6 Forms of Joint Welding and Why They Matter

Last Updated on January 2021

Introduction

Welding joints is all about joining two metal parts together. Unique individual needs and applications inform the type of joint a welder can create.

The process requires the welder to select the most suitable welding process to maximize the strength and integrity of his construction and create a proper welding joint, which in essence, is the sole determinant of the usefulness of the finished structure.

Some welding joints are for lightweight while others for heavyweight use. Some are costly, generating strong welds while others are affordable, and generating soft welds. Each welding joint has its advantages, disadvantages, and applications.  We shall break down the six forms of welding joints and their applications.

Types of Welding Joints

1.  Butt Welding Joint

It is the simplest and most common type of welding joint formed by placing the ends of two parts together side by side or in the same pane.  It derived its name from the fact that the two plates typically butt up to each other end to end.

Butt Joint Applications

It is the universally accepted method of attaching a pipe to itself, fittings, flanges, valves, and other equipment.

It is common in situations where the quality of the weld is essential.

Weld Types in Butt Joint

  • Square butt weld
  • Bevel groove weld
  • V-groove weld
  • J-groove weld
  • U-groove weld
  • Flare-V-groove weld
  • Flare-bevel-groove butt weld

2.  Lap Welding Joint

Lap joints are formed when two pieces of materials are placed one on top of the other in an overlapping pattern and joined through the welding process. They are common when welding two parts that have different thicknesses.

Also considered a fillet type, the weld can be done on one or both sides of a sheet of metal depending on how strong the outcome needs to be. A lap joint is the most reliable welding joint due to the large surface area between the welds

Lap Joint Applications

Common in the electron beam, gas tungsten arc weld, gas metal arc welding, laser beam, and resistance spot welding.

The joint is useful in a variety of weight & exercise machines, as well as industrial equipment.

It is also used in plastic, wood, tabling, temporary framing, assembly of the frame in cabinet making, and automation related processes.

Weld Types in Lap Joint

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

3. Edge Welding Joint

Edge joints are formed when the edges of two pieces of material are set side by side and welded on the same margin. Usually, this joint is not used in stress and pressure applications because the weld does not wholly penetrate the thickness of the joint. Where heavier applications are involved, filler metal will be added to melt or fuse the edge entirely and reinforce the plate.

Sometimes this joint could have one butt weld on it or have fillets on the other sides. Due to their brittle nature, they are replaced quite often.

Edge Joint Applications

It is mostly applicable to sheet metal parts where the edges of the sheets are expected to be adjacent and in approximately parallel planes on the welding end

These joints are appropriate where the join is essential to weld two nearby pieces jointly, and where the thickness of sheets is less than 3mm.

Also useful for metal sheets that have flanging edges.

Weld Types in Edge Joint

  • Square-groove weld or butt weld
  • Bevel-groove weld
  • V-groove weld
  • J-groove weld
  • U-groove weld
  • Edge-flange weld
  • Corner-flange weld

4. Tee Welding Joint

Tee welding joints are formed when two metal parts intersect at a 90-degree angle with one edge lying at the center of the other, which makes the tips come together in the center of a plate or component. Tee Joints are considered a type of fillet weld, and can also be made when a pipe or tube is welded onto a base plate. Extra care is required to ensure adequate penetration into the roof of the weld.

When materials are welded together in this position, they form the shape of the letter ‘T,’ hence its name.

Tee Joint Applications

The tee joint constitutes an essential part of the construction of many structures and is majorly applicable when a metal part is connected to some type of base.

The applications of T-joint mainly include when a metal part is connected to some type of base, attaching thin plates, structural and machine applications

Weld Types in Tee Joint

  • Fillet weld
  • Plug weld
  • Slot weld
  • Bevel-groove weld
  • J-groove weld
  • Flare-bevel groove
  • Melt-through weld

5. Corner Welding Joint

Corner joint is formed by joining two pieces of metal at a right angle to each other, thereby forming an L-shape. This shape is widely used for the creation of different shapes you will find in the construction industry.

This type of wielding is commonly used in the sheet metal industry to attach pieces during the construction of boxes, frames, and other similar fabrications. Be careful to use moderate heat so that it doesn’t warp the joint.

It is important to note that this type of weld is typically done on the outside of the corner. Due to the pressure that most structural edges bear, they get weak quickly hence the need to replace them frequently.

Corner Joint Applications

The applications of Corner Joint include sheet metal, light sheets, more substantial metal sheets,

Also used in the designing of boxes, frames, and other such fabrications.

