Classic Mustangs List Archive
Plasma/tig?
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., Online, USA
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., Online, USA
|
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., Online, USA
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This read-only message was archived from a public mail list.
Mail From: keven (Coates, Keven)
>I don't know enough to recognize one and not sure how to find
Out.
I'd think it would be in the owner's manual. Otherwise it's going to be
hit and miss.
>so I'd probably be better off just getting a better quality stand alone
plasma cutter and stick to my mig welder for a while.
There's nothing wrong with MIG for frame welding if you know how to do
it. The main problem with MIG is that you can make good looking welds
that have poor penetration and you won't know it until it breaks. I've
done this. Now I use a new heat setting method. Turn the heat all the
way up and regulate the wire (and weld) speed to regulate heat. I only
have a 90-100 amp MIG (which is what most of the 110V MIGs are if you
look into them), and this works well. The goal is to get as much heat
in the weld as you can without burning through. If you see the metal
start to get yellow all around the weld, stop and turn the wire speed
up. This will make you weld faster and the heat per unit area will go
down.
The key again, is to make sure you're melting the heck out of the metal
so you get good penetration. Obviously this only goes so far. For
sheet metal you've got to turn down the heat, but keep it as high as
possible.
>I also have an option of purchasing an unknown name tig welder off of a
robotics assembly line. It's a monster 3 phase 100% duty cycle water
cooled
thing for 2g.
Sounds great, but 3 phase is a pain and it's probably way more than you
need. 100% duty cycle is a very heavy duty unit as I'm sure you know.
For TIG you're into the more exotic machines, so the weld "power supply"
is often sold separately and you can mix and match torches. Most of the
connections in the good machines are fairly universal or easily
adaptable.
> I was worried about consumable for it also.
What you've got here is a weld power supply. You'd have to buy a new
torch since the robots use torches that seldom work for handheld use.
Good 150A torches with GND leads run about $120. Leads longer than 12'
cost more. Higher current torches cost a little more, but not much.
It's really more of a personal preference. Most people prefer a 150A
torch for most light work (steel ~5/16" or less and aluminum ~3/8" or
less). The light torch head and air cooling make for a nice flexible
line that's easy to move around a frame or pipes, etc. I've run my 150A
torch at 200A, but it gets hot fast.
>It's a 4 piece thing with water pump/tank/lines box, inverter(I think),
and two control box doodads with lights and pretty buttons and such.
There will be a power unit and one or two control units. One unit may
control the high frequency starting and inverter frequency. The other
may control the overall weld current control for starting and stopping
the weld. All these controls are nice, but not necessary for hand held
use. You can use the foot control to control your starting and stopping
current manually. It is nice to control inverter frequency. This makes
the arc more of a ray gun instead of a wandering lightning bolt. This
isn't possible on non-inverter sine wave units. On inverter units you
can adjust the "balance" as well, which I'll get into later.
>One control box has a gun and controller modified for a robotic arm
(missing the hose and peddle), the other for hand welding with a foot
peddle and such. The hose connection I think had water in it, not sure
why the hose would be cooled
It's a water cooled torch. Anything above 150A is typically water
cooled. This makes it possible to keep the torch small, but it still
increases the line weight and decreases flexibility. Water cooling
systems like this cost big bucks. Look on ebay, but the water cooling
radiator alone goes for $200 easy.
>Is there a way to turn it into a plasma cutter?
No. Plasma cutters are normally a completely different power supply.
They take 90V, and most TIG units can only output 15-25V. Unless it's
designed that way, it's not possible. You'd be better off starting from
scratch.
>How could I tell if one is DC only?
It's not easy sometimes, but the rule of thumb is that it's DC unless it
states that it can weld aluminum, or has a high frequency switch and an
AC setting somewhere. High frequency is the way they start welds on
most non-inverter AC units. It puts about 20KV-40KV on the torch to
start the arc.
