Common Mistake of Conducting FMEA
FMEA is hard enough to implement without any mistake. Actually, FMEA’s mistakes are the most common non-conformity in almost IATF 16949 audit (formerly ISO/TS 16949). In following sections, I will describe the common mistakes of FMEA with the reason and resolution.
1. Process Step of PFMEA does not match with Control Plan
Number and Name of Process Step do not match with those in Control Plan. Control Plan and PFMEA have explicit linkage in the process and they need to be the same in both PFMEA and Control Plan.
Example: PFMEA does not mention about shipping process even though Control Plan does.
This is the most common mistake when Control Plan and PFMEA are developed separately. Control Plan or PFMEA change from time to time, the team might forget to update the remaining document when one change. The effective solution is using a specialized FMEA software. The software will automatically update the other document whenever the team changes one.
2. Missing linkage between PFMEA and DFMEA (1)
DFMEA’s failure modes are not considered to reflect in PFMEA’s failure effects. Logically, process’s failure effects that occur on the product are product’s failure modes.
Example: A fuel tank’s DFMEA mentions about leaking problem. However, the responding PFMEA does not mention about this effects.
Not all DFMEA’s failure mode can become PFMEA’s failure effects, however, the team should consider if there is any linkage between process failure and product failure. If any, the team should mention product failure as an effect of process failure. With above example, the leaking problem can be considered an effect of failure in the corresponding process such as welding or piping assembling.
3. Missing linkage between PFMEA and DFMEA (2)
DFMEA’s potential causes are not considered to transfer to PFMEA’s failure mode. Logically, a potential cause of a product failure can become a failure in the responding process so it should be mentioned in both DFMEA and PFMEA. However, it should be transferred with considering to the scope of PFMEA.
Example: A fuel tank’s DFMEA mentions that leaking failure causes because of broken welding join. However, responding PFMEA does not mention this failure from the production aspect.
While using DFMEA as an input for PFMEA, the team should consider if any potential cause of DFMEA could also happen in the process. With above example, welding joint can also be broken if welding current is set too low.
4. The ranking is not correct.
Detection, Occurrence, and Severity aren’t evaluated consistently with the criteria and ranking system. Example, two detection controls have different ranking even though they use the same method. 2 failure modes have same effects but they have different severity rank.
Each organization may have its criteria to evaluate detection, occurrence, and severity. Sometimes, the criteria come from customer standard. The team should apply the criteria consistently in the whole project and both PFMEA and DFMEA.
5. Mixing of Prevention Control Method and Detection Control Method
Some member may misunderstand which control method is prevention method and which one is detection method. A Prevention method eliminates or reduces the chance a failure or cause of failure to happen while a detection method detects an existing failure.
Example: in a turning process, there are 2 controls in place: checking tooling position and checking the diameter of the workpiece. Are both of them detection method? No, checking tooling position can be considered a prevention method because it prevents detention defects that cause by tooling in the process.
6. PFMEA or DFMEA does not reflect recent defect or customer reject.
Recent defects or customer rejected products always are the reason to start investigation process and review PFMEA and DFMEA. If a similar failure was mentioned in FMEAs, then some causes may be ignored or the current control methods are not effective. If any similar failure was not mentioned, the team should it reflect in FMEAs and update the FMEAs with new failure to prevent it happen again.
Example: if a leaking product is found in the market, the team should start to review the PFMEA and see if it is mentioned or not. If leaking failure is mentioned in FMEAs, the current controls do not effective or some failure causes are unknown.
7. No improvement plan or risk reduction activity
Some organizations make FMEA document because their customers request it. After getting customer approval, FMEA document was put in a file and never be reviewed again. They are wasting the most valuable tool to improve their product and save their business.
Making an FMEA is just beginning of FMEA process. The main purpose of FMEA is reducing the risk by conducting corrective actions. If they don’t have an activity to continuously reduce the risk with FMEAs, the problem will come.