Practical MIG Welding: Aluminium

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Aluminium

08.19

00:00	Our third and final material in this material specific welding guide is aluminium.
00:04	Mild and stainless steel are quite similar in terms of MIG welding characteristics.
00:09	Aluminium on the other hand is a different beast altogether and can really ruin your day if you're not setting it up correctly.
00:15	Don't be discouraged though, once you're set up to weld aluminium with your MIG welder, you can weld up large structures in a fraction of the time that it would have taken using the TIG welding process.
00:24	While we're on that subject, it should be said that TIG welding is a much better match for smaller aluminium tasks and provides a lot more control.
00:32	This is something that you can learn about in detail inside of our practical TIG welding course.
00:37	However, for larger and thicker aluminium welding, the MIG welder can be an extremely useful tool to get a project completed quickly and efficiently so let's get into it.
00:47	It is worth setting our expectations correctly at the start however and unless you have the benefit of a pulsed MIG welder, the finished appearance of the MIG welded aluminium project is unlikely to give you that stacked dime appearance of a quality TIG weld.
01:02	Now, I know we're always going on about the importance of part preparation in this course but if there was ever a time to take this advice seriously, right now would be it.
01:11	When preparing aluminium through cutting, marking and drilling, we need to shy away from using high speed abrasive tools like angle grinders as they can deposit contaminants into the weld area through the cutting process.
01:23	This can make the welding a real pain and lead to results that will leave you questioning what went wrong.
01:29	Using slow speed cutting techniques like a cold saw, slow speed hole saw, file or even a hacksaw will eliminate a lot of these contaminants that would otherwise become lodged in the soft material.
01:40	You also need to be careful using any cutting fluids or aerosol sprays like CRC to assist in the cut as these can contaminate the material and make welding an absolute nightmare.
01:51	Cutting wax on the other hand won't contaminate the cut area so this is a really good option for cutting aluminium.
01:57	Extreme care needs to be taken to make sure every part of the weld area and the surrounding material is clean and free from contaminants and oils prior to welding.
02:06	This also includes the back surface of the weld area if it can be accessed.
02:10	Linishing abrasives should also be dedicated for aluminium use only to avoid cross contamination with ferrous particles.
02:18	It's a good idea to use scotch brite to thoroughly clean the weld area and then wipe our work piece down with acetone prior to welding.
02:25	Once our material is cut and cleaned, it needs to have the aluminium oxide layer removed.
02:30	On steel, this oxide layer is visible as rust but on aluminium, it's a tough invisible layer that only melts at over 2000°C.
02:38	That's over 3 times the melting point of the aluminium beneath it.
02:42	Removing this oxide is a must and this should be done with a stainless steel wire brush, scotch brite pad or a buffing disc that's not been used previously on any other steel.
02:52	Because the oxide layer forms very quickly, it's best to do this immediately before welding along with a quick wipe of acetone to ensure that it's clean and contaminant free.
03:01	Setting our machine up to weld aluminium is a fairly straightforward process.
03:05	First we need to select and use the right consumables which as usual means the gas and the type of wire.
03:11	If we're setting up a MIG welder from new to weld aluminium, then we'll be already eliminating a source of contamination that we could expect if we were to change out a mild steel wire spool in an old machine.
03:22	As we've already discussed, this is because the mild steel wire runs inside of the MIG lead liner and this can introduce contaminants to the weld.
03:30	As we learned in the last module, we can fit a new liner into our existing torch to give our wire a resistance and contaminant free passage of travel from the wire spool out to our contact tip.
03:41	Because aluminium is so soft and ductile, we need to decrease this resistance to allow a smooth passage of wire from the drive rollers.
03:47	We also need to remember that the rollers must match the diameter of wire we're using and must be tensioned properly to ensure that we don't end up with a bird's nest of wire inside the machine.
03:57	Too much tension on the rollers will also deform the wire and affect the contact tip's current delivery into the wire.
