PPAP PFMEA & CONTROL PLAN HELP

[STEALTH]

Hi,

I am newer to PPAP's and doing my first dig at a PPAP for a stamped part. I have a couple questions on how this PFMEA should be constructed. I am confused on picking a "Potential Failure Mode" and "Potential Effects Of Failure". I have two examples that will help explain my confusion:

Example 1
Failure Mode: "Through Hole Undersized/Oversized"
Potential Effects of Failure: "Rejected Parts, Assembly Fitment Issues, Possible Tool Rework, Delay to Customer"
Potential Causes: "Worn/Broken Punch, Tooling Misaligned, Wrong Punched Installed During Repair, Etc"

Example 2
Failure Mode: "Broken Punch"
Potential Effects of Failure: "Through Hole Undersized/Oversized"
Potential Causes: "Tool Wear, Improper Tonnage, Punch Damaged During Repair/Installation, Poor Lubrication, Etc"​

To me, it seems like first example is much more part/feature specific and details all the way this could effect the production run as a whole. For the 2nd example being so generic, it leads to the question of "Which punch?", "Which feature is this punch dealing with?", and seems to not exactly cover all areas that the failure will effect. With example 2, it would also be hard to bring that into the control plan, as you would be controlling a "Broken Punch" which would be controlled with something like tooling maintenance. In example 1 you could link that you controlled the through hole using a first/last part inspection as well as an in process inspection. Example 1 also seems like a better fit if there is critical characteristics you need to control.

In my short history of doing PPAP's, I have always constructed PFMEA's similar to example 1, but upon reading a thread on here today, I saw people talking about how stating something like "OD/ID undersized" as a failure mode would be denied if they came across it. Please let me know your thoughts.

 

[Miner]

From your examples, it appears that you have skipped an earlier step. For each process operation, you should also list the function associated with that operation. The potential failure mode is directly linked to that function. The potential failure modes will fall into the following categories:

• No function
• Partial/excessive/deteriorated function
• Temporarily suspended function
• Unintended function
• Impermissible side effects

Take your example 1. The function is to create a hole of size X +/- Y at a specific location. The potential failure modes are:

• No function - No hole created
• Partial/excessive/deteriorated function - Hole is undersized, hole is oversized, hole is partially stamped through
• Temporarily suspended function - ?
• Unintended function - Hole is double punched? Hole is stamped off location (this could also be broken out by direction).
• Impermissible side effects - Hole has burr, hole has excessive breakaway

Your potential failure effects are too generic (e.g., rejected parts, assembly fitness, etc.). The effect of an undersized hole is different with a different cause, severity, occurrence, etc. from an oversized hole, so you need to keep them separate. Some potential effects:

• No hole created - Unable to assemble (next assembly may be internal or at customer)
• Hole is undersized - Unable to insert fastener
• Hole is oversized - Unable to maintain assembly dimensions (see how the effect is different?)
• Hole is partially stamped through - Unable to assemble (next assembly may be internal or at customer)
• Hole is double punched? - Unable to maintain assembly dimensions
• Hole is stamped off location - Unable to maintain assembly dimensions
• Hole has burr - Laceration of operator, under torque of fastener
• Hole has excessive breakaway - Appearance issue, fastener clamp force diminished over time

Some potential causes (not all inclusive):

• No hole created - broken punch
• Hole is undersized - worn punch
• Hole is oversized - wrong punch, galled punch (see how the cause is different?)
• Hole is partially stamped through - low tonnage, press setup
• Hole is double punched? - press mis-cycle
• Hole is stamped off location - die setup
• Hole has burr - chipped punch
• Hole has excessive breakaway - dull punch

Unfortunately, there are a lot of misunderstandings and poor practices for FMEA, so you will see a lot of misinformation online, even here.

 

[Bev D]

What Miner said!

 

[STEALTH]

From your examples, it appears that you have skipped an earlier step. For each process operation, you should also list the function associated with that operation. The potential failure mode is directly linked to that function. The potential failure modes will fall into the following categories:

• No function
• Partial/excessive/deteriorated function
• Temporarily suspended function
• Unintended function
• Impermissible side effects

Take your example 1. The function is to create a hole of size X +/- Y at a specific location. The potential failure modes are:

• No function - No hole created
• Partial/excessive/deteriorated function - Hole is undersized, hole is oversized, hole is partially stamped through
• Temporarily suspended function - ?
• Unintended function - Hole is double punched? Hole is stamped off location (this could also be broken out by direction).
• Impermissible side effects - Hole has burr, hole has excessive breakaway

Your potential failure effects are too generic (e.g., rejected parts, assembly fitness, etc.). The effect of an undersized hole is different with a different cause, severity, occurrence, etc. from an oversized hole, so you need to keep them separate. Some potential effects:

• No hole created - Unable to assemble (next assembly may be internal or at customer)
• Hole is undersized - Unable to insert fastener
• Hole is oversized - Unable to maintain assembly dimensions (see how the effect is different?)
• Hole is partially stamped through - Unable to assemble (next assembly may be internal or at customer)
• Hole is double punched? - Unable to maintain assembly dimensions
• Hole is stamped off location - Unable to maintain assembly dimensions
• Hole has burr - Laceration of operator, under torque of fastener
• Hole has excessive breakaway - Appearance issue, fastener clamp force diminished over time

Some potential causes (not all inclusive):

• No hole created - broken punch
• Hole is undersized - worn punch
• Hole is oversized - wrong punch, galled punch (see how the cause is different?)
• Hole is partially stamped through - low tonnage, press setup
• Hole is double punched? - press mis-cycle
• Hole is stamped off location - die setup
• Hole has burr - chipped punch
• Hole has excessive breakaway - dull punch

Unfortunately, there are a lot of misunderstandings and poor practices for FMEA, so you will see a lot of misinformation online, even here.

