23 Specifications, 23 Sets of PPAP? —— Five-Step Method for Family Part Submission and Representative Part Selection

A hardware supplier provides 23 different specifications of pins to the same customer, with varying hole diameters and lengths but identical process routes. At the start of the project, the engineer prepared 23 sets of PPAP: 23 process flow diagrams, 23 PFMEAs, 23 control plans, and 23 initial process studies. After reviewing one set, the customer's SQE asked, "Aren't these parts from the same family? Just submit the extreme parts once for the family." The supplier had no answer—there was no clear definition of "family" internally, nor any basis for consolidation, so they had to complete all 23 sets.

Another common and more dangerous scenario is when engineers think a couple of parts "look similar" and simply modify the previous PPAP with new part numbers and size data. This often results in nonconformities from the customer—because the modified PPAP does not cover the new part numbers, and the characteristics in the PFMEA and control plan do not match.

Both approaches stem from the same issue: the company has not clearly defined and documented the concept of "family." The main cost in PPAP is not in writing the documents but in determining "how many sets should be prepared and which part numbers are included in each set."

1. "Family" is a Process Concept, Not a Similarity in Appearance

The determination of family parts (Family Parts) focuses on the production process, typically requiring all four conditions to be met simultaneously:

• The same production line, the same set of equipment, using the same tooling and process parameter ranges;
• The same PFMEA and control plan, and their coverage must include all part numbers within the family;
• Consistent special processes such as material, heat treatment, and surface treatment;
• Differences between parts are only in end attributes such as size values, color, and packaging, all of which fall within the same process window.

Counterexamples best illustrate the issue: two almost identical brackets, one made by stamping and welding, the other by stamping, welding, and then deburring. The additional process step means they are not in the same family. Conversely, three different specifications produced on the same equipment using the same mold but different cavities, if they have the same tolerance grade and control method, can be considered for family submission.

2. Five Steps to Create an Approved Family Submission

Step 1: Group parts by process route, not by part number. Arrange part numbers for the same customer or production line into a matrix based on "process sequence + equipment group + material." Group part numbers with identical process sequences together to form candidate families, then screen each family using the four conditions outlined in the first step. The list should clearly state all part numbers in each family, their specification limits, annual usage, and characteristic lists.

Step 2: Define family boundaries using extreme specifications. Select a representative part for each family, the principle being to choose the most "difficult to produce" part: the one with the tightest tolerance band, the largest or smallest size, the thinnest wall, the most severe deformation, or the most cavities. The logic of family submission is to "prove the entire family using the extreme part," so the representative part must first prove the family boundaries, and other part numbers within the family are then considered covered. Once the boundaries are set, they should be written as numerical values (e.g., diameter 8-20 mm, length 30-120 mm), not just as "similar parts."

Step 3: Obtain written confirmation from the customer. Family submission is a customer-approved matter, not something the supplier can decide independently. The basis for this must be derived from the customer's supplier manual, CSR documents, or written responses from the SQE, and should at least include: acceptance of family submission, identification of the representative part, which part numbers are covered, and how to handle new additions. Without written confirmation, revert to individual submissions. Skipping this step is like building the entire set of documents on a shaky assumption that can be overturned at any time.

Step 4: Submit and document the coverage relationships. Fill out the PSW according to the customer's requirements and note that it is a family submission. Attach a complete list of part numbers to make the coverage range clear to the customer. Submit the size report, material report, and initial process study for the representative part as usual, and retain an applicability statement for other part numbers—explaining that the processes are consistent, the specifications fall within the proven boundaries, and the control plan and PFMEA apply to them. Keep the documents in the factory for reference, ensuring they are the same version as the submitted materials.

Step 5: Write the rules for "additions and changes" into the process. Compare new part numbers to the family boundaries first: if the process remains unchanged and the specifications fall within the boundaries, proceed with the continuation confirmation. If any part exceeds the boundaries (larger specifications, tighter tolerances), or if new or removed processes, equipment or tooling changes, material or supplier changes, or production site relocation occur, a new submission is required. This rule should be written into the change management procedure and signed by both engineering and quality.

3. An Example

The pin supplier followed the five steps to redo the submission: first, they arranged the processes, and all 23 specifications went through cold heading, turning, heat treatment, and grinding on the same line with the same control plan; then they split them into two candidate families based on material and hardness requirements; next, they selected a representative part for each family—one with the largest diameter, longest length, and largest grinding allowance, and the other with the highest hardness requirement and tightest tolerance band; finally, they confirmed the part numbers and boundary values with the customer's SQE, obtained written approval, and consolidated the 23 sets into 2 family submissions. A year later, 5 new part numbers were added, 4 of which fell within the family boundaries and were confirmed for continuation, while 1 exceeded the upper length limit and required a complete PPAP resubmission. The customer did not issue any nonconformities because the covered part numbers, boundaries, and how new parts are judged were all clearly documented and easily verifiable by the auditor.

4. Three Misconceptions

Misconception 1: Treating "similarity" as a family. Merging parts based solely on similar appearance or part numbers, ignoring differences in processes, materials, and tolerance grades. The criterion for a family is the process, not the appearance.

Misconception 2: One set of documents for all, but not covering each part number. The most common reason for nonconformities in family PPAP is that the PFMEA and control plan do not explicitly state which part numbers are covered. The value of a family submission lies in the "list plus boundaries," and without this, part numbers not covered within the family become management gaps.

Misconception 3: Expanding family boundaries to reduce submissions. Forcing parts with different materials or processes into the same family may save on documents in the short term but can have greater long-term costs. If a part within the family has a quality issue, tracing back will reveal that it was never individually proven, leading to a significant loss of trust from the customer, far exceeding the initial document savings.

Family submission saves on repetitive work, not on evidence. Within the boundaries, the evidence chain behind a single document must be complete; outside the boundaries, no part can be carried over.

The prerequisite for family submission is process consistency plus written customer approval, and the representative part must stand at the family boundary. No carry-over outside the boundary.

Knowledge code: 8.3.3

Version: v20260928

Author: QTank QTank is dedicated to providing systematic professional knowledge, methodologies, and practical tools for quality management practitioners, helping companies continuously improve their quality capabilities.