PPAP (Pre-Production Approval Process) – Planning for success

The acronym PPAP has become more commonplace in industry, and is trickling down from automotive and heavy equipment OEM’s to smaller organizations, which are now adopting the concept.  One’s 1st experience with PPAP can be harrowing, but if you break it down in to bite sized pieces, it can be handled without undue stress.

The PPAP “package” starts with a Part Submission Warrant (PSW).  The PSW outlines an overview for the PPAP, which includes the Customer, control document identification and revision, PPAP Level, and a proven production rate, which is to reflect the capacity of the process and tooling.  This PSW also serves as the official document to formalize the entire PPAP “package”, as the vendor must sign and take responsibility for the accuracy and completeness of the details of the PPAP.

The next document is normally the Process Flow Chart (PFC), which is normally an illustrated flow chart showing the steps for the process, and the sequence of steps to complete the finished product.  This document should detail the process steps, and identify movement between departments.  It should also identify validation or measurement steps.  This document is normally used as the basis for setting up audits, and for differentiating other possible process options that may be chosen to produce a product.

Generally, the next document is the Control Plan.  The Control Plan follows the outline of the PFC, but gets into much greater detail regarding each of the process steps, and how they will be validated and ultimately controlled.  Control Plans break down the process flow into exact steps, and detail the quantity of product that will be checked when validation steps occur.  Control Plans also reflect what happens if one of the process steps is found to be out of control.  The Control Plan steps are important, as they are numbered, and will correspond to the same number in subsequent documentation.

The Control Plan sets the stage for the PFMEA (Process Flow Material Element Analysis), which is essentially a document that applies “Murphy’s Law” to the Control Plan.  This document asks the vendor to outline possible processing problems, and what the contingency/correction plan is for if/when they happen.  This document should rate the possible issues in terms of severity and likelihood of occurrence, and should be rated statistically accordingly.  If the process shows possible problems that should be addressed, the vendor should detail the specific steps it is taking to minimize the possibility of occurrence, and rank them before and after the minimization moves.  Vendors should be cautious, as this is the document that will raise the most questions from customers, and be the focal point of audits.

PPAP’s may vary in terms of sequence, but a report showing the dimensional results of the 1st parts produced is normally expected, along with a statistical analysis of the results, referred to as Cpk.  Most customers will require that the dimensional results be provided per cavity for molded parts, and most customers require a Cpk of 1.67 or higher to show statistical capability in the process.  If the Cpk falls below 1.25, the process is normally regarded as not capable of meeting the control dimensions.

The dimensional results are generally supported with a Gauge R & R Study, which is a document showing that the measurement equipment used to capture the dimensional details provides consistent and reliable results, regardless of operator.  This document reflects measurements taken by (3) independent personnel with the same measurement equipment, and the results are captured and tabulated.  The range in any difference found in this document should be within (1) standard statistical deviation, which should reflect a capable measurement system.  If the range is greater than (1) standard deviation, the measurement system will likely fall into question.

PPAP’s normally will also include physical testing results and packaging specifications, as well as APAP documentation, and in some cases, capability studies.  If properly done, the PPAP process can be an advantage for both customer and vendor, and establish metrics for finished product that minimize the potential for non-conformances.

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