TIG welding is the preferred process for getting attractive beads that have a smooth, consistent texture. The biggest drawback to TIG welding is that there is no flux or cleaning agent involved. That means that the metal you are TIG welding must be spotless before you can start welding it. Unlike other processes, you must clean the metal before TIG welding.
How do you clean and prepare metal for TIG welding? Metal for TIG welding needs to be ground or sanded, then treated with cleaning agents to remove chemicals. Only clean, shiny metal will take a strong bead from TIG. Dirty, rusted, oily, or otherwise contaminated metal won’t hold a weld.
Here is a full list of the things you can TIG weld:
- Shiny, clean metal
Here is a partial list of things you can’t TIG weld:
- Aluminum oxide
- Mill scale
Before you can TIG weld, you need to remove all the garbage off the surface of your joint. There are two processes you need to use: mechanical and chemical. Mechanical processes include grinding, filing, sanding, sandblasting, and other treatments that physically remove the surface of the metal. Chemical processes use solvents and acids to remove paint, oil, grease, and aluminum oxide.
You don’t have to use all these techniques for every TIG weld. You need to pick one or two techniques that will work with your metal to prepare it. What metals work best with each technique? I’ll explain below.
Why You Need to Clean
Before we go into the details of different cleaning methods, you need to understand why TIG welding requires so much cleaning. When you TIG weld, you are melting the edge of each piece of metal along with the filler rod. The melted metals flow together and are permanently fused. If you weld metal that is dirty or rusted, the filler doesn’t stick to the joint – it sticks to the rust. When the bead or joint is stressed, the rust pulls off and the weld breaks.
Other welding processes include flux with the filler rod. The flux reacts with surface contaminants to remove them from the weld. TIG welding doesn’t include any kind of flux, so you have to remove the contaminants before you crack an arc. There are two steps to removing the contaminants, mechanical cleaning, and chemical cleaning. You need to do both before TIG welding.
The first step to prepare metal for TIG welding is mechanical cleaning. You need to remove the surface contaminants from the surface physically. Tools you can use for mechanical cleaning include wire brushes, angle grinders, sanders, and bench grinders. Each has its place, depending on the surface condition and the size and shape of the stock. Let’s take a look a look at each one.
Wire brushes are good for cleaning very dirty metal and very thin metal. Brushes are good for very dirty metal because they can knock off big chunks of dirt and grime with a brush. When you are welding things like farm or road construction equipment, there are likely to be big chunks of dirt and grease stuck to the metal. Wire brushes are the fastest way to get these off.
Wire brushes are also good for really dirty stuff because they don’t clog up, and they are easy to clean when they do. If a brush gets clogged up, you can just tap the brush against a hard surface to knock the crud out of the bristles. Grinders and sanders will gunk up faster than brushes. When they do, you need to use a wire brush to clean the gunk out. You might as well start with the brush.
To use a wire brush for cleaning metal, just grab a brush and start scrubbing. You should be able to get all of the loose or crusty stuff off the joint in short order. The drawback of wire brushes is speed. They don’t remove material as quickly as other tools, and it’s hard to get really deep cleaning with a brush. Brushes are the best starter, but they won’t get metal TIG-ready.
The slow nature of brushes makes them a good choice for sheet metal and thin-walled tubing. If you aren’t careful with a power tool, it’s easy to grind a hole in thin metal. Brushes don’t usually have this problem. Unless you are obsessive-compulsive and just can’t stop, you won’t grind a hole in metal with a wire brush.
One of the most common power tools in welding shops is the angle grinder. Grinders spin a small abrasive wheel at high speed. Angle grinders are small, hand-held grinders that use internal gears to spin the wheel at a right angle to the motor. Every welding shop should have an angle grinder because they are flexible and very useful.
Angle grinders are good for cleaning big pieces of metal. If your workpiece is too big to hold, you can hold the grinder with one hand and work your way along the joint. They don’t work well for small pieces. If you need to clean a small piece of metal with an angle grinder, put it in a vice before you start grinding.
