Journal of Materials Processing Technology, 29 (1992) 133-144 133 Elsevier

The effects of process variables on the bead width of submerged-arc weld deposits

L. J . Y a n g

School o[ Mechanical and Production Engineering, Nanyang Technological University, Nanyang Avenue, Singapore 2263

R.S . C h a n d e l

Metals Technology Laboratories, Canada Centre for Mineral and Energy Technology (CANMET), Ottawa, Canada KIA OG1

M . J . B i b b y

Faculty of Engineering, Carleton University, Ottawa, Canada KIS 5B6

(Received April 25, 1991; accepted in revised form July 7, 1991 )

Industrial Summary

The results of bead-on-plate weld measurements are presented to determine the effects of the process variables on the bead width for the submerged-arc welding process, at a heat input of 3 kJ/mm. It is found that bead width is affected by the electrode polarity, electrode diameter, elec- trode extension, welding current, welding voltage and welding speed. A positive electrode polarity, a large electrode diameter, a small electrode extension and a high welding voltage encourages a large bead width in most cases. For a particular electrode diameter and extension, it is found that the bead width initially increases as the current and the welding speed increase. The bead width reaches a peak value, and then decreases as the welding current and speed are further increased. It has been suggested in a recent tungsten-inert-gas welding investigation that heat input could be used as an independent parameter for predicting bead width. However, the present work sug- gests that heat input alone is not sufficient for predicting bead width in submerged-arc welding.

The bead width is not affected significantly by the power source, constant voltage or constant current, when an acidic fused flux is used. However, when a basic fused flux is used, constant- current operation gives somewhat larger bead widths. It is found also that basic fused flux welds have a somewhat larger bead width than acidic fused flux welds. Regression equations are pre- sented for computing bead width from the welding parameters, the analysis including both linear and curvilinear multiple-regression analysis techniques. Surprisingly, the correlation coefficients of the linear multiple-regression equations were found to be somewhat better than those of the curvilinear analysis.

1. Introduction

T h e r e l a t i o n s h i p b e t w e e n a r c - w e l d i n g p a r a m e t e r s a n d w e l d - b e a d g e o m e t r y is c o m p l e x , s i n c e a n u m b e r o f f a c t o r s a r e i n v o l v e d . E x t e n s i v e s t u d i e s h a v e b e e n

0924-0136/92/$05.00 © 1992 Elsevier Science Publishers B.V. All rights reserved.

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carried out to determine the effects of the various process variables on the weld-bead geometry. This is necessary since in practice all variables must be selected before a weld can be specified for a given welding situation, especially where automated welding equipment is used. The work of various authors con- cerning weld-bead shape prior to 1978 has been summarized by Shinoda and Doherty [ 1 ].

McGlone [ 2 ] and McGlone and Chadwick [ 3 ] carried out further work sub- sequent to the review on submerged-arc welding [ 1 ], the variables included in these studies being welding current, welding voltage, welding speed, joint prep- aration angle and electrode diameter. The effects of these variables on weld penetration, deposit area, fusion area, bead width and bead height were studied.

Chandel et al. [4-6] extended the study to include the effects of electrode polarity and electrode extension on weld penetration, total fusion area and electrode melting rate. It was found that both electrode extension and electrode polarity were important variables with regard to both weld bead size and shape. However, the Chandel study did not include bead width. The bead width affects the number of passes required to fill a joint and is therefore an important geometrical feature of the submerged-arc welding process.

This investigation is an extension of the Chandel investigation to study the effects of process parameters on bead width. Included in this work are electrode polarity, electrode extension, electrode diameter, welding current, welding voltage, welding speed, machine setting (constant current or constant voltage) and flux (acidic or basic) as the variables that must be considered when pre- dicting bead width. Following the presentation of the experimental work, the results of regression analyses are considered. While predicting weld bead ge- ometry is an uncertain business, mathematical expressions are nevertheless useful when welding schedules are planned and specified in fabrication prac- tice. The relationships suggested from this investigation add another dimen- sion to this capability.

2. Experimental procedure

The base material used for investigation was a 19 mm thick ASTM A36 steel plate. This plate was cut into 600× 150 mm work pieces which were sand- blasted to ensure clean, oxide-free conditions. Lincoln L60 electrodes of 2.4, 3.2 and 4 mm diameter were used along with Linde 124 (acidic) and OP121TT (basic) fused fluxes.

