AC (Alternating Current) and DC (Direct Current) is used to describe the polarity of the electric current that the welder generates and in what direction it travels. If you use the wrong polarity for a certain welding rod, your weld strength will not be very good.
The general terms associated with polarity are reverse polarity and straight polarity. These are common to the welding trade. Another way to describe the two terms are electrode positive and electrode negative. Electrode positive is the same as reverse polarity. Electrode negative is the same as straight polarity. Hence the + and the - written on your welder where the cables connect to it.
Any type of welding rod you buy will be labeled as to what polarity should be used for welding with it. Using the correct polarity will ensure the proper penetration and the over all look of the final bead.
If you use the wrong polarity you can tell by the signs. There will be an excessive amount of spatter, you will have bad penetration, and you will have less control of your arc.
Some welding machines have a switch to adjust the polarity. If your welder doesn't have one you will need to switch the welding cables around where they plug into the machine. If you want reverse polarity, you need to make sure the electrode holder is plugged into the + terminal.
The easiest way to tell if you are using the wrong polarity is by the sound and the feel of the weld you are laying down. If you don't have much experience with stick welding you will have a little more trouble determining the difference. I have seen guys weld all day long with the wrong polarity. Then I would grab their welder to use for couple of minutes and I could tell right away. It all comes down to experience.
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The only way to tig is to have your ground clamp hooked to the positive side of the welding machine. The negative lead will go to the tig torch. If it is reversed you will find out very quickly when you strike an arc. Most metals will be welded using this Polarity (straight). Most Aluminum TIG welding is performed using A C current.
MIG welding works only with reversed polarity, DC+, + at the torch. The reason is mostly the stability of the arc. Using DC- will result in a very unstable arc with lots of spatter.
smaw welding is sheilded metal arc welding
Gas Tungsten Arc Welding Gas Metal Arc Welding Flux Cored Arc Welding
SAW welding is a type of arc welding while ERW welding is spot or seam welding. SAW stand for submerged arc welding while ERW stands for electric resistance welding.