Articles by Results

FMEA | Function Tree - Defining Product Design Functions

Posted by Graham Cripps on Wed, Aug 05, 2015 @ 10:46 AM

Function Tree - Defining Product Design Functions

Defining the product design functions (or design intent) is one key to the success of conducting a successful Design FMEA.

FMEA is a risk management tool that looks at and manages the risk of failure of the products function(s). Failure to identify these leads to the inability to manage the risk of failure of missed functions.

If we know all of the functions that a design has to achieve, then we can consider how those functions could potentially fail to meet the customers requirements. This is the key to understanding the exact functions that the product performs.

This often causes difficulties with FMEA's as there is a tendency to generalise functions as a combination of functions.  Let me explain, using a fountain pen as an example.

FMEA_FT_Blog_P1Lets consider the design of a fountain pen. What is a primary function of a pen? To write?

We cannot design this pen to write on its own!

We have to consider several design functions which might include: to retain ink, to dispense ink, to provide a comforatble grip, to allow for left and right handed use, to resist leaks, to provide smooth contact on a writing surface

The outcome that a user expects is that (in the hands of a capable person) the pen will write. However, this is not a single function of the pen's design (as seen above) but a combination of functions that deliver the customer requirement.

Developing A Function Tree

A robust method of defining a products' function is the application of the Function Tree. The function tree is a process used to determine prime functions and their subordinate functions for a given product. The process steps are as follows:

  • Brief the Team
  • Brainstorm the functions of the product
  • Agree primary functions
  • Organise the brainstorm outputs onto a function tree

Brief The Team

The Team is led by the designer owner and briefed on the process steps and methodology for defining the functions.

At this stage it is important to establish that all the team members are sufficiently familiar with the FMEA process to be able to fully contribute to the FMEA effort. The Team meeting would be arranged, with appropriate Team roles (leader, scribe, time manager and facilitator) and an agenda that sets time aside for briefing, brainstorming, organising the brainstorm outputs and reveiwing.

Brainstorm The Functions Of The Design

Follow the rules of brainstorming:

  • Keep the output visual
  • Keep to the alloted timescales (time managers role)
  • Volume is King!!
  • Do not discuss the ideas (this comes later)
  • Do not criticise
  • Involve all of the team (facilitators role)
  • Do not 'organise' the brainstorm (this comes later)

We use a VERB - NOUN sentencing technique to describe each function

FMEA_FT_Blog_P2

Organise The Brainstorm Outputs Onto A Function Tree

It is very seldom that design specifications are written in this way, so we use the Function Tree tool to capture and sort all the functions of a design from Primary functions to Tertiary functions.

Primary Functions - those that are identified as nearest to the customer usage intent

Secondary Functions - those unique functions that support the primary functions

Tertiary Functions - functions that support the secondary functions and typically suppport more than one

Measureable Level - sometimes referred to as Actionable Level, these functions have a specific measurable or set of measurables that can be specified.

Function Tree Construction

FMEA_FT_Blog_P3

 

First, organise the Brainstorm Output by selecting the primary functions, then secondary and so on. Remember there may be more or less than the four levels shown here, and it is okay to add or duplicate functions

 

 

FMEA_FT_Blog_P4

 

To check that the functions actually support one another you should ask 'How?' the primary function is achieved, through to the secondary and so on

 

 

 

FMEA_FT_Blog_P5

 

 

 

Then look at the tertiary functions (lowest level) and ask 'Why?', moving back up the tree and providing the answer at each level, making grammatical sense throughout.

 

 

 

Assessing Questions

  • Have all functions been transferred from the brainstorm to the function tree?
  • Have all primary functions been developed to an actionable level?
  • Is the sentencing technique obvious and correct?
  • Have all primary functions been recorded on the FMEA record?

 

graham_cripps_dec_2010_formal

Graham Cripps
ResultsResults

 

Topics: Design FMEA, Process FMEA, FMEA Form, FMEA Action Planning, DFMEA, FMEA FAQ's

FMEA - Some frequently asked questions answered!

Posted by Graham Cripps on Fri, Jul 24, 2015 @ 01:30 PM

FMEA FAQ's (Frequently Asked Questions)

"When do I carry out an FMEA?"

FMEA is a predictive risk assessment tool and looks at the probablility of failure of a design or process.

As Machinery FMEA and System FMEA are also based upon  Design FMEA, you can assume the followingcomments apply accordingly.

For Design FMEA (DFMEA), the FMEA should be carried out prior to setting up the process and already have the output from the DFMEA. The FMEA concentrates on the probablity of failure of the process to perform in terms of the process purpose or outcome and requires the following information:

  • Design specification
  • Design verification test planning
  • Reliability test data

For a Process FMEA (PFMEA), the FMEA should be carried out prior to settng up the process and already have the output from the DFMEA. The FMEA concentrates on the probability of failure of the process to perform in terms of the process purpose or outcome and requires the following information:

  • Critical charateristics of the design
  • Process capability (if known)
  • Machinery FMEA if available
These are ideal conditions, however an FMEA performed on existing products or processes can also provide valuable data and information for both the design and process teams

Download your FREE FMEA template

 

"How do I ensure that our FMEA efforts are well managed?"

For FMEA to be a useful tool for any business it must be an integrated part of the business process. Therefore this process, like any other, requires management support.

