Different Types of Welded Joints: Lap, Fillet, Butt, Square, Corner, Groove, Bevel

So, you just bought your new TIG welder or engine driven welder, and you’re trying to become a better pro. Well, this is the article you need.

Contrary to what most would think, the joints formed by welding come in different types. But for anyone with an untrained eye, they may all just look the same.

What you probably don’t realize is that these varying types are not just about the style or aesthetics but they serve legitimate purposes. Metals and plastics are welded together using either a butt weld or a fillet weld in different positions to meet specific needs and forces, but the joints they form are varied.

Don’t have a clue what these different types are? We’ve got you covered! In this article, you will know about each of the five major types of welded joints present according to the American Welding Society and learn about what sets them apart from each other. That way, you can choose which one to use for your next project. We hope you get as much excitement out of reading about this topic as we have pride of publishing the article on it. We spent a great deal of time on it, and we hope that the quality of it reflects it.

If you’re very much so a beginner, we may also encourage you to read this article on the very basics of welding.

Butt Joint

If you have ever seen metals or plastics lying flat whose parallel edges are welded together, the joint you are looking at is a butt joint. This consists of welding the edges or “butts” of the material that are placed side by side and in the same plane. Doing a butt joint is considered as the simplest method, that is why it is also considered as the most popular.

Butt joints may be done as it is or weld preps, or cutting off sections of the edges to be welded, may be necessary. They are created through different welding styles, namely:

  • Bevel groove weld – only one of the materials has a diagonally straight bevel that extends from top to bottom
  • Flare-bevel-groove butt weld – same as the bevel groove weld but has a groove
  • Flare-V-groove butt weld – each parallel sides of two materials have grooves running from top to bottom
  • Square-groove butt weld – no bevels or grooves are made; the parallel edges are simply welded together
  • J-groove butt weld – only one material has a groove at the edge, but this groove only passes through around 3/4 the entire length of that edge, thus forming a ‘J’
  • U-groove butt weld – both materials have parallel edges with grooves that take up 3/4 of each edges’ length
  • V-groove butt weld – bevels on both parallel edges are made from top to bottom

This type of joint is often used for various materials and equipment, such as pipes, fittings, flanges, and valves, but it should not be used for those that will receive loads at high impact. Butt welding can be done for metals and plastics with a thickness ranging from 3 mm to 12 mm. But if it is 5 mm thick or more, you need to bevel one or both edges first before you can weld them.

Some also opt to have a double butt weld for those involving bevels. Unlike a traditional butt weld that only involves one side, a double butt weld involves making the same type of bevels on both sides of the edges so that they are mirror images of each other. This allows the parallel edges to be welded on both sides.

Aside from doing a double butt weld, you can also opt for a full penetration weld to strengthen the joint formed. Beveling the materials and doing a full penetration weld will result in a strong butt joint. Do note that excessive heat can result in a twist or bow, not a straight finish.

Edge Joint

An edge joint is made when edges of two metals are placed parallel to each other, and their adjacent edges are welded together using a butt weld. This edge joint is formed either with the metals stacked on top of each other and welded at the side, or they are placed next to each other and welded at the top. Instead of being on the same plane like a butt joint, they are welded at parallel planes.

The edge joint is highly similar to the butt joint, that is why the many of the welding styles used to create this type of joint are the same:

  • U-groove weld
  • J-groove weld
  • V-groove weld
  • Square groove weld or butt weld
  • Bevel-groove weld

You can also use the edge flange and corner flange welding styles to form an edge joint. An edge flange weld typically consists of two curved metals with their edges welded at their parallel points, while a corner flange weld involves one straight metal and one curved metal also welded at parallel points.

Edge joints are weaker because the weld done is shallow and does not completely penetrate the joint, that is why they are typically used on sheet metal plates that are less than 6 mm thick, such as mufflers. It is also not recommended if the welded materials are expected to undergo a lot of pressure, tension, or bending.

To strengthen the edge joint, you can either do a full penetration weld or add filler material as you weld. It is essential that the materials be clamped together before you weld because it can separate as you weld and start opening up like a clam.

Tee Joint

You might have guessed that the tee joint has something to do with the letter ‘T’. A tee joint, or sometimes referred to as a t-joint, consists of two metals or plastics intersecting to form a right angle and are welded together. The upright material is typically placed at the center of the flat one, forming a ‘T’. Welding is done using a fillet weld at both corners formed by their intersection at the base of the upright material.

