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Thread: More on MIG selection
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18th January 2006, 09:34 AM #1
More on MIG selection
Gas Metal Arc Welding (MIG) This process consists of feeding a bare metal filler wire made of the same material being welded--in conjunction with a shielding gas through a hand held torch unit. The welding wire picks up electric current supplied by a standard power source. On contact, it creates an arc that does the welding.
As wire is fed from the unit to the work, it functions as a continuous, consumable electrode, therefore requiring fewer starts and stops.
For routine joining applications, a MIG welder probably offers more advantages than any other welding process. Here's some advantages of MIG welding:
• It's the easiest welding process to learn. With a little practice, even a first-time MIG user can achieve a good-looking weld.
• Welds light gauge material or thick plate (with multiple passes).
• Welds all common metals_carbon steel, stainless steel and aluminum.
• Welding can be done in all positions, including overhead.
• There is no need to remove flux, as the shielding is provided by a gas.
• High welding speeds can be obtained_up to four times faster than stick welding_reducing repair or fabrication time.
A power supply that gives direct current reverse polarity (DCRP) is recommended for use with the MIG welding process. Generally, (stick ) welders use straight polarity current, which means the flow of electricity moves from the torch to the workpiece. In reverse polarity welding, current travels from the workpiece to the welding torch. For MIG welding, a DCRP current produces the best arc transfer and a smoother weld surface than other types of currents.
Special consideration is required when welding outdoors or in drafty areas with a MIG welder because air or drafts can blow the shielding gas from the weld puddle and cause porosity. The MIG welding process also requires more complex equipment, which is initially more costly. The following equipment and supplies are necessary for MIG welding:
• A power supply and welding cables,
• An electrode wire feeder/MIG welding gun system, and
• A gas cylinder with 75 percent argon and 25 percent CO2, plus hoses and regulators.
The same constant voltage equipment used for MIG welding also performs flux cored welding. The difference is the wire that is used as an electrode. Rather than running a solid wire coupled with a shielding gas, flux cored welding uses self shielded wire with flux inside (some flux cored wires require a shielding gas).
Cored wires are generally used on thicker material (4 mm and up) than the solid wires used with the MIG process. Advantages of flux cored welding are:
• Less affected by drafts, so better suited for outdoor work.
• Works as well as stick welding on rusty or dirty material.
• Continuous wire feed, which minimizes starts and stops.
• Deep penetration for welding thick sections.
• Increased metal deposition (two or three times that of stick welding
Porosity is a problem for welders. It often occurs in drafty areas when welding with a shielding gas. This difficulty can be overcome by using self shielded, flux cored wire. It performs similarly to a stick welder in such conditions so windy conditions are less detrimental on the weld. (Note this requires a machine where the polarity can be switched – if you intend to do this buy a model that can perform both functions are some are fixed on one process)
Importantly, the material used to fill flux cored wires can be custom formulated to match the base metal, which helps produce a better weld. This can also make flux cored welding less sensitive to rust and scale on the welded piece than other processes.
Between its MIG and flux cored capabilities, a wire welder can perform most tasks a stick welder can do, and often more efficiently. While a good quality wire welder costs $1000 to $4,000 (depending on its size), the costs for consumables (wire and gas) are less than that for stick welding rods. Coupled with the ability to weld aluminum and sheet metal, a wire welder can pay for itself very quickly. (note I said sheet metal -not aluminium sheet. Take a MIG to most tinnies ( small aluminium boats of 3mm metal thickness and less) and you are liable to end up with more holes than boat.
Other considerations for welding alumininium is that pure argon shielding gas is required and the torch gun assembly supplied for welding steel is poorly suited to running aluminium wire as the wire is soft and “pushed” up the gun/torch assembly made for steel wire. There are dedicated aluminium”mig” welding torches,but they are specialised beasts and accordingly they are priced at a level making them inaccessible to most handyman welders.
- still more to come on setting up and welding
cheers
Grahame
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18th January 2006 09:34 AM # ADSGoogle Adsense Advertisement
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19th January 2006, 03:50 AM #2
This is GREAT Colin - keep it coming.
The system won't let me give you any more Greenies at the moment.
So here some of these ones.
Your advice and clear presentation is very much appreciated.
Interwood
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19th January 2006, 10:45 AM #3
Graham
You should get paid for these posts, however you'll have to make do with our gratitude.Bodgy
"Is it not enough simply to be able to appreciate the beauty of the garden without it being necessary to believe that there are faeries at the bottom of it? " Douglas Adams
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20th January 2006, 10:40 PM #4
Its a pleasure to help
Thanks for the kind words,
I think its only fair I should pay you fellas back the help I have from forum members in my wood butchering efforts.
I will post a new section on setting the GMAW machine up to weld when I am feeling a bit more able.I have got a touch of carpal tunnel and my right arm is giving me pigs rrrs.
Give us a week or two.
At least time to get over the shock of class loads of new cherubs to teach.
Grahame
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21st January 2006, 05:50 PM #5
What happen to my reply:confused:
Excellent work HD
So what welds thin ally?
Are liners for the hoses storagble, so change when doing ss, then Ally, then steel?
The regs for the gas bottles are they different for the different gases?