In order to have a framework for managing FMEA's someone that has a vested interest in the outcome of the FMEA and in a management role would be tasked with assessing each stage of the process to ensure all process steps have been completed successfully.

There are a whole set of assessing questions that are asked at the end of each stage of the FMEA process. These questions are designed to assist the team and the manager to focus upon each stage of the FMEA process to ensure full completion.

The following is a small selection of the questions but a full copy can be accessed by selecting the button at the end of this article.

These assessing questions are those followinng the review of existing design controls of a DFMEA:

  • Have all the failure modes within the scope of this DFMEA been considered?
  • Have all the controls been realistically onsidered and entered onto the FMEA record?
  • Have the design verification specifications been used as part of the controls review?
  • Have all outstanding questions on the question log been answered?
  • Are there any new questions to be added to the log?
  • Has the DFMEA been communicated to all involved / interested parties?

 Download your FMEA Assessing Questions!

 

"What is an FMEA Application Workshop?"

There are a lot of training courses, including the ones we offer, that tell you how to carry out an FMEA. However, the most effective way of learning is doing.

Our application workshops are run over two to four days and are a mixture of "show and tell" on your own design and process, not a case study. 

The purpose of the workshop is not to fully complete an FMEA but to provide the ooportunuty for the attendees to be able to practice all steps on a design or process they are familiar with and have an outcome that can be taken away and completed with the new knowledge and experience. 

This approach provides a feeling of relevance for the attendees and the opportunity to practice in a facilitated environment.

We also offer a review service, during the Workshop process,  whereby one of our experienced practitioners will review one or more of your FMEA's and provide constructive fedback on the content. We have found this to be a valuable addition to the Workshop format, providing guidance and support for our clients.

To find out more about our FMEA Application Workshops please click the button below.

FMEA Application Support

 

"How do I use RPN to prioritise actions to be taken?"

In its simplest form, the RPN figure is used to rank priority of actions to be taken by considering the highest RPN number first. It has long been recognised that this method does not discriminate between the severities of the effects of failure.

There are two available methods (RPN and SOD)and we would recommend the following method.

Known as S-O-D (Severity - Occurrence - Detection) it involves looking at the severity ratings of 10 first. To prioritise these, take S x D (product of severity and detection) to prioritise within this group. If the two are the same, then use the RPN number within that sub-group.

Then repeat for severities of 9 etc. See the following example: 

                 

PRIORITY

 

S

 

O

(s X o)

D

 

RPN

 

RPN Method

S-O-D Method

EX 1

10

 

1

10

1

 

10

 

9

3

EX 2

10

 

6

60

3

 

180

 

3

1

EX 3

10

 

3

30

2

 

60

 

5

2

EX 4

4

 

7

28

1

 

28

 

8

5

EX 5

4

 

3

12

3

 

36

 

7

4

EX 6

4

 

10

40

10

 

400

 

1

6

EX 7

2

 

10

20

10

 

200

 

2

7

EX 8

2

 

7

14

3

 

42

 

6

9

EX 9

2

 

7

14

7

 

98

 

4

8

 

If we use the RPN method then moderate severity becomes the first priority for action, whilst a failure mode with an effect of 10 and a relatively high probability of occurrence is third.

The S-O-D method is more logical and still provides a reliable structure for prioritisation.
 
Download your free FMEA ranking Table

 

Topics: Design FMEA, Process FMEA, FMEA Template, FMEA Form, FMEA Action Planning, FMEA ranking tables, DFMEA, How to construct a boundary diagram, Continuous Improvement, FMEA FAQ's

FMEA Saves Lives!

Posted by Graham Cripps on Tue, Dec 18, 2012 @ 02:35 PM

FMEA Saves Lives!

FMEA

"How long has FMEA been around, Graham?" I was recently asked.

"About 60 years" was my reply

"Why aren't we all getting it right then?" Good question I thought.

"People need too get their act together. Its your duty to tell them how!"

So, on that note, allow me to share some thoughts with you.

When I have challenged FMEAs in the past I have been given various reasons for failure:

  • It was just a paperwork exercise to satisfy an audit
  • Compliance
  • We didn't understand

This frustrates me becasue the consequences of a badly executed FMEA could result in injury or even death!

So if you think that you could benefit from a better understanding then read on,, as there are four aspects that need to be fully considered if an FMEA is to be effective.

The four aspects are as follows:

Boundary Diagrams which will focus your efforts

Understand design functions

Understand unintended design functions

Get control and stop things going wrong

 

1. Boundary Diagrams Focus Efforts

FMEA Boundary DiagramGet your team focused!

Set a boundary diagram for the FMEA.

After the design functions have been established, revisit the boundary to ensure that the FMEA considers the design in the context of its full operating environment.

Check with the team to see if any new knowledge or support from outside your team is required. Why guess when the knowledge exists with others in your organisation?

 

For the most part, boundary diagrams are produced without looking beyond the 'obvious', only considering the direct connections

The boundary diagram MUST reflect ALL conditions of use and application.

2. Understand Design Functions

Why is it that we don't look beyond the obvious functions?

Why don't we look at functions from a customer perspective?

What is the function of a pen? (see answer at the end!)

This is a basic design principle that all too often is not applied!

