mistake proofing techniques

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 the time)

• Understand that Mistake Proofing should be focused on process steps that rely on operator vigilance and concentration

• Recognise that simple, low cost devices can be the most effective solutions

• Use a simple process for implementing a Mistake Proofing system



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 use of simple, low cost methods – zero defects

• Mistake Proofing should take over repetitive tasks that depend on vigilance or memory



5


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 wrong place

Materials

3. Missing materials/information

Eg form not filled out completely, order not complete, screw left out

4. Wrong materials/information

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

6


Shutdown Process

Control Process

Warn Operator

Shutdown Process

Control Flow

Warn Operator

Functions of Poka Yoke

Eliminate

Defects

Predict Defect

(about to occur)

Detect Defect

(occurred)



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.

8


ABC Fix Explanation Scenario

The “ B” Fix:

Place cross gates at crossing to further deter crossing of vehicles.

Dilemma: Vehicles are alerted and have limited crossing ability; however does not prevent those who arbitrarily want to cross. Problem deterred but not solved.

The “A” Fix:

Build overpass for vehicles to crosstrain tracks without incident.

Dilemma: None. Problem solved.



9


Blade can stay out without operator touching it

Sharp point

Rounded point

Spring loaded--when operator lets go, the blade goes back in

Guard protecting blade only releases when button is pushed

Extra safety guards make it difficult toaccidentally contact blade

Original Box Cutter

Safety Example

10


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 under

high 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



11


Medicine (Bottles)

• Up to one in five toddlers can open medicine bottles and chemical containers, even if they have child-resistant tops

• Every year 25,000 under-fives are taken to casualty, suspected of swallowing substances ranging from medicines to household cleaning products

• One in five are admitted to hospital for treatment

• Child-resistant tops are now commonplace on most medicine bottles and household chemicals -but they are child-resistant, not child-proof

Source BBC News

12


Electrical (Household)

• RCD (Residual Current Device)

� Automatically cuts off power supply if a leakage current to ground is detected

• Mains Socket

� Earth pin first to make and last to break contact

� Earth pin has to enter socket to move protective shields from Live and NEUTRAL 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



13


Electrical (General)

• Shapes and colours extensively used to prevent equipment

being incorrectly connected

14


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



15


Low Brake Pad Warning

Indicators• Brake pad wear indicators are fitted to

most modern cars. They are made up of 2 insulated wires which fit in a hole inside the brake pad

• As brake pads wear the insulated cables become exposed and the metal brake disk connects them like a switch

• An electrical signal then lights up a warning lamp on the cars dashboard alerting the driver before the brakes fail

16


Using Shapes and Colours



17


Software Warnings and

Reminders

18


Using Dialogue Boxes and

Software Checks



19


Using Switches and Automatic

Braking• Safety switches need to be pressed and held before the start

levers will operate.

• Upon release of start lever, brakes automatically come on stopping the cutting blades etc

• Safety interlocks or light beams used to automatically shut down or stop processes

20


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



21


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, Signs

and Barriers



23


Amsterdam Airport: Problem-Airport Cleanliness

Target Practice?!

Error Proofing and FMEA –Complimentary Techniques?




History of FMEA

• First used in the 1960’s 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 1970’s, 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




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 is the input ?

What can go wrong with the

input?

What can be done?

What is the

effect on the

output?

What are the causes?

How bad?

How often?

How well?

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

Completing an FMEA

How are

these found or

prevented?




Definition of Terms - Failure Mode

• Definition

� The way a specific process input fails

� Will cause the effect to occur if not corrected or removed

• 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 include downstream 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




Definition of Terms - Cause

• Definition

� Sources of process variation that cause the failure mode to occur

� Identification of causes starts with failure modes associated with 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 - Current

Controls

• Definition

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

� Prevention consists of failsafing, automated control and setup verifications

� Controls consist of audits, checklists, inspection, laboratory testing, training, SOP’s, preventive maintenance, etc

• Which is more important to process:

improvement, prevention or detection?




Definition of Terms - Risk Priority Number (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

EffectsEffects CausesCauses ControlsControls


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




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 failure mode(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 Hazardous 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



37


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

Flat beer Expiration date

Tilted glass Visual

Slow Pour Operator training

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



39


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

Severe

is the

effect to

the

cusotm

er? What causes the Key Input to

go wrong?

How

often d

oes c

ause

or

FM

occur? 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

well

can y

ou

dete

ct cause o

r F

M? 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.

40


Poka Yoke Workshop 1Process: Tightening nuts

Problem: Washers left out before tightening

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

Prevent Error/Detect Error

Shutdown/Control/Warn

Before improvement: It is possible

to tighten the nuts even if washers are missing.

After Improvement:

Solution:

(Delete as appropriate)


Nut, tightened with no washer

Nut driver



41


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

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



Before Improvement: Operators watch

incoming work pieces carefully and remove upside down parts. some are always overlooked.

After Improvement:

Solution:



Upside DownCorrect Work piece

42


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 cassettes to check the performance of the unit. It is important that the tests are performed in the correct order and that all tests are done.


shutdown/control/warn

Before Improvement: A slotted rack was used to store tapes. If a tape was placed on workbench or carried off then inspector could lose track and make errors.

After Improvement:

Solution:



1 2 3 4 5 67

Storage Rack



43


Poka Yoke Workshop 4

The inspectors found medical notes were confusing – written up with the same “RR”initials for women needing a “routine recall”and those needing a “recall recall”, an urgent reassessment…!!!

44





45



46



• 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……..?



47


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



49


Poka Yoke Workshop 1Process: Tightening Nuts

Problem: Washers left out before tightening

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



Before Improvement: It is possible

to tighten the nuts even if washers are missing.

After Improvement:

Solution:



Nut, tightened with no washer

Nut driver Nut driverStopper

Washer

thickness

50


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

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



Before improvement: Operators watch

incoming work pieces carefully and remove upside down parts. Some are always overlooked.

After Improvement:

Solution:



Upside downCorrect Work piece

Notch



51


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 cassettes to check the performance of the unit. It is important that the tests are performed in the correct order and

that all tests are done.



Before Improvement: A slotted rack was used to store tapes. If a tape was placed on workbench or carried off then inspector could lose track and make errors.

After Improvement:

Solution:



1 2 3 4 5 67

Storage rack

52



The inspectors found medical notes were confusing – written up with the same “RR”initials for women needing a “routine recall”and those needing a “recall recall”, an urgent reassessment…!!!



53



54





55



• 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……..?

mistake proofing techniques

Documents

defects mistake proofing

defects defects

mistake proofing systemlean

role of mistake proofing

proofing pokayoke

idiot proofing

wrong information

wrong address