Measurement of the force exerted by a welding arc
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Fig. l - - E x a m p l e of variable penetration welds made on Ti-6AI-4V with a 325 ampere gas tungsten arc. The shallow weld to the left was made with pure argon shielding, while the deeper weld on the right was made with argon and 0.25 m m of CaF2 flux.
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DISPLACEMENT TRANSDUCED Fig. 2 - - Schematic of torsion balance apparatus. The counterweight, dashpot, ground cable, test plate insulator, electrostatic and electromagnetic shielding and positive displacement limits are not shown. The ground cable was connected from the test plate to the base plate by a series of thin copper foils.
J As expected, the weld penetration increased with increasing current; however, it cannot be concluded that the increased penetration is a result solely of the increasing arc force, for an increase in the current also increases the total volume of metal melted. Measurements of the arc force made on different metals produced very similar results. This has been explained recently by Converti 4 who showed that the force, F, of the plasma jet is equal to F=
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where I is the welding current,/x0 is the permeability of free space, R1 is the radius of the arc where it contacts the welding electrode, and R2 is the radius of the arc where it contacts the base plate. For the measurements shown in Figure 3, the ratio R2/R1 = 4. The arc force was also measured on titanium-6A1-4V plate with various alkali-earth halides present. These halides are known to cause variations in weld penetration depth,1 but as Figure 4 illustrates, no apparent correlation was found in this study between the penetration and the arc force when using different surface fluxes. VOLUME 14A, JUNE 1983-- 1223
non cannot be tested with the torsion balance used in this study. Verification of these changes would require direct measurement either of the current distribution in the plasma or of the actual surface depression of the weld pool. It should be noted that explanations of variable penetration other than changes in the weld surface depression due to the arc force have also been presented. Recently Heiple and Roper have shown that liquid metal flows in the weld pool resulting from surface tension may alter the pool shape. 7 Oreper and Szekely have performed calculations which support this hypothesis.8
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This work was supported by the Office of Naval Research under contract N00014-77-C-0569. The assistance of Mr. Lane Wilson with some of the experiments is appreciated.
WELDING CURRENT IAMPERESI Fig. 3 --Corrected arc force vs welding current for argon shielded titanium welds. The data points are corrected for extraneous electromagnetic deflection, and the solid line represents the theoretical value for R2/R~ = 4.
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REFERENCES 1. S. Glickstein and W. Yeniscavich: Welding Research Council Bulletin #22
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