FMEA for Manufacturing and Assembly Process

7/22/2019 FMEA for Manufacturing and Assembly Process

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International Conference on Technology and Business Management March 26-28. 2012

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FMEA for Manufacturing and Assembly Process

A. A. Nannikar

D. N. Raut

R. M. Chanmanwar

S. B. Kamble

[email protected], Mumbai

D. B. [email protected]

Siemens Ltd., Mumbai

1. IntroductionFMEA is a systematic method of identifying and preventing system, product and process problems before they

occur. It is focused on preventing problems, enhancing safety, and increasing customer satisfaction. Ideally,FMEAs are conducted in the product design or process development stages, although conducting an FMEA on

existing products or processes may also yield benefits.FMEA is a tool that allows us to:

Prevent System, Product and Process problems before they occur. Reduce costs by identifying system, product and process improvements early in the development cycle. Create more robust processes. Prioritize actions that decrease risk of failure. Evaluate the system, design, and processes from a new vantage point.

FMEA is

Description

A procedure that examines each item in a system, considers how that item can fail and then determines how that

failure will affect (or cascade through) the system.

Acronyms

FMEA: Failure Modes and Effects Analysis FMECA: Failure Modes and Effects and Criticality Analysis

2. Review of LiteratureFailure Mode and Effects Analysis (FMEA) for ensuring that reliability is designed into typical semiconductor

manufacturing equipment (Mario Villacourt 1992). The FMEA is taken during the design phase of the

equipment life cycle to ensure that reliability requirements have been properly allocated and that a process for

continuous improvement exists. The guide provides information and examples regarding the proper use of

FMEA as it applies to semiconductor manufacturing equipment.

This Executive Summary is designed in a what, why, when, how format to allow the reader a relatively quick

overview of the main issues surrounding an FMEA which are contained in the main part of the Guidance

Document itself (IMCA 2002). FMEA does not attempt to give comprehensive answers to the frequentlyanswered questions (FAQs), which are addressed in the main document.

3. Purpose of FMEAThe purpose of performing an FMEA is to analyze the product's design characteristics relative to the planned

manufacturing process and experiment design to ensure that the resultant product meets customer needs and

expectations. When potential failure modes are identified, corrective action can be taken to eliminate them or to

continually reduce a potential occurrence. The FMEA also documents the rationale for the chosen

manufacturing process. It provides for an organized critical analysis of potential failure modes and the

associated causes for the system being defined. The technique uses occurrence and detection probabilities in

conjunction with severity criteria to develop a risk priority number (RPN) for ranking corrective action

considerations.

The FMEA can be performed as either a hardware or functional analysis. The hardware approach requiresparts identification from engineering drawings (schematics, bill of materials) and reliability performance data,


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for example mean time between failures (MTBF), and is generally performed in a part-level fashion (bottom-

up). However, it can be initiated at any level (component/assembly/subsystem) and progress in either direction

(up or down).

Typically, the functional approach is used when hardware items have not been uniquely identified or when

system complexity requires analysis from the system level downward (top-down). This normally occurs during

the design development stages of the equipment life cycle; however, any subsystem FMEA can be performed at

any time. Although FMEA analyses vary from hardware to software, and from components (i.e., integratedcircuits, bearings) to system (i.e., stepper, furnace), the goal is always the same: to design reliability into the

equipment.

Thus, a functional analysis to FMEA on a subassembly is appropriate to use as a case study for the purposes of

this guideline.

When to perform FMEA

Equipment Life CycleThe recommended method for performing an FMEA is dictated by the equipment life cycle. The early

stages of the equipment life cycle represent the region where the greatest impact on equipment

reliability can be made.

Total QualityFMEA is recommended along with Process Analysis Technique, Design of Experiments and Fault TreeAnalysis, as a part of quality assurance that a company should use systematically for total quality

control. All indicators from the total quality management perspective and from examination of the

equipment life cycle tell us that the FMEA works best when conducted early in the planning stages of

the design.

