The choice of weld joint greatly affects the overall quality of a part. Welding is the joining of two metal parts with a gap using molten metal. However, the way you join the two parts greatly affects the strength and durability of the part.
You can overlap the two parts, join them along a line (side by side), or select one of the welding joint types outlined in this article that matches most engineering applications.
In this article, we will outline the importance of choosing the right type of weld joint, where you’d typically find them, and their characteristics.
Welding Joint Definition
Welding is a popular fabrication technique where electric discharge or heating results in fusing two metals or plastics often with a metal filler. The type of weld joint is the result of the relative arrangement of the metal pieces and their orientation during welding.
Welding Joint Types
There are many ways you can align the metal pieces and produce a welding joint. Each method produces a different kind of weld joint such as a T joint which forms by welding the corners of two perpendicular pieces.
Each welding joint has a different load-bearing capacity, structural strength, and material specifications.
Butt Joint
A butt joint forms when a metal plate or substrate is aligned parallel next to another plate and the edge is welded shut. This is the most common weld type in construction and piping industry.
Typical root gap for a butt joint is between 1.5 mm to 3 mm and for thick materials butt joint require edge preparation. You can find more about the type of groove welds in the next section.
Tip! For single bevel groove weld the typical angle is 30° for each edge and included angle of 60°.
Corner Joint
A corner joint is the simplest weld that you can get by perpendicularly aligning the two workpieces. Corner Joints form a 90° angle making an L shape. You can find three types of corner joints
Closed Corner Joint
Closed corner joints form a sharp corner and have no gaps in the meeting edges.
Open Corner Joint
Open corner joints leave an opening for the weld pool. The meeting edges have a gap below the intersecting points of contact. This is also called half-open corner joint.
Flanged Corner Joint
Flanged corner joints are different from full open corner joints because one of the pieces is bent to provide more welding area. This is typically common in elbows where the edge flange meets another edge at right angles.
Tee Joint
Tee joints are the simplest kind of joints and are easy to weld. The configuration of a Tee joint is a aligning a horizontal metal piece with a vertical piece forming a 90° angle.
When welding T-joints both sides should be exposed for full penetration. Typically these weld joints are used in vertical pipes, construction like scaffoldings and in the ship industry.
Lap Joint
A lap joint gets its name from overlapping the two weld metal surfaces. Lap joints are common for welding sheet metal. You can weld lap joints from both sides to get a strong and tough joint.
Lap weld works well when the sheet metal is of different thickness. This ensures the weld temperature doesn’t melt the substrate and the weld forms on the side. Lap joint requires minimal edge preparation and is easy to fabricate.
There are two variations of a lap joint
Single Lap Joint
When the weld is applied only on side and is great for very thin metals
Double Lap Joint
When the fillet weld is on both sides for maximum strength. This lap weld is advised for steels with at least 3 mm thickness or aluminum with at least 4.5 mm thickness.
Edge Joint
Edge joint configuration is aligning two workpieces edge to edge and welding the metal edges together. The alignment is parallel and on the same surface level.
Edge weld is typically used for thinner material and when the loading on the welded components will not be high. Edge joints are not suitable for thick sheet metal and typically are added as a reinforcement weld in the sheet metal industry.
Welding Grooves And Their Application In Weld Joints
More important than the welding joint are the welding grooves. Groove welds are important for the integrity of the weld and joint preparation.
There are many types of groove welds and each has a different edge preparation technique in the welding process. The above defined types of weld joints use these grooves and plugs.
Square Groove Weld
Square groove requires no edge preparation and the workpieces have flat square edges. The groove forms when the edges meet and the weld fills the gap where the square groove forms.
Butt Joint
In butt joints when the two edges of workpieces meet with no overlap, a square butt joint forms and the two pieces are welded along the faces.
Square butt joints are great for thin materials because thinner materials can be distorted from welding heat. However for thicker materials and full penetration other grooves like the U groove or the V groove are used.
Tee Joint
Tee joints use square grooves at the intersection when the perpendicular aligned pieces meet. The square groove forms at the face on top of the T joint.
Edge Preparation For Square Groove Weld
A square groove for butt weld requires no special preparation but the pieces are cut straight at 90°. It has a small root opening and you can use fillet welds or groove welds.
Bevel Groove Weld
A bevel is a sloping edge. Bevel groove weld forms when the two meeting faces have a sloping edge forming a V shape.
Bevel groove weld can use a single or double beveled edge. For a single bevel groove weld, one of the edges remains square and another is cut at an angle between 30° – 45°. For double bevel groove weld, both edges have a sloping angle of 30°-45°.
Bevel grooves provide complete penetration of the filler metal and are generally used for thick materials. Bevel grooves use more filler material and the edge preparation adds cost to the fabrication. Bevels are essential for joint penetration, butt welds use them most efficiently.
They are commonly used in shipbuilding, pressure vessels, and pipe welding.
Butt Joint
Butt joints can use single and double beveled edges for deeper penetration.
Tee Joint
Tee joints typically use a single bevel edge on the vertical section of the T for better penetration and welding
Corner Joint
Corner joints use single or double-groove weld if both sides are open and accessible. This gives the joint full strength for heavy loading and cantilever-style hangs.
Edge Joint
Edge joint use single or double bevels for a strong weld and the application is similar to butt joints.
