How to set up your MIG welder for Aluminium welding
An easy-to-follow, plain english guide on setting up your MIG with Aluminium wire. These instructions apply to most makes and models of MIG welders.
An introduction to welding Aluminium
Aluminium is a high thermal conductor (which causes the heat to transfer away from the weld pool faster than other metals), with a melting temperature about half that of steel. This makes it challenging to apply enough heat to maintain the weld pool and achieve penetration, whilst avoiding burn-through and distortion. The thinner the material, the more challenging this becomes. Also, it can be challenging to achieve a 'quality' start to each weld, as this is when the material is at the lowest temperature and therefore draws the most heat away from the weld pool.
In addition, aluminium material has an oxide layer which the arc must penetrate through to be able to initiate a weld. This can make it challenging to start the arc, whilst achieving an aesthetically pleasing weld and avoiding puddling or cratering.
Pulse MIG welders are the ultimate weapon when it comes to welding aluminium. Arc pulsing and functions such as start current (or hot-start), start-slope, end-current, end-slope etc, all allow the operator to control heat and eliminate puddling or cratering & even eliminate spatter. However pulse machines are costly and can require higher experience or skill levels to master.
However, with the right equipment and by following best practice, it is possible to successfully MIG weld aluminium, even with relatively basic MIG welding machines. Nowadays, the vast majority of welding machines used (especially single-phase) are inverter machines with "stepless" or "infinite" output adjustment, which allows for much better control of the arc (or heat) - compared to older transformer style machines.
Material thickness: Most reputable MIG machines can be used to weld aluminium down to 3mm thickness. To successfully weld materials thinner than 3mm, it may be neccessary to use specialist MIG or TIG welders with pulse capability. (Note: to TIG weld aluminium, you will need an "AC/DC" machine such as the 202T).
The Welding Machine
If your MIG welder has a torch with "Euro" style connection (like the example above), then setting up for aluminium is usually fairly straight-forward.
The majority of welders in Australia have Euro-connect torches, however some smaller (or low cost) machines have "direct-connect" torches that are "hard wired" into the machine and are not easily disconnected. We do not recommend using these machine for welding aluminium. In some cases it is not possible to make the neccessary changes to the torch, and often these machines will have basic controls that work OK for welding steel, but are not ideal for aluminium.
If your welder has "inductance" and/or "soft-start" adjustments, these are also an advantage when it comes to aluminium. Whilst they are not essential, they do help to fine tune the arc characteristics, control heat, and get a better result. All Weldclass MIG welders (with euro connect torches) have inductance control, with the exception of 180MST.
See more information below regarding "inductance" and/or "soft-start" controls.
Weldclass MIG welders & their suitability for aluminium:
Suitable (Euro torch connection):
Better: 200MST (has inductance control)
Best: 250MST (unique 'ATC' Advanced Thermal Control technology, for superior arc control especially when welding thinner materials)
Aluminium MIG Wire
Wire Size: Being a soft metal, wire feeding with aluminium can be challenging. You may be accustomed to using 0.9mm as your "go to" size for welding steel, however when it comes to aluminium, we strongly recommend using ø1.0mm or ø1.2mm and avoid ø0.9mm wire where possible, and especially avoid ø0.8mm which can be extremely difficult to wire feed.
a) ø1.0mm wire will typically weld material down to 1.0-2.0mm thickness (depending on the machine), so there is there is very rarely any need to chose wire smaller than ø1.0mm. The ability to MIG weld thin aluminium material is actually more to do with the performance of the welding machine, rather than the wire diameter. And b) the risk of experiencing wire feed issues is greater if using wires smaller than 1.0mm.
If you are using a spool gun torch (more on this topic below), wire size is not as critical becuase the wire has only a very short distance to travel from the spool to the contact tip. 0.9mm & even 0.8mm wires can be much easier to use with spool guns, however that said often 1.0mm wire will do the some job equally as well.
Wire Type / Grade: The most common grade of wire used for 'general purpose' aluminium fabrication is 5356. For specialist applications you may need to research further to identify the correct wire type.
Drive Rollers for Aluminium
Standard V-groove rollers for steel wire (normally supplied as standard with new machines) will squash softer aluminium wire out of shape. For aluminium, U-groove rollers should be used. These will usually need to be purchased seperately.
