What an MES is, and whether your factory needs one

Someone has told you that your factory needs an MES. Perhaps it was a consultant, perhaps a software vendor, perhaps a line in a buyer's audit. You want to know three things: what an MES actually is, whether your factory needs one, and what to ask for if it does. The answers are simpler than the vocabulary around them.

In one sentence: a manufacturing execution system is the software that runs and records the work on the factory floor, between the plan that says what should be made and the machines and people that make it. The rest of this article explains that sentence, gives you the vocabulary you will hear in meetings, and ends with a way to decide.

Where an MES sits: the ISA-95 picture

The clearest way to understand an MES is by its position. The international reference for this is the ISA-95 standard, published internationally as IEC 62264, which describes a manufacturing enterprise in levels.

• Levels 0 to 2 — the process and its control. The machines themselves, the sensors on them, and the control systems that run them second by second: PLCs, SCADA screens, machine controllers.
• Level 3 — manufacturing operations management. Running the floor over shifts, hours and minutes: which order goes to which line, who is working on what, what has been completed, what failed inspection, what is stuck. This is where an MES lives.
• Level 4 — business planning and logistics. Orders, customers, purchasing, inventory value, accounts, planning over days, weeks and months. This is where an ERP lives.

The useful idea in that picture is the time horizon. The ERP thinks in days and money: this order is due on the twentieth and is worth this much. The machines think in seconds. Level 3 is the layer that turns the first into the second and reports back what actually happened. In most small and medium factories nothing occupies that layer except paper, spreadsheets, a WhatsApp group and the supervisor's memory — which is why problems there are so hard to see. How garment factories lose production time when line tracking runs on WhatsApp walks through what that costs on a real floor.

What an MES actually does

MESA International, for many years the industry association for manufacturing operations software, described the job of an MES as a set of functions. MESA has since wound down and passed its work to ISA, the society behind ISA-95, but its original model, which named eleven functions, is still the most common way to describe what an MES does. You do not need all of them, but knowing the list lets you recognise what a vendor is and is not offering.

• Resource allocation and status — which machines, tools and people are available, and in what state.
• Detailed scheduling — sequencing orders on lines and machines at the level of hours and minutes, not days.
• Dispatching production — releasing work to the floor and moving it when plans change.
• Document control — making sure the operator sees the current instructions, drawings and specifications.
• Data collection — recording what happened: quantities, times, stoppages, readings.
• Labour management — who worked on what, for how long, with which skills.
• Quality management — inspections, defects, and holding back work that fails.
• Process management — following the route an order takes through its operations, and alerting when it deviates.
• Maintenance management — planned and breakdown maintenance tied to the machines that need it.
• Product tracking and genealogy — the history of each order or batch: which materials, which operations, which people and machines. This is traceability.
• Performance analysis — comparing what happened against what was planned, while there is still time to act.

Later versions of MESA's model reorganised these into broader groups of activities, but the eleven are still the most practical checklist a factory owner can use.

MES, ERP and MRP: which is which

These three are confused constantly, often by the people selling them.

MRP is usually a module inside an ERP. Some ERPs also sell a "manufacturing" module that covers a thin slice of MES — creating work orders and recording their completion. That slice is often enough for a small workshop. It is rarely enough for a factory with several lines, many operations per product and a real quality process, because it records the order's start and finish and very little of what happened in between.

The terms you will hear in meetings

• Work order. An instruction to make a quantity of one product. The unit an MES tracks.
• Routing. The sequence of operations a product goes through, with the line or machine for each.
• WIP. Work in progress: everything started and not finished. Too much of it hides problems; too little starves lines.
• OEE. Overall equipment effectiveness: availability multiplied by performance multiplied by quality. It tells you how much of a machine's potential output you actually got, and why you did not get the rest.
• Traceability or genealogy. Being able to say, for any finished item, what it was made from and how. Some buyers require it.
• SCADA and IIoT. The systems that collect data from machines directly. Useful, but an MES can start without them: people recording the right event at the right moment gets you most of the value.

Does your factory need one?

This is the question you came with, so here is a direct test. You probably need MES capabilities — whether or not you buy something called an MES — if three or more of these are true.

• More than one line or more than one shift, and nobody can see them all at once.
• Several orders on the floor at the same time, sharing machines or people.
• Status questions from buyers or management that take more than a few minutes to answer.
• Recurring disagreements about quantities between stages.
• Defects found at final inspection that were made several operations earlier.
• A buyer or a certification asking for traceability you cannot currently provide.
• Planning done from memory because there is no live view of what each line is doing.

You probably do not need one if you run a single line, the owner is on the floor all day, and the orders are few and similar. A good spreadsheet and discipline will serve you better than a system nobody updates.

What to start with

Almost no small or medium factory should try to implement all eleven functions at once. The ones that return the most for the least effort are usually:

1. Data collection and product tracking — recording completed quantities and handovers at each stage, so there is one true picture of where every order is.
2. Dispatching — releasing orders to lines from that picture rather than from memory.
3. Quality at the operation — recording defects where they happen, tied to the order and operation.
4. Performance analysis — a daily view of plan against actual, per line.

Scheduling at minute level, maintenance, labour management and machine integration can follow once the floor trusts the basic record.

What to ask a vendor

• Which of the MESA functions does your system cover, and which does it leave to other software?
• How does an operator or supervisor record an event, and how long does it take? Show me on a phone or a tablet.
• What happens when the factory's network goes down?
• How does it exchange data with our ERP or accounting system, and in which direction?
• Can it run on hardware we already own, and where is our data stored?
• What does it cost per user, per line or per site, and what does it cost to add a line next year? Comparing business software on evidence and the five-year cost of business software cover how to hold those answers side by side.

The next step

Before talking to any vendor, write down your routings — the operations each product passes through — and the five questions your floor cannot answer today. That page is worth more in a first meeting than any demonstration. Softwiro builds execution software for small and medium factories, including MESwiro, which is aligned to ISA-95 at the execution level and runs on the factory's own hardware. If you want a second opinion on whether you need an MES at all, send us that page.

Sources

• ISA-95 Standard: Enterprise-Control System Integration — International Society of Automation. The standard, also published as IEC 62264, that defines the levels and the exchange between business and manufacturing systems.
• Lean Manufacturing Techniques for the Ready-Made Garments Industry — International Labour Organization, Cairo office. Floor-level practice that an MES records: bottlenecks, line balance, work in progress.
• Takt time — Lean Enterprise Institute. The pace against which floor performance is measured.