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Expert alloy tig welders. I need advice


yoeddynz

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Thought I should have a ramble on this topic. Have held various tickets including an Ali one so might just clarify a few things:

 

1. Aluminium MUST be cleaned prior to welding but the predominant reason for this is not to remove dust and dirt but to remove the oxide layer which forms on it naturally which is the reason it doesn't corrode. Cleaning can either be done with IPA or mechanically with a stainless wire brush. The wire brush should be kept in a zip lock bag or plastic container when it's not being used so it doesn't get contaminated. If the brush accidentally gets used on carbon steel then don't use it on Ali again.

 

The reason Ali is almost always CNC router cut such as in Alloy boat production and not lasercut is because the CNC router leaves a nice clean freshly cut edge whereas the laser heavily oxidises the edge which would all need to be cleaned back again to weld.

 

2. AC balance -  You can quite safely probably leave at 50% for what you're doing. This setting is all about how much penetration you get.

 

Some info on why you need an AC Tig for Aluminium:

 

A standard DC Tig for Stainless or mild runs DCEN which means your earth is positive and your electrode (The tungsten in the torch) is negative. When welding Aluminium the oxide layer requires a 'cleaning action' whilst welding which is only achieved if you switch the polarity to DCEP (Negative Earth, positive electrode) The problem with this is that running a positive electrode will melt your electrode away almost instantly hence the reason you have to cycle between polarities which is what AC does. It cycles between DCEN and DCEP so the DCEP part of the cycle achieves the desired cleaning action of the oxide layer while the DCEN part of the cycle prevents your tungsten getting hot enough to melt away.

 

Some more info on AC Balance control:  http://www.millerwelds.com/resources/articles/Understanding-AC-TIG-GTAW-Balance-Control/

 

3. Tungsten grinding - Never grind from side on if you can avoid it, it tends to cause arc wander. Your grind marks should follow the same direction as the length of the Tungsten.

 

For DC TIG (Stainless and Mild) grind to a sharp point. The length of the point should be twice the width of the tungsten you're using and the sharp tip knocked off ever so slightly. If you leave it super sharp at the point it can result in a small piece of tungsten melting off and falling into your weld which causes a tungsten inclusion and would fail an Xray test. If you don't knock the point of it's not a big deal, many people don't do this.

 

For AC Tig (Alloy) grind the tip at a 45 degree angle but leave a flat spot on the end the same length as the angle section. There are numerous ways to 'ball' the tungsten but this is not at all critical, just grind as above and start welding. Having a clean tungsten is critical. If you contaminate it with the filler rod or in the weld pool you MUST regrind it.

 

Gas Flow- TOO MUCH GAS WILL INTRODUCE POROSITY INTO YOUR WELD. More is not better. Should be roughly 8-10Lmin.

 

A few other things:

 

Use the correct cutting and grinding discs for Ali which won't contaminate the material and introduce contaminants into the weld.

 

When finishing the weld don't back off the pedal too suddenly. Taper it back gently. Important for Ali or you get crater cracks which can spread down the length of your weld.

 

Torch angle is important!

 

NEVER EVER use brake cleaner or anything with chlorine to clean any metal prior to welding!!!!! It creates phosgene gas and can kill you very very quickly. If it doesn't kill you it'll FUCK you up and leave you with permanent health problems.

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