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the adequacy of the production lead times that have been established. If the number of red orders is too low, then it is a clear indication that the production lead time is larger than it needs to be. The allowed time is large enough that few, if any, orders are experiencing disruptions that have any consequence. This suggests an opportunity to reduce the planning production lead time used in the DBR system and eventually to reduce the lead time quoted to customers. Conversely, if the number of red orders is large, then it suggests that a large number of orders are experiencing significant disruptions relative to the time allowed for their processing. In this case, the production lead times are too aggressive and need to be increased. It has been our experience that the total number of orders in the red should be around 10 percent. If the percentage of red orders exceeds 15 percent, then we should consider increasing the size of the buffer. If the percent of red orders is less than 5 percent, then we should consider reducing the size of the time buffers.

Complex Production Environments and a Classification Scheme

Real-life production environments are much more complex than the simple flows used in explaining the DBR system. Even a medium-sized factory has hundreds, and often thousands, of parts and products and has tens, and often hundreds, of different resources. In other words, the detail complexity of production operations is immense. When the focus is on the detail complexity, one is overwhelmed and tends to believe that each operation is unique and there is little that can be transferred in learning from one operation to the next. Typically, production is lumped with the business as a whole and is described in terms of the industry segment to which they belong, such as an auto plant or food and beverage plant. In this section, we present a scheme to organize the production operations based on their product flow characteristics. This classification scheme will bring together elements of detail complexity and dynamic complexity that have an impact on managing the production operations effectively. By managing effectively, we mean deliver the products as promised to customers, while keeping investments in resources and inventory to a minimum. The development of the classification begins with a change of perspective, from a view centered on resources to a view that is centered on product flow.

The Fundamental Elements of the Classification Scheme

Since we are used to the resource centric view of production, we have to learn how to view the same operation in a way that focuses on flow. Such a view is provided by the view of production represented in Fig. 8-2 and Fig. 8-3—the view of operations from the point of view of the materials. It is a time-oriented description of the manufacturing process. As indicated earlier, the resulting diagram of the production operation is referred to as a PFD.12 We now explore PFDs in more detail.

Consider the simple case where we have three different raw materials (RM-A, RM-B, RM-C) that are fabricated into three component parts (A, B, C) and that these are assembled together into a finished Product D. This simple production operation has only one finished product.

To construct the PFD, we begin with raw material A (RM-A) at the bottom left-hand side of the diagram (Fig. 8-11). Each step in the fabrication of the component part A is represented by a box vertically above the box for RM-A. If the fabrication process consists of four steps (this information is typically contained in the routing file or process sheet for component A in the company’s ERP system), then we have a series of four boxes in a vertical line as shown in Fig. 8-11. For clarity, inside the box we have designated the process step and the resource used in that step—again a piece of information found in the routing file. The first step is designated A-010 and is performed by resource R1. The second step is A-020 performed by R2, and so on. Similarly, the fabrication process for component B made from RM-B