When You Need More Than ERP Only

When selecting and implementing manufacturing execution systems (MES), industrial companies are confronted with an overlap of functionality offered by separate suppliers. “Which functionality should we implement in which system?” they wonder.

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This sometimes leads to inefficient choices. Some enterprises have taken their “SAP-only” policy too seriously, and they now have to deal with an unnecessarily expensive and inflexible information technology (IT) landscape. They’ve interwoven their enterprise resource planning (ERP) and MES layers as if it were spaghetti. So now, when they purchase a new plant, the complete spaghetti has to be rolled out.

The ISA95 standard helps to avoid such cost-inefficient choices. The standard makes clear which functions of manufacturing enterprises belong within the Enterprise Domain (level 4) and which belong within the Control Domain (level 3). For example: Product Cost Accounting is a level 4 function, so it’s logical to support this with an ERP system. And Production Control is a level 3 function, so this had better be supported by MES.

But there are also a few functions that cross the boundary of the Enterprise Domain and the Control Domain. Like Production Scheduling. When you implement scheduling functionality, you have to pay special attention to the boundary between the ERP and the MES layer. Level 4 scheduling aims at producing the right product in the right amounts, at the right quality, and deliver it at the right time to the right client. But level 3 scheduling focuses on efficiency. Within the bandwidth of the Master Production Plan, it combines orders, thus reducing the number of changeovers and cleanings.

The same is true for Material and Energy Control. It also crosses the boundary of the Enterprise Domain and the Control Domain, meaning that you will be confronted with the question of whether specific functionality should be supported by the ERP system or by the MES. On level 4, you encounter the inventory strategy with the reordering parameters such as safety levels. But on level 3, people worry about the physical handling of the materials. What should be stored where? Has the lab already released this lot?

In short: quite different decisions are taken on each level, and for these decisions, different kinds of information are needed. Note that ISA95 does not tell us that we may not use a solution from an ERP vendor to implement level 3 functionality. But you should at least make a conscious decision and separate the different kinds of information in a logical way. That way, your IT landscape will remain flexible over time.

There are many different opinions about the usability of ERP from SAP AG, the Walldorf, Germany, enterprise software vendor, in the MES layer. The table above may help to make a good choice in case of an SAP-only policy:
 
The world is changing. SAP and other traditional ERP suppliers are buying MES companies and starting to offer dedicated MES solutions. The boundary between ERP and MES suppliers is disappearing. That doesn’t matter. But the boundary between the ERP application and the MES application should remain clear.

Traditional SAP modules can probably support this:
•Simple processes, stable routings
•Long production runs (days, weeks)
•1-to-1 relationship between the order on level 4 and the order used in the factory
•Many manual activities; the system has to guide the operator through the steps

It is not likely that traditional SAP modules can support this:
•Complex processes, unstable routings
•Short runs (minutes, hours)
•Splitting or merging of orders from level 4 to make specific orders for production efficiency
•A highly automated production process; time critical integration with the process control layer.

Bianca Scholten, bianca.scholten@ordina.nl, is a Principal at IT integration firm Ordina Technical Automation, in The Netherlands, and a member of the ISA95 committee. The White Paper “IT or Engineering…Which of them should support MES?” is available at www.ISA.org.

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