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in severe service applications but also notorious for difficulty in meeting cosmetic and dimensional require- ments within a reasonable leadtime. Because of their high yield strength, high material stiffness, and toler- ance of deflection without damage, steel castings also can be effective in lightweight applications. Pushing the limits of minimum as-cast wall thick- ness is important in reducing weight in this type of application. H.A. Burrow Pattern Works

(HAB), Silesia, Mont., collaborated with the Metalcasting Consortium (AMC) sponsored by the Defense Logistics Agency (DLA), the Army’s Research, Development & Engineer- ing Command (RDECOM), Benet Laboratory at Watervliet Arsenal, Watervliet, N.Y., Acme Castings, Huntington Park, Calif., and the Steel Founders’ Society of America (SFSA) to convert an original 15-piece fabricated steel design to a one-piece, lightweight 19.5-lb. cast steel design.

The 15-piece fabrication design

was difficult and expensive to manu- facture and had an unacceptably high rejection rate. One of the first decisions in the new design was to choose a different steel alloy, because the carbon steel used for the fabrica-

The deflector tray casting had difficutl thin-to-thick sections where walls transitioned from 0.08-in. to 1.5 x 1.75-in. mounting areas.

tion would not be a good casting candidate due to fluidity issues in the thin 0.08-in. wall sections. HAB determined an investment cast 17-4 PH alloy in H1100 condition had the fluidity and strength to be a good cast substitute. After numerous solid model

iterations, additional features previ- ously welded to the fabricated tray were added to the one-piece casting design, while still keeping the com- ponent’s total projected weight to 20 lbs. The additional features were added to the model casting require- ments, and the technical data pack- age (TDP) was modified accord- ingly. Benet sent a request for quote (RFQ) and TDP to a number of investment casters with the require-

ment to provide one prototype cast- ing for testing, and then the project hit a snag. Benet received a few bids that were unacceptably high in price and leadtime. Many investment casters who did not bid provided the following reasons: • The walls were too thin • The thin-to-thick cross sections were difficult (0.08-in. walls to 1.5-in. x 1.75-in. mounting areas).

• The casting was too rangy to readily be straightened.

• Grade B and C x-ray require- ments were too difficult for the casting configuration. After careful consideration by the

team, it was determined the deflec- tor tray still was a viable casting design, and TDP requirements could be produced. HAB, with 85 years of experience in the tooling casting industry and extensive work with many casting facilities, took the lead and sent out a more detailed RFQ. HAB selected Acme Castings, Huntington Park, Calif., to produce the part based on an agreement that HAB would supply the stereolithog- raphy (SLA) patterns, rigging and design and take total responsibility for the finished casting, paying for it regardless of meeting all requirements.

From Order to Completion The printed inspection fixture indicated minimum straightening was needed after heat treatment. 24 | MODERN CASTING July 2013

Benet issued a purchase order and the manufacturing process was started. Heat treatment of rangy parts is prone to cause distortion. The first process was to develop a means to achieve the dimensional requirements. HAB added tie bars, which would be cut off prior to

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