Using the Function Tree, develop a full understanding of your design funtions, then carry these prime functions forward into the FMEA

 3. Understand Unintended Functions

Do you open the microwave door to turn it off sometimes?

Do you use the steering wheel as a support to help you get in and out of your car?

Have you ever used a small screwdriver as a bradawl?

Let's face it, this is real world stuff - not all of your customers will use your products in the same or even in the intended way! Some users will intrduce unintended functions - from light to heavy use.

In terms of the design intent should you take these into consideration? Of course you should, it is necessary to consider unintended functions. Sometimes, defining such functions is critical to the products success.

4. Stop it going wrong!

The great thing about FMEA is that it never limits creativity but it does help you to decide the best available option - especially when it concerns customer safety!

In Design FMEA (DFMEA) current controls are all based around the design process and confirmation, verification and validation testing of that design. However there must be a thorough and honest review of how effective these controls will be in detecting failure.

Consider the following:

  • Do your tests contain the conditions for both light and heavy customer usage profiles? A light user could cause higher levels of stress upon a given design
  • Is the test population significant enough to ensure that the failure mechanisms will be present? If only 5 are tested, is this a significant enough quantity when you are looking to sell 5 million with a life expectancy of 5 years or 250,000 cycles?
  • Does the test sample represent a true manufactured situation? Often prototype parts are used that do not feature the process variation experienced during manufacture
  • Are design strength issues considered as part of the test? Depending on the manufactured condition the design strength has a distribution of its own
  • Is the control in question in use now or intended to be used / developed at some time in the future? Only those controls in use / available at the time of the FMEA should be considered

So what is stopping you from doing it right?

Don't think you need to? Don't want to? Don't know how to? Didn't know it was important? Don't have the time?

Now you have no excuse! Go to our FMEA page to review all of the resources available for download

Alternatively, if you have a question or need help, you can contact me directly:

graham_cripps_dec_2010_formal

 

Graham Cripps

graham.cripps@resultsresults.co.uk

Tel: 01371 859 344

www.resultsresults.co.uk

 

 

You can also access an FMEA snapshot by clicking on the icon below:

FMEA Template P.S. What is the function of a pen?

If you said write, I’d say wrong!

Here are just a few functions of a pen: contain ink, provide grip, dispense ink

A pen will only write if it is used as part of a larger system – got it?

 FMEA Life Style

Topics: Design FMEA, FMEA Template, FMEA Form, FMECA, DFMEA, Risk Management, Boundary Diagram

FMEA - Plan and implement improvement actions - Recalculate the RPN

Posted by Graham Cripps on Thu, Aug 16, 2012 @ 03:21 PM

FMEA - Plan and implement improvement actions and establish revised RPN

GrahamCripps, DirectorWe are now nearing the completion of the DFMEA process whereby the identified and agreed actions are to be planned and implemented. To this end, as well as throughout the FMEA process in general, we use the Deming P.D.C.A. Cycle.

 

fmea_snapshot

 

Introduction

In this final FMEA article I will discuss the process of planning and implementing the actions necessary to reduce RPN numbers in the order of: -

  • Reduce the severity of the effect of failure – this is the most difficult to do as it will normally involve designing out the function. If this cannot be done: -

  • Reduce the likely occurrence – this is the most cost effective in most cases and certainly so when compared with the above option

  • Improve detection methods – this can be costly, particularly if involving detection rather than prevention

As already mentioned the planning and implementation is best served by using the Deming Plan-Do-Check-Act cycle. It is applied as follows: -

Plan DO Check Act CyclePLAN – plan the implementation of the corrective or improvement action. These may have wide ranging impacts across the design and design verification processes. All actions should be comprehensively considered in terms of the likelihood of success. This means that testing modifications may need to be modelled during the planning stage. Establish how success will be measured or assessed.

DO – Carry out the modifications as planned to the design, design processes or test processes. This includes documenting the changes in all associated processes and reviewing test data outcome requirements. It is important to ensure that the changes are made permanent to ensure “old or established” methods are not readopted (Ensure procedural documentation is updated and re-issued. Make the change sustainable).

CHECK – Carry out checks to ensure that the changes have taken place and are effective. This may not be feasible using practical methods, so modelling may be required, which should have been planned for as above. Have the changes had the planned effects, has the previous Severity, Occurrence or Detection levels been improved as planned?

ACT – Ensure that all data has been recorded, review the DFMEA and update the Severity, Occurrence and Detection ratings accordingly. This should result in a required reduction in the RPN. If outcomes are not as planned, take further actions to achieve the required improvements.

What Next?

What we have been through with these series of articles is just the beginning. FMEA fits within the processes of new product introduction and release and has direct linkages with other design tools including: -

  • Product reliability

  • Piece part approval

  • Design verification process

  • Adjoining FMEA efforts

  • Problem Solving

  • Robustness engineering

  • To name but a few………………………..

The message therefore is quite clear - FMEA is only successful when and if it is an  integrated part of the business and quality processes. Failure to do so makes FMEA a “bolt-on” activity. This less effective.

Assessing Questions 

  • Have all recommended actions been completed?

  • Have all required process and system documentation been completed in accordance with company standards?

  • Have any shortfalls in terms of expected outcomes been addressed through further considered action planning?

  • Have all outstanding questions been closed, new ones added and the question log updated?

