Teaching Notes

Answers to Discussion and Review Questions

2. There are five basic process types:

a. Job-shop: Job-shop is used when a low volume and a large variety of goods or services are needed. Job-shop involves intermittent processing, high flexibility, skilled workers, relatively large work-in-process inventories and general-purpose machinery. An example is a tool and die shop that is able to produce a wide variety of tools.

b. Batch: Batch processing is used when a moderate volume of goods and services is demanded. It is designed to handle a moderate variety in products. The processing is intermittent. The flexibility of the process to produce a variety of goods, the skill of the workers, amount of work-in-process inventories are all less than job shop. Typical examples of batch processing are paint manufacturing and clothes making.

c. Repetitive: This type of a process involves higher volumes of more standardized goods or services. The flexibility of the process to produce a variety of goods, the skill of the workers, amount of work-in-process inventories are all less than batch process. Typical examples for this type of process include appliances and automobiles assembling.

d. Continuous: This type of a process involves very high volume of highly standardized goods or services. These systems have no flexibility in output or equipment. Workers are generally low skilled and there is no work-in-process inventory. The machines are dedicated to perform specified tasks. Typical examples include petroleum products, steel and sugar processing.

e. Project: Projects are designed to be used with non-routine, unusual tasks or activities. These activities are generally not repeated. Equipment flexibility, level of worker skills and work-in-process inventory can range from very low to very high. Examples include construction of a dam or a bridge, conversion of the production system from job-shop to cellular manufacturing, installing and implementing a new inventory and bar coding system.

3. Advantages: Highly uniform output, boredom and fatigue are not factors, machines don't go out on strike, etc.

Disadvantages: Rigidity, expensive, setting up is hard.

4. Computerized numerically controlled (CNC) machines are programmed to follow a set of processing instructions. Robots have movable arms that enable them to handle a wide variety of tasks such as welding, loading and unloading machines, painting, and testing.

Flexible manufacturing systems (FMS) are groups of CNC machines that have a supervisory computer, automatic material handling, and automatic processing. Systems usually range from 3 machines to a dozen. They are designed to handle a variety of processing requirements (similar to intermittent systems) with some of the benefits of automation.

Computer-integrated manufacturing (CIM) is a system for linking manufacturing activities through an integrated computer. These include engineering design, flexible manufacturing systems, and production planning and control.

5. (See question #4 above for description.) FMS is usually used as an automated manufacturing cell working on a family of similar parts.

6. Process selection decisions often include aspects that require highly technical knowledge. Many managers do not possess such expertise. However, if those decisions are delegated to engineers or others who do have the expertise, there is the danger that managerial issues will suffer. The solution is for managers to increase their knowledge of technological advances. In the meantime, managers must be prepared to ask questions and impress upon technical experts their goals and objectives.

7. A process flowchart or diagram is a graphical representation of steps of process (operations, delays, etc.)

8. The trade-offs between product layout and process layout include the following:

a. Process layout has more equipment flexibility.

b. Process layout generally has higher skilled workers.

c. Product layout involves higher volume manufacturing.

d. Process layout benefits from high flexibility to be able to produce a variety of products, while product layout benefits from large volume manufacturing at low cost.

e. The major goal of process layout is to minimize the transportation and material handling costs while the primary objective of the product layout is to minimize idle time and maximize efficiency of the process.

f. The utilization of process layout generally results in higher levels of work-in-process inventory than the product layout.

g. For a product layout, the flow of work is straight, while for process layout, the flow of work is mixed depending on the product produced.

h. There is more dependency between workstations for product layout than for a process layout.

i. The preventive maintenance and machine reliability are more important in a product layout than process layout because equipment breakdown may involve shutting down a work station which may in turn result in shutting down downstream work stations.

j. Routing and scheduling is much less complicated for processes with product layout than processes with process layout.

9. - Estimate space requirements. Is there enough space available?

- Determine the roads and rail access to the site.

- Draw a process flowchart and superimpose it on the map of shop floor, starting from receiving and ending in shipping.

- Allow space for material handling.

- Rearragne the layout seeking feedback from affected workers.

- Mark out line of machines on the shop floor.

10. Product layouts are generally characterized by specialized labour and equipment designed for continuous processing. The layout is often arranged on the basis of processing sequence. Process layouts are more general in nature, in terms of labour, processing equipment and material handling equipment. Process layouts often feature machine groups or departments. Items processed in process layouts tend to follow differing paths through the system.

11. The main advantages of product layouts include:

a. A potentially high rate of output.

b. Low unit costs.

c. Low training costs and wide span of supervision due to specialization.

d. Low unit cost for material handling.

e. High utilization of labour and equipment.

f. Routing and scheduling are built into the design.

g. Accounting, purchasing and inventory control are fairly routine.

The main disadvantages of product layouts include:

a. Specialization can mean dull, repetitive jobs with little opportunity for personal satisfaction or creativity.

b. Workers may have little interest in maintaining equipment or in the quality of output.

c. The system is not particularly adaptable to changes in process design or changes in the volume of output.

d. The system is highly susceptible to shutdowns caused by equipment failure or excessive absenteeism.

e. Preventive maintenance costs and the capacity for quick repairs are necessary to ensure high utilization.

f. Incentive plans tied to individual output are impractical.

12. The main advantages of process layouts are:

a. They can handle a variety of processing requirements.

b. The system is less vulnerable to equipment failures than product layouts.

c. The general purpose equipment used is often less costly than the specialized equipment used in product layouts. It is also usually easier and less costly to maintain and repair.

d. Individual incentive systems are possible.