Weld Types in Corner Joint

Fillet weld

  • Spot weld
  • Square-groove weld or butt weld
  • V-groove weld
  • Bevel-groove weld
  • U-groove weld
  • J-groove weld
  • Flare-V-groove weld
  • Edge weld
  • Corner-flange weld

6. Square Welding Joint

This is a butt welding joint with two flat pieces that are parallel to each other. One-piece lays flat, while the other stands on its tip flush to get butt welded together. The material used can be equal or different lengths, widths, and thicknesses.

Square joints are similar to ‘T’ joints, but the difference is that they form an ‘L’ shape instead and are also not as strong as ‘T’ joints.  This is because a square joint has a butt weld on one side with a fillet on the other, giving it uneven strengths, unlike the tee joint, which is more stable due to the presence of two fillet welds on either side.

Important Note

Now that you have understood the six categories of welding joints, it is essential to note that there are only two (conventional) continuous welds. These are Fillet Welding joint and Butt Welding Joint. A good welder should understand the difference between the two and when to use each.

Continuous welds are those that cover the entire joint – whether it is a butt weld or fillet weld.  This means that the pieces that are welded together do not appear tacked; instead it seems smooth.

Basics of Butt Welding

When two surfaces are butted up against each other on the same plane, then welded together, that is a butt weld.

For a butt weld, two pieces of metal are brought together until almost touching. Typically there will be a gap of around 1/8” (3mm). The welder strikes an arc and feeds in filler to create a pool of molten metal. This pool is then moved along the joint with filler added continuously. The gap is there to ensure molten metal penetrates through the pieces being joined. If the gap is too small, there may not be enough penetration. Make it too big, and you’ll get a large or heavy seam on the reverse side of the pieces.

Metal thickness influences penetration. When pieces are more than 3/16,” a chamfer is usually ground on one or both top edges. This makes the gap wider and lets the metal flow down the full thickness. Conversely, if the pieces are fragile it might not be necessary to have any gap at all.

A compelling particular case is when you’re welding pieces of different thickness, but that is in the same plane. These are overlapped to create a lap joint. Then on each side of the joint, there’s a ninety-degree angle between the two pieces, making this a fillet weld.

Basics of Fillet Welding

When two surfaces are perpendicular to each other (there is a 90-degree angle between them), that is a fillet weld. The fillet joint forms a 45-degree angle between two pieces of metal or plates. A fillet is an old word used to describe a triangle-shaped piece of material similar to the shape of the inside angle you weld a fillet weld into hence the name of the joint.

Fillet welded joints such as tee, lap, and corner joints are the most common connection in welded fabrication. In total, they probably account for around 70 to 80% of all joints made by arc welding. No edge preparation is needed, and assemblies in piping systems are more straightforward. Therefore, fillet welds are usually cheaper than butt welds.

In fillet welding, the idea is to build up a triangular section weld between the two pieces. When finished, the weld surface should be at 45 degrees to both parent materials with the fillet size related to their thickness. More specifically, the throat of the weld – the distance from the inside corner out to the weld surface – should be the same as the thickness of the base metal. A fillet weld smaller than this probably lacks strength while one larger has wasted time and filler, and may have put too much heat into the metal.

When the pieces being welded are thick – say 3/16” or more – the welder usually makes several passes rather than trying to deposit a lot of metal all at once.

Conclusion

Welding is a skill that many people can learn and, therefore, practice. However, to stand out from the crowd, a great welder is one that practices and never stops learning and reinventing him or herself. It takes constant practice and experience to make consistently high-quality welds.

Because welding is the universally accepted method of joining metals permanently, demand for the skill has been rising in recent years. Additionally, welding has now expanded to serve a wider audience such as mining, transportation and even agriculture. Gone are the days when welding was specific to the construction industry.

The rising demand for welders across the board is the main reason why many people are enrolling to learn and practice the art. However, utmost care must be taken to ensure that strict qualification benchmarks are reinforced to allow a practice that produces high quality or premium work. We all need to appreciate the sensitivity of welding because shoddy work can lead to unimaginable losses in terms of cost, time, and even lives.

The strength of welding depends on which parts of the base materials are welded and how. Consequently, performing high-quality welding requires consideration of the directions of the forces that will be applied to the products after welding.

The penetration in a weld joint is vital to the strength, quality, and operation efficiency of welding. It must be selected according to the shape of the base materials and necessary strength.

Understanding the different types of welding joints and welding styles applicable in the various joints is paramount for anyone interested in constructing top-notch quality of welded structures. This is only the beginning of a long journey that will ensure your sustainable relevance in this fast-paced and fast-growing industry.

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