Since the old sine wave transformer based (read "large"
machines switch
polarity so slowly (due to the sine wave shape), they need this high
voltage, high frequency power to continue the arc until the polarity
reverses and there's enough current to continue the arc. Inverter
machines use a square wave output and so they switch polarity so fast
they don't need high voltage, so they can start and continue the arc
easier using a number of different methods. Either way, the AC machines
always have an AC setting and their output lead bolts aren't marked +
and - like the DC machines are. Cheaper units (less than $1K new) are
almost always DC.
>I thought all tigs would pretty much weld anything depending on the
tip and gas used.
That's what I used to think too, but it's not true. Take the $200 TIG
from harbor freight. It's a cheap unit, but probably would be O.K. for
DC TIG welding on steel. It doesn't have much in the way of controls,
just a current knob. This is a dead giveaway. AC machines will have a
way of switching the output to AC (a knob or switch or something) and
will have at least two starting methods (usually high frequency and
scratch start). This $200 machine can only scratch start. You can get
the same results from a motor driven car alternator with a current
control. See DIY TIG on the web and you'll find a few people who have
built nice DC TIGs using this method.
DC TIG will weld anything but aluminum. Aluminum is a tricky one, since
it's always got an oxide built up on it. Aluminum oxide melts at 3x the
temp aluminum melts at, so you'll melt the base metal into a puddle
before the top of it will weld to anything! The reverse polarity part
of the weld (which usually happens during the reverse phase of the sine
wave) blasts the oxide away and then the phase reverses, putting more
heat into the metal.
This reverse polarity happens 50% of the time during the downward
(negative) phase of the sine wave, but inverter machines use square
waves and so can control the reverse polarity duty cycle. The more
expensive machines have a "balance" control that can alter the negative
phase from about 20% to 80%. This lets you tailor the cleaning and
welding action.
It's been said you can use reverse polarity DC to weld aluminum, but I
think this would be difficult, and is certainly not the norm.
For more TIG info, Miller has some great articles online. Check them
out. If you're going to spend this kind of money, it's good to know
what you're getting.
Keep in mind an argon cylinder will add to your costs. This is not
included with any new TIG and most used TIGs. About $150.
For a good AC TIG you need all these controls:
Current knob with foot control
Starting method (high frequency, scratch, or lift is even better)
Polarity switch
These are all great to have, but not essential:
Post flow (for gas "on" time after weld is done)
Lift start (inverter type fancy start method without high frequency)
Balance (for adjusting AC negative duty cycle)
Inverter frequency (for adjusting output square wave frequency on
inverter units)
Pulse frequency (slow on and off time for welding on thin materials)
High frequency intensity (for adjusting the arc for starting on
non-inverter units)
Keven
Mail From: keven (Coates, Keven)
>I don't know enough to recognize one and not sure how to find
Out.
I'd think it would be in the owner's manual. Otherwise it's going to be
hit and miss.
>so I'd probably be better off just getting a better quality stand alone
plasma cutter and stick to my mig welder for a while.
There's nothing wrong with MIG for frame welding if you know how to do
it. The main problem with MIG is that you can make good looking welds
that have poor penetration and you won't know it until it breaks. I've
done this. Now I use a new heat setting method. Turn the heat all the
way up and regulate the wire (and weld) speed to regulate heat. I only
have a 90-100 amp MIG (which is what most of the 110V MIGs are if you
look into them), and this works well. The goal is to get as much heat
in the weld as you can without burning through. If you see the metal
start to get yellow all around the weld, stop and turn the wire speed
up. This will make you weld faster and the heat per unit area will go
down.
The key again, is to make sure you're melting the heck out of the metal
so you get good penetration. Obviously this only goes so far. For
sheet metal you've got to turn down the heat, but keep it as high as
possible.
>I also have an option of purchasing an unknown name tig welder off of a
robotics assembly line. It's a monster 3 phase 100% duty cycle water
cooled
thing for 2g.
Sounds great, but 3 phase is a pain and it's probably way more than you
need. 100% duty cycle is a very heavy duty unit as I'm sure you know.
For TIG you're into the more exotic machines, so the weld "power supply"
is often sold separately and you can mix and match torches. Most of the
connections in the good machines are fairly universal or easily
adaptable.
> I was worried about consumable for it also.
