RIM's a key for next-generation fob

Advanced RKE systems need a fob for unlocking doors and setting alarms. Transponders that signal cars to start — along with circuit boards, batteries, and button pads — all reside directly in the head of the key.

But squeezing that much hardware in a confined space posed a challenge for Ortech, Kirksville, Mo., a Tier-1 supplier of key locksets. But, rapid injection molding (RIM) was able to provide complex, high-quality prototypes with short lead times. Developed by The Protomold Co. Inc., Maple Plain, Minn., RIM combines 3D CAD with high-speed CNC machining equipment to quickly manufacture injection molds. The process is a good fit for production quantities between traditional rapid prototyping and conventional injection molding (i.e., 10 to 10,000 parts).

With RIM it's possible to build prototypes with no exterior blemishes such as sink marks, flow lines, and visible parting lines. "It would have been difficult to produce production-quality prototypes with other prototyping methods considering the intricacy of RKE integrated key heads," says Brian Bolton, Ortech design manager. He figures RIM saved at least $20,000 compared to traditional molding methods and put out production-grade parts in two weeks. The prototyping process also had to accommodate rigorous design validation testing to ensure the transponder worked with RKE electronics in place.

Prototype parts saw a vast array of tests. They often included mechanical endurance, environmental exposure, thermal shock, as well as functional checks, says Bolton. "For these tests, parts are considered dimensionally 'perfect,' because they were produced by prototyping methods and therefore not subject to variations associated with mass production." Prototypes must closely approximate production versions dimensionally. Small disparities, such as prototype warping, shrinking, or poor surface definition can wreak havoc on functional testing.

"Design validation tests aren't possible if mock-ups are too rough, so Protomold's ability to provide production-quality prototypes is extremely beneficial," Bolton said. "RIM is the only method that lets us rigorously test such intricate and innovative components." Prototypes that incorporate sufficient detail also let process validation proceed with confidence in the basic design, he adds.

"Design changes are influenced by many people, ranging from industrial designers all the way to consumers," said Bolton. "Although appearance isn't a key design issue for many automotive-parts suppliers, lockset keys and ignitionlock cylinder bezels and knobs are in the line of sight of passengers and drivers. And they must reflect the image of both the automotive manufacturer and the particular vehicle being developed."

Ortech previously relied on stereolithography (SLA), pourmolded polyurethane using rubber molds, an in-house tool shop, and various other prototyping methods to produce part mock-ups. But SLA lacked the definition needed for the intricate transponder RKE designs, and inhouse machining from raw material stock produced multiple-week lead times for the quantity of parts needed.