VIDEO: How to Clean Metal Before MIG Welding

In this video, I want to explain to you how I clean metal for the best possible MIG welds

Now, as I've mentioned before in other videos, strictly speaking, you don't need to get back to bare metal in order for a MIG weld to work

But for it to work to its full potential and for the bead to look as nice as possible and be as strong as possible, you do need to get back to bare metal

This is a piece of black iron pipe. It's called black iron because it's black on the surface, although the actual metal isn't really black

What you're seeing on the surface here is something called mill scale

So, you can imagine this started off as molten steel and it was extruded

Actually, this is welded pipe. I don't know if you can see that, but there's a weld bead in there

So, it actually started off as some flat stock and it was bent in a factory and welded

And it's seamlessly welded. You can't really see the weld on this side. But during that process of heating and forming and manufacturing, there's a kind of... well, the mill scale forms on the surface

It's a product of oxygen and, I guess, manufacturing oils and pressures and all kinds of things

And that's why this is black. Now, it's starting to rust a little bit here, too, because it's been outside

Bottom line is that we want fresh, clean steel, if we can, for the best possible welds

And the usual tool for that is something like this. An angle grinder with what's called a flap wheel, which is an abrasive

It removes a fair amount of metal. It does it fairly quickly in most cases

But it's not the best for this sort of thing, because it actually travels so quickly

Like this, the maximum RPM on this disc is over 12,000. I think it probably spins at a full 10,000

I don't know if it says anywhere here. Yes, sorry, 8,500. So, it's really spinning very quickly, and so quickly, in fact, that it can actually burnish the surface of the metal

and not remove the mill scale as fast as you might like, or as you can

What I have found works better than that, and it's nicer to use, too

it's more controllable and it's more effective, and that's a regular woodworking sander

This is a five-inch random orbit sander. As I said, it's meant for working with wood, but it happens to do a great job getting off this mill scale

So, I'm going to show you that. But before I do, I just want to point out a couple of different abrasives

This is the sort of abrasive disc that's sold most commonly for use on a five-inch random orbit sander

It works great on wood, and it works pretty good on metal, too

But what works better on metal is this mesh-style abrasive. So, you can see my fingers through it, I think

The advantage there is that there's... Well, the advantage for woodworking is that there's all kinds of holes in here

and sanders like this have a built-in vacuum system, a little vacuum system

These holes suck the dust in, trap it in this canister. So, something like this maximizes the airflow and the sawdust pickup when you're dealing with wood

But what I have found with metal is that the open weave clogs up less

The abrasive lasts longer, quite a bit longer than regular sandpaper-type abrasives, and it just does a great job

So, there's probably different companies that make this kind of thing. This is made by Diablo

This grit is actually a little fine. 180 is a bit fine for what I'm doing here

80 grit would be better. But anyway, let's take a look, and I'll show you how it works and what clean steel really looks like

Now, that is bare metal

And you can see where the sander kind of worked through the mill scale

This isn't as big of a job as you might think, because you really only need to do it where you're going to actually do the welding

Later on, subsequent steps might involve cleaning the whole thing that you've made and applying some kind of paint

but as far as cleaning metal for welding goes, that's the ticket

It's perfectly clean, and you'll get really good results if you try to weld to that