Introductory Operations Management: Lecture 10 - Chapter 6

CHAPTER 6 – PROCESS SELECTION AND FACILITY LAYOUTLecture 10 – September 25th

1 2 3 4

5

6

78910

In

Out

Workers

A U-SHAPED PRODUCTION LINE

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Dept. A

Dept. B Dept. D

Dept. C

Dept. F

Dept. E

Used for Intermittent processingJob Shop or Batch Processes

Process Layout(functional)

PROCESS LAYOUT

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ADVANTAGES AND DISADVANTAGES OF PROCESS LAYOUTS

Advantages Can handle a variety of processing requirements Not particularly vulnerable to equipment failures Equipment used is less costly Possible to use individual incentive systems

Disadvantages In-process inventory costs can be high Challenging routing and scheduling Equipment utilization rates are low Material handling slow and inefficient Complexities often reduce span of supervision Special attention for each product or customer Accounting and purchasing are more involved

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FIXED POSITION AND CELLULAR LAYOUTS Fixed Position Layout:

Layout in which the product or project remains stationary, and workers, materials, and equipment are moved as needed.

Nature of the product dictates this type of layout Weight Size Bulk

Large construction projects Cellular Production

Layout in which machines are grouped into a cell that can process items that have similar processing requirements

SMED (single-minute exchange of dies) Right size equipment

Group Technology The grouping into part families of items with similar design or

manufacturing characteristics

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Process Layout - work travels to dedicated process centers

Milling

Assembly& Test Grinding

Drilling Plating

PROCESS LAYOUT

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-1111 -1111

222222222 - 2222

Assem

bly

3333333333 - 3333

44444444444444 - 4444

Lathe

Lathe

Mill

Mill

Mill

Mill

Drill

Drill

Drill

Heat treat

Heat treat

Heat treat

Gear cut

Gear cut

Grind

Grind

CELLULAR MANUFACTURING LAYOUT

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SERVICE LAYOUTS

Warehouse and storage layouts Retail layouts Office layouts Service layouts must be aesthetically

pleasing as well as functional

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DESIGN PRODUCT LAYOUTS: LINE BALANCING, CYCLE TIME

Line Balancing is the process of assigning tasks to workstations in such a way that the workstations have approximately equal time requirements.

Cycle time is the maximum time allowed at each workstation tocomplete its set of tasks on a unit. 9

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OTOutput rate =

CTOT operating time per day

D = Desired output rate

OTCT = cycle time =

D

DETERMINE MAXIMUM OUTPUT

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DETERMINE THE MINIMUM NUMBER OF WORKSTATIONS REQUIRED

min

min

( t) N =

CT

t = sum of task time

N Theoritical mimimum

number of stations

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EXAMPLE

Suppose that the work required to fabricate a certain product can be divided up into five elemental tasks, with the task times and precedence relationships as shown in the following diagram:

Minimum and maximum Cycle Time? Output rate per day?

Assuming the line operates eight hours per day For example, suppose that the desired output rate

is 480 units, the necessary cycle time is? The minimum number of stations required to

achieve this goal of producing 480 units?

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Precedence diagram: Tool used in line balancing to display elemental tasks and sequence requirements

A Simple Precedence

Diagrama b

c d e

0.1 min.

0.7 min.

1.0 min.

0.5 min. 0.2 min.

PRECEDENCE DIAGRAM

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EXAMPLE 1: LINE BALANCING For the figure below:

What is the minimum workstations required? Use a cycle time of 1.0 minute

Arrange tasks shown below according to the minimum workstationsAssign tasks in order of the most number of followers

a b

c d e

0.1 min.

0.7 min.

1.0 min.

0.5 min. 0.2 min.15

EXAMPLE 1 SOLUTION

WorkstationTimeRemaining Eligible

AssignTask

RevisedTime Remaining

StationIdle Time

1 1.00.90.2

a, ccnone

ac-

0.90.2

0.2

2 1.0 b b 0.0 0.0

3 1.00.50.3

de-

de-

0.50.3 0.3

0.5

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CALCULATE PERCENT IDLE TIME

Idle time per cyclePercent idle time =

(N )(CT)actual

Efficiency = 1 – Percent idle time

Calculate the Percentage idle time and efficiency for example 1

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LINE BALANCING RULES

Assign tasks in order of most following tasks.Count the number of tasks that follow

Assign tasks in order of greatest positional weight.

Positional weight is the sum of task time for itself and all following tasks.

Some Heuristic (intuitive) Rules:

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EXAMPLE 2 Draw a precedence diagram. Assuming an eight-hour workday, compute the cycle time

needed to obtain an output of 400 units per day. Determine the minimum number of workstations required. Assign tasks to workstations using this rule: Assign tasks

according to greatest number of following tasks. In case of a tie, use the tiebreaker of assigning the task with the longest processing time first.

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EXAMPLE 2

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Station 1 Station 2 Station 3 Station 4

a b ef

d

g h

c

EXAMPLE 2

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1 min.2 min.1 min.1 min. 30/hr. 30/hr. 30/hr. 30/hr.

Bottleneck

BOTTLENECK WORKSTATION

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PARALLEL WORKSTATIONS

1 min.

2 min.

1 min.1 min. 60/hr.

30/hr. 30/hr.

60/hr.

2 min.

30/hr.30/hr.

Parallel Workstations

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Information Requirements:1. List of departments2. Projection of work flows3. Distance between locations4. Amount of money to be invested5. List of special considerations6. Location of key utilities

DESIGNING PROCESS LAYOUTS

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EXAMPLE 3

Assign the three departments shown in table 1 to locations A, B, and C, which are separated by the distances shown in table 2, in such a way that transportation cost is minimized.

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Table 1: Distance between locations (meters)

Table 2: Interdepartmental work flow (loads per day)

1 3 2

30

170 100

A B C

EXAMPLE 3: INTERDEPARTMENTAL WORK FLOWSFOR ASSIGNED DEPARTMENTS

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CLOSENESS RATINGS

Read from the textbook Look at the example 4

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