Simulation of Buffering and Batching Practices in the Interface Detailing-Fabrication-Installation of HVAC Ductwork

Modeling the supply chain for heating, ventilation, and air conditioning (HV A C) ductwork presents challenges at different stages because of the nature of the product involved. Metal coils and sheets can be quantified in terms of material, gauge, width, and weight. However, when they are transformed into ducts and fittings, quantification becomes more complex. First, some sheet metal companies measure their throughput in terms of mass of sheet metal per time and not in units of fittings and ducts per time, regardless of the level of complexity to fabricate these parts. Second, fittings and ducts have some of their characteristics specified but not all of them; there is a quite high degree of customization for both products. To improve understanding of this production process, this paper investigates the activities in the interface detailing-fabrication-installation of HV AC ductwork. The simulation software STROBOSCOPE is used to mimic different scenarios, including the behavior and outputs of these activities as well as the interaction among them. The data used to develop this model comes from an ongoing study of HV AC contractors. The model specifically deals with variations in batches and buffers sizes and their impact on system throughput, work in process, and lead times for a pull system. This paper presents more detail on inventory buffers; capacity, time and plan buffers are not elaborated on. Analysis of different scenarios provides insights as to how lean concepts can be used to trigger improvements in the interface investigated.