Precision Aerospace Machining and the Seven Wastes of Lean Manufacturing (part 7)

The final of the seven wastes that we are looking at is waiting.  Any time that a part is waiting is additional time that you are holding the costs of the part without receiving the income of the part.  Waiting, as we have identified it internally comes from three main places:  1) having a part or batch finish with one machine and the next machine required for the part is not available and 2) any part that is in a batch but is not currently being machined, 3) inventory.

The first of these items is very self-explanatory.  A batch of parts sitting by a machine waiting to be run through that machine is very obviously waiting.  What is a bit less obvious is that even while the batch is being machined, the majority of the parts are still waiting.  If there is a batch of 500 parts that each take 1 minute to complete an operation then at minimum each part will have 499 minutes of waiting while the rest are getting machined.

In any production facility where resources are shared between multiple batches / parts, it is extremely difficult to schedule all of the jobs so that no part is ever waiting at all.  In fact this scenario is used to illustrate a difficult to impossible problem to solve with computers – known as the Job Shop Problem.  This problem may be especially difficult in the aerospace machining industry.  With long lead times and large numbers of operations requiring many different resources, scheduling jobs to move through the shop at the best possible rate is exceptionally difficult.

At CNC Industries we address the problem of time wasted while a part is waiting in several different ways.  One of the main approaches is our design of a universal fixturing system.  We have designed a system of attaching fixtures to our milling machines that will allow a fixture to be machine independent in it’s use.  We may design a fixture assuming that the part will be run in one of our Haas VF-2 Superspeed machines, but find that our Toyoda Horizontal is a better choice.  With our universal fixturing system we can easily move the part to the most appropriate machine at the correct time and with minimal disruption.

Additionally we focus on redundant machines.  Our capacity for production needs to be unaffected by any downtime that a given machine may have.  We keep all of our machines well-maintained to prevent any problems, but there is on way to completely prevent down-time.  With redundant machines we have the security of knowing that we are not going to be in trouble meeting our deadlines if a machine has any unexpected down-times.

Finally we have worked very hard to get our batch sizes as small as is reasonably possible while also reducing the setup time of each batch.  This allows us to eliminate a sizable portion of each part waiting while the rest of the parts in the batch are being machined.  The smaller batch sizes also help us to reduce our inventory and prevent the third source of waiting that we have identified.

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CNC Industries is a Fort Wayne, Indiana based machine shop specializing in precision CNC machining, fabrication and assembly of application-critical and custom machined parts for the Aerospace, Defense, Medical, Industrial and Transportation  markets.   The company presently employs approximately 55 people.

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June 9th, 2010|