True Square wave Power Sources?

Date 10-05-2011 13:07

I've been doing research into pulsing and PWM for various reasons. And I'm split. Most commercial literature seems to tout the advantages of DC pulsing in that it "stiffens" and narrows the arc, which increases power density giving more penetration. This lets you increase travel speed or control penetration.

However I'm sitting on several papers, plus my own research that shows pulse welding does not increase penetration, regardless of frequency from 0HZ to 5Khz. I've tended to see some benefit from increased ratio of background to peak current, but there's a practical limit and the benefit is not substantial. Some further research digs up that in tube mills welding was considered a speed limitation. Companies such as Liburdi developed "True Square wave" power sources. Ones that output current extremely close to an actual square wave. http://www.liburdi.com/LiburdiAutomation/Pages/LT1000-HS.pdf

Apparently without a "true square wave" the arc would never constrict. Now I'm having a hard time cutting through what is marketing hype and what's reality. I'm also having a hard time figuring out how the output would compare from a "true square wave" system like Liburdi and a conventional inverter based industrial or robotic power supply from miller or lincoln. I'm guessing I'm going to have to find an electrical tech, and hook up an oscilliscope.

Any thoughts or experience?

By Metarinka (****)

Date 10-05-2011 13:16

Note:
A lot of the times when "true square wave" technology is talked about. It is in reference to AC welding of aluminum. Where they will use an off-balanced square wave to increase DCEN time which increases penetration. I've been evaluating DCEN pulsing where the only goal was to increase process efficiency and control... seems to be less information in general on DC waveform generation for welding.

By js55

Date 10-05-2011 13:31

Not exactly sure about your question but IMO any statement that pulse increases penetration is bullshyt. The very nature of, and reasoning behind, pulsing argue against this. YOur non mfg research is the more accurate IMO. Also, IMO if mfg literature is saying this it is a bad attempt to try and sell higher cost machines. Not unlike gas suppliers trying to sell all these fancyazz tri and quad mixes. As for true square wave, to my knowledge it still does not exist although I think they are much closer. There is always wave imperfection.

By rlitman (***)

Date 10-05-2011 17:52

There is no such thing as a "true square wave". Such an animal would require infinite bandwidth (it's FFT has harmonics up to infinite frequencies).

Any inverter should be capable of producing a cleaner square wave than can be transmitted through your welding cables (they act as an LR low pass filter that removes the highest frequency harmonics, which will leave you with "ringing" around the corners, no matter how good your inverter is at creating a "true" square wave).
On that note, I'm thinking that it's all marketing hype.

By defaced (**)

Date 10-05-2011 14:55

I've done experiments in this area and can say that penetration does increase, but you must be mindful of the other welding variables.

A scope will only show you voltage, you need a coil or shunt and a scope to see current. Be careful if you use a shunt, ground loops will turn your setup inside out.

"Apparently without a "true square wave" the arc would never constrict. "
Not the case, but it would probably help. I suspect finding a power supply that can deliver a true square wave at any meaningful current or frequency will be fun.

By Metarinka (****)

Date 10-06-2011 04:26

Do you have any details on what type of power supply you were using or the parameter range you were in. Another theory was that we were simply getting out of a parameter space where we would see benefits of pulsing. I have data in-house data on pulse welds from 6 IPM to 20 IPM on base material .1-1" thick, in all cases penetration was not varied by any significant amount.

All that being said we have found some benefits in controlling penetration I.e reducing variation, and there tends to be better surface finish and wetting at the toes, good enough to evaluate it's use for such ends. But still no difference in penetration.

By ravi theCobra (**)

Date 10-14-2011 17:45

You have finally shaken the B.S. tree -

Forty years ago Airco started in Pulse MIG and then resurected Pulse MIG II and despite all of these advances we are still stuck with the S A M E machines -

Just a thought from someone ready to retire . . . .

By Dualie

Date 10-15-2011 02:53

Ha i still have one of those original antique airco pulsed migs in storage. If anyones feeling sentimental i would be willing to part with it. It was in a lab and is in very good condition.

By ravi theCobra (**)

Date 10-17-2011 21:57

Better still and thank God I was nearly talked into one of those by a welding salesman who told me that Pulsed MIG would produce technicolor welds. How many people have had a shot at this new MIRACLE process ?

By Lawrence (*****)

Date 10-18-2011 00:15

I have good things to say about newest generation GMAWP for aluminum and stainless below 11 ga.

I think they are pretty much useless for steel, with the exception of open pipe roots in the shop/

By defaced (**)

Date 10-18-2011 13:05 Edited 10-18-2011 13:15

My work was done with GTAW on Nickel based materias. I don't see a process named in your original post, the Liburdi link goes to a GTAW system, but gathering from the other posts in the thread, you're talking about GMAW, so....?