Layout and Line balancing

Antti Salonen
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Antti Salonen
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What is layout?
Layout refers to the configuration of
departments, work centers and
equipment with particular emphasis on
movement of work (customers or
materials) through the system.
The need for layout planning arises in
the process of designing new facilities
and redesigning existing facilities.
Layout decisions:
•  Require substantial investments
(money and effort)
•  Involve long-term commitments
•  Impact the cost and efficiency of
short-term operations
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Layout types
Layout requirements are determined by the type of operation.
Less customization and higher volume
Less complexity, less divergence, and more line flows
Process
Characteristics
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(1)
Customized process,
with flexible and unique
sequence of tasks
(2)
Disconnected line flows,
moderately complex
work
(1)
Low-volume
products, made
to customer
order
(2)
Multiple products with low
to moderate volume
(3)
Few major
products,
higher
volume
(4)
High volume, high
standardization,
commodity
products
Job
process
Small batch
process
Batch processes
Large batch
process
(3)
Connected line, highly
repetitive work
Line
process
(4)
Continuous flows
Continuous
process
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Layout strategy
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Fixed position (Project)
Extremely low volumes (one of a kind), e.g. bridge, airplane.
• 
Process oriented (Job shop)
Low volumes, high variety, least efficient, e.g. customized
products.
• 
Product oriented (Line flow/batch production)
High volumes, most efficient, e.g. books, furniture.
• 
Continuous flow
Extremely high volumes, standard products, e.g. paper, milk.
• 
• 
• 
Hybrid layouts
Warehouses
Service layout
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Production and Inventory Strategies
Make-to-Stock Strategy
Used by manufacturers that hold items in stock
for immediate delivery, thereby minimizing
customer delivery times.
Supply
Assemble-to-Order Strategy
Used by manufacturers that produce a wide
variety of products from relatively few
subassemblies and components after the
customer orders are received.
Prognosis Driven (PD)
MTS:
ATO:
DD
Consume
PD
DD
Consume
OP
PD
DD
OP
Used by manufacturers that make
products to customer specifications in low
volumes.
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PD
OP
MTO:
Make-to-Order Strategy
Demand
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Consume
Demand Driven (DD)
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Layout strategy
•  Job shop process
A process with the flexibility to produce a wide variety of products in
significant quantities, with considerable complexity and divergence in the
steps performed => Resources allocated around the process
•  Line Process
A process with high volumes and standardized products => Resources
organized around the product
•  Hybrid layout
Create flow lines in parts of the workshop to increase efficiency, e.g. One
worker – multiple machines, Cell/Group technology.
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Process vs product focus
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Reasons for redesign
•  Inefficient operations (e.g. bottlenecks)
•  Accidents or safety hazards
•  Changes in the design of products/services
•  Introduction of new products/services
•  Changes in volume (output or mix)
•  Changes in methods or equipment
•  Changes in environmental or other legal requirements
•  Morale problems (e.g. lack of face-to face contact)
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Designing Process Layouts
•  Layout planning involves decisions about the physical
arrangement of economic activity centers within a facility.
•  An economic activity center could be anything that
consumes space (e.g. a machine or a cafeteria)
•  The goal is to allow workers and equipment to operate most
efficiently.
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Designing Process Layouts
1.  What centers to include?
2.  How much space does each center need?
3.  How should each center be configurated?
4.  Where should each center be located?
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Designing Process Layouts
Gather information
• 
Space requirements of each center
• 
Available space in the facility
• 
Closeness factor indicates which centers
need to be located next to each other
Closeness Factors
1.  Develop current block plan (allocates space
and indicates placement of each department by trial
and error)
Department
1
2
3
4
5
6
1. Administration
―
3
6
5
6
10
―
8
1
1
3
9
―
2
2. Social services
3. Institutions
4. Accounting
5. Education
6. Internal audit
―
―
1
―
2.  Develop proposed block plan
3.  Compare the two (e.g. using load-distance
method) and make choice!
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EXAMPLE
1
Designing process layouts
(Block plan)
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Salonen machining is a machine shop that produces a variety of small metal products on general-purpose equipment. A
full shift of 26 workers and a second shift of 6 workers operate its 32 machines. Three types of information are needed
to begin designing a revised layout for Salonen machining: Space requirements for each center, available space and
closeness factors. Departments 3 and 4 can not be moved because of constraints in the building design.
