RS-68 castings produced straight from 3-D models

BY JOHN MITCHELL

Development and certification time for Rocketdyne's new RS-68 engine was half the cycle time required to develop and certify previous rocket engines, thanks to the use of advanced design techniques.

The RS-68 is the first liquid propulsion system in the world to be developed from the ground up based on a design approach called Cost as an Independent Variable, said Byron K. Wood, vice president and general manager of Boeing Rocketdyne, in a white paper report on RS-68 development. Simply explained, Cost as an Independent Variable focuses designers on optimizing the cost in meeting product goals through practical tradeoffs among capability, performance, schedule and cost. The RS-68 engine will be used in the new Delta IV, with first launch now targeted for this fall from Cape Canaveral Air Force Station, Fla.

Another of the intriguing new processes used in the creation of the RS-68 was the latest three-dimensional modeling software, said Wood. Using 3-D modeling, the RS-68 was, in a sense, created before it was created. Computer-aided design and 3-D modeling techniques also are used extensively in other Boeing business units.

Three-dimensional modeling, along with a wide array of analysis and design tools used in the design of the RS-68, was simply unavailable a generation ago when the Space Shuttle Main Engine was developed. With the RS-68, these tools and disciplines were used in new and cooperative ways by the RS-68 team, in a parallel and integrated product development environment that yielded extensive information sharing by integrated product development (team) members, said Wood.

This included team sharing of a common 3-D-model geometry of each component, which allowed team members to work from the same model to perform unique analyses and update the design, said Wood. That analysis was then extended to manufacturing operations by producing direct castings for parts from the 3-D-geometry models.

Typically, hard tooling for a 1,200-pound fuel pump component casting can cost more than $400,000 and take up to a year to produce and qualify. And if the hard tooling must later be modified, the price increases. With 3-D modeling and associated processes, design changes can be made to the model easily, resulting in an order of magnitude cycle time improvement in casting development over the hard-tooled approach, said Wood. And once the design is finalized, the part can be hard-tooled for production without casting iterations.