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As we have already discussed about DMAIC (Define-Measure-Analyse-Improve-Control) phase of Six Sigma in my previous articles in this paper we will discuss about the formulas and the deliverables of the measure phase of Six Sigma.
Before proceeding ahead a brief recap of the Measure phase. Every organization measures various performance parameters during the course of the day to access whether their plans are working and achieving the desired results. If there are no measurements it will be not possible to know whether the organization is meeting customer requirement and making profits. At the same time it is not economical to measure every activity and control all the parameters. When there is a specific problem in the organization to be eliminated the first step is to measure the extent of the problem. Measurement of key performance parameters of any process is a key to find solutions and eliminate the problem in the process. During measure phase the performance of the current process is measured to identify the problem area.
We ask the following questions given below in measure phase:
In Measure phase we will be faced with 2 types of Data that is 1] Continuous Data 2] Discrete Data.
Continuous data are the data which are measured to the finer elements and expressed in units of physical property such as length, height, diameter, temperature and weight and Discrete data is that data which cannot be measured these are data regarding characteristics like colour, odour, and count data such as pass/fail.
To measure data to improve the process of a part manufacturing factory we should also determine the sampling plan from the sampling types such as 1] Simple random Sample here the lot we collect is homogeneous that is from the same category. 2] Stratified Sample this is a refined method of random sampling where the lot is segregated based on certain criteria from a heterogeneous lot. 3] Systematic Sample in this samples are taken after every fixed interval of time when the machine produces the part 4] Rational Sample is done when the team finds there are large numbers of data already existing, it is possible to identify a critical area from the past records and collect samples only from specific area.
Formulas used in Measure Phase:
Calculate the Process Capability – Process Capability is measured by comparing the variation in the product to the upper and lower specification limits, assuming that the product mean value is exactly centred between the upper and lower specification limits
The process capability is calculated using the formula CP = USL-LSL/6 * Standard Deviation where CP = process capability index, USL = Upper Specification Limit and LSL = Lower Specification Limit.
The Process capability measure indicates the following
When the process is spread well within the customer specification the process is considered to be fully capable that means the CP is more than 2.In this case, the process standard deviation is so small that 6 times of the standard deviation with reference to the means is within the customer specification
The Deliverables of the Measure are given in the table below:
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Project Stage |
Deliverables |
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Measure |
Detail Process Map with points at which to gather data |
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Data collection forms |
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Measurement tools, include gauge R&R studies |
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Data on the Process |
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Process capability and Six Sigma Calculation |
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Cost of Quality |
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Project Status Form |
It is very important to know that if the process is found to be stable using Capability Analysis formulas and by Gage R&R Study we can directly move to the Improve or control Phase else we have to start again from Define Phase.
The Author Suresh .V. Menon is a Certified Lean Six Sigma Black Belt accredited by IASSC and is also a Subject Matter Expert on ERP who has been working in various capacities as Test Manager, ERP Consultant, Principal Consultant-QA, and Project Manager & Six Sigma Consultant.