MIG Torch Set Up for Aluminium
Torch Liner: If your machine is set up for welding steel, you will need to remove the existing steel liner and replace this with a teflon/poly liner, together with a brass or copper neck liner. You may also need to make some changes to the torch connection on the machine, to accomodate the liner. Click here for instructions on this.
Torch Length: As we've already mentioned, wire feeding with aluminium can be challenging due to aluminium being comparitively very soft. The safest torch length for welding aluminium is 3m, or max 4m. Keep in mind that the longer the torch, the more friction there is on the wire, which equals more potential for wire feed problems. Where a longer "reach" is required, push-pull torches can be used (which are up to 10m long) - however these can be costly and not all machines are suitable for operating with push-pull torches.
Additional Torch? If you need to swap between welding aluminium and steel, it can be inconvenient changing over your torch liner etc and then changing it back again. You may want to consider purchasing an additional torch to use as your 'aluminium torch'. For an additional torch, we recommend the Promax BZL 25 torch for machines up to 250A capacity, or the Promax BZL 36 torch for machines 250A and above.
Contact Tip: You will likely need to replace the contact tip in the torch, with the correct size tip to match the wire you are using. Aluminium wire requires slightly "over size" tips. These will usually be available as a specific aluminium tip. For example a 1.0mm aluminium tip will be marked as "1.0A" or "1.0ALU".
Torch Polarity: Most aluminium wires operate on "DC+" polarity, where the torch/wire is connected to the (+) positive terminal, and the earth clamp is connected to the (-) negative terminal.
Puddling & Cratering
Avoiding unsightly puddles or craters (especially at the beginning or end of the weld) are some of the most frequent challenges that operators face when welding aluminium.
To completely eliminate these issues 100% may demand the luxury of a Pulse MIG, however experiementing with the following settings can help, even if your machine is non-pulse.
Output/Voltage: A poor start to the weld on aluminium can be due to not enough voltage/heat at that point, or sometimes too much. But more often it is not enough. The reason is that the start of the weld is when the material coldest and therefore draws the most heat away from the weld pool. Experiment with turning up the output (if using synergic mode, dial up to a higher mm thickness setting than what you are actually welding), or if in manual mode, increase the voltage.
The challenge here is that the perfect setting for starting the weld may then be too hot for the remainder of the weld. If you're using a Pulse MIG then you will likely have the luxury of being able to set different current levels for the start, middle & end of the weld. But with standard MIG machines, you will either need to find the best compromise setting, or run short stitch welds to allow a higher start current.
Inductance Control: In some respects, inductance is like adjusting the nozzle on a garden hose.
Low inductance = wide, smooth, fluid arc, which can reduce spatter and improve weld appearance.
High inductance = narrow, focused, crisp arc which can increase spatter levels, but in some applications (especially thinner materials) allows a tighter 'pin point' weld bead.
Note: Some machines may not have inductance control, especially lower cost units.
Soft-Start Adjustment: When a weld is started, the workpiece and the wire will be ‘cold’ compared to welding temperature. This can cause an uneven and poor start to the weld using the voltage and wire feed speed selected as optimal once the arc is established. Soft-Start setting slows the wire speed down at the start of the weld which can improves the weld starting performance.
Note: Some machines may not have soft-start adjustment, especially lower cost units.
Gas for Aluminium MIG welding
Most aluminium wires require 100% Argon shielding gas (as opposed to Argon "mixed" gas - such as Ar+CO2 - which is frequently used for welding steel).
Welding Aluminium with Spool Gun MIG Torches
Spool guns are not essential for welding aluminium. Spool guns have pros and cons, with the deciding factors being more related to the type of work you do and your work environment, rather than the type of wire or material you are welding. Also, not all MIG welders are suitable for operation with a spool gun (this requires specific programming and a control cable connection).
Pros: Spool guns are available with cable length of up to 8m, allowing welding in areas or parts of a job that may be difficult to access. Swapping between different wires (say steel to aluminium & vice-versa) is also easier with a spool gun than it is with a conventional torch, where you need to replace the complete torch liner and guide tubes in the wire feeder, etc. Spool guns make good sense for smaller jobs and where flexibility and longer torch length is desired.
Cons: Spool guns are less suited to higher volume work. The torch is heavier, bulkier and can be uncomfortable to use for longer periods. With a spool gun you are also restricted to use of 100mm mini-spools, which come at a significantly higher cost per kg of wire than larger spools.
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