What does a high frequency box do?

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Hello all,           So I just got a miller big 40 and I need to hook a mig up to it. It is not cc/cv only cc. So what would a high frequency box do, I've searched and searched but have gotten no straight answer. Does it give a DC machine AC? Does it create a cv current?           And I have found a nice ln-25 Lincoln for just the right price, so how well would that work on my welder? Would it do the job of fabricating and laying a pretty decent bead? Is it something I could do certifiable work with? Is it pretty limited to certain mig processes or can it do them all?       Thanks for the help in advance-Jordan
Reply:Superimposes high voltage pulses onto the weld lead which is capable of arcing through the air giving you the ability to strike an arc without electrode to work contact. Once the air is ionized and an arc forms the large weld current can pass through and you're welding. Used for arc starts in TIG, or continuously used on older tig sine wave machines to help keep the arc lit when welding aluminum with A/C. not really needed or often used for stick.Welding/Fab Pics: www.UtahWeld.com
Reply:And won't do anything for mig.GravelThe difference between theory and practice is that in theory there is no difference.
Reply:A hf box is no good for mig. In fact if I remember correctly trying to run a VS feeder in CC mode off a power source with HF on is a good way to destroy your VS feeder.The good news is an LN 25 will work off a CC only power source. The bad news is it won't run well in short arc with solid wire which is what most people think of when they think of "mig". A VS feeder like an LN25, Hobart Hefty, Miller S32P or 8VS/12VS mimics CV by changing the wire speed constantly while welding versus the constant wire speed you usually use when running mig off a CV power source. The problem is in short arc at low power settings the feeder can not respond fast enough to give you a consistent arc. That changes as you up the power and move into spray mode. Now the wire tends to want to melt at a consistent distance from the work and the feeder doesn't have to make as drastic a change in wire speed constantly. It works well with FC wires that go into spray at lower voltages. However spray mig is a hot process and is poorly suited for out of position welds like vertical and overhead because it's so fluid and because it's so hot it's not a good choice for thin steel. 1/4" and up is usually a good range for spray mig, though it is doable down to 1/8" with practice..No government ever voluntarily reduces itself in size. Government programs, once launched, never disappear. Actually, a government bureau is the nearest thing to eternal life we'll ever see on this earth! Ronald Reagan
Reply:Mike said it all. A low voltage arc can't start until the gas between tungsten and grounded workpiece is ionized, ( atoms made unstable by a differing number of electrons and protons), the very high voltage of the HF (maybe 1200 volts) with a widely ranging frequency in the thousands will arc much farther than welding current. The HF maintains ionization while sine wave welding power (low voltage/ high current) starts and stops 120 times a second. Aluminum welding wouldn't work as well without HF. The Electrode negative half of the cycle starts reasonably well from a pointed tungsten electrode nearly free of non conductive contaminants. On the return stroke, (EP) electrons have a tough time initiating an arc from a surface much more diffuse, effectively insulated from ionizing the gas. HF helps. I've never heard of HF in welding except in TIG welding.
Reply:Originally Posted by Mr. Chainsaw          So I just got a miller big 40 and I need to hook a mig up to it. It is not cc/cv only cc. So what would a high frequency box do, I've searched and searched but have gotten no straight answer. Does it give a DC machine AC? Does it create a cv current?