TWI Knowledge Summary
Self-Piercing Riveting
Process description
Self-piercing riveting is a high-speed mechanical fastening technique for point joining of sheet material components. The process cycle is illustrated in Fig. 1.
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Fig. 1. Schematic representation of the self-piercing riveting process |
A semi-tubular rivet is driven into the materials to be joined between a punch and die in a press tool. The rivet pierces the top sheet and the die shape causes the rivet to flare within the lower sheet to form a mechanical interlock. The rivet may be set flush with the top sheet when using a countersunk rivet head. The die shape also causes a button to form on the underside of the lower sheet; ideally, the rivet tail should not pierce this button.
The equipment normally comprises a C-frame with a hydraulic force application for setting the rivet. Manual or robotic gun systems are available for relatively short reach applications, whereas long reach applications normally use fixed C-frames.
Current status
Self-piercing riveting is used in many industries as it is a simple, one-step joining technique. As it relies on a mechanical interlock rather than fusion, it can be used on materials and combinations of materials , where, for instance, resistance spot welding is difficult or even impossible. Examples are heavily zinc-coated, organic coated or pre-painted steels, combinations of steel to aluminium alloys and some plastics to metals. However, all materials should have sufficient ductility, and the sheet on the die side should have an elongation of at least 12%. In steel. joints can be made in sheet from about 0.5 to 3mm thickness, with a total joint thickness of up to about 6mm. For aluminium alloys, a total joint thickness of up to about 10mm can be riveted.
Self-piercing riveting is used for joining heavily zinc-coated steel sheets in the automotive, heating, ventilation and building industries, for pre-painted steels for white goods, and for joining aluminium alloys which are used for road sign manufacture or in the automotive industry.
Important issues
The forces for self-piercing riveting are high, typically 30 to 50kN. This necessitates large stiff C-frames, particularly if long reach is required. For robotic applications, these C-frames are too heavy, and lightweight equipment would be required.
As many industries (e.g. automotive) are driven by weight-reduction, manufacturers are moving towards thinner and stronger materials. These may be less suitable for self-piercing riveting, due to a lower ductility and elongation. However, further process optimisation for those specific materials may make self-piercing riveting feasible.
Benefits
The main benefits of self-piercing riveting are:-
- Simple, one-step process with no pre-drilled holes required;
- Fast, automated operation possible;
- Suitable for many different materials and materials combinations;
- Little or no damage to pre-coated materials;
- Joining of more than two sheets possible;
- No fume or heat and low noise emission;
- Long tool life (typically greater than 20,000 joints);
- Low energy demand;
- Process monitoring equipment available;
- Good fatigue performance, often better than spot welds.
Risks
The principal risks to the operator during self-piercing riveting are mainly from trapping hazards. However, this can in general be avoided by using two-handed or fully automated operation. In addition, safety goggles should be worn to avoid injuries resulting from the failure of hydraulic piping, or the high speed release of rivets and/or machine parts during operation.
Further information
Additional content on self-piercing riveting can be found in:
Self-piercing riveting in automotive applications
Self-piercing riveting - process overview
Self-piercing riveting - Design guidelines
Self-piercing riveted joints - Performance data
FAQ: How much does it cost to set-up and run a self piercing riveting system?
FAQ: What should be checked when making a detailed examination of a self piercing riveted joint?
The two case studies indicate the benefits gained from the use of self-piercing riveting:
Self-piercing riveting case study - electric window winders
Self-piercing riveting case study - Volvo FH12 truck cab
You can use the Weldasearch literature database to supplement what you find in JoinIT.
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