A Miller DC 1500 power supply, which could be operated as either a con- stant-current or constant-voltage source, was used to deposit experimental bead-on-plate welds. A total of 138 and 115 welds were made successfully using positive and negative electrode polarity, respectively. For each weld, electrode diameter, polarity, electrode extension and welding speed were pre-selected and the welding current and arc voltage were recorded continuously. Electrode

18

extension for the purposes of this investigation is taken as the distance from the bottom of the electrical contact collar surrounding the electrode to the surface of the workpiece. Each weld was cross-sectioned at mid length, polished and etched with 2% nital before the bead width was measured. Several mea- surements were made for each weld to ensure that the representative mean value is reported.

3. Experimental results

3.1. The effect of electrode polarity It can be seen from Fig. 1, which shows the effects of current and polarity on

the bead width for an electrode diameter of 3.2 mm and an electrode extension of 76.2 ram, that generally the bead-width values are larger for positive-polar- ity welds than they are for negative-polarity welds, similar trends being found for electrode diameters of 2.4 and 4.0 mm and an electrode extension of 25.4 m m .

3.2. The effect of welding current Figure 2 shows the average bead width against welding current, for electrode

diameters of 2.4, 3.2 and 4.0 mm, each with an electrode extension of 25.4 and 76.2 ram. The bead widths are the average of all measured values for welds deposited with the same current setting, for a particular electrode diameter and extension, but without taking into account the effects of voltage and speed. While this may seem somewhat arbitrary, the voltage and speed must be ad- justed at all t imes to ensure a constant heat input of 3 k J /mm. It can be seen

20

12

16 z

< 14

ELECTRODE POLARITY + POSITIVE + NEGATIVE

135

10 I I 200 400 600 800

WELDING CURRENT (AMPS)

Fig. 1. The effects of changes in current and polari ty on bead width (electrode d iameter = 3.2 mm; electrode extension = 76.2 ram) .

136

20

: 2 = b - -

c~ 16

LLI n n

,,, 1 4 -

1 2 - ELE

• - , . . , . . .

10 I I l 200 400 600 800 1000

WELDING CURRENT (AMPS)

Fig. 2. Average width versus welding current for electrode diameters of 2.4, 3.2 and 4.0 m m and for electrode extensions of 25.4 and 76.2 ram.

that, for a particular electrode diameter and extension, the bead width in- creases initially as the current is increased. After the bead width has reached a peak value, it decreases as the welding current is increased further. It can be seen also that the gradients of the lines are similar after passing through the peak value. Such observations are valuable in interpreting the form and results of regression analyses.

3.3. The effect of electrode extension It can also be seen from Fig. 2 that, for electrode diameters of 2.4 and 3.2

mm, the smaller electrode extension of 25.4 mm gives larger bead-width values, for both electrode polarities. However for an electrode diameter of 4.0 mm, similar bead widths are obtained for both electrode extensions and both polarities.

3.4. The effect of electrode diameter It is apparent from Fig. 2 that at the lower end of the current range, i.e. below

the peak value of the bead width, the effect of electrode diameter is not clear, presumably because of scatter in the results. However, at the higher end of the current range, it is clear that a larger electrode diameter encourages larger bead widths.

3.5. The effect of welding voltage Figure 3 shows the variation of average bead width with welding voltage, for

electrode diameters of 2.4, 3.2 and 4.0 mm, each with electrode extensions of 25.4 and 76.2 mm, respectively. Average bead widths were obtained by taking

137

18

~ " 1 6 -

o

~ 14

ELECTRODE EXTENSION (MM) - POLARITY - - - e - 25.4 - POS. ---t-- 25.4 - NEG, ---'4e-- 76.2 - POS. --m--- 76.2 - NEG.

1 2 3 0 I I I I 32 34 36 38 40

WELDING VOLTAGE (VOLTS)

Fig. 3. The effect of variation in welding voltage on bead width (electrode diameter--3.2 mm).

18

b-

~z 14

3.2 - 25.4 3.2 - 76.2 --*e-- 4.0 - 25.4 ~ 4.0 - 76.2

12 I I I l 30 32 34 36 38 40

WELDING VOLTAGE (VOLTS)

Fig. 4. The effect of variation in welding voltage on bead width for electrode diameters of 2.4, 3.2 and 4.0 mm and for electrode extensions of 25.4 and 76.2 ram.

the average of all measured values for welds deposited with the same voltage setting, for a particular electrode diameter and extension, but without taking into account the effects of current and speed. Once again it is necessary to note that current and speed are adjusted to ensure a heat input of 3 k J /mm. It can be seen that in most cases, for both electrode extensions (25.4 and 76.2 mm) for both positive and negative electrode polarities and for all electrode diame- ters (2.4, 3.2 and 4.0 ram), there is an increase in bead width when the voltage is increased from 32 to either 35 or 38 V.

