Tuesday, July 20, 2010

Common Myths of Bottlenecks

The complexity of operations has increased tremendously since the days of Henry Ford and therefore requiress more thinking.

The identification of the bottleneck becomes much more difficult as we move from the high volume low variety repetitive manufacturing scenario towards low volume high variety job shops and finally to the project environment.

In a recent post I talked about how to identify a bottleneck and leverage a constraint to your advantage.  However, there are several misconceptions or myths about bottlenecks that we need to debunk.

Consider a 6 step process for which the market demand is 13 pieces/hr.  Process "A" can produce 17 pieces/hr, "B" 14 pieces/hr, etc.

 A    à    B   à   C   à   D   à   E   à   F
(17)      (14)      (13)      (12)      (10)      (12)

Myth 1: Any resource whose capacity is less than the demand placed on it is necessarily a bottleneck.

Reality: A resource can be a non-bottleneck even if its capacity is less than the demand placed on it.  In the above example consider operation "B" which can produce only14 pieces/hr, 3 pieces/hr short of the demand from "A".  This is a non-bottleneck operation since it has higher capacity than the market demand.

Myth 2: The resource having highest workload is necessarily the bottleneck.

Reality: A resource can be a non-bottleneck even if its workload is highest.  Process "A" has the highest workload in the sequence.  It is a non-bottleneck operation since the next operation "B" has a lower capacity than "A".

Myth 3: Any resource with a queue before it is necessarily a bottleneck.

Reality: A resource can be a non-bottleneck even if an infinite queue forms before it.  Process "C" will have a queue before it since process "B" has a larger production rate.  However "C" is not a bottleneck since it produces at the market demand of 13 pieces/hr.

Myth 4: The resource having the biggest queue before it is necessarily the bottleneck.

Reality: A resource can be a non-bottleneck even if the queue before it is bigger than all other queues.  Operation "B" will have the largest queue in front of it but again operation "B" produces at a rate more than the demand.

Myth 5: A bottleneck resource is necessarily a critical resource.

Reality: A resource can be a bottleneck even if it is non-critical.  Process "D" is a bottleneck operation since it is lower than the market demand.  This does not mean "D" is critical or not.

The constraint in this system is the bottleneck operation "E".  Increasing the capacity at any operation other than "E" will not change the output of the system.  Understanding reality will help you define a bottleneck so that it can be easily identified in your processes.  Then you can use the 10 principles to manage a constraint to improve your system.


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3 comments:

  1. Great post. Just one rankle: "...and finally to the project environment"; "Projects" are hardly an end-point or ideal state, are they? :}

    - Bob

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  2. Great post, Tim. This is a conversation I have been having with some of the facilities I have been working with. They are getting worried about bottlenecks, when in reality they are still producing what the customer demand is. They don't have bottlenecks, but they claim they do. Because of this, they are asking for more capital to buy more equipment, that isn't needed. Not to mention long setups and downtime issues, but that is another post.

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  3. Bob, I was referencing a range of manufacturing environments. Not unlike a job shop some businesses could be considered a project shop. This a little different than ordering existing established products.

    Matt, I find constraints is a very difficult conecpt for many. Even if you get lucky and they can recognize the constraints they don't know what to do with them. Most times I find their actions can actually make it worse not better. This post came from some work I was doing with a European plant struggling with the concepts.

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