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What is a Plug Weld? (Everything You Need To Know)


A plug weld, also known as a rosette weld, is a process that fuses two metals together by making a weld inside small circular holes. This typically involves two overlapping sheets or pieces of metal with the holes in the top one. The weld fills the hole in the uppermost material, joining the two workpieces together.

Creating a circular weld similar to spot welding, the difference is that plug welds can be performed where difficult angles or a lack of space make it difficult to use a spot welding machine. Plug welds are also a good alternative for when a spot welder is not available and, if completed properly, these joins can be stronger than a spot weld.

To understand it better, we will investigate the plug welding process…


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Plug Welding Process

The plug welding process can be broken down into five steps, as follows:

1. Workpiece Preparation:

To avoid any welding defects, it is important to first clean the workpieces.

2. Marking Out:

Next, mark out the position of your plug welds on the uppermost workpiece (which is generally the thicker of the two), making sure to evenly space the welds if you are using more than one.

3. Drilling:

Once you have marked the position of the welds, it is time to make the holes for the plug welds to fill. This is commonly done by drilling through the top workpiece. The size of the holes differs depending on the size of the workpieces being joined, with thicker sheets requiring larger holes but, as an example 7.5mm should be large enough for 0.8 or 1mm sheets.

4. Clamping:

It is important to use a plug weld clamp to hold the metals together and stop them moving during the welding process.

5. Make the Weld:

The final stage is to make the plug weld itself, this requires experience and practice to master. Most welders recommend starting by welding around the edge of the hole with the welding gun at an angle to ensure fusion, as with a successful fillet weld. Once the outer edge is secured, you can work in circles towards the centre to complete the weld. This technique allows the bottom metal to come up to temperature with the top metal, improving the weld strength and reducing the chance of a defect occurring. However, more experienced welders are able to begin in the middle of the circle, using their experience to see how the weld pool flows while ensuring there is good penetration on the back plate.

Common Plug Welding Mistakes

Common mistakes include making the welding holes too large in the piece of metal you are going to fill to create the plug weld.

Other mistakes include not cleaning the metals enough or even over-cleaning, which can result in the hole burning away as you start to weld. Over burning the metal sheets or parts can weaken the integrity of your finished weld.

It is also possible to over-penetrate the weld hole or overfill it, although over-filling is much easier to fix. The hole needs to be deep enough to allow a firm bond to be created but not so thin as to burn through once the welding begins.

It is often recommended that you practice drilling the plug weld holes on a spare piece of metal, especially if you are trying plug welding for the first time.

Plug Weld Symbols

Welders use plug weld symbols to show the amount, diameter, locations and spacing of the holes to be drilled.

These symbols may also include details of the angle of the countersink for the plug weld holes, as well as the depth of fill that is required (in fractions of an inch). The symbols may also include other details such as how the parts are to be finished, which side they are to be performed on and whether there should be any contouring.

These symbols work to allow welders to understand and work to set specifications.


Plug welding offers a number of advantages, including:

1. Speed

Plug welding is a fast process that can lead to manufacturing time savings.

2. Strength

Plug welds create strong joints because the weld penetrates deep into the metal, making it ideal for joining parts or components for heavy-duty usage.

3. Versatility

This process is suitable for use on materials including aluminium, steel and stainless steel, making it a versatile process that is suitable for a range of applications.

4. Clean and Safe

Plug welding is a relatively clean process that requires very little cleaning up once finished, in addition it releases minimal fumes or smoke as there is no need for preheating. The lack of open flames or sparks and the fact that plug welding produces very little heat makes this a safer welding process than some others.

5. Economical

Plug welding doesn’t require a lot of electricity or material, which makes it an economical process.

6. Easy-to-Learn

Plug welding is relatively easy to learn, meaning that new employees can be quickly trained to undertake welding jobs.

7. Portable

Plug welding equipment is portable, making it ideal for use in difficult-to-reach places.


The primary disadvantages associated with plug welding relate to poor quality welds should the process be applied incorrectly.

This includes poorly filled joints, gaps between the welded materials that create a weaker bond, poorly sealed seams due to using too small a rod, weak joins from using a rod that is too large, using too much filler material, or applying inadequate pressure.

However, if the weld is completed correctly, it is a good process that is used for applications including many among automotive enthusiasts.

Uses and Applications

Plug welding has a range of uses and applications. Able to join dissimilar metals, this type of weld is used for welding sheets of metal as well as for welding a rod inside a pipe or to weld exhaust pipes onto vehicles.

Widely used in the automotive industry, plug welding is also used to install new floors into old vehicles, using small holes drilled around the edge of the new floor pan.

Often used to replace spot welds, plug welding was used by hot rod enthusiasts in the 1960s, who removed the original spot welds in their wheel hubs before reversing the hubs and reattaching them with plug welds. This created deep dished wheels that were then painted or chrome plated.

Plug welding is also used for construction projects where it is used to attach metal beams and support bars.

Plug welds are also used where access is difficult for spot welders, acting as a replacement technique where spot welding is not possible.


Why are plug welds used?

There are several advantages associated with plug welding (see above) which make it a desirable process for a range of applications. These include being able to weld in hard-to-reach positions, low cost, speed of welding, strength, and cleanliness, as well as being a portable process that is relatively easy to learn.

Is a plug weld strong?

Plug welding is strong as the join allows the surfaces to flow together while the weld is also placed within the metals themselves. Plug welding is recognised as one of the strongest methods for joining steel parts as there are no gaps through which force can be exerted in either side.

How big should a plug weld be?

Plug welds need to be large enough to create pressure across the whole surface where the two metals meet. This ensures there are no weak points in the seam, delivering a strong bond. The size of the hole differs according to the size of materials being joined.

Can you plug weld aluminium?

It is possible to plug weld aluminium, although it is recommended that you first use a stainless steel brush to remove any aluminium oxide on the surface as it has a higher melting point than the metal itself. This would mean that you could end up melting the underlying aluminium while trying to melt through the surface oxide.


Pipe welds are used to join two pieces of metal together. Used for a range of applications, this process can be used to join dissimilar materials and produces strong welds quickly.

The process involves making a hole or holes in the uppermost piece to be joined, which are then filled as the two pieces of metal are clamped tightly together.

The appearance of the finished weld is similar to a spot weld as it is circular, but the processes are very different and plug welds can be made in places that may be difficult to reach with a spot welder.

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