Engineering and IT Insight: MES vs. ERP for manufacturing

Can’t we just use our enterprise resource planning (ERP) system instead of buying a manufacturing execution system (MES) system? The answer isn’t as obvious as the question.

By Dennis Brandl October 14, 2011

Almost every time a company starts a MOM (manufacturing operations management) project, this question comes up: “Can’t we just use our ERP system instead of buying an MES system?” This is a natural question. Many companies have spent tens to hundreds of millions of dollars on their ERP system and they want to get the maximum benefit from that investment. However, the answer to the question is not always obvious. Modern ERP systems cover a wide range of business processes, including finance, logistics, transportation management, human resources, sales, and distribution. Manufacturing is just one small part of a company’s business processes. So the real question is: Can the ERP software handle the company’s manufacturing operations management processes in addition to handling the business processes? The answer is that some ERP systems can, sometimes, but usually only under limited conditions.

The main activities that make up manufacturing operations management are now well understood and documented in the ANI/ISA 95 and IEC/ISO 62264 standards. These standards are rapidly becoming the basis for most MOM project requirements. The standards define the activities of MOM, but they do not define an implementation architecture or define what type of software system should be used. Traditional MES vendors provide support for most MOM activities, and some ERP vendors also provide MOM level functionality. Deciding on an MES or ERP solution for your company will, therefore, be based on several factors, including:

  • Basic required functionality
  • Size of the company and scope of the EFP effort
  • The requirements and ability to run production without system support for periods of time
  • Local vs. centralized control of production procedures

Basic required functionality

The basic functionality normally required for MOM activity support includes:

  • Automated workflows to support production processes
  • Automated data collection from production equipment information and sensors
  • Management and tracking of production materials within workcenters and across workcenters
  • Management and tracking of production equipment
  • Generation of production documentation.

This basic functionality is often extended to include:

  • Detailed production scheduling, such as finite capacity scheduling
  • Integration of workflows with production equipment
  • Management and tracking of personnel qualifications and training
  • Production, process, and procedure analysis tools for process improvement projects and production troubleshooting
  • Generation of KPIs (key performance indicators).

Any ERP or MES system that claims to support MOM activities must provide your basic required functionality. Carefully evaluate how the vendor meets your requirements and if it is provided by standard, configured, or specially programmed modules. It’s important to determine if custom ERP coding to support MOM activities would save money versus a commercial MES solution.

Company size, ERP scope

Two usually unexpected factors in deciding on MES versus ERP for manufacturing operations are the size of the company and scope of the ERP effort. ERP systems can be large and all-encompassing, or small and tightly focused. If your ERP implementation is large, covering multiple business units, dozens of factories, and a large percentage of your business processes, then it may be unable to handle the full detail required for MOM support. MOM systems require detailed knowledge of equipment layouts, production recipes, and operational workflows. MOM systems will often coordinate maintenance, quality, inventory, and production activities down to the level of individual instruments, material sublots, and basic manufacturing steps. For large companies this level of detail is difficult to manage and maintain in a centralized system. For example, many ERP systems will not easily scale to handle inventory at the rack, bin, and slot levels across the entire enterprise. Most company-wide ERP systems operate best with a limited number of inventory storage points needed to handle costing and reordering activities. In a medium-sized facility there can be dozens of materials movements per minute, each requiring a coordinating business process.

  • If the company in question has only a few plants, then an ERP system may be able to handle the detailed information required to support manufacturing operations.
  • If multiple plants have different manufacturing processes, then an ERP is not the best choice for MOM support.

Another consequence of the scope of the ERP system is the expected transaction rate supported by the system. The rate of MOM transactions within a medium-sized facility can be hundreds of transactions per minute. This rate can be handled by ERP systems. However, if it must be scaled up to dozens facilities scattered across multiple states or countries, the combined rate would overwhelm most transaction/message-based ERP systems. The larger the scope of the ERP system, in terms of number of facilities handled and transaction rates, the greater the advantage in having a local MES solution that can bundle together updates to the ERP system.

