8/14/2019 Mathematical Model of Melting Rate for SAW

1/6

Mathematical Modeling of Melting Ratesfor Submerged Arc WeldingModels of melting rates take into account the effects ofwelding variables

BY R. S. CHANDEL

ABSTRACT. The effects of welding current, arc voltage, wire diameter, electro de exte nsion (EE), ele ctro de pola rity,power source type and f lux classif icat ionon melt ing rates (MR) have been evaluated for the submerged arc weld ing process. The results show that for a givenheat input, greater melting rates areobtained when higher current, longerelectrode extension, smaller diameterelectrodes and electrode negat ive polar ity are used. Arc voltage, power sourcetype and f lux classif icat ion do not haveany significant influence on melting rates.Mathematical models to correlate process variables and melting rates havebeen computed f rom the data.I n t roduct ion

Researchers and welding engineershave been trying to increase product ivityby increasing melting rates since theincept ion of the submerged arc weldingprocess. Histor ically, welding current hasbeen found to have the greatest influence on the melt ing rate and weld beadgeometry (Refs. 1-4). However, it is alsorecognized that when welding current isincreased to enhance the melt ing rate,there is a corresponding increase in heatinput, which may inf luence the weldmetal toughness. Alternat ively, t ravelspeed can be increased to maintain thesame heat input; however, this canincrease the propensity for defects suchas center l ine cracking and incompletepenetrat ion (Ref. 5). However, melt ingrate can be increased for a given heatinput and welding current by using electrode negat ive polar ity, longer electrodeextension, and smaller diameter electrodes (Refs. 6-9 ). In order to p redict andcontrol the melt ing rate, the quant itat iveeffect of all the var iables must be known.Wilson and Jackson (Ref. 9) formulatedR. S. CHANDEL is with Physical MetallurgyResearch Laboratories, Canada Center forMineral and Energy Technology, Ottawa, Canada.

the following mathematical relat ionshipbetween welding var iables and melt ingrate in Imperial units, which are c o n ver ted here to the fo l lowing SIunits:

MR (for DCEN) 1 1 (3)

MR (kg/h) = 9.45 +1 10.042 D 2 + 2.906 X 10 ~4

IL 122 -,

(1)

D2 Jwh e r e I = welding current (A)D = wire diameter (mm)L = electrode extension (mm)

Such a relationship is very useful, as itenables the preselect ion of welding variables for a part icular melt ing rate. However, it has some drawbacks, as it doesnot take into account the effect of voltage, polar ity, the type of power sourceand flux basicity.Robinson (Ref. 10) observed that Equat ion 1 was no t valid for alternat ing current (AC) or direct current electrodenegat ive (DCEN), so he modif ied it totake the effect of electrode polar ity intoconsiderat ion. His modif ied equat ions,or iginally in Imperial units, are convertedto SI units as follows:

MR (for DCEP) = 1 1 (2)

0.042d 2 + 2.906 X 1 0 4 ' ^ 1d 2 J+ [ 4.5 X 10~ 5 ( I )1 6 8 6 + 3.565 1

K E Y W O R D SSAW Electrode Melt ingMelt ing Rate ModelsMathemat ical Model l ingSAW Heat InputSAW Process VariablesHeat vs. Weld CurrentElectrode PolarityElectrode ExtensionMelt Rate Equat ionSAW Polarity Effects

0.042d2 + 2.906 X 10~41 22 1d 2 J+ [ 3 . 0 7 1 X 10-4 (l )1-51 3 ]

MR (for AC) = 1000 [ (4)0.042d2 + 2.906 X1 . ILd 2 -I

(I)2721 + 3.565 ][ 3.485 X 10 8where MR = melt ing rate(kg/h)I = weld ing cur rent

