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First Pass Yield

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  • #48742

    corona91719
    Participant

    Trying to calculate first pass yield but have a question. We test various units that require adjustments in regards to rig, free pins, tensions, etc. to pass. Would having to make one of the aforementioned adjustments constitute a failure?
    Thanks

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    #165221

    Dr. Scott
    Participant

    Yes.
    Regards,
    Dr. Scott

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    #165222

    Brandon
    Participant

    Corona, Dr. S is correct. Anything that comes off the line and is not ready “box & ship” is a defect.
    Clearly your first pass yield “number” will suffer for this but isn’t that the point. You are seeking quantification and identification of the defects so you can fix them.
    Don’t worry about how bad things “are” – worry about them staying that way. Look at it this way – you have plenty of opportunties to improve performance and get a huge raise and bonus. 

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    #165223

    Heartland
    Participant

    I almost agree with Dr Scott –
     
    If your process is designed to have an installation step (where no attempt to achieve the correct values is made) and a step to make the adjustments (what you refer to as “test”) – then I would say that it is part of your process as designed and not a failure.  I would, of course, re-design the process so that the install step produced the correct measurements – Then any adjustment would be failures as far as 1st pass yield was concerned.

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    #165226

    Ward
    Participant

    Brandon, I wish more people understood that uncovering and studying defects is a good thing! Early in my career, I had a Japanese professor who said, “When it comes to improving quality, you can’t be afraid to open your kimono!”

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    #165227

    GB
    Participant

    Heartland, an in-process “test”, whether planned, or not, is symptomatic of a lack of trust in the orig process, and done as a correction.    Therefore it IS a defect.
    Dr. Scott is right on.

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    #165228

    Heartland
    Participant

    HBGB B^2
     
    Usually your statement is correct, but not always.  We (used to) have a product that was installed through the use of large amounts of heat (think similar to welding).  During the install the heat changes the characteristics of the item being installed.  Tuning was done as second and separate step in the process.  The process performed exactly as designed – no defect.  The process was (I readily admit) not a good process and it has since been changed such that the heat from install is reduced, the item is shielded and no adjustment is needed.  If you re-read my post you will notice that I called it an adjustment and said the original post called it a test.  I made this distinction because in our original process the adjustment step was also called a “test”.  I am only trying to give an example of how one size does not fit all.  Not make a specific recommendation to this situation.  I would hate for good advice (such as Dr Scott’s) to be applied regardless of ALL of the facts.  Again I do not know if this situation in any way mirrors the one I described, but I stand by my 1st post for the reasons stated.  BTW I agree if it is a test then it is a defect – no questions.

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    #165229

    corona91719
    Participant

    Thanks for the very informative responses. You are correct as the initial thought is that the numbers are going to look terrible. And they do!! I don’t know about the raise and bonus :-)

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    #165230

    GB
    Participant

    The fact that your process allowed heat to change the product characteristics  is symptomatic of a defect.  Your subsequent Process improvement (shielding) serves to mitigate/eliminate the defect.
    the pre-change process FPY would be lower than post-change, no?
    When a widget, or transactional vehicle passes through a process and any “tweaking” is needed to influence the meeting of specs, that is a defect, or source of variation and thus impacts FPY.
    I think we are aprox on the same train of thought, just differing in level of in-process/out of process focus.

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    #165233

    Heartland
    Participant

    HBGB B^2
     
    I agree we are not for off from one another.  For the example I gave I still believe that the adjustment is not a defect – here’s why
     
    Think of the adjustment as a step in the defined process such as bolting on a widget.  The tuning or adjustment in question is to select the correct channel on a multi-channel piece of equipment.  Without the adjustment (takes a few seconds) we would need to stock approximately 200 additional SKUs and custom build each unit.  The process (as it was) had the tuning/adjustment step after install due to heat impacting the product.  We re-designed the process and tuning/adjusting is now done prior to install, but it is still done.  So why change the process?  The impact of the heat WAS causing a defect (not the tuning) – the defect was a cracked part.  We had about 4.83% reject due to cracked parts 0% reject due to tuning/adjustment.  Post re-design we dropped the cracked part defect to less than 0.05% so yes or post FPY is better than the pre FPY, but not due to the tuning step.  All I was trying to say is look at the specific situation to be sure you calc FPY correctly.

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    #165234

    corona91719
    Participant

    It can get confusing. The example that comes up is a TV. It has controls that allow you to change settings. Factory settings are not always optimal. Is this a failure? Or is the fact that you have controls that allow you to make adjustments for the optimal picture make it acceptable?

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    #165235

    Brandon
    Participant

    Good question Corona. That’s what you & those you work with will have to decide. Is the resultant variation something that can be removed? What are your spec limits based on customer demand? Etc?
    We don’t know enough about your process – nor can we.
    All I can say is SS gives you tools to remove variation if that is needed or merited.

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