What are the Differences Between 6 Types of Welding Joints?
Are you finding it difficult to understand welding joint terminologies or wondering about the best way to weld a specific joint for your project? It can be a challenging task without a comprehensive guide or sufficient experience. In this article, we will discuss the six different types of welding joints, their distinctions, and essential tips to consider when welding them.
In welding, there are two categories of welds that are performed in six distinct joints. Each name of the welding joint has a helpful word hook that makes them easy to understand once explained. So, keep reading to learn more.
Both of these welds can be executed in the same manner. However, their strength may differ based on their preparation and execution within the respective settings. The main factor that determines their name is the space into which the weld is made.
- Butt weld: A butt weld is formed when the edges of two plates are placed tightly against each other, with their tops flush. While they may be slightly angled, they are generally aligned straight. This type of weld is named after the way the two plates meet end-to-end. Weld preps, which are sections cut out of the corners of the plates in various shapes and sizes, can be added to provide greater depth of weld to the joint. The more weld prep is added, the stronger the joint will be, but it will also add time to the job. For projects that do not require it, it’s best to weld the square ends without any weld prep.
- Fillet weld: This type of weld is located in the internal corner of two plates. The corner is usually a 90° angle, but it can be any angle less than or up to about 145° as long as it can be welded. The name “fillet” comes from the old word used to describe a triangle-shaped piece of material similar to the shape of the inside angle where a fillet weld is placed. It’s called a fillet weld because it fills up the corner with weld, unlike the butt weld, where the corner is typically covered with weld.
The Types of Welding Joints Below are the six types of welding joints:
1. Tee Joint
The tee joint looks like a T shape. One piece of metal lies flat, while another section is welded standing on its side or end upwards. It’s a simple joint, but it can be challenging to execute because the weld can pull in either direction due to a lack of surface area holding between the two welds. Typically, this joint has welded on both lengths of the upright plate and frequently has the ends welded, resulting in four sides fused to the base plate.
What to know when welding tee joints It’s crucial to be aware of how welds pull and distort the metal. The upright piece must be at a certain angle, and if you tack it at the right angle and weld it there, it will always pull towards the side you weld first. Two good options can prevent this from happening:
#1 Tack the plate in position, so it’s sitting at the right angle and location. Then, tack some braces to both sections being welded, making sure it hasn’t moved or pulled in the process. Once there are enough braces to stop it from moving, weld the joint fully, wait for it to cool, cut the braces off (ensuring you don’t cut into the job), and grind off the weld with a soft grinding disk, like a flapper wheel, to leave a clean finish. This option is typically used for large sections where straightening after welding is difficult.
#2 Tack the plate on a slight angle away from the side you will weld first so that when you fuse it, it pulls into the position it needs to be in. This takes experience and will never be mastered right away. You’ll need to learn how much the plate will pull in different circumstances, as it will depend on the material and size of your welds. Over time, you will become more accurate with it, but in the meantime, keep practicing with gradual adjustments on scrap pieces of plate to get a feel for it.
After completing the welding process, verify that the angle is accurate. Ensure that your measuring tool can move freely over the weld to provide a precise reading. For instance, if the joint requires a 90° angle, the square tool you use must have its corner trimmed between the two measuring sides to avoid obstruction by the weld.
In case the angle is incorrect, use a soft hammer to tap the welded plate gently to adjust it into position. The heat of the weld will make it easier to move. However, ensure that the plate is bending at the weld and not creating a crease above it. It’s important not to use a steel hammer since it may leave dents on the plate when struck.
2. Square Joint
The L-shaped square joint is similar to the tee joint, but instead of a T shape, it’s an L shape. Plate A lays flat, while plate B is positioned upright and aligned with the end of plate A for a butt weld connection. A fillet weld is applied on the opposite side of the plate, creating a 90° angle joint. The plates can vary in length, width, and thickness. Depending on the project requirements, either end of plate A can be welded to plate B. The name “square joint” refers to its 90° angle, similar to that of a square.
When welding a square joint, it’s important to note that they are typically not as strong as tee joints due to the uneven distribution of fillet and butt welds. The joint has a butt weld on one side and a fillet weld on the other. To increase the joint’s strength, it’s advisable to include a weld prep in the butt weld. To prevent the plate A from pulling away and creating a corner joint, follow either of the two options provided in the tee joint section to complete the square joint.
3. Butt Joint
The butt joint is a commonly used joint for butt welding. Two plates are joined end to end, with their surfaces flush across the top and bottom. This joint can be challenging to weld since it lacks a visible guiding line, unlike most other joints. It also requires a weld prep to ensure sufficient strength unless it’s a non-critical weld or has a large convex finish with deep penetration.
When welding butt joints, a larger weld prep will result in a stronger weld. However, be careful not to blow out the bottom of the weld prep with excessive heat. In such cases, a backing weld is required, where a small section at the bottom of the weld prep is filled with weld before being fully welded.
While adding more weld will create a stronger joint, excessive heat can cause the project to bow or twist. Welding both sides may help, but too much heat can still warp the plates.
4. Lap Joint
The lap joint occurs when one plate overlaps another, leaving two sections for fillet welds, one on the top and one underneath. This joint is often considered the most reliable welding joint due to the large surface area between the welds, and it is generally straightforward to weld. The term “lap joint” comes from the word “overlap,” with the two overlapping plates referred to as a “lap joint.”
When welding lap joints, once the plates are positioned correctly, there’s usually very little else to worry about other than welding them. It’s an excellent joint for beginners to start with and can add extra strength to a project. However, as with other joints, it’s crucial not to apply too much heat to the welds, as they can still warp, despite having a decent overlap. If there is a distortion to the plates, it will occur at the ends without overlap, as these are the weakest points.
5. Edge Joint
When two plates are joined face to face with edges meeting, it is called an edge joint. Typically, this joint only has one butt weld, but it can have additional welds on the other three sides with fillets or butt welds. When welding an edge joint, it is important to be aware that the plates may separate like a clam opening when welded. To prevent this, it is recommended to clamp or tack the weld closed before fusing the joint. If multiple welds are used, the edge weld can be a strong joint due to the large surface area between the welds. It can be challenging to achieve a good appearance when welding an edge joint without weld preps. To improve strength and appearance, it is a good practice to cut a single V butt between the plates if time permits.
6. Corner Joint
Corner joints are joints where only the corners of two plates touch each other. The angle between the plates can vary, but it is often 90°, leaving a V-shaped gap that needs to be filled. Typically, both sides of the corner joint are welded, but the inside corner may be left without a weld. When done correctly, corner joints can produce a smooth concave finish that looks great.
When welding corner joints, it is important to clamp or brace them to prevent them from pulling out of angle. Excessive heat should be avoided, as it can contribute to pulling and warping the joint, even with braces in place. The strength of the plates depends on the corner alone, as it is usually the only area welded, unless permanent braces are used. Therefore, the welds on the corner must be impeccable.
When deciding which type of welding joints to use for your project, consider the position of the parts, the accessibility for welding, and the required strength. It’s important to know the load that each part will bear to ensure the appropriate joints are used.
Each type of joint is named after a hook-like feature, making it easy to identify. If you have any questions or comments regarding welding joints, feel free to share them below.