Engineering, Rapid Prototyping Achieves Cast Conversion.

General Dynamics Defense System (GDDS), Pittsfield, Massachusetts, was looking to convert an existing fabricated and welded VME sub-rack to a casting. This component is an electronic enclosure for the command and communication-related circuitry used by the U.S. Navy. GDDS determined that a one-piece casting would provide a significant cost savings and reduce production cycle time and sought out K + P Agile, Inc., Naperville, Illinois, to help with the conversion.

Designing, manufacturing and quality-related requirements were laid out at the onset of the program. The primary objective was to perform the conversion without affecting any other equipment in the assembly or function of the assembly. The initial risk assessment performed at the beginning of the program highlighted the need for an agile manufacturing process focused on making the casting within specification and meeting all requirements the first time.

K + P served as the Tier 1 supplier on the component redesign and executed the industrial contract, project management and client communications for the project while sub-contracting the tooling, casting, machining and finishing. The first step was for engineers to convert the weldment to a one-piece casting design while maintaining manufacturability. While creating the master model, which consisted of geometry for the machined part, rough casting and tooling, design issues were discussed with the tool shop and foundry. The final design was validated by overlaying the solid model of the existing weldment on the casting design. The engineering firm also produced a scale laminated object manufacturing (LOM) rapid prototype for the customer to validate form and fit.

The casting quality was optimized and validated using shock and vibration finite element analysis and fracture mechanics tests, Then, the firm worked with the foundry and tool shop to develop a gating and risering system, which allowed further validation to be carried out using process modeling simulation for mold filling and casting solidification.

Some of the final finished cast component specifications included: cast edge radii--sharp to 0.188 in.; cast fillet radii--0.250 in. minimum; and tolerances of [+ or -] 0.06 in. up to 6 in., 0.09 from 6 in. to 12 in., and 0.12 at more than 12 in.

The prototype tooling for the molds and coreboxes then was made using CNC milling and manual bench patternmaking, sand molds and cores were made, and two castings were poured. The castings were made in nobake sand molds with A356 aluminum alloy that was T7 heat-treated.

The cast component from concept to delivery, including design, analysis, production tooling and casting, was carried out in 14 weeks. The product unit cost was reduced by 40%, component weight from 24.9 lb to 23.2 and the production cycle from 40 weeks to 14. Currently, the component is in production and a modified version will be incorporated into three different end-uses in the future.