iSixSigma

RTY

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  • #44399

    Tim Krall
    Member

    When calculating RTY, is it valid to count waiting for material as a defect.  It is definitely a form of waste, but should it be considered as a defect?

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    #142135

    Simon Wei
    Member

    Tim,
    It depends on your project objective.
    More conditions of your project I think is helpful for other guys support you here.
    Best regards,
    Simon

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    #142143

    michael spearman
    Participant

    Wait time can be a defect if it violates cycle time in the process, or will cause a unit to be defective if it is not at a proper place in the proper amount of time.
     
    [email protected]
     

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    #142188

    Anonymous
    Guest

    Michael,
    I hope you won’t mind me attaching my thoughts to your post –
    I feel uncomfortable with this argument.
    Sometimes wait time is part of the process and there is nothing that can be done about it. For example, in optics the glass has to ‘de-stress.’ In this case this could hardly be considered a ‘defect’ unless one was completely ignorant of the process, which unfortunately is often the case these days with ‘belts.’
    I also qusetion how a unit arriving late can be considered a ‘defect.’
    In the context of RTY, a defect renders the unit useless, therefore, I can’t see how a unit arriving late at an operational step can be considered a defect. It is just late – and late is wasteful – but not necessaarly defective.
    We also have to consider the possibility of defective specifications. The notion the ‘customer is always right’ invokes the possibility of ‘ignorant’ and ‘unreasonable’ customers. How often do we have to endure unreasonble demands from marketeers, who have no footing in the real world, and spend most of their training ‘passing the grapefruit.’
    In TPS the 3 Ms include ‘no unreasonableness’ and in my experience there are many instances of defective, unreasonable tolerances.
    One of the most important arguments against the ‘defect’ theory of Quality is due to Taguchi, who noted that there is hardly any difference in quality between a unit just inside a specification and one just outside. Therefore, to base a system of quality upon a theory of ‘defects’ seems quite flawed.
    Andy

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    #142194

    Srinivas
    Member

    Hi,
    I agree with Michael, a unit renders useless is included in the calculation of RTY, but not a unit coming late. If RTY stands for Rolled Throughput Yield, the following is how you calculate:
    Say materia for ‘n’ no.of units is fed at the first step of the process. At the end of the process some are found to be defective and you recycle them. Keep on recycling defective ones out of these ‘n’ nos till you reach a point where few of the defects are beyond rectification (say ‘x’). Then:
    RTY = (n-x)/n%;
    It is apparent there is no term in the above formula for the delays in the process. RTY gives ultimate material wastage in a process, but can not give a measure of other wastages like waiting.
    There is another important metric called FPY (First Pass Yield). If you feed  material for ‘n’ no. of units and you get ‘y’ no. of defects in the first pass (without recycling);then
    FPY = (n-y)/n%
    FPY is always less than or equal to RTY
    Regards
    Srinivas

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    #142195

    Hans
    Participant

    I agree with Andy. If this a call center environment where wait times lead to abandons and may ultimately lead to customer defection, there is a case to be made for counting a certain wait time a defect (even the requirements from customer to customer may differ quite dramatically, but that is another issues).
    Based on the manufacturing application of the original question, I agree: wait time is waste. It’s unproductive, but it doesn’t alter the “quality of the product”. (Unless of course we are dealing with the transportation of perishables. But then again, wait is something to be removed to ensure quality).

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    #142197

    michael spearman
    Participant

    Andy thank you for the reply, it helps me understand how everybody equates a defect, even though I’m 50-50 with your reply, i still say that time can be a measured defect, if time is what is considered as the main factor of customer satisfaction, then in your RTY or  FTY (FPY), you could measure how many calls meet the established cycle-time, if thier is an established cycle time, time has to have either a Upper and Lower Spec limit, or a set number that can move but has to be met to ensure a robust process. In the process of the call center if the operator is the only person the customer talks to – the operator is a supllier to the process, and their productivity(Time/ number of calls/ Satisfied customers etc…) can be measured. If the operator has to pass that call to another source, they then become a supplier to the process and a customer, because he/she then has to pass that call onto another source – meaning that they have an obligation to the next step in the process to pass that unit (Which is the Customer on the Phone) to the next step in the process, which can be measured in time. The operator could have serval causes for defects in a RTY, their opportunities for a defect have to be established and given to them so they can understand what is good and what is bad, maybe an initial Gage R&R should be done to make sure each operator understands what a defect is in thier process. In RTY or FTY (FPY) a unit can have serval defects or opportunities for a defect, in this process for the call center, maybe FTY(FPY) should be used since the operator has a chance for multiple defects, that can’t be re-work back through the system, unless the customer on the phone is re-routed back to them to be re-directed to the proper source that they didn’t get the first time around. Maybe a good process map of how a call is handle would shed a little more light on how to handle this process.
    Thank you Andy for your response……

