Manufacturing and Assembly Process FMEA

The Process FMEA ensures that, potential failure modes and their associated causes or mechanism have been considered. This document includes a list of an analysis of items that could go wrong based on the experience of similar processes. Some of the technical limits have been taken already in the Design FMEA into consideration such as tolerance performance, surface finish, spacing for assembling or tooling, etc.

What kind of information can I get from an FMEA? How to fill correctly an FMEA form?

The header of the FMEA form offers information about the name of the product being analyzed, information related to this particular document, as team members, dates, edition, etc.

The header of the Process FMEA form contains the following information:

1. FMEA Number: Enter the intern number of the Document;

2. Item: Enter the name of the Item decided by the team;

3. Prepared by: Enter the name, tel. nr. of the engineer responsible for preparing the FMEA;

4. Process Responsibility: Enter the department, supplier name, if applicable;

5. FMEA Date: Enter the date the original FMEA was compiled;

6. Model Year(s)/ Program(s):  Enter the intended model year(s)/program(s) that will use and/ or be affected by the process being analyzed;

7. Key Date: Enter the initial FMEA due date, which should not exceed the scheduled production process;

8. Revision Date: Enter the latest revision date;

9. Core Team: List the names of responsible individuals;

10. Page: Enter number of pages include this document;

Then it comes the complex part related to the manufacturing process, and different modes of failure of every function.

11. Process Function: Enter a simple description of the process or operation being analyzed (for ex. Turning, cutting, molding, drilling, welding, assembling). It is recommended to record the associated process or operation number for the step being analyzed. Where the process involves numerous operations for example assembling with multiple operations, it may be desirable to list all the operations separately.

12. Potential Failure Model(s): The failure mode is the manner in which the process could fail to meet the process requirements or the design intent as described in the Function column. In preparing the FMEA assume that the incoming part or material is correct.

Start identifying the potential failure modes by comparing them with similar processes or customer reviews.

Typical failure modes:

  • Cracked
  • Bent
  • Handling damage
  • Surface to rough
  • Open circuited
  • Burred
  • Hole to shallow
  • Dirty
  • Deformed
  • Short circuit
  • Hole-off location
  • Hole missing
  • Hole too deep
  • Surface to smooth
  • Mis-labeled

13. Potential Effect: Potential Effects of failure are defined as the effects perceived by the customer. Describe the effects of the failure in terms of what the customer might notice or experience. The customer could be the next operation, location, dealer, or the vehicle owner.

For the end-user the typical failure effects could be:

  • Noise
  • Erratic Operation
  • Poor Appearance
  • Intermittent Operation
  • Unstable
  • Leaks
  • Scrap
  • Customer dissatisfaction
  • Rough
  • Vehicle Control impaired
  • Inoperative
  • Unpleasant odor
  • Operation Impaired
  • Effort
  • Rework/ Repair

If the customer is the next operation, the effects should be:

  • Cannot fasten                     
  • Cannot bore/tap                
  • Cannot mount                    
  • Cannot face                        
  • Damages equipment        
  •    Does not fit
  • Does not connect
  • Does not match
  • Causes excessive tool wear
  • Endangers operator

14. Severity: The rank is associated with the most serious effect for a given failure mode. The reduction of this rank can be achieved only through a design change or redesign the process. Severity should be estimated using the next Table as a guideline.

The evaluation criteria can be personalized by the team to meet their expectations.

Note: Failure modes with a rank of severity 1 should not be analyzed further. It is not recommended to modify criteria for ranking values 9 or 10.

15. Potential Cause of Failure: Potential cause of failure is defined as how the failure could occur, described in terms of something that can be corrected or controlled. If correcting the cause has a direct impact on the failure mode, then this portion of the FMEA thought process is completed. Many causes, however, to correct or control, a design of experiment may be considered to determine the major root cause of the problem.

Typical failure causes:

  • Improper torque- over, under
  • Improper weld- current, time pressure
  • Inaccurate gauging
  • Improper heat treat – time, temperature
  • Inadequate gating/ venting
  • Inadequate or no lubrification
  • Worn locator
  • Worn tool
  • Chip on locator
  • Broken tool
  • Improper machine setup
  • Improper programming
  • Part missing or mislocated

Note: Only specific errors or malfunctions (operator fails to install seal) should be listed, ambiguous phrases (operator error, machine malfunction) should not be used.

16. Occurrence (O): The occurrence is the likelihood that a specific cause/mechanism of failure will occur. Preventing or controlling the causes of failure through a design or process change is the only way to reduce this value.

Estimate the likelihood of occurrence of potential failure cause on a 1 to 10 scale.

The Possible Failure Rates are based on the number of failures that are anticipated during the process execution.

Note: The ranking value of 1 is reserved for ‘Failure is unlikely’.

17. Current Process Control: Describe the controls either prevent the failure mode from occurring, or detect when it occurs. These controls can be an error-proofing system, statistical process control (SPC), or can be post-process evaluation.

There are 2 types of design controls to consider:

  • Prevention: Prevent the mechanism of failure or the failure mode from occurring, or reduce their rate of occurrence;
  • Detection: Detect the cause/ mechanism of failure or the failure mode, and lead to corrective actions.

Ones the process controls have been identified, review all prevention controls to determine if any occurrence rankings need to be revised.

18. Detection (D): Detection is the rank associated with the best detection control listed in the process control. To achieve a lower ranking, generally the planned process control has to be improved.

A- Error proofed
C-Manual inspection

19. Risk priority number (RPN):  RPN = Severity (S) x Occurrence (O) x Detection (D)

20. Recommended Action: The recommended action intends to reduce the rankings of S, O, D. In general, practice, when the severity is 9 or 10 special attention, must be given to ensure that the risk is addressed through existing design control or process preventive/ corrective actions.

 In all cases where the effect of an identified potential failure mode could be a hazard to manufacturing or assembly personnel, preventive or corrective actions should be taken to avoid the failure mode.                                  

The following actions should be considered:

  • To reduce the probability of occurrence, process, or design revision is required. An action-oriented study of the process using statistical methods could be implemented with ongoing feedback;
  • To accomplish a reduction in the ranking use error/ mistake-proofing methods;
  • Improving detection control is costly and ineffective for quality controls. Increasing the frequency of the quality controls should be used just as a temporary measure. In some cases, a design change to a specific part may be required;

The following table indicates, besides Severity rank equal to 9 or 10, which ranking requires corrective action. Every organization determines a personalized ranking system, based on team analysis, experience, similar product service history.

The letters and numbers indicate:

N- NO corrective action needed

C- Corrective action needed

Orange Cells- Corrective action needed if the Detection rating is equal or higher than the given number

If Occurrence = 5 and Severity = 6 and Detection = 4 or higher, action is required.

The primary objective of the recommended action is to reduce risk and increase customer satisfaction by improving the design.

Note: Only a design revision can bring about a reduction in the severity ranking.

21. Responsibility, for the Recommended Action: Enter the name of the individual responsible for each recommended action.

22. Action Taken: After the action has been implemented, enter a short description of the action and effective date.

23. Action Result: After the preventive/ corrective actions have been identified estimate the resulting severity, occurrence, detection. Calculated record the resulting RPN. If no actions are taken, leave the columns blank.

Besides the theoretical explanation of the form we prepared an example, which you can find here:

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