Fema-bosch

Quality Management in the Bosch Group

14. Failure Mode and Effects Analysis FMEA

Edition 08.1998

Work group booklet 14

K1/EQS Viehmann* K3/QSG Länder K5/QSG Kaczynski UC/WAY Gatter** ZQF Eilers

* moderation ** at times

We are also very grateful for the work of those employees who have contributed to this booklet with their ideas and their constructive criticism.

 1998 Robert Bosch GmbH

Contents 1

Introduction 6 FMEA Objectives .......................................................................................................... 6 FMEA History................................................................................................................ 6 Possibilities of and limits to the FMEA......................................................................... 6 FMEA-types - methodological differences.................................................................... 7

2

Description of Method 8 Deadlines for doing the FMEA...................................................................................... 8 FMEA-Team .................................................................................................................. 9 FMEA-sequence plan................................................................................................... 10 Systematic Preparations ............................................................................................... 10 Special Characteristics................................................................................................. 11 FMEA-Documents ....................................................................................................... 11 Updating....................................................................................................................... 11

3

System FMEA 13 Structuring.................................................................................................................... 14 Functional Analysis ..................................................................................................... 14 Risk evaluation............................................................................................................. 16 Optimizing ................................................................................................................... 19

4

Design FMEA 20 Structuring.................................................................................................................... 21 Functional analysis....................................................................................................... 22 Failure analysis ............................................................................................................ 22 Risk evaluation............................................................................................................. 23 Optimizing ................................................................................................................... 25

5

Process FMEA 27 Structuring.................................................................................................................... 28 Functional analysis....................................................................................................... 29 Failure analysis ............................................................................................................ 29 Risk assessment............................................................................................................ 30 Optimizing ................................................................................................................... 33

6

Cooperation with customers 34 FMEA presentation for customers ............................................................................... 34 System or interface FMEA in cooperation with the customer..................................... 34

7

Cooperation with suppliers

8

Further FMEA-applications 36 Interface FMEA ........................................................................................................... 36 Logistics FMEA........................................................................................................... 36 FMEA for software ...................................................................................................... 37 FMEA for control units................................................................................................ 37

9

Selection/Prioritizing for FMEA 38 Selection according to application criteria .................................................................. 38 Selection with QFD...................................................................................................... 38 Further possibilities for selection................................................................................. 38

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35

4

Contents

10

Relation to other methods 39 FMEA and Quality Function Deployment (QFD) ....................................................... 39 FMEA and value analysis ............................................................................................ 39 FMEA and Team Oriented Problem Solving (TOPS) ................................................. 40 FMEA and review procedures ..................................................................................... 40

11

Computer assistance 41 IQ FMEA ..................................................................................................................... 41 Sibylle for windows ..................................................................................................... 41

12

Bibliography

13

Appendix 43 Appendix 1: Forms....................................................................................................... 43 Appendix 2: Short description ..................................................................................... 46 Appendix 3: Questions on the columns of the form .................................................... 48

Index

42

49

Foreword

Foreword In this booklet, the Failure Mode and Effects Analysis (FMEA) is described as method for risk evaluation. The method used at Bosch is oriented on the successful procedures of the automobile industry. The objective of this manual is a methodological description (introduction) of a RB-uniform FMEA procedure. The already existing training material ‘Basic Seminar for System-, Construction-and Process-FMEA‘‚2. Edition (2/95) has been integrated in its contents. QSP0305 ‘FMEA and the existing FMEA procedures in the division have also been taken into consideration. In this booklet, some of the terms specifically used at RB have been substituted by more common terms. The expert is already familiar with these terms; those who have just started to get into this subject should be aware of the fact that within the period of change, they will still find outdated terms like ‘failure effect‘, ‘severity‘, ‘scope‘ and ‘RZ‘ in the existing documents. With the publication of this booklet, there is also a change of software. The programs used so far are no longer up-to-date and are not further developed. With the now available IQ-FMEA program, we have the possibility to efficiently support the FMEA. You will find more information in chapter ‘Computer assistance‘. The efficiency of the FMEA is dependent on its timely implementation, on the cooperation of competent employees and the concentration on relevant aspects. The FMEA-documentation and its contents are together with other documents, for example drawings, production- and inspection notes a know-how which is worth protecting and should only be handed on under defined circumstances (see chapter ‘Cooperation with customers’). The FMEA is organizationally tied up in existing design and production planning sequences. It is also successfully used in new areas of employment, for example in the SW-development or logistics-planning. Please use the FMEA in view of the fact that systematic analyses in regard to potential failures and their documentation help to prevent failure causes with means of the FMEA. In the long run, the early and thus preventive usage of FMEA helps securing the success of the organization.

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5

6

Introduction



,QWURGXFWLRQ

)0($2EMHFWLYHV The Failure Mode and Effects Analysis (FMEA) is an analytical method of the preventive quality assurance. It serves to find the potential failure of a product/process, to recognize and evaluate its importance and to identify appropriate actions to prevent the potential failure or to discover it in time. The systematic analysis and removal of weak points leads to the minimization of risks, to the reduction of failure costs and to an improved reliability.

)0($+LVWRU\ In the mid-1960s, this method was developed within the Apollo-project in the USA. It has first been used by the aerospace industry and the nuclear technology and later by the automobile industry and also in other sections. Today, FMEA is an important part of the Bosch-quality system.

3RVVLELOLWLHVRIDQGOLPLWVWRWKH)0($ A FMEA is a good means to analyze risks caused by individual failures. The individual risks are weight against each other to recognize priorities. A FMEA does not provide a statement on the total failure risk. For the analysis of failure combinations, the fault-tree analysis is more appropriate. The advantages of a FMEA prove that the effort to prevent failures from the beginning of the development process of a product are justified because the very much higher resulting costs are eliminated later. Advantages are, e.g.: • Prevention of failures in design and development • Less subsequent product changes and thus reduction of costs • Prevention of repeated failures through systematic consideration of expert/failure knowledge on the product or process. An argument which is often used against FMEA is its high expenditure. The following topics play an important role: • Complexity of the product • Level of analysis/type of FMEA • methodological experience of moderator/team • Quality of preparations • Terms of reference/scope of analysis Especially the two last topics offer big saving potentials. Important things to note with a systematic preparation are described in chapter 2. The scope of analyses can be reduced in co-ordination with the client and the team. Approaches for savings are: • Priority system and selection of analyses (compare chapter 9) • a decision analysis that shows the critical component groups • the use of existing products/processes with similar FMEA • the use of a ‘Basis-FMEA‘ with parts / products / processes which are repeatedly analyzed

Introduction

Whereas the expenditure of a FMEA can be easily determined, the savings can often not be directly measured. The implementation of a FMEA is necessary when products are newly developed, when there are changes on the product or procedures, products with safety regulations or customer requirements (see [QSP0305]). Besides all that, the FMEA implementation shows the following positive aspects, for example.: • all project participants are ready for team work at an early stage • better understanding of the system for all participants • early detection of problem areas • consequent taking of actions up to implementation The biggest benefit is gained when the FMEA is made at an early stage simultaneous to the development and planning of the production. It is important that the results can be used in the product development process and so unnecessary recurrences are avoided.

)0($W\SHVPHWKRGRORJLFDOGLIIHUHQFHV There are different types of FMEA depending on the time, the depth and the object of the analysis. Basically, all FMEA types are identical in their procedure; the useage of the same form proves this.

System FMEA The system FMEA analyzes the correct functional interrelation of the system components and their connections. The goal is to avoid defects in system selection and layout and field risks. The system requirements are the basis for the analysis. The system development department is responsible for the system FMEA . Design FMEA The design FMEA analyzes the design and layout of products/components according to the specification to avoid design errors and process defects influenced by the design. The product/component design department is responsible for the design FMEA. Process FMEA The process FMEA analyzes process planning and performance for products/components according to the drawing specifications to avoid planning errors and manufacturing defects. The product planning department is responsible for the process FMEA.