What does it contain?

An FMEA covering the complete system (which may include FMEAs of various subsystem manufacturers)

should encompass those FMEAs by a review and an analysis of the interfaces between the subsystems. An

FMEA should contain a practical test programme and the results from those tests.

Who carries out an FMEA?

An FMEA team should be well knowledge of the each system. They are specialist having discipline in each

system required in design process. For example, machinery systems, electrical systems, DP control systems and

other control systems.

4. Process ImprovementFMEA is done in any equipment. In this process, to identify the possible failure modes and find the effect of this

failure to the equipment. To prevent this failure, possible changes in design and improvement can be made. This

identification of potential failure mode leads to a recommendation of effective reliability program.

Mainly failure mode can be set according to the FMEAs Risk Priority Number (RPN) system. A concentrated

effort can be placed on the higher RPN items based on the Pareto analysis obtained from the analysis. As the

equipment proceeds through the life cycle phases, the FMEA analysis becomes more detailed and should be

continued. The FMEA consist of following steps:

FMEA Prerequisites Functional Block Diagram Failure mode analysis and preparation of work sheets Team Review Corrective action

R.R. -Review Requirements

R.F.D. - Review FRACAS Data

G.S.D.- Get System Description

F.B.D.- Functional Block Diagram

D.F.M. - Dtermine Failure Mode

C.P.- Changes Proposed?

C.A.R.- Corrective Action Required

N.C.R.- No Change RequiredR.E.- Reliable Equipment


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Figure 1 Steps of FMEA

5. FMEA ProcessesFMEA Pre-requisites

Review specifications such as the statement of work (SOW) and the system requirement document(SRD).

Collect all available information that describes the subassembly to be analyzed. Systems engineeringcan provide system configuration

Compile information on earlier/similar designs from in-house/customer users such as data flowdiagrams and reliability performance data from the company's failure reporting, analysis and corrective

action system (FRACAS).

The above information should provide enough design detail to organize the equipment configuration to the

level required for analysis.

Functional Block Diagram

This diagram shows how different parts are interact to each other to verify the critical path. It is easy to

understand relations of the parts.

The recommended way to analyze the system is to break it down to different levels (i.e., system, subsystem,

subassemblies, and field replaceable units). Review schematics and other engineering drawings of the system

being analyzed to show how different subsystems, assemblies or parts interface with one another by their critical


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support systems such as power, plumbing, actuation signals, data flow, etc. to understand the normal functional

flow requirements.

Failure Mode Analysis and Preparation of Work Sheets

Determine the Potential Failure ModeAnswer of asking simply question determines the failure. Thats the simple question is What can go

wrong? Subassembly examples of failure modes Assembly examples of failure modes Manufacturing/Process examples of failure modes Component examples of failure modes

The Reliability Analysis Centre (RAC) has developed a document designed solely to address

component failure mechanisms and failure mode distributions for numerous part types including

semiconductors, mechanical and electromechanical components.

Determine the Potential Effects of the Failure ModeThe potential effects for each failure mode need to be identified both locally (subassembly) and

globally (system). Customer satisfaction is key in determining the effect of failure mode. Safety

criticality is also determined at this time based on Environmental Safety and Health (ES & H) levels.Based on this information, a severity ranking is used to determine the criticality of the failure mode on

the subassembly to the end effect.

Determine the Potential Cause of the FailureMost probable causes associated with potential failure modes. As a minimum, examine its relation to:

Preventive maintenance operation Failure to operate at a prescribed time Intermittent Operation Degraded output or operational capability Design causes

Determine Current Controls/Fault DetectionMany organizations have design criteria that help prevent the causes of failure modes through their

design guidelines. Checking of drawings prior to release, and prescribed design reviews are paramount

to determining compliance with design guidelines.

