TIG & ARC

[Maker]

If my current thinking is correct, a TIG torch adapted, (else with an adaptor lead), to connect to the box, a bottle of Argon and regulator and possibly a rectifier for having the option of DC output would be all that would be required to try the basic tests/process?

As far as I know, there's no such thing as scratch AC, you'll need the rectifier. AC scratch start would require you to scratch the tungsten every time the polarity changes, AC tig machines use HF for this.

 

[Maker]

Over on the Miller forum, they all say you need HF, but that might just be a ruse to trick people into buying blue.

As an aside, it's nice how no one here lists all their welders and equipment in their signature.

 

[MattF]

Over on the Miller forum, they all say you need HF, but that might just be a ruse to trick people into buying blue.

I'm guessing people managed quite well without those luxuries for years. That tends to be the problem these days. People just get the stuff and use it, and tend to think there's no other way. Same as few seem to interested in the underlying processes, judging by how hard it is to find information on various subjects, including this one.

As an aside, it's nice how no one here lists all their welders and equipment in their signature.

It'd make for some large sigs if everyone listed all of their equipment. Welder info is on a persons profile page, is it not?

 

[hotrodder]

In the old days I'm pretty sure they didn't have HF start or overlay on AC tig machines...

Yep, they did. In the really early days of TIG it was DCEP using helium to weld magnesium more effectively (avoiding issues from flux with oxyfuel) as explained in the link to the origional patent. That was 1941, IIRC Miller introduced AC/DC rectifiers with HF (start for DCEN, continuous for AC) and started developing AC balance in the 1950s

Once it's going, the arc is pretty resilient - otherwise, why do you not have to scratch an MMA electrode 50 times a second?

Because an MMA electrode that's designed for AC use is very different to a non consumable tungsten electrode and a welding process like TIG that doesn't transfer metal across the arc...
Not all MMA electrodes will work properly with AC and those that are happy with AC usually run better with less arc wander/flutter in DC unless say trying to deal with 'arc blow' from residual magnetism in the part being welded etc

While MMA and TIG both use constant current supplies the volt-amp curves differ. This is one of things that the MMA/TIG switch changes explained in more depth here http://www.millerwelds.com/resources/articles/constant-current-CC-welder-training/
Newer MMA inverters often have one of these and in TIG mode offer lift start instead of being 'true' scratch TIG

 

[MattF]

IIRC Miller introduced AC/DC rectifiers with HF (start for DCEN, continuous for AC) and started developing AC balance in the 1950s

Does that mean that the HF circuitry is constantly in circuit for AC use? Would a TIG torch maintain the arc on AC without additional circuitry, if running from the stick unit?

This subject seems to be becoming more and more confusing.

While MMA and TIG both use constant current supplies the volt-amp curves differ. This is one of things that the MMA/TIG switch changes explained in more depth here http://www.millerwelds.com/resources/articles/constant-current-CC-welder-training/

Cheers for that link.

 

[Bill Edwards]

My understanding is that you can't run AC without HF as each cycle (i.e the switch between torch positive and torch negative) will extinguish the arc. If trying to make it work off a buzzbox you'll be set at 50hz - which is 50 switches a second. The HF is always there to keep it going.

 

[MattF]

Now, HF overlay is touted to 'improve arc stability'. In my mind, using the specific word 'improve' means that it's still possible to do the same job without HF overlay, it'll just be a bit less stable.

What I'll do is find out, without referring to marketing leaflets and patent wording. Won't be tonight though.

Cheers. It'd be handy if you could test on that front. I'd know whether to delve deeper or not into that side of things then, depending on the outcome.

My understanding is that you can't run AC without HF as each cycle (i.e the switch between torch positive and torch negative) will extinguish the arc. If trying to make it work off a buzzbox you'll be set at 50hz - which is 50 switches a second. The HF is always there to keep it going.

It's beginning to look like I may have set myself off with a right old task, by becoming curious about this.

On a different point, when I get around to having a play with this, what would be a decent but cheap torch to use for testing purposes? No point spending too much on something which may get the slightly rough end of the stick and chopped and changed for testing with.

 

[MattF]

I just read that last message back and the last line reads much more argumentative than intended.

Nah. Merely blunt at worst.

 

[hotrodder]

Does that mean that the HF circuitry is constantly in circuit for AC use? Would a TIG torch maintain the arc on AC without additional circuitry, if running from the stick unit?

This subject seems to be becoming more and more confusing.