There is a wide range of abrasive wheels for angle grinders. Some are useful for prepping metal for TIG welding, while others are not. Straight wire or looped wire brush wheels are great for cleaning. They have all the advantages of hand-held brushes but work faster. Be careful using a wire brush on the end of tubing or pipe – the brush can catch on the end of the tube and kick the tube or the grinder back.
Flap wheels are another good choice for use with an angle grinder. These wheels have small flaps of sandpaper attached. They are a little more aggressive than wire wheels, but not as much as grinding wheels. Flap wheels are also good for rounded or uneven surfaces because the flaps will adjust to the surface. They are also better for working the ends of tubing than brushes because they won’t catch and kick it out.
Grinding wheels are wide wheels coated with abrasive. They come in a wide range of abrasiveness. Medium to fine wheels are best for cleaning before TIG welding. They will remove material, but not so fast that you get the metal out of shape. Coarse wheels remove metal very quickly – they can create gouges and holes along your joint.
Grinding wheels work best on rusty metal or very thick stock. If you need to get a lot of material off the workpiece in a hurry, a grinder is the way to go. Don’t use grinding wheels on thin tubing or sheet metal. You will make holes and ruin your piece before you ever start welding.
Cutoff Wheels – a Special Case
One kind of wheel to be careful with is a cutoff wheel. These are thin wheels with coarse abrasive. As the name implies, cutoff wheels are used for cutting pipe and tubing. They don’t make good cleaners for large areas because the cutoff wheel will catch the metal and make gouges and cuts.
However, there are some special circumstances where a cutoff wheel is needed. If there are already deep scratches and gouges along the weld joint that are filled with grease or dirt, use a cutoff wheel to dig into the scratch and get the grease out.
The bench grinder is the big brother of the angle grinder. As the name suggests, these grinders are fixed to a workbench. Most bench grinders have two wheels, usually coarse and fine. They can use all the same types of grinding wheels as angle grinders except cutoff wheels.
Bench grinders are best used for small parts you can hold in your hand. Getting big, heavy pieces aligned with the bench grinder is hard to clean it without damaging the joint.
Belt and Disc Sanders
Sanders are less aggressive than grinders but still clean quickly. Because sanders are wider than grinders, they are a good choice for cleaning along large joints. You can cover many areas with a sander without making gouges or uneven places.
For small pieces, you can clean with sandpaper. It will remove more metal than a wire brush and help you get to bright metal sooner. Like the wire brush, it is not likely to damage the workpiece because you will stop as soon as you hit bright metal. Sandpaper isn’t a good choice for big pieces, mostly because it takes forever to hand-sand a large metal joint.
How to Clean
With all the mechanical cleaning equipment, the cleaning method is simple. Just grind along the joint until the rust is gone, and the metal is shiny. Whether you are using a brush, grinder, or sander, you just keep taking away metal until it shines. Just be careful to stop before you make a hole or damage the joint.
When you start cleaning the metal, you need some basic safety equipment.
- Safety goggles or glasses. Even wire brushes and sandpaper can throw off small particles of metal that can get into your eye. Metal in your eye isn’t just an irritant – it will scratch your eyeball. Having a scratched eyeball feels like a big piece of grit in your eye until it heals, which takes about a week. It’s awful, so wear your goggles.
You don’t need welding goggles or even dark glasses for brushing and grinding. Clear lenses are fine. Any kind of shop glasses or goggles will work to keep grit and debris out of your eyes.
- Gloves. Scratches from burrs, busted knuckles, and other cuts and scrapes will happen to your bare hands when you work with metal. Put on gloves to stop this.
Basic leather work gloves are the best choice here. Welding gloves will be too thick and clumsy to handle tools or small parts. Knit or cloth garden gloves don’t give enough protection against sparks or burrs on metal. Plain leather is the best balance of protection and sensitivity.
- Long pants and sleeves. If you are using a power grinder or sander, you need long sleeves and pants to protect your skin from sparks.
The clothes you wear to weld are good for running grinders as well. The go-to pants for welding and metalwork are heavy jeans or cotton duck work pants. These pants are thick enough to protect your legs, and the heavy cotton fabric resists sparks. Denim or twill shirts are the best upper body protection.