  • Has the FMEA record been updated and communicated to all interested parties?

  • Have all the team members been thanked for their contribution?

Next Time

Next time you are tasked with carrying out an FMEA, I hope you will feel better equipped. Remember to download the FMEA Snap-Shot and use this as a reminder of the steps that need to be taken to get the best from your FMEA efforts.

Finally, thanks for sticking with me through these articles. I hope they have helped. If you need any further assistance, please visit www.resustsresults.co.uk/fmea.

Graham Cripps

Results Consotium Ltd

www.resultsresults.co.uk

Download your free FMEA SnapShot

Topics: Design FMEA, FMEA Template, FMEA Form, Risk Priority Number, FMEA Action Planning, FMECA, FMEA ranking tables, DFMEA, RPN

FMEA - Rate all existing Design Controls and calculate RPN

Posted by Graham Cripps on Thu, Aug 16, 2012 @ 02:55 PM

FMEA - Rate all existing Design Controls, calculate the RPN, and establish corrective actions required

 

Graham Cripps, DirectorIn this article I will discuss design controls and their effectiveness and look at how to calculate RPN and establish a priority for any necessary actions.

As I come to the end of this series of FMEA articles I would like to invite you to download a free copy of our FMEA Snap-Shot. The Snap-Shot series are key process documents that have been produced as a guide to the process steps of (in this case) FMEA. Our clients use these during FMEA meetings as an aid for the team. Please use the button at the end of this article.

Unlike previous articles I will discuss this activity in two sections and include assessing questions at the end of each section.

 

Introduction – Determine Existing Design Controls and Establish Rankings

At this stage we are considering the existing design controls, this will include all those that are part of the current design and design verification processes. These controls may fall into one of four categories: -

  •  Detection controls that will detect the cause of failure

  • Detection controls that will detect the failure mode

  • Preventative controls that will prevent the cause from occurring

  • Preventative controls that will prevent the failure mode from occurring

Design Controls are those activities within the design and design verification processes that are already in place to prevent or detect and might include: -

  •  Life cycle testing

  • Design verification plans

  • Life cycle modelling

  • Design validation

  • Stress testing

  • Design reviews

  • Inspection of design

  • Etc.

It is critical to ensure that the following are taken into account when ranking current design controls: -

  • Product life cycle – if the failure mode happens during the useful life span of the product does the control (e.g. life testing) consider longevity?

  • Have all customer usage profiles been considered in the control?

  • Have all robustness issues been addressed?

  • How representative is the control with respect to actual populations (product and customer/environment)?

NOTE: If you are new to FMEA and Reliability issues, please consider an FMEA Application Workshop. For more details please contact us at www.resultsresults.co.uk and we will be happy to help in any way we can.

FMEA Flow 3Once established, we use the DFMEA rating tables to rate how likely these controls are to work, the higher the number the less likely the control will work. In the FMEA Flow diagram it can be seen that the flow is important to establish which control detects which cause and which cause is associated with which failure mode.

For example, if a design verification test does not consider or test for the failure mode then this test will rate 9 or 10. If the it does test for the failure mode or the cause of failure and is such that it includes for the most demanding customer profile and life cycle, then the rate could be 2 or 3 (ranking needs to consider the size of the tested population).

This process is repeated for all failure modes. In many cases, the causes will impact on more than one failure mode.

Assessing Questions (1)

  • Have all the failure modes within the scope of this DFMEA been considered?

  • Have all the controls been realistically considered and entered onto the FMEA record?

  • Have the design verification specifications been used as part of the controls review?

  • Have all outstanding questions on the question log been answered?

  • Are there any new questions to be added to the log?

  • Has the DFMEA been communicated to all involved/interested parties?

Introduction - Calculate the RPN and establish priority of required actions

FMEA is a risk management tool. This and the next stage are all about minimising the risk of potential failures. We now have a record of the current detection and prevention design controls rated in terms of likelihood of detecting or preventing each failure mode.

Armed with this information we can now consider which of the failure modes is of greatest concern to the business. To do this we need to consider how we are going to prioritise them. To do this we calculate the Risk priority Number.

The Risk Priority Number (RPN) is the product of: -

Severity X Occurrence X Detection

Where: -      

  • Severity is the severity ranking of the effects of failure

  • Occurrence is the likelihood of the failure mode occurring

  • Detection is the ranking of the current design control on terms of their likelihood of detecting/preventing the failure mode or the causes of failure

However, the RPN used in isolation can be misleading. I can best demonstrate this with an example.

Example: I am the designer of a domestic stainless steel toaster. My FMEA team have identified a potential failure mode of “electrical insulation fails” and this has a severity of 10. However the likely occurrence is 1and the detection is 1. My RPN is therefore (10 X 1 X 1) 10.

My FMEA team have also identified a failure mode “appearance degrades” with a severity of 2. However the likely occurrence is 10 and the detection rating is also 10. My RPN in this case is (2 X 10 X 10) 200. Using just the RPN to determine priority of actions would put the second scenario as the higher priority when clearly the first is of greater priority.

So, Results’ recommend the following generic approach when considering the priority of any required actions: -

Level 1 – Effects with severity ratings of 9 or 10 are considered first.

Level 2 – Severity X Occurrence are then used to sort.

