Q. 192 In Process FMEA, do existing process controls affect only the Detection Rating? Or do they influence the Occurrence Rating as well? Provide examples to explain your answer.

 

Note for website visitors - Two questions are asked every week on this platform. One on Tuesday and the other on Friday.

• All questions so far can be seen here - https://www.benchmarksixsigma.com/forum/lean-six-sigma-business-excellence-questions/
• Please visit the forum home page at https://www.benchmarksixsigma.com/forum/ to respond to the latest question open till the next Tuesday/ Friday evening as per Indian Standard Time.  
• The best answer is always shown at the top among responses and the author finds honorable mention in our Business Excellence dictionary at https://www.benchmarksixsigma.com/forum/business-excellence-dictionary-glossary/ along with the related term.

 

Existing Process controls affects the detection rating and also has influence on the occurrence rating

Steps	Potential failure mode	Potential effect of failure	SEVERITY	Potential causes	OCCURRENCE	Current control	DETECTION	Comments
What is the step	In what ways can the step go wrong	Impact if the failure mode is not prevented/corrected	How severe is the impact on customer	What causes the step to go wrong	How frequent is the cause likely to occur	What current control are there that prevent the failure mode from happening or detect it if it occurs	How probable is the detection of failure mode
Report to be saved in the respective location	Report was missed to be saved in the location	SLA not met	7	Assuming report is saved but not saved in the location/ other issue	1	Self check/Sample audit	6	Sample audit / Self check has influence over the occurrence on the report not being saved
Team contacts the customer if no remittance details are available.	Team contacts wrong customer	SLA not met	6	Lack of attention/ name not clear in invoice	1	Checking previous history before contacting	7	Referring the historical data for exceptions will help for better clarity
Log into Application	Incorrect user ID	Unable to log in	3	Typo error or Typing in urgency	2	System display the Alert message when User ID is Incorrect. User ID same as Z ID hence available with TL as well	3	System control supports in typo error or error to to urgent typing

What are existing process controls?

Simply stated these are the measures taken in the process to ensure that defective items are not produced. 

 

What are the types of existing process controls?

There are two types 

1. Preventive

2. Detective

 

Preventive process controls have an effect on Occurrence ratings as they prevent the occurrence of the failure modes. 

Detective controls have an effect on Detection ratings as they help detect that a failure mode has occurred.

The same principle is applied when Mistake Proofing is done in the Control phase of a six sigma project. 

 

Let us take some examples

1. Production checklist that an agent uses is a preventive control as it ensures that processing is done correctly. If it is used, it will reduce the occurrence of defects. Audit checklist is a detective control as it checks if a defect has occurred or not

2. Using coding best practices is a preventive control as it reduces the number of bugs. Unit testing is a detective control as it checks for bugs present in the system

3. The spelling auto correction or highlighting of the word with red underline in MS word is a preventive control which reduces the number of spelling mistakes (while writing the article). However, a spell check in MS word is a detective control as it detects the incorrect spellings (after the article is written). By the way, in Excel there is only spell check and no auto correction

4. Preventive Maintenance is done in manufacturing. It reduces the occurrence of unplanned downtimes due to faults and hence impacts the occurrence rating

5. The "Caps Lock is on" warning is a preventive control in order to prevent instances of entering incorrect passwords and hence impacts the recurrence rating. The system not allowing to log in if an incorrect password is entered is a detective control which first checks for a valid password and hence impacts detection rating

6. In certain websites, one cannot enter alphabets if it is a numeric field. This is a preventive control which reduces the occurrence of incorrect entry in the field. The warning that some mandatory fields are left blank and system not allowed to go the next screen is the detective control where it checks for entries in all mandatory fields

7. Metal detectors and smoke detectors are examples of detective process controls. These will not impact the occurrence but will definitely have a bearing on the detection rating.

8. The seat belt not worn is a detective process control as it detects that the seat belt is not worn. In some advanced cars, the car will not start unless the seat belt is worn. This is a preventive control as it does not let the occurrence happen

 

In all the above examples, preventive controls impacts the occurrence rating while detective controls impact the detection rating.

 

To sum it up, while doing process FMEA, the below format is more useful where it clearly shows that preventive process controls impact Occurrence ratings and detective process controls impact Detection rating.

 

Source: APQP FMEA format sourced from Google images

 

Benchmark Six Sigma Expert View by Venugopal R

Process FMEA is usually done to evaluate the potential failure modes in a process that is newly developed or has undergone some modifications.

 

For determining the probability of occurrence, the process capabilities and historical data from similar processes are taken as inputs and the ‘Occurrence ratings’ determined using the rating guidelines.

 

The ‘Detection’ ratings are determined based on the existence and effectiveness of “Current Process Controls” that are meant to prevent the defect from going undetected. Strictly speaking, the idea of ‘Current Process Controls’ is to improve the detection and prevent the ‘occurred’ defects from escaping unnoticed and reach the internal or external customer.

 

There are certain situations where the ‘detection’ is not practically easy. Some of you would recall the term ‘Special Processes’ introduced by the ISO 9000 standards. The quality characteristics of such processes cannot be fully assessed after the process is completed. One of the examples that I have experienced is that of ‘soldered joints’ on a PCB. Sometimes we may need elaborate testing or even destructive tests to fully evaluate such special characteristics. For these characteristics, by their inherent nature, the detection will be poor or the ‘Detection rating’ will be high in the FMEA. Here, it is extremely important that the ‘Occurrence’ possibilities are kept very low and hence a low Occurrence rating is essential.

 

Coming more specifically to our question as to whether Process Controls help in affecting not just  ‘Detection rating’, but can they also influence the ‘Occurrence rating’, I would like to take a look at the guidelines given for detection rating as per AIAG or any other major standard. For a Detection rating of 2, it says “Error detection in station (automatic gauging with automatic stop feature). For Detection rating of 1, it says “Discrepant parts cannot be made because item has been error proofed by process / product design”.

 

Thus, if a particular failure mode gets 1 or 2 as detection rating, as per the above guidelines, it means that the occurrence of the defect has been eliminated! So, doesn’t it appear that due to effective process control, not only the detection rating has been made favorable, but also the occurrence rating?

 

However, there’s one thing that I would like to add. In the above situation, we are highly dependent on some mistake proofing technique, that is very often dependent on technological methods. I would be concerned that one fine day the ‘mistake proofing’ shouldn’t fail to work, for which a ‘control’ to assure the continued effectiveness of the mistake-proofing would be essential.

 

For example, while doing payment processing, one of the critical failures was a mistake in the cheque amount, which resulted in cheques being returned. An automated mistake proofing was successfully introduced for digital comparison of the cheque amount with the invoice amount using a script. However, a periodic validation to keep a watch that the script remains 'active and effective' is a necessary control to be introduced.

In case of FMEA, the existing process control will affect both detection and occurance ratings. 

Example is that in case of a VFD, dusting out of modules periodically is one of the process controls. 

This is predominantly done to detect any conductive dust deposition on cards which will result in the failure of the VFD system. In the due course of dusting out the module, as the modules are completely opened, and again repacked any open space which may lead to future dust accumulation inside module are taken care of there by resulting in reduced occuance of dust accumulation. 

The winner this time is Natwarlal for perfect response and many meaningful examples. Neelakandan has also provided correct response and an example.