(A)d = electrode diameter(mm)L = electrode extension(mm)Martin (Ref. 11) and Jackson (Ref. 12)had ob serve d that arc voltage also has aninf luence on the melt ing rate. Robinson(Ref. 10) reported that for direct currentelectrode negat ive, an increase in arcvoltage resulted in a decrease in melt ingra te . How ever , nei ther Wi lson's nor Robinson's equations reflect this. Mantal (Ref.13) reported that for arc welding themelt ing rate for AC is the geometr icmean of the melt ing rates for DCEN andDCEP. Lesnewich (Ref. 14) also compared

the me lt ing rates for A C, DCEN and DCEPand observed that the melt ing rate duringAC is the ar ithmetic m ean of melt ing ratesduring DCEN and DCEP. Robinson'sexperimental results and theoret ical calculat ions show that for welding currentsof up to 750 A, direct current electrodepositive (DCEP) gives higher melting ratesthan DCEN. Thus, in the light of thiscontroversy, the validity of Robinson's(Ref. 10) equat ions becomes quest ionable.There have been a few other at temptsto formulate mathematical relat ionships

between weld ing var iables and melt ingrates (Refs. 15-18). However, most ofthese models are useful only for part icu-

WELDING RESEARCH SUPPLEMENT 1135-s

8/14/2019 Mathematical Model of Melting Rate for SAW

2/6

Table 1Welding Variables and Mel t ing Rates for DC WeldsMel t ing rate (kg/h)Constant vol tage Constant current

Wire dia.(mm)4.00

E.E.W(mm)25.4

Current(A)40040040060060060080080080010001000

1000

Vol tage(A)323538323538323538323538

Flux A Flux Flux A Flux BDCEP DCEN DCEP DCEN DCEP DCEN DCEP DCEN

4.914.94.97.167.167.1610.1810.20

10.1713.7413.7413.74

6.306.306.3010.9410.9410.9415.1315.1315.1318.5918.5918.59

4.0 76.2 400400400600600600800800800100010001000

323538323538323538323538

5.225.225.239.49.49.416.4016.4016.4020.6120.6120.61

6.446.446.4412.4312.4312.4318.1318.1318.1325.4725.4725.47

2.4 25.4 300300300400400400475475475550550550

23538323538323538323538

3.713.713.714.934.934.936.206.206.207.807.807.80

4.884.884.887.057.057.058.758.758.7510.6110.6110.61

(a) Electrode ex tens ion

lar situations and are thus not applicableto shop f loor welding. Therefore, the aimof this w or k was tw of ol d: 1) to study theeffect of welding current, arc voltage,electrode diameter, electrode extension,e lect rode polar i ty , type of po we r source,and flux classification on the melting ratefor submerged arc welding, and 2) todevelop mathemat ical models to cor relate the melt ing rates with the weldingvariables.

Exper imenta l WorkThe base mater ial used for the experimental work was a19-mm(0.75-in.) thickASTM A36 steel plate. This plate was cutinto 600- X 150-mm (24- X 6-in.) pieces,and both surfaces were cleaned (sandblasted) to remove dir t and oxides. AWSEL12 electrodes of 2.4-, 3.2- and 4-mm

( 2-, Va - and 2-in.)d iameter w ere used,along with Fluxes A and B. Flux A was afused acid flux with a basicity index of 1,while Flux B was an agglom erated basicflux with a basicity index of 3.

DC 1500 and AC square wave 1000power sources were used. The DC 1500can be operated on both constant cur rent and constant voltage modes, whilethe AC square wave 1000 is designed forthe constant vc l tage mode only . Theexper imental work was designed tostudy the effect of welding current, volt age,e lect rode extension, e lect rode diameter, polar ity, type of power source, andflux classification on melting rate. Thewelding cur rent and arc vol tage wererecorded on a chart recorder for eachdeposi t , whi le the cor responding wirefeed speed (which was conver ted intomelt ing rate) was read from a digital wirefeed tachometer. A total of 336 weldswere made, and their welding var iablesand corresponding melt ing rates are given in Table 1.

ResultsThe results of the investigation aregiven in Figs. 1-4 and Tables 1 and 2.Figure 1 show s the effect of we lding

current and wire diameter on the melt ingrate. It can be seen that for a given wirediameter, melt ing rate increases withweld ing cur rent . However , for a g ivenweld ing c urrent, the m elt ing rate is higherwhen a smaller diameter electrode isused. Figure 1 also indicates that thedif ference in melt ing rate due to wirediam eter is greater at higher currents.Vary ing the vol tage between 30 and38 V did not have any effect on themelt ing rate.The effects of polar ity and electrodeextension on the melt ing rate are shownin Fig. 2. For the same welding variables,DCEN results in a higher melting rate thanDCEP W he n AC is used, the melt ingrates are slightly higher than those ofDCEP and signif icant ly lower than DCENwhen a25.4-mm (1- in.) electrode extens ion is used. However , when a76.2-mm(3.0-in.) electrode extension is used, themelt ing rates with AC become similar tothose of DCEP.The ef fects of power source type(constant voltage and constant current)and flux classification on the melting rate

