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An effect on process performance or operator safety is determined for each failure mode and listed in the Process FMEA. The severity of that effect is rated to determine the impact.

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Quick reference

PFMEA Severity Rating

Step 5 of the Process FMEA methodology is to conduct scoring of the failure modes.  The first score that is determined is the score for the severity of the effect created by the failure.

When to use

Once the process steps are clarified and failure modes have been identified for each step, the FMEA analysis team should determine the effect that failure will have on the customer, user, operator, product, or process.  Based upon that effect, the severity score is assigned.

Instructions

The first three columns of the Process FMEA form are the process step, the functions performed at that step, and the failures associated with the function.  Based upon the failure modes, the FMEA analysis team determines the impact or effect of each failure.  A failure could have multiple effects.  The effects are associated both with the effect on the product performance and the customers or users of the product, as well as with the effect on the process performance and the operators of the process. The effects are listed in the next column of the Process FMEA.  The severity score for each effect is then listed in the adjacent column.

The product severity score is based upon three factors:

  • The safety of the customers or users
  • The successful operation of the primary function or functions of the product
  • The successful operation of the secondary functions of the product. 

The process severity score is also based upon three factors:

  • The safety of the process operators
  • The yield of the process (percentage of defective items)
  • The nature of any rework or repair of the defective items

The severity score recorded is the higher of the two considerations – product and process.

The sources of data for making these assessments include the Design FMEA, in particular the severity scores from the Design FMEA.  From an external perspective, the sources of data are the customer complaints or returns and any information about customer uses and applications.  The internal process sources of data are the manufacturing operations safety and hazard analysis as well as the rework and repair procedures.

Ratings

The tables below show the scoring classification to be used for severity scores in a Process FMEA. 

Example

Building on the example used in earlier lessons, a Process FMEA for a portion of a ball point pen assembly is shown below.  The colors in the scoring column are provided for illustration and training purposes.  Colors do not need to be shown in an actual FMEA.

