What Is MES?
An order arrived, a work order opened, and then what happened? In Reverse View of Work Orders, we saw how a work order grows with revisions and changes from the floor. In What ERP Is and What It Is Not, we talked about how ERP was designed for finance, sales, purchasing, and inventory — not for real-time shop-floor data.
Today we are at that exact gap: MES.
What Is MES?
MES — Manufacturing Execution System — is the manufacturing management system that captures actual production data operation by operation, in real time, from the moment a work order opens until it closes.
The plan says one thing; reality says another. MES bridges that gap.
The Concrete Difference Between ERP and MES
When a work order opens in ERP, planning happens: material is reserved, operations are listed, the due date is set. ERP records all of this once, as a plan.
Then work begins on the floor. A machine sits idle for 2 hours. An operator uses a substitute material. The first part fails quality control and needs rework.
ERP does not live these moments. To feed this information back into ERP, a report is usually written afterward — or never written at all. That is why the answer to “where is the plan right now?” differs between ERP and the shop floor.
MES steps in exactly here:
- Records start and end time for every operation
- Captures downtime reason and duration instantly
- Logs scrap quantity and type at the operation level
- Creates actual performance data by machine, shift, and work order
ERP tells you what was done. MES tells you when it was done, how it was done, and how long it took.
Why Do You Need Both?
ERP and MES share the same data but speak in different timeframes and at different levels of detail. ERP tracks what the job is and what it cost. MES records how and when the job ran, capturing the gaps and losses in between.
This distinction becomes critical in customer-specific production. When every order follows a different route and different operations, the standard ERP plan becomes obsolete almost immediately. MES keeps the actual data for each work order, exposing the gap between plan and reality in real time.
Conclusion
MES is the layer that brings floor events back to ERP. ERP knows the plan; MES knows the truth. When both work together, the chasm between planning and execution closes.
In the next post, we will look at the relationship between MOM — Manufacturing Operations Management — and MES.