An MES, short for manufacturing execution system, is the software that directs and records production on the shop floor. It releases work orders to lines and machines and records what is made, by whom, on which machine, and with which materials. You see the status of every order as it happens, and you can trace every batch or serial number.
The MES sits between the ERP system, which plans, and the machines and their control systems, which do the work. Below, you'll follow one order through a factory and see in a table what each layer knows and decides.
What is an MES used for on the shop floor?
Your ERP system knows that 400 enclosures must be ready this week. It has no idea that line 2 has been down since 10:00, that the afternoon shift is using a different batch of sheet steel, or that three parts failed the last check. That knowledge of the moment belongs in the MES.
One order through the factory
Take a plant that makes metal enclosures. This is how one order moves through the MES:
- Release. The ERP sends the production order with quantity, bill of materials, and routing. The planner releases it to line 2 for the morning shift.
- Start. The operator sees the order at the machine, with the right version of the work instruction, and logs on. The system now knows who is working on it.
- Book material. The operator scans the label on the coil of sheet steel. The MES checks the material and links the supplier's batch number to the order.
- Produce. Machine status and counts come in through the control system. The order shows as running, with the count of good parts so far.
- Check during production. After every 50 parts, the system asks for a dimensional check. If a measurement is out of tolerance, the MES puts the order on hold until a quality inspector decides.
- Report back. The MES tells the ERP how many good parts and rejects there are, which material was used, and how many hours it took.
Three things follow that are hard to get without an MES:
- Status in real time. Planning and sales see where each order is and how far along.
- Traceability by batch or serial number. For every product you know which material, machine, and operator were involved, back to the supplier and forward to the customer.
- Quality during production. A deviation shows up at the machine while the order is still running, instead of at final inspection or at the customer.
Where the MES sits: the ISA-95 layers
The international standard ISA-95, also published as IEC 62264, divides a manufacturing company into five levels, from the physical process at level 0 to business planning at level 4. According to ISA, the MES belongs at level 3 and the ERP at level 4, and the standard mainly deals with the interface between the two. ISA-95 dates from the mid 1990s and is still widely used as a reference architecture.
In plain terms:
| Layer | Examples | What it knows | What it decides |
|---|---|---|---|
| ERP (level 4) | ERP, company planning | Orders, customers, stock, bills of materials, and delivery dates | What you make, how much, and when it must be ready |
| MES (level 3) | MES, planning and recording per line | Which order runs where, who works on it, which material goes in, and the check results | The sequence on the floor, which order is released, and when one stops |
| Control (levels 1 and 2) | PLCs and distributed control systems (DCS) | Machine status, counts, settings, and fault codes | How the machine carries out its operation, second by second |
| Machines (level 0) | Presses, lathes, ovens, conveyors | Nothing themselves, they do the physical work | Nothing, they follow the control system |
Each layer works on its own time scale. The ERP plans in weeks, months, or even quarters, according to a Georgia Tech report for the US standards institute NIST. The MES turns that plan into individual processing steps and has the control layer carry them out. So an ERP sees little of the shop floor: it only learns what happened when the order is reported back.
What happens at level 3
The same report describes a draft proposal within ISA-95 for the functions at level 3. They include:
- Detailed scheduling: turning the level 4 plan into work schedules
- Dispatching: assigning scheduled work to resources
- Execution: working with the control layer to carry out the dispatched work
- Tracking: using data from the control layer to update progress
- Data collection: recording which work started, finished, or was aborted
An MES package usually adds functions for quality, traceability, work instructions, and performance figures such as OEE. Our article on why OEE dashboards fail and what works covers that last one. You can start with release, recording, and traceability, and add the rest later.
MES vs ERP in short
The ERP is the company's record: what was ordered, what is in stock, and what should be made according to plan. The MES is the shop floor's record: what is happening now and what was actually made.
Many ERP packages have a production module for orders, bills of materials, and reporting back. Following machines, materials, and checks during the shift takes data from the floor, which comes together in the MES. Orders flow down and actual production flows back. A later article compares MES and ERP in depth.
When you need an MES
An MES pays off when the shop floor produces more information than paper and spreadsheets can keep up with. These signs point that way:
- Paper travellers move with the order. Their contents only reach a system when someone retypes them.
- Production status lives in Excel. A planner keeps a file that is always behind. Our guide to replacing Excel with a web application shows how to tackle that.
