AC pulsing

[zst]

Anybody has expierence with AC pulse at thin Al. sheets (around 1 mm thick)?
I am interested to achieve as better as possible control of molten pool at thin sheets to prevent of burn-through...
Do you think that AC pulse is a solution?
Do you have some starting parameters?

 

[hotrodder]

Could definately be an aid regarding pool control. TBH i've never really given it a fair trial with AC, had a little play and found it easier to get consistant results without pulse- made fantastic bead appearence easy but was getting erratic fusion and irregular root profiles. Found it slowed me down, got bored and never bothered again. My machine is limited to a slow pulse with AC though (upto 500Hz DC, only 2.5Hz AC). A high frequency pulse with AC potentially offers more i reckon but have never had the chance to have a play

Lots of stuff can be found on pulse settings beginning with this thread (has links to more threads and a pulse parameter calculator). Pretty much all to do with stainless and keeping the heat input down though. Parameter development is going to be a similar journey but as ally is such a good conductor of heat i would be leaning toward longer peak times and higher background currents as a starting point.

Another one i've never really bothered with is triangular wave AC. My machine offers it, idea is it's optomised for thin sections- not much time spent at the 'peak' of each wave cycle so better pool control. It does make thin stuff easier, quite a 'harsh arc' imo and again not done much with it as i rarely weld thinner than 1.2mm Al which is easy enough with regular squarewave

 

[Freshfabrications]

I would say that although slow pulsing is one way to controll heat imput on any metal in my experience with fusion welding 22 & 20 guage stainless sheet I actually found a very high frequency pulse helped more ( bare in mind I'm talking no filler here ) which runs true with Hotrodders statement about faster pulsing!

I use about half a second on high arround 90 amps and just over half a second at about 20 amps, which I'd discribe as slow pulsing, when I'm welding 4130 as thin as 0.8mm and as thick as 1.2mm.

If I was pulsing thin aluminium arround 1mm and had to try a test i'd start with say 150 - 180 hz with about 90 amps peak and about 30 background to start.

Remember to make obveous the results of chainging any single setting only ever play with one setting at a time, eg to see what higher or lower Hz pulse does there's not much point chainging the amps and the Hz or you won't know what's making the difference!!

Personaly the first thing I'd do is set up none pulsed and make sure the AC ballance is set so there is inough cleaning and resonable penetration!!

Then I'd start setting the puse set up.

First thing to look at is the effect of Hz, out of position stability, arc stiffness or fluidity of the weld pool.

Next once your happy with the Hz I'd just look at the PEAK amperage, does it melt the parent metal quick enough, how high can it be and still be controllable,
Is it still fluid enough when cooled by filler rod additions.

Then I'd say you should have a crak at lowering the background amps a tiny bit at a time untill you loose the desireable effects, ie fluidity, travel speed desired, penetration needed. Once the desired effects start to suffer come back up a bit with the background amps so you just keep things nice!

Once your happy with this go back and tweak the AC ballance very slightly to give cleaning or penetration as desired.

Play methodicaly and it will come.

Good luck