3 Layout and Flow

PowerPoint PresentationOperations Management, 4E: Chapter 7
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Operations Management, 4E: Chapter 7
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© Nigel Slack, Stuart Chambers & Robert Johnston, 2004
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Layout:
The layout of an operation is concerned with the physical location of its transforming resources, that is deciding where to put the facilities, machines, equipment and staff in the operation.
Layout types:
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Fixed position layout
In a fixed position layout, the transformed resource does not move between its transforming resources.
Equipment, machinery, plant and people who do the processing move as necessary because the product or customer is either:
Too large
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Process layout
In a process layout, similar processes or processes with similar needs are located together because:
It is convenient to group them together or
The utilization of the transforming resource is improved
Different products of customer have different requirements therefore they may take different routes within the process.
The flow in a process layout can be very complex.
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showing the path of just one customer
Entrance
Exit
Enquiries
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Cell layout
In a cell layout, the transformed resources entering the operation move into a cell in which all the transforming resources it requires in located.
After being processed in the cell, the transformed resource may move to a different cell in the operation or it may be a finished product or service.
Each cell may be arranged in either a process or product layout.
The cell type layout attempts to bring order to the complex flow seen in a process layout.
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showing the sports goods shop-within-a-shop
retail ‘cell’
Sports shop
Books and videos
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Product layout
In a product layout, the transformed resource flow a long a line of processes that has been prearranged.
Flow is clear, predictable and easy to control.
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product layout
Lecture theatre
9
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layout types
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The flow of the operation’s transformed resources
Process type
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B
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- Product/customer not moved or disturbed.
- Very high unit cost.
- High mix and product flexibility
- Relatively robust if in the case of disruptions
Low utilization of resources.
Complex flow.
- Fast throughput.
Can need more plant and equipment
Lo- w unit costs for high volume
- Gives Opportunities for specialization of equipment
Can have low mix and flexibility
Not very robust to disruption
Work can be very
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variable cost characteristics which seem to determine
which one to use. (b) In practice the uncertainty about
the exact fixed and variable costs of each layout means
the decision can rarely be made on cost alone
3) Consider total cost
Use cell or product
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Fixed position layout design:
The location of resources for each project is unique and it will be determined on the convenience of transforming resources themselves.
Although there are techniques which held to locate resources on fixed position layouts, they are not widely used because this layout can be very complex and planned schedules do change frequently.
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Collecting information such as:
cost per distance traveled
Relationship chart
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If direction is not important, collapses to
LOADS/DAY
(b)
LOADS/DAY
(a)
9
A
B
C
D
E
A
30
60
20
B
30
30
C
80
D
40
E
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Or alternatively
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If cost of flow differs between work centers, combine with
LOADS/DAY
(e)
(f)
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To give
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If direction is not important, collapses to
DAILY COST/DISTANCE TRAVELLED
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Cell layout design
Cells in an operation can be created based on two interrelated decisions:
What is the extent and nature of the cell i.e. the amount of direct and indirect resources the cell has as shown in Fig 7.28
Which resources to allocate to which cell using:
Cluster analysis – which process group naturally together
Parts and family coding – based on similar characteristics of parts of products
OR
(See Fig. 7.31)
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Amount of indirect resources included in the cell
Proportion of the resources needed to complete the transformation included in the cell
e.g.
e.g.
e.g.
e.g.
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to allocate machines to cells
Product
Machines
Product
Machines
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Product layout design
Product type layout is designed based on a technique called line balancing. The technique consist of the following steps:
Calculating the required cycle time.
Calculating the number of stages.
Producing a precedence diagram.
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Cycle time:
It is the time between completed products emerging from the process.
Example:
Suppose the regional back-office operation of a large bank is designing an operation which will process its mortgage applications. The number of applications to be processed is 160 per week and the time available to process the applications is 40 hours per week.
Cycle time = 40 = 1/4 hours = 15 minutes
160
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required cycle time
Where the total work content is the total quantity of work involved in producing the product given in time.
Example:
Suppose that the bank in the previous example calculated that the average total work content of processing a mortgage application is 60 minutes. The number of stages needed to produce a processed application every 15 minutes can be calculated
Required no. of stages = 60 minutes = 4 stages
15 minutes
If you get a fraction round it up to the higher whole number.
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Precedence diagram
This is a diagram representing the ordering of the elements which comprise the total work content of the product or service.
Two rules when constructing the diagram:
The circles which represent the elements are drawn as far to the left as possible.
None of the arrows which shows the precedence of the elements should be vertical.
a
b
c
d
e
f
g
h
i
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Allocating activities to the stages
The general approach is to allocate elements from the precedence diagram to the first stage, starting from the left, until the work allocated to the stage is as close to, but less than, the cycle time.
When the stage is full of work without exceeding the cycle time, move to the next stage.
Two rules help to decide which activities to allocate to a stage:
Choose the largest that will fit into the time remaining at the stage
Choose the element with the most ‘followers’.
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Balancing loss
The effectiveness of the line balancing activity is measured by the balancing loss.
This is the time wasted through the unequal allocation of work as a percentage of the total time invested in processing the product or service.
Balancing loss = Total idle time
No. of stages x Cycle time
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invested in processing the product or service
which is not used productively
Load
Stage
2.3
2.5
2.2
3.0
An ideal ‘balance’ where work is allocated equally between the stages
But if work is not equally allocated the cycle time will increase and ‘balancing losses’ will occur
Work allocated to stage
(3.0 - 2.5) +
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Worked Example
Consider Karlstad Kakes, a manufacturer of specialty cakes, which has recently obtained contract to supply a major supermarket chain with a specialty cake in the shape of a space rocket. It has been decided that the volumes required by the supermarket warrant a special production line to perform the finishing, decorating and packing of the cake. This line would have to carry out the elements shown in the next slide, which also shows the precedence diagram for the total job. The initial order from the supermarket is for 5000 cakes a week and the number of hours worked by the factory is 40 per week. From this:
The required cycle time = 40 hrs x 60 mins = 0.48 mins
5000
The required number of stages = 1.68 mins (total work content)
0.48 mins (required cycle time)
= 3.5 stages
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for Karlstad Kates
a
b
c
d
e
f
g
h
i
0.12 mins
0.30 mins
0.36 mins
0.25 mins
0.05 mins
0.17 mins
0.10 mins
0.08 mins
0.25 mins
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balancing loss for Karlstad Kates
a
b
c
d
e
f
g
h
i
Cycle time = 0.48 mins
Idle time every cycle = (0.48 - 0.42) + (0.48 - 0.36) + (0.48 - 0.42) = 0.24 mins
Proportion of idle time per cycle = 0.24 = 12.5%
4 x 0.48

3 Layout and Flow

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