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    #142200

    Anonymous
    Guest

    Michael,
    Thanks for the exchange of ideas ..
    I have no experience of call-centre processes. All I know is what I experience myself and with a few excpetions it’s not been good. My main gripe is I usually can’t understand the person at the other end, which obviously isn’t their fault. Other people complain about ‘correct information’ and ‘local knowledge’.
    I still believe any process – even a transational process –  based on ‘defects’ is fataly flawed, but I’m not sure whether I can give a good reason for this belief, other than the argument already provided. Since you’ve not countered Taguchi’s position I am also unpersuaded by your argument.
    Perhaps if you give Taguchi’s argument further consideration you might be persuaded by its inherent reasonableness :-)
    Cheers,
    Andy

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    #142201

    Anonymous
    Guest

    Hans,
    I hope you don’t mind but I’ve sent you some data to look at. (via morphologie)
    Cheers,
    Andy

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    #142202

    michael spearman
    Participant

    Thank you Andy for the reply, I can’t touch Taguchi’s argument, in a process like this – the noise factor, which is the customer and the operator, can’t really be measured accurately, the processes around them can be measured. Unless a defect is stated clearly and understood, then it can’t be properly measured, now a unit to be measured can be a multiple of things. Either the unit is time, or the customers satisfaction. Andy they have to measure one or the other, and to do that they need a defect. Taguchi’s argument is valid, but does it account for a process with interaction of two sources that are considered nosie in the process.
    Thank you Andy for your reply

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    #142203

    BBPT
    Participant

    Sorry guys,
    I simple just desagree with you (except Simon), cause does anyone knows what kind of process or defect you are comment?
    Without knowing the process, is not correct to assume that waiting time couldn’t be a defect!
    Some even mix waiting time with delay time?!
    If a process consider that a part should wait 30 seconds (to dry, to heat or else), waiting time defined to a later process. Waiting more time then 30 seconds could be considered a defect. Always depends what is the specification of defect, not the process.
    Any comments and sorry for my poor english!
    BBpt
     

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    #142206

    Anonymous
    Guest

    BBpt,
    Thanks for your contribution and insight.
    Assuming for the moment I’m willing to concede that a unit becomes defective simply through a process delay, can we call a delay a defect?
    I would argue not – because the cause of the defect might well be the reason the delay occured.  Consider a case where an operator is off sick and there is no cover because the company confuses Mean with Lean. Wouldn’t that be the true cause of the defect. In other words, the manufacturing process did not necessarily cause the defect! Someone might beleive this is a mute point, but I can assure you in many organisations it is not.
    As for your other comment about process specificity, are we now saying there are no general principle to allow someone to the difference between waste and a defect. Why is the distinction necessary. Why not call a defect a Defect and waste Waste? :-)
    Cheers,
    Andy

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    #142208

    Hans
    Participant

    I’ll look at your data later tonight. I hope I understand the data because of the difference in industry we’re working in. Talk to you later.

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    #142211

    Hans
    Participant

    Michael,
    If your process is truly the way you describe it (unless this is a hypothetical scenario), your first goal should be to review that convoluted process. Based on years of research in call center environments I can assure you that at a maximum customers tolerate one transfer! The the transfer process you describe is the defect in the eyes of the customer and the wait time is just an undesirable effect (i.e. symptom). Attaching a defect score to a symption rather than a customer expectation is very dangerous. So the irony may well be that the RTY is the problem! Regards.

