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With the right press, tooling and design, engineers can assemble parts without fasteners or other added materials.
Assembling one part to another usually requires a third material- screws, rivets, adhesive or filler metal-but it doesn't have to. In fact, sometimes all you have to do is bend, fold or deform a feature on one part to capture the other.
As long as one of the parts is made of a malleable material-typically metal-engineers can use a pneumatic, hydraulic or electromechanical press to crimp, stake, swage or clinch it to retain the other part. For added strength, the second part can include a ridge, groove or other feature to retain the material that flows from the first part.
Crimping involves pinching or compressing material around another part. This technique is used to attach terminals to battery cables and fittings to automotive hoses. Crimping is used to assemble solenoids, door locks, sprinkler heads and catheters.
In staking, downward pressure is applied to the end of a post or shaft, creating a head, or to the inside wall of a bore, forming one or more retaining points. The cover of a window lifter motor assembly is staked, as are the guide rings on timing belt pulleys. Bearings are often staked to shafts or bores to supplement the interference fit, and the ends of bolts are sometimes staked to prevent them from loosening.
In swaging and flaring, material from a post or cylinder is moved outward or inward radially to capture an edge or rim. Swaging is used to attach brass pins to circuit boards. It's also used on seat belt retractors, antilock brake system cartridges and swivel joints. It's even used on stents for cardiovascular procedures.
In clinching, a punch and die are used to plastically form a mechanical interlock between metal sheets. This technique is used on air bag housings, disk brakes, computer chassis and washing machine cabinets.
Much at Stake
When designing a staked assembly, engineers should start with the strength requirements for the joint, just as they would when designing a bonded or bolted joint, says David J. Zabrosky, North American sales manager for Schmidt Technology. By knowing how strong the joint has to be, engineers can determine how many points must be staked...