Equipment Efficiency: Quality and PokaYoke MistakeProof,

1
Equipment EfficiencyQuality and Poka-Yoke
(Mistake-Proof, ???)

• Operations Analysis and Improvement
• 2009 Spring
• Dr. Tai-Yue Wang
• Industrial and Information Management Department
• National Cheng Kung University

2
Presentation

• Shigeo Shingo developed a system to improve
  inspection tasks with the goal of guaranteeing
  100 quality for manufactured parts.
• Leading the charge toward a defect-free process.

3
Presentation

• This chapter will explain inspection processes
  based on mistake-proving (called Poka-Yoke).
• Complements Statistical Process Control (SPC).
• Poka-Yokes are visual and physical tools that
  should be utilized in conjunction with
  inspection.
• This concept will also be presented in this
  chapter.

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Introduction

• Poka-Yoke is part of the Just-in-time philosophy
  and key number 11.
• Poka-Yoke reduces the defect rate that is part of
  the OEE rate.

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Inspection and Statistical Quality Control

• Every production process generates defective
  products.
• The objective for all quality control systems is
  to reduce the number of defects produced.
• Types of defects.
• Isolated (a crack appeared on a product).
• Sequence (repetitive) defects.

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Inspection and Statistical Quality Control

• Product inspection is performed in order to avoid
  defective products from reaching the customer.

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A Taxonomy of Inspection

• Total or partial.
• 100 of the products or extrapolating a sample
  study.
• Statistical or not statistical.
• Based on statistical methods or not.
• Quantitative or qualitative.
• Number of elements or appearance of the product.

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A Taxonomy of Inspection

• Based on measures or based on functional trials.
• Numerical values or without measures.
• Sensory or physical.
• Through human senses or by means of devices.
• Subjective or objective.
• Evaluated by a person based on appearance or
  evaluated based on a specific measurable feature.
• Internal or external.
• Within the process or as an independent activity.

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Inspection and Statistical Quality Control

• Inspection should be able to identify defects.
• Develop a corrective action to eliminate the
  errors or more specifically the cause of the
  defects.
• Otherwise, inspection process will become a
  pointless exercise.

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Inspection and Statistical Quality Control

• Many years ago, it was believed that the only way
  of insuring the quality of all manufactured
  products was to inspect all of the parts - 100
  inspection.
• 100 inspection does not result in defect free
  products to the customer.

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Inspection and Statistical Quality Control

• To avoid this problem and reduce inspection cost,
  it is possible to duplicate the inspections.
• How many control stages would be necessary to
  guarantee the quality of the entire manufactured
  lot?

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Inspection and Statistical Quality Control

• Using this procedure, it is not possible to avoid
  product defects in an efficient way.
• Statistical quality control techniques (SQC) seem
  to be the right alternative.
• Some percentage of defects is always accepted.

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Inspection and Statistical Quality Control

• A high defect production rate (high defect level)
  can be deadly for a company well being.
• It is very important to eliminate or capture all
  defective parts before they reach the market.
• Shingo utilizes the term SQC.
• SQC is a term that today has become obsolete.
• SQC has been replace by SPC.

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From SQC to Zero defects

• Shingo introduced new ways of carrying out
  inspection processes that were based on SQC.
• The inspection process evolution should be
  similar to the historical evolution of these
  methods.

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From SQC to Zero defects

• SQC techniques are based on two principles.
• Evaluate (statistical samplings).
• Inform (feedback analysis until reaching the
  cause/process that created the defect).
• SQC implementation has two main problems.
• Do not guarantee the quality of all products.
• Because 100 of them are not inspected.
• Feedback and corrective actions are slow or in
  many cases do not even exist.

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From SQC to Zero defects

• Therefore, an inspection process, which is based
  on control charts, does not reduce the factory
  defective rate.
• It only detects defects.

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From SQC to Zero defects

• Shingo proposed two methods to avoid these
  problems.
• 100 inspection of the product utilizing
  Poka-Yoke devices.
• Accelerating feedback by self-checking
• Where production workers check their parts and by
  successive check systems.

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Poka-Yoke

• The Poka-Yoke concept was created by Shingo.
• fool-proof devices -gt Poka-Yoke
  mistake-proving
• To consider an inspection device as a Poka-Yoke.
• Ingenious, simple and cheap.
• Several Poka-Yoke devices can be found in our
  daily life activities.
• Recording protection window on floppy disks

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Poka-Yoke

• Poka-Yoke systems can be used in a company in
  order to mistake proof activities.
• Automatic part feeders.
• Poka-Yokes can reduce undesired workload
  components.
• It is possible to separate parts with different
  specifications.

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Poka-Yoke

• Poka-Yoke devices such as Go-no Go devices are
  utilized in order to avoid inspections based on
  trials.
• It is not always possible to design a Poka-Yoke
  to carry out 100 of the inspection.

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Self-check and successive check systems

• Self-check procedure.
• The worker who produces the part is the same
  worker that carries out the inspection.
• This system is the most efficient one.
• The worker obtains immediate feedback.
• Criticizing ones own performance may not be
  totally objective.

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Self-check and successive check systems

• Successive check.
• Next worker will typically conduct the inspection
  task.
• Can reduce the defect rate by as much as one
  fifth of the initial value in about one month.
• It is necessary to fix 2 or 3 check points.
• In the beginning of this checking procedure, the
  defect rate will increase.

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Self-check and successive check systems

• Sensory based inspections (scratches, painting
  quality).
• It is advantageous to place samples next to the
  checking point to show acceptable limits.

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Source inspection

• These techniques reduce the defect rate.
• Do not eliminate the error(s).
• Causal relationship between errors and defects.
• If the error source is eliminated, errors will
  never become defects.

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Source inspection

• Source inspection eliminated all the errors
  except the unnoticed errors.
• These unnoticed errors can be detected by an
  efficient use of Poka-Yoke devices.
• Types of source inspection
• Vertical -gt Before the process.
• Horizontal -gt Inside the same process

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Poka-Yoke design methodology

• Three suggested methods.
• Weight, the dimensions or the shape.

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Poka-Yoke design methodology

• The use of meters/counters, spare pieces method
  or a fixed sequence in the assembly process

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Poka-Yoke design methodology

• Use technology to design the Poka-Yoke devices.
• Contact mechanisms.
• Limit switches.
• Mechanisms without contact.
• Sensors.
• Meters/counters.

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Poka-Yoke examples

• Improper parts (extra material) can break or
  otherwise adversely affect the tool of the
  following process.
• The introduction of a mechanical blade stop can
  redirect the parts.
• It is possible to avoid the line from stopping by
  using a size limit Poka Yoke.

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Poka-Yoke examples

• Some templates (previously designed) eliminate
  the errors when adjusting the parameters before a
  process.
• By designing separate face covers for the proper
  product.
• The template patterns indicate the proper
  settings and values that should be utilized.

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Poka-Yoke examples

• A simple slot in the conveyor line can avoid an
  incorrect product.
• Without the utilization of a Poka-Yoke, filling
  material can be wasted and a major spillage can
  occur.
• With the Poka-Yoke the line will not stop and the
  improperly oriented parts will fall to collector
  box

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Summary

• The chapter had the primary objective to present
  one of the many quality related improvement
  tools The Poka-Yoke (mistake-proving devices).
  The Lean manufacturing philosophy considers this
  tool as one of the pillars to improve the overall
  equipment efficiency. The chapter has presented
  several examples of this kind of devices showing
  that in order for a device to be considered as a
  Poka-Yoke it must be ingenious, simple and cheap.