The different welding styles used to create a tee joint are:

  • Plug weld – a hole is made on one of the metals or plastics, and the edge of the other one must intersect with the hole. This hole is then filled or plugged up through welding, which then bonds the materials together
  • Slot weld – has similarities with a plug weld but the hole made is larger and can extend to one edge
  • Fillet weld – both corners made by the intersecting materials are welded together.
  • J-groove weld – similar to a fillet weld but the base of the upright material has a groove
  • Bevel-groove weld – same as a J-groove weld but it has a bevel instead of a groove at the base of the upright material.
  • Flare-bevel-groove weld – involves a tube-shaped material placed above a flat material and these are welded together at their intersecting points
  • Melt-through weld – only one side is welded but the weld fully penetrates so that it reaches the other side of the upright material

While a tee joint may seem simple, welding them together is complicated because the material placed vertically can move around when you weld the one side first or even be distorted. This upright material must either have a brace to hold it in place or allow it to stand at a slight angle so that it will move in the right position while welding. In case the tee joint is misaligned after welding, use a soft hammer to tap the welded section into place. Do it quickly while it is still hot so that it will be easier to move.

Tee joints are normally used for materials whose thickness do not exceed 3 mm and even for bonding a pipe to a metal. Also, all four sides of the intersecting sections are typically welded to give it strength. Some do opt to weld either the lengths or ends of the materials only, resulting in a weaker weld.

Corner Joint

A corner joint is done similarly to a tee joint but the upright material is typically placed at the edge of the other one lying flat, forming an ‘L’ or right angle. This type of joint, also known as a square joint, is also one of the most popularly used, especially for sheet metals. It also allows you to weld two materials that have varying thicknesses, lengths, or widths.

Because the corner joint involves a fillet weld on the intersecting side and a butt weld on the parallel side where the edges meet, its strength is uneven and it is generally weaker than a tee joint. Some of the most common uses of a corner joint are in creating boxes and frames using both light and thick materials.

These welding styles used in butt joints and tee joints are also used to form a corner joint:

  • Bevel-groove weld
  • Fillet weld
  • Square groove weld or butt weld
  • J-groove weld
  • U-groove weld
  • V-groove weld
  • Flare-V-groove weld

The following welding styles also form corner joints, but the resulting appearance does not form the ‘L’ shape that is why they are often mistaken for edge joints:

  • Corner-flange weld – involves one flat and one curved material but only the corners of their parallel edges are welded
  • Edge weld – done similar to a basic edge joint where the edges are placed parallel to each other and then welded
  • Spot weld – only small spots at the sides of the intersecting edges are welded

Corner joints are typically made with the entire edges of both materials touching each other, but it is also possible to weld only their corners. You can also only do a butt weld for a corner joint and leave the inside corner without a weld. To strengthen the joint, weld preps are done on the sides that will be butt welded.

Lap Joint

If you need to weld two materials that have different thicknesses, a lap joint is another way to do it if a corner joint is not suitable. A lap joint involves stacking two materials together so that they will overlap and welding is done on either the top or bottom only or both. While fillet welds are mostly used, the weld that creates a lap joint is also known as a lap weld.

You can choose among the following styles, aside from the fillet weld, if you need to create a lap joint:

  • J-groove weld
  • Slot weld
  • Plug weld
  • Bevel groove weld
  • Flare-bevel-groove weld
  • Spot weld

You can typically see a lap joint when resistance spot, laser beam, and electron beam welding is used, as well as in exercise and industrial equipment. Lap joints are among the easiest to create because there is hardly any preparation needed aside from positioning the materials. Not only that, they also often have the smoothest finish. However, it is also prone to warping if there is too much heat during welding.

Now that you are aware of the five different types of welded joints, you can now identify which joints are most suitable for your project. Yes, you can use various types in a single project.

But aside from choosing the suitable joints, always make sure to wear the appropriate personal protective equipment (PPE) as you work. Welding can be done easily but there are always various safety and health risks present no matter how small your project is. Safety first! Did you manage to learn what it was you came here to learn? We sure hope so, and that you didn’t just spend the time reading in vain.

A little bit more information about Atlantic Aspiration

While this information may not necessarily be specific to the different types of welding joints, we want to help you understand the mission that we are on, and what we are trying to accomplish with this website, which you can read more about in the about us section as well.

Atlantic Aspiration is basically a project made by people dedicated on bringing high level information and content in the professional space. Most of the current information out there has been geared towards consumers, and the professional market doesn’t nearly have the same amount of content available as does the consumer market. For now, that includes various different things like helping pros choose the best plasma cutters, the best engine welders, wide belt sanders, and as we continue to develop this site, we hope to be adding more and more information for you to take advantage of.

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