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There are many types of failures. When conducting an FMEA, all failure types must be considered, not just the most obvious. Each category of failure should be considered for every product component or process step.

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Quick reference

Types of Failures

The FMEA should consider all types of failures that could occur in a product or process.  There are many causes for the eight types of failures, some due to design, some due to management practices, some due to user/operator practices, and some due to unpredictable factors.

When to use

When initiating an FMEA, the analysis team should consider all types of failures for each part in a Design FMEA and for each step in a Process FMEA.  All failures should be included in the FMEA, not just the most prominent.

Instructions

The failure types are provided as an aid to brainstorming what could go wrong with a product or process.  When there is existing failure data, that should be used to identify failures.  However, in the design process, data seldom exists.  Therefore, these categories or types of failures are used to assist the team in developing the list of failures for analysis.

Complete failure

This is the most commonly considerd failure type.  In this case, the product or process stops working.  It is no longer able to perform any functions.  Some of the most common reasons this can occur include:

  • Inadequate part or step for the application – this is a design flaw.  The product or process is under-designed and is unable to perform the desired function.
  • Design defect or error – a mistake was made by the designers and the part or process step does not work.
  • Broken or missing part – this causes all functions to stop on a product.
  • Omitted or forgotten step – this can cause a process to stop.
  • Equipment malfunctions – something in the equipment fails to perform. In current processing equipment, this is often due to software errors.

Unwanted function

This occurs when the product or process performs a function that is not desired or not commanded.   The user or customer perceives no benefit from the function.  This unwanted function may damage the product or item to be processed and it almost always wastes time and effort doing the function.  Typical reasons that this occurs include:

  • Design error – The designers added functionality that was not desired or created a product or process control scheme that caused undesired action to occur.
  • Broken or missing part – This causes uncommanded functions to occur.
  • Operator / user error – Poor management of the operators or users (inadequate training, inadequate oversight, poor working conditions, etc.) leads to a situation where the operator or user makes and error and the product or process performs an unwanted function.
  • Setup / installation error – The operator or user does not setup or install the product or process correctly.  Therefore, the product or process performs functions not intended by the operator or user.
  • Equipment malfunction – A portion of the equipment does not operate correctly, which causes the equipment to perform uncommanded functions.

Partial failure

In this case the product or process performs a portion of its functionality, but not the full functionality.  This partial performance achieves some of the product or process performance goals but misses others.  Typical reasons for this type of failure include:

  • Inadequate design – The product or process is under-designed so it is not able to meet some performance goals.
  • Setup / installation error – The operator or user does not setup or install the product or process correctly.  Therefore, only a portion of the desired performance is completed.
  • Poor maintenance – Due to poor maintenance, portions of the product or process fail prematurely.  While some portions are still operational, others are not.
  • Operator / user error – Poor management of the operators or users (inadequate training, inadequate oversight, poor working conditions, etc.) leads to a situation where the operator or user makes and error and the product or process is unable to complete the desired functions.
  • Equipment malfunction – A portion of the equipment does not operate correctly, however a portion does.  Therefore, the product or process is able to achieve some performance goals, but not all.

Intermittent failure

These are failures which occasionally occur, but are not permanent.  They may be present at one use of the product or process and not be present at the next use.  Typical reasons for this type of failure include:

  • Fragile design – The product or process design has no design margin and slight changes in operating conditions or work item can result in failed performance.
  • Incorrect design tolerances – At target values for all parts and components, everything works as expected.  However, due to the design tolerances, if the right combination of minimum and maximum conditions occur, every part or component can be compliant, but the system will not work. 
  • Operator error – The operator or user must perform numerous manual steps and will sometimes make an error.
  • Setup / adjustment / installation errors – Once again, when there are numerous manual tasks to perform, the likelihood that something will be done incorrectly goes up.  If the product or process is re-initialized or re-installed correctly, the problem goes away.
  • Environmental factors – Some types of product or process components – especially electronics – are susceptible to heat and humidity.  When these are beyond the thresholds for performance, the electronics shut down.  However, they will work properly again when the conditions are within the “normal range.”
  • Equipment malfunction – This is commonly due to software bugs.  While normally working correctly, when the conditions are right, the software will stop working or will perform incorrectly.

