Intended learning outcomes: Explain the cumulative production figures diagram and the cumulative production figures principle.
The cumulative production figures principle originated, like the Kanban technique, within the automobile industry. It aids control of a supply chain with regard to deliveries by system suppliers and to coordination among different manufacturing companies. It is a simple technique that combines long-term resource management with short-term materials management and scheduling. In essence, in the manufacturing process of a certain product, it counts the number of intermediate products or states in the flow at certain count points and compares this amount to the planned flow of goods. Depending on the result, the work system can be sped up or slowed down.
For the manufacture of different products, and different variants of products, a particular quantity of cumulative production figures is required. The cumulative production figures principle is best suited to a product concept of standard products or standard products with (few) options and to batch production. The most important prerequisite is the same as that for the Kanban technique: continuous demand along the value-added chain, or production and procurement with frequent order repetition.
The following discussion of the cumulative production figures principle is based mainly on [Wien19].
A cumulative production figure (abbreviated below as CPF) is the cumulative recording of the movement of goods over time.
Figure 6.4.0.1 shows an example of cumulative production figures along a sample manufacturing process. The process has been divided into the part processes, also called control blocks, which in this case are parts production and assembly.
Fig. 6.4.0.1 The definition of cumulative production figures along the manufacturing process.
At the start and end of each part process, a cumulative production figure is defined: the entry cumulative production figure and the issue cumulative production figure. This is based on the assumption that there is always a process store, or buffer, between two part processes. For processing time within a part process, or control block, planning uses average lead time. In planning, this is also called the control block time offset.
The cumulative production figures curve is a graph of the measurement of a cumulative production figure along the dimensions of amount and time.
A cumulative production figures diagram is a summary of cumulative production figures curves throughout the manufacturing process for a particular product.
Each product or product variant has its own pair of cumulative production figures diagrams:
- The target cumulative production figures diagram describes the planning based on demand forecast or blanket order and the subsequent resource requirements planning on the time axis. Batch size need not be taken into account, so that between two points in time a cumulative production figure will take a linear course. The difference in amount corresponds to gross requirement during the time period defined by the two count points. The rest follows long- and medium-term planning in the MRP II concept.
- The actual cumulative production figures diagram describes the measurement of the actual manufacturing process. The diagram shows the actual, current progress in production, lead times, and inventory in work-in-process and in buffers. Jumps in the lines are caused by batch sizes.
Figure 6.4.0.2 shows an example of a possible target and actual cumulative production figures diagram for the manufacturing process in Figure 6.4.0.1.
Fig. 6.4.0.2 Cumulative production figures curves and target (dotted) and actual cumulative production figures diagram. (Example is based on [Wien19]).
The cumulative production figures principle (CPFP) is the planning & control of the manufacture of a product by means of comparing the target cumulative production figures diagram to the actual cumulative production figures diagram.
Through putting the two cumulative production figures curves, or whole cumulative production figures diagrams, one on top of the other, it is possible to bring the actual diagram closer to the target diagram through speeding up or breaking the manufacturing process. However, the following must be kept in mind:
- The diagrams give no information on the actual operation times and the current load on the work system: Incoming goods to a part process do not necessarily start the process immediately. In addition, there may be several different products being manufactured in the system. Therefore, the cumulative production figures principle cannot provide the basis for capacity management.
- Thus, for capacity management, the accuracy of the lead times, particularly interoperation times, is an absolute prerequisite.
- Count points must be placed in a way that guarantees accurate counts. A good point in time is at quality control: Here, both the amount of scrap and yield or good quantity are registered. The actual cumulative production figures can now be corrected accordingly at the already measured points, or appropriately marked special demand orders can be released.
In practice, it becomes clear that to keep to the target diagram, sufficient capacity reserves, or capacity that can be implemented flexibly in time, must be available. This is even more the case because capacity management in short-term planning (that is, control) is not possible with the cumulative production figures principle. Only continuous demand along the entire value-added chain will ensure that these reserves will not have to be tapped often.
Course 6: Sections and their intended learning outcomes
Course 6 – The Lean / Just-in-Time Concept and Repetitive Manufacturing
Intended learning outcomes: Produce an overview on lean / just-in-time and repetitive manufacturing. Explain the lean / just-in-time concept in detail. Describe the Kanban technique. Identify the cumulative production figures principle. Disclose an implementing procedure and a comparison of techniques.
6.1 Characterizing Lean / Just-in-Time and Repetitive Manufacturing
Intended learning outcomes: Explain Just-in-Time and Jidoka: Increasing productivity through reduction of overburdening, unevenness, and useless effort, or waste. Describe characteristic features for simple and effective planning & control techniques of repetitive manufacturing.
6.2 The Lean Concept / Just-in-Time Concept
Intended learning outcomes: Explain lead time reduction through setup time reduction and batch size reduction as well as further concepts. Describe line balancing through harmonizing the content of work. Disclose Just-in-Time Logistics. Present generally valid advantages of the lean / Just-in-Time concept for materials management and for capacity management.
6.3 The Kanban Technique
Intended learning outcomes: Explain Kanban as a technique of execution and control of operations as well as a technique of materials management. Disclose the adequate long- and medium-term planning for Kanban.
6.4 The Cumulative Production Figures Principle (CPFP)
Intended learning outcomes: Explain the cumulative production figures diagram and the cumulative production figures principle.
6.5 Implementing Procedure and Comparison of Techniques
Intended learning outcomes: Present procedures in implementing effective logistics. Differentiate between Kanban and the order point technique through a comparison of the techniques.
6.6 Summary
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6.7 Keywords
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6.8 Scenarios and Exercises
Intended learning outcomes: Operation time versus operation cost: disclose the effect of varying setup time and batch size. Calculate the effect of cellular manufacturing on lead-time reduction. Perform line balancing through harmonizing the content of work. Determine the number of Kanban cards.
6.9 References
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Case [Course 6]
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