introductory operations management: lecture 10 - chapter 6
TRANSCRIPT
CHAPTER 6 – PROCESS SELECTION AND FACILITY LAYOUTLecture 10 – September 25th
1 2 3 4
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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
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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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