Are You Running the Right Contact Tip?

[Allen]

How many of you pay attention to the contact tip of your GMAW welding gun?

Is it merely an afterthought? How do you know which length contact tip buy and use?

Incorrect contact tip recess inside of the weld nozzle can cause extreme problems at both ends of the weld spectrum; poor penetration and excessive weld spatter, burn through and excessive warping, even porosity. In addition to these common problems, using the incorrect tip can also make laying down a good bead difficult, or even impossible, no matter how good you or your equipment is.

Most fixed length contact tips cost about the same no matter how long or short. Buying the right length tip, and knowing when to use it can improve your weld experience, and save you work and effort afterwards with less clean up and less distortion of your welded assembly.

The consumable parts of a GMAW gun you will most commonly replace are the nozzle, the contact tip, and sometimes the gas diffuser. Generally, the diffuser gets replaced only when it?s clogged so badly that you can?t get it clean enough to provide the proper amount of shielding gas, or it?s worn to the point that it no longer holds the nozzle firmly. By and far, you?ll replace the contact tip the most, with an occasional nozzle here and there unless you really abuse them.

The contact tips sole function is to guide the wire and transfer the weld current (voltage) to that wire. Since the recesses of the tips can vary, that also affects one major weld parameter that greatly affects weld quality, stick-out.

Stick-out is measured as the length of wire from the work surface to the end of the contact tip in your Mig gun. The longer the contact tip that you use, the shorter the stick-out. The shorter the contact tip used, the longer the stick out.

So why is this so important?

The longer stick-out you run when welding, the more you increase the voltage and decrease the amperage. Remember, voltage is your heat, and the amperage is your wire speed.

Increased voltage and decreased amperage can cause you several difficulties; burn through and excessive heat on thin materials, slow travel speeds (aggravating burn through, warping and other heat related issues), an unstable weld arc, excessive weld spatter, and arc wander.

While excessive heat is still fresh on your mind, remember that in electrical circuits heat increases resistance, thus inhibiting the contact tips? ability to transfer the desired amount of weld current. Insufficient current (heat) results in poor penetration, cold lap at the weld edges, and also excessive spatter. Excessive heat is also tough on the tip itself. If severe enough, it can ?weld? or ?fuse? the wire inside of the tip itself, thus making it useless and a replacement necessary.

As a rule of thumb, as your weld current increases, your contact tip recess should also increase, in other words a shorter tip.

Since the vast majority of us use smaller power sources of less than 200 amps, the most common tip we use is one that should be flush with the end of the weld nozzle. That will allow a proper stick out of ?? to ?? for the short circuit process. If you have a difficult joint, you can do two things to help you access it; hammer the nozzle opening into an oval shape, and use a contact tip that extends 1/8? beyond the end on the nozzle.

For the best weld performance, you want the least stick-out that is recommended by the wire manufacturer. The shorter your stick-out, the better your welder will perform. The arc will be more stable, and you?ll get better weld penetration.

If you?re running above 200 amps, your contact tip should be recessed 1/8? to ??, especially using a semi-globular or spray transfer process.

One word of caution, extended contact tips also in turn force longer stick-out, thus moving the shielding gas source further from the weld. Chances for porosity increase as well as poor penetration, cold lap, excessive spatter, especially when outdoors with a breeze. At most, increase your gas flow 5 CFH, no more. Too much shielding gas also adversely affects weld quality.

To sum it all up, what you?re really after is the correct length stick out, which is very important, and you can?t possibly achieve that using the wrong contact tip.

[Joe Dillard]

I must admit, I should pay more attention to my nozzle and tips. You brought up some excellent points and I haven't given them much thought in the past. But now that you've shared some good info, I'll be more aware of what's happening and how these items affect the overall work being done.

Which brings up a question concerning the nozzle I have been wondering about.

Sometimes I can weld and my nozzle will last a good while before needing to be cleaned and knock the slage off of it. While at other times, the slage and build-up seems to build up less quickly.

Do you think my working surface and overall cleanliness has more to do with this? Or other items I should be aware of?

I mainly weld mild steel with a MM 175 with a mix tank regulated to ~20.

[Allen]

Originally Posted by Joe Dillard

I must admit, I should pay more attention to my nozzle and tips. You brought up some excellent points and I haven't given them much thought in the past. But now that you've shared some good info, I'll be more aware of what's happening and how these items affect the overall work being done.

Which brings up a question concerning the nozzle I have been wondering about.

Sometimes I can weld and my nozzle will last a good while before needing to be cleaned and knock the slag off of it. While at other times, the slag and build-up seems to build up less quickly.

Do you think my working surface and overall cleanliness has more to do with this? Or other items I should be aware of?

I mainly weld mild steel with a MM 175 with a mix tank regulated to ~20.

What percent of CO2 is in your mix?

The more CO2, the more weld spatter. The more Argon, the less. CO2 also smooths out the arc, as in the sound it makes. Argon makes it more harsh. That old saying "If it crackles like bacon, it's good to go.", isn't always the case. Running 100% CO2 is virtually silent in some cases.

So it could be the gas mix.

It could also be too much stick out, as you don't weld often enough to train your hands to not only hold a steady travel speed, but also a consistent distance from the work.

So it could be incorrect stick out, even with the correct length contact tip.

It could also be joint design. A "T" joint or butt joint will clog up a nozzle much less than say, welding the inside of a box. Especially when coming up to the corner where 3 plates and 3 welds meet. The spatter has no where else to go.

Bump up your gas to 25 CFH and leave it there.

Run 75/25 if you aren't already.

If it isn't those two things, pay attention to the joint design.

If you're getting excessive slag build up from an open joint; i.e. "T" joint or butt joint, then it's you. Practice some more.

[Joe Dillard]

Originally Posted by Allen

What percent of CO2 is in your mix?

IIRC 75/25 mix.

Originally Posted by Allen

It could also be too much stick out, as you don't weld often enough to train your hands to not only hold a steady travel speed, but also a consistent distance from the work.

You're right on the spot when mentioning I don't weld often enough and train myself in this area.

Originally Posted by Allen

Bump up your gas to 25 CFH and leave it there.

I'll try that.

Originally Posted by Allen

If you're getting excessive slag build up from an open joint; i.e. "T" joint or butt joint, then it's you. Practice some more.

Practice is what I'm lacking big-time. Right again.

Thanks for the excellent feedback. Much appreciated.