DFMEA vs PFMEA: design and process FMEA, and when to use each

DFMEA vs PFMEA is a question of what you analyze. A DFMEA, or design failure mode and effects analysis, asks how the product design can fail to meet its requirements. A PFMEA, or process failure mode and effects analysis, asks how the manufacturing or assembly process can fail to make the product as designed. You need both, in that order.

Both methods use the same logic: functions, failure modes, effects, causes, controls and a risk rating. They differ in scope, owner, inputs and outputs. This guide explains what each one is, compares them side by side, shows how the AIAG-VDA 7-step approach and action priority apply to both, and walks through a short example of how a design risk turns into a process control.

What is a DFMEA?

DFMEA stands for design failure mode and effects analysis. It is a structured risk analysis of a product, system, subsystem or component while it is still being designed. The team lists the functions and requirements of the design, asks how each function can fail, what the effect would be for the end user and what in the design could cause it.

Typical DFMEA causes are design decisions: a wall that is too thin, a material that ages too fast in heat, a tolerance stack-up that allows interference, or a missing requirement. The controls are design controls. Prevention controls are things like design rules, proven designs and simulation. Detection controls are tests and analyses that find a weak design before it is released, such as prototype tests or design verification.

What is a PFMEA?

PFMEA stands for process failure mode and effects analysis. It analyzes each step of a manufacturing or assembly process, including receiving, transport, storage, rework and inspection. For each step the team asks how the step can fail to deliver the product characteristic it should, what the effect is on the next operation, the plant, the customer and the end user, and which process cause is behind it.

Typical PFMEA causes are process causes: a wrong machine setting, a worn tool, a missing part, a wrong part or an operator error. The controls are process controls, such as error proofing, setup checks, parameter monitoring, gauging and inspection. Our guide to the PFMEA and control plan explains in depth how these controls become shop-floor instructions.

What is the difference between DFMEA and PFMEA?

The short answer: the DFMEA asks whether the product will work if it is made correctly. The PFMEA asks whether the process will make it correctly. The table compares the two methods point by point.

Both use severity, occurrence and detection ratings, but each on its own scale. In a DFMEA, occurrence rates how likely the design cause is, given the design controls. In a PFMEA, occurrence rates how likely the process cause is, given the process controls. Detection in a DFMEA means finding the weakness through tests before design release. Detection in a PFMEA means finding the defect or the cause in the plant before the part leaves.

When do you use a DFMEA and when a PFMEA?

Use a DFMEA when your company is responsible for the design: a new product, a design change, a new application of an existing design or a new operating environment. A supplier that builds to the customer’s drawing usually has no DFMEA of its own, but it still needs a PFMEA for its process.

Use a PFMEA for every new or changed manufacturing process: a new line, a new plant, a new tool, a process change or a move of production to another site. In product development the DFMEA comes first, and the PFMEA starts as soon as the process flow is known. In automotive, both are deliverables of APQP: the DFMEA in phase 2 and the PFMEA in phase 3. The two overlap, and both must be updated during the product’s whole life.

What is the AIAG-VDA 7-step approach?

Most automotive suppliers now follow the AIAG and VDA FMEA handbook, first published in 2019. It describes one method in seven steps, used for both the DFMEA and the PFMEA. Only the content of each step changes.

1. Planning and preparation
   Define the scope, the team, the tasks and the tools. The handbook summarizes this as the 5T: intent, timing, team, tasks and tools.
2. Structure analysis
   DFMEA: break the product into system, subsystem and component, usually with a block diagram. PFMEA: break the process into steps and work elements such as machine, material, method and people.
3. Function analysis
   DFMEA: name the functions and requirements of each element, often with a P-diagram. PFMEA: name what each process step must achieve and the product and process characteristics.
4. Failure analysis
   Build the failure chain for each function: the failure effect, the failure mode and the failure cause.
5. Risk analysis
   Record the current prevention and detection controls. Rate severity, occurrence and detection, then read the action priority from the table.
6. Optimization
   Plan actions for high and medium priority items, assign an owner and a target date, and rate the risk again after the actions are done.
7. Results documentation
   Report the results and the actions taken to management and, where needed, to the customer.

