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Process Selection and Facility Layout -- Supplement to Chapter: Linear Programming

Key Ideas

1. Process selection involves making choices concerning the way an organization will produce its products or provide services to its customers. It has major implications for capacity planning, layout and work methods.

2. Managers can select from five different types of processes: job shop, batch, repetitive, continuous and projects. Job shops are used to produce a low volume of each of a large variety of products or services. Equipment flexibility must be high to handle the high variety of jobs. Batch processing involves less variety, less need for equipment flexibility, and higher volumes of each type of product. Repetitive processing has even less variety, less need for equipment flexibility, and higher volume. Continuous processing has the lowest variety, the lowest need for equipment flexibility, and the highest volume.

Job shops and batch processing are classified as intermittent systems, meaning that output frequently switches from one product or service to another. Repetitive and continuous systems are classified as continuous processing because there is little or no switching from one product to another. Projects are used for non-routine work that is intended to meet a given set of objectives in a limited time frame. Job variety is high, volume is usually low, and equipment flexibility needs can range from low to high.

3. Process selection may lead to automation or computer-aided manufacturing. [You should find it helpful to list the different types of computer-aided manufacturing, along with a brief description and advantages and limitations of each type.]

4. A key issue in process selection is the management of technology. See the discussion under the Operations Strategy section. Another key issue in process selection is flexibility.

5. There are three fundamental types of plant layout, respectively corresponding to the three different types of production operations situations.

  1. A product layout implies that a single product or else a single type of product, for example, automobiles, is manufactured on an assembly line, with the production tasks assigned to workstations along the line.
  2. A process layout involves the movement of batches of goods between departments via forklift truck, moving belt, or some other type of conveyance.
  3. A fixed-position layout is appropriate for a large end item such as a house or airplane, where all material is assembled to a major structure or product at a specified site.

6. A product layout such as that associated with automobile factories is a good idea when it is justified by the volume. The advantages of product layout are that it involves continuous flow of the work in process, minimum work-in-process inventory, maximum specialization, low material handling costs, efficient utilization of labor and equipment, and systematized routing, purchasing, accounting and inventory control. The disadvantages are dull repetitive jobs, inflexibility and susceptibility to frequent shutdowns.


7. A process layout allocates floor space to work centers so as to sustain a logical flow of semi-finished goods, and minimize transportation and inventory costs. It is more flexible than product layout in the sense that a variety of products can be made without incurring extensive changeover costs. It also makes better use of the specialized skills of employees, so that incentive pay systems can be effective in enhancing productivity. Process layout is appropriate when each type of product or semi-finished goods has low volume, but there are potentially high costs for unused equipment, excess inventory, slow or irregular movement, and a need for extensive production control paperwork.

8. A fixed-position layout is appropriate for large construction projects or for assembly of very large products such as airplanes, which are difficult to move. An example of a fixed position service system is a subway, which is an economical way to move large masses of people.

9. An assembly line is balanced to smooth the flow of semi-finished goods, and to achieve the best possible utilization of both the labor force and the plant. The work is subdivided into groups of tasks, and each group is performed at some specific location along the line called a workstation. A workstation might be a single employee, or possibly a small cluster of employees, if the services of more than one person are required for the tasks.

10. The cycle time is the span of time a unit of product is at a workstation. In balancing the line, we determine both the cycle time and the number of workstations, based on the number of units of product to be produced in a working day, the total of the times of the tasks needed to make one unit of the product, and the amount of effective clock time available in a day, after allowing for rest periods, breaks and planned shutdowns of the line.

11. There are several different meanings of the term "cycle." The minimum cycle time is the time required for the longest task. The maximum cycle time is the sum of the task times for a single unit of product. The actual cycle time is somewhere between these two extremes; it is the amount of time at the workstation with the largest sum of task times.

12. The minimum number of workstations in the product layout is the quotient of the sum of the task times for a single unit of product divided by the cycle time, rounded to the next highest integer. Assigning tasks to workstations is done with heuristics (rules of thumb):

  1. Consider precedence; make sure that all jobs are done in a logical sequence.
  2. Try to keep all stations busy all of the time by filling up the cycle time with tasks. Do not assign a station more tasks than it has time to perform.
  3. The greatest positional weight rule, one of several heuristics for assigning tasks to stations assigns tasks according to the greatest sum of remaining task times to a free station. Other heuristics are: most following tasks, most preceding tasks, and greatest sum of task times for tasks that precede.

13. Measures of effectiveness guide decision makers to satisfactory, but not necessarily optimum decisions on process layouts. The simplest approach involves ranking of departments or work centers according to workflow (Distance x Number of loads carried), and assigning work center locations so as to minimize the total intraplant transportation costs.

14. The Muther grid is an alternative approach to process layout planning that allows for subjective opinions that consider multiple criteria on the closeness of work centers to one another. Work centers are rated in pairs on a six-point closeness scale from A (absolutely necessary) to X (undesirable). First the A's are paired, and then the X's are separated; then the E's (very important) are paired, etc., until all centers are accounted for.

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