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8

Description of Method

2 'HVFULSWLRQ of 0HWKRG 'HDGOLQHVIRUGRLQJWKH)0($ As soon as possible, a FMEA is prepared in a team. The knowledge and experience of experts from all affected areas are taken into consideration. The FMEA analyzes the state of a project and is to be continually updated as changes occur. System FMEA For base projects, the system FMEA is implemented after the drafting of system concepts or the proposing of. For specific individual projects, the system FMEA is done after the description of the function scope including project sheet, if possible before the component design accounts are issued and before the design FMEA for new concepts is made. Design FMEA First draft is done before the start of B-sample manufacturing and testing. Corrective actions should be completed before product release. Process-FMEA First draft is concurrent with preparations of the production sequence plan and the planning of operational supplies, to the release of the product. Corrective actions should be completed before the start of production. System development Component development Concept Design

Testing Production Engineering Department Planning Procurement Pre-Series Series

System FMEA First draft

Completion of corrective actions

further updating

Design FMEA First draft

Completion of corrective actions

further updating

Process FMEA First draft

System development order

Component development order

Fig.1:

Completion of corrective actions

further updating

u

u

u

Proposal for special characteristics, QB1

Definition of special characteristics, QB2

Realization of special characteristics e.g. Cpk, QB3

Start of B(C)-sample production/ testing

Planning order./ product pre-release

Product release

Chronological integration of the FMEA (example)

Start of series (product deliveryrelease)

Description of Method

9

)0($7HDP To improve efficiency, the FMEA is performed by a team of experts from all responsible and affected areas. Team work should lead to • parallel instead of serial work at an early stage • the benefit of a greater potential of knowledge and experience • an open way of dealing with existing information • increased creativity • quicker harmonized decisions • consensus building and improved acceptance of results • the promotion of cooperation within different departments. For an efficient FMEA implementation, core teams are created (approx. 3 to 5 members). If necessary, additional experts are included. System FMEA Core team

Supplemental members

Table 1:

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Design FMEA

•

System development (responsible)

•

Design (responsible)

•

Application

•

Testing

•

Moderator

•

Plant (production engineering department or quality assurance)

Process FMEA •

Production engineering department (responsible)

•

Quality assurance

•

Manufacturing operations department

•

Moderator

•

Moderator

•

Component development

•

Application/ System development

•

Development (design and/or testings)

•

Sales

•

Endurance testings

•

Departments

•

Department

•

Departments

•

Purchase department

•

Purchase department

•

Sales department

•

Plant

•

Purchase department

FMEA team members (example)

10

Description of Method

)0($VHTXHQFHSODQ The following table shows the individual criteria and sub-criteria which are important for a FMEA. 0. Preparation and Planning • determine problem, problem definition and objective • team, sequential planning of action • materials for team • functional description 1. System structuring • numbering • component or working operations 2. Functional analysis • functions/characteristics 3. Failure analysis • potential types of failures • failure effects and failure causes 4. Risk assessment • failure prevention and failure detection • significance of failure effect (S) • occurance probability (O) • detection probability (D) • risk priority number RPN = S x O x D 5. Optimizing / Quality improvement • chose priority order of risks (analyze S, O, D and RPN) • determination of actions for improvement with R: and I: • introduction of actions for improvement • assess improvements (O,D)

Table 2: FMEA-sequence plan

6\VWHPDWLF3UHSDUDWLRQV Before beginning with a FMEA, you have to do the following: • define scope (type of FMEA) • define objective • select team members • determine need for training, if necessary organize training • prepare tables and diagrams • plan topics which have to be dealt with • estimate expense • do organizational preparations A systematic preparation of the FMEA can reduce the expenditure of the actual FMEA, i.e. the time spend on team work. Involved in the preparations are the moderator of the FMEA, if necessary also the FMEA-coordinator, the representative of the FMEA team (the expert) and sometimes the client. The representative of the team is an important contact person for producing departments (production area, plant) and thus an important contact person for the moderator and he/she advises him with his expert knowledge. When planning and preparing a FMEA, scope and objectives have to be clearly defined. At this stage, you have to decide which parts of a system or a process have to be analyzed. If several FMEA are planned, set the priorities according to urgency and required time which has to be spend.

Description of Method

The employees needed for a FMEA are to be exempt from their usual work, i.e. they should be available during team work. Precondition for the cooperation in a FMEA team is the knowledge of the FMEA method. If no training of this method takes place, there are unnecessary methodological discussions when working in a team. After the definition of the topics which have to be dealt with, the moderator estimates the expense and coordinates this with the client. Before the actual team work starts, all necessary documents have to be prepared. At the beginning of the FMEA team-work, the team is supported by a functional description with the help of drawings and sample parts. Is the product a successor product, the already existing data (failure data, change applications, improvement proposals, field failures) can be additionally used to support the team. Important influence factors for the quality of FMEA are: − time of the FMEA/start in time − composition of team − ability of employees of working in a team − knowledge of the FMEA-method − in a process-FMEA : knowledge on the possibility of translating the measures through MA into action in the production − willingness to hand on information

6SHFLDO&KDUDFWHULVWLFV When determining and dealing with special characteristics (critical/significant/ R/D/ SPC) you have to take note of the following: • special characteristics which result from customer requirements have to be merked in the FMEA. • The special characteristics (critical/significant/ R/D/ SPC) are deduced from the FMEA and the marking is done according to the stipulations of the division.

)0($'RFXPHQWV The following documents are recommended for the publication of the FMEA as provided on the FMEA- cover sheet: − cover sheet with general information and a summary − description of product which is to be analyzed (drawings, sketches,...) − list of used documents (used rating chart) − FMEA-forms − evaluation (time schedule, FMEA-summary,...)

8SGDWLQJ FMEA updating includes entering product and process changes and changed operating conditions; information on manufacturing, zero-mileage and field experiences are entered and the measures are reviewed. A redistribution follows the revision. The associate responsible for updating of the FMEA (see cover sheet) must be informed by the associate responsible for introducing quality improvement measures when these are introduced. The effectiveness of these measures must be checked and the ratings reviewed, if necessary. The old ratings are put in brackets - [ ] or < > -. The new and valid ratings do not have any brackets.

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12

Description of Method

The updating of the FMEA has to be guaranteed in documenting the development and production of a product. When updating, especially the latest actions have to be taken into consideration. It is recommended to update the FMEA every six months to every year.

System-FMEA



13

6\VWHP)0($

The system FMEA analyzes the correct functional interrelation of the system components and their connections. The goal is to avoid defects in system selection and layout and field risks. The system requirements are the basis for the analysis. The system development department is responsible for the system FMEA. System-FMEA Quality Assurance No. Component or Process (1)

Page: Department: FMEA-Number: Date:

Product: Number:

Function

Failure modes

Failure effects

C

Failure causes

Failure prevention

Failure detection

(3)

(4)

(5)

(6)

(7)

(8)

(9)

(2)

S

O

D

(10) (11) (12)

RPN

Actions R:/I:

(13)

(14)

 This document is the exclusive property of Robert Bosch GmbH. Without their consent it may not be reproduced or given to third parties.

Fig. 2:

The FMEA-form

Preparations The following documents should be prepared for the first team meeting: (also see chapter 2 - systematic preparations) − system-requirements, e.g. system target specification, machine list and block diagram with detailed functional description. − field failure statistics and failure rates of comparable products − failure lists − prepared structuring and functional analysis Base data The base data are entered in the form (see following table). Field

System FMEA contents

RB-Logo

Notes Additional customer-logo with joint FMEA

FMEA type

System FMEA

Product

The system or sub-system which is analyzed in the FMEA

Article number

The identity number of the analyzed system or the project number (as far as it exists)

Confidence note

if necessary note on how to treat the FMEA

Here, a conficence note can be entered

Page

Page number of the FMEA-forms

Is generated automatically through SW

Department

The department responsible for the realization of the FMEA

FMEA-NR.

Numbering according to BOSCH-standard N12A or N10

Date

Date of the corresponding FMEA-edition

Footnote

Includes copyright and if necessary an explanation to the appreviations used in the FMEA

Tabelle 3:

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Base data

another numbering can be determined Is generated automatically through SW

14

System-FMEA The following description of the system FMEA procedure is oriented on the FMEA-sequence plan (see page 10) and on the FMEA-form.

6WUXFWXULQJ A successful possibility to structure the system FMEA is the component/function-matrix of the system. The SW IQ-FMEA offers more possibilities for system structuring (e.g. system tree, functions- or failure grid.

No. Component or Process (1)

(2)

Column (1)

No.

The numbering of the component is taken, e.g., from the block diagram or the machine list and supplemented through a number for the failure cause, e.g. 010.01 or 01.001. Column (2)

Component or Process

In column 2, the system components, component groups to be analyzed are entered according to block diagram/machine list or component/function-matrix. Software-modules/-functions can also be analyzed.

)XQFWLRQDO$QDO\VLV No. Component or Process

Function

(3)

Column (3)

Function/ Purpose

The system FMEA lists all functions of the system components on the basis of the system requirements in view of operating conditions, starting from a black-box analysis. The scope of the FMEA is determined within a functional analysis. The more exact the description of the functions and characteristics is, the more exact the potential failure types can be derived. The functions should be described with a noun, verb.

