4 equipment efficiency quality

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Equipment Efficiency:Quality and Poka-Yoke (Mistake-

Proof, )Operations Analysis and Improvement

2010 Fall

Dr. Tai-Yue WangIndustrial and Information Management Department

National Cheng Kung University

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PresentationShigeo Shingo developed a system toimprove inspection tasks with the goal ofguaranteeing 100% quality formanufactured parts.

Leading the charge toward a defect-free

process.

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PresentationThis chapter will explain inspection

processes based on mistake-proving (called

Poka-Yoke).Complements Statistical Process Control(SPC).

Poka-Yokes are visual and physical toolsthat should be utilized in conjunction withinspection.

This concept will also be presented in thischapter.

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IntroductionPoka-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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1612119

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14 5

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Thinkingrevolution

The 5S

Standardoperations

One-Pieceflow

Poka-Yoke Jidoka

TPM

JUST IN TIME

W or k f or c e

o p t i mi z a t i on

V i s u

a l C on t r o l

LevelingProductionKanban

Multi-functional

workers

SMED

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Inspection and Statistical Quality

ControlEvery production process generatesdefective products.

The objective for all quality control systems isto reduce the number of defects produced.

Types of defects.

Isolated (a crack appeared on a product).Sequence (repetitive) defects.

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A Taxonomy of InspectionTotal or partial.

100% of the products or extrapolating a samplestudy.

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 InspectionBased 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 orevaluated 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

ControlInspection should be able to identify defects.

Develop a corrective action to eliminate the errorsor more specifically the cause of the defects.

Otherwise, inspection process will become a pointlessexercise.

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Inspection and Statistical QualityControl

Many years ago, it was believed that the only

way of insuring the quality of allmanufactured products was to inspect all ofthe parts - 100% inspection.

100% inspection does not result in defect free products to the customer.

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Inspection and Statistical QualityControl

To avoid this problem and reduceinspection cost, it is possible to duplicatethe inspections.

How many control stages would be necessaryto guarantee the quality of the entire

manufactured lot?

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Inspection and Statistical QualityControl

Using this procedure, it is not possible toavoid 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 QualityControl

A high defect production rate (high defectlevel) can be deadly for a company well

being.It is very important to eliminate or capture alldefective 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 outinspection processes that were based onSQC.

The inspection process evolution should besimilar to the historical evolution of these

methods.

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From SQC to Zero defects

Therefore, an inspection process, which is based on control charts, does not reduce thefactory defective rate.

It only detects defects.

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Poka-Yoke

The Poka-Yoke concept was created by Shingo.“fool - proof devices” -> 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 ourdaily life activities.Recording protection window on floppy disks

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Poka-Yoke

Poka-Yoke systems can be used in a company inorder 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 areutilized in order to avoid inspections based ontrials.It is not always possible to design a Poka-Yoke tocarry out 100% of the inspection.

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Self-check and successive checksystems

Self-check procedure.The worker who produces the part is the sameworker that carries out the inspection.

This system is the most efficient one.The worker obtains immediate feedback.

Criticizing one’s own performance may not be totallyobjective.

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Self-check and successive checksystems

Successive check. Next worker will typically conduct the inspectiontask.

Can reduce the defect rate by as much as one fifth of theinitial 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 willincrease.

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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 becomedefects.

Error Defect Information

Feedback

Error Information

Feedback

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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 piecesmethod or a fixed sequence in the assembly

process

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Poka-Yoke design methodology

Use technology to designthe Poka-Yoke devices.

Contact mechanisms.Limit switches.

Mechanisms without contact.

Sensors.Meters/counters.

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Poka-Yoke examplesImproper parts (extra material) can break orotherwise adversely affect the tool of the

following process.The introduction of a mechanical blade stop canredirect the parts.It is possible to avoid the line from stopping byusing a “size limit” Poka Yoke .

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Poka-Yoke examples

A simple slot in the conveyor line can avoid anincorrect product.

Without the utilization of a Poka-Yoke, filling materialcan 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 oneof the many quality related improvement tools: The

Poka-Yoke (mistake-proving devices). The Leanmanufacturing philosophy considers this tool as oneof the pillars to improve the overall equipment

efficiency. The chapter has presented severalexamples of this kind of devices showing that inorder for a device to be considered as a Poka-Yokeit must be ingenious, simple and cheap.