MES or ERP: what is the difference, and do you need both?

What an ERP does

An ERP is the administrative backbone of the business. Sales enters orders in it, purchasing orders materials with it and accounting invoices from it. Among mid-sized manufacturers, Exact Online and Microsoft Dynamics 365 Business Central are well-known examples.

An ERP thinks in days, weeks and money. It knows that order PO-88213 for 12,000 bottles must ship on Friday, what the materials cost and how much is in stock. What an ERP usually manages:

• Sales orders, customers and delivery dates
• Purchasing, suppliers and purchase prices
• Items, bills of materials and recipes
• Stock in quantities and in value
• Cost price, invoices and the financial accounts
• The rough plan: which orders in which week, and which materials they need

What an MES does

An MES directs execution on the floor. It thinks in minutes and hours and knows what really happened: that the filler on line 2 stopped for twenty minutes at 09:40 because of a jammed cap, which lot of labels went into batch 88213 and that the eleven o'clock weight check passed.

What an MES usually manages:

• A plan per line, per day and per hour
• Work instructions and the right steps for the operator
• Material consumption per lot, so every batch can be traced
• Quality checks during production, including deviations
• Counts, downtime and its reasons, and from those OEE (Overall Equipment Effectiveness, how effectively a line runs)
• The batch record: the account of what happened in each batch

The difference at a glance

The simplest distinction: the ERP is about what should happen and what it costs, the MES about what actually happens on the floor. A few concrete differences:

• Time scale: the ERP plans in days and weeks, the MES directs in minutes and hours
• Users: the ERP is for the office, sales and finance, the MES for planners, operators and quality
• Detail: the ERP knows the order, the MES knows every step, every lot and every stop within that order
• Place: the ERP runs in the office, the MES on tablets and screens at the line
• Records: the ERP records what was agreed, the MES what was made, consumed and checked

Why most manufacturers need both

Many ERP packages have a production module. It creates production orders, reserves materials and books finished goods. It usually does not answer the questions on the floor: which order is running on line 2 right now, why did it stop, which lot is in this batch and was the eleven o'clock check done?

In practice that gap is filled with Excel, whiteboards and paper work orders. The plan lives in a sheet next to the ERP, completions are retyped at the end of the day or week and the batch record is pieced together afterwards. An MES fills that gap with one system that talks to the ERP.

The other way round, an MES does not replace the ERP. Finance, purchasing, invoicing and master data stay in the ERP, and the MES needs that data to do its work.

How ERP and MES work together

A good connection works both ways, with the ERP as the source for orders, items and stock. Every piece of data has one source: agreements and money in the ERP, execution in the MES. That way nobody has to retype anything.

This is how order PO-88213 moves through both systems:

• Sales enters the order in the ERP, with customer, item, quantity and delivery date
• The MES picks up the order with its item and bill of materials, and the planner puts it on line 2 on Tuesday
• The warehouse picks the materials and the operator scans the lots at the line
• During production the MES records counts, downtime and checks
• After completion the MES books the quantities produced and the lots consumed back into the ERP
• The ERP updates stock and invoicing can start

Where it often goes wrong

When ERP and MES are used side by side, things usually go wrong in the same places:

• Keeping master data twice, so an item code or bill of materials in the MES differs from the ERP
• Changing the plan in two places, with no agreement on which one leads
• Booking production back only at the end of the week, so stock and cost price are wrong in between
• Introducing an MES as an island, without reporting back to the ERP
• Customising the ERP into an MES, so every update becomes a project

Where Frontlink fits

Frontlink works alongside your ERP, not instead of it. Orders, items and stock come from your ERP, such as Exact Online or Business Central. Frontlink plans at line and hour level, runs production and warehouse, and writes back what was actually made, consumed and shipped.

A Frontlink engineer builds it at your site, on your own data and ERP. You start with one process, which is usually running within a few weeks.