In Manufacturing, Downtime will continuously grow the cost of the overhead operations by producing Zero Value. Most of the downtime is unplanned and brings the entire or part of the unit to a stand-still. It is a nightmare for every maintenance team. Though downtime is inevitable, with the right approach & planning; the impact can be reduced by recovering quick and reducing the downtime frequency.
The primary analysis starts with the following historic downtime information and logs. There are few formulas, to begin with
Mean Time Between Failures (MTBF): This is a measure of total uptime divided by number of failures for a repairable system. Uptime can be arrived by the expected time the machine should be operational and the number of failures is the failure count during this expected period.
Mean Time to Repair (MTTR): This is a measure of average downtime – i.e. dividing the system downtime with number of failures. MTTR is used to effectively plan maintenance repair process and a key input for preventive maintenance. Some people use Mean Time to Recover as MTTR from the Failure occurrence time as against the Repair start time.
Mean Time to Failure (MTTF): This is a measure of reliability for non-repairable systems. This MTTF helps to arrive at the lifespan of the system by arriving at the average of total hours of operation by each system against the total number of systems.
Failure Rate: This is the inverse of Mean Time Between Failures. While planning and designing systems, the failure rate predicts the component’s or system’s performance. This is measured in number of failures per hour.
Reliability: This is the probability of a component’s or system’s chance of failure. This metrics is used to design redundancy into a system. If the probability of the failures is high, then it is recommended to plan for an identical system for redundancy.
For relatively small failure time the following formula can be applied,
Whereas for relatively larger failure time the following formula can be applied,