A new shell design for a future weapons system called for only 20 production units. Although the program was two months behind, castings could not become critical path, so Texas Instruments hit the target with stereolithography (SL).

The Challenge
Low volume production is frequently prohibitive for cost-conscious manufacturers. Yet many programs call for small numbers of actual production units for such applications as assembly verification, testing and full production. That's why when only 20 production units of a new design for an outer shell enclosure on a weapons system had to be readied for contract delivery dates, the project team at the Defense Systems & Electronics Group of Texas Instruments (TI DSEG), faced several formidable challenges. First, the program was two months behind schedule. Second, the new part design had to be delivered as a finished production unit in just six months. More important, TI’s rapid prototyping (RP) team had to transform the design into metal castings quickly enough to stay within their tight deadlines. Converting the design to metal could be done by traditional machining, welding, and dip brazing, but with a price of further program delays. Because a follow-on contract for 120 production shipsets was in the pipeline, the project team became convinced their only option was to move from design to metal as rapidly as possible - that meant SL.

The Results
By exploiting the full potential of SL, TI DSEG discovered a multitude of immediate and long-term benefits. In fact, when the cost/benefit analysis was complete, the team realized that despite the original time deficit, SL gained back an additional month's iteration time to debug their design. Even if there had been enough time for hard tooling, there may not have been enough time to optimize the design configuration. Clearly, SL was pivotal to program success by enabling TI DSEG to:

• Successfully produce 20 production units for an Armed Services customer
• Use SL prototypes in electronic and vibration testing with precision accuracy
• Eliminate time and expense of hard tooling by moving directly from SL pattern to metal casting
• Overcome a one-month time deficit to meet a critical contract delivery date
• Free-up mechanical engineering team to move to another time-critical program
• Post an overall program savings of $450,000

The Process
The design size of the outer shell enclosure was 36.25" in length and was built in halves to accommodate the SLA system. In the CAD file, SL specialists divided the design in two and developed a butt joint. A larger part was made to function as a fixture. With the fixture complete, TI DSEG could glue halves together to ensure overall part length and orientation. Parts were set up in the machine to face one another and then joined together with break off tabs, giving maximum dimensional stability to the unit.

"SL gave us the ability to prove out concept models early which reduced the total of actual part numbers we had to establish for the project. In turn, we reduced warehousing and stocking costs."
               - Own Baumgardner Manager Fab Producibility
               Engineering Texas Instruments Defense Systems and Electronics