Detection methods are - Local hardware concurrent with operation, downstream or at a higher level,

Built-in test (BIT), Application software exception handling, Time-out, Visual methods, Alarms.

After the detection by previous method, determining the recovery method is another part. Recovery

methods are- Retry, Re-load and retry, Alternate path or redundancy, Degraded, Repair and restart.

Determining the Risk Priority Number (RPN)RPN is the indicator for the determining proper corrective action on the failure modes. It is calculated

by multiplying the severity, occurrence and detection ranking levels resulting in a scale from 1 to 1000.RPN = Severity Occurrence Detection

The small RPN is always better than the high RPN. A Pareto analysis is based on the RPN. In this all

the possible failure modes, effects and causes are determined. High RPN is gives idea for corrective

action on failure mode.

The engineering team generates the RPN and focused to the solution of failure modes. After findingsolution, improvements can be made.

Rating Scale Example:

If Severity = 10, indicates that the effect is very serious and is worse than Severity = 1.

If Occurrence = 10, indicates that the likelihood of occurrence is very high and is worse than

Occurrence = 1.

If Detection = 10, indicates that the failure is not likely to be detected before it reaches the end user is

worse than Detection =1.

An RPM is comparable to other RPMs in the same analysis, but an RPM is not comparable to RPNs

in another analysis. Because similar RPNs can result in several different ways and represents different

types of risk.

Preparation of FMEA WorksheetsAction takes tasks recommended for the purpose of reducing any or all of the rankings. Only designrevision can be bringing about the revision in the severity ranking.


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Actions All critical or significant characteristics must have recommended actions associated

with them

Recommended actions should be focused on design, and directed toward mitigatingthe cause of failure, or eliminating the failure mode

If recommended actions cannot mitigate or eliminate the potential for failure,recommended actions must force characteristics to be forwarded to process FMEAfor process mitigation

All recommended actions must have a person assigned responsibility for completionof the action

Responsibility should be a name, not a title Person listed as responsible for an action must also be listed as a team member There must be a completion date accompanying each recommended action Unless the failure mode has been eliminated, severity should not change Occurrence may or may not be lowered based upon the results of actions Detection may or may not be lowered based upon the results of actions If severity, occurrence or detection ratings are not improved, additional

recommended actions must to be defined.

WorksheetTable 1 Work Sheet of FMEA

SourceBook of Quality and Reliability Management by Lalit Wankhede

DescriptionItem/Function Name or concise statement of function performed by the equipment.

Potential Failure Mode- A answer of asking simply question determines the failure.

Potential Local Effect(s) of Failure subassembly consideration.

SEV Severity ranking.

Class - A safety critical failure mode.

Potential Cause(s)/ Mechanism(s) of Failure - Most probable causes associated with

potential failure modes.

Occur- Occurrence ranking based on the probability of failure.

Current Design Controls- methods of prevention and detection.

Detect- Detection ranking based on the probability of detection.

RPN- Risk Priority Number.

Recommended Actions Action recommended to reduce the possibility of occurrence of thefailure mode, reduce the severity (based on a design change) if failure mode occurs, or

improve the detection capability should the failure mode occur.

Response and Target Complete Date- This area lists the person responsible for evaluation

of the recommended actions. Besides ownership, it provides for accountability by assigning a

completion date.

Actions Taken Following completion of a recommended action, the FMEA provides for

closure of the potential failure mode.

SEVFollowing recommended corrective action.

OCCFollowing recommended corrective action.

DETFollowing recommended corrective action.

RPNFollowing recommended corrective action.


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6. Team ReviewThe engineering team suggested comments and review the worksheet to consider the failure modes based upon

RPNs. Engineering team determines potential problems, identify possible changes in design, data fill in the

worksheet etc. are updated. The worksheets need to reflect the changes until final design of equipment. When

the design is finalized, the worksheets are then distributed to the users, design engineering, technical support and

manufacturing. The worksheets may also provide information to other engineering areas.