138

Data for electrode diameters of 2.4 and 4.0 mm are added to Fig. 4 but the polarity is held constant. An excellent linear relationship between bead width and welding voltage is apparent for the electrode diameter of 3.2 mm and for both electrode extensions (25.4 and 76.2 mm). It might be possible to establish similar relationships for electrode diameters of 2.4 and 4.0 mm with further investigation. However, from the data at hand it is observed that the bead width decreases for an electrode diameter of 4.0 mm when the voltage is at the high end of the range (38 V).

3.6. The effect of welding speed Figure 5 shows the effect of welding speed on bead width, for an electrode

diameter of 3.2 mm. The average bead widths are the average of all measured values with the same welding speed and electrode extension, but without tak- ing into account the effects of machine setting (constant voltage or constant current) or flux (acidic or basic) used. It is apparent that for each current setting, the majority of cases show an increase in bead width with speed. Figure 5 shows clearly that for a current of 300 and 450 A, the bead widths for positive polarity are larger than they are when the polarity is negative. However, at a current level of 600 and 750 A, the bead widths for either polarity are similar. For each current setting, the bead width increases as the speed is increased.

Figure 6 shows the effect of welding speed on average bead width, for elec- trode diameters of 2.4, 3.2 and 4.0 mm, each with electrode extensions of 25.4 and 76.2 mm. It can be seen from this figure that the bead width increases initially as the welding speed is increased. However, after a peak value has been reached, the bead width decreases as the speed is increased further.

20

18

n,.-

16 t--,

IL l

14

12

10

POLARITY - CURRENT (AMPS)

- . -e - - POS. . 300 - . -¢- - NEG. - 300 --v#--- POS. - 450 - m - - NEG. - 450

- - x - - POS. - 600 -4 , . - - NEG. - 600 ~ POS.- 750 - - e - - NEG. - 750 I I I

4 6 8 10

WELDING SPEED (MM/S)

Fig. 5. The effect of variation in speed in bead width (electrode diameter = 3.2 rnm ).

139

20

18

I. .- • "~ 16

1 2 ELECT.

2.4 - 25.4 ~ 2,4 - 76.2 ~ 3.2 - 25.4 ! - - m - - 3.2 - 76.2 ~ 4.0 - 25,4 - - 4 , - 4.0 - 76.2

10 i l i , 4 6 8 10 12

WELDING SPEED (MM/S)

Fig. 6. The effect of variation in welding speed on bead width for electrode diameters of 2.4, 3.2 and 4.0 mm.

TABLE 1

Average bead width against machine setting and flux (electrode diameter = 3.2 ram)

Electrode Welding extension speed (mm) (mm/s)

Linde 124 Flux 0P121 TT Flux

Constant Constant Constant Constant voltage current voltage current

25.4

76.2

3.51 16.27 16.00 15.50 16.67 5.25 17.60 16.87 19.40 19.27 6.99 16.60 16.33 16.87 17.43 8.76 13.30 13.33 15.60 15.60 Average 15.94 15.63 16.84 17.24 3.51 16.20 16.53 14.60 17.23 5.25 17.43 17.57 17.15 19.70 6.99 13.83 13.53 15.70 17.40 8.76 11.90 11.80 13.03 13.43 Average 14.84 14.86 15.12 16.94

3. 7. The effect of machine setting and flux Data in Table 1 are presented to show the average bead width against ma-

chine setting, constant voltage or constant current, and flux type (acidic or basic), for an electrode diameter of 3.2 ram. Bead widths were obtained by taking the average of all the measured values for welds deposited with the same machine setting, the same flux type and the same electrode extension, but without taking into account the effects of current, voltage or speed. Once again it must be pointed out that, the heat input of all welds is 3 kJ /mm. It can be

140

seen from the table that there is no significant change in average bead width by switching from constant-voltage to constant-current operation when the acidic fused flux, Linde 124, is used. On the other hand, somewhat larger bead widths are apparent when a constant-current machine setting with the basic fused flux, OP121TT, is used. For the same machine setting, the basic fused flux also leads to somewhat larger bead width values.

4. Regression analysis

The above results indicate that bead widths are dependent on welding cur- rent, arc voltage, welding speed, electrode diameter, electrode polarity and electrode extension. In practice it is useful to be able to compute the width expected with a mathematical expression. In order to determine such an expression, a multiple-regression analysis of all of the experimental was car- ried out, using both the linear and curvilinear techniques, the following equa- tions being obtained:

For electrode positive (DCEP),

Wd (lin) = 25.81 -- 0.019L- 0.0281- 0.18V+ 0.36D + 1.73S (1)

Wa (log) = 21.84L -°°~°I-°'24V°'3SD°°'9 (2)

For electrode negative (DCEN),

Wd (lin) = 20.74 -- 0.024L - 0.13 V+ 0.69D - 0.030•+ 2.18S (3)

Wd (log) = 1.60L - °'°v9S - 0.090 V °'73D o.o~z ( 4 )

where Wd=bead width (mm); D--electrode diameter ( ram); /=welding cur- rent (A); L = electrode extension (mm); S--welding speed (mm/s); V= welding voltage (V); lin = equation obtained by using linear regression analysis; log-- equation obtained by using curvilinear regression analysis.

