Process Improvement via Bottleneck AnalysisIn Bottleneck Analysis we are seeking to understand imbalances within a process, which cause delays, inventory build-up’s, process stoppages. Ideally, we want a smooth continuous, even process flow, however, in reality process input flows can at times exceed the throughput capability of a process. In some situations, it can be relatively easy to identify a consistent point of constraint within a process, especially when such a constraint remains continually in place, however, in many situations, an unbalanced line will result in bottlenecks moving throughout the process, continually changing between various process steps, test & inspection points, etc.. In this latter situation, it can be very difficult to identify and understand the sources of imbalances.
Consider a process where there are different sequential stages of processing, where “Raw material” goes through “Grinding, “Polishing”, “Packaging”, “Sterilization” and finally onto a “Shipping” stage.
Through measurement we can determine individual process throughput / cycle times.
In this following example, a batch of product can progress through a “Grinding” process in 10 hours, then goes through a “Polishing” process in 20 hours. We have two product “Packaging” stations, where the process time for a batch of product through each station is 30 hours. Finally, there is a single “Sterilization” process, where a batch of product takes 30 hours to complete.
If we take a snap shot of the process at the start of the process (i.e. t= 0 hours), we may see batches of product as follows:
Lot 1 – Has completed Sterilization and is “ready” to ship (i.e. has completed the Sterilization process).
Lot 2 – Has completed Packaging station and is “ready”.
Lot 3 – Will be ready (i.e. will be complete) in 15 hours at packaging station.
Lot 4 – Has completed Polishing.
Lot 5 – Has completed Grinding.
If we now look at the process 15 hours later (t= 15 hours), we see the batches of product as follows:
Lot 1 – Has completed Sterilization and shipped.
Lot 2 – Will be ready in 15 hours in Sterilization.
Lot 3 – Has completed Packaging, is ready to start Sterilization and will be waiting for 15 hours.
Lot 4 – Will be ready in 15 hours in Packaging.
Lot 5 – Will be ready in 5 hours at Polishing.
Lot 6 – Has completed Grinding and currently waiting to progress.
If we further look forward to immediately before 30 hours (t= 30 hours):
Lot 2 has just completed Sterilization and is now ready to ship (i.e. no waiting time).
Lot 3 had completed Packaging 15 hours earlier.
Lot 4 has just completed Packaging (i.e. no waiting time).
Lot 5 has been waiting 10 hours.
Lot 6 has been waiting 15 hours.
If we further look forward to immediately after 30 hours (t= 30 hours):
Lot 2 has shipped.
Lot 3 has just commenced Sterilization and will be ready in 30 hours’ time.
Lot 4 has completed Packaging and is now waiting.
Lot 5 has just commenced Packaging and will be ready in 30 hours’ time.
Lot 6 has just commenced Polishing and will be ready in 20 hours’ time.
Lot 7 has just commenced Grinding and will be ready in 10 hours’ time.
From the previous relatively simple example we have seen over a period of 30 hours, bottlenecks within the process move from Grinding and Packaging at t=15 hours, to bottlenecks at Grinding, Polishing and Packaging immediately before t=30, then reduce down to having a bottleneck at Packaging only immediately after t = 30 hours.
Over a much larger process and over a longer time scale, bottlenecks will arise over differing stages and will be difficult to understand. Gut feeling, engineering guess can often lead to incorrect investment decisions. Only with detailed analysis of the capability of each process stage, which includes realistic estimates of peak flows, realistic measures of the process constraints impacting on the process, can flows be optimized with minimal necessary investments.
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