19 mistake proofing techniques

5/26/2018 19 Mistake Proofing Techniques

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Lean Six Sigma Operational - Delegate Workbook

SSG06101ENUK - MP/Issue 1.1/ September 2008 1 The British Standards Institution 2008

Mistake Proofing Techniques

2

SSG06101ENUK Delegate Slides/Issue 1.1/ September 2008

Learning Objectives

At the end of this section delegates will be able to:

Explain the role of Mistake Proofing within Lean Six Sigma

Recognise that defects can be eliminated (100% of thetime)

Understand that Mistake Proofing should be focused onprocess steps that rely on operator vigilance andconcentration

Recognise that simple, low cost devices can be the mosteffective solutions

Use a simple process for implementing a Mistake Proofingsystem


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3


History of Error Proofing

Dr Shigeo Shingo attributed with developing the methods

Originally called Idiot Proofing but recognised that this label

could offend workers so changed to Mistake Proofing (Poka

Yoke in Japanese)

Literally translated

Yokeru: to avoid

Poka: inadvertent errors

Target of Zero Defects and elimination of QC Inspection

4


Human Error

Humans make mistakes (errors) because of

- Forgetfulness - Misunderstanding

- Lack of experience/skills - Lack of concentration

- Laziness - Lack of standards

- Rushing - Taking short cuts

- Malicious intent (deliberate action)

Errors (can) lead to defects

Defects are not inevitable and can be eliminated by the useof simple, low cost methods zero defects

Mistake Proofing should take over repetitive tasks thatdepend on vigilance or memory


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Types of Error

Four main types of error:

Processing

1. Omitted Processing - Step in process not carried out

Eg form not checked, discount not included, invoice not sent, hole not drilled,part not cleaned

2. Processing Errors - step in process carried out incorrectly

Eg wrong discount included, invoice sent to wrong address, hole drilled in wrongplace

Materials

3. Missing materials/information

Eg form not filled out completely, order not complete, screw left out4. Wrong materials/information

Eg wrong form filled out, wrong information supplied, wrong screw used

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Shutdown Process

Control Process

Warn Operator

Shutdown Process

Control Flow

Warn Operator

Functions of Poka Yoke

EliminateDefects

Predict Defect(about to occur)

Detect Defect(occurred)


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7


ABC Fix Explanation Scenario

The Problem:

Automobiles are crossing the

train tracks and getting hit by

a train.

The C Fix:

Place flashing cross signs at

the crossing to alert vehicles.

Dilemma: Vehicles are alerted

of oncoming trains but can still

cross. Problem not solved.

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ABC Fix Explanation Scenario

The B Fix:

Place cross gates at crossing to furtherdeter crossing of vehicles.

Dilemma: Vehicles are alerted and have

limited crossing ability; however doesnot prevent those who arbitrarily want tocross. Problem deterred but not solved.

The A Fix:

Build overpass for vehicles to crosstrain tracks without incident.

Dilemma: None. Problem solved.


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Blade can stay outwithout operatortouching it

Sharp point

Rounded point

Spring loaded--when operatorlets go, the bladegoes back in

Guard protecting bladeonly releases when

button is pushed

Extra safety guardsmake it difficult toaccidentally contact blade

Original Box Cutter

Safety Example

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Elevators

Some common safety features are listed below:

Doors sensors detect if an object/person is blocking

entrance, if so they automatically open

2 separate braking systems used. The first is opened by

electrical current, if power is lost the brake closes underhigh spring tension. The second is a centrifugal brake

governing the maximum speed

A host of switches and sensors control the positioning of

the elevator

Acceleration/deceleration alters with weight in carriage


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Medicine (Bottles)

Up to one in five toddlers canopen medicine bottles andchemical containers, even if theyhave child-resistant tops

Every year 25,000 under-fives aretaken to casualty, suspected ofswallowing substances rangingfrom medicines to householdcleaning products

One in five are admitted tohospital for treatment

Child-resistant tops are nowcommonplace on most medicinebottles and household chemicals -but they are child-resistant, notchild-proof

Source BBC News

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Electrical (Household)

RCD (Residual Current Device)

