Master Plug Welds: Symbols, Tips & Techniques

Written By: Liam Bryant

Reviewed By: Russell Egan

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A plug weld, or rosette weld, is a welding method that joins overlapping metal sheets by filling pre-cut circular holes with molten metal, creating strong, discreet joints. Widely used in automotive and construction industries, plug welds offer strength and versatility for various applications.

A plug weld is a type of weld created by pushing a solid rod into a hole drilled in the workpiece. It is most commonly used to attach heavy objects such as metal plates onto vehicles, machinery, or equipment. It is distinct from other welding methods because the plug weld does not involve melting the workpiece. Instead, the plug weld does create the bond using pressure only.

Learning to do a plug weld requires a lot less skill than other types of welding, so it’s perfect for people who want to learn this process but don’t want to spend years learning all the different techniques involved with traditional arc or gas welding.

plug weld

What is a plug weld?

The plug weld is a welding process in which a metal rod, usually larger than the opening for inserting is installed through the thru-hole and then pushed to form a butt joint between two overlapping plates or members that can be stronger than either component alone.

Plug welding can be used with any material, although it is most commonly associated with metals like steel and magnesium. Plug welding is commonly used when welding vehicles.

welding symbols
Source: Wikipedia

What are plug weld symbols and how to read them?

You will notice plug welding symbols used on machinery that welds steel. Sometimes these symbols are also referred to as punch welding symbols. Plug welding symbols can be a bit confusing at first.

However, there are only three things you need to know about plug weld symbols such as distance between plugs (X or V), the direction of pressure, and the number of plugs.

Distance Between The Plugs

This is either X or a V; it is easy to remember which is which because a V is the same upside down. The distance between the X’s or V’s is directly proportional to how far apart they are in millimeters. If there is more distance between the symbols, then it indicates there should be a larger gap between holes.

Direction of Pressure

This will always be pointed up or down, arrows pointing up to indicate that the metal on top pushes the plug into the metal on the bottom. This works just like an ordinary push-pin would work: you are pushing it from above and letting gravity do its job.

Similarly, arrows pointing down indicate that the metal on top pulls the plug out of the bottom. This is just like having a magnet taped to the bottom and pulling the plug from it.

Number of Plugs

This can be 1, 2, or 3. These numbers will tell you how many times a plug was repeated over a certain distance. If there is only one plug, it will be repeated over a total length. If there are two plugs, they will be repeated over half the length; if there are three plugs, they will be repeated over a third.

Where is plug welding used?

Many industries use plug welds in different applications. For example, the automotive industry uses certain types of plug welding to produce body parts or panels that usually consist of multiple pieces.

These smaller parts are then pieced together for a larger structure. Moreover, plug welding is commonly used in construction projects when attaching metal beams, support bars, etc. because it ensures that strength and durability are not compromised.

Why are plug welds used?

Plug welds are usually used when there are obstructions in the workpiece’s way, making it difficult to fix by using other welding methods. It can also be a great option in places where gas or plasma cutting equipment cannot reach the workpiece, even with an obstruction in place.

TIP: Since plug welds don't need to be completely clean, they are also very useful in dirty or dusty industrial work environments.

Less Expensive

Plug welds save money because they do not require a clean workspace. This makes them ideal for dirty or dusty industrial areas, so it is also very useful in the aerospace industry where there are many times when the dust comes in contact with the material.

In addition to this, plug welding equipment tends to be less expensive than other types of metal-joining equipment, such as lasers and plasma cutters.

Saves Time

Another reason plug welding is used is that it can be done easily with hand tools. This means that this method is easy to use when there are many different pieces of materials to join, which saves your time.

Is Plug Welding Strong?

Plug welding is strong because it allows the surfaces to flow together. This results in a stronger bond than if the metal were only held together with friction, which is what typically happens with rivets, for example.

Even though plug welding can be done on an obstructed surface, it does not produce significantly weaker joints as compared to other methods. Additionally, when it comes to joining steel, plug welding is the strongest. It works like a wedge, pushing the seams together and creating pressure at the top of the seam.

This makes it very strong for this type of material, i.e, steel because there are no gaps through which force can be exerted on either side. On the contrary, other welding methods create partial penetrations in the metal, which are then filled in with filler material. This reduces the structural integrity of the workpiece since there are lots of small holes for force to be exerted through instead.

KEEP IN MIND: Plug welding has a very tight seam, which makes it ideal for joining metal together where precision is needed because less filler material means less slag to clean up later.