System-FMEA

15

Failure analysis

No. Component or Process

Column (4)

Function

Failure modes

Failure effects

C

Failure causes

(4)

(5)

(6)

(7)

Failure mode

In the failure mode column, it is described why a required function or characteristic could not have been fulfilled. The system FMEA analyzes all potential malfunctions and functional deficits that are inferable from the functions of the system components and from their connections. Column (5)

Failure consequence

A failure consequence is a short and precise description of a causal chain from failure mode to effect on the highest system level (e.g. vehicle) or the environment or the customer (external and internal). This description should be done in different steps - direct, next, end. Column (6)

Special characteristics

The special characteristics are identified according to the stipulations of the division (see also chapter special characterlistics, page 11). Column (7)

Failure causes

In this column, those failure causes are to be listed that might lead to the analyzed failure mode (= potential failure causes). The actual cause has to be described in such a way that any necessary measures for improvement can be directly introduced. The system FMEA looks at failures of functional groups or components and their connections; for the design as well as for the field. All operating conditions (lifetime, temperature, time acceleration factors etc.) and operating conditions (e.g. complete load, partial load, ABS breaking, partial breaking,...) have to be analyzed. Failure causes during the system development phase and system testing phase are to be looked for in the selection, co-ordination, design and development.

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16

System-FMEA

5LVNHYDOXDWLRQ For the risk evaluation, the already introduced actions are listed in the columns failure prevention and detection.

No. Component or Process

Column (8)

Function

Failure modes

Failure effects

C

Failure causes

Failure prevention

Failure detection

(8)

(9)

Failure prevention

Failure prevention is a preventive action taken during the system design phase to prevent failure causes to occur or to complicate their occurrence. In a system FMEA (field and interpretation), the introduced actions are to be analyzed that minimize the risk of system interpretation failures, prevent or limit the failure consequences. Column (9)

Failure detection

In a system FMEA , everything from failure detection during system development to systemrelease (design failures) is analyzed and failure detection through the system even in the field (field failure) are analyzed. Actions for failure detection during the design are e.g. the system testings, testings in the vehicle, simulations and endurance testings. Actions for failure detection in the field are e.g. internal diagnosis (together with appropriate substitutional functions), warning lamp/display, symptoms (noises etc.)

No. Component or Process

Function

Failure modes

Failure effects

C

Failure causes

Failure prevention

Failure detection

S

O

D

(10) (11) (12)

Column (10)

RPN

(13)

Relevance of failure consequence (S)

In column 10, the significance of the „end“- or. „distant effect“ of the failure type on the system and/or the customer is evaluated. The evaluation criteria are covered by the VDA-Evaluation tables (see VDA vol. 4.2) or QS 9000 evaluation tables. The product-specific adaptation of the rating charts can be of importance for the individual divisions.

System-FMEA

17

System FMEA: S - Severity of failure consequence

Rating

Extremely serious failure, which affects safety and/or violates legal requirements, without previous warning.

10

Extremely serious failure, which possibly affects safety and/or violates legal requirements with previous warning or leads to “breaking down“.

9

Serious failure, failure of primary functions, e.g. vehicle not in running order.

8

Serious failure, reliability of vehicle very restricted, immediate servicing required.

7

Moderately serious failure, failure of important operational and comfort systems; immediate servicing not required.

6

Moderately serious failure, limited functioning of important operational and comfort systems.

5

Moderately serious failure, little reliability restriction of operational and comfort systems; detectable by any driver

4

The failure is insignificant. The customer is only slightly bothered, and will probably only notice slight interference;can be noticed by the average driver.

3

It is unlikely that the failure could have a noticeable effect on the behavior of the vehicle; only noticeable by experts or experienced drivers.

2

No effect

1

Table 4:

Column (11)

Evaluation criteria for the importance of the failure consequence (B) in system FMEA Occurrence probability (O)

The rating ‘O’ says how probable it is that the failure type occurs at the customer’s/user‘s because of a certain failure cause. Actions which have been introduced to avoid the failure cause are analyzed and are assumed to be efficient. System FMEA O - occurance probability

Possible failure rate*

Very high It is almost certain that the type/cause of failure will occure very often.

1/10

100.000

10

1/20

50.000

9

High The type/cause of failure occurs repeatedly. Problematic, not perfect system.

1/50

20.000

8

1/100

10.000

7

Moderate The type/cause of failure occurs occationally. Advanced system.

1/200

5.000

6

1/1.000

1.000

5

1/2.000

500

4

Low The probability that the type/cause of failure occurs is low. Proven system design.

1/15.000

67

3

1/150.000

6,7

2

Unlikely. The occurence of the type/cause of failure is unlikely.

<1/1.500.000

<0,67

1

Rating points ppm*

*pro LD (LD = product lifetime)

Table 5:

Rating chart for probability of occurrence (O) in system FMEA

The failure rates (e.g. λ - rates, ppm) in the rating chart are based on the number of failures that are expected to occur within the required lifetime of a product. The dependencies of operating time (h), road performance (km), cycle numbers are to be taken into account. Plant, 0-mileage and field experiences are to be considered.

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System-FMEA

Column (12)

Detection probability (D)

In the system FMEA, there are different “D“ ratings for the detection probability of system design and field failures. With design failures, ‘D’ assesses the actions taken for inspection and detection of the system development phase, e.g. simulation, functional testings, vehicle inspection, endurance testing, customer-initial sample testing according to system target specification and test plan. With field failures, ‘D’ assesses the detection measures, displays and symptoms that are perfect for detecting field failures in time, e.g. system-immanent tests (e.g. self-diagnosis), service, diagnosis, driver, warning lamps, changed functions. System FMEA : D – detection probability Evaluation criteria ”design”

Rating

Unlikely It is impossible or unlikely that a type and/or cause of failure is detected through test and analysis measures in the development phase.

10

Very low The probability is very low that the type and/or cause of failure is detected through test and analysis measures in the development phase.

9 8

Low The probability that the type and/or cause of failure is detected through test and analysis measures in the development phase is low.

7 6

Moderate The probability that the type and/or cause of failure is detected through test and analysis measures in the development phase is moderate.

5 4

High The probability that the type and/or cause of failure is detected through test and analysis measures in the development phase is high.

3 2

Very high It is certain that the the type and/or cause of failure is detected through test and analysis measures in the development phase.

1

Evaluation criteria ”field“

Rating

It is impossible or improbable that the failure is detected at all or on time.

10

The failure can be detected through, e.g.: - reading of the fault memory during service work, substitue measures of the system do not exist - changed secondary function or another symptom (e.g. noise, noticeable smell)

9 8 7

Diagnosis and substitute functions of system are active, warning lights at vehivle have to be turned on (e.g. emission)

6

Clearly noticeable impairement of secondary function (e.g. very loud noise) or slowly increasing impairement of function

5

Diagnosis and substitute function of system are active, light does not have to be turn on.

4 3 2

The failure is definitely detected and ist effect is definitely prevented.

1

Table 6:

Rating criteria for probability detection (D) in system FMEA

Column (13) Risk priority number The risk priority number is the product of S, O and D. It is the standard for the ranking of existing risks. RPN = S x O x D

System-FMEA

19

2SWLPL]LQJ The RPN and the individual ratings S, O and D clearly show the system risks. If there is a high RPN or high individual ratings, improvements are required. • If B ≥ 9, actions that reduce the importance of the failure consequence should possibly be taken. Usually, these are system changes. If this is not possible, A has to be reduced to such a degree that only a small and warrantable risk remains. • Other limiting values for S, O, D, and RPZ are set by the team in such a way that the different quality objectives for the product have to be met at the start of production. In some areas, the following is valid: • Dependend on the degree of FMEA specification (system, subsystem, component), the limit for introducing quality improvements should have a RPN between 60 and 300.

No. Component or Process

Function

Failure modes

Failure effects

C

Failure causes

Failure prevention

Failure detection

S

O

D

RPN

Actions R:/I: (14)

Column (14)

Actions R:/I:

After the actions have been written down in the FMEA-form, they have to be completed by the responsible person (R) and the deadline (I). The ratings for the planned improvement are entered in the round brackets (). If there are extreme concept changes, all 5 steps of the system FMEA are retaken for all concerned sections – from system structuring to optimizing. The final assessment is done after the action has been taken and after testing its effectiveness. If a type of failure does not exist any longer because of the proposed action, the assessment numbers S, O, D, PRZ are to be put equal zero. If a failure cause does not exist any longer because of an action, the assessment number for O and RPN are to be put equal to zero. Alternatively, the cancelled failure type/cause can be documented.

