Process and Product FMEA : Control Special Characteristics with Skill FMEA Pro

The Gordian knot of special characteristics

In the high-precision engineering ecosystem, particularly in the automotive (IATF 16949) and aeronautics (IAQG) sectors, the management of Special Characteristics (SC) represents the ultimate test of a quality system's robustness. A Special Characteristic (SC) is a classification assigned to a product characteristic or manufacturing process parameter, the variation of which may critically affect product safety, regulatory compliance, form, function or performance.

The challenge is not simply to identify these SC. The real challenge, and the source of many audit non-conformities, lies in demonstrating uninterrupted traceability and control of these SC, from their cradle in the design office (Product FMEA / DFMEA) to their monitoring on the production line (Monitoring Plan), via their control in manufacturing engineering (Process FMEA / PFMEA).

This "SC cascade" is often broken by the use of disconnected office tools, such as Excel. Each workbook becomes a silo, creating risks of desynchronization, data entry errors and an inability to prove the coherence of the control chain. It was to address this fundamental technical issue that an integrated engineering solution like Skill FMEA Pro was developed.

1. The technical anatomy of the SC cascade

To grasp the complexity of the problem, it is essential to break down the flow of technical information as required by standards (notably the AIAG-VDA harmonized manual).

Stage 1: Identification

It all starts at the design stage. During its DFMEA analysis, the design office identifies the product's potential failure modes.
- The Effect : The analysis focuses on the effects of the failure on the end-user or the system (e.g. "Loss of braking", "Non-compliance with anti-pollution standards").
- Criticality (Severity) : If this effect is deemed critical (e.g. Gravity = 9 or 10, impacting safety or regulations), the design team must go back up the chain.
- The Characteristic (Cause) : The team identifies the product characteristic (dimension, material property, etc.) whose non-conformity is the cause of this failure mode. This characteristic is then "marked" as a Special Product Characteristic (SPC).

Technical example:
- Effect (G=10): Fuel leak (fire hazard).
- Failure mode: Poor seal.
- Cause (Product Feature): Surface roughness of gasket surface.
- Classification: "Surface roughness" becomes a SC-Product.

Step 2: The "Translation" (DFMEA → PFMEA)

This is where the first chain break occurs in traditional systems. The Process FMEA (PFMEA) must take over.

The "Methods" team must analyze how it will reliably manufacture this "Surface Roughness" (our SC-Product). The PFMEA's objective is to identify the manufacturing parameters which have a direct influence on obtaining this SC-Product.
- The Challenge: The PFMEA does not control roughness directly; it controls the parameters of the machining operation (e.g. tool speed, feed rate, lubrication, insert wear).
- The Link: The PFMEA team must identify which of these parameters is the main cause of variation in SC-Product. This parameter then becomes a Special Process Characteristic (SPC-Process).

Technical Example (continued):
- SPC-Product (from DFMEA): "Surface roughness".
- Process Operation: Machining the joint face.
- Process Failure Mode: Roughness out of tolerance.
- Cause (Process Parameter): Incorrect tool cutting speed.
- Classification: "Cutting speed" becomes a SC-Process.

Step 3: Control (PFMEA → Monitoring Plan)

Once the SC-Product and SC-Process have been identified in the PFMEA, the auditor's question is simple: "How do you control them?" The answer is the Control Plan.
The Control Plan is not an independent document; it must be the direct consequence of the prevention and detection actions defined in the PFMEA.
- For CS-Product ("Roughness"): The PFMEA has defined a detection action (e.g. "100% control by roughness meter at end of line"). This action becomes a mandatory line in the Monitoring Plan.
- For CS-Process ("Cutting speed") : The PFMEA has defined a preventive action (e.g. "Statistical control (SPC) on cutting speed every hour"). This also becomes a mandatory line in the Monitoring Plan.

