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Takt time versus pull system

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  • #46918

    Quainoo
    Member

    Hello,
    I am interested to have your input about what seems to me like a contradiction.
    A pull system is designed to make the parts needed to satisfy the customer demand. If demand fluctuates a lot, the production will also fluctuate. As an example, this month I may produce 500 parts and next month 800 parts. Obviously in that case, the takt time will be totally different. My question is, in this situation, what is the point of calculating a takt time that is different from month to month?
    As far as I know, the purpose of calculating the takt is to make sure that all the processes of the factory will produce at the same pace as the customer demand, but wouldn’t it be enough to have a well designed pull system without the need to calculate the takt? (by the way, I am currently testing a pull system using Access instead of physical cards).
    Vincent
     

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    #155773

    jtomac01
    Participant

    Pull Systems are a means by which you achieve Takt Time.  If I read your situation, sounds like you are having more of a Leveling Issue (i.e. month-to-month variation in demand) which probably impacts your cycle & lead times.
    I have seen instances where, based upon the demand, Takt Time (TT) was recalculated on a daily basis (i.e. this was in a warehouse).  TT can be used for a Plant Wide or process metric.
    Takt Time is also used to calculate the number of workstations or people to balance a line or workcell.
    Good idea on using ACCESS, question I have is how do you make the PULL system Visual when a refill is needed?

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    #155778

    annon
    Participant

    The basic idea (although it sounds like you have that well in hand) is to work with your suppliers to level your demand function (reduce variability in amount and frequency of orders) and then calibrate your lines to operate closely (app. 90% of takt time in some circles) to average TT. 
    Often small buffer stocks are used to absorb these flucuations in demand and TT can be recalibrated often at the beginning, although this is not the advocated solution…better to continue to level demand and speed up process velocity (sometimes easier said than done) than chase an ever-changing TT.  Good luck.

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    #155782

    Prediction of customer demand
    Participant

    The challenge for creating takt time is the prediction of customer demand. I would be surprised if your company only produced one line of products. You may want to investigate the issue of workload balancing in case you have the kind of varying demand that you described and several product lines.

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    #155800

    Quainoo
    Member

    jtomac,
    Many thanks for your reply,
    Thanks for all other people who replied to my message.
    The pull system I am currently putting in place is not visual.
    Bellow is a brief description of how it works:

    The assembly department enter in the database the parts that have been consumed during the day (reference and quantity). Of course, a list of all parts concerned by the kanban is available at a click of a button so that minimum time is required for this operation.
    The system automatically recalculate the fundamental values for the kanban parameters such as means, standard deviation and so on.
    Once a day (or more if required), the planning department make a printout of the parts that, according to the kanban, should be produced (this operation requires a single click).
    Based on this information, the planning will create work orders and CNC machines will produce the parts.
    In fact, for internal reasons, the production people want work orders to be generated every time we manufacture something.
    The intention of using Access is to:
    – Take into account the fluctuations of our demand (30 % increase per year over the last 3 years) in an automatic way without re-calculating ‘by hand’ the cards parameters.
    – Avoid cards manipulation (from assembly to production them to planning and so on) within the factory.
    – Have a flexible system that can be adjusted at any time in order to find the best compromise between inventory level and parts availability.
    I am confident it will work.
    Vincent
     

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    #155844

    GrayR
    Participant

    Takt time is based on the average.  You should work to level your production to an average level and buffer the variable customer demand (e.g., finished goods) with inventory.

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    #155871

    jtomac01
    Participant

    Vincent,
    Very interesting how you are utilizing Access to recalculate all of the card levels and help control the outside influences that can adjust the cards.  I am sure it will be successful.
    A suggestion to go with this is to make the PULL System (i.e. current card level for the kanban) as visual as possible.  Some of the ways is to use a flexible racking system or mark spots on the floor of where the kanbans go & how many.  This helps in two ways: 1) helps reinforce what the database is telling everyone 2) helps the entire factory help manage the system (i.e. the spikes that are typically associated to poor quality or increased customer demand not forecasted).

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    #156048

    AlexanderSO
    Participant

    Hi, I just want to add one thing, I have seen your explanation of how you run your replenishment system, and is great, because you are using the effect of the variation, and it allows you to keep syncronized with the demand changes.
    This follow up of the demand is one of the reasons to recalculate the Takt Time every period, the other main function of knowing the actual Takt Time is to constantly compare it with you Cycle Time and be sure that your facility or process is capable of following the demand and waht adjustments you need to do to do it, for example when your cycle time is bigger than the requiered Takt Time, you can decide to use outsourcing, extra time or create temporal inventory, in the other hand when Takt Time is bigger you can decide to schedule personnel vacations, miantenance or other activities that slow your process a little.