What you've got here is a weld power supply. You'd have to buy a new
torch since the robots use torches that seldom work for handheld use.
Good 150A torches with GND leads run about $120. Leads longer than 12'
cost more. Higher current torches cost a little more, but not much.
It's really more of a personal preference. Most people prefer a 150A
torch for most light work (steel ~5/16" or less and aluminum ~3/8" or
less). The light torch head and air cooling make for a nice flexible
line that's easy to move around a frame or pipes, etc. I've run my 150A
torch at 200A, but it gets hot fast.
>It's a 4 piece thing with water pump/tank/lines box, inverter(I think),
and two control box doodads with lights and pretty buttons and such.
There will be a power unit and one or two control units. One unit may
control the high frequency starting and inverter frequency. The other
may control the overall weld current control for starting and stopping
the weld. All these controls are nice, but not necessary for hand held
use. You can use the foot control to control your starting and stopping
current manually. It is nice to control inverter frequency. This makes
the arc more of a ray gun instead of a wandering lightning bolt. This
isn't possible on non-inverter sine wave units. On inverter units you
can adjust the "balance" as well, which I'll get into later.
>One control box has a gun and controller modified for a robotic arm
(missing the hose and peddle), the other for hand welding with a foot
peddle and such. The hose connection I think had water in it, not sure
why the hose would be cooled
It's a water cooled torch. Anything above 150A is typically water
cooled. This makes it possible to keep the torch small, but it still
increases the line weight and decreases flexibility. Water cooling
systems like this cost big bucks. Look on ebay, but the water cooling
radiator alone goes for $200 easy.
>Is there a way to turn it into a plasma cutter?
No. Plasma cutters are normally a completely different power supply.
They take 90V, and most TIG units can only output 15-25V. Unless it's
designed that way, it's not possible. You'd be better off starting from
scratch.
>How could I tell if one is DC only?
It's not easy sometimes, but the rule of thumb is that it's DC unless it
states that it can weld aluminum, or has a high frequency switch and an
AC setting somewhere. High frequency is the way they start welds on
most non-inverter AC units. It puts about 20KV-40KV on the torch to
start the arc.
Since the old sine wave transformer based (read "large"
machines switchpolarity so slowly (due to the sine wave shape), they need this high
voltage, high frequency power to continue the arc until the polarity
reverses and there's enough current to continue the arc. Inverter
machines use a square wave output and so they switch polarity so fast
they don't need high voltage, so they can start and continue the arc
easier using a number of different methods. Either way, the AC machines
always have an AC setting and their output lead bolts aren't marked +
and - like the DC machines are. Cheaper units (less than $1K new) are
almost always DC.
>I thought all tigs would pretty much weld anything depending on the
tip and gas used.
That's what I used to think too, but it's not true. Take the $200 TIG
from harbor freight. It's a cheap unit, but probably would be O.K. for
DC TIG welding on steel. It doesn't have much in the way of controls,
just a current knob. This is a dead giveaway. AC machines will have a
way of switching the output to AC (a knob or switch or something) and
will have at least two starting methods (usually high frequency and
scratch start). This $200 machine can only scratch start. You can get
the same results from a motor driven car alternator with a current
control. See DIY TIG on the web and you'll find a few people who have
built nice DC TIGs using this method.
DC TIG will weld anything but aluminum. Aluminum is a tricky one, since
it's always got an oxide built up on it. Aluminum oxide melts at 3x the
temp aluminum melts at, so you'll melt the base metal into a puddle
before the top of it will weld to anything! The reverse polarity part
of the weld (which usually happens during the reverse phase of the sine
wave) blasts the oxide away and then the phase reverses, putting more
heat into the metal.
This reverse polarity happens 50% of the time during the downward
(negative) phase of the sine wave, but inverter machines use square
waves and so can control the reverse polarity duty cycle. The more
expensive machines have a "balance" control that can alter the negative
phase from about 20% to 80%. This lets you tailor the cleaning and
welding action.
It's been said you can use reverse polarity DC to weld aluminum, but I
think this would be difficult, and is certainly not the norm.