Why is action priority used instead of RPN?

The older FMEA manuals ranked risks by the risk priority number, or RPN: severity multiplied by occurrence multiplied by detection. The weakness is that very different risks can get the same RPN. A rare failure with a safety effect could score lower than a frequent cosmetic defect.

The AIAG-VDA handbook replaces the RPN with action priority, or AP. A table assigns every combination of severity, occurrence and detection to high, medium or low priority. Severity carries the most weight, then occurrence, then detection. High priority means the team must act or document why the current controls are enough. The same logic applies to the DFMEA and the PFMEA, each with its own rating tables.

How does the DFMEA feed the PFMEA and the control plan?

The DFMEA, the PFMEA and the control plan form one chain. Customer needs enter the design, for example through quality function deployment. The DFMEA shows which product characteristics are critical for safety, regulations or function. Those become special characteristics on the drawing.

The PFMEA takes these characteristics over. For each process step that creates or changes a special characteristic, the team analyzes how the process can miss it. The effects from the DFMEA are reused, so the severity of the effect on the end user should be the same in both documents. The process controls from the PFMEA then go into the control plan, with sample size, frequency and reaction plan.

1. Requirements: customer and legal requirements, functions and interfaces.
2. DFMEA: design risks, design controls and the special characteristics.
3. Drawing and specification: special characteristics marked with the agreed symbols.
4. Process flow diagram and PFMEA: process risks for each step, with the same special characteristics.
5. Control plan: how each process control is carried out in series production.

The link also works backward. When the PFMEA shows that a characteristic cannot be made reliably with the planned process, the design team should hear about it while the design can still change. When a defect reaches the customer, the problem solving, for example an 8D report, should update the PFMEA and, if the cause is in the design, the DFMEA too.

What does a DFMEA and PFMEA example look like?

This short example is illustrative, not a client case. The product is a molded plastic clip that holds a cable bundle to a car body panel. Its function is to keep the cables in place under vibration and heat over the life of the vehicle.

The two analyses look at the same failure from two sides. The DFMEA fixed the design weakness and named the latch arm thickness as a special characteristic. The PFMEA made sure the molding process keeps that thickness, and the control plan says how it is checked in series production.

What are the most common DFMEA and PFMEA mistakes?

• Process causes in the DFMEA: “operator assembles wrong” belongs in the PFMEA. The DFMEA should name design causes.
• Design causes in the PFMEA: a wrong tolerance on the drawing is a design issue. Send it back to the DFMEA team.
• Different severity for the same effect: the end-user effect and its severity should match in both documents.
• Special characteristics lost on the way: a characteristic marked in the DFMEA is missing in the PFMEA or the control plan.
• FMEA as paperwork: a DFMEA filled in after design release, or a PFMEA written only for the customer audit, cannot change anything.
• One person fills in the form: without a cross-functional team, the analysis misses the knowledge of design, production and testing.
• No update after changes or complaints: both documents must be revised after every design or process change and every field or customer complaint.

How can an interim FMEA or quality engineer help?

Many plants have FMEAs that exist on paper but do not prevent failures. The DFMEA and PFMEA were written by different teams, the special characteristics do not match and the control plan is out of date. An experienced FMEA moderator or interim manager can lead the workshops, align the DFMEA, PFMEA and control plan for a product family, move the analysis to the AIAG-VDA format and train your engineers to keep it current.

GQ Interim has delivered 1,550+ projects in manufacturing and industrial companies across Central and Eastern Europe since 2011, for clients such as Stellantis, Porsche, Siemens, Valeo and Magna. Our database holds 7,500+ verified experts, including FMEA moderators, quality engineers and supplier quality engineers. We are certified to ISO 9001 and TISAX. See our FMEA consultant service.

Conclusion

The DFMEA makes the design reliable. The PFMEA makes the process capable of producing that design. Use the same 7-step method and action priority for both, start the DFMEA early, start the PFMEA as soon as the process flow is known, and carry the special characteristics through to the control plan. Then the two analyses work as one system that prevents defects.

Frequently asked questions