Comparison of the pulsed MIG welding process for different median current

Comparison of the pulsed MIC welding process for diferent median current51Comparison of the pulsed MIG welding process fordifferent median current*Wen Yuanmei, Xue Jiaxiang, Yao Ping and Huang Shisheng文元美，薛家祥,姚屏, 黄石生**Abstraet Based on the high speed rideo system with electrical signals cllecting and wavelet analyzing , the welding processesunder three diferent median curents with the same median time were detected. The experimental results shon that, when themedian current is higher, the input peak energy is louver. And the droplet transfer is almost in spray mode. The weldingprocess is the stablest.Key words are welding, median current, droplet transfer, spatter0 Introductionand peak time to express the area of ODPl5). N JacobsenThe metal transfer process of pulsed MIC welding is abuilt up the relationship of peak current and the minimumcomplicated procedure that combines multiparameter cou-droplet transfer timel6]. To study the effects of differentpling and nonlinearity. To realize the control of dropletmedian current on the welding process, the current wave-transfer, Y M Zhang put forward an approach, in whichform control strategy was applied and the experiments werean oscillation of the droplet was excited by switching thecarried out by increasing the front -median phase. Basedcurrent from a peak level to a base level to initiate an ac-on the high speed video system with electrical signals col-tive detachment period. The droplet oscillation was thenlecting and wavelet analyzing, the welding phenomenamonitored. When the droplet moved downward, the cur-were investigated and analyzed.rent was switched back to the peak level, which createdan ejection action and concluded the active detachment1 Experimental conditionperiod. The droplet was detached by downward momentum1.1 The front-median current methodand the increased current-induced electromagneticThe common pulsed MIG welding has 5 pulse param-force1. Q L Wang contolled the droplet transfer by de-eters: the peak current, the peak time ，the backgroundtecting the are light2. K Y Wu presented a method ofcurrent, the background time and pulse frequencycurrent waveform control with median phase. By selecting(Fig. 1a). The front-mnedian current method adds the me-an appropriate median current and median time , the drop-dian phase, shown in Fig. lb. It adds the median curentlet transfer can be cortolldBl.and the median time. The adding median phase promotesOne droplet per pulse ( ODPP) is an ideal form ofthe control of droplet transfer and the consistency of drop-droplet transfer. Now the ODPP formulae are almost foundlet size and arc length.by experiments. Based on the static force balance theory,The front-median current method means that the me-Y S Kim proposed a model to estimate the condition ofdian current is added between the background current and0DPP[4]. N Amin built up the relationship of peak currentthe peak current. The function of background phase is to* This work was Bupported by National Natural Science Foundaion of Ch中国煤化工975088 ) and GuangongScience Foundaion ( Grant No. 07006479).MHCNMHG。** Wen Yuanmei , Faculty of Informnation Engineering, Guangdong University ot Technology, Cuangzhou, )1U043. Wen Yuanmei, XueJiaxiang, Yao Ping and Huang Shisheng, School of Mechanical and Automotive Engineeing, South China University of Technology ,Guangzhou, 510640. Wen Yuanmei, Corresponding author, E-mail: Wen_ yuanmei@ 163. com52CHINA WELDINC Vol. 18 No. 2 June 2009maintain the arc between welding wire and molten pool.The median phase decides the droplet sizes. The pulsepeak current, which is normally higher than the criticalcurrent of spray transfer , afcts the droplet transfer force几几and the penetration of workpiece. Generally speaking, the .Time /gpulse peak time is shorter'7).(a) Non-median current waveform1.2 Experimental parametersThe experimental power supply is the ICBT pulsedMIG inverter developed independently. The welding wire&( HO8Mn2Si) is 1. 0 mm in diameter and the workpieceTime/s(mild steel) is 3 mm in thickness. The shielding gas isb) Front-median curent waveformAr, whose flow rate is 15 L/min. The welding speed is400 mm/min. The other welding parameters are shown inFig.1 Non-median current waveform andTable 1.front-median curreat waveformTable 1 The welding parametersPeak currentPeak timeBackground currentBackground timeMedian currentMedian time//ms/A30041008120 - 2502 Experimental results and analysisrarely. The probability distribution of arc voltage is con-According to the welding parameters shown in Table 1,centrated (Fig. 2a)，which shows three voltage peaks.the experiments with three different front-median currentsThe probability distribution of welding curent is also con-(250A, 160 A, 120 A) are carried out. The weldingcentrated ( Fig. 2b)，which shows three curent peaks thatprocesses are observed by the high speed video systemare correspondingly the pulsed background current, medi-with laser in the background and electrical signals waveletan current and peak current. The U-I diagram ( Fig.2c)analyzing system.shows the welding process is stable, the tracks of voltageFig. 