Riveting in Sheet Metal Fabrication(casting types Stanley)
- source:BREDA CNC Machining
How Rivets Work
A rivet consists of a cylindrical shaft and a head. To join two or more sheets of metal together, holes are drilled through the sheets at the point of attachment. The rivet is inserted into the holes and the head is upset, or smashed down using a hammer or rivet gun. This causes the shaft to flare out and clamp the sheets together. The flared end is called the shop head, while the original head on the rivet is called the factory head.
There are two main types of rivets:
- Blind rivets - These have a mandrel through the center of the rivet that is pulled to flare the rivet. The mandrel is discarded afterwards, leaving a hollow center. Blind rivets can be installed from one side making them ideal for situations where you can only access one side of the assembly.
- Solid rivets - These are hand set using a hammer or rivet gun to form the shop head. Solid rivets can come with round, flat or countersunk heads depending on the application.
Benefits of Riveting
Compared to other joining techniques, riveting in sheet metal fabrication offers several benefits:
- Does not distort or weaken the base metal - The riveting process does not involve heating metal like welding or apply torque like screws. This prevents warping or weakening of the base metal.
- Quick installation - Rivets provide a fast way to assemble components. Hand tools allow operators to quickly insert rivets and form the shop head.
- Easy to automate - Riveting lends itself well to automation and several types of rivet setting machines and tools are available. This improves efficiency and consistency.
- Allows for vibration resistance - The flaring of the rivet shaft locks sheets together while allowing movement. This makes riveted joints ideal for assemblies that will undergo vibration.
- Joint strength - Rivets form a permanent clamping force between metal sheets that is very resistant to shear and tensile stresses. Joint strength depends on rivet design and material.
- Corrosion resistance - Many rivets are made from corrosion resistant alloys that do not deteriorate in harsh environments. Stainless steel and aluminum rivets are common.
- Disassembly and reuse - Rivets can usually be drilled out if necessary allowing parts to be disassembled and rivets replaced. Screws are usually damaged when removed.
- Versatile - A wide range of rivet designs exist including various head styles and materials. This allows rivets to be customized for the application.
Riveted Joint Design Considerations
Properly designing riveted joints is important to achieve maximum strength and durability:
- Rivet diameter - Should be 1.5 to 2 times sheet thickness for soft materials, and equal sheet thickness for harder materials.
- Rivet spacing - Rivets should be spaced at 3 to 4 times the rivet diameter apart in the direction of load. Closer spacing may be required for vibration resistance.
- Edge distance - Minimum recommended edge distance is 1.5 times rivet diameter. Increasing this adds strength.
- Hole clearance - Rivet hole diameter should be 1.02 to 1.05 times the rivet shaft diameter for hand set rivets. Tighter clearance is needed for machine set rivets.
- Material thickness - As material gets thicker, rivet length needs to increase and diameter may need to increase to avoid shear failure.
- Rows and columns - Multi-row joints better distribute load compared to single row. Columns prevent buckling. Staggering rows/columns also adds strength.
- Washers - Washers can be used to prevent rip out of soft materials and improve joint flexibility.
- Joint type - Lap joints are simplest but butt joints are stronger though more complex to fabricate. Scarf and diamond joints are also very strong.
Riveting Process for Sheet Metal
The process of riveting sheet metal components together generally involves the following steps:
1. Planning - Engineer determines the rivet type, material, size and layout based on the application requirements and joint design considerations.
2. Drilling holes - Sheet metal components to be joined are clamped together and holes are drilled through the parts at precise marked locations using a drill press. Deburring may be required.
3. Preparing rivets - Rivets are obtained based on planned size and length. Solid rivets are inserted into holes. Blind rivets are loaded into rivet gun.
4. Setting the rivets - Solid rivets are set using a hammer or pneumatic rivet gun to upset the rivet shaft, forming the shop head. Blind rivets are set by pulling the mandrel to flare the rivet.
5. Inspection - Set rivets are inspected to ensure shop head is formed properly without damage to the surrounding material.
6. Finishing - Any burrs around the rivet heads are removed. Surface finishing operations like grinding or painting follow.
While riveting sheet metal requires more initial holes to be drilled compared to welding, it allows relatively unskilled operators to quickly and reliably join components in production. The combination of speed, joint strength and ease of automation make riveting an indispensible process in modern sheet metal fabrication. CNC Milling CNC Machining