Process fmea

Failure Mode and

Effects Analysis

Lawrence Hallett!

Purpose

How to conduct an FMEA.

OriginFailure mode and effect analysis (FMEA) was one of the first systematic techniques for failure analysis. It was developed by reliability engineers in the 1950s to study problems that might arise from malfunctions of military systems

http://en.wikipedia.org/wiki/Failure_analysis

http://en.wikipedia.org/wiki/Reliability_engineering

http://en.wikipedia.org/wiki/Reliability_engineering

Definition of FMEA

A Failure Mode and Effect Analysis uses a disciplined technique to identify and help eliminate product and process potential failure modes.

o By ID of potential failures o Assessing the risks caused by failure modes and Identify

corrective actions o Prioritizing corrective actions o Carry out corrective actions

Most COMMON Types of FMEA's

Design (Potential) Failure Modes and Effects Analysis-DFMEA • Focus is on potential design- related failures

and their causes. !

Process (Potential) Failures Modes and Effects Analysis-PFMEA • Focuses is on potential process failures and

their causes.

PFMEA's!

● Focus is on potential process –related failures and their causes. ▪Main drive is to understand the process through the identification of as many potential failures as possible.

o e.g. Incorrect material used

● PFMEA typically assumes that the design is sound.

● Development of Recommended Actions is targeted at eliminating the Root Cause of the potential failures.

PFMEA's benefits•Identifies Process Functions and Req’s!•Identifies potential failure modes!•Assesses effect of failure!•Identifies causes of failures!•Identifies process controls!•Identifies confirmed Critical Characteristics!•Provides an objective base for action

PFMEA's outputs

PFMEA's - who prepares it

•A team effort - including!•Manufacturing/production!•Engineering!•Design !•Quality!•Test!!

•However it is a moving feast

Related Documents

PFMEA

Three Parts: ●Process Flow Diagram (PFD) ●Process Failure Mode and Effects

Analysis (PFMEA) ●Process Control Plan (PCP)

Product Definition:Key Product Characteristics, DFMEA

Process Definition:Process Flow Diagram (PFD),

Failure Mode Analysis:PFMEA

Control Strategy:Control Plan,Error proofing

Customer Requirements:

Manufacturing:Work Instructions & Process Monitoring

Information Flow

SOR, Vehicle Tech Specs, System Technical Specs

Product and Process Characteristics

DFMEA/PFMEA Information Interrelationships

DFMEA Design FMEA

Process Flow Diagram

PFMEA Process FMEA

Boundary (Block) Diagram, P- Diagram,

Etc.

Design Verification Plan & Report

(DVP&R)

Process Control Plan

Process Function/Requirements

Process Flow Diagrams● The Process Flow

Diagram provides a logical (visual) depiction of the process that is being analyzed.

12

● The SAE/AIAG PFMEA guidelines describe two methods of defining process functions. Either or both may be used.

● Process Functions may be described in terms of: ▪The product features/characteristics that are

created or

▪The process actions that are performed ● Process functions should be identified in detail

as necessary to provide information for the PFMEA to develop effective Process Controls

Process Function / Requirement

13

● Consider a simple operation to drill a hole in a metal part

● The product characteristics & requirements are: ▪Hole size: 4.00 mm +/- 0.13 ▪Hole Location:

X = 28.0 mm +/- 0.2 Y = 15.0 mm +/- 0.2 ▪Perpendicular to surface, no burrs, etc.

● The process operation must create these product characteristics and meet the requirements


XY

4.00

●To drill the correct hole size in the specified location, the process must: ▪Position and hold the part ▪Align the part fixturing

with the drill position ▪Assure the correct drill

bit size is used ▪Set and control drill speed ▪Anticipate tool wear and

schedule preventive maintenance

● If the Function/Requirement is defined in the PFMEA as “Drill Hole” could any of these be missed?


Process Flow Diagram (PFD)

● Process Flow Diagram is the foundation ▪ The process must be defined step by step, including

interfaces ▪ The PFD provides the structure to document what product

characteristics and requirements (OUTPUTS) are affected by a given operation and how these characteristics and sources of variation are controlled (INPUTS)

▪ PFD is a graphical representation of every possible path a part can take through the anticipated manufacturing process

▪ A well defined PFD establishes the foundation for the PFMEA

● Helps in developing equipment specifications. ▪ How will the process control non-conforming material? ▪ How and when will inspections be performed, what is

required? ▪ How and when will parts be re-introduced into the

process?

