A simple lower bound to the dynamic assembly problem

We consider the multi-stage assembly problem where many components are assembled to make a final product. Demand is dynamic but known over a finite horizon. Optimal solutions are available but only with considerable computations. To properly evaluate heuristic solutions, good lower bounds with relatively low computational requirements are needed. We describe a very simple bound and illustrate that despite its simplicity it compares reasonably with more sophisticated bounds. The bound readily admits of many improvements and generalisations.