Emhart Upgrades SPR System New technique makes it easier to bond dissimilar materials A new Self-Piercing Rivet (SPR) assembly system from Emhart Fastening Teknologies may encourage automakers to switch more automotive parts to aluminum and plastics from steel.

The Mt. Clemens, MI-based company is showcasing an electronically driven SPR assembly system, used to join two different materials, such as an aluminum hood and steel hinge, that the company says is more efficient and less costly than the hydraulic system currently used by competitors.

Using an electronic motor, instead of hydraulics, to set rivets means less downtime for maintenance to flush, clean and replace hoses, to clean up leaks or spills and there's no disposing of hydraulic fluids. "The biggest difference will be the maintenance," says Bill King, Emhart service technician.

While the Emhart system is used on the new Audi A2 in Europe, there currently are no U.S. applications. "I think you'll probably hear something next year," says Randy Leedy, product manager, Self-Piercing Rivets. "We're working with several automakers."

A source labels General Motors Corp. as the "most interested."

Emhart's invention is important to automakers trying to lighten vehicles to improve fuel efficiency. That's often accomplished by switching certain parts from steel to another material rather than converting the entire product to, say, an all-aluminum structure, which usually is too expensive.

Emhart's system holds two materials together and drives the rivet through the top layer and into the lower layer. A bottom die then reshapes the lower material and rivet to form an interlocking joint that is corrosion proof and gas and liquid tight. "There's no pre-punching or drilling. There's no lining up of holes, which is needed in some systems," says Mr. Leedy.

Furthermore, Emhart's system measures material thickness to determine the rivet's length. "Hydraulics can't do that," says Mr. Leedy.

However, there are a couple of issues facing SPRs. Preferably, Emhart would like the bottom material to be thicker and stronger than the top material layer. Sometimes this is not possible when attempting to make mid-lifecycle product enhancements. Also, Emhart hasn't had much success using SPRs on magnesium, a material becoming increasingly important in automotive design.