PFD Example

PFD Feeds PFMEAIdentify the Function(s)

● Function is a description of what the Process does to meet the requirements ➢Related to process specification and product

characteristics ➢Comes from the PFD operation description column

● Functions can be described as: ➢Do this operation… ➢To this part or material… ➢With this tooling or equipment…

Potential Failure Mode

Potential Failure Modes

Often missed

Potential Effect of Failure

Example

Failure Modes

Effect of Failure

Case assembled but not to the correct height

Fails height check causing rework(3) if not detected Connector corrosion leading to intermittence premature part failure(8)

Potential Effects

of Failure

Potential Effects

of Failure

Severity Ranking

Severity

Potential Cause of Failure

Cause of Failure

How to identify Cause of Failure

Developing CausesAlways assume a direct correlation between cause and failure i.e if the cause occurs then the failure mode occurs

Assumptions

Assumptions

Occurrence

How to identify Occurrence

Occurrence Evaluation Criteria

Probability of Likely Failure Rates Over Design Life Ranking Failure

SUGGESTED OCCURRENCE EVALUATION CRITERIA

Very High: Persistent failures

High: Frequent failures

Moderate: Occasional failures

Low: Relatively few failures

Remote: Failure is unlikely

≥ 100 per thousand vehicles/items

50 per thousand vehicles/items






0.5 per thousand vehicles/items

0.1 per thousand vehicles/items

≤ 0.01 per thousand vehicles/items

10

9

8

7

6

5

4

3

2

1

Current controls

Current Controls

2 types of controls Prevention Prevent the Cause/mechanism or failure mode/effect from occurring or reduce their rate of occurrence !Detection Detect the cause/mechanism and lead to corrective action

How to identify process controls

Current Controls

Detection ranking

Detection Rankings

Risk Priority Number

Analysis Of Risk

▪ RPN / RISK PRIORITY NUMBER ▪ What Is Risk? ▪ Probability of danger ▪ Severity/Occurrence/Cause

Evaluation by RPN Only

▪ Case 1 o S=5 O=5 D=2 RPN = 50

▪ Case 2 o S=3 O=3 D=6 RPN = 54

▪ Case 3 o S=2 O=10, D=10 = 200

▪ Case 4 o S=9 O=2 D=3 = 54

WHICH ONE IS WORSE?

Example

▪ Extreme Safety/Regulatory Risk o =9 & 10 Severity

▪ High Risk to Customer Satisfaction o Sev. > or = to 5 and Occ > or = 4

▪ Consider Detection only as a measure of Test Capability.

Actions taken

Actions

Re-rating RPN After Actions Have Occurred

Re-rating RPN After Actions Have Occurred▪ Severity typically stays the same. ▪ Occurrence is the primary item to reduce / focus on. ▪ Detection is reduced only as a last resort. ▪ Do not plan to REDUCE RPN with detection actions!!!

o 100% inspection is only 80% effective! o Reducing RPN with detection does not eliminate failure mode,

or reduce probability of causes o Detection of 10 is not bad if occurrence is 1

Outputs

● PCP will be based on the previous activities in PFD and PFMEA.

● Review the PFMEA information developed & supplied and use to identify: ▪ Specific controls that may be needed due to the

information added ▪ Identify which controls are Product or Process

o Note any Special Characteristics o Identify evaluation methods, frequency and Control

Methods o Note Reaction Plans (particularly related to NC parts)

Process Control Plan

Process Control Plan Example

Part/ Process Number

Process Name /Operation Description

Machine, Device, Jig,

Tools for Mfg.

CharacteristicsSpecial Char. Class.

Methods

Reaction PlanNo. Product Process

Product / Process Specification /

Tolerance

Evaluation Measurement

Technique

SampleControl MethodSize Frequency

300 Initiate weld sequence /

Perform TIG weld of frame parts.

Robotic Arm controller.

TIG welders.

Weld beads per design specification.

Tube welds meet pull test with failure in parent material.

Pull test using test fixture 20-1.

1 pc.

Per shift.

Hydraulic pull test instruction TI21-01 Process monitoring form PMF-20-01

Quarantine material since last good pull test.

