Case history: diecasting firm helps give fighter pilots oxygen.

Gentex Respiratory Products, Rancho Cucamonga, Calif., designs, develops and manufactures aviation oxygen masks and positive pressure breathing systems that help fighter pilots maintain consciousness during high-G maneuvers. The company's CRU-60/P Connector, which mates the pilot's mask to the oxygen supply and features an emergency bailout elbow that connects with an oxygen bottle in the seat to allow the pilot to breathe when ejected from the aircraft, was exhibiting porosity issues.

"If the diecast part is too porous, especially in critical areas like the O-ring groove, it won't meet leakage requirements," said Bill Kirk, Gentex respiratory products manufacturing manager. "In today's high-G, high altitude aircraft, excess porosity could deprive a pilot of essential oxygen in a combat or emergency situation."

Gentex selected a diecasting firm, Alloy Die Casting (ADC), Buena Park, Calif., to help solve these issues and reduce scrap rates on the connector. Gentex set a target scrap rate of less than 4% rejects after all testing is completed for the part.

ADC, a manufacturer of large, small and complex die castings in aluminum and zinc/aluminum alloys for the military, aerospace, medical, automotive and industrial markets, was equipped to meet Gentex's needs.

"Many diecasting facilities today focus on high-volume production," said Gary Gray, ADC design engineer. "We've become very adept at designing diecast tools and processes for intricate, close-tolerance parts that other shops might shy away from in low to medium volumes."

As the industry standard for restraint harness connectors, the CRU-60/P meets all requirements of U.S. Air Force specification MIL-C-38271B. Typically secured to a dovetail mounting plate attached to an airman's parachute harness, the design delivers positive locking and prevents flailing during an ejection.

The component connects to a conventional three-pin bayonet oxygen mask hose connector. The aircraft supply end incorporates an omni-directional quick disconnect to ensure proper alignment at all times.

The CRU-60/P Connector is cast from A380 aluminum. Ingots of raw material are melted in a gas furnace at 1,200F (649C), and a measured shot is injected at 8,000 lbs./sq, in. (562 kg-force/ sq.cm), producing a gate velocity of 1,200 in./second (3,048 cm/second).

To hold down the part cost, Gray elected to design a two-cavity, custom-built family die to cast both components of the connector, since they must be assembled together to create a complete unit. The angles involved on the components meant standard tool holders would not work, so ADC built a dedicated tool with five slides.

"We took great pains to design-in excellent venting and precise temperature control," Gray said. "Because of the porosity restrictions, we really wanted to avoid trapped gas in the casting, so the gates and runners were sized and located with that objective in mind."

For such a critical application, the finished parts needed tolerances as tight as 0.003 in. and were subjected to a battery of performance tests before certified as field-ready.

During trial runs, ADC engineers took the first castings into the company's extensive testing facility, where they used real-time x-rays to evaluate the porosity. "Secondary operations like milling and grinding have a tendency to make porosity issues more apparent," Gray said. "The x-ray inspection helps us spot potential problems with trapped gasses, so we can adjust the shot speed and other parameters to force trapped air to the overflow, Visit www.alloydie.com for more information.