“One of the most debatable pieces of data that goes into a simulation is the stochastic behavior of machine downtime”.

Simulation expert Brian Harrington explains the key learning points modelers should consider when working with downtime…..

Early in my career at Ford Motor Company as a simulation engineer I remember building simulations of our plants and wondering what values to put in for the downtime. In addition, I was also unsure of what distributions to use or why there were default distributions within the software. What was the impact of populating the simulation with breakdown behavior? It didn’t take long to realize that downtime had significant effects upon the overall throughput. This white paper explains the key factors that should be considered when working with breakdowns within your simulation.

When considering downtime, the starting point should be to consider the following questions (See Appendix A for definitions):

1. How often does a machine fail (MTBF)?
2. How long does it take to repair it (MTTR)?

These two questions may seem simple, however are often abstracted within the forest of machinery and clouded by human behaviour. When a breakdown occurs on a machine, it’s likely there is time associated with certain phases of a typical repair such as; reaction time, lockout procedure, actual repair and the start-up.