It depends on the kit. Rectifier/transformer based stuff always relies on constant HF for AC TIG. Even squarewave machines as while squarewave spends more time at the peak of the waveform it still can't switch fast enough to keep the arc 'lit' as it crosses 0. At least i've never seen or used one that only used HF start in AC... virtually all of them a continuous/start/off switch for the HF while some do this automatically (at least start/continuous) when selecting TIG/MMA and polarity etc

Inverter based kit switches a LOT faster because it uses witchcraft to 'cut up the leccy and rebuild it' and as a result inverter squarewave is 'squarer' than a rectifiers. Obviously not all inverters are created equal... cheapnese, Chinese, cutting edge stuff from one of the big names etc but pretty much all, if not all of them only use HF to initiate the arc in AC as they switch fast enough to keep the arc going reliably as it crosses 0

Lift start is a whole different thing to scratch start - scratch requires nothing more than the 'power' being there whereas lift needs control.

Now, HF overlay is touted to 'improve arc stability'. In my mind, using the specific word 'improve' means that it's still possible to do the same job without HF overlay, it'll just be a bit less stable.

What I'll do is find out, without referring to marketing leaflets and patent wording. Won't be tonight though.

Believe it or not some of us are actually speaking from personal experience not google i.e. we have tried it to see what happens etc. We have used a wide variety of kit from ancient to cheapnese to basic (for example AC buzzbox with an 'add on' HF box after finding out it doesn't work without it) to cutting edge and in many cases owned as well as used them

ETA, a few years back a mate of mine got himself a Murex transtig 352 (ESAB heliarc in disguise) and over the course of a few weeks i got multiple phone calls which involved me talking him through the front panel (again!) 'cause it wasn't working properly... favorites included him leaving the HF on continuous when in DCEN, forgetting it to switch it to continuous for AC etc and then calling to ask about the weird behaviour he got as a result

 

[MattF]

We have used a wide variety of kit from ancient to cheapnese to basic (for example AC buzzbox with an 'add on' HF box after finding out it doesn't work without it) to cutting edge and in many cases owned as well as used them

What were those add-on boxes called?

 

[Maker]

I just had a thought regarding the rectification, it won't be a constant voltage, it will be a 100Hz pulse with a sine waveform. Would this be a problem or could it be a good thing, controlling heat input and all that.
Maybe you could put a big capacitor across the output to smooth it?

 

[MattF]

A cap would definitely smooth it. As you mention though, not sure whether that would be a desirable thing or not.

Just been outside and grabbed myself a bit of light reading for tonight. Remembered that I have an old Lincoln Electric book: "Procedure of ARC welding; Design and practice". The thing's that thick it could be used as a doorstop. Only problem is that it's a 1937 book, so Heliarc probably won't have a mention.

 

[Maker]

What about a crap load of LM317 's in parallel connected to the output after the cap to get an even smoother output.

 

[MattF]

You make me wonder, sometimes. Muppet.

 

[hotrodder]

What were those add-on boxes called?

TIG HF add-on boxes or control boxes. Some that turn up used are brand specific in that they're designed for modular powersources and have specific umbilicals for communication. Others are generic for example http://www.newarc.co.uk/products/14-tig-300/ but i don't think they do an AC/DC version i.e. just HF start and gas solenoid/slope controls

Here's the thing, HF is obviously High Frequency. In agreement so far?

If it has a frequency higher than 1 it's AC (that's not 1Hz, that's just simply 1, partnered with 0 to switch DC on and off - as soon as 'Hz' comes into play you aren't playing DC any more).

I did actually cheat a little and asked the goigleator - I found a 'thing' which talked about "in the old days we were stuck with AC tig welding on 50 or 60 Hz because it was just transformed wall power" or words to that effect. The same document went on to say that a sine wave output doesn't need HF to maintain the arc, but square or triangle waveforms (from some inverters) do. It also mentioned about variable frequency and how the higher the frequency the tighter the arc is making comparisons betwixt 40Hz and 200Hz.

Off the top of my head typical numbers for TIG HF are a few thousand volts, very little amperage and hundreds of kilohertz IIRC? Pretty sure it's 5000V for my Lincoln v205t. The sentice i highlighted in bold... utter nonsense

Reading more of your post than just that snippet, I'm assuming that by 'rectifier' you are referring to a transformer/rectifier unit. Maybe my assumption is wrong, it wouldn't be the first time ever.

Yep, that's why i used the phrase rectifier/transformer in the paragraph above the one you quoted

Thing is, the only way you will ever get a squarewave out of a transformer is to feed a squarewave into it - even then it'll not be actually square because transformers don't like instant switched inputs. I've never seen a squarewave mains socket on any wall I've ever looked at.

Also, sticking a rectifier onto a transformer doesn't give you a squarewave either, what it gives you is rippled DC (more or less rippled depending on whether you're using a half wave, full wave or bridge rectifier). If you want anything near 'real' DC you need to smooth what comes out of the rectifier.

