GlossaryKind of term: Manufacturing termMES
What is MES?
An MES is software that directs and records production on the shop floor: which order runs on which machine, for how long and with what result.
MES stands for manufacturing execution system. The system releases works orders to workstations, records start, stop, downtime, quantities and scrap per operation, and keeps track of which material and which revision went into an order. It sits between the ERP, which plans and administers orders, and the machines with their controls. Data come in from operator bookings, from machine signals, or from both.
Where does an MES get its times from?
An MES time is only as good as its source. An operator booking measures the time between logging on and logging off, including waiting, inspection and interruptions unless those are booked separately; a forgotten log-off gives a time that is too long. A machine signal, such as spindle running or program active, records more precisely when the machine is running, but measures something other than a cycle time: loading, unloading and inspection away from the program are excluded, while a warm-up program or prove-out at reduced override is included. Nor does it say which order or operation was running unless it is tied to the works order. The ISA-95 reference model (IEC 62264) places MES functions at the level between business planning and process control; it describes functions and data flows, not a required configuration.
How does an MES work in practice?
Booked times per operation let you compare the estimate with what actually happened, provided the estimate and the booking system break the work down into the same operations. A time that differs is not automatically a better standard: first judge whether it is representative; a first batch with prove-out, or an order hit by a breakdown, often is not. In a smaller shop a works order with start and stop times, on paper or in the ERP, does the same job in less detail.
What is an MES often confused with?
An MES is not an ERP: the MES follows execution per operation and workstation, the ERP the order with its stock and invoicing. Nor is an MES post-calculation: it supplies booked times and quantities, and comparing them with the estimate, and judging the difference, is a separate step.
Frequently asked questions
Do I need an MES to know my actual times?
Not necessarily. A works order with machine, start and stop time per operation already gives a time. An MES records that without retyping and can add downtime, scrap and machine signals; how reliable the times are depends on how consistently people book.
Do my estimates get better with an MES?
Only when someone sets booked and estimated time per operation side by side, judges the outliers and adjusts the standards. The MES supplies the record; deciding whether a time is representative, and what changes in the estimate, remains a person's job.
Can an MES calculate OEE?
Many MES packages calculate OEE from availability, performance and quality. The figure depends on how downtime, the ideal cycle time and scrap are defined and booked, so compare OEE figures only where the definition is the same.