How Do I Determine Buffer Size?

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    Hello all.
    I am quite new to this area.
    I have a situation where on a production line a product consist of 2 sub-assemblies.
    In order to build the full assembly one sub-assembly needs to be built first.
    Engineer has set a buffer size for one sub assembly 24 pcs. So the whole time operators are making the buffer there is no output from the line for about 30 minutes. then there is a quick changeover and the second sub assembly production starts. after the first sub assembly of the second version is ready the final assembly can start- until the buffer runs out again.

    I couldn’t figure out a method or a formula to calculate the optimal size for the buffer so that the waiting time would be as small as possible without building a second station to be able to build 2 sub assemblies at the same time.

    I am really hoping someone could share some good knowledge about some tools or tecnhiques.

    Just for the sake of discussion
    To make Part Final assembly X one needs sub assembly Y1 and Y2.
    When starting the line they build Y1 24 pcs which takes 75 sec per piece.
    Then there is a changeover 2 min and they start building Y2 which also takes 75 sec per piece.
    Final assy takes 150 sec per piece.
    so the first actual final assembly comes out after the start of the shift (24sec X 75) + 120 + 75 + 150 = 35,75 minutes which is a big waste. In a 430 min shift there will be this waste after every hour so a lot of waste.



    Aaron Olson

    I agree that this is a lot of potential waste but I have a few questions to clarify:
    -Where does output compare with takt time?
    -Is demand higher than current capacity and/or output?
    -Is there another process that can be mixed in to utilize the waiting time of the operator (assumed that it’s an operator and not an automated process)

    The ideal solution would appear to be where you would be able to switch between the two subassemblies without a setup so that you would have a small buffer (1 or 2 of each) between Y1&Y2 and X and produce to the final assembly rate. You could do 75sec for Y1 and 75sec for Y2 and then another operator could be making X final assembly. That (theoretically) could be a balanced process with maximum output. Running the two subassemblies at the same time would not help, though, because the final assembly process is the apparent bottleneck (twice as long as the subassemblies).



    Have you looked into Theory of Constraints? It may provide some insight into balancing the process.

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