Good welds, no visible defects.

yes Weld appearance meets visual standard.

Operator evaluation to Visual Std TB20-VS1

100% Each piece.

Visual inspection OWI #20-01.

Remove part and send to repair.

Weld voltage yes 24 Volts AC +/- 2.0 volts

Machine Control

100% Each weld cycle.

Closed-loop machine control.

Scrap part & Re-start welder.

Weld voltage yes 24 Volts AC +/- 2.0 volts

Visual Once each

Shift start or change-over or maint. event.

Set-up OWI #20-02 & Form PMF-20-02 Periodic maintenance per PM-WI #20.

Scrap current part. Shut down.Notify maintenance.

Inert gas flow rate

yes 5 cubic feet / min.+/- 0.5 cfm

Visual twice Per shift. Operator cleans gas cup twice per shift PM-WI-20. Process monitoring form PMF-20-01

Notify maintenance.

Inert gas flow rate

yes 5 cubic feet / min.+/- 0.5 cfm

Visual of verification of Flow Meter

Once each

Shift start or change-over or maint. event

Set-up OWI #20-02 & Form PMF-20-02. Equipment Calibration Procedure #368

Quarantine material since last good pull test.Notify maintenance.

Form 818-1 (Rev 12Apr02)

CONTROL PLAN Control Plan No:Part Number/Latest Change Level Key Contact/Phone Date (Orig.) Date (Rev.)

Customer Part Number Core Team Customer Engineering Approval/Date (If Req'd.)

Part Name/Description Supplier/Plant Approval/Date Customer Quality Approval/Date (If Req'd.)

Supplier/Plant Supplier Code Other Approval/Date (If Req'd.) Other Approval/Date (If Req'd.)

Prototype Pre-Launch Production

Process Control Plan Example

Initiate weld sequence / Confirm Wire feed rate

Initiate weld sequence / Confirm Weld voltage

Initiate weld sequence /Perform TIG weld of

frame parts.

Initiate weld sequence / Confirm Inert Gas flow

rate

Scrap part & Re-start welder


Each weld cycle.

100%Machine Control

300 mm / minute +/- 10 mm / min.

yesWeld wire feed rate

Scrap part & Re-start welder


Each weld cycle.

100%Machine Control

24 Volts AC +/- 2.0 volts

yesWeld voltage

Notify maintenance.

Operator cleans gas cup twice per shift PM-WI-2500. Process monitoring form PMF-20-10

Per shift.twiceVisual5 cubic feet / min.+/- 0.5 cfm

yesInert gas flow rate

Remove part and send to repair.

Visual inspection OWI #20-010.

Each piece.

100%Operator evaluation to Visual Std TB20-VS1.

Weld appearance meets visual standard.

yesGood welds, no visible defects.

Scrap current part.Shut down.Notify maintenance.

Set-up OWI #20-020 & Form PM-20-020 Predictive maintenance pinch roller replace @ 180 days.


100%Operator setup check and verification

300 mm / minute +/- 10 mm / min.

yesWeld wire feed rate

Quarantine material since last good pull test. Notify maintenance.

Set-up OWI #20-02 & Form PM-00-02. Equipment Calibration Procedure #368


Once each

Visual verification of Flow Meter

5 cubic feet / min.+/- 0.5 cfm

yesInert gas flow rate

Scrap current part. Shut down.Notify maintenance.

Set-up OWI #20-02 & Form PM-20-02 Periodic maintenance per PM-WI #20.


Once each

Visual24 Volts AC +/- 2.0 volts

yesWeld voltage

Quarantine material since last good pull test.

Hydraulic pull test instruction TI41-01 Process monitoring form PM-20-010

Per shift.

1 pc.

Pull test using test fixture 20-1.

Tube welds meet pull test with failure in parent material.

Weld beads per design specification.

Robotic Arm TIG welders

and controllers.

300.

.!Robotic Arm TIG welders

!Initiate weld sequence / Close and latch curtain

300

FrequencySize

Reaction PlanControl Method

SampleEvaluation Measurement

Technique

Product / Process Specification /

ToleranceProcessProductNo.

MethodsSpecial Char. Class.

CharacteristicsMachine,

Device, Jig, Tools for Mfg.

Process Name /Operation Description

Part/ Process Number

Business

Process fmea