By Jon Miller | Post Date: August 23, 2010 8:31 AM | Comments: 3
Steve C asked:
This is a fairly common challenge. For example the Boeing 737 line ran at a rate of between 19 and 22 units per month when I visited a few years ago. That is basically a one day takt. They had tried a moving line but found the line stops to be too disruptive and went to a pulse line. I am sure it evolved many times since that point towards a truly lean operation. Machine tool manufacturers, semiconductor equipment manufacturers, vehicle maintenance operations and various other business that have 22 units of customer demand per month run at this timescale.
When we say "one part every day" timescale, we first need to clarify whether that means a 24 hour takt, a two-shift 16 hour takt, an 8 hour takt for a one-shift operation or something else. For the sake of simplicity let's take a one-shift, 8-hour operation with 1 unit of customer demand per shift and set the "one day" takt at 8 hours.
If the total work content of the unit is less than 8 hours then the design of the lean operation is a fairly straightforward "start the day, finish the day" flow of work. If the time to complete one unit is more than 8 hours, the flow line or workstation be they paced or non-moving lines, simply need to be visibly divided into the first 8 hour (takt) section of work, the second 8 hours of work and so forth until completion. However many such sections there are, that is the lead time for that process. These work pieces represent something called standard in-process stock. Define the repeatable work sequence within these takt sections and we have standardized work for a one day takt operation.
My experience with lean for products that have a demand of one unit per day has mostly been with large pieces of capital equipment containing hundreds of parts and sub assemblies. Most of the technical aspects of lean work involved laying out the workstation properly, designing the parts presentation and material logistics to the line, using the yamazumi to balance the work on the main line as well as the off-line sub assemblies, and problem solving rapidly. The essential human aspects of lean operation design are no different regardless of takt length.
If the product is a small, simple item that can be built in a few hours it is best just to have one person finish it at a work station, or incorporate the demand for this one unit into a mixed model line. But there are other types of situations, products and demand profiles within a one-day takt operation no doubt.
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