PFMEA for Receiving Inspection

One of the rules of PFMEA is that an operation should consider the incoming component as good. A way to handle potential defective incoming material is to use the "receiving inspection" operation for the purpose of screening for failure modes and defects that can affect subsequent operations. The receiving inspection operation is already included in most PFMEAs. Sadly, the opportunity is almost always squandered.

Typically the entries are:

Potential Failure Mode (PFM): 

• Part damaged in shipping,
• Damaged packaging
• Dirty
• Defective

Be Specific About Failure Modes of Concern

Failure modes such as "dirty" and "defective" are too general to be useful. Sometimes you do find more specific PFMs:

• Part length too long or too short.
• Out of round

This is more specific, but focused on specific defects and not on potential failure modes.  More can be done to use the PFMEA beneficially to improve receiving inspection..

Include Failure Modes of High Risk to Your Operation

Why not use receiving inspection to actively question incoming material for ways it may affect subsequent operations? Try to use your Process Flow Diagram and PFMEA development to populate the receiving inspection operation with specific defects that can be a concern to your plant.

For example, consider an incoming die casting with sealing surface that your plant assembles with a seal. In terms of PFMEA you might include:

• PFM: Sealing surface does not seal
• Potential Effects of Failures (PEF): Leak fail at leak test
• Potential Cause or Mechanism of Failure (PCMF):
• Seal groove too rough
• Seal groove depth too deep or too shallow
• Sharp edge or missing chamfer

Using the PFMEA to focus in on areas of concern, like leak test failures, could help you populate receiving inspection with thing to spot check. In this case you might want to have receiving inspection spot check the sealing surface for roughness, grove depth, and sharp edges.
Another source of ideas are past supplier defect report (or 8Ds, or PRR, etc).

Include Failure Modes of High Risk to Your Customer

Another type of PFM that can be included in the receiving inspection operation are those related to component features that are not processed, used, or tested inside your plant. You might call these features "customer features" or "pass through features". An example of a customer feature might be a tapped hole on a machined housing that your plant assembles into a compressor.  Your plant does not assemble a bolt into the hole, your customer does.  If that tapped hole is defective for some reason, then your plant is responsible.  You can roll back the pain to your housing supplier eventually. But, everyone loses. You do the PFMEA exercise for these items in your receiving inspection section:

• Potential Failure Mode (PFM): Customer could not drive their bolt
• Potential Effects of Failures (PEF): Rejects at customer, containment, scrap costs
• Potential Cause or Mechanism of Failure (PCMF):
• Tap wrong size
• Tap too shallow
• Debris in tapped hole

Your controls section could include:

• Run a thread gauge for tap size
• Also check tap depth.
• Spot check for machining debris or swarf or turnings, etc

Example:

Take a simple example of an incoming wooden handle for a hammer.

Some typical incorrect Potential Failure Mode (PFMs) might be:

• Wood is dirty
• Wood is scratched
• Wood is wet

Some typical Potential Effects of Failures (PEF):

• Rejected hammer
• Bad handle attachment

A typical PCMF: 

• Bad receiving inspection

These PFMs are pretty much what you would come up with from the top of your head. There is no real additional value in listing them out. But what if we consider how the incoming material could lead to a failed operation? This is a situation where it makes sense to switch from specific defects to general PFMs. We want to use the PFMEA process to probe for new PFMs and PCMFs (in the case of receiving inspection, these will be incoming defects) that could nip us in the butt.


Here are a few examples of how this might work:

• PFM: Wood has some defect that prevents varnish adhesion
• PEF: If varnish does not adhere to handle it will flake off in the field
• PCMF: (need to consider defects that would cause poor adhesion of varnish)
• Wet wood? 
• Oily wood? 
• Rough texture?

Controls (detection) might be:

• Visual inspection for wet or oily wood.  No! typical and useless.
• You could do a humidity test with a sensor. (for water) 
• Maybe do a water bead test. (for oily)

Detection vs Prevention

By now you may be asking, why are we laying all of this work on receiving inspection?

True, what we have laid out are all detection type controls.  You really want to focus on prevention controls.

You can consider that we may be robust during launch with heavy receiving inspection activity.  And, leading up to launch the specific defects should be driven back to purchasing and supplier quality to confirm the suppliers have these defects in their PFMEA failure mode sections with good controls.

Over time the receiving inspection activity can be reduced based on data.

To reduce the burden on receiving inspection some of the defects could potentially built into your own process:

 As a poke yoke to detect incoming defects. Example, a pin to detect a machined hole.

 As potential failure modes in our own plant in operations that might can CAUSE the defect.  Example, damaging the tapped hole in your plant with an alignment pin or fixture. Or with a varnish or coating operation.

Summary:

• Be Specific About Failure Modes of Concern
• Include Failure Modes of High Risk to Your Operation
• Include Failure Modes of High Risk to Your Customer
• Continually Drive for Prevention at Your Supplier.