3.5 Types of Layout
3.5.2 Process-Oriented or Functional Layout
It is a layout that deals with low-volume, high-variety production. In this type, all the machines and equipment of the same type are grouped together in one section or area or department. For example, all welding equipment are kept in one section; all drilling machines in other; all lathes in third section, and so on. It is used in intermittent (discontinuous) type of production. Figure 3.5 shows the movements of two different jobs through different departments according to their sequence of operations. It is most efficient when making products with different requirements or when handling customers, patients, or clients with different needs.
Rawmaterials
Foundry shop
Grinding shop
Drilling shop
Brazing shop
Polishing shop
Inspection
Finishedproducts
Press shop
Heat treatment
Painting shop
Milling shop
Packing shop shop
]
Figure 3.5. Process layout.
In this job-shop environment, each product or each small group of products undergoes a differ- ent sequence of operations. A good example of process layout is a hospital or clinic. Patients with their own needs, requires routing through admissions, laboratories, operating rooms, radiology, pharmacies, nursing beds, and so on. Equipment, skills, and supervisions are organized around these processes.
Advantages
••••• different products can be made on the same machine, so the number of machines needed is
reduced. This gives lots of flexibility with less capital needed.
Layout Planning 47
••••• When one machine goes out of order, the job can be done on other similar machines.
••••• When a worker is absent, another worker of the same section can do the job.
••••• A worker becomes more skilled and can earn more money by working harder on his machine.
••••• Varieties of job make the work more interesting for the workers.
••••• Layout is flexible with respect to the rate of production, design and methods of production.
Limitations
••••• General purpose equipment requires high labor skills, and WIP inventories are higher because
of imbalances in the production processes.
••••• This layout needs more space.
••••• Automation of material handling is extremely difficult.
••••• Completion of a product takes more time due to difficult scheduling, changing setups, and
unique material handling. Total production cycle time is more also due to long distances and waiting time.
••••• Raw material has to travel longer distances, thus the material handling cost is high.
••••• Needs more inspection and coordination.
3.5.2.1 Approach to Process Layout
When designing a process layout, the most common tactic is to arrange departments or work centers so that the costs of material handling is minimum. For this, departments with large flows of parts or people between them should be placed next to one another. Material handling costs in this approach depend on:
••••• The number of loads or people to be moved between two departments during some period of
time, and
••••• The distance linked costs of moving loads or people between departments. Cost is considered
to be a function of distance between departments.
The objective function can be written as follows:
Minimize cost = Σ
i n
=1 Σ
j n
=1 Xij Cij (3.1)
where n = total number of work centers or departments i, j = individual departments
Xij = number of loads moved from department i to department j Cij = cost to move a load between department i to department j.
The term Cij combines distance and other costs into one factor. We thereby assume that the difficulty of movement is equal and the pickup and setdown costs are constant. The steps in this approach can be understood by the following example.
Example 3.1. A company management wants to arrange the six departments of its factory in a way that will minimize interdepartmental material handling costs. They make an initial assumption (to simplify the problem) that each department is 20 × 20 feet and that the building is 60 feet long and 40 feet wide. The process layout procedure that they follow involves six steps:
48 A Modern Approach to Operations Management Step-1: Construct a ‘from-to-matrix’ showing the flow of parts or materials from department to depart- ment (Table 3.4).
Table 3.4
Department Assembly Painting Machine shop Receiving Shopping Testing
Assembly (1) α 50 100 0 0 20
Painting (2) α 30 50 10 0
Machine shop (3) α 20 0 100
Receiving (4) α 50 0
Shopping (5) α 0
Testing (6) α
Step-2: Determine the space requirements for each department (Figure-3.5 shows the available plant space).
Step-3: Develop an initial schematic diagram showing the sequence of departments through which parts must move. Try to place departments with a heavy flow of materials or parts next to one another (Figure-3.6).
