You cannot burn out impurities in metal through the welding process – there, we said it. For some reason a lot of people think that the welding process is so hot that it eliminates impurities in the material. This is not the case. One of the most often underestimated steps in making a sound weld that is aesthetically appealing is base metal prep.
Always clean the base metal to the best of your ability. Particularly if this is something that needs to be held to standards/code. Obviously for small projects around the house and other odd jobs this isn’t as much of an issue, but it’s a good habit to get into. Each type of base metal will have a different cleaning method that works best for it.
For instance, due to the iron content in steel, it has a tendency to rust or heavily oxidize when exposed to the elements. Additionally, due to the manufacturing process, hot rolled steel has a mill scale on the outside surface that occurs naturally. Wire wheels are not strong enough to remove the mill scale and zirc wheels typically just polish the surface and don’t really remove it. Your best option is to use a hard rock wheel to remove the contaminants on the surface, as well as the mill scale.
Material: Stainless Steel
When it comes to stainless, you can just wipe it down with a half decent degreaser and follow up with a clean water rinse. However, there may be times when you want to buff the area to be welded with a zirc wheel. In our experience, there wasn’t much change in the weldability or the outcome between the two methods. One thing to be careful with, is not to use wire brushes, wire wheels, grinding wheels etc. on stainless that have ever been used on steel. Using these items on steel and then on stainless could “impregnate” the stainless with iron oxides and it could induce rusting in our stainless.
Moving on to aluminium; aluminium has a layer of oxide on the surface that melts at around 2000°C. This is a big consideration when dealing with aluminium welding because the aluminium under that thin layer of oxide melts at around 650°C. That is why we use A/C TIG welding for aluminium. The ability to use A/C allows us the ability to use the DC+ side of the cycle to get cleaning action, which helps to break up and lift the layer of oxide and follow it up with DC- to get penetration into the piece. Are you starting to see how each material is very different in terms of preparation?
Although the oxide is very thin, it is also very hard. As crazy as it may seem, the best thing to clean off the oxide layer is a stainless wire brush. Some people think a grinder would be the best, but since aluminium is so soft, you can actually cause contamination in the welding area with a grinding wheel, and as it works it will push the top layers of contaminants further into the material. Also keep in mind that you only want to use discs and attachments approved for aluminium on aluminium. Using a grinding wheel made for steel could clog up the wheel and throw it off balance. Additionally, if you have used the wheel on steel previously, you could cross contaminate your aluminium. Impregnatating it with iron oxide, which will cause rusting in your materials.
As you can see, base material prep is critical to the overall outcome of your welding. The key to a good weld is 80% prep work and 20% skill. Completing a thorough pre-clean and prepping your materials correctly will make your life easier in the long run. Cleaner materials will weld better, and the bead appearance will be much better than its contaminated counterpart.
If you found this useful make sure to check out our other blog posts! Until then, this is Neil’s Steels signing off.