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Self Piercing Rivets
A self-piercing (or metal piercing) rivet is similar to a tubular rivet except that they are produced from a stronger material and can be heat-treated to increase piercing capability. Self piercing rivets are manufactured from a variety of grades of carbon steel, aluminum and stainless steel materials. Rivet plating or coating options are selected dependent on the application.
Self-piercing rivets often replace spot welding and other “button” style clinch methods when a stronger fastened joint is required. Self-piercing riveted joints rely on the strength of the permanently fastened hardened rivet rather than the softer material being fastened or a difficult to inspect weld. Successfully clinched self pierce riveted joints are much easier to inspect (visually) compared to spot-welded or “button” style clinch methods. When properly installed, self pierced riveted joints will not come apart.
Application: The rivet is driven through the top sheet of work-piece material and the bottom sheet is then stretched or extruded into a forming die (anvil). As the bottom sheet is extruded into the anvil form, the tubular end of the rivet is flared out on the forming die (fig 1), securing the sheets together. Depending on rivet length and anvil selected, the flared end of the rivet can be designed to pierce completely through the sheet layers or can be flared within the bottom sheet. When piercing leather or other soft materials, the work piece material “slug” created when the tubular hole at the end of the rivet is driven remains up inside the tubular end of the rivet.
A properly designed metal piercing rivet produces a strong fastened joint. Work piece materials of standard low carbon steel, aluminum and stainless steel typically work well for self piercing, especially if hardness of work piece material is lower than RB 50. The length of the rivet selected and the anvil form design determines what the final clinch will look like. In the fig 1 and 2 pictures, the rivet and tooling was designed to have the rivet pierce through the top layer of material but not completely through the bottom sheet.
|Figure 1 (cross section)||Figure 2 Clinch side of fastened joint|
Why use self-piercing rivets?
- High-speed assembly. Rivets feed automatically in impact Rivet Machines that cycle in approximately 3/10th of a second
- No need for pre-drilled or punched work-piece holes
- Does not destroy painted or coated work-piece finishes
- Inexpensive perishable tooling is used
- Provides strong permanent fastened joints that are easy to visually inspect. If the rivet has pierced and clinched work-pieces, the joint is good
- If desired, the riveted joint can be air and watertight
- Low cost of fastener
- Easily adapted for automation
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