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20

Design FMEA



'HVLJQ)0($

The design-FMEA analyzes the design and layout of products/components according to the specification to avoid design errors and process defects influenced by the design. The product/component design department is responsible for the design FMEA. Design-FMEA Quality Assurance No. Component or Process (1)

(2)

Page: Department: FMEA-Number: Date:

Product: Number:

Function

Failure modes

Failure effects

C

Failure causes

Failure prevention

Failure detection

(3)

(4)

(5)

(6)

(7)

(8)

(9)

S

O

D

(10) (11) (12)

RPN

Actions R:/I:

(13)

(14)

 This document is the exclusive property of Robert Bosch GmbH. Without their consent it may not be reproduced or given to third parties.

Fig. 3:

The FMEA-form

Preparations The following documents should be available at the first team meeting (see also chapter 2 systematic preparations): − Target specification − Development drafts − Parts lists − prepared FMEA structure In addition, the following documents are also very helpful: − System FMEA − Functional description − Test sheet, sample − Technical customer documents − Endurance test results − 0-mileage and field failure statistics of comparable products − Failure lists − Uncleared-topics-list − Failure rates of comparable products

Design FMEA

21

Base data The base data are entered in the form (see following table). Field

Design FMEA contents

Notes

RB-Logo FMEA type

Design FMEA

Product

The product analyzed in the FMEA

Article number

The identity number of the analyzed product

Confidence note

if necessary note on how to treat the FMEA

Here, a conficence note can be entered

Page

Page number of the FMEA-forms

Is generated automatically through SW

Department

The department responsible for the realization of the FMEA

FMEA-NR.

Numbering according to BOSCH-standard N12A or N10

Date

Date of the corresponding FMEA-edition

Footnote

Includes copyright and if necessary an explanation to the appreviations used in the FMEA

Table 7:

Another numbering can be determined Is generated automatically through SW

Base dates in design FMEA

The following description of the design FMEA procedure is oriented on the FMEA-sequence plan (see page 10) and on the column structure of the Bosch FMEA form.

6WUXFWXULQJ The structuring of the design FMEA can be derived from the component-function-matrix. No. Component or Process (1)

(2)

Column (1)

No.

The number serves the clear identification of the analyzed failure cause. In the design FMEA, it consists of, e.g., the position numbers of the parts lists and of a serial number for the failure cause. Column (2)

Component or Process

In column 2, the component groups (component parts which are to be analyzed are entered according to parts list.

H14 (43-08/98)

22

Design FMEA

)XQFWLRQDODQDO\VLV No. Component or Process

Function

(3)

Column (3)

Function

The design FMEA lists all important functions and operating conditions of components; on the basis of the component target specification and the design characteristics. The total product life cycle up to the recycling of the product is to be analyzed. The scope of the FMEA is determined within the functional analysis. The more exact the description of the functions and characteristics is, the more exact the potential failure types can be derived. The functions should be described with a noun, verb.

)DLOXUHDQDO\VLV No. Component or Process

Column (4)

Function

Failure modes

Failure effects

C

Failure causes

(4)

(5)

(6)

(7)

Failure mode

In the failure mode column, it is described why a required function or a characteristic could not have been fulfilled. The design FMEA analyzes all potential malfunctions and functional deficits that are inferable from the component functions and which are described as physical expression. The design which meets the requirements of production is also to be analyzed; however, the process FMEA is not anticipated. Column (5)

Failure consequence

A failure consequence is a short and precise description of a causal chain from failure mode to the effect on the highest system level (e.g. vehicle) or the environment or the customer (external and internal). This description should be done in different steps - direct, next, end. The failure consequence can be derived from the system FMEA. Column (6)

Special characteristics

The special characteristics are identified according to the stipulations of the division (see also chapter 2 - special characteristics). Column (7)

Failure causes

In this column, the failure causes are to be listed that might lead to the failure mode under consideration (= potential failure causes). The actual cause has to be described in such a way that any necessary measures for improvement can be directly introduced. The design FMEA looks at failures which result from the design, selection or system as well as production and assembly failures which can be constructively influenced. All operating conditions (lifetime, temperature, time acceleration factors etc.) have to be considered.

Design FMEA

23

5LVNHYDOXDWLRQ For the risk evaluation, the already introduced actions are listed in the columns failure prevention and detection.

No. Component or Process

Column (8)

Function

Failure modes

Failure effects

C

Failure causes

Failure prevention

Failure detection

(8)

(9)

S

O

D

RPN

Failure prevention

Failure prevention is a preventive action taken during the design phase to prevent failure causes to occur or to complicate their occurrence. Preventive actions are derived from theoretical knowledge and practical experience. DoE (Design of Experiments) prevents failures for the designs and processes (robust design/robust process). Column (9)

Failure detection

Defect detection within the design FMEA are inspections and testings in the development and other detection possibilities up to the product release. To keep the testing expense as small as possible, actions which prevent failures have to be taken. Testings have to be done to provide security for the design. Through a specific planning of experiments, the expense for the testings is minimized.

No. Component or Process

Function

Failure modes

Failure effects

C

Failure causes

Failure prevention

Failure detection

S

O

D

(10) (11) (12)

Column (10)

RPN

(13)

Relevance of failure consequence (S)

In column 10, the ‘end’ or ‘distant effect’ of the failure mode on the system and/or the customer are evaluated. The evaluation criteria are covered by the VDA-rating charts or QS 9000 rating charts (see [VDA4/2(96)], [CFG9000(95)]. It is better to make new rating charts for none Kareas.

H14 (43-08/98)

24

Design FMEA

Design FMEA: S - Importance of failure consequence

Rating

Extremely serious failure, which affects safety and/or violates legal requirements, without previous warning.

10

Extremely serious failure, which possibly affects safety and/or violates legal requirements with previous warning or leads to “breaking down“.

9

Serious failure, failure of primary functions, e.g. vehicle not in running order.

8

Serious failure, reliability of vehicle very restricted, immediate servicing required.

7

Moderately serious failure, failure of important operational and comfort systems; immediate servicing not required.

6

Moderately serious failure, limited functioning of important operational and comfort systems.

5

Moderately serious failure, little reliability restriction of operational and comfort systems; detectable by any driver

4

The failure is insignificant. The customer is only slightly bothered, and will probably only notice slight interference;can be noticed by the average driver.

3

It is unlikely that the failure could have a noticeable effect on the behavior of the vehicle; only noticeable by experts or experienced drivers.

2

No effect

1

Table 8: Evaluation criteria for the importance of the failure consequence (S) in design FMEA Column (11)

Occurrence probability (O)

The rating ‘O’ says how probable it is that the failure type occurs at the customers/users – without previous detection - because of a certain failure cause. Actions which have been introduced to avoid the failure cause are analyzed and are assumes to be efficient. The failure rates (e.g. λ - rates, ppm) in the rating chart are based on the number of failures that are expected to occur within the required lifetime of a product. The dependencies of operating time (h), road performance (km), cycle numbers are to be taken into account. Plant, 0-mileage and field experiences are to be considered. Design FMEA O - occurance probability

Possible failure rate*

Very high It is almost certain that the type/cause of failure will occure very often.

1/10

100.000

10

1/20

50.000

9

High The type/cause of failure occurs repeatedly. Problematic, not a perfect design.

1/50

20.000

8

1/100

10.000

7

Moderate The type/cause of failure occurs occationally. Advanced design.

1/200

5.000

6

1/1.000

1.000

5

1/2.000

500

4

Low The probability that the type/cause of failure occurs is low. Proven design.

1/15.000

67

3

1/150.000

6,7

2

Unlikely. The occurence of the type/cause of failure is unlikely.

<1/1.500.000

<0,67

1

Rating points ppm*

*pro LD (LD = product lifetime)

Table 9: Rating chart for probability of occurrence (O) in design FMEA

Design FMEA

Column (12)

25

Detection probability (D)

In the design FMEA, ‘E’ assesses the test and detection measurements of the development phase, e.g. functional testings, endurance testings, vehicle testings, customer-initial sample testings according to target specification and test plan. Actions within the design FMEA that make the detection of the failures possible only after the product release should be rated with E=9 or 10. Design FMEA: D – detection probability Evaluation criteria ”design”

Rating

Unlikely It is impossible or unlikely that a type and/or cause of failure is detected through test and analysis measures in the development phase.

10

Very low The probability is very low that the type and/or cause of failure is detected through test and analysis measures in the development phase.

9 8

Low The probability that the type and/or cause of failure is detected through test and analysis measures in the development phase is low.

7 6

Moderate The probability that the type and/or cause of failure is detected through test and analysis measures in the development phase is moderate.

5 4

High The probability that the type and/or cause of failure is detected through test and analysis measures in the development phase is high.

3 2

Very high It is certain that the the type and/or cause of failure is detected through test and analysis measures in the development phase.