Degraded performance

This is similar to partial performance.  The difference is that degraded performance still performs all functions, but not to the desired standard.  Whereas, partial performance is described as performing some functions to the desired standard and not performing other functions.  Typical reasons for this type of failure include:

  • Under-designed product or process – Due to design decisions, some product or process components reache end of life much sooner than expected.  At end of life, these components are no longer able to perform as specified.
  • Poor maintenance / no maintenance – The lack of maintenance is particularly a problem with devices or equipment that have moving parts or sensors that require regular cleaning.  Some products are designed to prevent maintenance operations.  This may be to simplify operations or it may be to limit the useful life of the product or process.
  • Setup / installation errors – Due to incorrect setup or installation, the product or process undergoes excessive wear and tear resulting in decreased performance of parts or components before the end of their expected life.
  • Operator / user errors or fatigue – When operators or users are tired, they make mistakes that must be corrected.  The result is often a degradation in performance of the product or process.
  • Environmental factors – Many parts and materials will change material properties at high or low temperatures or other extreme environmental conditions.  This change in material properties changes the overall system or device performance.  The use of these materials are design decisions.

Excessive performance

In this case, the product or process does what it is supposed to do, but it does too much.  Unlike the Unwanted Function failure, this performance is desired, but the product or process fails to stop once the desired level of performance is achieved.  The excessive performance wastes resources and often damages the product or process.

  • Design error – The designers failed to include limits on performance which allow the product or process to exceed the desired performance.
  • Operator/user error – Poor management of the operators or users (inadequate training, inadequate oversight, poor working conditions, etc.) leads to a situation where the operator or user makes and error and the product or process performs beyond the desired level.
  • Setup / installation error – The operator or user does not setup or install the product or process correctly.  Therefore, the product or process does not appropriately limit performance.
  • Equipment malfunction – A portion of the equipment does not operate correctly, which causes the equipment to perform beyond desired limits or controls.

Too early / too late

A function that is part of a sequence of functions does not occur in the right sequence or with the correct timing between functions in the sequence.  This out-of-sequence occurrence typically requires the product or process to undo and repeat a portion of the sequence, which wastes resources.  In some cases the out-of-sequence function will harm or damage the individual or item associated with the product or process.  Reasons for this type of failure include:

  • A design error – Often a software error will create conditions that change the sequence of a program embedded within a product or process.
  • Setup / installation error – The operator or user incorrectly initializes the product or process which results in the wrong sequence of steps.
  • Operator / user error – Poor management of the operators or users (inadequate training, inadequate oversight, poor working conditions, etc.) leads to a situation where the operator or user direct the product or process to perform functions in an incorrect order.
  • Equipment malfunction – A portion of the equipment does not operate correctly, which causes the equipment to perform functions in the wrong sequence.

Over-processing

This type of failure is often overlooked in the FMEA.  However, the over-processing will reduce useful life of the product or process.  In addition, the extra processing can introduce damage or other errors.  Therefore, it should be treated as seriously as the other types.  Typical reasons for this failure types include:

  • Poor design planning and control – With poor designs, the operator or user is forced to perform many unneeded or redundant steps.  This reduces performance and increases opportunities for errors.
  • Complicated / incorrect instructions – The more complicated the instructions, the more likely it is that the user or operator can become confused and does something wrong.  This error then often leads to one of the other failure types such as complete or partial failure.
  • Operator / user error – Poor management of the operators or users (inadequate training, inadequate oversight, poor working conditions, etc.) leads to a situation where the operator or user makes mistakes and must use additional operations of the product or process in order to reach the level of satisfactory performance.
  • Equipment malfunction – A portion of the equipment does not operate correctly, which causes the equipment to over-process items.

