TIG What's wrong with DC only (Maxstar 150)

[boustany]

TIG What\'s wrong with DC only (Maxstar 150)

Thanks for the help regarding gas - I finally found a local dealer who will sell me a tank, vs rent it (BOC in Guelph, Ontario). Plus they have a nearby depot that open Saturday.

I was sort of thinking about TIG welders the other day, since I have to replace the AC/DC stick my brother lent me and I noticed that some TIGs do stick to, but DC only. Then I read up on TIG and found out that the high end ones do DC/AC as well as square wave. For example the Miller Maxstar 150 is DC only, although it has a number of fancy start up modes. Some old welding books I have suggest DC TIG can only weld steel, and seem to imply the problem is with the start up.

So, whats the major drawback to DC only TIG? Can you still weld cool stuch like Aluminum and Stainless with DC? Any experience with the Maxstar 150?

Thanks again in advance.

 

[slowzuki]

Re: TIG What\'s wrong with DC only (Maxstar 150)

Need AC tig to "stir" the puddle when welding aluminum. I suspect it can be done DC but not as strong.

Ken

 

[MadReferee]

Re: TIG What\'s wrong with DC only (Maxstar 150)

Go to the Hobart/Miller welders forum and ask there. Those experts can really help.

Hobart/Miller welders forums

 

[Spencer]

Re: TIG What\'s wrong with DC only (Maxstar 150)

</font><font color="blue" class="small">( Can you still weld cool stuch like Aluminum and Stainless with DC? )</font>

Yes you should weld stainless steel with DC only (DCEN). You really need AC for Aluminum though.

Spence

 

[EdDekker]

Re: TIG What\'s wrong with DC only (Maxstar 150)

You can weld thin aluminium with a DC TIG. There are some problems or restrictions. Because of these problems AC is usually used on Aluminium (and Magnesium).

DC TIG welding was the first TIG technique used for production Aluminium welding.

In TIG welding when the Electrode has a negative potential (relative to the work) more heat is applied to the work than the electrode and torch, when the electrode is positive much more of the heat is absorbed by the tungsten and torch but there is a cleaning effect stripping the oxide layer off the work.

An AC TIG alternates between electrode positive (EP) and electrode negative (EN), allowing a mixture of high heat and cleaning. The better AC TIGs allow the user to select the balance (ratio) between the EP and EN periods. This selection allows less cleaning (EP) time and more heat applied to the work for very clean aluminium workpieces or more cleaning time for slightly dirty aluminium.

Aluminium forms a tough oxide surface very quickly. Welding the aluminium requires the cleaning action of some EP periods. While EP a larger amount of heat is absorbed by the electrode there is still enough heat applied to the work to melt the aluminium.

This means we can weld aluminium with a DC EP TIG. The problems are that the penetration will be shallow and the tungsten and torch must absorb a great amount of heat. With thin aluminium the penitration is sufficient and a sufficiently large tungsten and torch can absorb the heat.

With thin aluminium and a thick tungsten it is possible to get excellent welds As a rule of thumb is to use a tungsten diameter must be at least as large as the thickness of the aluminium being welded.

An air cooled torch will heat up to the uncomfortable levels quickly. A water cooled torch quickly becomes a requirement if one will do much DC TIG aluminium welding. (Either using a water cooler to recycle torch cooling water or by just hooking the torch up to tap water and a drain to minimize equipment.)



This is a frequent topic of the sci.engr.joining.welding newsgroup. A google search will result in a lot of good information.

DIsclamer: I own a Maxstar 200 DX. I have not developed my DC aluminium welding skills yet, I am still developing my skills on steel. If I were to purchasing a welder today I would get the Dynasty 200 DX to have AC available.

 

[Henro]

Re: TIG What\'s wrong with DC only (Maxstar 150)

<font color="blue"> If I were to purchasing a welder today I would get the Dynasty 200 DX to have AC available. </font>

I wanted to buy the Dynasty 200 dx but since money was an object I ended up buying a Thermal Arc 185 tsw kit, which was considerably cheaper than the Miller and almost as good for my purposes.

If you do a search for these two welders on the Hobart site you will find a lot of info on them and comparable machines that will help you choose what is best for you.

Personally I would not buy a tig welder that did not have ac capability...fearing I would regret not having it later, if for no other reason... /forums/images/graemlins/smile.gif