The main disadvantages of process layouts are:

a. In-process inventory costs can be high (manufacturing).

b. Routing and scheduling must be done for each new job.

c. Equipment utilization rates are usually low.

d. Material handling is slower, less efficient, and more costly per unit than with a product layout.

e. There is often a lower span of supervision compared to a product layout.

f. Unit costs tend to be higher than comparable output produced with a product layout.

g. Accounting, inventory control and purchasing are generally more involved than with a product layout.

13. The main goal of line balancing is to achieve a set of task groupings at work stations in the line that have equal time requirements in order to get a high utilization of labour and equipment. Unbalanced lines have bottlenecks at some work stations and idle time at others. The resulting output is lower than it would be if the line were balanced.

14. Routing and scheduling are continual problems in a process layout because a variety of jobs pass through the system, and they tend to differ in terms of routing and schedule requirements. In contrast, product layouts typically handle items with little or no variety—all have the same or similar routing and scheduling requirements.

15. With a product layout, equipment breakdown has serious implications because the separate pieces of equipment are closely tied together. If one piece of equipment fails, the line will quickly come to a halt. Consequently, preventive maintenance to reduce the failure rate is advisable. In contrast, a process layout often contains duplicate equipment so that if one particular piece of equipment fails, the work can usually be shifted to another piece of equipment. Consequently, there is less need for preventive maintenance, and less need for repair of equipment when it does break down. Moreover, process layouts utilize more skilled workers who tend to take better care of the equipment than their lower skilled counterparts in a product layout system.

16. Job processing sequence usually determines the arrangement of equipment in a product layout. In a process layout, job processing sequences vary, so there is much less influence on equipment arrangement. Because of differences in job requirements, sequencing is a continual task in a process layout.

17. The subway system is essentially a fixed-path arrangement—a product layout. Its advantages are often low operating cost, more efficient handling, and low cost per unit moved. On the other hand, a bus system is more flexible in terms of varying routes. This can be desirable if there are shifts in where potential riders are coming from and going to. For example, a new bus route could easily be established to service a new shopping area, a new apartment complex, or a large industrial facility. Other considerations are initial cost (high for subway and relatively low for bus), severity of difficulties that would arise from a breakdown (high for subway, low for bus), the possibility of alternative uses (none for subway, private groups, etc., for bus during off times), and possible disruptions caused by weather (higher risk for bus than subway—e.g., snowstorms stall highway traffic).

18. Fixed-path material handling equipment in supermarkets includes the belts at the checkouts which move items up to the cashier, the roller conveyors which transport boxes of groceries outside to pickup areas, conveyors in the meat department to move carcasses from storage to cutting tables, roller conveyors to off-load goods from trucks and move them to storage. Variable-path material handling equipment includes grocery carts, "trucks" and palletjacks used to transport goods from storage to display shelves, and movable racks to transport baked goods from ovens or from deliveries to the bakery counter.

19. Heuristic approaches are rules designed to guide decision makers to satisfactory decisions by reducing the number of alternatives that must be considered. They do not necessarily yield optimal solutions. They are usually employed when there is a problem involving an exceedingly large number of potential solutions.

20. Nonmanufacturing environments do not usually lend themselves to product layouts because they tend to involve more processing variety than many manufacturing environments. One exception is a cafeteria.

21. The original car was one of a large number of similar cars produced on an assembly line, which was set up to speed the flow of work. That is, inventories of parts were on hand, specialized machinery, workers and material handling equipment were arranged specifically for the job. As well, parts and components are made in large batches reducing the unit cost. As a result of this, the unit cost of the car was relatively low. In contrast, constructing a car from “scratch” is essentially a cross between job shop and a project, with none of the economies of mass production. A list of the parts must be assembled. Some might be available locally, but others would have to be shipped individually from suppliers. The parts would have to be held until all were on hand. Workers would not be highly familiar with this particular car. Consequently, the work would progress at a fairly slow rate, and probably with a certain amount of back-tracking. Obviously, construction of a replacement would be considerably more costly than the initial car.

22. Layout can lead to high productivity if it contributes to a smooth flow of work with high utilization of labour and equipment. This requires careful consideration of work requirements to determine what will be needed and a certain amount of effort to obtain an optimal (or satisfactory) layout. A poor layout will hinder productivity with bottlenecks, lower utilization of labour and equipment than is necessary, and require more handling or movement between work stations than is necessary (particularly in process layouts).

23. In cellular manufacturing, machines are grouped into a cell. The basis for grouping can be operations needed to process a group of similar items or part families. Advantages of such systems include relatively short throughput time, reduced material handling, less work-in-process inventory, and reduced setup time.

24. Group technology involves selecting items that have similar design or processing requirements and grouping them into part families for cellular manufacturing. It also includes a coding system for items.

25. Although, we treated the task times as fixed in balancing assembly lines, it is more realistic to assume variable task times whenever humans are involved. The lower the level of automation, the higher the variability of tasks. If the assembly line consists of tasks with variable times, it will be more difficult to balance the line. In order to deal with variability of task times, we can require a minimum amount of idle time to be available at each workstation. As the variability of task times increase we can increase the minimum idle time available at each workstation. In addition workstation idle time can also be used for slower or less experienced workers who take longer than normal to complete a task.

26. Factors such as opportunity to use available, less expensive equipment, familiarity with machines and equipment, expertise of workers, space minitations, choice of alternate materials, and strategic implications of this process.