Space requirements for each center: Salonen machining has grouped its processes into six different departments: burr
and grind, NC equipment, shipping and receiving, lathes and drills, tool crib, and inspection. The exact space
requirements of each department, in square meters, are listed below.
Department
Area needed m2
1. Burr and grind
100
2. NC equipment
95
3. Shipping and receiving
75
4. Lathes and drills
120
5. Tool crib
80
6. Inspection
70
TOTAL:
540
The layout designer must tie space requirements to capacity plans, calculate the specific equipment and space needs
for each center, and allow circulation space such as aisles and the like.
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Available space:
A block plan allocates space and indicates placement of each department. When
describing a new facility layout, the plan need only provide the facility’s dimensions and
space allocations. When an existing facility layout is being modified, the current block
plan also is needed. Salonen machining’s available space is 36 meters by 15 meters,
or 540 square meters. The designer could begin the design by dividing the total
amount of space into six equal blocks (90 square meters each), even though
inspection needs only 70 square meters. The equal space approximation shown in the
figure below is good enough until the detailed layout stage, when larger departments
(such as lathes and drills) are assigned more block space than smaller departments.
Current Block Plan
2
4
3
15m
6
5
1
36m
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Closeness factors:
The layout designer must also know which centers need to be located close to one
another. Location is based on the number of trips between centers and qualitative
factors.
Below is Salonen machining’s trip matrix, which gives the number of trips (or some
other measure of materials movement) between each pair of departments per day.
Trips between departments
Department
1
2
1. Burr and grind
-
20
2. NC equipment
3 Shipping and receiving
4 Lathes and drills
-
3
4
5
20
10
-
80
75
15
-
90
70
5 Tool crib
-
6 Inspection
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6
-
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Develop an acceptable block plan for Salonen machining, using trial and error. The
goal is to minimize materials handling costs.
Solution:
A good place to start is with the largest closeness ratings in the trip matrix (say, 70 and
above). Beginning with the largest number of trips and working down the list, you might
plan to locate the departments as follows:
5
Departments 3 and 6 close together
Departments 1 and 6 close together
Departments 2 and 5 close together
Departments 4 and 5 close together
4
3
15m
2
Departments 3 and 4 should remain at their current locations because of the ”other
considerations”.
If after several attempts you cannot meet all five requirements, drop one or more and
try again. If you can meet all five easily, add more (such as for interactions below 70).
The block plan in the figure shows a trial-and-error solutoion that satisfies all five
requirements. We started by keeping departments 3 and 4 at their current locaitons. As
the first requirement is to locate departments 3 and 6 close to each other, we put 6 in
the southeast corner of the layout. The second requirement is to have departments 1
and 6 close together, so we place 1 in the space just to the left of 6, and so on.
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Proposed Block Plan
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1
6
36m
16
Improvement analysis:
The table below includes all department pairs that have some load in between them. The Distance figures are
based on recti-linear movements.
Current plan
Proposed plan
Proposed Block Plan
Department
pair
Load
Distance
Load-Distance
Distance
Load-Distance
1-2
20
3
60
1
20
1-4
20
2
40
1
20
1-6
80
2
160
1
80
2-3
10
2
20
3
30
2-5
75
2
150
1
75
3-4
15
1
15
1
15
3-6
90
3
270
1
90
4-5
70
1
70
1
70
Tot:
785
5
4
3
15m
2
1
6
36m
Current Block Plan
400
2
4
3
15m
6
5
1
36m
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Technical considerations
•  Requirements of different tasks
If these are quite different, it may not be feasible to place the tasks in the
same workstation.
If these are incompatible, it may not even be feasible to put the work
stations near each other.
•  Human factors
When humans are involved, tasks may take different amount of time to
complete.
•  Equipment limitations
•  Space limitations
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Designing Product Layouts
•  Line balancing is the assignment of
work elements to stations in a line.
•  The goal is to achieve the desired
output rate with the smallest number of
workstations.
