QMS and MES: closing the quality loop

Quality lives in more than one system. That's not a problem in itself. The problem is when a defect found on the shopfloor never makes it into the process that's meant to stop it happening again.

Who does what

QMS (Quality Management System) handles enterprise quality processes. They run over weeks and months, and across sites and suppliers:

• CAPA (corrective and preventive action)
• Customer complaints
• Audits and certifications
• Document control and training records
• Supplier quality and approvals

MES/MOM handles quality at the point of production. In real time, against the order that's running:

• In-process inspections, triggered by what's actually being made
• SPC on critical characteristics
• Recording non-conformances at the source, with photos
• Holding and releasing lots
• Linking every result to the as-built record

ERP handles the business consequences of quality. Stock status (available, blocked, in inspection), supplier returns, scrap cost, and quality inspections at goods receipt in many setups.

I covered shopfloor quality in MES functionality: quality operations, and SPC in SPC on the shopfloor.

Where the loop breaks

Here's the typical story. An operator finds a defect. They record it in MES/MOM, scrap the part, and carry on. A week later, quality runs a report, spots a trend, and raises a CAPA in the QMS. The CAPA team asks for details. Nobody can remember which shift, which lot, which machine, which operator.

The information existed. It just didn't travel.

A connected loop looks different:

1. MES/MOM records the non-conformance with full context: order, operation, lot, machine, operator, measurements, photo.
2. Rules decide what happens next. One-off scrap stays in MES/MOM. A repeat defect, a critical characteristic or a customer-impacting issue raises a non-conformance or CAPA in the QMS automatically.
3. The QMS owns the investigation, root cause and action.
4. Actions that change the process come back to the shopfloor: a new inspection, a tighter limit, a revised instruction.

Integration options

There's more than one way to wire this up.

Through ERP. MES/MOM posts quality results and blocked stock to ERP. The QMS reads from ERP. Simple, one hub, but you usually lose the rich detail. ERP carries the status and quantity, not the 40 measurements and the photo.

Direct MES/MOM to QMS, with ERP for stock. Non-conformances and inspection data go straight to the QMS with full context. Stock status changes still go through ERP, because ERP must know what's blocked. This is the pattern I see working best where quality is critical.

One platform. Some MES/MOM platforms cover a good part of the QMS scope, and some QMS products reach down to the shopfloor. If one system does both well enough for your industry, fewer integrations is a real benefit. Be wary of stretching either one too far. A shopfloor system with a token CAPA module, or a QMS with a clunky operator screen, helps nobody.

Holds must be everywhere at once

One rule that applies whichever option you choose: when a lot goes on hold, every system that could move or consume it must know immediately.

If quality blocks a lot in the QMS but MES/MOM doesn't know, the line will happily consume it. If MES/MOM blocks it but the warehouse system doesn't, someone will ship it. Decide which system raises the hold, and make sure it propagates to ERP, MES/MOM and any WMS in minutes, not at the next batch interface run.

Don't forget the documents

Document control usually sits in the QMS. Work instructions, specifications and inspection plans are approved there. But the operator reads them in MES/MOM.

So the same revision question comes up as with PLM: the operator must see the approved revision for this order, not a copy someone saved locally in 2023. Either publish from the QMS to MES/MOM, or have MES/MOM reference the QMS directly. Just don't maintain two copies.

When a CAPA concludes "retrain operators", how do you prove the retraining happened before that operator next ran the job? That's where skills you can enforce close the loop.