Simulation of material delivery systems with dolly trains

Well designed material delivery systems should support the production systems with timely delivery of material from its point of arrival to the plant to its point of use. This paper describes a simulation methodology to model and capture the behavior of systems which use dollies to deliver material. The models evolved over time by modeling several real world applications in a variety of manufacturing facilities. As compared to forklift systems, modeling dolly delivery is much more complex and requires several special features. Crate, dolly, and train entities merge to model loading at the dock and split to model dropoff at the aisles. Data structures are used to transfer and maintain information across these different entities. Decision logic must also be added to model dolly selection, train routing, and alternative actions when resources are not available. New control entities must be used to control loading dollies from the floor and periodic collection of empty dollies. All these techniques are described in the paper along with the model flow logic traced from dock unloading to aisle and line feed delivery to return and reloading of empties on the truck. Application of the models to a JIT implementation at an assembly plant and to the manufacturing facility design problem are also presented.