From your examples, it appears that you have skipped an earlier step. For each process operation, you should also list the function associated with that operation. The potential failure mode is directly linked to that function. The potential failure modes will fall into the following categories:

• No function
• Partial/excessive/deteriorated function
• Temporarily suspended function
• Unintended function
• Impermissible side effects

Take your example 1. The function is to create a hole of size X +/- Y at a specific location. The potential failure modes are:

• No function - No hole created
• Partial/excessive/deteriorated function - Hole is undersized, hole is oversized, hole is partially stamped through
• Temporarily suspended function - ?
• Unintended function - Hole is double punched? Hole is stamped off location (this could also be broken out by direction).
• Impermissible side effects - Hole has burr, hole has excessive breakaway

Your potential failure effects are too generic (e.g., rejected parts, assembly fitness, etc.). The effect of an undersized hole is different with a different cause, severity, occurrence, etc. from an oversized hole, so you need to keep them separate. Some potential effects:

• No hole created - Unable to assemble (next assembly may be internal or at customer)
• Hole is undersized - Unable to insert fastener
• Hole is oversized - Unable to maintain assembly dimensions (see how the effect is different?)
• Hole is partially stamped through - Unable to assemble (next assembly may be internal or at customer)
• Hole is double punched? - Unable to maintain assembly dimensions
• Hole is stamped off location - Unable to maintain assembly dimensions
• Hole has burr - Laceration of operator, under torque of fastener
• Hole has excessive breakaway - Appearance issue, fastener clamp force diminished over time

Some potential causes (not all inclusive):

• No hole created - broken punch
• Hole is undersized - worn punch
• Hole is oversized - wrong punch, galled punch (see how the cause is different?)
• Hole is partially stamped through - low tonnage, press setup
• Hole is double punched? - press mis-cycle
• Hole is stamped off location - die setup
• Hole has burr - chipped punch
• Hole has excessive breakaway - dull punch

Unfortunately, there are a lot of misunderstandings and poor practices for FMEA, so you will see a lot of misinformation online, even here.

Hi Miner,

That was an awesome explanation, thank you for laying taking the time to lay that out for me! The PFMEA is much more clear and gives me a good baseline route to take on future PPAP's. I can see where the potential failure modes is much more clear this way and outlines a number of circumstances for a specific function. It also makes it easier to link the failure effects and causes.

With your last statement, I would have to agree. I have seen a wide variety of how PFMEA's are created and even seen them be accepted with complete bare minimum of "Dimensions Out of Tolerance" for the potential failure mode and effects of "Shipping Delay, Rework Parts". Unfortunately I have gone down the rabbit hole of threads on PFMEAs and it seems like it is never ending confusion and changes drastically from person to person. I am only 1 year into the work force and it has been tough picking up all this without any mentorship or training. I appreciate responses like yours as it helps me develop better practices for the duration of my career and not fall into the "good enough" category.

 

[Golfman25]

Hi,

I am newer to PPAP's and doing my first dig at a PPAP for a stamped part. I have a couple questions on how this PFMEA should be constructed. I am confused on picking a "Potential Failure Mode" and "Potential Effects Of Failure". I have two examples that will help explain my confusion:

Example 1
Failure Mode: "Through Hole Undersized/Oversized"
Potential Effects of Failure: "Rejected Parts, Assembly Fitment Issues, Possible Tool Rework, Delay to Customer"
Potential Causes: "Worn/Broken Punch, Tooling Misaligned, Wrong Punched Installed During Repair, Etc"

Example 2
Failure Mode: "Broken Punch"
Potential Effects of Failure: "Through Hole Undersized/Oversized"
Potential Causes: "Tool Wear, Improper Tonnage, Punch Damaged During Repair/Installation, Poor Lubrication, Etc"​

To me, it seems like first example is much more part/feature specific and details all the way this could effect the production run as a whole. For the 2nd example being so generic, it leads to the question of "Which punch?", "Which feature is this punch dealing with?", and seems to not exactly cover all areas that the failure will effect. With example 2, it would also be hard to bring that into the control plan, as you would be controlling a "Broken Punch" which would be controlled with something like tooling maintenance. In example 1 you could link that you controlled the through hole using a first/last part inspection as well as an in process inspection. Example 1 also seems like a better fit if there is critical characteristics you need to control.

In my short history of doing PPAP's, I have always constructed PFMEA's similar to example 1, but upon reading a thread on here today, I saw people talking about how stating something like "OD/ID undersized" as a failure mode would be denied if they came across it. Please let me know your thoughts.

We do stamping and here is how we do it -- much closer to example 1.
Requirement: We list the operation, i.e.; form, pierce, etc.
Failure mode: We list the issue which may arise if the requirement isn't working. So, for example, for a Pierce operation we list hole US/OS, location and Excessive burrs.
For Effects: We list the the effects of each failure mode. So "improper diameter,"; assembly difficulty; processing difficulty.
For Cause: We list the causes. So punch OS/US; dull punch, blank out of location, etc.

The challenge is to balance the generic vs. detail with the potential length of the paperwork. Remember, most of these issue were addressed by tool makers long before the concept of a formal FMEA was even thought of. Good luck.