Until now, a major concern in air bag manufacture has been the control of fastener components at final assembly. Because small objects could end up as projectiles upon air bag deployment, it was literally a matter of life and death to keep track of rivets and screws.
Construction of air bags has progressed into high-volume production with low-cost fastening installation, an aerospace concept applied to the auto industry. Air bag design and manufacturing engineers, interested in reducing labor-intensive installation of blind rivets and screws, embraced the "open flange" concept -- using the open flange as the fastening surface for installation into the automobile.
Solid and semi-tubular riveting cannot replace blind riveting in all applications and many passenger side air bag canister designs have evolved from an "internal retaining ring" to the open flange design, allowing use of less expensive rivets and installation tooling.
But while semi-automated assembly via open flange saved cost, the concern remained about keeping loose fasteners from being lost within the air bag during assembly. Assembly equipment that counts rivets, screws, and rivet pull mandrels wasn''t enough, as stations would be shut down to search for missing fasteners.
Consulting with automotive air bag designers and manufacturing engineers, Orbitform''s application team developed a process that eliminates fasteners from the final assembly. The bag itself is attached to the canister. This concept utilizes fasteners incorporated into the canister sheet metal component as a subassembly.
The form was designed to allow the rivets to become an integral part of the canister. They have been staked into the canister at an offline workstation or the supplier''s plant. This is accomplished by adding a small shoulder to the rivet.
Advantages of this method of assembly are:
- Loose fasteners are eliminated from final assembly.
- Fasteners and fastening system are lower cost.
- Preinstalled fastener installation allows quality control responsibility to shift to offline areas or sources.
- Fastener shanks aid in alignment of components.
At final assembly, the canister with preinstalled fasteners is placed into a fixture at a multiple-peen orbital riveting station, with rivet shanks pointed up. The manufactured rivet heads rest against the fixture nest, providing additional insurance against dislodging during assembly and forming. The bag with metal mounting ring and outer retaining flange is then placed over the secured rivet shanks, and Orbitform''s assembly machine cycles, orbitally forming the fastener ends to complete the assembly.