2 shows the electrical waveforms and pholographand curent are overlapping.of weld appearance when the median current is 250 A,Fig. 3 shows the electrical waveforms and photographwhich is higher than the critical current of spray transfer.of weld appearance when the median curent is 160 A,At the median phase, the droplet grows up and transfers towhich is lower than the critical current of spray transfer.the molten pool probably. When the median time is shor-The droplet impossibly transfer to the pool at the medianter, the droplet grows up. But it transfers to the pool justphase. When the current rises up to the peak phase, thewhen the current rises to the peak current phase. Thus thedroplet grows big enough to transfer to the molten pool indroplet size is great and the welding process is stable.the action of electromagnetic force. Adjusting the medianWhen the median time is longer, the droplet transfers totime, the droplet transfer can be controlled properly. Thethe pool at the median phase. The diarmeter of droplet iswelding proces shows that. the are breaks rarely andsmall and the welding process is also stable. The weldingshort-中国煤化工th a imiable weldingprocess shows that, the are is successive and the phenom-voice.YHC N M H Gi arc voltage is decen-enon of short-circuit appears hardly, the welding voice istralized ( Fig.3a)，which distibutes from0 V to 84 V.soft, the welding process is stable and the spatter appearsThe probability distribution of welding current is also de-Comparison of the pulsed MIG welding process for different median current53centralized ( Fig. 3b), which distributes from 0 A to 580wire feed rate is a constant, the short. circuit and arc breakA. The U-I diagram (Fig. 3c) shows the welding processare inevitably taken place. The welding process showsis almost stable. The area of are break ( zero current withthat, the are break and short- circuit happen now and then84 V voltage) and the area of short- eirecuit ( zero volagewith much spatter, meanwhile the welding voice is irita-with 580 A current) are obvious. The tracks of voltage andle. The probability distribution of are volage is decen-current repeat largely.tralized ( Fig.4a), which distributes from 0 V to 84 V.Fig. 4 shows the electrical waveforms and photographWhen the volage equals to 73 V, arc break occurs. Theof weld appearance when the median current is 120 A,probability distribution of welding current is also decentral-which is far low from the eritial current of spray transfer.ized (Fig. 4b) , which distributes from0A to 580 A. TheThe so litle electromagnetic force exerted on the dropletU-I diagram (Fig. 4c) shows the welding process is notcannot impel the droplet transfer to the molten pool at thestable. The area of are break and short-circuit are in evi-median phase. The function of median current is only todence, the tracks of voltage and current repeat badly. Themaintain the are in succession, which equals to increaseuniformnity of the arc voltage waveform (Fig. 4d) is bad.the background time. It loses the significance of designingMuch spatter appears on the photograph of weld appear-the median phase. The prolonged equivalent backgroundance (Fig.4g). .time reduces the melting speed of welding wire. When the50 r).1|40 E0.010.020 E2(4(80200 400 600100200300 400Volage/VCurent/A .Current/A(a) Probability denesity of arc voltage(b) Probability density of welding current(c) UI diagram45630 wwwwwwwvwwvv5E152.￥.￥444....4176 4277 4 378447S4580 4 681417642774378447945804681Time 1 ms(d) Waveform of instantaneous are volage(e) Waveform of instantaneous welding current16g 1/./........41764277 4 3784479 4580 4 681中国煤化工(f) Waveform of instantaneous input energyMHCN M H GearanceFig.2 The electrical waveforms and photograph of weld appearance under median current 250 A54CHINA WELDING Vol. 18 No.2 June 2009100800.10山0.010)20406080100200 400 60020000600Volage/VCurrent/A(a) Probability density of arc voltage(b) Probability density of welding current(c) U-I diagram40wwhwmwhWWWWWwW..446546646746846946” 44684Time 1 msTime/ ms(d) Waveform of instantaneous are volage(e) Waveform of instantaneous welding current16(8MM..wwwwwM.