Automatically cuts off power supply if a leakage current to ground isdetected

Mains Socket

Earth pin first to make and last to break contact

Earth pin has to enter socket to move protective shields from Live andNEUTRAL connections

Shape prevents incorrect fitment

3 Pin Plug

Only fits one way round

Ergonomically designed so it is picked up by the case

Insulation on Live and Neutral to prevent accidental touching of pins

If wired correctly and plug pulled out by cable, Live first to pull out,Neutral second, Earth last

Fuse standard for plug no other fuses will fit. Maximum fuse size 13 amp

If cover is not in place pins push back and cannot enter socket


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Electrical (General) Shapes and colours extensively used to prevent equipment

being incorrectly connected

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Appliances

Microwave

Will not work until the door is shut

Washing machine

Will not start until door is closed

Will not allow door to be opened until cycle is

complete


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Low Brake Pad WarningIndicators Brake pad wear indicators are fitted to

most modern cars. They are made upof 2 insulated wires which fit in a holeinside the brake pad

As brake pads wear the insulatedcables become exposed and themetal brake disk connects them like aswitch

An electrical signal then lights up awarning lamp on the cars dashboardalerting the driver before the brakesfail

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Using Shapes and Colours


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Software Warnings andReminders

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Using Dialogue Boxes andSoftware Checks


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Using Switches and AutomaticBraking Safety switches need to be pressed and held before the start

levers will operate.

Upon release of start lever, brakes automatically come on stoppingthe cutting blades etc

Safety interlocks or light beams used to automatically shut down orstop processes

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Using Checklists

Backup generator functional6

Generator voltage (Min 220v Max 250V)5

Hydraulic pressure (Min 30 bar Max 40

bar)

4

Ailerons functional3

Altimeter calibration (+50 Metres)2

Fuel level (min 1500 Max 2500)1

Pre-flight Checklist


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Visual Prevention Methods

Some solutions are better

than others

Which signs would be the

most successful in

preventing different

nationalities entering the

incorrect toilet?

Ladies Gents

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Using Lights, Sounds, Signsand Barriers


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Amsterdam Airport: Problem-AirportCleanliness

Target Practice?!

Error Proofing and FMEA Complimentary Techniques?


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History of FMEA

First used in the 1960s in the aerospace industry

during the Apollo missions

In 1974, the US Navy developed MIL-STD-1629

regarding the use of FMEA

In the late 1970s, driven by product liability costs,

FMEA moved into U.S automotive applications


FMEA Inputs and Outputs

Inputs

Process map

Process history

Process technical procedures

Outputs

List of actions to prevent causes or to detect failure

modes

History of actions taken


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FMEA Team

Team approach is necessary

Responsible black/green belt leads the team

Recommended representatives:

Operators/administrators/supervisors

Design

Engineering

Operations

Distribution

Finance

Information Technology

Human Resources


Process

Step/InputPotential Failure Mode Potential Failure Effects

S

E

V

Potential Causes

O

C

C

Current Controls

D

E

T

R

P

N

Actions

Recommended

0 0 0 0

0 0 0 0

0 0 0 0

0 0 0 0

0 0 0 0

What istheinput ?

Whatcan gowrongwiththe

input?

Whatcan bedone?

What isthe

effecton the

output?

What arethe causes?

How

bad?

How

often?

How

well?

(1-10) (1-10) (1-10)

Completing an FMEA

How are

these foundor

prevented?


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Definition of Terms - Failure Mode

Definition

The way a specific process input fails

Will cause the effect to occur if not corrected orremoved

Examples

Temperature too high

Incorrect PO number

Surface contamination

Dropped call (customer service)

Paint too thin


Definition of Terms - Effect

Definition

Impact on customer requirements

Generally an external customer focus, but can also includedownstream processes

Examples

Temperature too high: paint cracks

Incorrect PO number: accounts receivable traceability errors

Surface contamination: poor adhesion

Dropped call: customer dissatisfaction

Paint too thin: poor coverage


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Definition of Terms - Cause

Definition

Sources of process variation that cause the failure mode tooccur

Identification of causes starts with failure modes associatedwith the highest severity ratings

Examples

Temperature too high: thermocouple out of calibration

Incorrect PO number: typographical error

Surface contamination: overhead hoist systems Dropped call: insufficient number of CS representatives

Paint too thin: high solvent content


Definition of Terms - CurrentControls

Definition

Systematised methods / devices in place to prevent ordetect failure modes or causes (before causing effects)

Prevention consists of failsafing, automated control andsetup verifications

Controls consist of audits, checklists, inspection,laboratory testing, training, SOPs, preventivemaintenance, etc

Which is more important to process:

improvement, prevention or detection?