For more TIG info, Miller has some great articles online. Check them
out. If you're going to spend this kind of money, it's good to know
what you're getting.
Keep in mind an argon cylinder will add to your costs. This is not
included with any new TIG and most used TIGs. About $150.
For a good AC TIG you need all these controls:
Current knob with foot control
Starting method (high frequency, scratch, or lift is even better)
Polarity switch
These are all great to have, but not essential:
Post flow (for gas "on" time after weld is done)
Lift start (inverter type fancy start method without high frequency)
Balance (for adjusting AC negative duty cycle)
Inverter frequency (for adjusting output square wave frequency on
inverter units)
Pulse frequency (slow on and off time for welding on thin materials)
High frequency intensity (for adjusting the arc for starting on
non-inverter units)
Keven
|
., Online, USA
|
This read-only message was archived from a public mail list.
Mail From: chrisstephens (Chris Stephens)
Thanks again Keven.
Looks like I have some reading to do on welding before I get a tig. I may
end up just going to the local Halox, give them my wallet, and say I want a
reasonibly priced plasma cutter. I don't need to spend that much but I hate
getting home with Micky Mouse junk that will barely work.
I'm reasonably good with my mig considering I never had training. I
purchased the biggest 220 volt that Home Depot had at the time I decided I
wanted one and just went at it. I've built a few cars now and do some custom
stuff as a hobby. I mostly use a grinder and cut of wheel to cut everything
right now. I also have a small sheetmetal brake and cheepo bead roller but
the cutting dies on it are almost useless.
Chris
Coates, Keven wrote:
>> I don't know enough to recognize one and not sure how to find
> Out.
>
> I'd think it would be in the owner's manual. Otherwise it's going to
> be hit and miss.
>
>> so I'd probably be better off just getting a better quality stand
>> alone
>
> plasma cutter and stick to my mig welder for a while.
>
> There's nothing wrong with MIG for frame welding if you know how to do
> it. The main problem with MIG is that you can make good looking welds
> that have poor penetration and you won't know it until it breaks. I've
> done this. Now I use a new heat setting method. Turn the heat all
> the way up and regulate the wire (and weld) speed to regulate heat.
> I only have a 90-100 amp MIG (which is what most of the 110V MIGs are
> if you look into them), and this works well. The goal is to get as
> much heat in the weld as you can without burning through. If you see
> the metal start to get yellow all around the weld, stop and turn the
> wire speed up. This will make you weld faster and the heat per unit
> area will go down.
>
> The key again, is to make sure you're melting the heck out of the
> metal so you get good penetration. Obviously this only goes so far.
> For sheet metal you've got to turn down the heat, but keep it as high
> as possible.
>
>> I also have an option of purchasing an unknown name tig welder off
>> of a
>
> robotics assembly line. It's a monster 3 phase 100% duty cycle water
> cooled
> thing for 2g.
>
> Sounds great, but 3 phase is a pain and it's probably way more than
> you need. 100% duty cycle is a very heavy duty unit as I'm sure you
> know. For TIG you're into the more exotic machines, so the weld
> "power supply" is often sold separately and you can mix and match
> torches. Most of the connections in the good machines are fairly
> universal or easily adaptable.
>
>> I was worried about consumable for it also.
>
> What you've got here is a weld power supply. You'd have to buy a new
> torch since the robots use torches that seldom work for handheld use.
> Good 150A torches with GND leads run about $120. Leads longer than
> 12' cost more. Higher current torches cost a little more, but not
> much. It's really more of a personal preference. Most people prefer
> a 150A torch for most light work (steel ~5/16" or less and aluminum
> ~3/8" or less). The light torch head and air cooling make for a nice
> flexible line that's easy to move around a frame or pipes, etc. I've
> run my 150A torch at 200A, but it gets hot fast.
>
>> It's a 4 piece thing with water pump/tank/lines box, inverter(I
>> think),
> and two control box doodads with lights and pretty buttons and such.
>
> There will be a power unit and one or two control units. One unit may
> control the high frequency starting and inverter frequency. The other
> may control the overall weld current control for starting and stopping
> the weld. All these controls are nice, but not necessary for hand
> held use. You can use the foot control to control your starting and
> stopping current manually. It is nice to control inverter frequency.