Level 3 – Severity X Occurrence x Detection (RPN) is used to sort all other actions.

Note: where there is conflict of rankings (i.e. several 10’s) go to the next level to sort.

Remember – you know your products and customers best, let this be your guide as you establish your action priorities.

At this stage, actions are recommended to reduce the risk and consequences of potential failures including agreeing actions and dates to be completed. Remember to make individuals responsible for actions, not departments or general areas.

Assessing Questions (2)
  • Have all the failure causes been considered and the right prioritisation process used in all cases?

  • Has the agreed prioritisation process been used consistently throughout?

  • Have all interested parties been involved in discussions around problem areas?

  • Have actions been recommended for all problem areas?

  • Have individuals been tasked with the actions, including an agreed completion date?

  • Have all outstanding questions been cleared or new ones added to the question log?

  • Has the FMEA report been updated and circulated?

Next Time

FMEA Snap-ShotIn the final article in this series I will describe how to ensure actions are taken and how the RPN is reduced as a result. In the meantime, please download your free FMEA Snap-Shot.

Graham Cripps

Results Consortium Ltd

www.resultsresults.co.uk

 

 

 

 Download your free FMEA SnapShot

Topics: Design FMEA, FMEA Template, FMEA Form, Risk Priority Number, FMEA Action Planning, FMECA, FMEA ranking tables, DFMEA, RPN

FMEA - Determine Causes of failure and Rank their likely occurrence

Posted by Graham Cripps on Tue, Aug 14, 2012 @ 10:15 AM

FMEA - Determine Causes of failure and Rank their likely occurrence

Graham Cripps, DirectorHaving identified the failure modes and the effects of failure, we now need to determine the possible causes of failure. In this article we will be looking at establishing those causes and the processes used to ensure all causes are considered and their likely occurrence determined by the FMEA team.

 

 

 

Introduction

FMEA Sentencing At this point we need to understand that the effect of the failure mode and the cause are not linked, other than through the failure mode itself. In other words, we are looking for the cause/s of the failure mode. The failure mode has effects that are experienced (sometimes called symptoms) as a result of that failure mode.

This is described in the sentencing model opposite.

 

 

To ensure that the best result is achieved the following should be noted: -

  • Ensure that brainstorming is managed effectively (this a creative process and should have the basic rules applied)

  • Do not constrain thoughts around current detection methods, this comes later

  • Keep the boundary diagram and other visual aids in view to focus the brainstorming effort

  • One cause can be the cause of more than one failure mode

  • All failure modes are captured and recorded for discussion and analysis after the brainstorming session

  • Causes are limited to those of the specific failure modes and cannot include errors outside of the boundary diagram

  • Potential mistakes that could be made during manufacture of the design can only be considered if they are as a direct result of poor design (the principles of design for manufacture).

  • A causal theory should be developed to root cause level for all failure modes with a severity of 9 or 10.

  • Robustness linkages should be considered if they are within the agreed scope of the FMEA.

The team should brainstorm all the possible causes of failure. Failure of the design to perform as intended.


FMEA Form Flow GraphicOnce the causes of failure have been established, they are arranged in order against the failure mode (a continuation of the flow established during the last process step (see diagram below).

Using the Design FMEA Ranking tables, each potential cause is ranked as to the likelihood of occurrence. The ranking is recorded alongside the cause in question.

 

Because the use of ranking tables is not an “exact science”, the introduction of past experiences and other data is useful.

 

The FMEA flow is imprtant. Ensure that the causes are arranged against each failure mode. You will now have an FMEA report that has the effects of the failure mode and the causes of the failure mode aligned to the individual failure modes (see graphic above left). This is critical at the next stage because we will want to be looking at how to reduce the likelyhood of failure and this is around the failure mechanism for each failure mode.

Assessing Questions

On completion of this and every stage of the FMEA, assessing questions need to be addressed. This will include: -

  • Have all failure modes been considered fully?

  • Have cause theories been developed for all causes (these must be what could actually happen)?

  • Have causes met the correct sentencing criteria (see above figure)?

  • Has the scope of the FMEA been adhered to for each possible cause?

  • Has the FMEA report structure been completed correctly (this is important when calculating RPN)?

  • Have all previous questions been closed out and any new ones entered on the question log?

  • Has the FMEA report been communicated to all interested parties?

 

Next Time

In the next article I will explain how to assess current preventative and detection controls and their effectiveness. I will also describe how to calculate RPN as a method of establishing action priorities.

 

 Free FMEA Ranking Table Download

 

 

Graham Cripps

Results Consortium Ltd

www.resultsresults.co.uk

 

Topics: Design FMEA, Process FMEA, FMEA Template, FMEA Form, Risk Priority Number, FMEA Action Planning, Root Cause, root cause analysis, FMECA, FMEA ranking tables, DFMEA

FMEA - Determine and Rank the Severity of the Effects of Failure

Posted by Graham Cripps on Fri, Aug 10, 2012 @ 12:07 PM

FMEA - Determine and Rank the Severity of the Effects of Failure               

Graham Cripps, DirectorAt this stage of the FMEA process we have: -

  • Established the FMEA Team members

  • Defined the Scope of the FMEA

  • Determined the functions of the design

  • Determined the failure modes

 

The next step is to determine the effects of failure and to rank these failures in terms of their potential severity.