There are more than a few welding machine manufactuers that'd disagree with you as they've made/marketed squarewave transformer based machines for decades. Obviously there is more inside them than just a transformer and rectifier. As i said the 'squarewave' you get out of them isn't 'as square' as what you get from an inverter (miller call their inverters advanced squarewave) and the actual waveform of either of them won't look like the pretty little drawings in manuals. I don't have a clue how a squarewave transformer does its thing and as i said inverters use witchcraft. I have used a lot of different machines and am 99% confident that i could tell the difference between an old/basic sinewave machine like a Miller Econotwin or Cebora Uno, a squarewave transformer like a Miller Syncrowave or the aforementioned Murex/ESAB and an inverter in a blind test. Hell i could tell the difference between the AC arc from an advanced squarewave inverter and a transformer based machine by ear

ETA, http://www.millerwelds.com/pdf/spec_sheets/AD4-2.pdf note the pic that shows the HF start/continuous/off/lift start switch and the mention of squarewave being devopled in 1975
We're getting further away from the OPs initial subject but FWIW there are also some oddballs that don't fit the transformer vs inverter thing... Millers Aerowave is one http://www.millerwelds.com/pdf/spec_sheets/AD6-0.pdf replaced by inverters now

So what you're saying is that a DC source won't be able to start itself, it needs an HF unit - i.e. you need the HF AC to kick start it and then the DC self maintains after that.

Then, you say a buzz box won't work 'pure' because it's AC, so what you need is an HF addon to maintain the arc, so MOAR AC is what keeps the AC arc alight.

So, an actual question - have you tried to scratch start using an AC buzzbox 'pure' to weld aluminium and if so, how did you scratch, directly onto the aluminium?

I never said anything about a DC powersupply needing HF. Yep, trying to TIG weld from an AC buzzbox with a bottle of argon and a valved torch doesn't work properly. Yep, i have tried it, no it didn't work properly and no you don't scratch start on the aluminium part. Anyone that's ever done much TIG knows the various tricks associated with scratch TIG to avoid contaminating the tungsten and/or leaving arc marks
I've also tried to weld in AC with the HF set to start only (forgot the start/continuous/off switch as i'm more used to an inverter) multiple times. Soon remember when it won't maintain an arc, let alone a stable arc. I don't doubt with enough perserverance it's possible to stick some ally together. I do know the reasons why few if anyone bothers to try. Similar deal with TIG welding ally using DCEN & helium or DCEP and a huuuuuge tungsten... yeah it's possible but there's a VERY good reason why for 99% of applications/jobs everyone spends the ££££ on an AC/DC TIG or a decent MIG + (not always but a lot of the time) a push-pull gun or spool gun after being driven half made with birds nesting

 

[AndyStobbs]

Thought that might interest someone. Shows a voltage and current trace for HF initiation, up slope, constant current and down slope on my tig set. Voltage was inductive clamp so shows 0 except for the HF - its not designed to pick up small voltages.

 

[MattF]

Cheers for that link Hotrodder. You appear to have worked with most type of gear/variants out there, judging from your posts, so just thought I'd ask. Is this idea worth pursuing and playing around with, or is it likely to just cause more head scratching than its worth?

Btw, I have no problem with the topic straying. Info is info.

 

[hotrodder]

Personally i wouldn't bother, it ain't gonna work properly without an HF add on box and unless you can beg/borrow a valved TIG torch, bottle of argon, regulator etc it's gonna cost you over £100 to find that out. The cheapest of cheapnese TIGs bought second hand has much better odds of working.
Have you thought about oxy acetylene? Rent free bottles make keeping it about for occasional use much less expensive and there's still nothing that can touch it for versatility, it'll be nicer/quiter/more precise than carbon arc for heating & brazing more delicate stuff for a start. Granted learning to weld ally with oxyfuel ain't a walk in the park but it's difficulty is often exagerated IMO
Walk into most high end automotive coachwork/restoration shops and you'll find O/A is usually the weapon of choice- much less weld reinforcement than with MIG so instead of a grinding fest followed by filling all the pinholes the (softer) weld is planished and filed out instead dealing with distortion at the same time.

 

[Maker]

Oxyfuel does seem more your style Matt, what with you favouring a file over a grinder.

It's scary though, all the potential dangers, it doesn't sound like something to just buy and use without proper training first.

 

[MattF]

Aye, I've considered having oxy-acetylene, (else propane or oxy-propane), as I am fairly familiar with that method, although I haven't used it for donkeys. I just know I'd constantly be worrying about having gas tanks in the workshop. I'm bad enough triple checking that everything electrical is switched off. Can you imagine what I'd be like if I had gas tanks in there too?