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    #156315

    mcintosh
    Participant

    Lean is predicated on establishing flow, allowing the customer to pull value from the system, and takt time or the frequency of the customer demand.  Kanban is a tool, which is used on the production floor and is not an access program.  Your access program is simply a reincarnation of MRP, which could be used for strategic planning purposes but will fail on a tactical level during execution on the shop floor. 
    No one that has responded to this question understands lean on a fundamental level. If you want to begin understand lean find a copy of Ohno’s book Kanban Just In Time At Toyota and read it several times.  Please take these ideas and leave you computer and office and go onto the production floor and setup systems that are visual and easily understood without any explanation. 
    Once on the shop floor find a large piece of cardboard and with a pencil, eraser, and stopwatch create a value stream map in one day or less.  Since you have already calculated takt time, look at your value stream map, without leaving the shop floor, and find the process, which has the largest variance with takt time. Then go fix it.  Repeat the process many times. 
    Kanban at our level, we are not Toyota, must be visual and used to actually control production.  It does not require a computer and it must be on the shop floor.  A manager, supervisor, and anyone else who wants to understand production must be on the shop floor.   If you do theses things you have a chance of sucess. 
     
     

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    #156316

    mcintosh
    Participant

    Lean is predicated on establishing flow, allowing the customer to pull value from the system, and takt time or the frequency of the customer demand.  Kanban is a tool, which is used on the production floor and is not an access program.  Your access program is simply a reincarnation of MRP, which could be used for strategic planning purposes but will fail on a tactical level during execution on the shop floor. 
    No one that has responded to this question understands lean on a fundamental level. If you want to begin understand lean find a copy of Ohno’s book Kanban Just In Time At Toyota and read it several times.  Please take these ideas and leave you computer and office and go onto the production floor and setup systems that are visual and easily understood without any explanation. 
    Once on the shop floor find a large piece of cardboard and with a pencil, eraser, and stopwatch create a value stream map in one day or less.  Since you have already calculated takt time, look at your value stream map, without leaving the shop floor, and find the process, which has the largest variance with takt time. Then go fix it.  Repeat the process many times. 
    Kanban at our level, we are not Toyota, must be visual and used to actually control production.  It does not require a computer and it must be on the shop floor.  A manager, supervisor, and anyone else who wants to understand production must be on the shop floor.   If you do theses things you have a chance of sucess. 
     
     

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    #156380

    jtomac01
    Participant

    Tom,
    I learned this from more than one Sensei, ‘seek 1st to understand then to be understood’. 
    Judging by your post you have read all the latest books on ‘learning to see’, etc..  I might add one more suggestion to your literary library, ‘How to win friends and INFLUENCE people’. 
    It may also be inferred, by whomever reads your post, that whatever company you have deployed Lean at probably didn’t promote the “develop the employee concept”.
    I do agree on one key point of your post, that is all things revolve around the Gemba and those actually doing the work.  Unfortunately, we do not all work with people that see it this way and in those cases would it not be wiser to give them some leading bit of advice & let them learn the hard lesson(s)?
    Regards,
    JWDT

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    #156388

    Wayne Marhelski
    Member

    Takt time should be based on actual demand. You would then flex resources accordingly. Putting additonal people on a line, working additional shifts, controlling the speed on the equipment, etc.
    You would only look to an average takt time if your in a seasonal business and/or your present capacity can’t account for spikes in demand during those peak times. Look at candy canes for instance, they are made over the course of a year for the following Christmas because of a narrow window of demand.
    The other side of the coin is that pull isn’t, or shouldn’t, be the end goal. Pull systems are used when there is discontinuity within a process/operation in order to facilitate material/process flow. Attaining flow within the the process (from suppliers through to the customer) should be your real goal. A prime example is the typical value stream map and how often the solution is simply to add supermarkets/buffers between processes. How about fixing the problem in order to eliminate the need for that supermarket/buffer?
    Buffering with inventory is fine, but it should only be done for a short period of time and only until you can resolve the issue/s which require the need for it.
    From a process standpoint starting with the Best and working down you have: Flow, FIFO (First-in-First-out) Flow, Pull
    Wayne

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    #156407

    gt
    Participant

    Takt time should be as constant as possible , if not you will cause variation/unstability in the process. stability is key to a succesful implemantation of pull system. how u can stabilize is by creating supermarkets in the process (wip or finished goods) depending on  the service level you want to have, the buffer size will vary.) excellent tool that can help you to determine where to put the buffers/supermarket is the VSM.
     
