Saturday, February 13, 2010

Seven Wastes|Waste of Overproduction

In a previous post on how to implement lean manufacturing I discussed the seven wastes, within this post I will discuss the waste of over production. One of the most serious of the Seven wastes which leads to the waste of inventory.

The waste of over production is caused by producing more than is required or producing what is required faster than you need to. Why do we do this, generally because of the usual problem of oversized batches, poor scheduling, and poor balance of the processes causing one process to produce much faster than subsequent ones leading to build ups of work in progress.

But why do we use such large batch sizes? We use these excessive batch sizes because of the need to overcome other perceived problems within the factory. We use them because the setup times on our super machine are too long and we want to utilize the time available to produce parts, not in frequent periods of non-productivity caused by the setups. Why not use the technique of single minute exchange of die (SMED) to reduce the setup times rather than ignore this waste of waiting! I will discuss the application of SMED in a later post on how to implement lean manufacturing.

Why else do we use large batch sizes leading to the waste of over production? Well there are many reasons, but generally it is because of all the other wastes within our system that we try to insure against. We over produce just in case the machine breaks down tomorrow and we can’t keep the rest of the factory moving. So rather than deal with the problem of unreliability we hide it under a sea of inventory. Use techniques such as total productive maintenance (TPM) to tackle the problem of unreliability. We don’t trust the quality of our products so we produce extra to account for the defects that will be produced. How many companies have you worked in that always add a specific percentage to every requirement to allow for defects, this percentage being multiplied back in the process until you end up building twice as many of the initial assembly or component than you actually need!This is hardly how to implement lean manufacturing, hiding all of your problems rather than tackling them.

We plan to build to much because of the problems above, we perceive and worry about these problems and try to overcome them by building more than we really need. This often leads to us planning to not just build too many products but also planning in massive delays between processes to enable batches to be moved about, quality problems to be dealt with, waiting times to be overcome and so on.
When learning how to implement lean manufacturing we need to make the value flow at the beat of the customer, not produce at the rate we feel we need to overcome all the problems we have. Tackle the problems not hide them by implementing the waste of overproduction, one of the greatest of the Seven Wastes. Overproduction is a choice not a necessity. For a full list of wastes use this link for waste reduction.

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