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Definition of Terms - Risk PriorityNumber (RPN)

Definition

The output of an FMEA

A calculated number based on information you provide, regarding:

Potential failure modes,

Effects, and

Current ability of the process to detect the failures before reaching the

customer

Calculated as the product of three quantitative ratings, each one

related to the effects, causes, and controls:

RPN = Severity X Occurrence X Detection

Effects

Effects Causes

Causes Controls

Controls


Risk Priority Number

Risk Priority Number is not absolute

Scaling for severity, occurrence and detection can

be locally developed

Be aware of customer requirements

Other categories can be added

For example, one engineer added an impact score to

the RPN calculation to estimate the overall impact of the

failure mode on the process


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Definition of Terms

Severity (of Effect)(1 = Not Severe, 10 = Very Severe)

Importance of effect on customer requirements

Could also be concerned with safety and other risks if failure occurs

Occurrence (of Cause)(1 = Not Likely, 10 = Very Likely)

Frequency with which a given cause occurs and creates failuremode(s)

Can sometimes refer to the frequency of a failure mode

Detection (Capability of Current Controls) (1 = Likely to Detect,

10 = Not Likely at all to Detect) Ability of current control scheme to detect or prevent:

The causes before creating failure mode

The failure modes before causing effect


Example Rating Scale

Rating Severity of Effect Likelihood of Occurrence Ability to Detect

10 Haz ardous without warningVery high:

Cannot detect

9 Hazardous with warningFailure is almost inevitable

Very remote chance of detection

8 Loss of primary functionHigh:

Remote chance of detection

7Reduced primary function

performance

Repeated failuresVery low chance of detection

6 Loss of secondary functionModerate:

Low chance of detection

5Reduced secondary function

performance

Occasional failuresModerate chance of detection

4Minor defect noticed by most

customers

Moderately high chance of

detection

3Minor defect noticed by some

customers Low:High chance of detection

2Minor defect noticed by

discriminating customers

Relatively few failuresVery high chance of detection

1 No effect Remote: Failure is unlikely Almost certain detection


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Process

Step

Key Process

Input

Failure Modes -What can go

wrong? Effects Causes

Current

Controls

Pour into

glassBeer volume Overflow

Wasted Beer/

Wet LapDrunk None

Glass too small Visual

Not paying

attentionNone

Too much foam

Bad Taste /

Don't get as

drunk

No tilt Visual

Pouring too highVisual and operator

training

Pouring too fastVisual and operator

training

No Foam

No beer

mustache/ Poor

taste

Fla t beer Expiration date

Tilted glass Visual

S low Pour Ope ra tor tra ining

Empty glass No drink Too drunk None

Broken Glass Visual

No Money

Job / Process

Excellence - big

bonus

No Friends Personality

A Well-Loved Process FMEA

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FMEA Hints

Keep it simple; not complex (no wall charts)

Must involve a team, no lone ranger

development

Update it as you move through the roadmap

Make sure the FMEA is an action tool, not just a

document; use the right half of the tool


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POKA YOKE Connection to the FMEA

Process

Step/InputPotential Failure Mode Potential Failure Effects

S

E

V

Potential Causes

O

C

C

Current Controls

D

E

T

R

P

N

Actions

Recommended

What is the

process step/

Input under

investigation?

In what ways does the Key

Input go wrong?

What is the impact on the Key

Output Variables (Customer

Requirements) or internal

requirements?

How

Severeisthe

effecttothe

cusotmer?What causes the Key Input to

go wrong?

How

oftendoescause

orFMo

ccur?What are the existing controls and

procedures (inspection and test)

that prevent eith the cause or the

Failure Mode? Should include an

SOP number.

