How to reduce RPN of Visual Inspection Process

[nkson]

Dear all,
I works for a new tire manufacturing company, and there is a visual inspection process to check tire appearance.
For your information, tire appearance defects happen quite frequently, so Occurrence score is high (8~10). However, we use manpower only to check the tire, so Detection score is high to (7~8). Therefore, RPN always higher than 100, but we cannot do any improvement except training and re-training.
So I have 3 questions that need you guys to advice:
1. Is P-FMEA applicable for visual inspection process?
2. Do we have to improve with RPN >100 items for visual inspection process?
3. If we have to improve, what is the suitable way?

Thank you!

 

[sjared]

If you haven't done so I would start by ensuring there are inspection standards that the operators can refer to when doing the inspection so they can compare their sample with the standard. I would also be aware of the fact that there are vigilance issues with activities like this. In other words, the operators will not be as effective at catching defects after an extended period of time. Although very technical, the FAA has published guides for visual inspections. Just google "faa guide to visual inspection."

 

[Chennaiite]

1. Is P-FMEA applicable for visual inspection process?

The purpose of Process FMEA is to manage risk in the Manufacturing process. Visual inspection is very much part of Manufacturing process and therefore it is very much part of Process FMEA.

2. Do we have to improve with RPN >100 items for visual inspection process?

There's an excellent article here as to why RPN is meaningless in the first place and then also how it misleads

3. If we have to improve, what is the suitable way?

Generally, the idea is to work on causes of the visual defects (in this case) by setting up a preventive control or at minimum to detect the cause. Now, if you could share little more details on the failure mode, cause, etc, it will be much easier to streamline this discussion.

 

[nkson]

@sjared: Thanks for your information. We have all operation standards, trained properly to all operator with certificating before send them to station. Now I'm checking FAA document.
@Chennaiite: Our failure mode is only "Outflow of defective product" cause by operator cannot find the defect. We apply 200% visual inspection, and another person to sampling check the OK production of every inspector.

 

[Chennaiite]

I assume that defects in discussion are chronic in nature and all necessary steps have been taken to keep the occurrence under control. Some points to ponder are;
- Are you giving adequate time for Visual Inspection?
- Are you maintaining Limit samples?
- Are you keeping your Inspectors on rotation to kill fatigue?
- Is your Inspection area adequately illuminated?
- Did you investigate the cause of outflow whenever it happens?
- Are you isolating defective parts from OK parts?
Last question, did you ever speak to inspectors themselves, particularly from solution point of view?

 

[nkson]

@Chennaiite: please check my respond below:
- Are you giving adequate time for Visual Inspection?
>>> Actually we have fix standard time, but present inspection cycle time is all over standard time. So I can say inspectors have enough time.
- Are you maintaining Limit samples?
>>> No, we have not. I will consider to make some.
- Are you keeping your Inspectors on rotation to kill fatigue?
>>> No, we have not because of shortage manpower. Now continues training more.
- Is your Inspection area adequately illuminated?
>>> Yes, over 3000lux, and monitor monthly.
- Did you investigate the cause of outflow whenever it happens?
>>> Sorry but no.
- Are you isolating defective parts from OK parts?
>>> Yes.
Last question, did you ever speak to inspectors themselves, particularly from solution point of view?
>>> No, I have never.

 

[antonjav]

.... if the pFMEA process that was used is the latest version, which is version 4, you would discover that the the FMEA would be helpful and would naturally give insight as to how visual inspection may be improved.

It looks like that the older version was used ...

Hope that this helps.