An ECS Staff Report 

When Benet Laboratories, a research, development and engineering facility for the U.S. Army, was interested in developing a single-piece casting from a four-piece fabrication used to clean an 81-mm mortar, the lab contacted the American Metalcasting Consortium (AMC) to provide technical input on casting the part and identifying sources to produce the part.

AMC is a partnership between the metalcasting industry and the government to produce casting solutions that improve quality and reduce cost and leadtimes for military applications. Through its CAST-IT team, the organization works with military agencies and its OEMs to streamline the casting design process and smooth out the search for appropriate casting suppliers.

Since the research facility was interested in using its SLA machine to produce rapid prototype patterns to produce several prototypes for demonstration and testing, AMC connected Benet Labs with a capable investment casting facility. The 316 stainless steel castings were made and ready to be shipped in two weeks.

The well for a casting success story runs deep in the defense industry. Through research and development, relationships with casting-specific agencies like AMC, and funding initiatives, the military is rife with casting applications. Following is a look at just a handful.

MK Universal REXTORP

    •    During U.S. Navy fleet training, an inert MK Universal REXTORP is used to simulate a hybrid lightweight torpedo.
    •    Initial casting procurements did not meet requirements, so NAVSEA worked with AMC’s CAST-IT team to review the technical data package and visit the casting facility to assess the production capabilities.
    •    It was determined that vertical pouring would  achieve the necessary property requirements, and AlumAlloy Co., Ontario, Canada, stepped in to

F-5 Crossbleed Valve Body

    •    F-5 adversary aircraft is used by Active and Reserve Navy pilots in air-to-air combat training.
    •    A crossbleed valve body part for the aircraft was proving to be an inefficient design with poor reproducibility. Casting experts suggested a modification to the gating design for better directional solidification.
    •    The proposed drawing changes were hand fabricated onto a wax part from the current tooling, the gating was modified by the casting facility, and a sample casting produced.
    •    Production castings, produced in 17-4 PH steel via investment casting, have been machined for final delivery.

F-5 Gun Gas Deflector

•    Gas gun deflector shields for F5 aircraft feature 17-4 PH steel investment castings. 
    •    Recently, a backorder situation caused by two previous contracts being cancelled or delinquent was solved through working with the new casting source to optimize quality and delivery.
    •    While several government-owned tools and fixtures necessary to produce the castings were delayed in its transfer to the new supplier, the OEM and  casting supplier developed a fixturing solution for straightening and inspection.

MK-38 Handgrip

•    The handgrip used on a 25mm machine gun mounted on most U.S. Navy ships consists of four A356-T6 aluminum castings produced by Armstrong Mold Corp., East Syracuse, N.Y.
• Initially, the technical   data for the handgrip was incorrectly dimensioned and toleranced, but AMC assisted the Naval Surface Warfare Center in reviewing the technical data and specifying the proper geometric dimensioning
and tolerancing.
• SLA mock-ups were created with Benet Army Labs to verify the dimensions with the new solid model before the assembly was ready for full production at Armstrong Mold.

M777 Howitzer Spade

    •    The U.S. Marine Corps and U.S. Army have been working collaboratively to replace aging, steel-intensive M198 155mm Howitzers with M777 lightweight Howitzers.
    •    Part of the initiative consists of utilizing titanium in applications where steel was previously used. A recent conversion involved the Howitzer’s spade, which stabilizes it during firing.
     •    The National Center for Excellence  in Metalworking Technology worked with a titanium casting facility to come up with an investment-cast design.
    •    The single-piece titanium casting replaced a 60-part fabrication and weldment. It is expected to save the military agencies $27 million.

M88 Auxiliary Power Unit Cylinder Block

    • When a tank breaks down in a hostile environment a M88 Tank Recovery Vehicle is used to relocate the disabled equipment to a safer area for repair.  
    •     After 45 years of service, the M88’s APU cylinder block casting requires replacement, however the supply chain for this casting has disappeared. 
• Creating a new supply chain to support legacy weapon systems was difficult but necessary to maintain military readiness.
•  To date, this part’s technical data has been updated, and two purchase orders issued.  In July, the first two castings were poured by Clinkenbeard, Rockford, Ill., and are off for testing. 

SIDEBAR: Military Aircraft’s Control

Viasat Inc., Carlsbad, Calif., a producer of satellite and other wireless communication products, had been supplying the U.S. Department of Defense (DOD) a five-part assembly for control indicators for military avionics by machining all five of the parts individually in order to maintain the close tolerances and smooth finish required to pass the 100% testing requirements. But the DOD challenged Viasat to reduce the cost of the assembly, and the supplier began exploring diecasting as a cost-cutting alternative to machining. 

Viasat contacted Alloy Die Casting (ADC), Buena Park, Calif., to see if it was possible to reach the same quality standards of the machined parts with greater cost efficiency via diecasting.

The assembly involves a heat sink, front panel or bezel, access door and two door pivots.

“At first we were concerned that diecasting wouldn’t be cost-effective because of the low volumes and high quality requirements,” said Lon Plourde, Viasat design engineer. “But ADC showed us how it could be done efficiently so that our investment would pay off after just 600 parts.”

The assembly is subjected to harsh military environmental requirements and must withstand temperatures of -40C to 55C and storage temperatures of -62C to 85C. All parts are required to resist 100% humidity and must survive shock and crash loads according to MIL-STD-5400.

“One of our primary requirements was the thermal performance of the heat sink,” Plourde said. “The design had to dissipate enough heat energy to maintain component temperatures, and we found through testing that we could achieve the thermal properties we needed using A360 aluminum.”

The heat sink measures 5 x 3 in. with a series of 25 rectangular windows arranged in five columns. Cast on a 250-ton diecasting press, the 2-in. plunger delivers a gate velocity of about 1,200 in./second for a 30 millisecond fill time. The large gates on the tool help the die to fill quickly without much turbulence. And the low inlet velocity helps minimize tool erosion.

The 0.13-lbs. as-cast parts require five minutes of machining, during which they receive drilled and tapped holes. The heat sink also utilizes nine helicoil inserts, so the cast parts had to be lept flat within +/-0.10 in. to accommodate them.

The heat sink nestles inside the control indicator bezel, which measures 5.75 x 3.35 in. Cast on the same press, the panel requires a 35 millisecond fill time, yielding 60 of the 0.25-lb. parts in an hour. Because the heat sink is designed to transfer thermal energy away from the components inside the indicator and out through the panel, the same flatness tolerances of the heat sink applied to the bezel, as well.

The door of the assembly, measuring 2.5 x .075 in. and weighing less than 0.1 lb., required a 0.68-in. diameter hole on either end with a tolerance of +/- 0.005 in. These holes were cast in the part, while a pair of 0.25-in. holes are drilled during machining.

The two door pivots are a matching pair and were originally quoted in the same aluminum alloy as the other components. But ADC found it could achieve the fine detail required in the small part by casting it in zinc instead, taking advantage of zinc’s superior flow properties and ability to maintain close tolerances.

Because of the hole locations and part size (less than 0.75 x 0.5 in. dimensions and 2.5-oz. weight), ADC casts the door pivots on a four-slide machine, which produces complex, thin parts that would otherwise need to be assembled from two or more pieces.

The door, door pivots and bezel receive a chemical film after machining and are masked and powder-coated. ADC provides final assembly of the door pivots, with springs and other components in place for subsequent manufacturing steps in the Viasat facility.    ECS