CONTINUOUS FLOW (PRODUCT ORIENTED LAYOUT) AND BOTTLENECK ANALYSIS
Reference: Operations Management by Mark A. Vonderembse and Gregory P. White.
The Product Layout and System Capacity
The capacity of a product-oriented system can be visualized as a series of pipes of varying capacity, with the smallest diameter or capacity holding back the entire system. Exhibit 9.3 illustrates five pipes (departments or machines) with different diameters (capacities). The output from one pipe becomes the input to the next until the finished product exits pipe number five. In Exhibit 9.3, pipe number two cannot handle all the flow that pipe number one can deliver, and therefore it restricts the flow. Because of pipe number two’s limited capacity, it restricts the flow from upstream pipes and starves the downstream pipes. Pipes three, four, and five can work on only what pipe two can deliver. This restriction is called a bottleneck, and it determines the system’s capacity.
Analysis of System Capacity
In a product-oriented layout, identifying the bottleneck is critical. The importance of this analysis cannot be overstated because the results are used not only in determining capacity, but also in planning and scheduling production, which will be discussed in Part III on planning and managing operations.
The approach to determining the bottleneck is illustrated in Exhibit 9.4. Start at the beginning of the system, and determine the capacity of the first operation or department. This is the system capacity so far. Use this capacity as the input to the next department in the sequence. Can that department take the total input from the previous department and process it completely? If it can, then the system capacity has not changed. If it cannot, then the system capacity is reduced to the capacity of that department. The procedure continues until the end of the process is reached and the system capacity is known.
Consider the example shown in Exhibit 9.5. The basic oxygen furnace has a maximum rate of 4,200 tons per day (tpd), while the continuous casters rate is 6,000 tpd. Clearly, the capacity of that part of the system is limited by the 4,200 tpd of the slower operation.
Exhibit 9.3. A Bottleneck in the Product Flow
Exhibit 9.4. A Sequential Approach to Bottleneck Analysis
Determining the Bottleneck
Now consider the entire system for making steel shown in Exhibit 9.6. The capacities are listed below each department. At two points in the steel-making process, outputs from two departments are inputs to a single department. The ratio of each input is listed on the arrow that illustrates the flow. For example, in the blast furnace, 3 pounds of iron ore are mixed with 1 pound of coke. In these cases, the inputs to a department should be combined in the correct proportion until at least one of the inputs is exhausted.
What is the system capacity? Follow along in Exhibit 9.6. Iron ore processing and coke ovens can deliver 3,000 and 1,000 tpd, respectively. (Only 3,000 tons can
Exhibit 9.5. Simple Steel Production Flow
Exhibit 9.6. Steel Production Flow: A Product Layout
Exhibit 9.7.Determining System Capacity.
be used from iron ore processing because of the ratio requirements.) The combined 4,000 tpd is more than sufficient for the blast furnace, which requires only 3,000 tpd total. So far, the blast furnace is holding back production. The blast furnace and scrap handling, in turn, supply 3,000 and 1,500 tpd, which is more than adequate for the basic oxygen furnace capacity of 4,200 tpd. Because the basic oxygen furnace cannot process all available inputs, the blast furnace cannot be the bottleneck. The basic oxygen furnace cannot deliver sufficient output to the remaining departments. Therefore, the basic oxygen furnace is the...
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