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inspection, radiographic inspection and all other characteristics appli- cable to the casting. First Article Approval formally notifies the foundry of process acceptance, and introduces an obligation to continue production using the same processes and controls. Proposals for change must be commu- nicated through the buyer for review by Raytheon engineers who evaluate the potential impact and establish a test plan appropriate for reapproval. Simple changes might not justify any extra testing, but other changes might require revalidation of dimensions, strength, or internal soundness. Com- plex changes might require repeti- tion of the entire first article process approval test program. Studies of complex thin-walled aluminum investment castings have shown the greatest potential for vari- ability lies with dimensional integrity. Tis is because wax pattern sag, solidi- fication stresses, and quenching distor- tion are facts of life. Fortunately, these can be addressed by foundry processes, straightening tooling, and dimensional check fixtures. Consistent quality from the casting

supplier results from capable equip- ment and processes, skilled work- manship, and a well documented set

alcasting use during production and inspection operations.

Meeting Customer Expectations Experienced metalcasters appreci-

Figure 5. High stress areas were determined.

of work instructions. To ensure a consistent and well-focused appraisal process by all parties, Raytheon Preci- sion Manufacturing shares a Supplier Quality Plan unique to each casting part number. Tis SQP documents the parameters for casting inspection and communicates control dimensions from the perspective of machinability, product assembly, and in-service func- tion of the end item. Rather than create this SQP in a

vacuum, the producibility engineer develops the control dimensions in conjunction with the casting engi- neer to ensure key characteristics are understood and controls are well designed into the casting process. When appropriate, additional tooling and fixtures are developed for met-

ate that all suppliers are not created equal. Each operation brings differ- ent processes and experience toward solving customer challenges. Alloy and process differences aside, suppliers have significant niche capabilities in terms of rapid prototyping, mechanical property requirements, size, complexity and other aspects of product configu- ration. Tis requires an appreciation for how these capabilities influence the best fit within the OEM’s supplier base for each casting application. Te Raytheon North Texas

organization uses a casting team to coordinate the strategic issues of process enablers, preferred supplier list, supplier development, and technol- ogy roadmaps to ensure the interests of each organization remain balanced throughout the procurement process and casting production life cycle. Key stakeholders include the producibility engineering (representing design), supplier quality engineering and sup- ply chain management. Looking back, the LRAS3 sensor

housing remains a state-of-the-art casting with an incredibly complex die set, a tedious wax injection operation, and a demand for precision at every subsequent step in the process. But the results justify these efforts. Four suppliers—Shellcast, GSC, Alcoa Howmet Laval, and Uni-Cast—have produced more than 5,500 castings over the product life to date. Te design and development

Figure 6. The casting development process feeds mechanical development.

efforts of Raytheon experts, sup- plier teammates and customers were paramount. As a result, the LRAS3 system performs well and the cast housing structure continues to meet all objectives. Te lessons learned are collected by the casting team for use in each subsequent casting develop- ment project. Te Raytheon Casting Product Development Process (Fig. 6) continues to serve as the template for success in design and development of complex metal castings. Te next challenge is to make them cheaper, faster and better.

July 2013 MODERN CASTING | 31

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