(f) Waveform of instantaneous input energy(g) Photograph of weld appearanceFig.3 The electrical waveforms and photograph of weld appearance under median current 160 AThe waveforms of input energy, which is recorded inwhich occurs frequently at the median current 120 A. Inthe welding processes of three different median currents,the welding process, the less welding current and the low-are shown in Fig. 2f, Fig. 3f and Fig. 4f, respectively.er input energy can not melt the welding wire in time, 80When median current is 250 A, the peak energy (12 kW)the welding wire approaches to the molten pool. Alongis the lowest. The corresponding welding process is thewith the extending of electrode, the arc length shortensstablest and the spatter is the least. When median currentgradually, so that it finally leads to the short-circuit trans-is 160 A, the peak energy is 13. 6 kW. The correspondinger. When short-circuit transfer occurs, the spatter is se-welding process is stable and the spatter is litle. Whenmedian current is 120A , the peak energy (16kW) is theFig. 5b shows the photos of spray transfer mode,maximum. The corresponding welding process is the un-which is the typical mode at the median curent 250 A.stablest.The image 1 and 2 show that the head of welding wire aremolten gradually, and the droplet detaches from the elec-3 The analysis of spatter on different droplet transfertrode.中国煤化工he welding proce8s ismodesthe_hed droplet is small.Fig.5 shows the high speed photos of three typicalMeanCNM H G'detached droplet andmetal transfer modes observed in the experiments8!.molten pool is less. The downward momentum of the de-Fig. 5a shows the photo of short-circuit transfer mode,tached droplet is small. The molten pool is steady and theComparison of the pulsed MIC welding process for diferent median currentspatter is the least.8C0.1 ...0.1 t4(0.01M2002040608010200 400 600200400600Voltage/VCurent/A(a) Probability density of arc voltage(b) Probability density of welding current(c) U-I diagam0040mmwwwwwh.mmbtm7458851 02516513051 4451 1651 3051445Time 1 msTime/ ms(d) Waveform of instantaneous are voltage(e) Waveform of instantancous welding current16j1025 1 165 .1 445(I) Waveform of instantaneous input energy(g) Photograph of weld appearanceFig.4 The electrical waveforms and photograph of weld appearance under median current 120 A工hii1232(a) Short- circuit transfer(b) Spray transfer(c) Clobular transferFig.5 High spee video photographs of three types of droplet transfer modeFig. 5c shows the photos of globular transfer mode，Along with the melting of wire, the droplet grows up.which occurs at the median current 160 A. The image 1When the gravity is greater than the surface tension, theand 2 show that the droplet grows up gradually at the headdrop!中国煤化工lar transfer mode (seeof welding wire. The droplet transfer is afected by theFig.Y出CN M H Gof the tansfered dropgravity, the electromagnetic force etc. The electromagneticis large, the momentum or une aeuached droplet leads toforce and the spot pressure hinder the droplet detaching.the molten pool osillting. It brings the spatter.56CHINA WELDING Vol. 18 No. 2 June 2009Diferent median current resuls in different relation- [2] WangQL, LiP L. Are light sensing of droplet transfer andship between wire feed rate and input energy. Different e-its analysis in pulsed CMAW process. Welding Joumal,lectrode extensions and arc length also result in various1997, 76(11): 458s -469e.[3] WuK Y, Huang s s, Meng Y M. Control strategy of waveforms of metal transfer.form with median phase in droplet transter for pulsed MICwelding, Transactions of the China Welding Instution,4 Conclusions2004, 25(4): 51 -54, 58. (in Chinese)(1) The median phase is helpful to control the mode[4] Kim Y s, Eagar T. Metal transfer in pulsed current gas meltalof droplet transfer. The changes of median current andare welding, Welding Joumal, 1993 ,72(7): 279s -2878.median time influence the size of droplet and the mode of[5] Amin N. Pulsed current parameters for arc stability and con-metal transfer.tolled metal transfer in arc welding. Metal Constructin,(2) When the input peak energy is higher, the weld-1983(5): 272 -278. .ing process is unsteady. When the input peak energy is[6] Jacobsen N. Mono-pulse investigation of drop detachment inpulsed gas metal are welding. Joumal of Phyics D: Appliedlower, the welding process is stable.Physics, 1992, 25: 783 -797.(3) When the median curent is lower , the short-cir-[7] Ke LT, HuangSS, Wu K Y, et al. Research on a waveformxuit transfer occurs in high frequency. It brings muchcontrol method for pulsed MIG welding based on DSP. Weld-spatter. When the median current is higher, the metaling Technology, 2006, 35(5): 37 -40. (in Chinese)transfer is almost in spray transfer. It brings litle spatter.[8] WenY M, HuangSS, Xue JX, et al. Obervation and analysis of unstable metal transfer process of pulsed MICReferenceswelding. Transactions of the China Welding Institution,[1] Zhang Y M, Liguo E, Kovacevic R, et al. Active metal2008, 29(4): 13 - 17. (in Chinese)transfer control by monitoring excited droplet ocillation.Welding Joumal , 1998, 77(9): 388s - 3958.中国煤化工MYHCNMHG