- No loose clothing. Don’t wear any long or dangly clothes when working with a grinder or sander. Getting your sleeve caught in a rapidly spinning grinder wheel is a surefire way to visit the emergency room.
- No synthetics. The sparks from a grinder are hot enough to melt plastic. Synthetic fibers are just long threads of plastic woven together. Stick to heavy cotton clothes.
- Earmuffs or plugs. Grinders and sanders are loud, and damage from loud sounds adds up over time. You might not notice today, but if you make a habit of running power tools without protection, you won’t be able to hear your grandkids someday.
Muffs and plugs both work fine for hearing protection. It’s mostly a matter of personal choice which ones you use. Some people find earmuffs too bulky, while others don’t like poking plugs into their ear canals. Earplugs have the advantage of working under a welding helmet if you need them, but any hearing protection is better than no hearing protection.
Once you have removed the rust and dirt, you need to remove any grease, oil, paint, or other chemicals that are left along the joint. These are all chemicals that can be ground into pores in the metal. You need a chemical to remove these chemicals. You also need to remove any traces of the cleaning solution.
Acetone will remove all the chemicals from your surface and evaporate, leaving you a pristine joint to weld. The drawbacks of acetone are safety-related. It is extremely flammable, and it evaporates into harmful fumes. Acetone should be used in a well-ventilated area or under a fume hood. Make sure it has completely evaporated, and the can of acetone is safely stored before you start welding.
Paint thinner is like a less-extreme version of acetone. It is a fine degreaser and (as the name suggests) good at removing paint. The fumes are nasty, so make sure you have good airflow before using it. Paint thinner is also less flammable than acetone, but you still need to get it stowed safely before you weld.
Alcohol is a good degreaser and only a fair to poor paint remover. The fumes are less flammable than acetone or paint thinner, but the alcohol itself is still flammable. You still need to have good ventilation and lock away the alcohol before welding. “Denatured” indicates that the alcohol has been mixed with other chemicals to make it undrinkable and limit the alcohol to industrial uses.
If you are sure the metal has never been painted, citrus degreaser is a better choice. These cleaners are water-based and made from orange oil. They are much safer than acetone or alcohol. Since they are water-based, these cleaners won’t burn. They also smell like oranges instead of chemicals. If you use a citrus degreaser, you will need to use water to clean off the degreaser before you weld.
There are chemical mixtures available for cleaning metals before TIG welding. These are metal-specific. That is, a particular cleaner is formulated to clean a specific type of metal. A cleaner made for stainless steel should be used only for stainless, not aluminum or other types of steel. Know what kind of metal you are welding before you buy cleaning fluids.
Many of these cleaners require a neutralizing agent after application. Get the right neutralizing agent and read and follow all the manufacturer’s directions. Make sure to know how to dispose of used or excess cleaning fluids as well. Dumping it down a drain could get you in serious trouble.
Using Chemical Cleaners
The actual cleaning process is simple. Once you have ground down the joint, just dip the rag into the solvent and wipe down the weld joint. That is all you need to do. The trick is to be safe while you are doing it.
If you are using any flammable chemical, make sure you have good ventilation. The volatile organic compounds given off by acetone and paint thinner will make you sick if you breathe them. The best way to use acetone is under a fume hood that sucks away all the fumes before you have a chance to breathe them in.
You also need to put the solvents away and vent your work area after cleaning metal with a flammable solvent. In high concentrations, acetone and alcohol can ignite at room temperature. Liquid alcohol ignites at 750 degrees, and liquid acetone ignites at about 870 degrees. TIG arcs work at temperatures over 6,000 degrees. If you leave solvents out and start welding, you WILL have a fire.
Be safe – store solvents before you start welding.
TIG welding aluminum is a special case. Aluminum gets covered with a thin, almost transparent layer of aluminum oxide that is very tough. After you have degreased, but before you weld, you need to remove this layer. The best tool for removing aluminum oxide is a stainless-steel brush. Brass brushes also work to clean off aluminum oxide.
