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Poka - Yoke
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This is known as µMISTAKE-PROOFING¶
From Japanese:
Yokeru (avoid)
Poka (inadvertent errors)
What is Poka-Yoke?
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What does Poka ± Yoke do?
Eliminates the cause of an error at thesource.
Detects an error as it is being made;
Detects an error soon after it has been
made but before it reaches the nextoperation.
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5 Elements of Production
Objects of Production (What?). Raw material, Finished
products, Semi ± finished products ± WIP.
Agents of production (Who?). People, Machines, Tools, Jigs,Incidental devices, Inspection equipments, Environment.
Methods (How?). Processing systems, Load & capacity,
processing conditions.
Space (
Where?). Left to right, Front to back, Top to bottom.
Time (When?). Process time, Production time, Task time.
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1. Errors Are Inevitable
People always make mistakes.
While we accept the mistakes as natural, we
blame the people who make them.
With this attitude, we are likely to overlook
defects as they occur in production.
They may be detected at final inspection, or worse still, by the customer.
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2. Errors Can Be Eliminated
Any kind of mistake people make can be
reduced or even eliminated.
People make fewer mistakes if they are
supported by proper training and by a production system based on the principle
that errors can be avoided.
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Inspection
One method of detecting errors isinspection.
There are two major types of inspection.
1. SAMPLING INSPECTION.
2. 100% INSPECTION.
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Sampling Inspection
In some factories, the attitude is:
³It may take all day to inspect all
product.There may be a few defects, butsampling is the most practical way to
check´.
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Sampling Inspection - Reflection
With sampling, there is a chance that an
error may go undetected.
Even if 1 part in 1000 is defective, the
customer who buys that part has a 100%defective product!
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2. 100% Inspection
In the best factories, the attitude is:
³We won¶t tolerate a single defect! We willorganize production so that 100% of the
product can be easily inspected´.
³That makes the most sense´.
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100% Inspection - Reflection
Even one defective product is enough to destroy a
customer¶s confidence in a company.
To stay competitive a company must supply good product in thousands.
The best way to achieve this is to organize
production to inspect 100% of the products.
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Finding Defects in the Subsequent
Process Since subsequent processes are also µusers¶ of
the product being manufactured, they are also
expert at finding defects.
If products are produced in a flow, each
product is sent to the next process as soon as it
is finished and defects are therefore foundimmediately.
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Two Strategies for Zero Defects
1. DON¶T MAK E IT!
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1. Don¶t Make It!
Don¶t make product you don¶t need.
The more you make, the greater the
opportunity for defects.
Follow µjust-in-time¶ principles by only making
what is needed, when it is needed in the amountneeded.
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2. Build Safeguards
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2. Build Safeguards
The user is an expert in finding defects.
Therefore build safeguards into the
production process.
Quality can be built into products byimplementation of Poka-Yoke.
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Errors & Defects
Humans make errors ± Cause. Defects arise, because errors are
made. (Effect).
It is impossible to eliminate errors from tasks performed byhumans.
Errors will not turn into defects if feedback and action at place
at the error stage.
Corrective measures can reduce occurrences of errors.
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Causes of Defects
Process Defects
1. Process failures ± Operational or procedural.
2. Process errors ± Incorrect or imprecise.
Product Defects
1. Incomplete product.
2. Sub ± standard product.
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Levels of Defects
Level 1: Defects shipped out of factory (Taylor
Methods).
Level 2: Defects within the factory (SPC methods).
Level 3: Defects reduced (Demming/ Juran methods).
Level 4: Defects kept within production stage
(Demming/ Juran methods). Level 5: Defects nor produced (Poke ± Yoke
method).
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3 Methods of Inspection
Judgment Inspection (Taylor¶s inspection that discovers
defects). Absolute inspection that discovers defects at the end of the
process. Leads to rework cost, scrap cost.
Informative Inspection (Shewhart¶s inspection that reduces
defects). I nspection process which reduces defects at the end of the
process using inner process checks.
Source Inspection (Shingo¶s inspection that eliminates
defects). I nspection built into the operation to detect errors before its
occurrence.
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Shingo¶s Method
Zero defects.
Zero wastes.
Zero delays.
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Ask Five Questions
Why? Describe.
Why? Describe.
Why? Describe.
Why? Describe.
Why? Response.
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Inspection with Poka Yoke
Source Inspection (ZQC)
± built into process
± leads to a zero defect Systems Self Check Informative Inspections (SQC)
± built inside or outside immediate process
± reduces defects to a minimum
Successive Check Informative Inspection (SQC)
± built inside or outside sequential process
± reduces defects to a minimum
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Thanks«