STM Quality
Limited
Poka-Yoke
TOTAL QUALITY MANAGEMENT
Poka-Yoke
©©ABSL
Power Solutions
STM Quality
Limited 2007
What is Poka-Yoke?
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 This is known as ‘MISTAKE-PROOFING’
 From Japanese:
 Yokeru (avoid)
 Poka (inadvertent errors)
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What Does Poka-Yoke Do?
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 Eliminates the cause of an error at the
source;
 Detects an error as it is being made;
 Detects an error soon after it has been
made but before it reaches the next
operation.
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Are Errors Unavoidable?
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 There are two approaches to dealing
with errors:
 1. ERRORS ARE INEVITABLE!
 2. ERRORS CAN BE ELIMINATED!
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1. Errors Are Inevitable
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 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
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 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
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 One method of detecting errors is
inspection.
 There are two major types of
inspection.
 1. SAMPLING INSPECTION.
 2. 100% INSPECTION.
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Sampling Inspection
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 In some factories, the attitude is:
 “It may take all day to inspect all
product”.
 “There may be a few defects, but
sampling is the most practical way to
check”.
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Sampling Inspection - Reflection
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 Think about sampling.
 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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Sampling Inspection - Reflection
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SAMPLING INSPECTION MAKES
SENSE ONLY FROM THE
MANUFACTURER’S VIEW, NOT FROM
THE CUSTOMER’S!
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2. 100% Inspection
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 In the best factories, the attitude is:
 “We won’t tolerate a single defect!”
 “We will organize production so that
100% of the product can be easily
inspected”.
 “That makes the most sense”.
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100% Inspection - Reflection
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 Think about 100% inspection.
 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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The User Is The Best Inspector
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 No one intends to make mistakes.
 While we are working, errors can show
up without us noticing.
 How can we catch these errors before
they turn into defective products?
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Finding Defects in the
Subsequent Process
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 We don’t expect to find defects, but if a
product we use doesn’t do what it is
supposed to do, then we know it is
defective.
 Users are the best at discovering
defects!
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Finding Defects in the
Subsequent Process
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 Since subsequent processes are also
‘users’ 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 found immediately.
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Two Strategies for Zero Defects
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1. DON’T MAKE IT!
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1. Don’t Make It!
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 Don’t make product you don’t need.
 The more you make, the greater the
opportunity for defects.
 Follow ‘just-in-time’ principles by only
making what is needed, when it is
needed in the amount needed.
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Two Strategies for Zero Defects
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2. Build Safeguards
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2. Build Safeguards
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 The user is an expert in finding defects.
 Therefore build safeguards into the
production process.
 Quality can be built into products by
implementation of Poka-Yoke.
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Poka-Yoke Devices
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 Human errors are usually inadvertent.
 Poka-yoke devices help us avoid
defects, even when inadvertent errors
are made.
 Poka-yoke helps build quality into
processes.
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Poka-Yoke Devices
– Error Detection and Alarms
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Poka-Yoke Devices
– Checklists
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Poka-Yoke Example
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 It is possible to mount the blank the
wrong way onto the pierce tool.
BLANK
PIERCED BLANK
INCORRECT
 As the blank can fit the pierce tool in
many ways, how can this be prevented?
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Poka-Yoke Example
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 By fitting a block into the pierce tooling,
the blank plate can only go on one way.
BLOCK
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Poka-Yoke
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Limited
POKA-YOKE
MEANS
ZERO DEFECTS
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