Orbital forming is a process that uses an angled forming tool (peen) that spins off center at a 3 to 6° angle to securely fasten an assembly. The tool progressively heads, swages, crowns, flares, or draws a column or projection of malleable material to join pieces. The process works with a wide variety of materials from mild steel to 54 RC hardened metals. Candidates for the process include aluminum, brass, bronze, copper, lead, zinc, and stainless as well as many polymer composites and other plastics including ABS.
Compared to other riveting processes the small contact area that the orbital tool makes with the material being formed reduces axial compressive loads by as much as 80%. The reduction in compressive load reduces internal stresses in both the fastener and the mated parts, helping to improve the assembly's fatigue life. The lower compressive force also gives the formed heads smoother finishes and extends the life of the forming tool.
Unlike impact or compression forming, where the process completes in a single pass, orbital forming requires several tool revolutions to produce a 0.02 to 1.5-in.-diameter, hardened and slightly compressed head. The process generally takes from 1.5 to 3 sec. It usually takes longer to load the parts (either manually or via automation) than to complete the forming. Small-diameter soft materials process quicker than thicker materials. The total surface area and hardness determine the forming time.
Process monitoring and control systems give operators visual status of the forming process and let them make adjustments. Consistency and uniformity are the most important elements of orbit-formed heads. Controllers that run the forming process can give data on forming forces, variable rate of forming force, form height, and clamp loads between fastened parts.
Spindle stroke precision is under ±0.001 in. This gives designers the option for solid joints with selectable torque resistance or moving swing joints such as those in scissors or handcuffs.
New single-spindle, multispindle, and rollerforming powerheads let designers save assembly time and cut costs on applications from scissors to satellites:
A safety belt recoil component and hood brace illustrate the joining capabilities of orbital forming. In both applications, the process securely joins aluminum to steel where welding was not an option.
Orbital forming can create features that would otherwise be expensive to machine as in this motor mount assembly of mild steel.
An etch or engrave peening orbital-forming tool leaves embossed features such as dates, names, and trademarks on the fastener heads.
The use of orbital forming or roller forming "crimps" external material to retain components housed beneath. Orbit forming replaces clips, welding, and bolts in applications such air-bag canisters, solenoids, and ball joint assemblies. Likewise, the process can also crimp and form die-cast tabbed features at multiple points and on several surface levels in an antitheft mechanism made from zinc.
Retaining features such as snap rings can be replaced by the orbital forming of material inward or outward, into a groove.
A door latch assembly of mild steel is one example of how orbital forming can create a fastening feature by forming a tubular or semitubular component outward. The technique replaces a nut and bolt or welding.
Fastener-free air bags
Until recently, a major concern in air-bag manufacture was the control of fastener components at final assembly. Small objects such as loose, unretained fasteners can end up as projectiles during air-bag deployment in an accident. Manufacturers had to keep track of every rivet and screw during assembly, often using assembly equipment that counts rivets, screws, and rivet-pull mandrels. Even with such precautions, assembly lines had to shut down when fasteners went missing.
Air-bag designers trying to eliminate fasteners from their designs turned to Orbitform, Jackson, Mich., to help design a system that let the rivet be an integral part of the canister. The new design stakes the rivets to the canister subassembly at an off-line station. At final assembly, the canister with preinstalled fasteners, goes in a fixture at a multiple peen orbital-riveting station with rivet shanks up. The 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 next go over the secured rivet shanks. Orbitform's assembly machine then cycles, orbitally forming the faster ends to complete the assembly.
The air-bag inflater now has rivets that are an integral part of the canister. Advantages of this design include eliminating loose fasteners from final assembly, lower part and assembly cost, and offline quality-control inspection. An added benefit is the fastener shanks align components during assembly.