Pre-Weld Cleaning and Spool Gun Welding Tips for Aluminum MIG Welders

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Welding Buddy Experts

February 1, 2022
aluminum mig welders

The challenge of aluminum welding takes preparation. And in order for aluminum MIG welders to have a chance, they need to have knowledge of two important things: cleaning the aluminum and knowing how to work with the best aluminum spool gun they can get their hands on. So we're rolling out these quick tips to help you tackle aluminum with finesse.

Cleaning Tips Before Firing Up the Aluminum MIG Welder Spool Gun

Before turning on the MIG machine's switch and firing up the arc on the spool gun's tip, you need to do some pre-weld preparations first. To ensure you get good results, you need to treat your aluminum workpiece with enough care. Here's how you should do it.

Remove moisture with an agent

Melting aluminum attracts moisture and blends it with the liquefied portion of the metal. The moisture tries to escape from the aluminum bond as it cools down. This creates a porous weld quality.

That's why removing moisture is necessary. Oil and grease have moisture that can contaminate your welding. Fortunately, you can remove these contaminants without compromising the surface of the aluminum. First, get yourself a bottle of acetone and some lint-free cloth to wipe the aluminum surface with.

Use a clean steel brush

After removing moisture on the surface of your aluminum, the next thing you'll need to do is remove the oxidized surface. Aluminum can protect itself from corrosion by quickly forming a thin oxide layer on top of it. However, this same protective layer will make it hard to weld, even with a spool gun.

You'll need a clean steel brush to remove this thin layer. Gently run the steel bristles back and forth on the surface of the aluminum to grind the oxide layer into small particles, thus making it easy to remove.

It's important to make sure that the brush is clean and is labeled for exclusive use on aluminum metals. This way, you don't transfer any contaminants to the aluminum.

Use a grinder

Using a steel brush can be tedious if you're working with a larger aluminum workpiece. As an alternative, you can get a grinder to brush off the aluminum oxide layer prior to spool gun welding. Just be sure to label the flap discs you use for aluminum materials so you won't use them for others such as steel or iron.

Use alkaline to chemically remove oxides

Another way to easily remove oxides is to immerse the workpiece fully into any alkaline solution. If it's a small piece, and you can afford a tub of alkaline solution, you can submerge the aluminum piece into the solution and wait for it to dissolve the oxide surface. Note that you have to be careful while using chemicals to remove oxides, as they may cause chemical burns.

Use kraft paper

If you can't use the cleaned aluminum right away, wrap it up in kraft paper. This strong paper material will protect the clean aluminum from contaminants present in the air. It will also slow down the buildup of the anti-corrosion protective layer. This makes the aluminum weld-ready for a longer time, so you won't have to repeat cleaning the material again.

aluminum mig welders - A joint weld finish with a burn at the intersecting welds

Tips When Using Your Aluminum MIG Welder Spool Gun

MIG welding aluminum, even with a wire spool gun, can still involve a lot of technicalities. Producing good welds will take some knowledge and skill. Let's try to shorten the learning process with these welding tips you can immediately apply in your next session.

High input power

Aluminum has a high conductivity rate. To get a decent weld out of your aluminum workpiece, you'll need a high-powered input MIG welding machine that's capable of penetrating any oxidized material on the surface of the material. Aim to get a MIG machine that's capable of accommodating a spool gun with at least 230 volts. This power will feed enough energy to the arc and let you weld aluminum with ease.

Thick wire diameter

Look at your MIG machine's chart and check the range of metal thickness it's capable of working with. It will also let you know what types of welding wire diameters you can put through the machine. When working with aluminum, you'll need a thick wire diameter because it can feed the weld better, especially if you're working on thick aluminum. Aim for a machine and a spool gun that can handle a welding wire diameter of .035 inches.

Don't crack open a wire if you don't plan on using it

The filler wire metals that you'll use for your aluminum workpiece are also made of the same element. That makes it susceptible to oxidation. Keeping your filler wire in good condition means protecting it from outside elements. An oxidized filler wire will cause issues with your weld. You'll have a fickle arc, and weld soot will be more pronounced because the oxide buildup resists the heat coming from the arc. So as much as possible, try to keep the filler wire wrapped until it's time to weld.

Keep the pressure light

Keep the pressure on the wire tensioner of your spool gun light when you tighten it after loading your wire spool. This goes the same with the brass thumb tensioner near the tip. Tightening the screws a little too much will cause some wire feed issues. Worse is that it may cause the wire to get stuck in place and ruin your weld pass.

You want a smooth flow of wire coming out of the welding gun's tip, and the only way to ensure this is to keep the pressure light on the tensioners.

Keep a propane torch

Uneven heat distribution on your aluminum workpiece will drastically affect welding quality. In addition, the weld patterns will be inconsistent as some parts will have richer welding beads while some will fade out.

To prevent this scenario, you'll need a propane torch to preheat your aluminum workpiece until the temperature becomes consistent on the entire material. This will enable beautiful and consistently rich weld beads.

Watch out for your wire speed

Heat is an important factor when welding aluminum. As much as possible, you want to have control of all the heat-producing aspects of the welding activity, including the wire speed.

Wire-speed affects the heat going to your weld. The wire speed affects the amperage and heats up the arc to match the wire feed. As a result, it can cause a burn-through on your aluminum workpiece. So make sure to do your pre-weld wire-speed checks and do several samples until your spool gun is ready for real action.

Set your gun to its optimum angle and direction

The spool wire's positioning can also distinguish between a clean weld and a dirty one. The wrong tip angle and welding direction can produce soot—the charcoal-like burns on the side of your aluminum welding pass.

You'll need to tilt your spool gun's tip to an angle that's between 10 to 15 degrees from the workpiece. Also, pulling will cause soot buildup, so do the opposite by pushing the welding tip on the workpiece aluminum instead.

Use 100% argon

The shielding gas also plays a huge part in creating a fine weld finish. When working with aluminum, it's better to have pure argon inside the cylinder. This shielding gas keeps the arc stable as it prevents outside elements from causing welding impurities on the surface of the aluminum.

Use a longer wire stick out

For a MIG welding gun, ¼ inches of wire filler is enough to get a smooth weld pass. But if you're using a spool gun as a replacement, you'll need to extend the wire stick out at least ¾ inches from the gun's tip. This wire length gives enough room for both the aluminum wire and workpiece to fuse together nicely.

Another thing to consider is the wire tip consistency. When aluminum melts, it turns into a liquid with almost the same consistency as hydrogen, so it tends to have a balled-up tip when it cools down. Keeping this on may compromise the weld quality. When this happens, cut off the tip and extend the wire again to the recommended stick-out length before starting another pass.

Taking on Aluminum

The knowledge and tips imparted are meant to be used so you can weld aluminum with confidence. These tips serve as guidelines that will set you in the right direction as soon as you start the arc. So use them to learn and improve your MIG welding game, but more importantly, enjoy yourself while applying these tips because welding is supposed to be loads of fun to do.

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