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    #142212

    BBPT
    Participant

    Andy,
    A defect is a defect.
    Waste is waste.
    But waste can be consider a defect. Why not? “A defect is a failure to conform requirements” – Crosby ‘Quality Is Free’.
    Why can’t we insert some waste in this sentence? To me, depending of the project) we can consider waste a defect.
    Now back to other comments, when you say “because the cause of the defect might well be the reason the delay occured.” – you couldn’t be more right. Everybody knows that cause of defect is the reason of defect happennig!
    Imagine a process like this: A suplyer or your warehouse or a previous process must deliver you at time to time 100 parts. Then you start to process those parts in machine A.
    If material delays, you will not produce. Here is a problem.
     When you define the a project to this issue, can’t you define?:
    Defect: delay on material, lack of material.
    Cause: unknow! (reason of project).
    Costs To # : Unproductive machine A $.
    Instead of:
    Defect: Machine A Stopages.
    Cause: 1st why?- Lack of material. 2nd why? Unknow (reason of project).
    Costs To #: Unproductive machine A $.
    ??
    Defect doesn’t mean defective parts only, useless parts!
    Best regards,
    BBpt
     
     

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    #142214

    michael spearman
    Participant

    I agree, I can only give the point to find your defect, then measure it, if it is time, or customer satisfaction with a phone call. Thank you Hans.

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    #142217

    Anonymous
    Guest

    BBpt,

    Well I must be the only one who doesn’t know and doesn’t subscribe to this statement. It’s like saying this sub-assembly is defective because one of it’s parts isn’t available. Later, it’s suddently transformed into a good part when the part arrives but no doubt counts as a rework
    Cheers,
    Andy

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    #142218

    michael spearman
    Participant

    That would be re-work, but first it would be a defect because the unit would be missing a part that the customer is paying for and adds value to the unit. So RTY that would fail the 1st time and then pass the second time through the process. In FTY (FPY) it would fail, and that would be it, no rework of the part. And rework in any process in not Value added, and the customer does not pay for that, so that is considered a defect. so if a call is received, and the Operator sends the  customer to the wrong area, the customer on the phone is sent back to the prompts or the operator to correct the error in direction of the call, then its a defect that will not be considered good until the customer has reach the intended party that it wants to talk too in the process. In this process the unit is the process and the customer and  the customer goes through to achieve the desire result which is to talk to the right party. Just ask Dell, they have a horrible customer service center. You pay for Dell customer service when you buy a component from them, so to go to thier call center and get re-directed once back to your starting point is a defect in thier process, because you are the customer, the unit of measurement is the process and you;  you go through to get resolution to your question(s). Its confusing but rework is a defect in any form. The term Right First Time is used to illustrate that a unit needs to get to a point and have been fully assembled with no defects, defect are caused by your process, and established by the customer.
    Just a thought Andy U

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    #142219

    Hans
    Participant

    Andy,
    In the transactional environment such as call centers we are in the very unfortunate position that we don’t have a tangible end-product. So the classical distinctions between defect and waste are somewhat blurred. A wait can be both a defect and waste in the classical sense depending on the customer experience.
    For example, if a customer calls into a call center to resolve an issue (wrong charge on bill for example), a defect must already have occurred because that is why the customer calls (unless it is a simple inquiry about balance etc.).
    Now the call center experience becomes the focus of attention: Here the customer has the key expectation of reaching a rep quickly. Thus wait time beyond a psychological threshold may become a “defect”. Ironically, there are differences in tolerances of customers in regards to wait time based on factors such as time pressure, previous experience with the call center, personality etc. In most six sigma projects, we assume the customer to be a class with equal requirements and measure the wait time in terms of the number of times the phone rang until a rep picks up the phone. So here you are in the conundrum that on the one hand, wait time is a defect and waste at the same time.
    This is even more obvious in a patient service center environment. The wait time in a doctor’s office is both an undesirable effect of the througput of patients through the office, i.e. a defect, and waste (i.e. wasted time by the patient, but also the physician).
    Six Sigma in services is six sigma for the “poor people” (I don’t mean that in a deragotory fashion, just that we don’t have the advantages of the manufacturing Six Sigma side). There is a whole discussion about the degree to which Six Sigma developed in manufacturing is applicable to services. In my opinion, the best way to approach this is not to become ideological, but to look at “meeting customer expectations” and use that as our guide and whatever approach is pragmatic in getting that job done. We’ll always have to live with the consequences of the assumptions that we make. Best Regards!

