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

So, you just bought your new TIG 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 fused together using either a butt or a fillet method 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 welding 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.

Here’s a quick overlook before we really start digging into it.

Types
Butt Tee Lap
Edge Corner  

Butt Joints

If you have ever seen metals or plastics lying flat whose parallel edges are fused together, the joint you are looking at is a butt. 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 is considered as the simplest method, that is why it is also considered as the most popular.

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

  • Bevel– only one of the materials has a diagonally straight bevel that extends from top to bottom
  • Flare-bevel butt – same as the bevel groove but has a groove
  • Flare-V-groove butt – each parallel sides of two materials have grooves running from top to bottom
  • Square-groove butt– no bevels or grooves are made; the parallel edges are simply fused together
  • J-groove butt – 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 – both materials have parallel edges with grooves that take up 3/4 of each edges’ length
  • V-groove butt – bevels on both parallel edges are made from top to bottom

This type 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. Butts 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 for those involving bevels. Unlike a traditional butt that only involves one side, a double butt 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 fused on both sides.

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

Edge

An edge joint is made when edges of two metals are placed parallel to each other, and their adjacent edges are fused together using a butt. 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, they are fused at parallel planes.

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

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

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

They are weaker because the work 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 materials are expected to undergo a lot of pressure, tension, or bending.

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

Tee

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

The different  styles used are:

  • Plug – 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– has similarities with a plug but the hole made is larger and can extend to one edge
  • Fillet – both corners made by the intersecting materials are fused together.
  • J-groove – similar to fillet but the base of the upright material has a groove
  • Bevel-groove – same as a J-groove but it has a bevel instead of a groove at the base of the upright material.
  • Flare-bevel-groove – involves a tube-shaped material placed above a flat material and these are fused together at their intersecting points
  • Melt-through – only one side is welded but it fully penetrates so that it reaches the other side of the upright material

While a tee may seem simple, bonding them together is complicated because the material placed vertically can move around when you work 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 is misaligned after welding, use a soft hammer to tap the section into place. Do it quickly while it is still hot so that it will be easier to move.

They 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 join either the lengths or ends of the materials only, resulting in a weaker bond.

Corner Joints

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

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

These styles used in butt and tees are also used to form a corner:

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

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

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

They 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 for a corner joint and leave the inside corner without a weld. To strengthen it, preps are done on the sides that will be butt welded.

Lap

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

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

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

You can typically see these when resistance spot, laser beam, and electron beam welding is used, as well as in exercise and industrial equipment. They 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.

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

But aside from choosing the suitable one, always make sure to wear the appropriate personal protective equipment (PPE) as you work. It 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.

worker at construction site

A little bit more information about Atlantic Aspiration

While this information may not necessarily be specific to the different types of 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, 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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