Understand fundamental dynamic routing elements

To understand dynamic routing, let's first start by discussing routings in general. In Manufacturing Execution System (MES), a routing refers to the preferred or actual sequence of actions needed to manufacture something. To the extent these actions take place on different physical entities within a plant, a routing mimics the movement of material that occurs as a product is being made. In MES, a process is the set of planned actions required to manufacture something (or possibly more than one thing, if the products differ only in the ingredients or components that comprise them or in the details of how these actions are done, and not in the overall flow of how they are made).

A process consists of a set of major actions called operations, and possibly also of a set of steps for each operation, which can be considered to be sub-operations. Each operation accomplishes a transformation of the material being worked on. The normal assumption is that all steps for an operation will actually be done on a single entity. However, for planning purposes, multiple entities can be identified as candidates for a single operation. The association of one or more entities with each operation is also part of the routing of the process.

Unlike a process, which is purely a plan or template that is intended to be used many times, a work order represents the intention to manufacture a certain amount of a certain product. It will only be executed once. Like a process, a work order also has a routing. However, instead of consisting of a set of operations and their candidate entities, it consists of a set of jobs, which are instances of operations identified for specific entities. Like operations, jobs can also have steps. A work order is often created by instantiating a process and its routing, but it can also be constructed from scratch without first starting out as a process. The work order's jobs (and job steps if defined) are the things that are actually executed in the manufacturing facility. As the product is being made, the work order is transformed from a statement of intention to a record of what actually took place.

A dynamic routing is one that is designed to allow for change from its original form to accommodate events that happen during the actual manufacturing process. These events are usually deviations from plan because something did not occur as expected. If material is irretrievably spoiled, altering the routing cannot change that. But if the problem is correctable, it can typically be addressed through rework. In general, rework is extra processing that is performed on a specific amount of work-in-process material to recover from a problem experienced in a manufacturing job that caused some or all of the output of that operation to be unsuitable for continuing with its normal processing.

If production is reported to the system with a reason that does not indicate normal operation but also does not indicate an irrecoverable outcome for which the production must be scrapped, then MES adds extra processing by creating rework jobs. Some examples of problems that might be correctable through rework, and the sort of rework involved, are provided in the following table.

The term dynamic is used because while the work order is being done, new jobs can be created dynamically in response to the recording of production (either manual or automated) with a reason that indicates a recoverable problem. Some or all of these additional jobs are not represented by operations and entities in the original routing.

There is another situation for which the flow of material through a routing can be altered in response to events that occur during its actual manufacture, but for which the occurrence is a normal variation in the process and does not indicate a problem. This is referred to as conditional routing. With conditional routing, the routing—in the sense of which job is done next for some amount of production (and thus where the material from the current job flows or is moved)—depends on conditions encountered during the manufacturing process. The main difference between this and dynamic routing is that variation in these conditions can be anticipated to occur even during normal operation, and thus the potential set of operations and entities involved are defined as part of the normal manufacturing process. That is, additional jobs do not appear automatically, but the way material flows from one job to another is altered. The set of conditions that can cause these changes in routing is typically more inclusive than just an item reason entered for production. For example, a range of a particular dimension, even if within specifications and thus reported as normal, good production, might cause a change in which job (typically which operation) is done next.

Dynamic routing can be used to address some of the same effects of manufacturing variation as conditional routing, but the variation has to be reflected in the item reason, and the orientation towards it being a non-normal outcome imposes certain limitations while also opening up certain possibilities not allowed within conditional routing. The point is that dynamic routing is oriented towards handling rework, and its suitability for use in other situations must be evaluated carefully on a case-by-case basis.