1

Table 10: Column (13)

Rating criteria for probability detection (D) in design FMEA Risk priority number

The risk priority number is the product of S, O and D. This number shows the risk connected to the failure cause and allows a rating of the failure causes.

2SWLPL]LQJ The RPN and the individual ratings S, O, and D clearly show the system risks. If there is a high RPN or high individual ratings, improvements are required. • If S ≥ 9, actions that reduce the meaning of the failure consequence should possibly be taken. Usually, these are system changes. If this is not possible, O has to be reduced to such a degree that only a small and warrantable risk remains. • For high O-ratings, actions have to be taken that guarantee the set quality objective for the product at the beginning of the production. That means that normally O=2 to 3 should be reached. If there is safety relevance, the objective should be O=1. To make sure that the quality objectives will be met, action for detection have to be taken. In some areas, the following is valid: • If RPN exceeds a limit which is to be set (e.g. 125), actions for quality improvement have to be taken. • If RPN are close to the set limit (e.g. between 50 and 125) actions for continuos improvement have to be taken to reach the quality objective at the production-start.

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26

Design FMEA

No. Component or Process

Function

Failure modes

Failure effects

C

Failure causes

Failure prevention

Failure detection

S

O

D

RPN

Actions R:/I: (14)

Column (14)

Actions R:/I:

After the actions have been written down in the FMEA-form, they have to be completed by the responsible person (R) and the deadline (I). The ratings for the planned improvement are entered in the round brackets (). If there are extreme concept changes, all steps of the FMEA are retaken for all concerned sections – from system structuring to optimizing. The final assessment is done after the action has been taken and after testing its effectiveness. If a type of failure does not exist any longer because of the proposed action, the assessment numbers S, O, D, PRZ are to be put equal zero. If a failure cause does not exist any longer because of an action, the assessment number for O and RPN are to be put equal to zero. Alternatively, the cancelled failure type/cause can be documented. If an action is taken (e.g. change of the design draft or change of the production procedure), it has to be examined which new risks arise. If actions are found which lead to the canceling of a failure type/cause, the new actual state is to be analyzed. The old and new actual state have to be weight up.

Process FMEA



27

3URFHVV)0($

Definition: The process FMEA analyzes process planning and performance for products/components according to the drawing specifications to avoid planning errors and manufacturing defects. System-FMEA Quality Assurance No. Component or Process (1)

(2)

Page: Department: FMEA-Number: Date:

Product: Number:

Function

Failure modes

Failure effects

C

Failure causes

Failure prevention

Failure detection

(3)

(4)

(5)

(6)

(7)

(8)

(9)

S

O

D

(10) (11) (12)

RPN

Actions R:/I:

(13)

(14)

 This document is the exclusive property of Robert Bosch GmbH. Without their consent it may not be reproduced or given to third parties..

Fig. 4:

The FMEA-form

Preparation The following documents should be available at the first team meeting (see also chapter 2 – Systematic preparations, Page 10): − Design FMEA − Parts lists − Production sequence plans − Production drafts − Functional description − Sample − Technical customer documents − 0-mileage and field failure statistics of comparable products − Failure lists − Failure rates of comparable products − Machine and process capability data − prepared FMEA structure

H14 (43-08/98)

28

Process FMEA

Base data The base data are entered in the form (see following table). Field

Process FMEA contents

RB-Logo

Notes Additional customer-logo with joint FMEA

FMEA type

Process FMEA

Product

The product under consideration in the FMEA

Article number

The identity number of the product under consideration

Confidence note

if necessary note on how to treat the FMEA

Here, a conficence note can be entered

Page

Page number of the FMEA-forms

Is generated automatically through SW

Department

The department responsible for the realization of the FMEA

FMEA-NR.

Numbering according to BOSCH-standard N12A or N10

Date

Date of the corresponding FMEA-edition

Footnote

Includes copyright and if necessary an explanation to the appreviations used in the FMEA

Table 11:

Another numbering can be determined Is generated automatically through SW

Base dates in process FMEA

The following description of the design FMEA procedure is oriented on the FMEA-sequence plan (see page 10) and on the column structure of the Bosch FMEA form.

6WUXFWXULQJ The structuring of the process FMEA results from the process sequence plan or the product quality assurance plan (PQP).

No. Component or Process (1)

(2)

Column (1)

No.

The number serves the clear identification of the failure cause and the assignment of the individual process in the FMEA to the product quality assurance plan (PQP). In the process FMEA, the first part of the number is the operation number of the sequence plan and the second part is, e.g. a serial number for the failure cause. Column (2)

Component/Process

In column 2, the working operations/steps which have to be analyzed are entered in the working plan.

Process FMEA

29

)XQFWLRQDODQDO\VLV No. Component or Process

Function

(3)

Column (3)

Function

The process FMEA lists all important process functions (working plan) and parts characteristics (drawing). The size of the FMEA is determined within the functional analysis. The more detailed the description of the functions and characteristics is, the more accurate the potential failure types can be derived. The functions should be described with substantive, verb and the criteria for compliance (target values, tolerances, ...).

)DLOXUHDQDO\VLV No. Component or Process

Column (4)

Function

Failure modes

Failure effects

C

Failure causes

(4)

(5)

(6)

(7)

Failure mode

The process FMEA analyzes all potential process failures that can be deducted from the required process functions and parts characteristics and that can be described as deviation. Column (5)

Failure consequence

A failure consequence is a short and precise description of a causal chain from failure mode to effect on the highest system level (e.g. vehicle) or the environment or the customer (external and internal). This description should be done in different steps - direct, next, end. It can be deducted from the design or system FMEA . Column (6)

Special characteristics

The special characteristics are identified according to the stipulations of the division (see also chapter 2.5). Column (7)

Failure causes

In this column, the failure causes are to be listed that might lead to the analyzed failure mode (= potential failure causes). The actual cause has to be described in such a way that any necessary measures for improvement can be directly introduced. Basically, all process-oriented failure causes are to be listed here. The term process includes all process sections, from supplying the material to transport, the actual production, cleaning, assembly, packaging, storing to the delivery to the customer. The commitment of the product to a certain design should no longer be questioned.

H14 (43-08/98)

30

Process FMEA

5LVNDVVHVVPHQW For the risk evaluation, the already introduced actions are listed in the columns failure prevention and detection. It is important to note that double-evaluations should be avoided. Double evaluations exist when the efficiency of a preventive or detective action are presupposed in an evaluation at some other place. Examples for a non-permissible argumentation: a) „The detection is very good, i.e. D=1, the failure does not reach the customer, he/she does not notice the failure; therefore S=1“, b) „The detection is very good, i.e. D1, therefore the occurrence probability is O=1.“ No. Component or Process

Column (8)

Function

Failure modes

Failure effects

C

Failure causes

Failure prevention

Failure detection

(8)

(9)

Failure prevention

Failure prevention is a preventive action taken during production preparations to prevent failure causes to occur or to complicate their occurrence. SPC is an action within the process FMEA to prevent failures (process capability) DoE (Design of Experiments) prevents failures of design and processes (robust design/robust process). Column (9)

Failure detection

Actions which lead to the detection of failures make an early detection of the failure in the process possible and prevent products with failures to get to the customer. Processes in control prevent failures and are thus preferred to inspections. Only established or obligatory testings and detections within the process (e.g. next working operation not possible) should be taken into consideration. In the process FMEA, it is distinguished between random and systematic failures. The SPCsampling inspection is a detective action for systematic but not for random failures (sampling inspection). Random failures can be detected with a 100% inspection; or if a working operation at some later time can not be realized (e.g. .....)

Process FMEA

No. Component or Process

Function

31

Failure modes

Failure effects

C

Failure causes

Failure prevention

Failure detection

S

O

D

(10) (11) (12)

Column (10)

RPN

(13)

Relevance of failure consequence (S)

In column 10, the ‘end’ or ‘distant effect’ of the failure mode on the system and/or the customer are evaluated. The evaluation criteria are covered by the VDA-rating charts or QS 9000 rating charts (see [VDA4/2(96)],[CFG9000(95)]). It is better to make new rating charts for none Kareas. Process FMEA: S - Importance of failure consequence

Rating

Extremely serious failure, which affects safety and/or violates legal requirements, without previous warning.

10

Extremely serious failure, which possibly affects safety and/or violates legal requirements with previous warning or leads to “breaking down“.

9

Serious failure, failure of primary functions, e.g. vehicle not in running order.

8

Serious failure, reliability of vehicle very restricted, immediate servicing required.

7

Moderately serious failure, failure of important operational and comfort systems; immediate servicing not required.

6

Moderately serious failure, limited functioning of important operational and comfort systems.