Thanks
Pulpo
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22nd January 2006, 12:43 AM #6
Pulpo's Answer
What happened to your reply-
I have no idea,
What welds thin ally?
Below 2mm thickness Tigs the go.Short answer is that small single phase units can weld aluminium but not very well. Take a look at welds on an aluminium tinny.Some of them are acceptable but only just. A home machine just can't achieve what a factory 3 phase machine can.
Are liners etc storable ?
Yes they can be exchanged time and again- but Mig driver wheels and ancillarry gear would have to be cleaned each time.
Regs ( and flow meter) for cylinders( beer comes in bottles) can be used on argon and argoshield mixes.Cylinders have up to 2000 psi of pressure.
Hope it helps
Grahame
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30th March 2006, 09:52 PM #7SENIOR MEMBER
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Originally Posted by Grahame Collins
I was very interested to read the above part mentioned reply. I am presently thinking of buying a AC/DC TIG unit but only a 10/15A (240V). The only AC Tig units I've used previously were 3 phase.
Why is it that the AC welding doesn't work so well on the smaller voltage please?. Is this also true of a DC Tig?.
Thanking you in advance of your reply.
Cheers
David
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31st March 2006, 12:20 AM #8GOLD MEMBER
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Single phase AC is a problem for all welding. This is caused by the sine wave going through a null period when in effect the arc stops momentarily. On 3 phase the current is continuous. If you can't afford a new 3 phase unit buy a used one. You will be rewarded with welder that is far easier to use. I have done just that with a MIG. I bought a used Esab 3 phase and it is a beautiful machine to use.
CHRIS
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31st March 2006, 06:41 AM #9
I remember way back in an intro to welding course at RMIT that the way TIG works on aluminium is one cycle of AC heats the metal, then the other rips off the oxide layer. ie the torch's polarity is reversing all the time.
To go from one cycle to the other requires crossing zero. It is Alternating Current after all.
Using DC on aluminium was demonstated.
One polarity heated the tungsten tip (bad) and did stuff all to the aluminium (to the naked eye).
The other polarity heated the aluminium, but the oxide layer persisted making it impossible to weld. End result a pool of useless molten metal where you used to have something useful.
With AC, you alternately heat, then rip off the oxide layer, successful welding results.
So if the current is continuous, it is in fact DC, and cannot be used to weld aluminium from my understanding.
What I can accept is that 3 phase will keep an internal capacitor more fully charged, allowing an inverter to run without hiccups.
The AC function is there by action of the inverter, but it's supply is much more stable thus giving a smoother arc. The AC from the inverter will be much higher frequency than the mains AC too, improving strikability.Ray
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31st March 2006, 07:11 PM #10SENIOR MEMBER
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Thanks Chris & Ray for your replies. Given that 3 phase maybe the way to go if I want AC Tig then I will have to get it installed. Given that I want this installed in my shed at home (residential) are there people (e.g. council, electrical company etc) that I have to get in touch with in order to get permission to do this?.
Secondly, would anyone have any idea (apart from alot:eek: ) how much it will cost to have 3 phase fitted and do I have to seek a special type of electrician to install it?.
I would also appreciate any other advice you this I should be made aware of about installing 3 phase?.
Thanking those in advance of their reply.
Cheers
David
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1st April 2006, 08:46 AM #11Originally Posted by Metal Head
It is worth it though. Once you have it you enter a new market where you can buy three phase machinery relatively cheaply. I bought a 200amp three-phase CIG MIG with traveller, two torches and a good roll of wire for $200.00, and it's been a gem. On Ebay during the week I bought a 2.2KW induction motor for $27.00, and so on....
You also enter a world of power. For instance, my stick welder runs up to 300 amps, and I bought a 10HP rip saw on Ebay that literally weighs a tonne. Because of this power, as Grahame has pointed out, three phase welders just seem to weld better. You can feel the smoothness the first time you use them.
If only I could actually weld, I'd be really happy (keep writing Grahame, I'm listening!). :confused:
If you need to justify it, just remember that once installed it can also be used for three-phase air conditioners with the power to run ducting through the house.
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1st April 2006, 12:55 PM #12
David,
wander out onto the street (if you have overhead powerlines) and count the wires running past your house. If there's four (3 phases and neutral) then you're fine. If you don't (and some areas don't) then unless you spend a lot of money, you're stuffed. If the power in your area is underground then you need to talk to the supply authority.
Mick"If you need a machine today and don't buy it,
tomorrow you will have paid for it and not have it."
- Henry Ford 1938
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1st April 2006, 04:38 PM #13
Sorry people,been off line for a time.
Originally Posted by Metal Head
What you are looking for, of course, is one that turns up when on time and on the day he said he would.
You can get caught with Tig too, if you are intending bigtime on the aluminium welding route .The torch will heat rapidly and unless you intend on welding for 3 mins and cooling for 10, avoid the air cooled torch.From what I have seen in industry ,the pros all use water cooled torches.
Another way around it may be to go to a A Fronious AC/DC unit.Yes they are very expensive but may well be under the set up cost of 3 phase.Once again I stress - air cooled torch.
The other side of the argument as noted by Ross Luck was the very cheap price good second hand 3 phase gear can be had for.In any case if you feel the ally work would justify it go for the water cooled torch.
Thats my two o bob's worth today
Grahame
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