A simple spreadsheet approach to understanding work flow in production facilities

Abstract

This paper looks at how queuing decomposition models, developed using spreadsheet software, can be used to obtain insight into work flow behaviour within a production facility. Relationships appropriate to model flow lines and job shops are developed. The approach proves valuable in helping to understand variance and covariance effects under different loading and routing assumptions. A particular benefit over the use of simulation or commercial rapid modelling software is that all relationships are transparent. This allows fundamental insights to be developed more readily. Understanding the relationships involved can help guide process design and improvement efforts. Comparisons with simulation results show that the queuing model performs well. Results are generated for the queuing model under different routing, utilization and variability assumptions. The behaviour observed is rationalized and opportunities for improvement of production systems are identified. For example, it is demonstrated that when processing time coefficients of variation are less than one, it is beneficial to have work flow that is as unidirectional as possible.