Hints & tips

  • Each effect is listed on a separate line.  A failure mode code have multiple effects and therefore multiple lines associated with that failure mode.
  • We are not evaluating the actual yield percentage at this time (that comes next).  Rather, the evaluation is based upon the assumption that the failure mode occurred.  If that happened, what is the effect on product and process performance.
  • The designation of primary functions and secondary functions should be done by a person representing the customer.  The designer's perspective of what is primary and secondary may not be in alignment with the customers or users.
  • Generally, if a function in the Process FMEA can be closely correlated with a function in the Design FMEA, they will have the same severity score.
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  • 00:04 Hi I'm Ray Sheen,
  • 00:05 now let's discuss how to bid the severity scoring on a Process FMEA.
  • 00:10 The severity ratings are the first of the three scores that
  • 00:15 are assigned during Step 5 of the Process FMEA process.
  • 00:19 Severity ratings are looking at the risk from the perspective of the customers,
  • 00:24 operators, and equipment, in particular, the impact of a negative risk event.
  • 00:29 A little hint in this area, if you have the Design FMEA for this product, get it.
  • 00:34 The severity ratings will typically be the same for
  • 00:36 critical characteristics between the two analyses.
  • 00:39 We start the evaluation of severity by listing the effect of the failure.
  • 00:44 The failure could create effects on the product, on the operator, or
  • 00:48 on the equipment being used in the process, look at each of these.
  • 00:52 There may be multiple effects as the failure impacts them differently,
  • 00:55 if you can't find any effect on anything,
  • 00:57 that begs the question why this was listed as a failure.
  • 01:01 Many times the effect is associated with the function that failed,
  • 01:06 the scoring of the failure may vary by industry.
  • 01:08 This is usually because of industry standards and regulations.
  • 01:12 Now, let's look at the sources of data for doing this scoring.
  • 01:15 One source that we've already mentioned is the Design FMEA.
  • 01:19 Not only does the Design FMEA severity score provide insight, but
  • 01:23 the DFMEA list of functions also helps the team know
  • 01:26 if the failure would render the product inoperable.
  • 01:30 It's also helpful to have a basic understanding
  • 01:32 of the customer application for the product, so
  • 01:35 that you again can tell if the failure renders the product inoperable.
  • 01:39 In fact, another good source to help you with this is the customer complaints and
  • 01:44 returns from other similar products.
  • 01:46 Finally, an important source is any internal safety documents for
  • 01:49 the facility or equipment that is involved in the process, a listing of the harms and
  • 01:54 hazards that need to be avoided.
  • 01:58 So let's start the scoring, with the Process FMEA we have to be concerned
  • 02:02 with severity from both the product and the process standpoint.
  • 02:05 I provided a high level description and the normal criteria used for
  • 02:09 both product severity and process severity.
  • 02:11 Your company or industry may tailor these to fit your application, so
  • 02:16 level 10 is hazardous without warning.
  • 02:19 People get hurt and there is no warning. On the product side, the customer or
  • 02:24 user gets hurt, on the process side, it is the operator.
  • 02:27 And this includes violations of federal regulations without warning.
  • 02:32 Use level 9, the people could get hurt, but they have an adequate warning time for
  • 02:36 either the operator to shut the process down or for
  • 02:39 the customer user to take some type of precautionary measures.
  • 02:43 Also, this goes for
  • 02:45 violation of federal regulations, there is warning before you do it.
  • 02:49 The next level, eight, is described as very high, on the product side,
  • 02:53 the product is totally inoperative.
  • 02:55 It is just a pile of scrap unless you wanna use it as a door stop.
  • 02:59 On the process side, the process shuts down, and
  • 03:02 anything that is already been processed is scrapped.
  • 03:05 Level 7 is classified as high.
  • 03:07 This is a major dissatisfaction. On the product side,
  • 03:11 the primary function of the product is operating at a sub par or degraded level.
  • 03:17 And a portion of the production run must be scrapped or
  • 03:19 significant deviation must occur in the process in order to keep it running.
  • 03:24 An example would be if automated equipment is shutdown, and
  • 03:27 now the process must be done manually.
  • 03:31 Level 6 is moderate, it is appropriate for a product where the primary function works
  • 03:35 correctly, but the secondrary functions are not.
  • 03:38 So if the product is an automobile, the car drives but the heater and
  • 03:42 air conditioning unit are broken.
  • 03:45 From a process perspective, 100% of the items processed
  • 03:48 require an offline rework step be added to make them acceptable.
  • 03:53 They can be made acceptable it just requires more work.
  • 03:56 Level 5 is classified as low, the impact causes complaints but
  • 04:00 it does not render the product inoperable.
  • 04:03 The primary functions still work and the secondary functions are operating but
  • 04:07 in a degraded manner.
  • 04:09 Continuing with the rework theme,
  • 04:11 the process criteria says that a portion of the items must be reworked offline.
  • 04:17 Level 4 is very low, on the product side, there's a minor performance loss that
  • 04:22 most customers would notice but they do have full functionality.
  • 04:25 For the process, the rework theme has now changed to 100% reworked in-line,
  • 04:30 it doesn't need to go to another station to be fixed,
  • 04:33 rather the operator can fix everything while working on the item.
  • 04:38 Level 3 is a minor nuisance, with no actual loss of performance but
  • 04:42 about half of the customers notice it.
  • 04:44 The process rework is now a portion of the items are being reworked in line.
  • 04:50 Level 2 is very minor, it's unlikely to be apparent to a customer or user less than
  • 04:55 25% will notice, and there's only a minor annoyance to the process operators.
  • 05:00 Level 1 is none, there is no severity impact, in fact,
  • 05:03 I question why you're even calling this a failure.
  • 05:08 So, let's take a look at the FMEA, we're using our ball point pen example.
  • 05:12 The first failure, misidentify parts, is an 8, because if the parts are wrong,
  • 05:17 the entire lot of parts where either need to be scrapped or reworked and
  • 05:21 I've chosen the worst case.
  • 05:23 Three of the failure modes involved damage to the product and
  • 05:25 the effect in all three cases, was that we're unable to assemble the damage item.
  • 05:30 This is scored a 7, since it would create a significant customer dissatisfaction
  • 05:34 that the products made it all the way to the customer.
  • 05:37 And on the process side, some of the parts will have to be scrapped,
  • 05:41 in two of the failures, the decal won't adhere.
  • 05:44 The score is 6, 100% must be reworked to reapply the decal,
  • 05:49 and that rework is at an offline station.
  • 05:52 Both the missalign decal and partially bonded decal are rated a five
  • 05:57 because they would generate customer complaints.
  • 06:00 The primary function, writing, would still be okay, but
  • 06:04 the secondary function of advertising for mom's diner is not.
  • 06:08 Now, hopefully the customer never sees this because the next step in the process,
  • 06:13 the inspection, would catch these.
  • 06:16 But the inspection's not perfect, so they might make it to the customer and
  • 06:19 that is the score if they do.
  • 06:22 The inspection step has two different effects with different severity.
  • 06:26 If bad parts are passed the customer will be dissatisfied, and
  • 06:30 that is a level 5 for a product reason.
  • 06:32 If good parts are failed that is an irritant to the business,
  • 06:36 so is a level 2, using the process criteria.
  • 06:41 Well that's how to score severity for
  • 06:43 the Process FMEA, use the scale that best fits your business context

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