Process Sigma calculation

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    I’m in a transactional, not a manufacturing, environment. We take complex machines manufactured by another entity and prepare them for sale to the end user. In the make ready process we use a checklist of 30 items to inspect or test, and make adjustments or repairs as needed prior to delivering the product to the end user. We do this make ready for about 1600 machines per year.
    1- how would I calculate the Sigma quality level to report back to the manufacturer, based on the number of repairs or defects we find in the make ready process?
    2- how can I calculate the Sigma quality level of our make ready process based on warranty repairs on machines delivered to customers?
    3- my Black Belt training focused on the process sigma, as indicated by rolled throughput yield. Since we are not the manufacturer, should I be looking at something else, like the number of warranty claims per machine or model family?



    First of all, you have to identify the VOC and then link it to your process metric. Once you define your process metric, you should be able to measure it and then calculate DPMO, which will indicate the sima value of your process.
    For calculating the sigma value you can use the following method:
    – Capture information on defect reported by the customer for each equipment. Using this information you can calculate the DPMO and refer the Z-table to get th sigma value. This is the sigma value of overall product.
    – Out of the total defects reported by the customer, categorise them into 2 types:  a. Ones which have been originated in ur processe and b.Ones which have originated in the suppliers process.
    Based on the above categorization, you can calculate the DPMO for the supplier end process as well as your process. You can also include the defects, which have been repaired or detected in the processes, which will indicate the true value of the process.
    Whatever metric you decide, you should be able to link it to end customer metric. This is importnt, because that will help you to validate the impact on the end customer due to improvement done in the individual processes.
    All the Best!

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