iSixSigma

DPMO

This topic contains 20 replies, has 11 voices, and was last updated by  CT 10 years, 8 months ago.

Viewing 21 posts - 1 through 21 (of 21 total)
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  • #51875

    JJ LEE
    Participant

    How can I define/measure the possibility of error for the DPMO calculation?
     

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    #181375

    Tuguchi
    Member

    Through brainstorming by SMEs in your business!

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    #181376

    JJ LEE
    Participant

    But it is no guarantee for a complete gathering of all possibilities. Is this correct? Consequently the six sigma value could be differently for brainstorming

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    #181378

    Tuguchi
    Member

    Yes
    That is correct!
    Good Luck

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    #181385

    BTDT
    Participant

    JJ-LEE:We have been asked to do this a few times, so we usually include a control chart of some kind with the calculation. The stakeholders can see if the defects are increasing, decreasing, or relatively constant.Our usual result is that it is constant. This allows us to ask the question, “What is likely to happen if we do not do this project?” This gets us some buy-in from the team to support the project.For the real numbers people, you can estimate plus-minus 2 standard deviations from the control chart and state that 95% of the time the defect rate or count will be between these two limits.Cheers, AlastairP.S. – I have only been asked to give a confidence limit on a Sigma level once in over ten years. Don’t worry about it.

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    #181390

    Mike Carnell
    Participant

    JJ-LEE,
    Calculating the “possibilities of error” has nothing to do with calculating DPMO. It works off the opportunities to do something correctly in the denominator and actual defects in the numerator. If it is an assembly type operation it is goint to be pretty close if you take the number of parts (the opportunity to get the correct part) and the number of connections (each connection can be done correctly once). It has nothing to do with the possible ways you can do it incorrectly. That is playing the game of increasing the denominator to make a poor capability look good. Improvement is about reducing the size of the numerator.
    DPMO, assuming it has some volume and complexity, isn’t a particularly sensitive number. Do your calculation then change the denominator by +/- 10% and you will find it doesn’t move much particularly if you are converting it to sigma.
    Just my opinion.

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    #181452

    Jonathon Andell
    Participant

    AMEN!!!

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    #181459

    Mike Carnell
    Participant

    JJ-Lee,
    An example just to make it clear. Assembling a bolt with hardware.
    Parts: 1 bolt, 2 washers, 1 lock washer, 1 nut (5 parts – 5 opportunities – correct parts)
    Assembly: one washer on the bolt, insert the bolt & washer into the correct hole, add one washer, add one lock washer, add one nut (5 assembly operations – 5 opportunities)
    Total opportunities 10.
    It doesn’t matter if I can find 100 different size washers, 20 different size bolts and 50 different size nuts that are the incorrect size (possible defects) – is is still only 10 opportunities because it is the opportunity to do it correctly.
    Where Motorola had issues with opportunities was in solder joints particularly on plated through holes where there is flow through from one side to the other. Some wanted to count the joint on one side and then the other side. The soldering operation forms both sides while being done from one side of the board so soldering is only 1 opportunity. It doesn’t matter that a solder joint can have excess, insufficient, cold, poor wetting to the pad, poor wetting to the lead, non-wetting to the board, non-wetting to the lead pinholes, pits, voids, etc. it is still 1 opportunity to form a solder joint correctly.
    Just my opinion.

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    #181462

    DPMO King
    Participant

    It is always better to inflate the count to improve the sigma level.
    Reporting bad numbers causes bad things.

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    #181463

    Chris Seider
    Participant

    Too bad there are way too many Six Sigma “lite” guys spreading the false word about opportunities being a chance of a defect. 
    The reason most don’t understand the power of DPMO is most people don’t have organizations that use this technique to pick projects along side financial impact.  The true power is capture defects involving reworking also…..easier in some industries. 

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    #181464

    Nik
    Participant

    I agree. I’ve found 3 strategies for determining opportunities and no definitive method:

    Any process step that changes the form fit or function of the thing being worked is an opportunity for an error.
    Every measurement or aspect inspected is an opportunity for an error (sometimes referred to as an “active” method).
    Number of parts plus the number of connectors (“passive” method).
    3 strategies, pick the one that works best for your system. Don’t go crazy with the counts: too few or too many.
     