2. The failure of conventional tools (Excel) in the face of Synchronization

The technical flow described above immediately exposes the flaws of a non-integrated system:
- Break in DFMEA-PFMEA traceability: How can the PFMEA engineer be sure of having identified all the SC-Products defined by the design office? If the DFMEA is an A File and the PFMEA a B File, the only guarantee is a manual rereading, which is fallible and time-consuming.
- PFMEA-Monitoring Plan desynchronization: This is the most frequent point of non-conformity. The FMEA team improves the PFMEA (e.g. changes the inspection frequency or detection method). But who thinks to update the Monitoring Plan (C-File) accordingly? The Monitoring Plan quickly becomes obsolete and no longer reflects the real control of risks.
- Lack of overview: During an audit, it is impossible to "click" on a SC and see its complete cascade. The auditor has to manually cross-check three documents, hoping that the terminology and version indexes are consistent.

3. Skill FMEA Pro: engineering continuity

Skill FMEA Pro is not a "better Excel"; it's a paradigm shift based on a relational data model (single database) where the FMEA and the Monitoring Plan are not documents, but views of the same data set. Here's how this architecture technically solves chain breaks.

3.1. Native feature flow-down (DFMEA → PFMEA)

Synchronization is not an "import", it's a dynamic link.
- The Product/Process Repository: Skill FMEA Pro is based on a "Product Structure" and a "Process Structure" (manufacturing routing). The software knows which manufacturing operation (PFMEA) is supposed to produce which product characteristic (DFMEA).
- The Intelligent Interface : When the Methods engineer opens his Process FMEA for the "Machining of joint surfaces" operation, the software automatically presents him with the product characteristics he has to guarantee, including "Surface roughness" marked as SC-Product.
- Risk Coverage: The software ensures coverage control. It can alert the user if a SC-Product is not processed (i.e. no SC-Process parameter is linked to it) in the PFMEA. Traceability is no longer a hope, it's a system requirement.

3.2. Dynamic generation of the Monitoring Plan

This is the most critical technical feature for SC control. In Skill FMEA Pro, the user does not "write" the Monitoring Plan. It is generated automatically from the FMEAs.
- The mechanism: the software scans the FMEA database (DFMEA and PFMEA) and applies management rules:
          1. it extracts all Special Characteristics (Product and Process).
          2. for each, it recovers the Prevention (e.g. Poka-Yoke, SPC control on the process parameter) and Detection  (e.g. dimensional control, functional test) actions defined in the PFMEA.
          3. compiles these elements (characteristic, inspection method, frequency, person responsible) in the format of the Monitoring Plan.
- The Result: Absolute consistency. If the FMEA team decides to change the control frequency of a SC in the PFMEA (from "1/hour" to "100%"), the Monitoring Plan is instantly updated. Desynchronization becomes technically impossible. The FMEA (the "why" we control) and the Monitoring Plan (the "how" we control) are two sides of the same coin.

3.3 Capitalization (RetEx): The Holy Grail of SC management

SC management is not limited to a single project. The real challenge is to never make the same mistake twice. Skill FMEA Pro integrates powerful "Generics" management (capitalization).
- The Concept: Once a SC control method has been validated (e.g. the combination of "tool type + cutting speed + SPC control method" to guarantee "Roughness < 0.8µm"), this block of knowledge (DFMEA + PFMEA + CP) is saved as a "generic".
- Application: When a new project ("child" project) includes a similar feature, the engineer doesn't start from scratch. He "instantiates" the generic. He instantly inherits the proven Product FMEA, Process FMEA and MControl Plan.
- The advantage: It saves more than 50% in time, but above all it's an anti-risk barrier, guaranteeing that the company's best know-how is applied by default to the control of new Special Characteristics.

From static to dynamic management

Mastering Special Characteristics is the backbone of IATF 16949 compliance and product risk management. Relying on fragmented desktop tools to manage this critical flow of information is like navigating a high-risk area at a moment's notice.

An integrated software solution like Skill FMEA Pro doesn't just digitize FMEA forms. It re-builds the engineering process around a single database, ensuring native synchronization and unalterable traceability of the DFMEA → PFMEA → Control Plan cascade.

By making desynchronization impossible and ensuring complete risk coverage, Skill FMEA Pro enables engineers to spend less time "proving" compliance and more time designing robust products and processes.