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Up Topic Welding Industry / Technical Discussions / TIG pulsing question
- - By DaveSisk (**) Date 12-29-2002 18:39
What are the benefits of pulsed TIG (in either DC or AC squarewave). What are the circumstances where it's beneficial? What thicknesses of materials, types of joints, etc., is pulsing useful?

Thx,
Dave
Parent - - By RonG (****) Date 12-30-2002 15:29
In a word! Controle (heat input and puddle)

Parent - - By DaveSisk (**) Date 12-30-2002 18:44
Give me some details here! I'm seeking knowledge...!

Thx,
Dave
Parent - By RonG (****) Date 12-30-2002 19:30
Straight spray arc is a very hot process and the puddle is very fluid.

The pulse goes back and forth between welding current to Back ground current.

The pulse puts less heat in to the work and will allow or make for much easier out of position welding.

There are publications available at most supply houses, they like to make the advantages available so they can sell more machines. Ask for some next time you go there.



Parent - - By Lawrence (*****) Date 12-31-2002 18:48
Dave,

Pulsation in GTAW (manual) is a pretty limited application thing. If you are doing lap welds on thin materials (under 0.090) in great production quantity a pulser may be helpful. Forget pulsation on AC aluminum.

Pulsation with GTAW is more often used in automated or semi-automated production runs for buildup with minimal heat input. Sciaky for instance has a setup that synchronizes the high pulse to the wire feeder so that as the current slopes up the wire is added. This is a pretty hard trick to accomplish with any consistency manually unless meticulous prep, fitting and fixturing are applied for large production runs.

I have seen pulsation used to put lap patches on stainless pipe elbows with good effect. (tight fitup no filler). but thats about it.
Parent - - By Niekie3 (***) Date 01-04-2003 10:24
Interesting that you do not like GTAW pulse on Al. This is one of the typical applications for manual pulse welding that I have come accross.

It helps you to freeze the weld puddle momentarily before again melting it. This is great to reduce the possibility of "burn through" that is often a problem when welding Al.

Regards
Niekie Jooste
Parent - - By Lawrence (*****) Date 01-05-2003 08:13
Awsome,

I've never seen such a thing.

Niekie, could you please say a little more about how this is done? Maybe share an example you have experienced?

High-Low amps and pulse durations, Balance control settings, Thickness of aluminum and joint geometry etc.

Thanks a bunch

Lawrence
Parent - By Niekie3 (***) Date 01-05-2003 19:09
Hi Lawrence

You are asking a bit much for me to remember all the details, but here is some idea:

Base metal thickness around 5mm
Single V prep. butt
Pulse duration around 2 - 3 seconds
Background current around 50% of peak

I am aware that this weld can be performed by a skilled Al welder without any pulsing, but pulsing gives a less skilled Al welder the ability to perform a full penetration weld without such a big chance of burn-through.

There are a number of problems with welding Al. There are two that tend to work together to make it a "difficult" material to weld. These are:

1) The high thermal conductivity of Al
2) The narrow melting range of Al

To get the Al to melt, you need to get as much heat into the material as soon as possible. If your amps are too low, the heat is conducted away as fast as you pour it into the material. This means no melting. So, you need to crank your amps up as much as possible. Once melting does however start, you go from a solid to a total liquid within a very short space of time. There is a very small liquid + solid zone. (Also called the "mushy" zone.) - This is obviously also very dependant on the alloy being welded. If you are welding commercially pure Al this becomes a big problem.

What therefore happens, is that as the material looks like it is just making a really nice puddle, it suddenly burns right through the base metal and your wleding puddle suddenly falls on the floor.

To ease this problem, you set the pulse on the machine so that you get melting for a second or two, followed by a "freezing" cycle. During the high current cycle, you feed filler metal and move forwards with the weld. As the lower current cycle starts, you stop moving forwards and allow the puddle to freeze momentarilly. The high current cycle then again starts etc.

I hope that this is what you had in mind.

Regards
Niekie Jooste
Up Topic Welding Industry / Technical Discussions / TIG pulsing question

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