“T e bottom line is, the PPAP is a time stamp of what the supplier did when it made this part and it is a living document that is reviewed and updated periodically,” Helgeson said. “For instance, when an engineer changes a part, he can go back and look at the history of the PPAP and see what the issues were that might be a concern to him, as well.” Caterpillar will review the PPAP if it sees a dimensional trend in the castings it receives, where a dimension is drifting and the measurements are diff erent than expected. In the review, the supplier and Caterpillar may fi nd if control of a process is slipping or if tool wear is occurring. “T e PPAP is not just done once and then put away,” Helgeson said. Dimensional results aren’t the only
measurement examined. Caterpillar pays close attention to metallurgical results, as well. T ese can be addressed in PPAP documentation. “Due to the additional strength
requirements of the applications being developed, the metallurgical results are just as important, and many times the casting supplier may not pay as much attention to those,” Helgeson said. “T e yield strength, hardness, fatigue strength, excessive wear, etc., are all very critical in the application, depending on the type of metal and application.”
Roles and Review At Caterpillar, the PPAP is evalu-
ated by three parties—engineering, pro- cess engineering and quality, and each party is focused on diff erent sections. Engineering evaluates whether the
part is defi ned correctly, the FMEA is current and complete and critical char- acteristics are appropriately defi ned. Engineering also checks that it can trace key elements of the FMEA and critical characteristics through to the control plan. T e process control engineer/
manufacturing engineer is responsible for making sure all the elements are complete and reviewed. Quality evalu- ates sample inspection and measure- ment correlation, determines whether appropriate lab tests and analysis are complete and reviews the inspection and control plans.
Jul/Aug 2013 | METAL CASTING DESIGN & PURCHASING | 35
Process fl ow diagrams are required in Section 2 of the PPAP.
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