How

wellcanyou

detectcauseorFM? What are the actions

for reducing the

occurrance of the

Cause, or improving

detection? Should

have actions only on

high RPN's or easy

fixes.

0

0

0

Good POKA YOKE devices drive down

occurrence and detection rankings.

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Poka Yoke Workshop 1Process: Tightening nuts

Problem: Washers left out before tightening

Description of process: Operator adds washer and nut, then tightens usingan automatic nut driver.

Prevent Error/Detect Error

Shutdown/Control/Warn

Before improvement: It is possible

to tighten the nuts even if washersare missing.

After Improvement:

Solution:

(Delete as appropriate)


Nut, tightened withno washer

Nut driver


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Poka Yoke Workshop 2Pprocess: Parts Transport LineProblem: Parts supplied upside down toautomatic machinery

Description of Process: A transportation chute feeds parts from a press into the nextprocess. in the next process parts are mounted in the same position as they arrive.



Before Improvement: Operators watchincoming work pieces carefully and removeupside down parts. some are alwaysoverlooked.

After Improvement:

Solution:



Upside DownCorrect Work piece

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Poka Yoke Workshop 3Process: Inspecting Cassette Tape Decks

Problem: Inspection Tapes out of Sequence

Description of Process: When a cassette deck is inspected, the inspector uses a series of cassettesto check the performance of the unit. It is important that the tests are performed in the correct order andthat all tests are done.


shutdown/control/warn

Before Improvement: A slotted rack wasused to store tapes. If a tape was placed onworkbench or carried off then inspector couldlose track and make errors.

After Improvement:

Solution:



1 2 3 4 5 67

Storage Rack


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Poka Yoke Workshop 4

The inspectors foundmedical notes wereconfusing written upwith the same RRinitials for womenneeding a routine recalland those needing arecall recall, an urgent

reassessment!!!

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City Trader buys $1000000000 worth of shares

instead of $10,000,000.00!

Accounts pays supplier twice

Failure to invoice customer for services provided

Miscalculation in currency exchange

Your experiences..?


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Poka Yoke Summary

Defects can be eliminated

Target process steps that are repetitive and rely

on operator vigilance and checking

Use simple, low cost devices

Involve the operator in identifying, developing and

implementing devices

Devices should be challenge tested by

introducing error (defect)

Solutions


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Poka Yoke Workshop 1Process: Tightening Nuts

Problem: Washers left out before tightening

Description of Process: Operator adds washer and nut, then tightensusing an automatic nut driver.



Before Improvement: It is possibleto tighten the nuts even if washersare missing.

After Improvement:

Solution:



Nut, tightened withno washer

Nut driver Nut driverStopper

Washerthickness

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Poka Yoke Workshop 2Process: Parts transport lineProblem: Parts supplied upside down toautomatic machinery

Description of Process: A transportation chute feeds parts from a press into the nextprocess. In the next process parts are mounted in the same position as they arrive.



Before improvement: Operators watchincoming work pieces carefully and removeupside down parts. Some are alwaysoverlooked.

After Improvement:

Solution:



Upside downCorrect Work piece

Notch


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Poka Yoke Workshop 3Process: Inspecting Cassette Tape Decks

Problem: Inspection tapes out of sequence

Description of Process: When a cassette deck is inspected, the inspector uses a series of cassettesto check the performance of the unit. It is important that the tests are performed in the correct order andthat all tests are done.



Before Improvement: A slotted rack wasused to store tapes. If a tape was placed onworkbench or carried off then inspector couldlose track and make errors.

After Improvement:

Solution:



1 2 3 4 5 67

Storage rack

52



The inspectors foundmedical notes wereconfusing written upwith the same RR

initials for womenneeding a routine recalland those needing arecall recall, an urgentreassessment!!!


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City Trader buys $1000000000 worth of shares

instead of $10,000,000.00!

Accounts pays supplier twice

Failure to invoice customer for services provided

Miscalculation in currency exchange

Your experiences..?

19 mistake proofing techniques

Documents

defects mistake proofing

role of mistake proofing

proofing pokayoke

idiot proofing

mistake proofingsystem5262018

defects defects

wrong information

wrong address