04:03	Too little will cause the wire to stop feeding whenever a small amount of pressure is applied to it.
04:08	It's a fine balance and something that we can easily check when setting up our machine.
04:12	Next, it's important to note here that aluminium MIG welding requires the use of straight argon gas, the same as a TIG welder would require.
04:20	If you already have a TIG welder, then you can share this bottle between a MIG and TIG, if not, it's still worth setting our MIG up for aluminium as the argon can be used for any multiprocess DC TIG welding if the machine offers it.
04:33	Keep in mind that not all machines are designed to MIG weld aluminium but that doesn't mean that they can't.
04:38	If our machine has a synergic function then it should offer the ability to select aluminium and be set up for this process.
04:46	If our welder doesn't have that capability, then we'll often find settings listed on the inside of the machine door or in our resources section you'll find a PDF with baseline settings useful for working with aluminium.
04:57	It's a good idea to print this out and have it next to your machine for easy reference.
05:01	The technique of welding aluminium remains very similar to that of mild and stainless steel.
05:05	There are some key differences though but before we go any further we should point out the respiratory risks that this material poses.
05:13	The white clouds of smoke emitted from this process is magnesium oxide and aluminium oxide formed from the aggressive arc combined with the argon gas.
05:22	What you can't see though is ozone gases that are also emitted during the process.
05:27	Ozone is a lung irritant and we should do all that we can to limit our time spent inhaling it.
05:32	This could mean using a fan, extraction system or a filtered face mask.
05:37	With our machine set up, our material prepared and our PPE fitted, we can perform a dry run along the proposed weld area which is the best way to understand if we'll be comfortable for the duration of the weld.
05:48	It's going to tell us if we need to reposition our body or move into an area that'll give greater visibility of the weld.
05:54	MIG welding aluminium is done in a pushing motion that sees the torch leant over at a 15 to 30 degree angle to point the nozzle in the direction of travel and make sure that the arc is being shielded correctly with argon gas.
06:06	While we do this, we need to be mindful of keeping our wire stick out length close to our target 10mm and not allowing this to fluctuate in or out.
06:15	We also need to consider inputting even amounts of heat into each edge of the material that we're welding together.
06:21	Aluminium's ability to spread heat through the workpiece will require us to weld thinner sections first as the heat soak may make the penetration too deep for the given material.
06:30	Remember we don't have a lot of control of the heat input with MIG welding so we need to be smart and consider our parts ability to spread out or soak in that heat.
06:40	On the topic of managing heat, there's no better tool to use than the pulsed MIG transfer method.
06:45	This refers to the action of a MIG welder that offers the pulse or double pulse mode.
06:50	And this is ideal for aluminium MIG welding as it takes the best parts of all the transfer methods that we spoke about in our practical skills section.
06:58	A droplet of filler wire forms with every pulse and creates a longer cooling off period that reduces the heat input to the workpiece.
07:05	Completing test welds and dialling in our machine is the key in aluminium MIG welding.
07:11	Diagnosing these test welds should involve looking for any air bubbles, craters or discolouration which would indicate a lack of shielding gas or dirty base material.
07:20	A good looking weld is usually a strong one.
07:23	While a small thin weld that sits on the surface will indicate a lack of heat, and on the flip side, a wide sunken weld will indicate too much heat and this may also result in problems on the backside of the material due to burn through.
07:35	We can always double check our welds with some destructive tests as we've covered in the practical skills section of the course.
07:43	Let's cover the key takeaways from this module.
07:45	MIG welding aluminium is completely achievable and the key to success is in meticulous preparation, careful heat management through correct settings and technique as well as good PPE practices to ensure that you're not inhaling toxic fumes.
08:01	Remember practice makes perfect and although MIG welding will never replace the precision of TIG welding when it comes to aluminium, a dialled in machine and plenty of practice will see you creating large scale aluminium projects in a short amount of time.