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A PPAP PRIMER

Documentation is key to the Production Part Approval Process.

by Rick Hudson

In our previous issue I explained how RL Hudson’s in-house engineering department is a Hudson Advantage, something that really sets us apart from other suppliers. Engineering expertise is not the only Hudson Advantage, however. We also excel in the area of quality assurance. We are ISO 9001 and QS 9000 certified, and Quality Assurance Manager Richard Stanaland heads up a dedicated and highly skilled quality team. Our inspectors utilize sophisticated spectrometry and video imaging equipment to verify materials and analyze finished parts.

Another tool that we use to ensure quality is the Production Part Approval Process (PPAP). You may already be familiar with this process. If so, you know that PPAP provides a framework for approval of production and service commodities prior to the first production shipment of parts. PPAP’s purpose is to ensure that suppliers fully understand customer design specifications and can meet those specifications consistently during production. Quality and consistency are the keys. If you’re not familiar with PPAP requirements, here’s a look at the ten essential parts of a PPAP submission and how they help ensure a consistent supply of quality parts.

PART SUBMISSION WARRANT The Part Submission Warrant (PSW) documents the precise reason for submission and the requested submission level. Reasons might include an initial submission, engineering change(s), tooling alterations, correction of a discrepancy, use of tooling that had been inactive for more than a year, a change to an optional construction material, a sub-supplier or material source change, a change in part processing, or production of parts at a new location. Submission levels range from Level 1 (often requiring that only a warrant be submitted to the customer) to Level 5 (requiring that the warrant with product samples and complete supporting data be reviewed at the supplier’s manufacturing location). As the default (and therefore the most common level), Level 3 requires that a warrant with product samples and complete supporting data be submitted to the customer. In addition to indicating the reason for, and level of, submission, the PSW states whether the parts in question meet specifications; if they don’t, nonconformity is explained. You might think of the warrant as the summary statement for the entire process. The remaining nine PPAP elements support this summary.

SAMPLE PRODUCT These are representative samples of production parts from each mold cavity. A mold with 20 cavities would result in at least 20 samples, one from each cavity, being inspected and measured.

PRINT Everything in a PPAP submission stems from the revision of the customer print to which the sample parts were manufactured. ASTM callouts, specifications, and critical dimensions are all noted on the print. Whether given in SI units (millimeters) or English units (inches), dimensions must be numbered to match Dimensional Results (see below).

DIMENSIONAL RESULTS Dimensional results verify that the sample parts are within tolerance of the print dimensions. For multiple cavity molds, parts from each cavity must be measured, and all print dimensions from all cavities must be included. All tolerances are per the print unless otherwise specified by the customer. The unit of measure (mm/inch) should be the same as is on the print. Any dimensions that are out of spec must be noted on the Part Submission Warrant.

MATERIAL TEST RESULTS This document details the results of chemical, physical and/or metallurgical testing performed to see if the product material meets customer requirements. Material Test Results should ensure that all of the print’s material callouts (ASTM D2000 or SAE J 200) are met. In some cases, an A2LA-accredited lab may be required for testing. Test results must be included for all materials (rubber, metal, coatings, etc.). Any failed tests must be noted on the Part Submission Warrant.

PROCESS FLOW DIAGRAMS Process flow diagrams describe the production steps and sequence. The diagrammed steps should match the steps in the Control Plan (see below). Any post-production processes (such as the application of a special coating to a completed part) can be reflected in an additional flow diagram.

PROCESS FMEA FMEA is Failure Mode and Effects Analysis, and it’s an analytical technique that pinpoints potential process failures, identifies possible causes, and addresses them. FMEA ensures that process failure modes have been considered and, if of high risk, addressed. An RPN (Risk Priority Number) is generated based on severity, occurrence, and detection. High RPNs require corrective action to decrease the likelihood of occurrence or to increase detection of the failure.

CONTROL PLAN The Control Plan is a summary of the operations (steps) used to control the manufacturing process. In devising the Control Plan, one must ask: Are there enough controls (such as inspection) to contain any potential product defects? The Control Plan should include equipment parameters (such as time, temperature, and specifications), and all specifications should match the Print on final inspection.

PROCESS CAPABILITY STUDIES This is a statistical method for answering the question: Is the process capable of always producing good parts? A comparison is made between the product dimensional variation and the product specifications (tolerance/variation=Cp). A Cpk of greater than 1.33 is typically required. This is equal to 4 sigma, meaning that 99.994% of the parts are good. Process Capability Studies require a minimum 100-piece sample, and studies are done on every critical dimension for automotive applications.

MEASUREMENT SYSTEM STUDIES Also known as Gauge Repeatability and Reproducibility (R&R), this ensures accurate inspection results by evaluating both equipment and operator variation during inspection. Gauge R&R studies calculate the percent of tolerance taken up by this variation. Critical dimensions should have a variation of less than 10%, while normal measurements should have less than 30% variation. Gauge R&R should be done on the same dimensions as the Process Capability Studies.

QUALITY AT WORK As you can see, PPAP submissions can be lengthy and complex, but at its heart the process seeks to ensure that only quality parts reach customer hands. That’s something we here at RL Hudson appreciate, because we’ve always had the same goal: to make sure you receive nothing but the best. Our in-house quality assurance department’s adherence to the Production Part Approval Process helps make that possible. If you’re having a quality-related issue that we can solve, please don’t hesitate to call us at 1-800-722-6766.