5

Moderately serious failure, little reliability restriction of operational and comfort systems; detectable by any driver

4

The failure is insignificant. The customer is only slightly bothered, and will probably only notice slight interference;can be noticed by the average driver.

3

It is unlikely that the failure could have a noticeable effect on the behavior of the vehicle; only noticeable by experts or experienced drivers.

2

No effect

1

Table 12:Evaluation criteria for the importance of the failure consequence (S) in process FMEA Column (11)

Occurrence probability (O)

The rating ‘O’ reflects the probability with which the failure type occurs as a consequence of a certain failure cause - without previous detection. Actions which have been introduced to avoid the failure cause are analyzed and are assumed to be efficient.

H14 (43-08/98)

32

Process FMEA

Process FMEA O - occurance probability

Possible failure rate*

Very high It is almost certain that the type/cause of failure will occure very often.

1/10

100.000

-*

10

1/20

50.000

-*

9

1/50

20.000

-*

8

1/100

10.000

-*

7

1/200

5.000

0,94

6

1/1000

1.000

1,10

5

1/2000

500

1,17

4

1/15000

67

1,33

3

6,7

1,50

2

< 0,67

> 1,67

1

High The type/cause of failure occurs repeatedly. Problematic, not a perfect design.

Moderate The type/cause of failure occurs occationally. Advanced design.

Low The probability that the type/cause of failure occurs is low. Proven design.

1/150.000 Unlikely. The occurence of the type/cause of failure is unlikely.

< 1/1500000

Cpk ppm*

Rating points

*data not sensible

Table 13:

Rating chart for probability of occurrence (O) in process FMEA

The failure rates (e.g. λ - rates, ppm) in the rating chart are based on the number of failures that are expected to occur within the required lifetime of a product. The dependencies of operating time (h), road performance (km), cycle numbers are to be taken into account. Plant, 0-mileage and field experiences are to be considered. Column (12)

Detection probability (D)

In the process FMEA, ‘D’ assesses the test and detection measurements of the production and assembly. The rating is oriented on verbal criteria or on the portion of non-detected parts in relation to the portion of nonconforming items in the lot. Actions within the process FMEA that make the detection of the failures possible only after the product release should be rated with D=10. Process FMEA: E – detection probability

Certainty of the testing processes

Rating 10

Unlikely The failure is not detected or cannot be detected. Very low The probability that the failure is detected is very low.

90%

9

Low The probability of detecting the failure is low.

98%

8 7

Moderate The probability of detecting the failure is moderate..

99,70%

6 5 4

High The probability of detecting the failure is high.

99,90%

3 2

Very high The probability of detecting the failure is certain.

99,99%

1

Table 14:

Rating criteria for probability detection (D) in process FMEA

Process FMEA

Column (13)

33

Risk priority number

The risk priority number is the product of S, O and D. This number shows the risk connected to the failure cause and allows a rating of the failure causes.

2SWLPL]LQJ The RPN and the individual evaluations B, A and E show the risks. If there are high RPN or high individual ratings, improvement measures are necessary. • The objective for safety relevance is O = 1. If this is not possible, you have to make sure with suitable detection measurements that no nonconforming products get to the customer. • If there is a high probability of failures to occur, actions have to be taken which ensure the reaching of the quality objective. In general, this means that processes in control coincide with Cpk > 1,33 - 1,67 or A = 1 or 2. In some areas, the following is valid: • If RPZ exceed a limit which is to be set (e.g. 125), actions for quality improvement have to be taken. • If RPZ are close to the set limit (e.g. between 50 and 125) actions for continuos improvement have to be taken to reach the quality objective at the production-start.

No. Component or Process

Function

Failure modes

Failure effects

C

Failure causes

Failure prevention

Failure detection

S

O

D

RPN

Actions R:/I: (14)

Column (14)

Actions R:/I:

After the actions have been written down in the FMEA-form, they have to be completed by the responsible person (R) and the deadline (I). The ratings for the planned improvement are entered in the round brackets (). If there are extreme concept changes, all steps of the FMEA are retaken for all concerned sections – from system structuring to optimizing. The final assessment is done after the action has been taken and after the testing of its effectiveness. If a type of failure does not exist any longer because of the proposed action, the assessment numbers S, O, D, RPN are to be put equal zero. If a failure cause does not exist any longer because of an action, the assessment number for O and RPN are to be put equal to zero. Alternatively, the cancelled failure type/cause can be documented.

H14 (43-08/98)

34

Cooperation with customer

6

Cooperation with customers

Customer contacts for FMEA are regulated by the K/VKK directive ‘Submittal of FMEA’s to customers’, dated 1/26/1995. Cooperation with customers takes place when the customer whishes so on sight or after the FMEA is handed over or after a cooperaqtive preparation of a system or interface FMEA.

FMEA presentation for customers The FMEA presentation is usually performed and organized by the sales department together with other responsible departments. On the first presentation of a FMEA, the RB-FMEA-method and the used rating charts should be explained. The FMEA with regard to its contents should be presented by an employee of the responsible department. System and design FMEA are usually done by the development department, process FMEA by the plant. The FMEA resume (enclosure...) can be handed over to the customer, if requested. Details should be regulated specific to the division.

System or interface FMEA in cooperation with the customer A system or interface FMEA in cooperation with the customer investigates the functionally correct interaction of the input and output functions on the interface between RB and customer components of a system. This can be software or hardware components. This can be conducted by FMEA moderators of RB or by the customer. The FMEA in cooperation with the customer should be well prepared and structured by RB. First, rating charts have to be determined which are accepted by both parties. Working on a system or interface FMEA in cooperation with the customer has to be approved of by the responsible division.

Cooperation with supplier



&RRSHUDWLRQZLWKVXSSOLHUV

Basis for the cooperation with the supplier is the guideline for suppliers. To guarantee the quality of fabricating parts, Bosch demands of its suppliers, among others, that they make a and present FMEA (supplier FMEA). Procedure with (sub-) system or design FMEA After the draft has been made by the supplier, the Bosch development department wants to inspect the (sub-)system of design FMEA through RN-MA (development and purchase department) and wants to discuss the draft with the supplier. Process FMEA procedure After the production process has been planned by the supplier, the Bosch purchase department wants to inspect the process FMEA through RB-MA (production, quality assurance, purchase department) and wants to discuss the production process with the supplier. Representation of a FMEA-request − Product, component, drafts and article numbers − RB-specification, target specification or lists of functionally important measures and characteristics. − Notes on the significance of failure consequences and their rating, specific to the application of products. − Date of FMEA and discussion − Form for FMEA-summary Criteria for FMEA discussion at supplier • Submittal of FMEA-summary • The FMEA of the supplier is comparable to the RB-FMEA-methodics • Assessment of the significance (S), occurrence probability (O) and detection probability (D) • Introduction of actions with responsible persons and deadline • Scope of FMEA

H14 (43-08/98)

35

36

Further FMEA-applications



)XUWKHU)0($DSSOLFDWLRQV

,QWHUIDFH)0($ The interfaces between different systems, subsystems or components are analyzed in this type of FMEA. The interface FMEA can be part of a system or design FMEA and is methodically a system or design FMEA. It is done if required. The system development or product/component development department is responsible for the internal interface FMEA. Initiation and preparation of the external (with customer) interface FMEA by the RB system development or product/component department is preferred. The FMEA is done by RB in cooperation with the customer.

/RJLVWLFV)0($ The methodology of the logistics FMEA is comparable to that of the process FMEA. The logistics FMEA analyzes the logistical flow of products from receiving at Bosch until delivery to the customer. Logistics errors comprise a large portion of the customer complaints statistics. It is advisable to analyze and evaluate these customer complaints with logistics FMEA. Logistics procedure of a product • from packing at the end of the production line (usually end of process FMEA of the assembly) to the delivery to the customer • from delivery of parts or materials to the receiving goods department at Bosch to the delivery to the production line. For the evaluation and assessment of the significance, the occurrence probability and the detection probability, the rating charts of a process FMEA are used for the logistics FMEA as well. For the evaluation of the significance, the occurrence probability and the detection probability, the rating charts of the process FMEA are used.

