1OM3 Chapter 8  Facility and Work Design© 2012 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part.

FACILITY AND WORK DESIGN

CHAPTER 8

DAVID A. COLLIER AND JAMES R. EVANS

Facility Layout

Facility layout refers to the specific arrangement of physical facilities. Facility-layout studies are necessary whenever:

1. a new facility is constructed, 2. there is a significant change in demand

or throughput volume, 3. a new good or service is introduced to

the customer benefit package, or 4. different processes, equipment, and/or

technology are installed.

Exhibit 8.1 Product Layout for Wine Manufacturer

Facility Layout

Product Layout• Advantages: Lower work-in-process

inventories, shorter processing times, less material handling, lower labor skills, and simple planning and control systems.

• Disadvantages: A breakdown at one workstation can cause the entire process to shut down; a change in product design or the introduction of new products may require major changes in the layout, limiting flexibility.

Facility Layout

• A process layout consists of a functional grouping of equipment or activities that do similar work.

• Examples: Legal offices, shoe manufacturing, jet engine turbine blades, and hospitals use a process layout.

Exhibit 8.2 Process Layout for a Machine Shop

Facility Layout

Process Layout• Advantages: A lower investment in

equipment, the diversity of jobs inherent in a process layout can lead to increased worker satisfaction.

• Disadvantages: High movement and transportation costs, more complicated planning and control systems, longer total processing time, higher in-process inventory or waiting time, and higher worker-skill requirements.

Facility Layout

• In a cellular layout, the design is not according to the functional characteristics of equipment, but rather by self-contained groups of equipment (called cells), needed for producing a particular set of goods or services.

• Examples: Legal services, such as labor law, bankruptcy, divorce; medical specialties such as maternity, oncology, surgery.

Source: J. T. Black, “Cellular Manufacturing Systems Reduce Set Up time, Make Small-Lot Production Economical,” Industrial Engineering Magazine, Nov. 1983. Used with permission from the author.

Exhibit 8.3 Cellular Manufacturing Layout

Facility Layout

Cellular Layout• Advantages: Reduced materials-handling

requirements, quicker response to quality problems, more efficient use of floor space, more worker responsibility increasing morale.

• Disadvantages: Duplication of equipment among cells, greater worker skills requirements.

Facility Layout

• A fixed-position layout consolidates the resources necessary to manufacture a good or deliver a service, such as people, materials, and equipment, in one physical location.

• Examples: The production of large items such as heavy machine tools, airplanes, buildings, locomotives, and ships. Service-providing examples include major hardware and software installations, sporting events, and concerts.

Fixed-Position Layout

• Advantages: Work remains stationary, reducing movement.

• Disadvantages: High level of planning and control required.

Facility Layout in Service OrganizationsService organizations use product, process, cellular, and fixed-position layouts to organize different types of work.

- Examples: Libraries, hospitals, insurance companies

• Product Layout—Service organizations that provide highly standardized services tend to use product layouts.

- Examples: Restaurant kitchens

• Process Layout—Services that need the ability to provide a wide variety of services to customers with differing requirements usually use a process layout.

Exhibit 8.6 A Typical Manufacturing Workstation Layout

Designing Product Layouts

• An assembly line is a product layout dedicated to combining the components of a good or service that has been created previously. - Examples: Automobile assembly,

Subway sandwich shops, insurance policy processing • Assembly line balancing is a technique

to group tasks among workstations so that each workstation has—in the ideal case—the same amount of work.

Assembly-Line Balancing

Required information:

1. The set of tasks to be performed and the time required to perform each task.

2. The precedence relations among the tasks—that is, the sequence in which tasks must be performed.

3. The desired output rate or forecast of demand for the assembly line.

• One workstation: In an eight-hour day, could produce (1 part/1.0 min)(60 minutes per hour)(8 hours per day) = 480 parts/day

• Three workstation s (one for each task): The first operator can produce 120 parts per hour, or 960 parts/day. The second could produce 1,600 parts/day. The third operator can produce 2,400 parts/day. Maximum output is 960 parts/day.

• Two workstations (A/BC): Since each operator needs 0.5 minute to perform the assigned duties, the line is in perfect balance, and 960 parts per day can be produced.

Exhibit 8.7 A Three-Task Assembly Line

Assembly-Line Balancing

Cycle time is the interval between successive outputs coming off the assembly line.

• In the previous example, with one workstation, the cycle time is 1 minute; that is, one completed assembly is produced every minute.

• If two workstations are used, the cycle time is 0.5 minute/unit.

• If three workstations are used, the cycle time is still 0.5 minute/unit, because task A is the bottleneck, or slowest operation. The line can produce only one assembly every 0.5 minute.