How To Plug Weld?

The plug weld process is simple. Below we have broken it down into five small steps for beginners to get an understanding.

Step 1. Prepare Your Work

Start by preparing your work area. Ensure that you have a clear space for this project. You will also need a metal surface to use as a table.

Step 2. Clamp the Workpiece

This is where you will secure your workpiece. Use a Welding Clamp to secure metal surface as firmly as possible, taking care not to move it, which can cause problems for your project later on. If required, mark a guide line onto the clamped material using a pencil or marker because this will be very helpful when attaching them together at the end of this process.

Step 3. Weld the Plug

Next, you will need to find the center of the work where you are joining the metal. Use a marker or pencil for this purpose if required. Then drill two holes into your metal at this point, making sure that they are just big enough to fit your welding rod through easily.

As we mentioned earlier, plug welding works by using a rod to push material together, so make sure that these holes are big enough for the welding rod to enter.

Step 4. Prepare Your Welding Rod

Once you have made your two small holes about a one-inch apart from each other, it is time to prepare your welding rod. In order to do this, simply slide it through both of the holes so that it sticks out of each opening equally, making sure that they are both pointing in the same direction.

Step 5. Plug Welding the Metal Together

The next and final step is to plug weld the material together. Ensure that your welding rod is at the same height as your workpiece by using a level or other device. Then adjust your welding machine for the correct heat output, which depends on the thickness of the metal you are working with.

Finally, apply enough pressure to make it easier to fill in each hole with your welding rod. Once completed, continue applying pressure until both holes are filled with rod.

TIP: If you notice that there appear to be any gaps or cracks, simply remove the welding rod and apply more heat before trying again.

Common Mistakes of Plug Welding?

Plug welding is no doubt a super fast and easy welding method. However, there are a few common mistakes most people make that can slow down the whole welding process, or might not bring you the desired outcome.

Filling Joint

It is very important to plug weld without adding filler material on the seam, making it nearly impossible to separate the pieces later. Additionally, when applying pressure, the plug welding rod must be inserted straight down through the hole for the materials to properly seal together.

Gaps Between Joints

If there are any gaps where you wish to join two materials together, it will be nearly impossible to create a strong bond. The pieces should be tightly clamped together because this will reduce the amount of filler material that must be used during the process. It also ensures a tight seam between them after they have been joined together.

Incorrect Rod Size

It is important to use the correct size plug welding rod for the materials to be the most promising in the joint. For instance, if the rod is too small, then it will not be able to create enough pressure to properly seal the seams together. Similarly, if it is too big, you risk creating weak joints because there are openings for force to travel through instead of being forced out of them and down through the rod and into the materials you are joining.

Too Much Filler Material

If there is too much filler material, then it will not be able to properly seal up all of the gaps between where the pieces meet. That is because there will still be holes for force to travel through rather than being forced out of them and down into the plug welding rod. This will lead to a problematic seam that will not be able to support much pressure and could end up falling apart or failing.

Inadequate Pressure

You must apply pressure at a straight angle when plug welding for better results. If you apply too much force, then it will cause problems with the material around where the pieces meet. Similarly, if you apply too little pressure, then it will not be enough to create a bond between the two materials and they will stay as two separate pieces.

Difference Between Plug and Spot Welds

A plug weld is a method of welding two pieces together that have been drilled with a hole for the filler material to flow through. In contrast to this, a spot weld is where two materials are joined together without any filler material between them. Instead, the spot weld has just one piece pushed up against another from about an inch below it so that it leaves marks behind as it cools.

Moreover, plug welding is a much stronger form of welding than spot welding because the materials can bond together better around where they meet and create a tight seal that can hold together under pressure. On the contrary, spot welds will never be as strong because this method still is bound to have gaps where one piece meets the next because of the lack of filler material.

Related Questions

How big should a plug weld be?

Plug welds should be of a substantial size to create pressure over the entire surface of the material where they meet. This ensures that there will not be any weak points in the seam between them and creates a really strong bond.

How do you remove a plug weld?

The best way to remove a plug weld is to drill out the hole and then use a chisel to scrape away the material around it. This will break apart the seal between them and allow you to separate the pieces.

How many pieces of metal can be welded together in a plug weld?

You can use a plug weld on as many pieces of metal as you like and the plug weld will be able to join them all together into one solid part. That is why it is such a useful type of welding technique, especially for those who work in manufacturing, where they might need to create hammered sheet metal.

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