Team members for FMEA Process engineer Manufacturing supervisor Operators Quality Safety Product engineer Customers Suppliers

7. Corrective ActionDesign Engineering

Design engineering uses the completed FMEA worksheets to identify and correct potential design relatedproblems. This is where the FMEA becomes the basis for continuous improvement.

Technical Support

From the FMEA worksheets, the engineering team can suggest a statistically based preventive maintenance

schedule based on the frequency and type of failure. A spares provisioning list can also be generated from the

worksheet.

Manufacturing

From the FMEA worksheets, the team could suggest a process be changed to optimize installations, acceptance

testing, etc. This is done because the sensitivities of the design are known and documented. The selection of

suppliers can be optimized as well. FMEA can be a way to communicate design deficiencies in the

manufacturing of the equipment.

8. Ranking Criteria for FMEASeverity Ranking Criteria

Calculating the severity levels provides for a classification ranking that encompasses safety, production

continuity, scrap loss, etc. It determines how affect the potential failure mode to the customers. Only applies to

the effect and is assigned with regard to any other rating.

Table 2 Severity Ranking Criteria

Effect Rank Criteria

None 1 No effect

Very Slight 2 Negligible effect on Performance. Some users may notice.

Slight 3 Slight effect on performance. Non vital faults will be noticed by many users.

Minor 4 Minor effect on performance. User is slightly dissatisfied.

Moderate 5 Reduced performance with gradual performance degradation. User dissatisfied.

Severe 6 Degraded performance, but safe and usable. User dissatisfied.

High Severity 7 Very poor performance. Very dissatisfied user.

Very High Severity 8 Inoperable but safe.

Extreme Severity 9 Probable failure with hazardous effects. Compliance with regulation is unlikely.

Maximum Severity 10 Unpredictable failure with hazardous effects almost certain. Non-compliant with regulations.

SourceBook of Quality and Reliability Management by Lalit Wankhede.

Environmental, Safety and Health Severity CodeThe Environmental Safety and Health (ES&H) severity code is a qualitative means of representing the

worst case incident that could result from an equipment or process failure or for lack of a contingencyplan for such an incident.


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Occurrence Ranking Criteria

The probability that a failure will occur during the expected life of the system can be described in potential

occurrences per unit time.

Table 3 Occurrence Ranking Criteria

Occurrence Rank Criteria

Extremely Unlikely 1 Less than 0.01 per thousand

Remote Likelihood 2 0.1 per thousand rate of occurrence

Very Low Likelihood 3 0.5 per thousand rate of occurrence

Low Likelihood 4 1 per thousand rate of occurrence

Moderately Low Likelihood 5 2 per thousand rate of occurrence

Medium Likelihood 6 5 per thousand rate of occurrence

Moderately High Likelihood 7 10 per thousand rate of occurrence

Very High Severity 8 20 per thousand rate of occurrence

Extreme Severity 9 50 per thousand rate of occurrence

Maximum Severity 10 100 per thousand rate of occurrence


Detection Ranking Criteria

This section provides a ranking based on an assessment of the probability that the failure mode will be detected

given the controls that are in place. The probability of detection is ranked in reverse order.

Table 4Detection Ranking Criteria

Detection Rank Criteria

Extremely Likely 1 Can be corrected prior to prototype/ Controls will almost certainly detect

Very High Likelihood 2 Can be corrected prior to design release/Very High probability of detection

High Likelihood 3 Likely to be corrected/High probability of detection

Moderately High Likelihood 4 Design controls are moderately effective

Medium Likelihood 5 Design controls have an even chance of working

Moderately Low Likelihood 6 Design controls may miss the problem

Low Likelihood 7 Design controls are likely to miss the problem

Very Low Likelihood 8 Design controls have a poor chance of detection

Very Low Likelihood 9 Unproven, unreliable design/poor chance for detection

Extremely Unlikely 10 No design technique available/Controls will not detect


9. Case StudyPerform FMEA on a Pressure Cooker

Figure 2 Pressure Cooker


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Pressure Cooker Safety Features

Safety valve relieves pressure before it reaches dangerous levels. Thermostat opens circuit through heating coil when the temperature rises above 250 C.