Introduction

A failure of a product or service to provide an intended function can have more than one effect. These effects will have varying levels of severity.

Example: one of the functions of a domestic toaster is to eject the toast at a determined level of browning. A failure mode could be “fails to eject the toast”. This failure mode could results in the toast continuing to heat. The effects could therefore be: -

  • On the toaster – elements and platform contaminated

  • The toast – burnt

  • The user – dissatisfied customer

  • The environment – smoke or possible fire

The first three effects will be less serious than a fire.

In this article we will look at the process for determining the effects of the failure modes and rank them in terms of their serverity (seriousness).

I will refer to 2 tools that are used, the Design Effects List and Ranking Tables.

Determine the Effects of Failure

Again, it is important to keep visible the boundary diagram, the FMEA record, question log and Function Tree for the team to refer to.

The effects of the failure modes are considered by the team in the following 7 categories: -

  •  Part (subject of the design FMEA)

  • Assembly (the next level assembly that the part fits)

  • System - the system that this part contributes to

  • Product - the overall product

  • Customer - the user of the product

  • Regulations - current legislation applicable in the country of use

  • Other - any other category that may be industry or market specific

NOTE: the terms used in this list are generic and should be replaced with your industry specific terms. For help with this please consider and FMEA Application Workshop. To find out more visit our web site at www.resultsresults.co.uk or e-mail for more information on info@resultsresults.co.uk .

FMEA Flow   1The effects are recorded on the Design FMEA effects list (optional) and the FMEA record against the failure mode being considered. This will give a natural left to right flow across the FMEA record. The importance of this will become apparent later in the process (see model opposite)

The use of visual management tools are important during the current process steps to remind the team of the focus of this FMEA.

Once recorded on the FMEA form, each effect is ranked in terms of its severity using the Design FMEA ranking tables. The highest severity is the one carried forward and recorded against the failure mode being considered.

Ranking (or rating) tables are available through a number of sources. However, Results have their own versions that are available as a free download (click the on button at the end of this article).

FMEA   SeverityThis section of the FMEA form shows 4 effects with severities of 3 to 9. As 9 is the highest, this is carried forward.

The Classification used depends upon your specific industry so will not be covered in this article. If you require further assistance consider an FMEA Application Workshop.

This activity is carried out for all failure modes on the FMEA form.

 

Complete the FMEA Form

Ensure that all ratings are completed for failure modes and complete the FMEA form.

If there are any outstanding questions not answered, complete the question log and assign someone to provide the answer for the next meeting (or before if urgent).

Assessing Questions

There are a number of assessing questions that should be asked at the end of this stage and include: -

  •  Have all questions from Question Log been actioned?

  • Have all failure modes been considered?

  • Have all failure modes been listed and considered against the effects list criteria?

  • Have all effects for each failure mode been recorded on the FMEA record?

  • Have all failure modes been rated using the correct rating table?

  • Have each set of effects been assessed in terms of overall criticality?

Next Time

In the next article we will look at determining causes of failure and looking at the likely occurrence of those failures.

 

Free FMEA Ranking Table Download

 

Graham Cripps

Results Consortium Ltd

www.resultsresults.co.uk

 

 

Topics: Design FMEA, Process FMEA, FMEA Template, FMEA Form, FMEA Action Planning, FMECA, FMEA ranking tables, DFMEA

FMEA - Define the Products Design Function(s) or Intent

Posted by Graham Cripps on Tue, Jul 31, 2012 @ 12:23 PM

FMEA – Define the Product Design Function(s) or Intent – Step 2

Graham Cripps, Director

Defining the product design function(s) is key to the success of conducting a successful Design FMEA.

FMEA is a risk management tool that looks at and manages the risk of failure of the product functions. Failure to identify these functions leads to failure of managing the risk of those failures.

Once again I will use the Design FMEA to demonstrate the FMEA process.

 

Introduction

If we know all of the functions that a design has to achieve, then we can consider how those functions could potentially fail to meet the customer requirement. This is the key to understanding the exact functions that the product performs.

This often causes difficulties with FMEA’s as there is a tendency to generalise functions as a combination of functions. In the first FMEA article I used a pen as an example.

Pen Example      

Let’s consider the design a fountain pen. What is a primary function of a pen? To write?. WeFountain Pen cannot design this pen to write on its own!    

We have to consider our design functions which might be: to retain ink, to dispense ink, to provide comfortable grip, to allow left and right handed use, to resist leaks, to provide smooth contact on writing surface etc.”

 

The outcome that a user expects is that (in the hands of a capable person) the pen will write. However, this is not a single function of the pen design as seen in the above example but a combination of functions that deliver the customer requirement.

Define the Product Design Function(s)

A robust method of defining a products function is the use of the Function Tree. I gave a brief description of the process in a previous article but I will explain further how this is applied. 

The function tree is a process used to determine prime functions and their subordinate functions for a given product. The process steps are as follows: - 

  • Brief the team

  • Brainstorm the functions of the product

  • Organise the brainstorm outputs onto a function tree

Brief the Team

The team is led by the design owner and briefed on the process steps and the methodology for defining the functions.

The team meeting would be arranged with appropriate team roles (leader, scribe, time manager and facilitator) and the agenda would be set to allow time for briefing, brainstorming, organising the brainstorm output and reviewing.