> This makes the arc more of a ray gun instead of a wandering lightning
> bolt. This isn't possible on non-inverter sine wave units. On
> inverter units you can adjust the "balance" as well, which I'll get
> into later.
>
>> One control box has a gun and controller modified for a robotic arm
> (missing the hose and peddle), the other for hand welding with a foot
> peddle and such. The hose connection I think had water in it, not sure
> why the hose would be cooled
>
> It's a water cooled torch. Anything above 150A is typically water
> cooled. This makes it possible to keep the torch small, but it still
> increases the line weight and decreases flexibility. Water cooling
> systems like this cost big bucks. Look on ebay, but the water cooling
> radiator alone goes for $200 easy.
>
>> Is there a way to turn it into a plasma cutter?
>
> No. Plasma cutters are normally a completely different power supply.
> They take 90V, and most TIG units can only output 15-25V. Unless it's
> designed that way, it's not possible. You'd be better off starting
> from scratch.
>
>> How could I tell if one is DC only?
>
> It's not easy sometimes, but the rule of thumb is that it's DC unless
> it states that it can weld aluminum, or has a high frequency switch
> and an AC setting somewhere. High frequency is the way they start
> welds on most non-inverter AC units. It puts about 20KV-40KV on the
> torch to start the arc.
>
> Since the old sine wave transformer based (read "large" machines
> switch polarity so slowly (due to the sine wave shape), they need
> this high voltage, high frequency power to continue the arc until the
> polarity reverses and there's enough current to continue the arc.
> Inverter machines use a square wave output and so they switch
> polarity so fast they don't need high voltage, so they can start and
> continue the arc easier using a number of different methods. Either
> way, the AC machines always have an AC setting and their output lead
> bolts aren't marked + and - like the DC machines are. Cheaper units
> (less than $1K new) are almost always DC.
>
>> I thought all tigs would pretty much weld anything depending on the
> tip and gas used.
>
> That's what I used to think too, but it's not true. Take the $200 TIG
> from harbor freight. It's a cheap unit, but probably would be O.K.
> for DC TIG welding on steel. It doesn't have much in the way of
> controls, just a current knob. This is a dead giveaway. AC machines
> will have a way of switching the output to AC (a knob or switch or
> something) and will have at least two starting methods (usually high
> frequency and scratch start). This $200 machine can only scratch
> start. You can get the same results from a motor driven car
> alternator with a current control. See DIY TIG on the web and you'll
> find a few people who have built nice DC TIGs using this method.
>
> DC TIG will weld anything but aluminum. Aluminum is a tricky one,
> since it's always got an oxide built up on it. Aluminum oxide melts
> at 3x the temp aluminum melts at, so you'll melt the base metal into
> a puddle before the top of it will weld to anything! The reverse
> polarity part of the weld (which usually happens during the reverse
> phase of the sine wave) blasts the oxide away and then the phase
> reverses, putting more heat into the metal.
>
> This reverse polarity happens 50% of the time during the downward
> (negative) phase of the sine wave, but inverter machines use square
> waves and so can control the reverse polarity duty cycle. The more
> expensive machines have a "balance" control that can alter the
> negative phase from about 20% to 80%. This lets you tailor the
> cleaning and welding action.
>
> It's been said you can use reverse polarity DC to weld aluminum, but I
> think this would be difficult, and is certainly not the norm.
>
> For more TIG info, Miller has some great articles online. Check them
> out. If you're going to spend this kind of money, it's good to know
> what you're getting.
>
> Keep in mind an argon cylinder will add to your costs. This is not
> included with any new TIG and most used TIGs. About $150.