Scope of FMEA for Pressure Cooker

Resolution - The analysis will be restricted to the four major subsystems (electrical system, safetyvalve, thermostat, and pressure gage).

Focus SafetyBlock Diagram of Pressure Cooker

Figure 3Block Diagram Pressure Cooker

Table 5 FMEA is shown in Table

ComponentFailure

Mode

Effects on

other

Components

Effects on

whole

System

Consequence

Category

Failure

Likelihood

Detection

Method

Compensating

Provisions

Pressure

relief valve

Jammed

open

Increased gas

flow and

thermostat

operation

Loss of hot

water, more

cold water

input and

gas

I - SafeReasonably

probable

Observe at

pressure

relief valve

Shut off water

supply, reseal or

replace relief

valve

Jammed

closedNone None I - Safe Probable

Manual

testing

No conseq.

unless combined

with other

failure modes

Gas valveJammed

open

Burner

continues to

operate,

pressure relief

valve opens

Water temp.

and pressure

increase;

water turns

to steam

III - CriticalReasonably

probable

Water at

faucet too

hot;

pressure

relief valve

open (obs.)

Open hot water

faucet to relieve

pres., shut off

gas; pressure

relief valve

compensates


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Jammed

closed

Burner ceases

to operate

System fails

to produce

hot water

I - Safe Remote

Observe at

faucet

(cold

water)

Thermostat

Fails to

react to

temp.

rise

Burner

continues to

operate,

pressure relief

valve opens

Water temp.

rises; water

turns to

steam

III - Critical Remote

Water at

faucet too

hot

Open hot waterfaucet to relieve

pressure;

pressure relief

valve

compensates

Fails to

react to

temp.

drop

Burner fails to

function

Water

temperature

too low

I - Safe Remote

Observe at

faucet

(cold

water)

10.ConclusionThe failure modes included in the FMEA are the failures anticipated at the design stage. As such, they could be

compared with Failure Reporting, Analysis and Corrective Action System (FRACAS) results once actual

failures are observed during test, production and operation. Take appropriate steps to avoid either possibility.

11.References1. B.G. Dale and P. Shaw, Failure Mode and Effects Analysis in the U.K. Motor Industry: A State-of-Art

Study, Quality and Reliability Engineering International,Vol. 6, 184, 1990.2. Mario Villacourt, Failure Mode and Effects Analysis (FMEA), Technology Transfer #92020963B-

ENG SEMATECH September 30, 1992.3. Texas Instruments Inc. Semiconductor Group, FMEA Process, June 1991 Ciraolo, Michael,

Software Factories: Japan, Tech Monitoring by SRI International,April 1991, pp. 15.4. Matzumura, K., Improving Equipment Design Through TPM, The Second Annual Total Productive

Maintenance Conference: TPM Achieving World Class Equipment Management, 1991.

5. Lalit Wankhede Quality and reliability management.6. BSI Standard, BS 5760-5:1991: 'Reliability of Systems, Equipment andComponents', Part 5: 'Guide to

Failure Modes, Effects and Criticality Analysis(FMEA and FMECA).7. IEC Standard, IEC 60812: 'Analysis Techniques for System Reliability Procedure for Failure Mode

and Effects Analysis (FMEA).

8. CEI/IEC812 Analysis techniques for system reliability - Procedure for failure modes and effectsanalysis (FMEA).

9. IMO MSC Resolution 36(63) Annex 4 Procedures for Failure Mode and Effects Analysis (HSCCode).

10. Analysis techniques for system reliability - Procedure for failure modes and effects analysis (FMEA) -CEI/IEC 812:1985.

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