American Welding Society Forum
Anyone know of advantages/disadvantages of using AC vs. DC for the hot wire current? I know AC would tend to prevent arc blow, but are there any other issues?
Educate me Marty, what is Hot wire GTAW?
I will help Marty answer your question....Hot Wire GTAW involves using a mechanize or automated system to do GTAW welding. The Hot Wire option uses coil to preheating the wire just before it is it hits the puddle. The theory is you can add more wire faster without cranking up you torch amps. I have seen some demo where this application is quite effective at adding alot of metal fast.
Marty--Sorry I don't know enough to help you with your question.
No one has responded so:
We used AC and DC for hot wire feeding back at an aerospace company I used to work for. This process was used to weld small to large diameter sheet steel (primarily rocket exhaust cones) of inconel or titanium, depending on the application. There was also cold feeders used at this facility for aluminum, but these were rarely used.
We had procedures for both AC and DC, I did not notice any difference. The AC was utilized to minimize any arc blow (as you already know) problems, but I never experienced any myself. I tried both programs with the AC and DC and could not tell the difference myself. I did not enjoy this mechanized station and prefered to work on the bench. Adjustment of the torch guides during operation was required now and then, but that was it, I found it boring.
The only thing I do remember about hot wire GTAW was keeping the shielding consistent about the heated wire assembly and the trailing cups. Something seemed to leak whenever it came time to qualify, but it ran fine during production. The shielding usually consisted of lots of tin foil and home-made trailing cups. If the shielding was compromised on the wire feeder for titanium, then the part was considered a very expensive paper weight.
Maybe it was the "watched pot never boils" effect.
Thanks for sharing your experience. I have not found much published technical data on hot-wire systems, even in the AWS handbooks. We've been using it with GTAW on 3/4" deep 1G groove welds in 304L stainless steel. Have been feeding 0.035" dia. wire at up to 500 IPM with good results, but it is more controllable at around 400 IPM. We're using a Liburdi system now that uses DC for the the hot-wire current, but needed to consider whether AC might be a better choice. If anyone has any technical references it would be appreciated. I'll also do a search on Welding Journal articles.
500 ipm of .035" wire is hauling ass (excuse my excitement)! That's a lot of wire going into that joint. Understandable for a groove weld though.
We had to implement the "slowly but surely wins the race" methodology for the rocket nozzles. Too much $$ at stake. The old Miller AB/P's laid down some beautiful beads with hot or cold wire feeder applications. We also had a tandem arc GTAW set-up. By the way, how many GTAW amps does it take to consume 500 ipm of 035 wire?
You might try some of the other "tech" sites like eng-tips.com and such. There are some very sharp individuals out there on this subject, you just have not found one yet.
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