Use a dedicated brush for cleaning aluminum – if you use the brush for other things, you may just smear contaminants on your workpiece. It doesn’t do you any good to remove aluminum oxide only to replace it with smears of steel from your last project. The steel will contaminate your aluminum weld just as surely as the oxide would have.
To remove the oxide layer, just give the weld joint a good scrub with the wire brush. The oxide layer is thin, so it doesn’t take much scrubbing. Once you have gone over the whole joint, it’s ready to weld.
If you let the piece sit for a couple of days after cleaning, oxygen in the air will react with the surface of the aluminum, and the oxide layer will re-form. If it’s been a couple of days since you started the project, brush the surface again before you weld.
Don’t use a sander for this kind of cleaning. The grit on sandpaper contains aluminum oxide and will leave particles of grit behind. Using a sander to clean aluminum before TIG welding makes the oxide problem worse, not better.
Once the metal is clean, you can start with joint preparation. If you are welding material that is 3/16 inch or less, you don’t have to do much prep. If you are welding thicker metal, the edges of the joint should be beveled. Beveling means grinding back one corner of the edge so that the pieces meet in a V-shape rather than in two parallel lines.
Beveling is important because it allows the heat of the weld to penetrate deeper into the metal. If you just weld along the edge of a thick joint, the bead will be “tall,” and the heat won’t penetrate the joint. If the heat doesn’t penetrate, the pieces won’t fuse, and the weld will be weak.
If you are welding very thick metal, it may take more than one pass to fill the bevel with filler. This is known as “root and cap” welding. The first bead is the root pass, while the bead (or beads) that go over the top are cap beads. Using a root and cap technique lets the joint fuse fully and gives the strongest weld.
Making the Bevel
Bevels are made with grinders. You can use the same grinder to bevel that you used to clean the joint earlier. You will need a medium or coarse grinder wheel for this. Coarse wheels work faster, but medium wheels offer better protection from mistakes. It’s harder to make a mistake and get a deep gouge with a medium wheel.
While some engineered projects call for precise bevel angles (37.5 degrees in pipe welding), you don’t have to get that precise for home projects. A 45-degree bevel is a good target. It’s halfway between vertical and horizontal.
The bevel doesn’t need to be deep, either. Calculate the maximum depth your welder will penetrate and leave that much unbeveled with the grinder. For example, if your welder can penetrate metal up to 3/16, you should leave 3/16 unbeveled with a vertical edge.
Closed vs. Open Joints
When you push the two pieces of metal into contact with each other before welding, it makes a closed joint. Closed joints are fine for thin metal, up to about 1/8 inch, but they aren’t as strong on thicker metal. For stronger joints, you need to lay out an open joint before welding.
Open joints are laid out with a small gap between the two pieces to be welded. The gap isn’t big – always less than the thickness of the base metal, and usually less than the thickness of your filler rod. You just need a little gap between the pieces to allow the filler rod to penetrate.
Open joints are a little trickier on corners. These are the strongest corners, but you have to lay them out carefully. For an open corner joint, you just touch the inside edges of the corners and leave a v-shaped gap along the rest of the corner. This gap acts like a bevel and allows you to fill it with the bead. For an even stronger joint, you can also run a bead on the inside of the corner after you’ve filled the outside.
Weld It Up
Once you have cleaned the metal, beveled the joint, and laid everything out, you are finally ready to TIG weld. It may seem like more work is spent on preparation than welding, but that’s what it takes to prepare a good weld. If you skip steps, the weld will be contaminated and won’t be as strong. It’s also subject to defects like porosity, slag inclusion, or even breaking.
The whole point of using TIG welding instead of arc or MIG welding is to get that attractive “stack-of-dimes” look for the weld bead. Trying to weld dirty or corroded metal will make a mess of your weld and guarantee an ugly, spotty bead. Skipping on joint preparation and layout will produce a weak weld that’s likely to break sooner or later.
If you have spent the time and money to set up a TIG welding shop, it’s because you want to lay down pretty beads. If you fail to grind, degrease, bevel, and lay out your joints properly, you can’t do that. To get the most from your TIG setup, take the time to prepare your joints before you weld.