Joining two or more sheet metal components is critical & important sheet metal fabrication operation. Therefore sheet metal joints need to be designed with extra care.
In this article, we are going to discuss various types of sheet metal joining operations and their applications. This article can add value to your product.
Selection of Type of Joint
Firstly we need to decide if we require permanent or temporary joint. After that according to the type of material, sheet thickness, assembly process and product final application, joint type is selected.
Types of sheet-metal Joint
- Hardware Assembly or Screw Joint
- Clinching Joints
- Folding or Tab Joint
- Adhesive Joint
Hardware Assembly / Screw Joint
Hardware assembly is a type of temporary joint. In this screws are used for making removable joints. Screw can make a blind joint between two sheet metal parts.
According to type of material, sheet thickness, assembly approach, cost and structural requirements hardware joint is selected
Machine screws makes a removable joint between two sheet metal parts. They require additional hardware (for example clinched, Riveted, welded nuts).
Additional hardware increases overall cost of the product.
Self Tapping Sheet Metal Screws
Self-tapping screw is economical method to join sheet metal parts.
Pilot hole or extruded hole (which is done during punching operation) is required for self tapping fasteners. On the other hand, machine screws require additional fasteners (clinch nut, weld nut or rivet nut) and extra assembly operation.
- Hardware assembly joints are temporary joints
- Blind Joint
- Wide variety of fasteners are available according to application.
- Hardware assembly is more reliable when compared with other joining operations.
- Easy to use compared with other assembly operations.
- Additional fasteners cost.
- Additional gaskets are required to make joint waterproof.
Riveting is a type of permanent joint operation. Prior to riveting, adjacent holes are punched in sheet metal plates.
For installation, firstly rivet is placed inside punched hole after that rivet tail is deformed. As a result of deformation rivet expands in diameter while holding the rivet and parts in their position.
Various types of rivets are available. We can select rivet according to our application, strength requirement, installation method and cost.
- Solid or round head Rivets
- Semi-tubular Rivets
- Oscar Rivets
- Blind or Pop Rivets – More commonly used in sheet metal industry
- Drive Rivets
- Flush type Rivets
- Low operational and material cost.
- Blind joints can be easily formed
- Assembled parts can be dismantled. This will result very less damage to component.
- Stress concentration will be high near riveted area.
- Additional riveting setup is required.
Clinching is a type of permanent joint operation using cold forming process. Sheet metal parts with different thickness and material can be joined using clinching operation.
Clinching process produces button-type positive connection between two or three layers of sheet metal.
- As explained above, Clinching does not require additional fasteners.
- Clinching is a type of permanent joint.
- Low operational cost
- Different material with different thickness can be joined.
- High initial setup cost
Welding is a type of permanent joint. Various types of welding operations can be done to join sheet metal parts.
Factors affecting type of Welding
- Sheet metal material
- Sheet Thickness
- Final Finish Requirement
- Airtight or waterproof joint requirements
- Working Temperature Range
Types of welding operations for joining sheet metal parts
- TIG Welding
- MIG Welding
- Spot Welding
- Seam Welding
Advantages of welding in sheet-metal
- Permanent Joint
- Leak proof joint can be achieved
- High load carrying capacity
- Any shape can be joined
Disadvantages of welding in sheet-metal
- Change in properties near welded area.
- Inspection of welded joint is difficult.
- For thin metal joints, avoiding warping and burn-through is difficult.
Folding / Tab Joints
Folding & bending tabs is economical way of making permanent joints. This process does not require additional hardware. Only forming machine is required to make permanent joint.
Soft steel, aluminium, copper and brass can be joined with this operation.
- Additional fasteners are not required.
- Low cost, reliable permanent joint.
- Waterproof joint can not be achieved.
- Limitation with size and type of joint.
Adhesive bonding is a type of permanent joint. For adhesive bonding, adhesive is placed between the surfaces of the components to be joined.
Factors affecting the type of Adhesive Bond
- Surface geometries
- Base material of the surfaces to be joined.
- Bonding strength requirement
- Moisture or water content in working environment
Types of Adhesive
- Cyanoacrylate Adhesives
- Acrylic based adhesives
- Epoxy based adhesive
- Silicon based adhesive
Availability of Adhesives
Adhesives are available in two forms:
- Double Sided tapes : Double sided tapes in various thickness and chemical composition are available. As per design requirement adhesive can be selected.
- Liquid Foam: Adhesives in liquid foam with different viscosity and chemical composition are available.
To sum up, various options for joining sheet-metal parts are available. As per design requirements and cost constrains, we can select the best.
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