Fillet Weld
Fillet welds are the opposite of groove welds. Unlike a groove weld, which requires edge preparation and cutting the face, fillet weld can be applied to any edge and protrudes like an odd triangle.
Fillet welds work when the meeting edges are close to a 90° angle. Despite no penetration or groove, fillet welds can withstand any bends and compression.
Continuous Fillet Weld
Continuous fillet welds are used for maximum strength. This type of joint design is a continuous seam.
Intermittent Fillet Weld
Intermittent welding uses gaps in between the line of beads to use less material and when the material is prone to heating distortions.
This welding is commonly used in T joints, lap joints, and where the corner joint meets the surface edges.
In all the welding joints mentioned, it is applied along the meeting edges of the two surfaces.
V Groove Weld
V groove welds provide significant weld penetration and sound weld integrity. The meeting edges form a sharp V configuration to hold the weld pool.
V groove welds are used in butt joints and corner joints but they can be used in almost all types of welding joints including edge joints.
The edge preparation for V groped welds are beveled edges between 60° and 90°. Higher angles achieve deeper penetration. The root gap for a V groove is less than 5 mm and typically around 2 mm.
Double V butt joint isapplicable in structural steel and automotive and aerospace industries for critical structures in aircrafts.
U Groove Weld
U groove welds are similar to V grooves but the weld joint design is shaped like a U instead of the extremely angular V. U groove weld provides full penetration but requires more time and edge preparation.
U groove welds are common in butt weld joints, edge joints, and corner joints. Making a U groove in T joints and lap weld joints is fairly difficult.
The edge preparation for the U groove requires machining or skilled grinding to form the U shape. U grooves are only recommended for material thicknesses of 20 mm or more. A U groove is better than V groove butt joint welding because it reduces stress concentrations and uses less filler material.
J-Groove Weld
A J-groove weld has its edges prepared in a J-shape. This means the J groove has one curved edge resembling the letter ‘J’ and a flat or square edge.
J groove weld is usually found in butt weld joints and corner welded joints when full penetration is necessary for structural strength.
The edge preparation for J-groove weld requires an angle between 10° and 20° and this requires machining or handheld grinding. The root gap is between 1 mm and 2 mm.
Flare Bevel Groove Weld
Flare bevel grooves have a curved edge and a flat surface. The configuration has a flared edge that meets a square edge at any angle.
Flare bevel grooves are applicable in corner joints, T-joints, and lap joints. There are no specific edge preparation angles rather flare bevels are a result of welding rounded surfaces like pipes. You can find these in automobiles when small pipes are welded to the chassis to secure them properly.
Plug Weld
Plug weld is a welding technique used for overlapped metal sheets or parts. Plug weld joints usually involve a cylindrical hole which is filled using a weld. Plug welds are a replacement for fasteners and bolts for permanent assembly.
The preparation for a plug weld joint involves drilling a hole or elongated cylinder into the upper workpiece for the weld filler.
You’ll find plug welding joints in the sheet metal market, car body panels, and aerospace applications as a replacement for rivets.
Slot Weld
Slot weld joints are similar to plug welds but the hole is shaped like a slot and accommodates more weld and filler material.
Slot welds are used in T joints and lap joints.
Seam Weld
This welding process is useful for long, continuous workpieces aligned edge to edge in the same plane. Seam weld is applicable in a lap joint or butt weld creating a line of unbroken weld beads.
This welding process is usually automatic and involves rollers which sandwich the metal sheets and move them next to a fixed welding arc.
General Welding Preparation Tips
Regardless of the types of welding joints, most weld types require careful preparation to ensure strong and durable joints. The following tips are crucial for a long-lasting weld.
Workpiece Cleaning or Etching
Before welding prepare the workpiece surface by removing contaminants like oil, grease, or paint. You can use wire brushes, grinders or a chemical etch to remove a micron-level layer from the surface for very specialized parts.
Edge Preparation
Always use the right bevels, grooves, and angles when preparing the edge for butt welds, edge joints, or other types of welding joints. Maintain the proper root gap which matches the welding technique.
Preheating Workpieces
Preheating the workpieces reduces the risk of cracking and failure for certain materials like carbon steel or thicker materials. This process can ensure proper penetration.
Welding Parameters
Voltage, current, and polarity like AC or DC settings can greatly affect the weld quality and bead formation. Depending on the material thickness you’ll need to adjust these parameters and the travel speed of your arc.
Compatible Filler
Choosing the right filler material produces a defect-free weld. Start with the base material and choose a metal with a similar melting point, chemical composition, and preferably the same bonding properties.
Depending on the types of welding styles (MIG, TIG, or stick welding) you’ll have to change your filler rod.
Which Welding Process Is Ideal For Your Project?
The choice of welding process is independent of the types of welding joints but rather depends on the material, application and ease of working.
| Welding Technique | Common Application Scenario | Advantage |
| MIG Welding | Body panels and frames | Higher filler deposition Easier on edge joints Suitable for thin and thick materials |
| TIG Welding | Aerospace industry Art pieces | Precise Welds For thin materials Ideal for aluminum and titanium |
| SMAW | Heavy duty metal work like shipbuilding and bridges | Good for outdoor conditions Cost effective |
Conclusion
A deep insight into the types of welding joints and which one is right for your project is crucial for producing durable parts in various industries. By following these tips you can improve your craftsmanship and build the quality of your parts.