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    #142220

    Anonymous
    Guest

    Michael,
    The point I’m trying to share in the forum is the cause of defects is variation. This fundamental tennet of Six Sigma is becoming obscured by some people with a quality assurance background, where the number of defects as predicted by a normal distribution is ‘everything’ to them. This is not what Six Sigma is about.
    If we can agree that variation is the true cause of defects, or perhaps more clearly ‘differential’ variation, then are we correct in describing waste as a defect? I don’t think so and the reason is because waste can still occur when there is no variation. After all isn’t this what Lean is all about – finding non-value addes steps in a process.
    Anyway, I appreciate your patience, and everyone else’s ..
    Cheers,
    Andy

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    #142221

    Anonymous
    Guest

    Hi Michael/ Hans,
    I replied in the meantime … I’m scanning some papers which is really boring, so I’ve been a little mischeavious wasting time –  making defects :-)
    Best wishes to you both!
    Andy

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    #142233

    michael spearman
    Participant

    To funny, i was enjoying the sun for a second outside.
    best regards Andy & Hans

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    #142235

    michael.spearman
    Participant

    Waste can happen after a project has gone through a Six Sigma process – Variation is always a defect, no matter how little. Sometimes we put-up with it, sometimes its to big and we have to narrow it. This is just a fact, The 7 Deadly Waste of industry are defects no matter what, we just choose to cope with the ones that do not upset our customers.
    Best regards and thank you for the reply Andy

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    #142236

    michael.spearman
    Participant

    Thats a good statement, Andy customer satisfaction is the biggest Output here.
    Thanks Hans & Andy for good brain storming

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    #142257

    Anonymous
    Guest

    Michael,
    I’m afraid I didn’t express myself very well yesterday.
    The point I was trying to make is while I do not deny defects are waste, not all waste are ‘defects.’
    I’m sorry not to give up and walk away, but this might be an important distinction. I also accept Hans’s point about transactional, but these debates are important because someone in production might not agree with the way their work is measured. (Perhaps this is a throwback to my days in a Japanese company and they’re the only ones who care about ‘concensus’ on the shop floor.)
    My rationale for my position is some waste, as you clearly point out, is not due to variation, but can express itself as a ‘constant’ in any process. One example would be an unnecesssary step in a process. Assuming there is no variation in this step, I would argue the presence of the step does not constiture a defect. Therefore, your argument about the Seven Wastes being equivalent to defects is not valid.
    The other final point I wanted to make is the example of an ‘incomplete’ build I gave yesterday cannot be considered defective because it hasn’t passed through the next process step, therefore the sub-assembly would have to be delayed at the previous step until the part shows up at which time the build would be completed and there would be no rework. Therefore, to my mind neither the delay nor the incomplete build can be considered a defect. Is the dealy wasteful? Yes it is!
    Anway, I’ve done my best and I’ll leave those final thoughts with you.
    Best regards,
    Andy

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    #142282

    michael.spearman
    Participant

    Andy you are correct in saying that, Japanese meaning of Quality differs from the USA meaning. In america the process would continue with or with out the unit being completely assembled, in Japan the process would stop to ensure a quality unit does not get to the end of the process incomplete, in the USA we would let the unit go through and then re-work it. I see your point Andy, thats why i debate these issues, for a clear picture of how everybody thinks.
    Now Waste as a defect, is still my moto, if a process has a step that is not necessary, it a lean issue, not really a six sigma issue, but if that step is causing efficiency and productivity problems, no matter how minor, that is a defect. Just my thoughts Andy.
    Thank you, and i enjoy the chatting

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    #142297

    Anonymous
    Guest

    Michael,
    Now I understand where you’re coming from – what a strange why to operate. My only experience of manufacturing in the USA was at Motorolo in Austin – but of course you can’t build integrated circuits that way …
    Cheers,
    Andy

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