>
> For a good AC TIG you need all these controls:
> Current knob with foot control
> Starting method (high frequency, scratch, or lift is even better)
> Polarity switch
>
> These are all great to have, but not essential:
> Post flow (for gas "on" time after weld is done)
> Lift start (inverter type fancy start method without high frequency)
> Balance (for adjusting AC negative duty cycle)
> Inverter frequency (for adjusting output square wave frequency on
> inverter units)
> Pulse frequency (slow on and off time for welding on thin materials)
> High frequency intensity (for adjusting the arc for starting on
> non-inverter units)
>
> Keven
> _______________________________________________
> Classic-mustangs mailing list
> Classic-mustangs at lists.twistedpair.ca
> lists.twistedpair.ca/mailman/listinfo.cgi/classic-mustangs
>
> Visit the Classic Mustang Wiki! sauce.donair.org/~cm/
Mail From: chrisstephens (Chris Stephens)
Thanks again Keven.
Looks like I have some reading to do on welding before I get a tig. I may
end up just going to the local Halox, give them my wallet, and say I want a
reasonibly priced plasma cutter. I don't need to spend that much but I hate
getting home with Micky Mouse junk that will barely work.
I'm reasonably good with my mig considering I never had training. I
purchased the biggest 220 volt that Home Depot had at the time I decided I
wanted one and just went at it. I've built a few cars now and do some custom
stuff as a hobby. I mostly use a grinder and cut of wheel to cut everything
right now. I also have a small sheetmetal brake and cheepo bead roller but
the cutting dies on it are almost useless.
Chris
Coates, Keven wrote:
>> I don't know enough to recognize one and not sure how to find
> Out.
>
> I'd think it would be in the owner's manual. Otherwise it's going to
> be hit and miss.
>
>> so I'd probably be better off just getting a better quality stand
>> alone
>
> plasma cutter and stick to my mig welder for a while.
>
> There's nothing wrong with MIG for frame welding if you know how to do
> it. The main problem with MIG is that you can make good looking welds
> that have poor penetration and you won't know it until it breaks. I've
> done this. Now I use a new heat setting method. Turn the heat all
> the way up and regulate the wire (and weld) speed to regulate heat.
> I only have a 90-100 amp MIG (which is what most of the 110V MIGs are
> if you look into them), and this works well. The goal is to get as
> much heat in the weld as you can without burning through. If you see
> the metal start to get yellow all around the weld, stop and turn the
> wire speed up. This will make you weld faster and the heat per unit
> area will go down.
>
> The key again, is to make sure you're melting the heck out of the
> metal so you get good penetration. Obviously this only goes so far.
> For sheet metal you've got to turn down the heat, but keep it as high
> as possible.
>
>> I also have an option of purchasing an unknown name tig welder off
>> of a
>
> robotics assembly line. It's a monster 3 phase 100% duty cycle water
> cooled
> thing for 2g.
>
> Sounds great, but 3 phase is a pain and it's probably way more than
> you need. 100% duty cycle is a very heavy duty unit as I'm sure you
> know. For TIG you're into the more exotic machines, so the weld
> "power supply" is often sold separately and you can mix and match
> torches. Most of the connections in the good machines are fairly
> universal or easily adaptable.
>
>> I was worried about consumable for it also.
>
> What you've got here is a weld power supply. You'd have to buy a new
> torch since the robots use torches that seldom work for handheld use.
> Good 150A torches with GND leads run about $120. Leads longer than
> 12' cost more. Higher current torches cost a little more, but not
> much. It's really more of a personal preference. Most people prefer
> a 150A torch for most light work (steel ~5/16" or less and aluminum
> ~3/8" or less). The light torch head and air cooling make for a nice
> flexible line that's easy to move around a frame or pipes, etc. I've
> run my 150A torch at 200A, but it gets hot fast.
>
>> It's a 4 piece thing with water pump/tank/lines box, inverter(I
>> think),
> and two control box doodads with lights and pretty buttons and such.
>
> There will be a power unit and one or two control units. One unit may
> control the high frequency starting and inverter frequency. The other
> may control the overall weld current control for starting and stopping
> the weld. All these controls are nice, but not necessary for hand
> held use. You can use the foot control to control your starting and
> stopping current manually. It is nice to control inverter frequency.
> This makes the arc more of a ray gun instead of a wandering lightning
> bolt. This isn't possible on non-inverter sine wave units. On
> inverter units you can adjust the "balance" as well, which I'll get
> into later.