FMEA for software

)0($IRUVRIWZDUH Basic is the functional approach of the system FMEA . Analyzed can be, e.g.: • the functional requirements and effects of their non-fulfillment • Failures on interfaces • Failures of individual software parts The following premises are valid for the use of FMEA for software − For reasons of efficiency, this method is only used in the early development phases before coding − Documents are required that are described on an abstract level (e.g. HW and SW block diagram or SW architecture model). − Failures which occur during coding are not individually analyzed. − Procedure and form are adopted without a change − In some cases, the rating charts have to be adapted. With a FMEA for software, a risk evaluation concerning quality characteristics reliability and safety is made. This method can be used in various software improvement/refinement levels. So, in a top-down procedure, results of a higher level of the FMEA can be used again for the level which is momentarily analyzed. Software can also be seen as part of the system of a system FMEA

)0($IRUFRQWUROXQLWV System FMEA Within the system FMEA of the whole system, the control units are regarded as black box. In some cases, the main actions or in the system FMEA for electronic the component-level are inspected. Function, redundancies and their functional failures and effects on the whole system are analyzed. In case of analyzing SW-functions, their intersections to the outside are analyzed. For a detailed analysis, other test techniques have proved to be good in the software development, e.g. reviews. Apart from the system FMEA there are also failure simulations. Design FMEA – mechanic proportion The procedure of the mechanic proportion corresponds to the known design FMEA. Design FMEA – electronic proportion If the design of the electronic proportion is analyzed with FMEA, it has been succesful to build the wiring plan corresponding to the functional groups and to treat the functional groups like components. In the electronic development, procedures like design-rules, tolerance analyses, checklists and design-reviews have been also succesful.

H14 (43-08/98)

37

38

Selection / prioritizing for FMEA



6HOHFWLRQ3ULRULWL]LQJIRU)0($

To reach a possibly high effectiveness, i.e. to recognize and prevent failure possibilities as far as possible, a high level of specification is necessary for the functional analysis/system structuring. To keep up effectiveness and efficiency during implementation, the use of selection and tightening approaches is useful.

6HOHFWLRQDFFRUGLQJWRDSSOLFDWLRQFULWHULD A possibility for prioritizing /selection are application criteria. The more criteria listed above apply to a component/process, the more important is a FMEA: • Customer requirements (FMEA) • Potential risk • Changed conditions for product usage • High depreciation in value when failure occurs • Basic new development of a product • Essential change • Parts important for functioning • Change of parts with correlation • Use of new materials, procedures • Recycling of problematic parts • Critical objective • Production transfer (new production line)

6HOHFWLRQZLWK4)' Quality Function Deployment (QFD) is a method for quality planning and communication. Above everything else, it serves a better and consistent planning of the individual quality characteristics, from customer and development to production. If a QFD is done for a product, it can be used for selection. Important and difficult characteristics should have priority.

)XUWKHUSRVVLELOLWLHVIRUVHOHFWLRQ Critical paths for critical failures of a system, component or process result from a system, functional and failure analysis according to the top-down principle (functional and fault tree analysis). The critical failures which are part of subsystems, components, characteristics or subprocesses should have priority.

Relation to other methods

 5HODWLRQWRRWKHUPHWKRGV )0($DQG4XDOLW\)XQFWLRQ'HSOR\PHQW4)' Chronologically, the QFD method (Quality Function Deployment) comes before the application of a FMEA. QFD aims at converting customer demands on a product into technical characteristics necessary for development and production. Core of QFD is the ‘House of Quality’. In this document, the customer requirements are put opposite to the technical characteristics. And opposing requirements on the product are listed (e.g. small case seize, loss of power). Also possible in the House of Quality is the comparison to products of competitors. The level of meeting the individual characteristics results in a product profile. QFD should be used in the market analysis phases and conceptional phases. Apart from the development and sales departments, the product planning and marketing department should also be involved when applying this method. QFD can lead to aspects important for following FMEA projects.

)0($DQGYDOXHDQDO\VLV The time of applying the value analysis (value engineering) mainly corresponds with the time of starting the FMEA: from finishing the concept to the production-start. Both methods are based on a systematic functional analysis but differ in their goals: − FMEA failure prevention − Value analysis minimizing costs However, minimizing costs should not have a negative impact on quality. The actions of a FMEA to prevent failures have an influence on the costs but do not always reduce costs. Preventing potential failures often includes investments in advance. To prevent unnecessary work, the use of both methods has to be coordinated.

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Relation to other mathods

)0($DQG7HDP2ULHQWHG3UREOHP6ROYLQJ7236 Whereas the FMEA methodically ‘looks into the future’ and analyzes the occurrence of potential failures, the TOPS method (Team Oriented Problem Solving) analyzes real problems whose cause is unknown. For such an analysis, it is necessary to ‘look back into the past’ to find out the reasons for the problems. TOPS is based on a problem analysis just like Kepner-Tregoe. It was further developed in the automobile industry (compare Ford “8D“=eight disciplines). With the systematic procedure of TOPS, the problem is described, potential causes are found out, the actual cause is identified and certain actions are taken. FMEA and TOPS complement one another: − To find out the reasons for a problem, a finished FMEA can be of help. − The basis for creating a new FMEA are the findings of problems with similar products.

)0($DQGUHYLHZSURFHGXUHV Review procedures are mainly used for software development, but they can also be used in other areas (e.g. layout – review ). Just like a FMEA, reviews are done according to a fixed order of sequence. Other than that, FMEA and review have the following in common: • Main objective is the early failure detection and thus the prevention of failures in the course of the system development. • Interdisciplinary team work with moderator • The result of the working group is dependent on the competence (system knowledge and experience) and creativity of the team members. The following are the differences of review procedures and FMEA: • Time Reviews can already take place during concept finding/selection. The making of a FMEA makes sense if a system concept is at hand. • Analyzed characteristics With a review, different quality characteristics like, e.g. usability or completeness (of demands) are tested, dependent on the selected technique. • Sequence Different review procedures are used dependent on the test object, the objective and the planned test expense. The FMEA is done according to a defined sequential plan of events whose main elements are risk analysis and risk evaluation.

Computer assistance

 &RPSXWHUDVVLVWDQFH ,4)0($ IQ FMEA has been on the market since 1992 and is being continually developed further in cooperation with users. The five FMEA steps are supported by IQ FMEA through several editors who visualize the data and guarantee an optimal access. IQ FMEA supports the Bosch form, and also the forms according to VDA and QS-9000. It is possible to switch between the different forms. Databases can be installed and administered in several languages. The language of the program interface can be dynamically switched; at the moment, German, English, French and Spanish. IQ-FMEA can export complete databases as SGML, forms can be stored in HTML-format. Other export possibilities are (RTF, CSV, TXT, WMF, MPX). • Prerequisites: − Sibylle for Windows requires an IBM-compatible PC (Processor 486 or higher). − Hard-Disk with 10 MB space − VGA (800 x 600 or more) − 12 MB memory for Win 3.x, 16 MB for Win 95, 24 MB for Win NT − MS-DOS Version 5.0 or higher (only for Win 3.x) − MS-Windows 3.1 or MS-Windows for Workgroups or Win 95 or NT IQ-FMEA is available via the Intranet (at ZQF). Via the exchange-distribution list “IQ-FMEA User“, information on IQ-FMEA are distributed. The news-group bosch.fmea.iqfmea is available for exchanging information. The seminar TQ012 offers information on the making of a FMEA with IQ-FMEA.

6LE\OOHIRUZLQGRZV Sibylle for Windows is a program to prepare RB-standard documents for FMEA. The RB-self-development can be received from your contact person or from the FTP-server in Frankfurt. Sibylle is a transitional solution until IQ-FMEA is introduced and it substitutes the MS-DOS variant of the program. • Prerequisites: − Sibylle for Windows requires an IBM-compatible PC (Processor 486 or higher, at least 4 MB memory). To print the FMEA, a postscript printer is recommended, other printers are also possible. − For a graphical operating system, Microsoft Windows is required, at least Version 3.1. The typeface Courier New has to be installed as True Type Face (TTF). • Compatibility: − Sybille for Windows has command of the storage format of the MS-DOS variant. So, FMEA between both programs can be exchanged.

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Bibliography

 %LEOLRJUDSK\ References: [CFG9000 (95)]

Chrysler, Ford, General Motors (QS9000): Potential Failure Mode and Effects Analysis (FMEA). 2. Auflage 1995, Carwin Continuous Ltd.

[K/VKK (95)]

RB: K/VKK-Vertriebshinweis - FMEA-Übergabe an Kunden. Stand: 26.1.1995.

[QFDa]

RB: QFD - Quality Function Deployment - Mit besseren Produkten schneller am Markt. (RB interne Unterlage - kann bei ZQF angefordert werden).

[SWFMEA (96)] RB: Leitfaden für die Durchführung von FMEA für Software. Ausgabe 1.2 (15.2.1996) (RB interne Unterlage - kann bei ZQF angefordert werden). [TOPS (89)]

RB: T.O.P.S. / 8 D - Leitfaden zur Problemlösung in der Projektgruppe. Ausgabe 8903/E5 (RB interne Unterlage - kann bei ZQF angefordert werden)

[VDA4/2 (96)]

VDA: Sicherung der Qualität vor Serieneinsatz - Band IV/2 - SystemFMEA. 1. Auflage 1996, VDA.