    good luck

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    #156408

    CT
    Participant

    Vincent
    I think you are confusing time to complete an order vs time to complete a part. Takt time of the process is the amount time to finish a single part through the entire process A to Z. Use this time to schedule your time to complete an order. for instance it takes 50 hours to complete 500 parts, therefore it should take 80 hours to complete 800 parts. The effeciency of the process should remain constant only actually Production hours should change. Do not confuse productivity with effeciency.
    CT

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    #156420

    GrayR
    Participant

    You are correct that long term (seasonal) average takt time won’t work very well. But short term takt time will have to based on an avereage.
    Unfortunately you can’t eliminate inventory in any system totally.  Inventory is necessary to buffer against the variability.  To better able to address your objective to reduce inventory, the inventory should be divided into two types — safety stock and buffer stock.  The buffer stock is necessary to buffer the manufacturing process (supplier) against variability in demand (customer).  The safety stock is used to buffer the customer from variability in the supply process.  E.g. one is supplier vs. customer, the other is customer vs. supplier.  Safety stock is needed because even the best suppliers sometimes have quality, machine, weather, personnel, etc. issues that cause the system to vary from what is expected to be available to deliver.  Of course, as quality and maintenance issues, for example, are improved, then the safety stock can be reduced.
    In TPS plants, these two inventories are actually separated (I’ve seen the safety stored on shelves and the buffer stock stored near the shipping floor — e.g., visual systems), and managed separately.  And the safety stock has standards for rotation.

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    #156421

    GrayR
    Participant

    Takt time should be as constant as possible — its purpose is to establish the standard for the process, and if the standard varies then instability is introduced into the process.  However, takt is part specific — if the process produces several or many different types of parts, the takt for each of them will vary based on their demand. Likewise the frequency of manufacture will vary with frequency of demand — e.g., the Hwijunka cycle that is used — A – B -A – B – C – A – B – A – B – C, etc.

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    #156592

    Quainoo
    Member

    Tom,
    Many thanks for your answers and suggestions.
    Just a couple of comments.
    The system I am going to try (using Access) is not a reincarnation of MRP.
    The MRP pushes, my system will pull.
    It will only try and solve a problem that we have had in the past when using cards to pull the parts (assembly pulling parts from CNC machines).
    When the demand was stable, our kanban system (that used physical cards) worked well but it started to deteriorate as demand began to increase by 30% per year (and nobody had time to recalculate the kanbans). What I am going to do will follow exactly the same logic as before but the kanbans will be recalculated on a regular basis.
    Yes, I agree, being on the shop floor is extremely important, I have already involved the shop floor people on this project and I intend to be on the shop floor on an every day basis when implementing it.
    Just one point to finish, the only way to know if a ‘new idea’ works is to try it out (as a pilot). If it does not work, we will try something else to improve the existing situation.
    Thanks again.
    Vincent

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    #158809

    dhonde
    Participant

    hi,
     Actually i have got an summer training project on takt time.can u plz tell me, how we can improve the takt time of a company how we can improve bin and bucket system to better construction of machinery.

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    #158811

    annon
    Participant

    P,
    Go do your homework regarding Value Stream Mapping and basic lean techniques.  ´Learning To See` is a great first read.
    Good luck.

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    #161152

    Carlos Ruiz
    Participant

    I’m offering an online web application etacktime.com to keep history in a database of your production lines if any one is interested.Regards

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    #161154

    Ahsan
    Participant

    i m interested
    ahsan

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    #161155

    Ahsan
    Participant

    Hi
          Friends, i think pull time should be based on takt time. They are same and depends on each other.
    Takt time is calculated from customer required production. While pull time is adjusted with calculated takt time
    thanks
    Ahsan

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    #163391

    walden
    Participant

    Regarding a visual kanban with MS Access.  I did the same type thing for our warehouse.  In my case, production was a good distance away from the warehouse, and we already had desktop pcs at every workstation so that the techs could pull documentation, ISO, engineering prints, ets.  I created an extremely simple access program that allowed them to simply click the part that was out (trigger the kanban card).  this would send a print off to one off three dedicated printers in the warehouse, based on where the part was stocked.  I had rigged an infrared motion sensor (the type that chime when you break its beam liek at a retail store) over every printer tray.  I put some reflective tape directly to the printer tray and bypassed the chime to trigger a 24 volt flashing LED strobe light also located on a pole high up at near the printer.  once the kanban printed off and slid onto the tray breaking the beam, the strobe went off until the material handlers came and picked up the card.  They saved the print offs and at the end of shift, a clerk would go back into the access database and clear all filled cards and expedited any back ordered parts.
    just thought I’d share my set up with everyone.

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    #163426

    Quainoo
    Member

    Chris,
    Thanks very much for your very interesting input.
    Vincent
     

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