Controlling defects on operator dependent operations

Six Sigma – iSixSigma Forums Old Forums General Controlling defects on operator dependent operations

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    Marco A

    Hello, I’m new at this and I’m looking for information and guidance regarding control and measuring (inspection and monitoring) of an assembly process that is highly operator dependent. 
    In Mexico, due to the cheap labor we have processes that are over 90% manual and very repetitive for the operators.  Most of the operations on the line are bonding PVC tubing to PVC components (typical medical device).  Current inspection methods (based on ISO Z1.4-2003) seem more of a waste of time than help.  Field failures are low (20 to 30 PPM)  I want to find ways to reduce to under 10 PPM
    Any ideas, experience, resources (literature, benchmarking, etc)?  Let me know.  
    M. Araya


    Reddy M

    The ppm can be driven down if each defect is traceable to a particular operator. In another word your need to have an excellent traceability system. Try to implement Poka Yoke system so that simple mistakes can be avoided.



    Dear Marco,
    I work in India, where the conditions are almost like in Mexico.I feel you are already doing a very good job.In order to achieve further, you may follow a little different path.
    Pl. do a Parreto analysis of warranty returned parts as per faillure modes.Do the engg. analysis of the failed components.
    Study the processes,which lead to these failure.Introduce poka yokes at these places.
    When there is worker related skill dependent operations, it is best to introduce low cost Poka yokes.
    With regards,



    This is in reponse to your query posted on the net. We are also engaged in a situation similar to yours. Youe have mentioned that the quality inspection seems to be more of a waste than of any substantial help.
    The failure at site is low, as you have said. I think that the occuring failure that you face may be due to long time that one particular induvidual in the assembly line may be sitting at his alloted post. If the personnel are rotated, i mean, if they are assigned to a new area every day and each area of the plant to come in a rotation, this problem has a good chance of being reduced. We have a total of five completely different posts in our plant, and we were facing the same problem. We tried to rotate the job assignment every day, so that one particular induvidual comes to one area not more than twice a week. And we were able to acheive a substantial imporovement.


    Abul Faisal

    We also have a manufacturing line in which inspection is manual. We are also rotaing the people in the Inspection activity after every one hour. In our process there are 3 to 4 check points and then packing . We used to rotate the operaorts after every batch is run. It was too long it was about 2.5 hours to complete a batch.
    We conducted a study to find out what is the optimum time after which defects start to creap in. We set the time for inspection as 2.5 hours , 2 hrs, 1.5 hrs. and 1 hr and after the job is completed we did sampling Inspection of the job to detect any defects passed in the initial 100% inspection. After getting the data for 3 months we found out that if we keep the oprator beyond 1 hr the defect rate used to incease .
    After the changes were made there was considerable decrease in the defects.
    Wish you good luck,

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