Theory of Constraints Handbook - James Cox Iii [148]
4. Sales and marketing managers complain about the lack of responsiveness from manufacturing.
5. Interdepartmental conflicts are common within the manufacturing area.
DBR in V-Plants
It is important to recognize first that in almost all cases, there is a considerable effort underway to address the problems faced by a typical V-type plant. Each of the issues is assigned a cause and a solution is either being designed or in implementation. However, the problems persist in most cases. A properly implemented DBR solution will address many of the root cause issues that underlie the V-plant problems and thereby help mitigate most of these problems at the same time. If a capacity constraint exists and these are the only conditions in which the full DBR system would be considered, then identifying which resource is the capacity constraint is the first task. In V-type plants, this is a simple task. Since the resources are involved in the flow of most products, material naturally accumulates in front of the resource with the highest load. The CCR is thus the resource with the largest in-process queue (measured in hours of work for that type of resource). In the case shown in Fig. 8-14, the constraint is resource R3. It is also true that the personnel in the plant have a common and usually correct knowledge of the constraint. As an aside, it should be noted that the presence of high levels of Finished Goods (usually the largest bank of inventory in the flow) suggests that setups are considered large at many key resources in the operation.
The next key step is to establish the drum. The challenge in most V-plants is the fact that the load placed on a specific resource is significantly influenced by the number of setups that result from this mix. In other words, changing the product mix can change the resource that is most loaded. For example, a textile mill running very large batches of a given color can significantly reduce the total load at the dyeing resources but can cause major problems at the cutting and sewing operations. This is because a single color material will have to be fabricated into apparel of many different sizes and styles and this causes overloads at these work centers. The key to establishing the drum is to find the proper balance between the market demand and the schedule at the constraint that satisfies the requirements for a drum:
1. It satisfies market demand.
2. It maximizes Throughput for the system.
3. It does not create new constraints.
The other factor in designing and implementing a DBR system in a V-type plant that needs special attention is the existence of a large number of divergence points. Each divergence point is a schedule control point and needs to be managed as such. Detailed lists that show the different products that need to be produced and the exact quantity that needs to be produced for each product are required at each divergent point resource.
The schedule control points are material release, constraint(s), divergence points and shipping.
A-Plants
A-plants are characterized by the existence of convergence points wherein a large number of component materials are assembled together into a few end items. The component parts are usually made up of parts that are fabricated in the plant (or other plants/departments in the division) and parts that are purchased from outside vendors. The typical PFD for an A-plant is shown in Fig. 8-15. One characteristic of A-plants, which is different from characteristics of T-plants, is the fact that the component parts tend to be unique to a single end item. Several levels of subassemblies may be involved prior to final assembly. Since the overall product flow is convergent rather than divergent, the product flow diagram resembles an inverted V, thus the designation A-plant.
FIGURE 8-15 Product flow diagram for a typical A-plant.
One example of an A-plant is provided by aircraft manufacturing. The PFD contains several thousand components that converge to a single product.