Data Model for Manufacturing Execution System (MES)

 Complete Data Model of the MES

The production data model requires a complete description of the product, the  product definition, and, based on this, the resources required and a description of the production environment (mainly machinery and equipment).  

The following aspects must be mapped in the MES database using adequate objects:

• Product definition data and the resources needed—or “with what” the product will be produced

• Description of the production environment and resources (“with what” will be produced):

• Machines, equipment, and workplaces

• Personnel resources

• Operating resources such as tools and means of transport

• Materials and preliminary products 

• Documents and data on product description and production control

• System and auxiliary data such as units of quantity.

• Data on the execution process (what is the “result” of the production):

• Order data

• Production data

• Equipment and machine data

• Performance data 

It is necessary to record all user interventions. For example, changes made to machine parameters, recipes, or article master data should be logged, including the date, time, and the person making the change. 

In the data model, historization of the most important objects is needed. This means that in addition to the currently valid version of the object (e.g., article master data), all previously existing versions of the object (e.g., the previous definitions of the article master data) are saved. This historization gives the  advantage that old versions of the object (e.g., a recipe that has already proved itself once in certain environmental conditions) can be “activated” again if needed.

For many objects of the data models, a grouping of the elements in a hierarchical structure is needed. Personnel, materials, and articles etc. are allocated to groups. Hierarchical grouping improves the overview and makes it easier to evaluate the data using group-related filters.

Creation of Master Data 

Master data may be imported from other systems or a master data management (MDM) system. This requires a flexible import interface in MES.  The system also requires the facility to update the data manually. It must be possible to create, edit, and delete all master data sets manually.

Product Definition Data Model  

Concepts Related to Product Definition in MES

• Article/article groups. The article is the product that is created in the production work plan using various resources. Different variants of an article can be manufactured in one production plant. The articles can exist in hierarchical article groups.

• Variant. Variants (or types) of articles are manufactured with the same work plan and the same resources as the “master article”; that is, the same operations and work plan can be used for all variants. Differences arise only in details of the operations. Here, different materials, colors, amounts, or work instructions can be entered for variants.

• Operation. An operation is a defined part of the production process that, as a part of the article-based work plan. It is linked with a machine/equipment (operation-machine combination).

• Work plan. A series of operations and their links with specific machines where they are to be performed are established in the work plan. This sequence also can contain conditional loops with alternative branches and . The actual route of the production unit (the alternative branch selected) is not determined until the fine-planning stage of the order. The work plan is defined per article and is also valid for its variants.

• Parts list. A parts list contains the definable individual components of an article in the form of a hierarchical list. These individual components may be raw materials or preliminary products. Internally manufactured preliminary products are also mapped as articles in the MES. Externally manufactured preliminary products (“purchased parts”) are treated as raw materials.  .

The Operation

The operation is an activity or a process.  Some examples are heating, mixing, extracting, rolling, drilling, milling, polishing, transportation, and testing.  

 An operation is determined by the following basic parameters:

• Name, description.

• Activity/process with regard to a general list of occurring activities/processes. 

• Quantity input, quantity unit input. 

• Transformation through an operation. 

• Quantity output, quantity unit output.

• Identification of “mixture.”  The materials used are no longer distinguishable as inputs from the previous operation (e.g., mixing process). 

• Parameters for cost monitoring. 

Time Data for the Operation

 For  MES, the following time types are particularly significant:

• te  = production time ( time per unit ).

• tr  = setup time. In process engineering,  cleaning time or preparation time is the term. The setup time is independent of the quantity produced.

• ta = order time = tr + te × quantity.

In some cases, the specifications on “machine cycle time” and “personnel 

time” are  additional data  

Use of Personnel: Personnel requirements are set only roughly for the operation; 

Use of Material: The use of material is defined with regard to the basic quantity unit of the article (e.g., 1 piece, 1 kg, 100 L, etc.) in the operation.

Use of Operating Resources: The use of operating resources is related to the basic quantity unit of the operation. It is also possible to list numerous resources per type with reference to the resource management master data:

• Tools. 

• Means of transport.  The planning process can use this to determine the need for means of transport.

• Packing. 

• Measuring equipment. 

 Information and Documents Related to Operation

Work instructions, process instructions, and test plans are linked with the operation.

The response to instructions can be termed in various ways. 

• Informative character. Information and directions for the workers can be viewed optionally in the execution process. The worker receives notification of the information but is not required to read it if he or she is familiar with the content.

• Information that must be acknowledged. This information is always displayed in the execution process. The worker must acknowledge the information.

• Execution of an activity and acknowledgment. The worker must carry out the instructions and then acknowledge. Test plans or rework protocols always belong to this group

Creation of Variants in the Operation 

The possible variants of the operation considered here are indicated with reference to the article variant list (part of the article master data). These are generally variants in materials, such as color variants of an article or raw materials from different suppliers. 

The Work Plan 

The work plan (bill of process) is the central control instrument of production. In it, the individual steps of production are defined for each article in the form of operation-machine combinations, hereafter referred to as work sequences. 

The following data define a work sequence:

• Sequence number. Work sequences are defined clearly within a work plan by means of a sequence number. 

• Operation. The operation defines the “action” and/or the “process” (what is conducted in the production step) and all allotted operating resources (how the production step is carried out). The operations have prior definitions or if needed can be created in the course of compiling the work plan.

• Machine/system/workstation. The link with a machine, a system, or a manual workstation ( collectively  machine) defines the location of the operation, where the production step is carried out. Operations can be carried out alternatively on several machines (e.g., either machine A or machine B). This alternatives are part of the work plan. The respective alternative or parallel machine can be selected in the operative planning system in the the execution process, depending on the circumstances.

• Specifying the relationship to predecessor/successor. Order of the work sequences. Predecessor operation (s) is specified. 

More Details of the Work Sequence

• Use of staff. Personnel requirements per time type, that is, for setup and manufacturing, can be roughly specified in the operation. These details must be specified more precisely in the work sequence by linking them with a real machine.

• Ratio of quantity to next sequence. Normally, input quantity is the same as output quantity; the quantity ratio is 1:1. But in some operations it can different due to shrinkage. 

• Start quantity. The start quantity indicates when an operation can begin with regard to its predecessor.  The next work sequence can start in a piece goods plant when a transport container has been delivered with parts from the previous process.  Cycle times can be reduced considerably by such “overlapping” operations between two machines.

Planning Costs: After the work plan has been drawn up, the planning costs for the article are set.  These planning costs can be saved with the article master data and also issued as a detailed report.

Creating the actual work plan, is a  complex parametric exercise. In order to make this exercise as user-friendly as possible,, graphic editors (for creating the work plan) should be used. Provision has to be there to view the the work plan created  in a graphical format.

The Parts List 

The parts list is a hierarchical classification of the product into individual components (raw materials and preliminary products) that can be derived from the work plan.  The hierarchy of these materials results from the production flow depicted in the work plan. The parts list of the work plan is not  an independent object related to product data but it is part of the work plan. 

Change Management and Product  History 

Change management above all must record changes in operation definitions and archive all previous versions. Older versions must remain accessible to support traceability and product liability. It also makes it possible to revert to “older” versions of the article and produce these.

Adapted from Manufacturing Execution System: Optimal Design, Planning and Deployment

Heiko Meyer, Franz Fuchs, Klaus Thiel

MES, Jurgen Kletti

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