Pom Lecture (22)

Figure 7.7 Original layout of library workroom

Figure 7.8 Original flow diagram of library workroom

Figure 7.9 Proposed layout of library workroom

*Source – Applied Production and Operations Management ( J. R. Evans at al) West Publishing Company In a simple problem layouts can be designed by visual inspection. However, in more complex industrial situations, handling cost is a major factor. Thus some quantitative analysis would appear to be helpful in process layout design. Dear students, let us learn now to appreciate the quantitative approach to process layout through the help of the following case study

. A quantitative approach to process layout

Home Video Equipment, Inc. (HVE), a California – based company, produces a line of video recording equipment. Increasing sales volume and new product lines have necessitated building a new plant in order to provide more effective distribution to the eastern United States. Eight major departments are necessary in the production of video recorders. These are listed below, along with space estimates of department size1. Receiving and storage

1200 square feet

2. Machining

1800 square feet

3. Pressing

2400 square feet

4. Cleaning

600 square feet

5. Plating

1200 square feet

6. Painting

900 square feet

7. Assembly

2400 square feet

8. Shipping

1500 square feet

In designing this new plant, management has determined that material handling cost is the principal criterion. Departments with large numbers of moves between them should probably located close to one another. In order to provide a quantitative basis for the layout analysis, we construct a load matrix, which lists the number of moves from one department to another over some time period, such as annually. This information can be

obtained from route sheets and planned production schedules. Since HVE’s original plant produces similar products, accurate estimates can be obtained from the current operation. Table 7.1 shows the annual number of moves between departments.

From\ To Receiving

Receiving Machining Pressing Cleaning Plating Painting Assembly Shipping 200

100

Machining Pressing

350 150

200

Cleaning Plating

60

20

100

250

500

200 50

Painting

400 300

Assembly Shipping Table 7.1 Load matrix for HVE, Inc. The handling cost is generally proportional to the distance traveled and the type of equipment used. For example, the cost of transporting by forklift truck is higher than using a conveyor due to higher capital investment, maintenance, and labour costs. We assume that all moves take place by forklift so that cost will simply be proportional to distance. In general, a wide variety of material-handling equipment can be chosen. The most effective layout planning methods attempt to integrate the material-handling selection decision with the layout itself. Clearly the distance traveled depends on the layout. We use the following approach: 1. Design a trial layout 2. Compute the distances between departments 3. Multiply the interdepartmental distances by the volume of flow between departments and compute the total cost

600

4. Use the volume-distance matrix created in Step 3 to propose changes in the current layout and repeat the process (from Step 2) until a satisfactory layout is obtained. From Table 7.1, we see that the basic flow is from receiving to machining and pressing to cleaning, plating, and painting, and finally to assembly and shipping. Using this information, we propose an initial layout, shown in Figure 7.11. This is just a rough approximation of the relative shapes and sizes of departments. Detailed architectural designs must account for aisles, support pillars, office space, restrooms, and other service facilities. In order to compute interdepartmental distances, we will consider rectilinear distance. If these distances are multiplied by the volume requirements in Table 7.1, we obtain the volume-distance matrix shown in Table 7.2.

Figure 7.11 Initial layout Table 7.2 Volume-Distance matrix for initial layout From\ To Receiving

Receiving Machining Pressing Cleaning Plating Painting Assembly Shipping 10,000

5,500

Machining Pressing Cleaning

14,250

23,000

24,500 1,800

1,400

5,500

28,750

30,000

12,000

Plating Painting

2,000

24,000 12,000

Assembly Shipping From this table, we see that the largest costs involve transportation between assembly and shipping, pressing and assembly, and cleaning and plating. The initial layout has other disadvantages. For instance, receiving and shipping are on opposite sides of the building. This causes a problem if rail is used and might also cause problems in constructing access roads. A second proposal, which places these on the same side of the building, You can verify that the total volume-distance for this layout is 2,14,550, which represents a 15 percent savings over the initial layout. This was gained by moving cleaning adjacent to plating and pressing closer to assembly. However, there is still a high cost involved in moving material from painting to assembly and from assembly to shipping. In an effort to reduce this, a third alternative, shown in figure 7.12 , is proposed.

39,000

Figure 7.12 Third proposed layout This layout has a total volume-distance requirement of 1,83,650. The basic shapes of the Machining and Pressing departments have been considerably altered. Shape requirements depend on machine sizes and processing requirements to a large extent and must be taken into account to a layout analysis. In addition, office space can be provided on the opposite end of the building from shipping and receiving; thus the building can maintain a rectangular shape. This type of trial-and-error approach is often the only way of designing process layouts, since so many factors must be considered. With that, we have come to the end of today’s discussions. I hope it has been an enriching and satisfying experience.

Activity 1. The Rai University president has asked the OM department to assign eight

biology professors (A, B, C, D, E, F, G and H) to eight offices (numbered 1 to 8 in the diagram) in the new biology building. North wing 1

2

3

4

5

6

7

8

South wing The following distances and two-way flows are given: Distance between offices (feet)

Two –way flows (units per period)

1 2 3 4 5 6 7 8

1

2

3

4

5

6

7

8

-

10 20 30 15 18 25 34

A

-

10 20 18 15 18 25

B

-

10 25 18 15 18

C

-

34 25 18 15

D

-

10 20 30

E

-

10 20

F

-

10

G

-

H

A

B

C

D

E

F

G

H

-

2

0

0

5

0

0

0

-

0

0

0

3

0

2

-

0

0

0

0

3

-

4

0

0

0

-

1

0

0

-

1

0

-

4 -

(a) If there are no restrictions (constraints) on the assignment of professors to offices, how many alternative assignments are there to evaluate? (b) The biology department has sent the following information and requests to the OM department: Offices 1, 4, 5, and 8 are the only offices with windows. A must be assigned Office 1. D and E, the biology department co-chairpeople, must have windows. H must be directly across the courtyard from D. A, G, and H must be in the same wing. F must not be next to D or G or directly across from G. Find the optimal assignment of professors to offices that meets all the requests of the biology department and minimizes total material handling cost. You may use the path flow list as a computational aid. Path

Flow

Path

Flow

Path

Flow

Path

Flow

Path

Flow

A-B

2

B-C

0

C-D

0

D-E

4

E-F

1

A-C

0

B-D

0

C-E

0

D-F

0

E-G

0

A-D

0

B-E

0

C-F

0

D-G

0

E-H

0

A-E

5

B-F

3

C-G

0

D-H

0

F-G

1

A-F

0

B-G

0

C-H

3

F-H

0

A-G

0

B-H

2

G-H

4

A-H

0

Points to Ponder