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Understanding MES - Manufacturing Execution Systems


In the first article of this series, we saw how the top level of Manufacturing Execution Systems (MES) work in the factory to deliver benefits against business goals and requirements, managing the flow of production for final products and sub-assemblies. Now it is time to delve into deeper levels of MES, looking at other areas within the factory that MES manages, that enable the final production flow to work smoothly and effectively.

There are many definitions of MES in terms of scope, what it includes, what it does not include etc. Most MES systems are designed for maximum reach across industries, supporting many different industry segments. In some cases, certain features are critical, and in others almost irrelevant.

There will probably never be a standard definition of what MES must contain or what it is expected to include. Arguments on this subject continue to evolve as expectations change based on technology advances such as the Industrial Internet of Things (IIoT). Modern expectations are for MES to connect bi-directionally with automated equipment to reduce the amount of operator support needed and also to reduce delays for data acquisition and process control.

MES should provide the single digital platform that connects these differing areas, such that visibility and control of potential causes of final assembly production disruption can be gained.

Factory Dependencies

The common design of production processes focuses on the main production schedule that delivers completed products to customers. The idea is that this production should never be interrupted, as this would threaten the on-time delivery performance. If interruptions were to be tolerated, the result would be reduced productivity and the risk of late completion, which then brings the need for excess finished goods stock, a significant and needless cost for the operation. Everything on which final production is dependent must be prepared perfectly in advance, preferably on a “Just In Time” (JIT) basis such that it is there when needed, but only when needed.

Key dependencies to consider include material preparation, engineering data, management of key tools and resources, including people. MES knows both the current and intended production plan as well as the current progress of production. The sequence for the provision of materials and utilization of resources can then be predicted, allowing MES to manage such resources in line with final production requirements, or even to adjust the final production schedule if resource capabilities are exceeded.

MES operates in a live environment working in many areas simultaneously and with many different kinds of data, essentially a “big data” environment. The range of values that MES adds is very much up to the design and scope of the software. Basic examples will calculate and show requirements for things, then monitor progress to show performance. More advanced MES systems will manage key aspects of the dependent areas, adding value to each for automation, management, and traceability.

MES Internal Supply-Chain Management

Materials are a critical element for successful production. The absence of even the most humble of parts such as the correct cable or resistor, which in themselves have almost zero cost, can mean that production cannot be completed and perhaps should not even be started. Every individual material needs to be treated by MES as critical. ERP recognizes materials simply by part number and quantity “on-site,” which starts from the arrival of the raw material through to work-order completion, which is often simply a multiplication of products made, multiplied by the material counts in the Bill of Materials (BOM).

Though locations of materials are supported in many ERP systems, material inventory by location cannot be relied upon, as it requires extensive manual material counting and data entry at busy times. Almost without exception, the ERP view of materials is quite different from the physical situation, due to spoilage and other unaccounted losses. The need for frequent, costly, disruptive stock-checks and the resultant need for adjustments in ERP is a symptom of this issue, as well as cases where materials could not be found when needed.

A basic MES system can help by providing knowledge of materials movements, though the ERP system will still frequently make poor planning decisions based on incorrect assumptions of material availability, which risks creating schedules that cannot be fulfilled.

The more advanced MES system will take full control of materials starting with the unique identification of materials, either individually for key components and sub-assemblies, or by the carrier for bulk materials such as reels of SMT parts in electronics manufacturing. MES will then decide and allocate storage locations, creating and managing logistics tasks for materials operators as materials are dispersed throughout the factory, including warehouses, local stock areas and delivery to points of consumption.

Mobile terminals are an ideal way for MES functionality to be present wherever needed, as materials are scanned into or out of locations. The requirement for material movement is best driven on Lean principles such as Kanban, and JIT delivery based on the predicted need for materials at the point of consumption. MES knows the quantity of each material required for production having full visibility of the current and near-term intended schedule, plus live feedback about progress from the production processes themselves.

More advanced MES systems will also collect spoilage data as well as consumption data, such that near-perfect material inventory control can be maintained, which when shared back to ERP, enables ERP to make better decisions. Advanced MES systems manage advanced aspects of materials, including such things as storage environment requirements, baking cycles for moisture sensitive materials, obsolescence and expiry, as well as material substitutions against the approved BOM.

MES technologies eliminate “internal” material shortages, meaning that production is never disrupted for lack of materials. Also, benefits have been seen such that bloated stock inventories can be reduced by 75%, material logistics reduced by 30%, warehouse space reduced by 50% and other savings for example related to production space and number of carriers required (such as feeders for SMT materials).

The potential savings in material related costs alone is for many, justification in itself for the purchase of an advanced MES system.

Engineering Data Management

Part of the job of a modern MES solution is to display electronic documentation at production processes. As more processes become automated, such documentation is targeted more at the setup of the process, while the automation follows an assigned sequence of instructions. These instructions are typically formatted and optimized using software provided by the machine vendor. The engineering data on which they are derived however comes from the design of the product and local BOM.

The conversion of design and BOM data and assignment of work to complete a product is divided between the various automated and manual processes by MES engineering systems depending on process capabilities and throughput metrics. Without such a tool, an engineer has to read in design data from many different formats, confirm data consistency, make adjustments depending on local BOM changes, and then manually split the data out to the various production systems based on their know-how. This process typically takes many days in the case of complex manufacturing such as electronics. Crucially, however, this process effectively dictates that engineering decides the production configuration with which to make each product in advance, with very little flexibility.  While this has been seen as a “cost of doing business” in the days of high volumes and low product mix, in today’s dynamic high-mix environment, this process is not sustainable. With advanced MES systems creating a digital product-model, taking data in electronic format from design and BOM, the conversion and assignment of work is automated following engineering preferences, taking minutes rather than days. The ability to effectively create process data on demand allows the MES planning function to decide which is the best configuration to use for each product depending on the actual condition of production and demand at the time. More flexible planning leads to significant improvement in asset utilization and productivity.

The MES planning function will consider lead times throughout the product hierarchy of sub-assemblies, optimizing execution considering all available configurations, changeover times, as well as product grouping strategies. This Lean approach to planning is executed for the coming hours or days, rather than weeks or months. This degree of flexibility allows a step-change in the ability of the modern factory to respond to changes in customer demand, being able to make transitions across a high-mix of products smoothly, while keeping utilization to a maximum without the need to produce excess finished goods stock.

Results seen by this practice can yield between 20% and 50% improvement in productivity. This resolves the traditional problem that occurs without MES, or with only a basic MES, where productivity declines very sharply as product mix increases, leading to increased costs and investment.

In the next article, the final part of this series, we will continue to look into areas of MES management, including quality, key resources, and maintenance, as well as summarizing the key aspects to consider when embarking on MES introduction or upgrade.

About the Author:


Aegis Software is the leading provider of innovative software solutions to improve speed, control and visibility throughout manufacturing operations. Founded in 1997 by two manufacturing engineers, Aegis has over 17 years of experience providing world-class software to customers around the globe. Our install base spans more than 1700 factory sites across the electronics, medical, automotive, military and aerospace industries.

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Topics: Manufacturing Supply Chain ERP