Process Monitoring through Six Sigma

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    I am a quality person and now I am in the job of implementing various statistical techniques and Six Sigma in our Process(I am not GB or BB ). Now I  have small doubt regarding application of Six Sigma in process monitoring.
    Our unit is  ISO 9001:2000 certified company. We have been implement a system for Monitoring process which is one of the requirement of new ISO version of Monitoring & Measurement of process(Cl:8.2.3).We have identified various area which directly affect Customer Satisfaction as well as Organization performance.
    Example : One of the process identified is “ Reply to Customer on Negative Feed back “.This process we have fixed lead time for comparing Actual time of the process.
    Ie Analysis of Customer feed back & Preparation of Report      :   8 hr
       Report given to Marketing Dept                                          :  4 hr
       Reply from Marketing to Customer                                      :  4 hr
      Total time req                                                                    : 16 hr
    Ie for any complaint we have to reply with in the time frame  of 16 hr to customer. But in the practical situation there may be some deviation in the time. This will be  monitor in Management review and accordingly actions are initiated. .
    For Example  we have replied 3 feed back to customer in the time frame of 20hr, 30hr & 40 hr.
    Ie Average time taken for sending reply to customer  =  ( 18+25+22)/3 = 21.67
        Allowed time                                             = 16 hr
        No of Hour loss                                                    = 21.67- 16 = 5.67
        Process loss%                                                      =  5.67/16=35.5%
        Yield %                                                                = 100-35.5       
        Six Sigma level                                                       = 1.875
    Whether I am in the write direction. Or if any other is method is there for calculating Six level of process for monitoring.
     If Yeild % is 64.5 or Sigme level is 1.875 How to interpet with this to process.
     Please let us inform.



    Your data shows three opportunities (three responses to give the customers). In each case, you were over your upper statistical limit. That means that you have three defects associated with those three opportunities. Your process sigma is zero, or actually below zero — you have a negative sigma!



    Thank you for your quick response..Here my question is how to calculate Sigma in such situation.How you have derived zero Sigma or Negative Sigma.Can you give the calculation.Any other method for deriving Process Monitoring


    Logan Luo

    The setup of your monitoring system is wrong. From your example, the monitoring system does not catch any valuable data and monitor the right parameters. You should measure and record the process performance – defect/reason for losing time, not only the process output – total hours loss.  I have seen similar problems in manufacturing industry that made the SPC go nowhere.
    Here are my suggestions:
    1) Develop a process map and identify opportunity for a defect for each step.  In your case:
    Step 1: Analysis of Customer feed back & Preparation of Report      USL  8 hr   Opt: 1 (I assume you need to conduct only 1 analysis in this step)
    Step 2 Report given to Marketing Dept                                          USL  4 hr   Opt: 1
    Step 3: Reply from Marketing to Customer                                      USL  4 hr  Opt: 1
    USL- upper specification limit
    2) Record defect in each step. I would suggest that you use a Traveler. Here is a Traveler would look like if you had one.
    Complaint 1
    Step #                          Total Time        USL     Lost Hour         Defect QTY
    1                                  10                    8          2                      1 (reason for losing 2 hr)
    2                                  5                      4          1                      1 (reason for losing 2 hr)
    3                                  5                      4          1                      1
    3) Do the same thing for each complaints or random selected complaints
    4) Now your can calculate DPMO, Yield and Sigma Level to represent your process performance. You can calculate these measurements in daily, weekly, monthly or annual basis.
    Complaint 1 Performance:
    DPMO= Total Defect/Total Opp =(3/3) *10^6= 1*10^6
    Yield= 1- (Total Defect/Total Opp)= 1-(9/9)=0%
    Sigma Level= -infinity Z
    Assume Complaint 2 and 3 are the same as Complaint 1
    Daily Performance:
    DPMO= (9/9)*10^6=1*10^6
    Yield= 1- (Total Defect/Total Opp)= 1-(9/9)=0%
    Sigma Level= -infinity Z
    5) Issue corrective action request to improve the weakness links.
    I have made lots of assumptions in your case in order to demonstrate what are going wrong in your monitoring system. I have a computer program, which will do all the works mentioned above. Send me an email at [email protected] if you want to try it or talk more about your case.


    Rick Pastor

    Point 1:  A the top right hand side of this page there is a sigma calculator. 
    Point 2:  I “like” Logon Luo description of what you need to do.  I would like to add that you probably have more opportunities for creating a defect than three.  Each opportunity is a potential point of improvement.   
    Point 3: The calculation of a sigma level is not very important if all that you ever processed was three replies ‑‑  “ Reply to Customer on Negative Feed back.”  Let me extend Logon’s example:  Suppose you processed 100 total replies and you had the 9 defects owing to the three replies that you used in your example.  What would your DPMO and sigma level be?  As you map the process per Logon’s recommendation locate other opportunities in which defects can be introduced. 
    Point 4:  Based upon the three steps, you might think about obtaining a yield and sigma level for each step.  Then you have to think about rolled throughput yield.
    Have fun!!

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