Hints & tips

  • The FMEA analyses the failure, not the failure type.  It doesn’t matter which type of failure you were considering when you listed the failure, the point is that the failure is included in the analysis.
  • Understanding the failure type can be helpful when considering mitigation actions – provided that failure scores high enough to require mitigation.
  • It is better to have too many failures in your analysis and then score them as insignificant, than to have too few failures and overlook a critical one.  So use these failure types to brainstorm failures for the product and process.
  • Most of these failures can be eliminated or mitigated by design decisions, which is why it is so important to do an FMEA during the design process.
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  • 00:04 Hi, I'm Ray Sheen.
  • 00:06 Well since we are doing an analysis of failure modes, let's take a few minutes to
  • 00:10 discuss the failures that we need to be concerned about.
  • 00:13 We have organized the failures into types, not because one type is better or worse
  • 00:18 than another but to help us brainstorm all the potential failure modes.
  • 00:23 When considering a product and process failure there are eight types.
  • 00:27 Complete failure, unwanted function, partial failure,
  • 00:30 intermittent failures, degraded performance and excessive performance,
  • 00:34 too early too late, and over-processing.
  • 00:37 We'll discuss each of these in another slide.
  • 00:40 But first, a few points about failures.
  • 00:42 Each item, part or process step that we analyze can have multiple failures
  • 00:47 from multiple categories and we want to make sure that we analyze all of them.
  • 00:51 In fact, for any given failure, there can be multiple reasons that that could happen
  • 00:56 and again, we want to analyze all of them.
  • 00:59 Which will lead to the structure of the FMEA worksheet.
  • 01:02 It allows us to create a separate line for each failure and failure mode combination
  • 01:07 and then analyze each one individually to determine which are significant.
  • 01:12 So let's look at the different failure types.
  • 01:15 The complete failure is just that, the product or process stops working.
  • 01:20 The user or organization receives no benefit, because nothing's happening,
  • 01:24 except possibly some yelling and cursing.
  • 01:26 Some of the typical causes for
  • 01:28 this type of failure include an under-designed product or process.
  • 01:32 It just can't handle the workload and therefore,
  • 01:35 it breaks, or it could be an error in the design.
  • 01:38 The design made a mistake and the product or
  • 01:40 process can't do what it's being asked to do.
  • 01:43 Of course there could be a broken, defective, or missing part, or
  • 01:47 there could be a forgotten or missing step in the procedure, and
  • 01:50 there's always a possibility of equipment malfunction.
  • 01:53 An unwanted function is a failure in that the product or
  • 01:56 process is doing something it should not be doing.
  • 01:59 The result is wasted resources or time while it is doing this unwanted activity.
  • 02:04 Some of the reasons for
  • 02:05 this type of failure include a design error in the product or process control.
  • 02:10 This could also be a broken, missing, or
  • 02:12 defective part that misdirects the product or process.
  • 02:15 And of course, there could be a user or
  • 02:17 operator error that creates this situation.
  • 02:21 Another common source of this error is an incorrect setup or
  • 02:24 installation that initializes the product or process in the wrong state, and
  • 02:28 of course, there can be an equipment malfunction.
  • 02:32 Now let's consider the partial failure.
  • 02:34 In this case, the product or
  • 02:35 process is still working, unlike that of the complete failure, but the product or
  • 02:39 process is not doing everything it is supposed to be doing.
  • 02:43 We get some of the desired benefit, but only a portion of it.
  • 02:47 Reasons for this type of failure often include an under-designed product or
  • 02:51 process that is not able to consistently meet the full set of requirements.
  • 02:56 Another common reason is that an incorrect setup or installation
  • 03:00 prevents the product or process from completing all of its functions.
  • 03:03 Poor maintenance can also create this failure as parts or
  • 03:07 components within a product or process begin to fail or wear out.
  • 03:11 And of course we can have some of our old standby reasons of user or
  • 03:14 operator error and equipment malfunction.
  • 03:18 A difficult one to diagnose is the intermittent failure.
  • 03:21 This is because it comes and goes.
  • 03:23 The product or process works great for a while, and then there's a problem, but
  • 03:27 that problem quickly disappears without the management or
  • 03:30 operators taking any specific action to make it go away.
  • 03:34 The issue now is the product or process reliability.
  • 03:37 When will the next failure occur?
  • 03:40 Some of the reasons for this include a fragile design or poor design tolerances.
  • 03:44 When those are present, the combination of all of the inputs to the product or
  • 03:49 processes will sometimes work together and sometimes not.
