Spring manufacturing has a linear sequence of processes: winding, heat-treatment, sanding, shot blasting, and painting. The size and required configuration of the spring affects which resources can be used for production. Even lot sizes can affect production times, as small batches might be done by hand.
Production work is driven by multiple, interspersed call-off orders. Orders have many different configurations, processing times, and lot sizes, and there are order priorities to consider, among other disruptions. Raw material availability also needs to be considered for scheduling.