What is a Rosette or Plug Weld?

Having an understanding of all the different welding types is key to becoming a welder that stands above the rest. One of the easiest welding types every welder should learn is the Plug or Rosette Weld. This is especially true for anyone wishing to go into the automotive manufacturing industry. But what exactly is a plug weld and how do you even make it?

The Rosette & Plug Weld Defined

A Plug Weld, also known as the Rosette Weld, is when two metals are fused through welds placed in small circular holes. This process is typically done on two overlapping metals, with the top metal having the holes for the weld to be deposited.

Good Plug Weld Example

If you’ve had the chance to learn about a spot weld, you should understand the usefulness of a plug weld. This is due to the plug weld making an exceptional alternative when you’re unable to perform a spot weld. Which can happen quite frequently.

There are numerous times that welders, especially hobbyists and small shops, won’t have access to a spot welder machine. They may also find that they can’t get their spot welder machine positioned properly due to awkward angles or space issues. In those times you can be thankful you know how to make a plug weld. Plus, if done properly the plug weld can end up being stronger than a spot weld.

How To Read The Plug Weld Symbol

Now that you have a basic understanding of what a plug weld is and why it is needed, it is time to learn how to read the plug weld symbol. Below you’ll find an example of a plug weld symbol that you might come across along with an explanation of each part.

Rosette and Plug Weld Symbol

Starting at the left of the plug weld symbol, you’ll notice a diameter symbol alongside a number. This number refers to the size of the diameter, hence the diameter symbol.

There will be times when you’re given a plug weld that doesn’t need the hole filled. When this happens, you’ll refer to the number in the middle of the symbol. This number will give you the depth of the hole to be filled.

You’ll also be required at times to apply more than one weld. In these cases, the number in parentheses given at the bottom of the symbol will tell you the number of welds to be placed. The number on the right side of the symbol will also be important here too. This number will give you the distance between each plug weld or the pitch.

How To Plug Weld

It’s finally time to get to the fun part, learning how to make a plug weld. However, the instructions given below will be just going over the basics. Things can vary depending on the job, but you’ll probably be given something to refer to.

Step 1: The first step is obviously to prep. You’ll need to clean the metals off so you don’t end up with any welding defects. Also please make sure to be wearing at least a welding helmet and gloves. The last thing you want is to get a welding burn on something small like a plug weld.

Prepping a Plug Weld

Step 2: Mark out on the top metal where you want to place the welds. If you’re placing multiple plug welds, they will need to be spaced out evenly.

Step 3: Using the marks you made on the top metal, start making the holes for the welds to be placed. This can be done multiple ways, but most of the time welders just use a drill.

Step 4: After making the holes, you’ll need to clamp the metals together so they don’t move around while you’re welding. This is best done with a plug weld clamp.

Step 5: Now the final step, placing the weld. The most important thing to remember is to start on the outside along the edges, working your way towards the middle. Doing this allows the base metal to come up to temperature with the top metal. Improving the strength of the weld and reducing the chances of a defect.

As we said before, this is the basic explanation of how to make the plug or rosette weld. To better help you, we’ve included a video below that demonstrates it perfectly.

Common Mistakes To Avoid

Some obvious mistakes can be made when you are learning how to plug weld for the first time. The most common error that is unique to plug welding is making the hole too large in the thicker piece of metal. Ideally, you will have smoothed and cleaned the metal components, and then either drilled or punched the hole you need.

Keep in mind, overcleaning or over-sanding the thicker piece of metal can result in burning away the hole as you begin the weld. It's for this reason that you must take care never to over-prepare your metal sheets or car parts. It's very easy to over-burn, and that will weaken the integrity of the weld.

Practice Makes Perfect

When it comes to plug welding, the most challenging stage is drilling the hole in the thicker piece of metal. It can take a few goes to get right, so it's always worth having some practice metal that is of a similar size as the piece you're working on. This is especially true if you're trying to plug weld for the first time.

There's a good chance that you will over-penetrate the hole, or even overfill it (although overfilling is a lot less of a hassle to fix than over-drilling). Remember that the hole needs to be deep enough to allow for a firm bond, but not too thin that you will burn through the bottom of the hole when your welding begins.

Vehicle Repair and Manufacturing

A mainstay of vehicle manufacturing and repair, a plug weld, is also used whenever you need to weld a rod that you want inside a pipe. Bolt studs and rods that are intended to fit tightly together will have a hole drilled into the tube, the rod will be inserted into the pipe, and then the plug weld can be performed. You may see this type of weld on a thin exhaust pipe, where the exhaust system needs to be secured to the bottom of a vehicle.

Plug Welding and Wheels

The hot rod drivers of the 60s were among the first to adopt more widespread use of the plug weld. By that point, steel wheels were very popular, and hot rod fanatics would create reversed steel wheels to improve their cars' look.

The process could be a lengthy one! They would start by drilling out the spot welds holding the steel wheel centers inside the wheel, and they would then reverse those centers. As you can imagine, the result would be a car that had very, very deep-dished wheels.

Once aligned, the drivers would then plug weld those centers in the same place as the original spot weld, creating a tough and durable weld that could then be either chrome-plated or painted.

Spot Welding a Vehicle Floor

As well as body paneling, exhaust pipes, and wheels, you can also use plug welds if you need to install a new floor in a, particularly older vehicle. You start by marking any rusted floor pan, making sure to leave a perimeter edge of metal that the new flooring can sit on. The old flooring is then cut out, and the replacement floor is put in its place.

The plug welding then begins! Small holes will be drilled into the new floor pan's edges, the pan will be positioned, and once in place, will be plug welded. The new floor will be joined firmly to the original metal thanks to a plug weld's effectiveness and durability.

Conclusion

With a little practice, plug welds can be a very useful addition to your welding skills. For those welders who work with heavy machinery or auto repairs, plug welding should be considered an essential skill to learn, even if you won't use the technique as much as other types of welding. Yet, when they are done well, the plug weld is a much better option than a spot weld and will be much longer-lasting.

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