Brainstorm the Functions of the Design

Follow the rules of brainstorming as follows: - 

  • Keep the output visual

  • Keep to the allotted time (time managers role)

  • Volume is king

  • Do not discuss ideas (this comes later)

  • Do not criticise

  • Involve all of the team (facilitators role)

  • Do not organise the brainstorm (this comes later)

 

We use a VERB-NOUN sentencing technique to describe each function.

 

Example - Using the fountain pen as an example, functions would look like this: -

VERB

NOUN

Dispense

Ink

Retain

Ink

Provide

Writing grip

Provide

Left and right handed use

Prevent

Leaks

Provide

Smooth contact on writing surface

Provide

Ink reservoir

etc.

 

Organise the Brainstorm Outputs onto a Function Tree

It is very seldom that design specifications are written in this way so we use the Function Tree tool to capture and sort all the functions of a design from Primary functions to tertiary functions. 

Primary Functions – those that are identified nearest to the customer usage intent 

Secondary functions – those unique functions that support the primary functions 

Tertiary functions – functions that support the secondary functions and typically support more than one function.  

Measureable level – sometimes referred to as actionable level, are those functions that will have a specific measurable or set of measurables that can be specified.

Function Tree - 1

 

 

First, Organise the Brainstorm Output by selecting the primary functions, then secondary and so on. Remember there may be more that four levels and it’s OK to add or duplicate functions (see fig 1).

 

 

 

The model used shows just four levels. However, in practice this may be more or less than four.

Function Tree - 2

 

 

To check that the functions actually support one another, start by asking “How?” the primary function is achieved, through to the secondary and so on (see fig 2).

 

 

 

Function Tree - 3

 

 

Then we ask of the tertiary functions "why?" and moving back up the tree, providing the answer at each level, making grammatical sense throughout.

 

 

 

 

The purpose of an FMEA is to precent failures of function. Therefore, if a functions is not fully described, prevention of failure of that function cannot be managed. This will become even more evident when I describe how to detrmine and record failure modes (the way a product funtion could potentialy fail).

Complete the FMEA Form

At this stage, all the primary functions are recorded on the FMEA Form. Recording the primary functions does not mean that the other functions will be missed, there is a discipline that needs to be observed for all FMEA meetings whixh is explained in the next section.

FMEA Discipline

 

Accepting that conducting an FMEA is a team event, it is also important to remeber the following: -

  • Keep the Boundary diagram displayed during every meeting

  • Keep the Function Tree displayed during every meeting

  • Complete the assessing questions at the end of each FMEA stage

  • If questions remain unanswered at the end of any meeting, keep a question log for the team.

 

Download your FREE FMEA template

 

Graham Cripps

Results Consortium Ltd

www.resultsresults.co.uk

 

Topics: Design FMEA, Process FMEA, FMEA Template, FMEA Form, FMECA, Risk Management, Boundary Diagram

FMEA – Determine the scope of the FMEA (FMECA) - Step 2

Posted by Graham Cripps on Wed, Jul 25, 2012 @ 03:30 PM

FMEA – Determine the scope of the FMEA (FMECA) - Step 2

Graham Cripps, DirectorHaving formed the FMEA team you now need to determine the scope of the FMEA.

 

 

 

Introduction

The scope of the FMEA describes, very precisely, what will and what will not be included in this FMEA. That’s not to say that items or interactions that are excluded will not be subject to an FMEA but just not in this one.

Defining the scope of the FMEA uses a tool called a boundary diagram. This is a simple tool based upon a block diagram and is explained later in this article.

This activity requires the core team to contribute as consideration will need to be given to not only the target item (the item that is the target of the FMEA) but also any direct or indirect interactions with other components, sub-assemblies or systems.

Constructing the Boundary Diagram

The Boundary diagram is constructed in three phases: -

  • Draw a block diagram of the item and it’s directly connecting items

  • Determine the interactions between the target item and all connecting parts

  • Agree the boundary to be considered in this FMEA 

Spark PlugFor the purposes of this article I will use a the design of spark plugto demonstrate how to construct the Boundary Diagram.

1. Draw the Block Diagram

The first step is to draw a block diagram including all of the directly connecting parts, sub-assemblies or systems.

Initial Block Diagram

 

I have used a generic example of a spark plug assembly to demonstrate how this might be done.

In this example I have simplified the blocks to show the main components that have a functional relationship to the spark plug assembly.

 

2. Determine the interactions

The second step requires the FMEA Team to consider the relationships between all the items in the block diagram.

Block Daigram with LinkagesIn this example I have suggested some linkages. 

E.g. The relationship between the plug assembly and the gasket ring is the retaining fit, the relationship between the spark plug assembly and the fuel mixture is the spark gap in the correct position.

I have kept this diagram fairly simple for demonstration purposes. In most cases at this point we would also consider the robustness issues as well.

 

Robustness - introduced by Genichi Taguchi and refers to the operation of a component, sub-assembly or system in the presence of the operating environment and all of the internal and external variations.

3. Agree the Boundary of this FMEA

Having agreed the block diagram and the connections or linkages between each of the blocks, the team now determine the scope of the FMEA. The scope of a design FMEA (DFMEA) is restricted to:-

  • Failures attributed to design only (i.e. does not include manufacturing , fitting or other induced errors unless through design issues) E.g. If a spark plug was fitted but cross threaded, this would not be considered unless the relationship between the cylinder head and the fitting tool induced the error.

