Demand Patterns With Batch Assembly

Assume a scenario where an assembly line builds three major variations of a similar end-product. Assume also that the upper component comes from three separate sources (vendors or workcenters). The graph at right shows average demand for each product.

On large assembly line, setup is often problematic. Parts are  brought in for a new job and remaining parts taken away for the just-completed job. Such lines often need re-balancing with different stations and task assignments. Then, there is the initial startup as everyone gets accustomed to the new configuration. If parts do not fit, or cannot be found, there is more disturbance. When, at last, the line is humming, nobody wants to disturb it with another changeover.

Such is the case with our hypothetical assembly line. And so, once setup, it runs for at least a week on the first product, 1-GRN. At the end of a week, 40 units are complete.

After another frenetic changeover to product 2-YEL, the line runs for 2.0 weeks since the demand for this part is higher. Another changeover and, for another week, the line runs 3-RED. The three frames below illustrate.

The three suppliers for the upper covers of, respectively, 1-GRN, 2-YEL and 3-RED, see high demand for one or two weeks and then no demand for 2-3 weeks. One way to deal with this intermittent upstream demand is to size upstream production for the overall average demand for each part and then build inventory between production runs. This, however, creates a host of inventory control, scheduling and quality problems.

The Mixed Model Assembly line addresses this situation. More>>