DFMEA Severity Rating

Quick reference

• 00:04 Hello, I'm Ray Sheen.
• 00:06 Well, let's begin the scoring process with our failure modes.
• 00:09 This is step 5 in your Design FMEA process.
• 00:13 We start with severity ratings.
• 00:16 Severity ratings address the impact of the failure.
• 00:19 What happens to the customer or user if the failure occurs?
• 00:23 If the failure impact is low,
• 00:25 it can occur even frequently with no significant problems.
• 00:29 If the failure impact is high, then we become very concerned
• 00:32 about the probability of occurrence and our ability to detect it.
• 00:36 We don't want this failure to happen.
• 00:38 So to determine the severity, we must first determine the effect of the failure.
• 00:42 This is usually easy to do.
• 00:44 Just look at the function and note what goes wrong when that doesn't happen, or
• 00:48 if it doesn't happen in the correct manner.
• 00:50 One note here, there may be multiple effects.
• 00:54 Each one should be on a separate line in the Design FMEA so
• 00:57 that their severity can be scored.
• 00:59 There are many sources of data for both determining the effect and
• 01:03 doing the scoring.
• 01:05 When data is available, use it.
• 01:07 If there is no data,
• 01:08 then let the subject matter experts provide their expert judgment.
• 01:12 So let's look at some of the sources of data.
• 01:14 Start with the use cases or user scenarios.
• 01:18 Look at what happens from the customer perspective.
• 01:21 Your product function analysis is also a good place to look.
• 01:24 That includes the interface matrix.
• 01:26 If there are similar products in the field,
• 01:28 what did the customer complaints tell you about failures?
• 01:31 You can also bring in focus groups for new products to get costumer opinions and
• 01:36 perspectives.
• 01:37 Finally, are there any know safety or
• 01:39 health hazards associated with any of the parts and materials,
• 01:43 use all of these sources and your team's expert judgment to list the effects.
• 01:48 Now, let's score the effects.
• 01:50 We use a one to ten scale where ten is really high and one is insignificant.
• 01:55 A ten then is hazardous effect without warning.
• 01:58 This effect will hurt people, and they can't see it coming.
• 02:01 It's a safety issue.
• 02:03 We normally also include in the ten category
• 02:06 a violation of government regulations without warning.
• 02:09 Meaning, someone goes to jail.
• 02:11 Next is nine, which is the same effect as the ten, but now, there is a warning.
• 02:16 The warning gives a customer/user time to either stop the product or
• 02:20 take precautions to reduce the chance of injury.
• 02:23 How much warning is a judgement call.
• 02:25 One second warning is probably not enough, but
• 02:28 you don't need to have a three day advanced notice either.
• 02:31 Then there is the score of eight.
• 02:33 At least now, no one is getting hurt.
• 02:35 But the product is a total bust.
• 02:37 It won't work and never has, or the customer is unable to install it.
• 02:41 From the customer's perspective, the thing is totally inoperative.
• 02:44 Recall from an earlier lesson that most companies treat any aspect of the product
• 02:48 that would result in a score of eight, nine, or ten as a critical characteristic.
• 02:53 Let's continue on.
• 02:55 Incidentally, the colors I'm showing of red, orange, and green for different
• 02:59 levels are just my interpretation of the differences in severity.
• 03:03 There is no other meaning or significance.
• 03:06 The seven rating is still considered a high score.
• 03:09 The product becomes inoperable.
• 03:11 It starts out working, but well before the expected end of useful life,
• 03:15 it stopped working and became inoperable.
• 03:18 If it is a component of a system,
• 03:20 this obviously has a major effect on overall system performance.
• 03:24 Continuing on to the score of 6, this represents a moderate severity.
• 03:29 The product works but not in the manner it is supposed to work or
• 03:32 is expected to work.
• 03:34 So the customer could install it, but it never did all that was promised.
• 03:38 If it is a system component, it affects system performance, and
• 03:41 the customer is dissatisfied.
• 03:43 On to the score of 5, which is considered low severity, the product or
• 03:47 component is working but not as well as it should.
• 03:51 There is an impact on system performance, and it's noticeable by all the customers.
• 03:56 A score of 4 is applied when the severity is considered to be very low.
• 04:01 This is often used with poor workmanship.
• 04:03 The product component doesn't look right to the customer.
• 04:06 They return it for repair or replacement.
• 04:09 It could do the job, but
• 04:10 the customer is annoyed that it doesn't meet their expectations.
• 04:14 A score of 3 is used when there's a minor effect.
• 04:17 Again, the product works, but
• 04:18 there are some workmanship or visual defect with the product.
• 04:22 The customer doesn't return it,
• 04:23 but they expect some type of corrective action before they would use another one.
• 04:28 The score of 2 is for very minor effects.
• 04:31 Once again, there's no problem with functionality, but there is some type of
• 04:35 workmanship or aesthetic defect that has them dissatisfied.
• 04:38 No return is requested and no further action is expected.
• 04:41 Finally, a score of 1 is for effects that are not a concern to the customer.
• 04:45 Performance is not affected, the customer doesn't notice the problem and
• 04:49 is satisfied with the product.
• 04:51 As I mentioned in an earlier lesson, these ratings and
• 04:53 descriptions come from the IEC standard.
• 04:56 Your organization may have more specific ratings
• 04:59 that are tailored to your industry or products.
• 05:01 If so, use them.
• 05:04 So let's score the severity for the ball in our ball point pen.
• 05:07 Recall we identified the functions and failures in the previous lesson.
• 05:11 For the first failure, the ball falls out, and
• 05:13 the effect is that the ink drains out of the tube.
• 05:15 That is a severity of 8.
• 05:17 There is no safety hazard, so it isn't a nine or ten, but
• 05:21 the pen is totally useless.
• 05:23 The next failure is the ball stops rolling.
• 05:26 The effect is that the ink is no longer deposited on the ball, so
• 05:30 it can't be deposited on the paper.
• 05:32 Since the failure is the ball stops rolling, it meant that at one time,
• 05:36 it was rolling.
• 05:37 So this is a seven, the pen worked for a while and then stopped.
• 05:41 Now, for the failure, the ball corrodes.
• 05:44 The effect is the ball becomes pitted, it does not roll smoothly, or
• 05:48 deposit ink smoothly.
• 05:49 This is a score of 5.
• 05:51 After a while, the product operates at a reduced level of performance.
• 05:55 And while it is still usable, the customer is dissatisfied.
• 05:59 Now, for the function of resist the abrasion, the failure was for the ball to
• 06:03 wear a flat spot, and the effect was that the ball will not roll smoothly.
• 06:07 The score is again a 5, and for the same reason.
• 06:10 After a period of time, the ball operates at a reduced level of performance.
• 06:14 It's usable, but the customer is not satisfied.
• 06:17 Final one for the analysis we're showing is the ball function of rolling smoothly,
• 06:22 and the failure was that the ball would skip.
• 06:24 Our effect is that the ink is uneven, and
• 06:26 there's unwanted blots deposited as the pen skips.
• 06:30 The score is six.
• 06:31 The effect is the same as the previous failure mode, but in this case,
• 06:34 it occurs immediately on use and not over some period of time.
• 06:38 It's doing the skipping and blotting right from the first day.
• 06:41 It works, but the customer is dissatisfied.
• 06:45 So that's the first of the scores, the value for
• 06:48 severity of the effect of the failure.

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