- A complaint starts a search. Nobody can quickly say which material batch a faulty product came from, which machine made it, or which orders got the same material.
- The ERP only knows the plan. You only see what actually happened once the order is reported back.
- Quality problems surface late. Measurements sit on paper, so nobody sees a trend until final inspection or the customer notices.
- Operators ask what to do next. The sequence lives in the team leader's head or on a whiteboard.
If you recognise three or more, it is time to look seriously at an MES.
Traceability as a legal duty
In some sectors traceability is mandatory. In the EU, businesses that make or trade food or animal feed must be able to identify at least their immediate supplier and their immediate customer, as the European Commission explains: one step back, one step forward. When a product is unsafe, they must withdraw or recall it.
The MES records what happens in between, inside your plant: which incoming batch went into which production batch. That link lets you limit a recall to the affected batches.
When you don't need an MES yet
With one line, a few stable products, and no traceability requirements, the production module of your ERP is often enough. If your processes still change every month, settle the way of working first and the software after that.
Standard MES software or custom software
You have three routes for MES software, and you can combine them:
- A standard package. A vendor supplies the functions above as standard and configures them for your lines. This fits when your process resembles others in your industry.
- The production module of your ERP. You extend what you already have. This fits when you mainly want to release orders and report back, with little machine data.
- Custom software for the part that makes your process different. You have software built for what no package covers well, such as your own inspection, an unusual routing, or screens that match how your operators work.
A combination works too: a package for the basics and custom software for the part that sets you apart. Custom software fits a part of the process when:
- your process differs there in a way your customers notice
- operators work around the package, with paper lists on the side
- you already have systems that do part of the work and want to keep them
A standard package fits better when your process follows the usual steps in your industry and you want updates and support from one vendor.
Isatis builds custom software and integrations for manufacturing, next to the package you choose or as a standalone application for a defined part of the floor. Our page on custom software development explains how we work, from discovery to production.
The integrations that make or break an MES
An MES is only as useful as the data going in and out. Two integrations decide whether it works.
Between ERP and MES
From the ERP to the MES go production orders, items, bills of materials, and routings. Back go produced quantities, rejects, material usage with batch numbers, and hours worked. Agree for each piece of data which system is the source, or the two will drift apart.
A standard format exists for this exchange: B2MML, which NIST describes as an implementation of IEC 62264 for linking ERP with manufacturing systems such as an MES. Our article on ERP integration explains how to set up and manage that link.
Between machines and MES
Machine status, counts, and fault codes come from the controls of your existing machines. The same NIST overview names OPC UA and MTConnect as standards that link shop floor control to MES and enterprise systems. For older machines, you read a signal or counter from the existing controls, and a middle layer converts it to the same format.
An integration is only reliable with these four parts:
- Error handling: a message that fails to arrive is resent and reported
- Working through outages: if the connection drops, the floor keeps running and the data follows later
- Monitoring: someone gets an alert when an integration stops
- A log: each message and its reply can be looked up later
Production cannot stop for new software, so we work in steps: old and new run side by side for a while, and we only take the next step once everything works.
Isatis has been building software for more than 30 years. With 30+ engineers in Nijmegen, in the Netherlands, and Sarajevo, more than 100 projects, and ISO 9001 and ISO 27001 certification, we build integrations between machines, MES, and ERP. Read more about our software for manufacturing, or talk to us about your production.
Frequently asked questions
What does MES stand for?
MES stands for manufacturing execution system: the software that releases work orders on the shop floor, records production, and tracks what happened to each batch or serial number.
What is the difference between MES and ERP?
The ERP plans what needs to be made and keeps track of orders, stock, and finance. The MES directs execution on the shop floor and records what was actually made, by whom, and with which materials.
What is ISA-95?
ISA-95, also known as IEC 62264, is an international standard for integrating business systems with manufacturing control systems. It divides a plant into five levels, with the ERP at level 4 and the MES at level 3.
Does a small manufacturer need an MES?
Not always. With one line, stable products, and no traceability requirements, the production module of your ERP is often enough. An MES becomes worth it once paper and Excel can no longer keep up.
Can you connect old machines to an MES?
Often, yes. Even without a modern interface, the existing controls usually have a signal or counter you can read. A middle layer converts that data to the same format as newer machines.