136-sIMA Y 1987

8/14/2019 Mathematical Model of Melting Rate for SAW

3/6

Table 1WeldingVariables and Melting Ratesfor DCWelds (continued)Melting rate (kg/h)Constant voltage Constant current

Wire d ia . E.E>>(mm) (mm)2.4 76.2

3.2 25.4

3.2 76.2

(a)Electrodeextension

a r e s h o w n in Figs. 3The resu l t s ind ica te

Current(A)300300300400400400475475475550550550300300300450450450600600600750750750300300300450450450600600600750750750

Vol tage(A)323538323538323538323538323538323538323538323538323538323538323538323538

a n d 4, r es pec t i v e l y .t h a t p o w e r s o u r c e

t y p e an d f lux c lass i f i ca t ion did not hav e

Flux ADCEP

4.924.924.928.278.278.2710.7110.7110.7115.1015.1015.103.833.833.835.565.565.567.387.387.389.879.879.874.794.794.797.577.577.5711.8011.8011.8016.4016.4016.40

DCEN6.426.426.429.769.769.7612.9212.9212.9217.0617.0617.064.984.984.988.168.168.16

11.7011.7011.7014.2914.2914.295.655.655.6510.3510.3510.3515.0515.0515.0520.6020.6020.60

FluxBDCEP

-----

3.533.533.535.185.185.187.007.007.009.789.789.784.414.414.418.158.158.1512.0812.0812.0819.0019.0019.00

DCEN----

6.146.146.148.728.728.7211.4411.4411.4414.8614.8614.86

6.336.336.3310.0710.0710.0714.1914.1914.1920.7720.7720.77

FluxADCEP

----------

3.743.743.745.665.665.667.867.867.8610.3510.3510.354.514.514.517.197.197.1911.5111.5111.5117.7417.7417.74

DCEN-------

4.984.984.988.538.538.5311.7011.7011.7014.2914.2914.29

5.755.755.7510.1710.1710.1714.6714.6714.6720.5820.5820.58

Flux BDCEP

--------

3.643.643.645.655.655.657.867.867.8610.3510.3510.354.314.314.317.677.677.6712.5612.5612.5617.8417.8417.84

DCEN--------

6.236.236.238.828.828.8211.4111.4111.4114.5814.5814.586.456.456.4510.6410.6410.6414.4814.4814.4820.5820.5820.58

any significant effect on melt ing rates. Table 2WeldingVariables and M elting Ratesfor ACWelds

Mathematical ModelThe above results have shown thatthemelt ing ra te dur ing submerged arc we ld

in g is a f fec ted by welding current, elect rode d iameter, e lec trode ex tens ion andelec trode po lar i ty . Topresent the aboveresults in a meaning ful ma thematicalexpress ion, some fundamenta l conceptsof mel t ing dur ing arcwe ld ing haveto becons idered.It iswe l l und ers tood thatthetotal melt ing iscomposed of mel t ingdueto arc energy and melt ing due to resistance heating ()oule heating effect) (Refs.9, 10 and 1 5-18 ).Arc heat isp ropo r t iona lto weld ing current , wh i le the Joule heating effect isp ropo r t iona lto the (current)2and e lec trode ex tens ion, and inverselyp ropo r t iona l to (e lec trode d iameter)2 .Anequat ion to correlate melt ing rate andwelding variables and incorporat ing arc

Melting rate (kg/h)

Wi re dia4.00

3.2

Electrode

Current(A)450450550550650650750750400400500500600600700700

extension.

Vol tage(V)32363236323632363034303430343034

25.4 mmE.E>>5.445.467.057.008.508.5010.5710.534.744.755.996.008.528.5110.8010.76

FluxA76.2 mm

E.E.5 . 935.968.148.1410.2510.0513.4113.385.55.58.148.1711.2411.2415.37

15.37

25.4 mrrE.E.< a>

----5.265.266.706.718.648.6410.5210.50

FluxB76.2mm

E.E.--

6.336.348.68.511.7211.7115.8315.83

WELDING RESEARCH SUPPLEMENT1137-s

8/14/2019 Mathematical Model of Melting Rate for SAW

4/6