  • ERP can be considered for MOM support, if the ERP system supports a few facilities and the number of data exchange transactions between the shop floor and ERP is a few transactions per minute.

Production without support?

A major concern of plant managers is to keep the plant producing. Many companies run 7×24 production and their operations support systems must have high availability and reliability. MES systems are usually locally hosted and designed for high availability. Many ERP systems are remotely hosted—and may even be on a different continent—and often have planned weekly or monthly downtime for backups and software updates. ERP downtime is usually planned for weekends, such as Saturday evening or Sunday morning, to minimize business impact. If the system supporting MOM activities is remotely hosted, then network outage can also cause unavailability. These outages are usually not under control of the company and could be caused by a wide range of problems, such as construction outside the plant cutting communication lines or trawlers cutting undersea cables. The ability to run unconnected is among criteria for deciding to use a remotely hosted ERP or local MES.

  • ERP can be considered for MOM support if your site can operate for 24 or more hours using manual processes because paper based backups and data communication alternatives, such as phone or fax, are readily available.
  • An ERP with a local data buffering system can be considered for MOM support if your site can operate between 8 to 24 hours without connectivity to the ERP system because paper backups and data buffering can handle short-term outages. 
  • An MES should be considered for MOM support if your site cannot run for longer than 8 hours using manual processes and paper backups.

Local vs. centralized control

A common ERP requirement is to make all plants look the same, as least as viewed by the logistics and financial business processes. This significantly reduces the ERP implementation and support costs, and it provides the consistency needed for logistics scheduling and product costing. This same level of consistency is difficult, if not impossible, to reach with MOM production processes. Few companies have plants that have the exact same physical layout, worker expertise, and regulatory requirements. Most plants have continual improvement projects that modify workflows, change production processes, re-layout equipment, change worker training, modify recipes or process instructions, and add automation equipment. MES systems are designed to handle these changes and are designed to handle differences between different parts of the production facility and even differences between production lines in the same area. ERP systems are not normally designed to support local procedures or to handle continual changes to the procedures.

  • ERP can be considered for MOM support if there are limited local workflows that are not handled by a DCS or batch execution system.
  • MES should be considered for MOM support if there is significant variability of production processes within the facility or there is significant variability in production equipment and local workflows within the facility.

Support, scope, workflow

The question of using an ERP or an MES system to support manufacturing operations activities can be a contentious, but applying a few well-defined criteria can make the question easy to answer. An ERP system can support MOM activities if the basic functionality is supported, the ERP system has a small scope covering a few plants, it supports site-level definitions of workflow procedures, and production can continue for one or more shifts without system availability. Otherwise an MES-based solution may be the best answer to your manufacturing operations management needs.

With a wide variety of production facilities, the “right” answer to the ERP or MES question may be different at each plant. The best solution may be a mixed system with some plants using a local MES solution and others using a centralized ERP solution. Some plants may be large enough and complex enough to justify a full local MES solution, while others can live within the constraints imposed by a centralized remote ERP system.

See related article in the November 2011 Control Engineering.

Dennis Brandl is president of BR+L Consulting in Cary, N.C., His firm focuses on manufacturing IT. Contact him at Edited by Mark T. Hoske, Control Engineering,

Related reading

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Engineering and IT Insight: What’s the best manufacturing operations management systems design?—Should your manufacturing operations management (MOM) systems be centralized or distributed? These key considerations can help you decide. MOM includes MES (manufacturing execution systems), LIMS (laboratory information management systems), WMS (warehouse management systems), tank farm management systems, and AMS (asset management systems).

More on MOM: Cut costs with manufacturing IT standards, best practices—If you had the opportunity to reduce automation project costs or times by over 30%, reduce costs for plant-to-enterprise integration by over 70%, or reduce maintenance support costs by over 10%, you would think that most manufacturing engineers or executives would stop ignoring this opportunity.