LETTERS TO THE EDITOR Reader Questions Tungsten Sizes and Droplets This letter concerns Gas Tungsten Arc Welding Using an Arcing Wire, by J. S. Chen, Y. Lu, X. R. Li, and Y. M. Zhang, published in the October 2012 Welding Journal (261-s to 269-s). The comments set forth by August F. Manz, an AWS Fellow, are in plain text. The answers and clarifications are italicized as submitted by corresponding author YuMing Zhang. This fine article left me with a few unanswered questions. 1. As shown in Fig. 4, both currents (I1 + I2) pass through the tungsten electrode. The current totals in the experiments ranged from 150 to 400 A. Such a range on tungsten electrodes would require a change in size, especially when compared to ordinary gas tungsten arc welding (GTAW) with a cold wire or hot wire addition. What was the authors’ experience? You are absolutely correct that a tungsten size should be appropriate to I1 + I2. However, in all our experiments, despite the amperage, we used the same tungsten (1⁄8 in. diameter) and torch (Weldcraft WP-18P 500-A GTA torch) to produce the welds/results documented in the article. We have not found noticeable adverse effects in our experiments when we use a relatively large tungsten size for a relatively small I1 + I2. 2. Again, referring to Fig. 4, what was the droplet transfer frequency? What was the droplet size? What was the direction of the arc force on the droplets? The transfer frequency and droplet size vary with the current of the side arc that is established between the wire and tungsten, i.e., I2. They also change with the current of the main arc (gas tungsten arc), i.e., I1. We did record high-speed videos for some of the experiments but not for all of those reported in the paper. We saw the presence of a few separate droplets with diameters much smaller than that of the wire forming a trajectory deviating more from the main arc axis as approaching the workpiece (probably due to the arc force from the main arc). We also saw a single large droplet with a diameter greater than that of the wire. Such large droplets transfer from the wire tip to the workpiece following a similar path, i.e., deviating more from the main arc axis when approaching the workpiece. We did not see the evidence that such large droplets affect the stability of the main arc, which does not have the wire as one of its two arc terminals. In addition, we did not see the evidence that such large droplets produce spatter probably because of the presence of the main arc. I expect that we will soon have quantitative results for the effect of various parameters on the metal transfer. 3. In hot wire, the resistance heating helps to remove volatiles from the wire before entering the work weld zone. In gas metal arc welding (GMAW), the effect of this resistance heating is minimal. As has been shown by Rykalin (see Manz, WRC Bulletin 223, Appendix A, January 1977), resistance heating of the GMAW electrode is minimal. It is the arc that melts the electrode. As a consequence, the volatiles are not removed in the same degree as in hot wire welding. You are correct. Our arcing-wire GTAW that melts the wire primarily by the side arc does not typically remove the volatiles in the same degree as in hot wire GTAW. In a typical GTAW application, we probably would not use a large wire extension. However, if we increase the length of the wire extension, we may increase the resistive heat to remove more volatiles. For GMAW, increasing the wire extension causes arc instability for the arc that directly affects the workpiece. For our arcing-wire GTAW, this cause for arc instability will be partially compensated by the main arc. Further, the arc that is subject to possible instability due to the increased wire extension is the side arc, which does not directly affect the workpiece. Hence, our arcing wire GTAW may have the possibility for a capability to approach the hot-wire GTAW in removing volatiles. However, at this time, we do not have any experimental data to support my argument.◆ ������������������������������ �������� ������ ������ ������������ �� �� �� �� �� ���� ������ ���������������� �� ���� ���������������� ������ ���� ������������������ �� �� �� �� �� ������������������������ ������ �� �� �� �� ���� �� �� �� ���� �� �� �� �� �� ������ ���� �� �� �� �� �� ���� �� �� �� ���� �� �� ���� ���� �� �� �� ���� ���� �� �� �� �� ���� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� �� ���� �� �� �� �� �� �� �� �� �� �� ������������������������ �������� �� �������������� ������������ �� �� �������� ������������������������ ���� �������������������� ���������������������������������� 58 JANUARY 2013
Welding Journal | January 2013
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