  •  Analysis of items within the boundary diagram

Boundary DiagramIn this example the boundary diagram shows that this FMEA will include the spark plug assembly, the provision for retaining the spark plug connector, the provision for retaining the retained gasket ring, the retained gasket itself, positioning of the spark gap and provision of a hexagonal shape for the fitting and removal tools.  However we won’t include the plug removal tool, spark plug connector, fuel mixture or the cylinder head in this FMEA.

 

 

 

What the boundary diagram does for the FMEA Team is to provide a focus for the analysis. This does not mean that all the other linkages and interactions are not subjected to analysis, just not in this instance.

Jig Saw Puzzle

 

FMEA is like a jig-saw puzzle. Each FMEA fits into the jig-saw puzzle to build the complete picture of the design

 

Using the Boundary Diagram

Once completed, the boundary diagram becomes a visual aid for the FMEA team to use at each meeting to ensure that they are focussed on the agreed scope of the FMEA.

FMEA Template

My previous article discussed forming the FMEA Team and included a free FMEA Template (FMEA Form). If you would like a copy please click on the link at the begining of this paragraph.

 

Download your FREE FMEA template

Graham Cripps

Results Consortium Ltd

www.resultsresults.co.uk

 

Topics: Design FMEA, FMEA Template, FMEA Form, FMEA Action Planning, FMECA, Boundary Diagram

FMEA - Form the FMEA Team - Step 1

Posted by Graham Cripps on Mon, Jul 23, 2012 @ 03:22 PM

FMEA – How to complete an FMEA (FMECA) - Step 1 – Form the FMEA Team

Grahasm Cripps, DirectorIn this short series of articles I will be sharing with you the steps to applying FMEA successfully as well as some handy tips to ensure you do not fall foul of the top six reasons FMEA's fail to deliver the required outcomes.

 

 

Introduction

In my previous FMEA article I described the 10 steps of FMEA (FMECA) which are: -

STEP 1 – Form the FMEA Team

STEP 2 – Determine the scope of the FMEA

STEP 3 – Define functions (DFMEA) or process purpose (PFMEA)

STEP 4 – Define potential failure modes

STEP 5 – Determine and rank the severity of the effects of the failure modes

STEP 6 – Determine and rank the likely occurrence of the causes of failure

STEP 7 – Establish and rank the all existing design controls

STEP 8 – Calculate RPN and establish priority of and determine actions required

STEP 9 – Plan and implement actions and establish revised RPN

STEP 10 – Close the FMEA process

I also included a free FMEA Template download which I recommend you do by following the link above so that you can closely follow the process steps.

Within this series of articles I will also be referring to a number of tools and techniques that will be supported by other free downloadable tutorials for those of you new to the FMEA process.

In this article I will be covering the step 1 and for the purposes of demonstration, I will concentrate on Design FMEA (DMEA).

Form the FMEA Team

Teamwork LogoFMEA is a team activity and should not to undertaken by an individual.

Having a team ensures that the required knowledge, experience and different objective views are taken into account at every stage of the FMEA.

There are two elements to the FMEA team, the core team and the support team.

Core Team: the core team are those that are present at every FMEA meeting and are the main contributors to the FMEA output. Typically this team would consist of the Design Engineer, Quality Engineer, customer representative and a supplier representative (for out sourced components/systems/sub-assemblies).

Support Team: could consist of a Process Engineer, Manufacturing representative, process or systems specialist etc.

Support team members would be “on call” to offer specialist knowledge and support to the core team when specific information of data is required.

At this point it is important to identify some important considerations when establishing the FMEA Team.

  • Ensure that at least 1 team member has had sufficient FMEA training or experience to lead the process

  • Establish clear team roles and responsibilities

  • Have a clear agenda for each team meeting

  • Ensure that there is full management support for all of the meetings

  • Agree communication channels for activities and outputs from the FMEA process

  • Ensure that all required data, information and support tools available for each meeting

At the first meeting, both core and support members should be in attendance so that there is awareness from the outset of the objectives and target of the FMEA.

 Completing the FMEA Form/Template

FMEA TemplateThe Results FMEA template provides for a record of the FMEA team members and this shoud be completed at the end of the first meeting along with the target item details etc.

 

 

 

 

 

 

 

 

Reasons That FMEA’s Fail

I have had over 20 years of experience of the application and consulting in the application of FMEA in the automotive, aerospace and other related industries. In that time I have been able to identify the top 6 reasons for FMEA’s failing to deliver the required outcomes. In no particular order, these are: -

  • Failure to clearly understand and define the design functions (DFMEA)

  • Poor training of the FMEA team members

  • Lack of management support to release people and allow time for the completion of the FMEA process

  • Failure to follow through with the actions necessary to reduce the risk of failures

  • Little or no communication outside of the FMEA Team

  • The scope of the FMEA being too large to be manageable

These are not the only reasons for failure, but are the most common in my experience.

 

Graham Cripps

Results Consortium Ltd

www.resultsresults.co.uk

 

 

Topics: Design FMEA, Process FMEA, FMEA Template, FMEA Form, FMEA Action Planning, FMECA

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