The key to any good weld is clean metal, but what is the best way to clean metal before you start welding? Depending on the tools you have and the overall goal of the project there are a few ways to prep your metal to get a nice clean weld every time.
The best welds come from pure clean metal to metal contact, any foreign materials in the welding area can cause welding imperfections. Even brand new metal must be prepped before it can be welded because there is usually a coating put on new metal so it does not rust or oxidize during the shipping process. This is a factor that is often overlooked and will always result in a weak and ugly weld. Be mindful, once you remove this coating the metal is exposed to the elements, if left out unprotected steel will begin to rust, even indoors.
To start, the type of welding you are doing will determine how you prep the metal. Inherently MIG welding steel does not need the metal to be perfectly clean. On the other extreme, TIG welding aluminum requires contaminant free metal to create a strong clean weld. In all of the examples below you can see the difference the dull color of the “new metal” (left) compared to how it looks after it is properly prepped (right).
Using an angle grinder with a flap disc works great to prep steel for MIG or TIG welding. Mild steel does not require the surface to be super clean to get a good weld. In the picture above you can see the left side is brand new untouched steel, it may look clean but it has a thin coating like stated earlier. Once you remove the coating with the flap disc, all it takes is a quick wipe down with Low VOC PRE or Acetone and you will be able to make clean and effective welds. This method works great for heavy welding on chassis parts, this area is always exposed to the elements which will build up contamination over time. Take the time and clean the metal, you’ll thank yourself later.
Be careful a flap disc will remove a lot of material so don’t use this on thin sheet metal, it may compromise the metals strength.
Similar to using a grinder this method will work great for MIG and TIG welding steel or stainless, but it can be time consuming and does not always remove all of the coatings. Like using a grinder, you must wipe the metal down with Low VOC PRE or Acetone before welding. In the picture above I used 80 Grit sandpaper, it worked well by removing the coating but also left deep scratches that may not look good.
If the metal you will be welding is very rusty and is not suitable to be sanded or removed with a grinder another option to prep the metal is to blast it. After blasting the metal may look clean but it will still need to be wiped down with Low VOC PRE or acetone to remove and chemical contaminants. The abrasive material can sometimes trap pieces of other metals that can cause the metal you are welding to rust or corrode. Never rely on a blaster to prep aluminum for welding, it is very sensitive to contaminants that can get trapped even after wiping it down.
When prepping aluminum there is a slightly different process that you will need to be mindful of. Aluminum is very susceptible to contaminants therefore the cleaning process must be done in reverse to produce clean welds.
First you must wipe down the metal with Low VOC PRE or acetone, this will remove any oils or grease on the surface. The next step is to remove any oxides on the surface of the metal. To do this use stainless steel wool or a stainless wire brush on the area to be welded. Make sure that the Steel wool or wire brush is used exclusively for aluminum to avoid contaminants from other metals. Once these tools come in contact with mild steel they can transfer steel bits into the aluminum which will eventually create rust. Finally wipe down the metal with Low VOC PRE or acetone with a clean cloth or rag, from here you are ready to weld.
It doesn’t matter what kind of welding you are doing its always important to take the time to clean your metal before welding. Not only will your welds look amazing they will be a lot stronger which is always an added bonus.