Step-4: Determine the cost of this layout by using the material handling cost equation:
Cost = Σ i
n
=1 Σ
j n
=1 Xij Cij
For this problem, the company assumes that a forklift carries all interdepartmental loads. The cost of moving one load between adjacent departments is estimated to be $1. Moving a load between nonadjacent departments costs $2. Thus, looking at Table 3.4, we see that the handling cost between departments 1 and 2 is
$50 (i.e., $1 × 50 loads), the handling cost between departments 1 and 3 is $200 (i.e., $2x100 loads), and the handling cost between departments 1 and 6 is $40 (i.e., $2 × 20 loads), and so on. The total cost for this layout is shown in Table 3.5.
Room 1 Room 1 Room 1
Assembly Dept (1)
Painting Dept (2)
Machine Shop Dept (3)
Receiving Dept (4)
Shipping Dept (5)
Testing Dept (6)
Room 4 Room 5 Room 6
40
60
Figure 3.6. Building Dimensions and a Possible Layout.
Layout Planning 49 Table 3.5
Movement Route Cost for route ($)
1-2 1 × 50 = 50
1-3 2 × 100 = 200
1-6 2 × 20 = 40
2-3 1 × 30 = 30
2-4 1 × 50 = 50
2-5 1 × 10 = 10
3-4 2 × 20 = 40
3-6 1 × 100 = 100
4-5 1 × 50 = 50
Total cost 570
1
4 5
2 3
6
50 30
100
10 20 100
50
50 20
Figure 3.7. Interdepartmental flow graph with number of loads per week.
Step-5: By trial and error, try to improve the layout shown in Figure-3.6 to establish a reasonably good arrangement of departments.
By looking at both the flow graph (Figure 3.7) and the cost calculations, it is obvious that placing depart- ments 1 and 3 together seem desirable. They are presently nonadjacent, and due to the high volume of flow between them the material handling cost is high. One possibility is to exchange the position of 1 and 2. Doing this will change the cost which is shown in Table 3.6.
1
4 5
2 3
6
50 100
30
20
20
100
50 50
10
Figure 3.8. Second flow graph with number of loads per week.
50 A Modern Approach to Operations Management Table 3.6
Movement Route Cost for route ($)
1-2 1 × 50 = 50
1-3 1 × 100 = 100
1-6 1 × 20 = 20
2-3 2 × 30 = 60
2-4 1 × 50 = 50
2-5 1 × 10 = 10
3-4 2 × 20 = 40
3-6 1 × 100 = 100
4-5 1 × 50 = 50
Total cost 480
This change, of course, is just one of the many possible combinations. For a six-department problem, the possible combination is 6! = 6 × 5 × 4 × 3 × 2 × 1 = 720. In layout problems, we seldom find the optimal solution and will have to be satisfied with a ‘reasonable’ one reached after a few trials.
I wonder, if the manager of this company is satisfied with this layout. If not, then we will have to try a few steps more to find a layout which is less expensive than the present one.
Room 1 Room 1 Room 1
Assembly Dept (1) Painting
Dept (2)
Machine Shop Dept (3) Receiving
Dept (4)
Shipping Dept (5)
Testing Dept (6)
Room 4 Room 5 Room 6
40
60
Figure 3.9. Feasible Layout for the company.
3.5.2.2 Computer Software for Process Layout
The graphic approach discussed is good for smaller layout problems but not for larger problems where say 20 departments are involved. In the case of 20 departments more than 600 trillion different configurations are possible. Luckily, computer software is available to deal with layout problems consisting of 40 departments. The most popular one is CRAFT (Computerized Relative Allocation of Facilities Technique). It’s a program that produces ‘good’ but not always the ‘optimal’ solutions. CRAFT is a search technique that examines the alternative layouts systematically to reduce the total material handling cost.
Other software packages include Automated Layout Design Program (ALDEP), Computerized Relationship Layout Planning (CORELAP), and Factory Flow.
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