Risk Analysis Mid-Section, Part 2, Process Mitigations
Design Transfer, Process Validation, Process Verification, Risk Analysis, Risk Analysis V&V
In a previous Device Tip, I discussed that Risk Analysis V&V takes place at three stages in the product lifecycle:
- during design and development (design risk mitigation)
- during design transfer (process risk mitigation)
- during manufacturing and commercial shipment (design and process risk mitigation)
Continuing on this topic, in this tip I want to address the 2nd part of the “mid-section” of Risk Analysis – verification and validation (V&V) during Design Transfer. Here’s the tip:
- during design transfer, utilize Process Verification to confirm that process risk mitigations have been implemented and operate correctly
- also during design transfer, utilize Process Validation wherever the results of a process cannot be fully verified by subsequent inspection and test
In Part 1 of Risk Analysis V&V, I discussed that Design V&V ensures that the product design itself has reduced risks from use hazards and design failure modes, to acceptable levels. These are the strongest measures to reduce risks.
Now in Part 2, during Design Transfer, Process Verification is used to ensure that a) process mitigations have been implemented in the manufacturing process, and b) these measures are effective in reducing risks to acceptable levels.
Most often, these process mitigations involve inspection and/or test to filter out units that have defects that could cause risks. Process mitigations can also involve Process Control measures that control process variables to prevent defects from occurring in the 1st place. Process control can be more effective than inspection and test if process variables are controlled continuously. Second, upper and lower control limits are established for these variables to ensure that the outputs of the process are within specifications, typically with some margin to allow for measurement variation. Thirdly, the process is validated at the upper and lower control limits on a statistically valid number of samples.
Both Process Verification and Process Validation are important parts of the overall goal of Design Transfer, to “ensure that the device design is correctly translated into production specifications”.
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As in Part 1 on design mitigations, well written process mitigations will pay big dividends when it comes to Process Verification and Process Validation. Again, the standard of “complete, clear and non-conflicting” is a good test. So mitigations like “inspection”, “production test” or “process validation” are inadequate.
Here are a few examples of process mitigations, for either when design mitigations still leave residual risk, or when no design mitigations can be identified.
Example 1 – Inspection
“Manufacturing to perform inspection of <specific part or assembly> for <specific defect that can cause risk>.”
Note that the specific part or assembly is identified, along with the specific defect that can cause risk.
Example 2 – Test
“Manufacturing to test for <specific part or assembly> for <specific out of spec condition>.”
Note that again the specific part or assembly is identified, along with the specific out of spec condition that can cause risk.
Example 3 – Process Control
“<Specific equipment> to incorporate <specific process variable control> of <specific process>.”
Note that this example assumes the process to be controlled utilizes a piece of equipment that can control process variables, and that a specific process variable has been identified that contributes to the process output. This example implies that such process development takes place prior to or during Design Transfer.
The next tip on Risk Analysis will look at an overall approach to risk management during manufacturing.