  • 03:52 Everything can be aligned in such a way that we have a failure, but
  • 03:56 it's based upon a combination of effects and not just one item,
  • 03:59 which is what makes this so difficult to find and diagnose.
  • 04:02 Other reasons, including user or operator error, and its set up or
  • 04:06 installation error.
  • 04:08 These types of failures are often related to environmental factors such as heat,
  • 04:11 humidity, contamination, and poor power quality, and
  • 04:14 of course it could be an equipment malfunction.
  • 04:18 Degraded performance is a failure that occurs over time.
  • 04:21 As the product or process is operated, it becomes slower, less accurate, or
  • 04:26 in some other way fails to fully meet the performance expectations
  • 04:30 that it had at one time achieved.
  • 04:32 This obviously reduces the benefit to be derived from the product or process.
  • 04:37 Typical causes for this are a product or process that is underdesigned for
  • 04:41 the application, which means it is quickly overstressed.
  • 04:45 When that happens, key parts of the product or
  • 04:47 process just can't keep up with the demand.
  • 04:49 Another very common reason for this is little or
  • 04:51 no maintenance performed, which leads to excessive wear and tear.
  • 04:55 Of course, we could also have some of our familiar reasons like setup or
  • 04:59 installation errors, operator/user error, and finally,
  • 05:03 this type of failure can be accelerated when certain environmental factors
  • 05:08 are present causing a harsh operating environment.
  • 05:11 The flip side of degraded performance is excessive performance.
  • 05:15 Now you might be asking, how could this be a failure?
  • 05:17 Well, if the excessive performance operates the product or
  • 05:21 process in a zone outside its safe operating zone, or
  • 05:24 if it is using up time and resources but not providing any added benefit, then this
  • 05:29 excessive performance will damage the product or process and waste resources.
  • 05:34 Reasons for this start with a design error in the product or
  • 05:37 process control that allows this condition to occur.
  • 05:41 Then there's the normal causes of operator or user error, set up or
  • 05:44 installation error, or equipment malfunction.
  • 05:47 Another failure mode is too early or too late.
  • 05:51 In this case, the product or
  • 05:52 process performs a series of functions in which the order matters, and
  • 05:56 one of those functions gets out of order, or occurs without a command to occur.
  • 06:01 This could potentially damage the unit and it almost always requires that something
  • 06:05 must be undone and then redone in the correct sequence, which wastes time and
  • 06:10 effort, not to mention irritating those involved.
  • 06:13 Reasons for this failure are similar to the last one.
  • 06:16 A design error in the product or process control, a setup or installation error,
  • 06:21 a user or operator error, or an equipment malfunction.
  • 06:25 Finally there's the failure of overprocessing.
  • 06:27 The product or process should stop but it doesn't.
  • 06:31 This is similar to excessive performance but the difference is that excessive
  • 06:34 performance gives the results that go beyond the target performance level.
  • 06:40 In this case, the results are right in line with the target level.
  • 06:43 But the amount of work being performed to get those is unneeded.
  • 06:47 The result is wasted time and resources.
  • 06:49 Typical reasons include the aforementioned design error and product or
  • 06:53 process control.
  • 06:54 But in this case we had a confusing or
  • 06:57 overly complex operating procedure that causes the user and
  • 07:00 operators to direct the product or process to perform unnecessary actions.
  • 07:05 And of course we can still have operator user error and equipment malfunction.
  • 07:11 So let's do a quick recap of the sources of these failures.
  • 07:14 All of the failures could occur because of some design, decision, or mistake.
  • 07:18 It could be an error in the design process, a design decision that results in
  • 07:23 an undersigned or fragile design, or potentially, it could be an inadequate
  • 07:27 design process that does not accurately or adequately test or verify the performance.
  • 07:32 Another common theme was the management of the product or process.
  • 07:36 This includes the setup, maintenance, and user operation actions.
  • 07:40 I'm considering user and operator errors as management mistakes,
  • 07:43 because management failed to provide the skills, training, tools, or assistance for
  • 07:47 the users and operators to do things correctly.
  • 07:50 And some of the failures are due items that are outside the control of
  • 07:53 the product or process users, operators, and managers, and
  • 07:57 are not due to design issues.
  • 07:59 These include things like environmental factors and equipment malfunction.
  • 08:03 They're unpredictable within the operation and when they happen,
  • 08:06 they create a failure.
  • 08:08 There are many types of failures, and when doing your FMEA, you want to make sure
  • 08:13 that you have considered all applicable failures for your product or process.

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