Intranet: [WWWzqf]

ZQF: Web-Seite der Zentralabteilung Qualitätssicherung (ZQ) Zentralstelle Qualitätsförderung (ZQF) - Methoden der Qualitätstechnik FMEA - Software für FMEA (Einstieg: http://www.intranet.bosch.de/zq/zqf/index.htm).

Other literature: [Mas (88)]

Masing (Hrsg.), Handbuch der Qualitätssicherung, 2. Auflage, München 1988

[MIL1629A (84)] Military Standard: MIL 1629A - Procedures for Performing a Failure Mode, Effects and Critically Analysis. Notice 2, November 1984. [IEC812 (85)]

IEC: Publication 812 - Analysis techniques for system reliability Procedures for failure mode and effects analysis (FMEA). CEI 1985.

[BS5760 (91)]

BSI: BS5760 - Reliability of systems, equipment and components - Part 5 Guide to failure modes, effects and criticality analysis (FMEA and FMECA). Britisch Standard, 1991.

[DIN25448 (90)] DIN 25448 - Ausfalleffektanalyse (Fehler-Möglichkeits- und -EinflußAnalyse). Mai 1990, DIN. [DIN25424/1 (81)]DIN 25424 Teil 1 - Fehlerbaumanalyse - Methode und Bildzeichen. September 1981, DIN. [DIN25424/2 (81)]DIN 25424 Teil 2 - Fehlerbaumanalyse - Handrechenverfahren zur Auswertung eines Fehlerbaums. April 19990, DIN. [DIN25419 (85)] DIN 25419 - Ereignisablaufanalyse - Verfahren, graphische Symbole und Auswertung. November 1985, DIN. [QFDb]

RB: QFD - Quality Function Deployment - Mit besseren Produkten schneller am Markt - Information für Fach- und Führungskräfte. (RB interne Unterlage - kann bei ZQF angefordert werden).

Appendix

 $SSHQGL[ $SSHQGL[)RUPV - Cover sheet - Form English

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Appendix

Appendix

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Appendix

$SSHQGL[6KRUWGHVFULSWLRQ What does FMEA stand for? ‘FMEA’ is short for ‘Failure Mode and Effects Analysis’. What are the objectives of FMEA? FMEA is a method to qualitatively assess the failure of individual components in systems, products or processes. Objective of the FMEA is a systematic safety and reliability analysis. Before the FMEA was introduced, it was only experiences of the past which were used when a new product was developed, i.e. failures which had occurred during or after the production were considered. The FMEA aims at the detection of potential failures before the productionstart, i.e. during planning, development and design. Potential failures are prevented by an early detection of weak points and the introduction of appropriate actions. Thus, the safety and reliability of the products is improved. When is the FMEA used? The FMEA is used for • New developments • Changes on the product or procedure • Products with requirements concerning the safety technique • New usage conditions for existing products • Processes and services Characteristics of the FMEA The following characteristics are typical for the FMEA method: • systematic procedure with working plan and form • functional oriented approach • interdisciplinary work group – team work leads to creativity • preventive usage The three FMEA types Depending on the task or the unit, it is distinguished between system, process and design FMEA. The system FMEA analyzes the correct functional interrelation of the system components and their connections. The goal is to avoid defects in system selection and layout and field risks. The system requirements are the basis for the analysis. The system development department is responsible for the system FMEA. Note: The system FMEA can also be used in software development. The design FMEA analyzes the design and layout of products/components according to the specification to avoid design failures and process failures influenced by the design. The process FMEA analyzes the process planning and performance for products/components according to the drawing specifications to avoid planning errors and manufacturing defects. Note: General processes like, e.g. services can also be analyzed with a process FMEA

Appendix

What is done in the FMEA? The individual steps in the FMEA are described in the FMEA-sequence plan (here shown as excerpt): 0. Preparation and Planning • determine problem, problem definition and objective • team, sequential planning of action • materials for team • functional description 1. System structuring • numbering • component or working operations 2. Functional analysis • functions/characteristics 3. Failure analysis • potential types of failures • failure effects and failure causes 4. Risk assessment • failure prevention and failure detection • significance of failure effect (S) • occurance probability (O) • detection probability (D) • risk priority number RPN = S x O x D 5. Optimizing / Quality improvement • chose priority order of risks (analyze S, O, D and RPN) • determination of actions for improvement with R: and I: • introduction of actions for improvement • assess improvements (O,D)

When finishing a FMEA, it is important to give the members a feedback, to distribute the documentation and, if necessary, to present the findings. For current products, actualizing the FMEA on a regular basis is important. Expense and prerequisites of a FMEA A FMEA only fulfils its purpose if the requirements for completeness and correctness are generally met. The correctness of the analysis is, e.g. guaranteed by a systematic procedure, clear evaluation criteria, critical assessments (worst case) and an extensive exchange of information within the work team. The completeness is reached by the analysis of all components or processes in order to recognize all possible failure modes. To shorten the FMEA, individual components can be left out if they are uncritical despite worst-case inspection. A frequent argument against a FMEA is its expense. Whereas the expense can be easily determined ‘if the books are well kept’, the savings cannot be exactly represented because failures which were not made and prevented changes can hardly be calculated. The advantages of the FMEA, e.g. • Prevention of failures in design and development • Reduction of costs for later product changes • systematic recording of expert knowledge to prevent repeated failures shows that the prevention of failures at the beginning of the life of a product can prevent higher costs at a later point in time.

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Appendix

$SSHQGL[4XHVWLRQVRQWKHFROXPQVRIWKHIRUP ... -FMEA Quality Assurance No. Component or Process (1)

Page: Department: FMEA-Number: Date:

Product: Number:

Function

Failure modes

Failure effects

C

Failure causes

Failure prevention

Failure detection

(3)

(4)

(5)

(6)

(7)

(8)

(9)

(2)

S

O

D

(10) (11) (12)

RPN

Actions R:/I:

(13)

(14)

 This document is the exclusive property of Robert Bosch GmbH. Without their consent it may not be reproduced or given to third parties.

Fig 4:

The FMEA-form

Structuring (2)

Which components/processes are to be analyzed?

Functional analysis (3)

Which functions have to be fulfilled?

Failure analysis (4)

How could the function be negatively affected?

(5)

Which are the consequences of the failure mode?

(7)

Which failure causes are possible?

Risk assessment (8a)

Which actions are introduced to reduce consequences? (BM)

(10)

How important is the consequence?

(8b)

Which actions are introduced to prevent failures? (VM)

(11)

How probable is the occurrence of the failure?

(9)

Which actions to detect failures are taken?

(12)

How probable is the detection of the failure?

(13)

RPN = S x O x D (RPN)

Optimizing (10 to 13)

Where a high risks? (via S, O, D, RPN)

(14)

Which actions are taken to reduce the risk?

(14)

Who is responsible?

(14)

Which deadline is planned?

Appendix

49

,QGH[ 8D 40 Analyses 6 Base data 21, 28 Design FMEA 7, 8, 20, 21, 22, 23, 24, 25, 27, 28, 34, 35, 36, 37, 46

Relevance of failure consequence 16, 17, 23, 24, 31 Review 40 Risk evaluation 16, 23, 30, 40 Risk evalution 47

Detection probability 18, 36, 47

RPN 10, 18, 19, 23, 25, 26, 31, 33, 47, 49

DoE 23

Selection 38

Failure analysis 29, 47

Sequence plan 10, 14, 21, 28

FMEA

Sibylle 41

Chronological integration of the FMEA 8 Functional analysis 47 Interface FMEA 34, 36 IQ-FMEA 14, 41 Kepner-Tregoe 40

Significance of failure consequence 47 Software FMEA for software 37 Special characteristics 11, 15, 22, 29 Structuring 14, 21, 26, 28, 33, 34

Logistics-FMEA 36

System FMEA 7, 8, 13, 14, 15, 16, 18, 19, 20, 29, 37

Preparation 10, 20, 27, 34, 36, 47

Team work 9, 11, 46

Prioritizing 38

TOPS 40

Process FMEA 7, 8, 11, 22, 27, 28, 29, 30, 31, 32, 34, 35, 36, 46

Updating 11

QFD 38, 39, 42 Rating charts 36

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Value analysis 39

Robert Bosch GmbH C/QMM Postfach 30 02 20 D-70442 Stuttgart Germany Phone +49 711 811-4 47 88 Fax +49 711 811-2 31 26 www.bosch.com