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    #181465

    Chris Seider
    Participant

    Mr. Carnell is going to love how you agreed with him but then gave 2 of 3 scenarios that don’t align with his posting.
    Let me just think of a process step that changes the fit or function.  A retail outlet stores its milk in an unrefrigerated environment for non aseptically stored milk.  That milk spoils so the fit of the milk has changed….this is NOT an opportunity.  It is a defect caused by a non-value added step that adds no opportunities.
    Inspection does NOT add value unless it changes the fit or form simultaneously–quite rare.

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    #181467

    Ron
    Member

    At Allied Signal we used a simple formula… three times the bill of material…  that was how we calculated DPMO.
    What you are actually looking for is the rate of improvement..so lock in on a methodology that works for you, standardize it across your company..don’t worry about what someone did 20 years ago and go forward.
     
     

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    #181475

    Nik
    Participant

    To clarify, Mr. Carnell’s answer was just one of the 3 methods I’ve run into, the other two were offered in case that scenario did not seem like a good fit to the original person posting.
    The phrase regarding changes to “form, fit, or function” is used to help identify value added steps where the inputs (material, information, equipment, etc.) were modified to bring it closer to the final form for the customer (that thing of value). Obviously, steps pertaining to storing milk in an un-refrigerated space is not an opportunity, and although the milk has changed (now “scrap”) that wouldn’t constitute a value added change of “form, fit, or function” expressed in the original post. However, there are value-added steps in that process which avail the system to the opportunity of that defect occurring, which could be counted.
    Inspection does not create quality, it ensures it, and in most cases is non-value added (there are some cases where the inspected product is of more value – separate topic). However, this technique allows for utilizing naturally occurring defect reviews (inspection) with the (hopefully) the value-adding aspects being inspected. The assumption here is that the value-added aspects are being inspected and each one of them is an opportunity for a defect. This does catch the problem after it occurs and makes it difficult to flag which step exactly created the issue. However, it does avail itself to possibly more frequent and easier data collection when other methods are impractical.
    There is little agreement in industry on any one solid method for determining opportunity counts. With metrics, the critical thing is that the data guides you toward action and most importantly improvement.

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    #181476

    Chris Seider
    Participant

    I understand what you are saying but I can come up with infinite opportunities IF I defined it as a chance to make a defect.  If I drop a product from one station to the next, do I get an opportunity?  Do I get an opportunity for each 10 feet….where does it go?
    I’ll stick with 1. transforms the product or service and 2. the customer is willing to pay for it and 3. not rework. 
    I do agree….let’s drive results that impact the bottom line. 

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    #181477

    ?
    Participant

    Pretty amazing when the supposed Masters of the Masters can’t even agree on a basic metric definition. Begs the question – so who really are the Masters?

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    #181479

    Mike Carnell
    Participant

    Nik,
    Your first proposed process:
    “Any process step that changes the form fit or function of the thing being worked is an opportunity for an error.”
    It has nothing to do with errors in the denominator (counting opportunities) that is the numerator.
    Your second proposed process:
    “Every measurement or aspect inspected is an opportunity for an error (sometimes referred to as an “active” method).”
    This makes absolutely no sense at all since you are increasing non-value add work to increase the opportunity count to drive down DPMO.
    Just my opinion.
     

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    #181480

    Mike Carnell
    Participant

    Ron,
    Two issues with your post. You are speaking as if you know what was done everywhere in Allied. I was part of the consulting group that was at Allied Automotive and we did not do it that way.
     You second comment: “..don’t worry about what someone did 20 years ago and go forward.” Allied started in 1995 so that was 14 years ago what is the difference?
    Just my opinion.

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    #181492

    Jonathon Andell
    Participant

    What scares me is that the erroneous approach (each error type being counted as an opportunity) actually showed up in training materials from a “big house” consulting firm that has an OK reputation. Saw the error with my own eyes.

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    #181493

    Chris Seider
    Participant

    2 concepts in demonstration (or lack there of) with your comment
    Continuous improvement…..and control plans
    Don’t be scared…..1.  Just remember that very few organizations actually use DPMO for project selection and 2. As long as an organization is consisent in its approach (some would argue my advocated one is wrong), then the name of the game is to reduce the numerator and DPMO is rarely discussed outside an organization’s walls. 
     
     

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    #181495

    CT
    Participant

    This is ok for internal focused measures but if your wanting a DPMO for your customer. Then have the opportunity of 1 and your defect is everytime you send them something with any error on it.
    This is what the customer feels so should be what you measure.

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