Welding is a complex craft that requires patience, attention to detail, and creativity. To do their job successfully, welders must have a deep understanding of the various techniques and practices used in the industry, including the types of welded joints.
The term “weld joint design” refers to the way metal parts are joined or aligned with one another. The design of each joint affects the quality and cost of the finished weld. Selecting the most suitable joint design for a welding job requires special care and skill.
What is Welding Joint?
A welding joint is a point or edge where two or more pieces of metal or plastic are joined together. They are formed by welding two or more workpieces (metal or plastic) according to a particular geometry.
There are five types of joints referred to by the American Welding Society: butt, corner, edge, lap, and tee. These configurations may have various configurations at the joint where actual welding can occur.
Types of Welding Joint
According to AWS, there are five basic welding joint types that are commonly used in the industry:
- Butt joint
- Tee joint
- Corner joint
- Lap joint
- Edge joint
1. Butt Joint Welding
A butt weld is one of the simplest and most versatile types of welded joints. The joint is made simply by placing two pieces of metal together and then welding them along the join. In the case of a butt joint, it is important that the surfaces of the workpieces to be joined lie in the same plane and the weld metal remains within the planes of the surfaces. As a result, the workpieces are almost parallel and do not overlap, as is the case with overlapping joints, for example.
Types of butt weld joints
Butt welds are made in different ways, and each serves a different purpose. Typical examples of butt weld joints include:
- Square butt weld. The square butt weld is primarily used for projects where metals are 3/16 inch or less in thickness. The square butt weld joint is quite strong, but it is not recommended if the finished structure is subject to shock loads or fatigue with prolonged use.
- Grooved butt weld. If you want to weld metals more than 3/16 inch thick, you will likely need to use the grooved butt joint. The grooving of the metal plates is used to give the connection the necessary strength. Thicker metals have more space to apply the filler and the grooving of the sheets results in a more permanent bond.
- V-butt welding. The single V butt weld is more common on frames 1/4 “to 3/4” thick. The tapered angle for the connection is generally about 60 degrees for the plate and 75 degrees for the pipe. You can prepare the metal with the help of a special chamfering machine or a cutting torch. The V-shaped weld seam is more expensive to manufacture than a square butt joint. You will also need more filler material for this weld than for the square joint.
- Double V butt welding. The double V butt weld is great for a wide variety of projects. Its main advantage is that metals greater than 3/4 inch thick can be grooved on either side. However, it can be used on thinner metal plates where load resistance is critical.
2. Tee Joint Welding
Tee welds are created when two parts intersect at a 90 ° angle. This causes the edges to converge in the center of a panel or component in a T-shape. Tee joints are considered a type of fillet weld and can also be formed when a tube or pipe is welded to a base plate.
Tee joints are usually not grooved unless the base metal is thick and the welding on both sides cannot withstand the load the joint must bear. A common defect that occurs in Tee joints is the rupture of lamellae, which occurs due to a limitation of the joint. To prevent this from happening, welders often use a stopper to prevent joint deformation.
3. Corner Joint Welding
Corner joint welding refers to instances in which two materials meet in the “corner” to form an L-shape. You can use corner joints to construct sheet metal parts, including frames, boxes, and similar applications.
To complete this joint, begin by tacking the outside edges, then make the same curved zig-zag weaving motion we made for our filleted tee weld.
Corner joints can be hard because you can’t often rest your hand on your material to steady your torch hand. You may want to practice a dry run along the joint to make sure you’re going to be able to weld comfortably, I’ve gone as far as clamping a vice grip to another piece of material to create a hand rest.
The styles used for creating corner joints include V-groove, J-groove, U-groove, spot, edge, fillet, corner-flange, bevel-groove, flare-V-groove, and square-groove or butt.
4. Lap Joint Welding
Lap welding joints are essentially a modified version of the butt joint. They are formed when two pieces of metal are placed in an overlapping pattern on top of each other. They are most commonly used to join two pieces with differing thicknesses together. Welds can be made on one or both sides.
Lap joints are rarely used on thicker materials and are commonly used for sheet metal. Potential drawbacks to this type of welding joint include lamellar tearing or corrosion due to overlapping materials. However, as with anything, this can be prevented by using the correct techniques and modifying variables as necessary.
5. Edge Joint Welding
Edge welding Joints are often applied to sheet metal parts that have flanging edges or are placed at a location where a weld must be made to attach to adjacent pieces. Being a groove type weld, Edge Joints, the pieces are set side by side and welded on the same edge.
In an edge joint, the metal surfaces are placed together so that the edges are even. One or both plates may be formed by bending them at an angle. The purpose of a weld joint is to join parts together so that the stresses are distributed. The forces causing stresses in welded joints are tensile, compression, bending, torsion, and shear.
The ability of a welded joint to withstand these forces depends upon both the joint design and the weld integrity. Some joints can withstand certain types of forces better than others. The welding process to be used as a major effect on the selection of the joint design. Each welding process has characteristics that affect its performance.
Types Of Welds
1. Fillet Welds
Fillet welding refers to the process of joining two pieces of metal together when they are perpendicular or at an angle. These welds are commonly referred to as tee joints, which are two pieces of metal perpendicular to each other, or lap joints, which are two pieces of metal that overlap and are welded at the edges.