>
>> One control box has a gun and controller modified for a robotic arm
> (missing the hose and peddle), the other for hand welding with a foot
> peddle and such. The hose connection I think had water in it, not sure
> why the hose would be cooled
>
> It's a water cooled torch. Anything above 150A is typically water
> cooled. This makes it possible to keep the torch small, but it still
> increases the line weight and decreases flexibility. Water cooling
> systems like this cost big bucks. Look on ebay, but the water cooling
> radiator alone goes for $200 easy.
>
>> Is there a way to turn it into a plasma cutter?
>
> No. Plasma cutters are normally a completely different power supply.
> They take 90V, and most TIG units can only output 15-25V. Unless it's
> designed that way, it's not possible. You'd be better off starting
> from scratch.
>
>> How could I tell if one is DC only?
>
> It's not easy sometimes, but the rule of thumb is that it's DC unless
> it states that it can weld aluminum, or has a high frequency switch
> and an AC setting somewhere. High frequency is the way they start
> welds on most non-inverter AC units. It puts about 20KV-40KV on the
> torch to start the arc.
>
> Since the old sine wave transformer based (read "large"
machines> switch polarity so slowly (due to the sine wave shape), they need
> this high voltage, high frequency power to continue the arc until the
> polarity reverses and there's enough current to continue the arc.
> Inverter machines use a square wave output and so they switch
> polarity so fast they don't need high voltage, so they can start and
> continue the arc easier using a number of different methods. Either
> way, the AC machines always have an AC setting and their output lead
> bolts aren't marked + and - like the DC machines are. Cheaper units
> (less than $1K new) are almost always DC.
>
>> I thought all tigs would pretty much weld anything depending on the
> tip and gas used.
>
> That's what I used to think too, but it's not true. Take the $200 TIG
> from harbor freight. It's a cheap unit, but probably would be O.K.
> for DC TIG welding on steel. It doesn't have much in the way of
> controls, just a current knob. This is a dead giveaway. AC machines
> will have a way of switching the output to AC (a knob or switch or
> something) and will have at least two starting methods (usually high
> frequency and scratch start). This $200 machine can only scratch
> start. You can get the same results from a motor driven car
> alternator with a current control. See DIY TIG on the web and you'll
> find a few people who have built nice DC TIGs using this method.
>
> DC TIG will weld anything but aluminum. Aluminum is a tricky one,
> since it's always got an oxide built up on it. Aluminum oxide melts
> at 3x the temp aluminum melts at, so you'll melt the base metal into
> a puddle before the top of it will weld to anything! The reverse
> polarity part of the weld (which usually happens during the reverse
> phase of the sine wave) blasts the oxide away and then the phase
> reverses, putting more heat into the metal.
>
> This reverse polarity happens 50% of the time during the downward
> (negative) phase of the sine wave, but inverter machines use square
> waves and so can control the reverse polarity duty cycle. The more
> expensive machines have a "balance" control that can alter the
> negative phase from about 20% to 80%. This lets you tailor the
> cleaning and welding action.
>
> It's been said you can use reverse polarity DC to weld aluminum, but I
> think this would be difficult, and is certainly not the norm.
>
> For more TIG info, Miller has some great articles online. Check them
> out. If you're going to spend this kind of money, it's good to know
> what you're getting.
>
> Keep in mind an argon cylinder will add to your costs. This is not
> included with any new TIG and most used TIGs. About $150.
>
> For a good AC TIG you need all these controls:
> Current knob with foot control
> Starting method (high frequency, scratch, or lift is even better)
> Polarity switch
>
> These are all great to have, but not essential:
> Post flow (for gas "on" time after weld is done)
> Lift start (inverter type fancy start method without high frequency)
> Balance (for adjusting AC negative duty cycle)
> Inverter frequency (for adjusting output square wave frequency on
> inverter units)
> Pulse frequency (slow on and off time for welding on thin materials)
> High frequency intensity (for adjusting the arc for starting on
> non-inverter units)
>
> Keven
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> Classic-mustangs at lists.twistedpair.ca
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>
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