Lean production of multiple products is built on the assumption that the process aim can be properly set for each short production run. This article will describe how to set the process aim so that your short production runs can be on target.

In a lean production environment, without a bank of in-process inventory to cushion the impact, and without adequate lead time to allow for reworking or refabricating the product, a single off-target run can shut down an assembly operation and create a massive pile of unintended, in-process inventory. (I once saw 25 jumbo jets parked outside their assembly building. When I asked why they were parked there, I was told that they were all waiting for parts—a billion dollar pile of in-process inventory!)

Aim vs. consistency

A plant had three suppliers for a piece of wire. When a shipment arrived they collected a sample of five pieces and measured their lengths. These five values were subgrouped together and placed on an average and range chart. The charts for each of the three suppliers, drawn to the same vertical scale, are shown in figure 1.

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