It should be noted that, due to the low tolerance of some of the process vari- ables, only four variables could be included in eqns. (2) and (4). Unrealistic equations were obtained by forcing all the variables into the regression anal- ysis. Different variables were selected for both eqns. (2) and (4) because of this problem.

The statistical data for the correlation equations are tabulated in Table 2. It can be seen from the table that the coefficients of multiple correlation (R) for eqn. (1) and eqn. (3) are somewhat better than those for eqn. (2) and eqn. (4). It is apparent that the correlation coefficients are considerably lower than normally reported for statistical analyses in engineering investigation. This reflects that predicting bead width is an uncertain business and it is doubtful that better correlation is possible without better control of the arc heat source. Such control is fundamental to the welding process, not just to the need for better equipment. Nevertheless, in spite of the low correlation, these relation-

TABLE 2

Statistical data for the correlation equations

141

Eqn. Correlation S.E. a of Intercept S.E. of Slope S.E. of No. coefficient, R Est. Intercept Slope

eqn. (1) 0.63 1.87 0.00 1.67 1.00 0.11 eqn. (2) 0.53 2.04 2.31 1.84 0.86 0.12 eqn. (3) 0.46 2.33 0.00 2.65 1.00 0.18 eqn. (4) 0.38 2.43 0.26 3.28 1.00 0.23 eqn. (5) 0.43 2.17 10.7 0.91 0.24 0.04

aS.E. = standard error.

ships are submitted to provide some basis for anticipating bead width. The user must, however, be aware of the uncertainty.

5. D i scuss ion

5. I. Interpretation of the regression equations Equation (1) indicates that an increase of electrode diameter, D, and weld-

ing speed, S, increases the bead width. On the other hand, an increase of elec- trode extension, L, welding current , / , and voltage, V, decreases the bead width. Equation (2) indicates that an increase of V and D increases the bead width while an increase of L and I decreases the bead width.

These trends are in general agreement with the results presented previously in Section 3, except that the variable V is open to interpretation by virtue of its carrying a different sign in each relationship. It seems that eqn. (2) tends to predict the general t rend that the bead width increases as the welding volt- age is increased, that is apparent in Figs. 3 and 4. On the other hand, eqn. (1) tends to predict the opposite t rend and would seem to be influenced strongly by the 4.0 mm electrode result at the higher end of the voltage range shown in Fig. 4. It should, however, be noted that for the electrode diameters of 2.4 and 3.2 mm, the bead width increases as the voltage is increased, as shown in Fig. 4 and in this respect eqn. (2) would seem to be the more reliable.

Equations (3) and (1) are similar, but eqn. (4) includes the welding speed, S, as a variable instead of the welding current , / , which is used in eqn. (2). It can be seen from Figs. 2 and 6 that the effects of I and S on the bead width are quite similar: this is because the constant heat input of 3 k J / m m was used throughtout this investigation, the welding speed having to be increased when- ever a higher current is used.

5.2. McGlone and Chadwick's equation McGlone and Chadwick [3 ] presented the following equation to predict the

bead width, for an electrode positive polarity:

142

Wd = 18.168 V°'SSD°51I-°'°2S -°"59(1 + t an A /2 ) -o.3~ (5)

where S is the welding speed (mm/min) and A is the joint included angle (rad). This equation can be applied to bead-on-plate welds by assuming the

joint included angle to be zero. It is similar to eqn. (2) in that the variables electrode diameter, D, welding current , / , and voltage, V, have similar signs. However electrode extension, L, is not taken into account in the McGlone and Chadwick work and it can be seen from Table 2 that the coefficient of multiple correlation is relatively lower. This equation is also not applicable to situations where the electrode polarity is negative.

