Six Sigma Common Causes and Special Causes

LEAN SIX SIGMA PART…. 22 MARATHON STUDY

‘’In my last article, we learned Six Sigma DMAIC Process - Improve Phase - Screen Against Musts and Wants

Please read along as we attain another height in PART..22..

We progress by understanding Six Sigma Common Causes and Special Causes

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Six Sigma Common Causes and Special Causes

Six Sigma DMAIC Process - Control Phase - SPC - Out of Control

A process is said to be out of control if:

???????? One or more data points fall outside the control limits

???????? Seven consecutive data points increasing or decreasing

???????? Eight consecutive data points are on one side of the average

???????? Fourteen consecutive data points alternating up & down

???????? Two data points, out of three consecutive data points, are on the same side of the average in zone A or beyond

???????? Four data points, out of five consecutive data points, are on the same side of the average in zone B or beyond

???????? Fifteen consecutive data points are within zone C (above and below the average)

Six Sigma Out of Control Charts-1

Six Sigma Out of Control Charts-2?

Six Sigma DMAIC Process - Control Phase - Leading Indicator vs

Lagging Indicator

While interpreting control charts we also talk of two indicators:

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Leading indicator:

A leading indicator shows the trend before the defect occurs. For example, you may be able to see a trend of six downward points. This is a leading indicator that the process will produce a defect outside the lower control limit.

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Lagging indicator:

A lagging indicator is an outlier that is already outside the upper or lower control limit. This is a lagging indicator that the defect has already occurred in the process.

Six Sigma DMAIC Process - Control Phase - Control Chart Selection

Points to keep in mind while selecting a control chart:

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Continuous Data: For continuous data, we can measure the average and the variation, thus X bar &R (Range) or X bar and S (Standard deviation) can be used.

Attribute Data: For Attribute data we first have to determine what are we measuring – Defects or Defectives. In case we are capturing defective data then determine if we are sampling for subgroup of equal sample size or not. In case if we are capturing data for defects then determine if the opportunity for the defects are the same for each subgroup or not. Based on the above we need to select the appropriate chart.

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Six Sigma Control Chart Selection Guidelines

Six Sigma Control Chart Selection – Continuous Y

Six Sigma Control Chart Selection – Discrete Y

Six Sigma DMAIC Process - Control Phase - Risk Assessment and Mistake proofing - Poka Yoke

Risk needs to be assessed on the “should-be” process to make the implemented solution more robust. Risk assessment of the new improved process makes sure that any potential effects of the possible failure modes do not result in loss of “holding of gains” over a period of time. Two key techniques to assess risk and make sure that no possible failures occur post-control phase are:

???????? Failure Modes and Effects Analysis

???????? Mistake Proofing (or Poke Yoke)

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Mistake Proofing – Poke Yoke:

Mistake proofing or poke yoke (derived from two Japanese words poka – inadvertent errors and yokeru – to avoid) helps de-link the Y’s from the X’s. Mistake-proofing eliminates the potential for a problem to happen.

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The key mistake-proofing techniques are:

???????? Shutdown – Shutdown or stop a process immediately on the occurrence of a failure

???????? Control – Eliminate the occurrence of failure in a process

???????? Warning – Proactively notify the occurrence of failure in a process before it occurs

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The three methods for prediction and detection approach are:

???????? Contact????? method????? – Contact with the part in the process highlights the errors

???????? Fixed-value method – Errors are detected in the process through counting

???????? Motion-step??????? method????? – Errors are detected by a motion or lack of it in the process

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Six Sigma DMAIC Process - Control Phase - Control and Implementation Plans

The four techniques used for process control plans are:

???????? Standardization

???????? Documentation

???????? Monitoring Plan

???????? Response Plan

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Standardization:

Standardization of the “should-be” process steps is required to ensure all responsible for execution have the same understanding. Standardizing the should-be process helps answer queries like:

???????? What are the steps in the process?

???????? Who does these steps in the process and when?

???????? Where more detailed work instructions can be found?

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Documentation:

Documentation is a necessary step to insure that the learning gained via improvement is institutionalized and shared across the team by having it documented with proper work procedures. Often the live processes have a tendency to evolve in an ad-hoc manner. How to accomplish each process activity is usually left up to the individuals and thus, much of the organizational knowledge resides only in the minds of all those responsible for execution. Procedure: A procedure is the documented sequence of steps & other instructions necessary to carry out an activity for a process.

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Monitoring Plan:

Monitoring: It helps detect changes as and when they occur in the process and assure that improvements continue to hold for us to be able to meet customer requirements over a period of time. While observing a process a monitoring plan helps define:

???????? Key process and output measures for ongoing measurement of the improved process

???????? When data is to be collected and at how often

???????? Define the method for gathering, recording, and reporting data on the measures

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Response Plan:

Response plan helps identify the next steps on what needs to be done if one detects a change in the process while monitoring. For each of the measure in the monitoring plan, the response plan helps define:

???????? What actions will be taken for an out-of-control event occurrence with a timeframe for the action

???????? Who takes action based on the monitoring data

???????? Where to find trouble-shooting procedures to fix problem

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The key elements of a full scale implementation plan are:

???????? Clear Objectives

???????? Pilot Learning's Incorporated

???????? Implementation Milestones

???????? Resource Needs

???????? Influence Strategy

???????? Implementation Budget

???????? Process Control Plan

???????? Process Documentation

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Thanks For Learning With Maxwell Stay close for part ,,,,23,,,,,

Next we shall study Six Sigma DMAIC Process - Control Phase - Review and Sign-off.