OPIM101 - Spring 2012 - Lecture 3

OPIM101 - Spring 2012 - Lecture 3 - Process Interruptions...

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Slide 1 OPIM 101, Spring 11, Profs Cachon/Savin, Lecture #3 Process Interruptions – Setup Times Lecture 3 January 31, 2012
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Slide 2 OPIM 101, Spring 11, Profs Cachon/Savin, Lecture #3 Milling machine at Novacruz § A milling machine is needed to make one steer support and two ribs per Xootr. § The setup time is the time needed to get ready for production during which no production actually occurs. § What is the capacity of the milling machine? The Xootr by Novacruz Setup time (min) Processing time (min) Steer support 60 1 Rib 60 0.5
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Slide 3 OPIM 101, Spring 11, Profs Cachon/Savin, Lecture #3 Capacity of a process with setups § Capacity can be defined like this § For example, if a process produces 12 units every 4 minutes then § How long does it take to produce a batch of items? § So the capacity of a process with setup times that produces in batches is: units those produce to Time produced units of Number Capacity = Capacity = 12 units / 4 minutes = 3 units / minute Time to produce a batch = Setup time + Batch size x Processing time time Processing size Batch time Setup size Batch Capacity × + =
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Slide 4 OPIM 101, Spring 11, Profs Cachon/Savin, Lecture #3 What are the batches for Novacruz? § Suppose Novacruz uses the following production cycle: 100 steer supports, 200 ribs, 100 steer supports, 200 ribs, etc. § What is the “batch”? A “batch” is defined by a set of flow units and an interval of time such that these intervals of time are identical and repeat themselves. It follows that … u successive intervals are of the same length u the same number of the flow unit are produced in each interval. = Setup and produce 100 Steer Supports = Setup and produce 200 Ribs Time
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Slide 5 OPIM 101, Spring 11, Profs Cachon/Savin, Lecture #3 Suppose “ribs” are the flow unit defining the batch Within each rib batch, the same number of ribs are produced Each rib batch includes the same amount of time: u This implies that certain events, like the start of rib production, occur at regular intervals Two things occur during a rib batch interval: u production of ribs u activities that do not produce ribs – we call this “setup time” for rib production 1st rib batch 2nd rib batch 3nd rib batch
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Slide 6 OPIM 101, Spring 11, Profs Cachon/Savin, Lecture #3 Setup time in rib batches Within each rib batch interval, the “setup time” is all time in which ribs are not produced: u Can include setting up to start rib production. u Can include idle time (in which workers/machines are doing nothing). u Can include time producing other things. 1st rib batch 2nd rib batch 3nd rib batch
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Slide 7 OPIM 101, Spring 11, Profs Cachon/Savin, Lecture #3 Analysis of rib batches § Batch size = 200 because 200 ribs are produced per rib batch § Setup time = time per rib batch in which ribs are not being produced = Rib setup time + Steer support setup time + Steer support production time = 60 min + 60 min + 1 x 100 = 220 min § With this schedule the milling machine can produce 0.625 ribs per min: 1st rib batch 2nd rib batch 3nd rib batch 625 . 0
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