(1): Wu, C. S Welding heat pocess and pool geomety. Beijing. China Machine Pess: (in Chinese). 13. Qi, B. J., Yang, M. X., Cong, B. Q., and Liu, F. J The effect of ac behavio on weld geomety by high fequency pulse GTAW pocess with 0C18Ni9Ti stainless steel. Intenational Jounal of Advanced Manufactuing Technology 66(9-1): Rokhlin, S. I., and Guu, A. C A study of ac foce, pool depession and weld penetation duing gas tungsten ac welding. Welding Jounal 7(8): 381-s to 390-s. 15. Kou, S., and Wang, Y. H Weld pool convention and its effect. Welding Jounal 65(3): 63-s to 70-s. 16. Oepe, G. M., and Szekely, J Heat and fluid flow phenomena in weld pools. Jounal of Fluid Mechanics 147: Kim, W. H., Fan, H. G., and Na, S. J Effect of vaious diving foces on heat and mass tansfe in ac welding. Numeical Heat Tansfe, Pat A: Applications 3: 6, Kou, S., and Wang, Y. H Compute simulation of convection in moving ac weld pools. Metallugical Tansaction A (17A): Tsai, M. C., and Kou, S Electomagnetic foce induced convection in weld pool with a fee suface. Welding Jounal 69(6): 41-s to 46-s. 0. Zachaia, D Weld pool development duing GTA and lase beam welding of Type 304 stainless steel, Pat I Theoetical analysis. Welding Jounal 68(1): 499-s to 509-s. 1. Boye, R., Welsch, G., and Collings, E. W., eds Mateials Popeties Handbook: Titanium Alloys. Mateials Pak, Ohio: ASM Intenational.. Misha, S., and DebRoy, T Measuements and Monte Calo simulation of gain gowth in the heat-affected zone of Ti-6Al-4V welds. Acta Mateialia 5(5): Oepe, G. M., and Szekely, J A compehensive epesentation of tansient weld pool development in spot welding opeations. Metallugical Tansactions A (18A): Kuma, A., and DebRoy, T Calculation of thee-dimensional electomagnetic foce field duing ac welding. Jounal of Applied Physics 94(): Tsao, K. C., and Wu, C. S Fluid flow and heat tansfe in GMA weld pools. Welding Jounal 67(3): 70-s to 75-s. 6. Choo, R. T. C., and Szekely, J The effect of gas shea stess on Maangoni flows in ac welding. Welding Jounal 70(9): 3-s to 33-s. 7. Yunlian, Q., Ju, D., Quan, H., and Liying, Z Electon beam welding, lase beam welding and gas tungsten ac welding of titanium sheet. Mateial Science and Engineeing, A-Stuctue 80: Yang, Z., Sista, S., Elme, J. W., and DebRoy, T Thee dimensional Monte Calo simulation of gain gowth duing GTA welding of titanium. Acta Mateialia 48(0): Win Potential Clients by Showing Them Videos on How to Save Money and Time By Using You Poducts! Fo moe infomation visit ou website at o please contact: Rob Saltzstein salty@aws.og (800) , ext. 43 Lea Paneca lea@aws.og (800) , ext. 0 Sanda Jogensen sjogensen@aws.og (800) , ext. 54 AUGUST 014 / WELDING JOURNAL 319-s