The weld is triangular in shape and may have a concave, flat, or convex surface depending on the welder’s technique. Welders use fillet welds when connecting flanges to pipes and welding cross-sections of infrastructure, and when bolts are not strong enough, and will wear off easily.
There are two main types of fillet weld: transverse fillet weld and parallel fillet weld.
2. Groove Welds
Groove weld is defined as an opening between the two joint members which provides the space to contain the metal. Groove welds are the most used welds after the fillet weld. The second most popular type of weld is the groove weld.
The groove weld refers to beads that are deposited in a groove between two members to be joined. The type of weld used will determine the manner in which the seam, joint, or surface is prepared.
3. Surfacing Weld
These are welds composed of one or more strings or weave beads deposited on an unbroken surface to obtain desired properties or dimensions.
Surfacing is a welding process used to apply a hard, wear-resistant layer of metal to surfaces or edges of worn-out parts. It is one of the most economical methods of conserving and extending the life of machines, tools, and construction equipment.
4. Plug Weld
A Plug Weld, also known as the Rosette Weld, is when two metals are fused through welds placed in small circular holes. This process is typically done on two overlapping metals, with the top metal having the holes for the weld to be deposited.
Plug welding is an alternative to spot welding used by vehicle manufacturers where there is insufficient access for a spot welder. For DIY car restoration, it’s generally used instead of spot welding on panels flanges that would have originally been spot welded.
Plug welds when done properly tend to be stronger than the original spot welds. Rally car builders often use the technique, and it is acceptable in a UK MOT test as an alternative to spot welds were repairing older cars
5. Slot Weld
A slot weld joins the surface of a piece of material to another piece through an elongated hole. The hole can be open at one end and can be partially or completely filled with weld material.
This is a weld made in an elongated hole in one member of a lap or tee joint joining that member to the surface of the other member that is exposed through the hole. This hole may be open at one end and may be partially or completely filled with weld metal.
6. Flash Weld
Flash welding is a type of resistance welding that does not use any filler metals. The pieces of metal to be welded are set apart at a predetermined distance based on material thickness, material composition, and desired properties of the finished weld.
Current is applied to the metal, and the gap between the two pieces creates resistance and produces the arc required to melt the metal. Once the pieces of metal reach the proper temperature, they are pressed together, effectively forge welding them together.
Railroads use flash welding to join sections of mainline rail together to create Long Welded Rail (LWR) in a factory setting or continuous welded rail (CWR) in track, which is much smoother than mechanically-joined rail because there are no gaps between the sections of rail.
This smoother rail reduces the wear on the rails themselves, effectively reducing the frequency of inspections and maintenance.
7. Seam Weld
Seam welding is the process of joining two similar or dissimilar materials at the seam by the use of electric current and pressure. Seam welding is possible thanks to the contact resistance created between the two metals. As current passes between the metals, heat gets generated at the small gap.
The process is mostly used on metals since they conduct electricity easily and can sustain relatively high pressures. As current passes between the metals, heat gets generated at the small gap. Electrodes maintain and control the flow of electricity.
8. Spot Weld
Spot welding (also known as resistance spot welding) is a resistance welding process. This welding process is used primarily for welding two or more metal sheets together by applying pressure and heat from an electric current to the weld area.
It works by contacting copper alloy electrodes to the sheet surfaces, whereby pressure and electric current are applied and heat is generated by the passage of current through resistive materials such as low carbon steels.
9. Upset Weld
Upset welding (UW)/resistance butt welding is a welding technique that produces coalescence simultaneously over the entire area of abutting surfaces or progressively along a joint, by the heat obtained from resistance to electric current through the area where those surfaces are in contact.
Pressure is applied before heating is started and is maintained throughout the heating period. The equipment used for upset welding is very similar to that used for flash welding. It can be used only if the parts to be welded are equal in cross-sectional area.
The abutting surfaces must be very carefully prepared to provide for proper heating. The difference from flash welding is that the parts are clamped in the welding machine and force is applied bringing them tightly together.
High-amperage current is then passed through the joint, which heats the abutting surfaces. When they have been heated to a suitable forging temperature an upsetting force is applied and the current is stopped. The high temperature of the work at the abutting surfaces plus the high pressure causes coalescence to take place. After cooling, the force is released and the weld is completed.
Advantage of welding
- Welded joint has high strength, sometimes more than the parent metal.
- Different material can be welded.
- Welding can be performed anyplace, no need enough clearance.
- They give smooth appearance and simplicity in design.
- They can be done in any shape and any direction.
- It can be automated.
- Provide a complete rigid joint.
- Addition and modification of existing structures are easy.
Disadvantage of welding
- Members may become distorted due to uneven heating and cooling during welding.
- They are permanent joint, to dismantle we have to break the weld.
- High initial investment
Application of Welding
The welding is widely used for the fabrication of pressure vessels, bridges, building structures, aircraft and space crafts, railway coaches, and general applications besides shipbuilding, automobile, electrical, electronic, and defense industries, laying of pipelines and railway tracks, and nuclear installations.
- Fabrication of sheet metal.
- Automobile and aircraft industries.
- Joining ferrous and non-ferrous metals.
- Joining thin metals.
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