Assembly-Line Balancing

Cycle time (CT) is related to the output (R) by the following equation:

CT = A/R [8.2]

• A = available time to produce the output. • The output (R) is normally the demand

forecast in units, adjusted for on-hand inventory if appropriate, or orders released to the factory.

• Both A and R must have the same time units of measure (hour, day, week, month, and so on).

Assembly-Line Balancing

Minimum number of workstations required = Sum of task times/Cycle time = t/CT [8.3]

Total Time Available = (Number of work stations)×(Cycle Time) = (N )(CT )

[8.4]

Total Idle Time = (N )(CT ) − t [8.5]

Assembly-line Efficiency = t/(N ×CT ) [8.6]

Balance Delay = 1 − Assembly-line Efficiency [8.7]

Assembly-Line Balancing

• Line balancing approaches use decision rules, or heuristics, to assign tasks to workstations to attempt to minimize the amount of idle time at workstations, but do not guarantee optimal solutions.

• Examples: - Assign the task with the longest task

time first to a workstation if the cycle time would not be exceeded.

- Assign the shortest task first.

Exhibit 8.9 Precedence Network and Workstation Assignment

Assembly Line Balance for In-Line Skate

Workstation Tasks Total Time Idle TimeA 1, 2, 5 5.7 0.3B 3, 4, 6, 7, 8 3.7 2.3

Total 9.4 2.6

Using equations [8.4] to [8.6] we may compute the following:

Total Time Available = (Number workstations)(Cycle Time) = (N )(CT ) = (2)(6) = 12 minutes

Total Idle Time = (N )(CT ) − t = (2)(6) - 9.4 = 2.6 minutes

Assembly-line Efficiency = t/(N ×CT ) = 9.4/(2 × 6) = 78.3%

24

Assembly-Line Balancing

Cycle time (CT) is related to the output (R) by the following equation:

CT = A/R [8.2]

• A = available time to produce the output. • The output (R) is normally the demand

forecast in units, adjusted for on-hand inventory if appropriate, or orders released to the factory.

• Both A and R must have the same time units of measure (hour, day, week, month, and so on).

25

Selected Solved Problems Chapter 8

Facility and Work DesignCollier/Evans OM3

26

Bass Fishing Solved Problem (p. 155)

Assembly line has six workstations. Management wants an output of 300 reels per day, (with a 7.5 hour workday). The sum of the task times is 8 minutes/reel.

What is the cycle time?CT = A/R

What is the assembly line efficiency?Efficiency = t/(N ×CT )

What is the total idle time?Total Idle Time = (N )(CT ) − t

27

Bass Fishing Solved Problem

Assembly line has six workstations. Management wants an output of 300 reels per day, (with a 7.5 hour workday). The sum of the task times is 8 minutes/reel.

What is the cycle time?CT = A/R = 1.5 min/reel

What is the assembly line efficiency?Efficiency = t/(N ×CT ) = 88.9%

What is the total idle time?Total Idle Time = (N )(CT ) − t = 1 min/reel

28

Assembly-Line Balancing

Minimum number of workstations required = Sum of task times/Cycle time = t/CT [8.3]

Total Time Available = (Number of work stations)×(Cycle Time) = (N )(CT )

[8.4]

Total Idle Time = (N )(CT ) − t [8.5]

Assembly-line Efficiency = t/(N ×CT ) [8.6]

Balance Delay = 1 − Assembly-line Efficiency [8.7]

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Exhibit 8.9 Precedence Network and Workstation Assignment

Given: CT = 6.0 min/unit (see pages 156-157) Workstation Tasks Total Time Idle Time

A B

Total

30

Exhibit 8.9 Precedence Network and Workstation Assignment

Workstation Tasks Total Time Idle Time

A 1, 2, 5 5.7 0.3 B 3, 4, 6, 7, 8 3.7 2.3 Total 9.4 2.6

31

Assembly Line Balance for In-Line Skate

Workstation Tasks Total Time Idle TimeA 1, 2, 5 5.7 0.3B 3, 4, 6, 7, 8 3.7 2.3

Total 9.4 2.6

Using equations [8.4] to [8.6] we may compute the following:

Total Time Available = (Number workstations)(Cycle Time) = (N )(CT ) =

Total Idle Time = (N )(CT ) − t =

Assembly-line Efficiency = t/(N ×CT ) =

32

Assembly Line Balance for In-Line Skate

Workstation Tasks Total Time Idle TimeA 1, 2, 5 5.7 0.3B 3, 4, 6, 7, 8 3.7 2.3

Total 9.4 2.6

Using equations [8.4] to [8.6] we may compute the following:

Total Time Available = (Number workstations)(Cycle Time) = (N )(CT ) = (2)(6) = 12 minutes

Total Idle Time = (N )(CT ) − t = (2)(6) - 9.4 = 2.6 minutes

Assembly-line Efficiency = t/(N ×CT ) = 9.4/(2 × 6) = 78.3%