5.3. The low correlation coefficients of these equations Although it has been shown that the curvilinear equation gives better cor-

relation results [ 1-5 ] under other circumstances, it is clear from Table 2 that this is definitely not the case for bead width. The linear equations, in fact, provide better correlation results, which is expected since the relationships between bead width, current, voltage and speed are observed to be mostly lin- ear (Figs. 2-6). It should be noted, however, that due to the occurence of peak bead-width values, no single linear relationship can be used to represent all effects. The effects of the electrode diameter and electrode extension are also different when the current setting is varied from the lower end to the higher end. Consequently relatively low correlations are obtained from these equa- tions. A refinement to the current investigation would be to suggest further regression relationships limited to particular variable ranges. However, a much larger data base is needed to do this and it was not considered a useful excercise in the present investigation. Despite the difficulties in analysing and inter- preting the data, the relationship suggested should be useful in practice for providing some estimate of bead width, albeit an estimate with considerable uncertainty.

5.4. Work by Alberry, Brunnstrom and Jones Alberry, Brunnstrom and Jones [7 ] suggested that for mechanized tung-

sten-inert-gas weld deposits the effective heat input could be used as a param- eter for predicting bead width. The effects of welding voltage and welding cur- rent contribute only to the heat input and its efficiency. Figure 7 shows the Alberry results for the variation of weld-bead width with effective heat input.

The results of this investigation show clearly that heat input is not sufficient to predict bead width in submerged-arc welding. In fact welding current, weld- ing voltage, electrode diameter, electrode extension, electrode polarity and welding speed all need to be viewed as independent variables. The present work may, therefore, help to explain the scatter found in the presentation of the measured results of these authors, as shown in Fig. 7.

12

10

t ~

c~

t l J t ~

6

4 I I I I I 0 200 400 600 800 1000 1200

EFFECTIVE HEAT INPUT (J/MM)

Fig. 7. The effect of variation in heat input on bead width (after Alberry et al. [7] ).

6. Conclusions

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The present work has shown that bead width in submerged-arc welding is affected by electrode polarity, electrode extension, electrode diameter, welding current, welding voltage and welding speed.

A positive electrode polarity, a large electrode diameter, a small electrode extension and a high welding voltage encourage a high bead width in most cases. For a particular electrode diameter and extension, it was found that the bead width increased initially with current and welding speed. After the bead width reached a maximum, it decreased as the welding current and speed were increased further. Although it has been suggested that for tungsten-inert-gas welding that the effective heat input could be used to predict bead width, this work indicates that it is not sufficient to combine all operating variables into this one parameter.

Bead width was not affected significantly by the power source, or by whether constant voltage or constant current was employed, when an acidic fused flux was used. However, when a basic fused flux was used, constant-current oper- ation gave somewhat larger bead widths. In addition, welds deposited with the basic fused flux were found to produce somewhat larger bead widths than welds deposited with the acidic fused flux.

Regression mathematical expressions for anticipating bead width have been advanced. It was found that the correlation coefficients obtained from the lin- ear multiple regression equations are better than those associated with the curvilinear relationships.

144

A c k n o w l e d g e m e n t

L.J . Yang acknowledges wi th t h a n k s the f inanc ia l suppo r t p rov ided by N a n - y a n g Techno log ica l Un ive r s i ty , f o rm er l y N a n y a n g Techno log ica l Ins t i tu te , S ingapore while a t t a c h e d to Car l e ton Un ive r s i ty on sabba t ica l leave; M.J . B ibby acknowledges wi th t h a n k s the s u p p o r t o f the N a t i o n a l Science a n d Eng inee r - ing R e s e a r c h Counci l G r a n t A4601.

References

1 T. Shinoda and J. Doherty, The relationship between arc welding parameters and weld bead geometry--A literature survey, The Welding Institute Report 74/1978/PE, 1978.

2 J.C. McGlone, The submerged arc butt welding of mild steel, Part 1: The influence of proce- dures parameters on weld bead geometry, The Welding Institute Report 79/1978/PE, 1978.

3 J.C. McGlone and D.B. Chadwick, The submerged arc butt welding of mild steel, Part 2: The prediction of weld bead geometry from the procedure parameters, The Welding Institute Re- port 80/1978/PE, December, 1978.

4 R.S. Chandel and S.R. Bala, Relationship between saw parameters and weld bead size, Physical Metallurgy Research Laboratories Report: PMRL 86-38 (J), Canmet, Ottawa, Canada.

5 R.S. Chandel, S.R. Bala and L. Malik, Effect of submerged arc process variables on penetration and its prediction, Weld. Met. Fabr., (August 1987).

6 R.S. Chandel, Mathematical modeling of melting rates for submerged arc welding, Weld. J., 66(5) (May 1987) 135s-140s.

7 P.J. Alberry, R.R.L. Brunnstrom and K.E. Jones, Computer model for predicting heat-af- fected-zone structures in mechanized tungsten-inert-gas weld deposits, Met. Technol., 10 (January 1983) 28-38.