•  Arranging stations in a sequence (line)
for the product to move from one station
to the next until its completion at the
end of the line.
•  The slowest station sets the output rate,
e.g. 500/week.
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Designing Product Layouts
The goal is to match the output rate to the
production plan.
1. 
2. 
The work is separated into work elements (the smallest
units of work that can be performed independently)
A precedence diagram is constructed, which shows
which work elements that must be performed before the
next can begin.
Description
Time
(sec)
Determine the desired output rate.
4. 
Calculate the cycle time (the maximum time allowed for
work on a unit at each station) = 1/output rate
A
Bolt leg frame to hopper
40
None
B
Insert impeller shaft
30
A
C
Attach axle
50
A
D
Attach agitator
40
B
E
Attach drive wheel
6
B
F
Attach free wheel
25
C
G
Mount lower post
15
C
H
Attach controls
20
D, E
I
Mount nameplate
18
F, G
D
B
E
30
40
Balancing the line gives the minimum amount of stations for a
determined output rate, still satisfying all precedence requirements
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6
A
Assign work elements to stations.
H
40
F
C
25
50
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Immediate
Predecessor(s)
Total 244
3. 
5. 
Work
Element
I
G
18
15
20
EXAMPLE
2
Designing product layouts
(Line balancing)
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EXAMPLE X.4
Green Grass, Inc., a manufacturer of lawn and garden equipment, is designing
an assembly line to produce a new fertilizer spreader, the Big Broadcaster.
Using the following information on the production process, construct a
precedence diagram for the Big Broadcaster.
Work
Element
Description
Time
(sec)
Immediate
Predecessor(s)
A
Bolt leg frame to hopper
40
None
B
Insert impeller shaft
30
A
C
Attach axle
50
A
D
Attach agitator
40
B
E
Attach drive wheel
6
B
F
Attach free wheel
25
C
G
Mount lower post
15
C
H
Attach controls
20
D, E
I
Mount nameplate
18
F, G
Total 244
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SOLUTION
The figure shows the complete diagram. We begin with work element A, which
has no immediate predecessors. Next, we add elements B and C, for which
element A is the only immediate predecessor. After entering time standards and
arrows showing precedence, we add elements D and E,
and so on. The diagram simplifies interpretation.
Work element F, for example, can be done
D
anywhere on the line after element C is completed.
H
40
B
However, element I must await completion of
20
E
elements F and G.
30
6
A
40
F
C
25
50
I
G
18
15
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Designing Product Layouts
Theoretical minimum no. of stations:
TM = ∑t/c [pc]
∑t = total time required to assemble each unit
c = cycle time
Idle time (total unproductive time for all stations)
IT= nc - ∑t [min]
n = no. of stations
Efficiency (ratio of productive time to total time)
E =(∑t/nc)*100
[%]
Balance delay (amount by )
BD = 100 – E
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[%]
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EXAMPLE
3
Designing product layouts
(Line balancing)
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EXAMPLE X.5
Green Grass’s plant manager just received marketing’s latest
forecasts of Big Broadcaster sales for the next year. She
wants its production line to be designed to make 2,400
spreaders per week for at least the next 3 months. The plant
will operate 40 hours per week.
a. What should be the line’s cycle time?
b. What is the smallest number of workstations that she could
hope for in designing the line for this cycle time?
c. Suppose that she finds a solution that requires only five
stations. What would be the line’s efficiency?
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SOLUTION
a. First convert the desired output rate (2,400 units per week) to an
hourly rate by dividing the weekly output rate by 40 hours per
week to get units per hour. Then the cycle time is
c = 1/r = 1/60 (hr/unit) = 1 minute/unit = 60 seconds/unit
b. Now calculate the theoretical minimum for the number of
stations by dividing the total time, Σt, by the cycle time,
c = 60 seconds. Assuming perfect balance, we have
Σt
244 seconds
TM =
=
= 4.067 or 5 stations
c
60 seconds
c. Now calculate the efficiency of a five-station solution, assuming
for now that one can be found:
Σt
244
= 81.3%
Efficiency =
(100) =
nc
5(60)
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Designing Product Layouts
How to assign work elements to stations then…
Ranked Positional Weight Technique (RPWT)
The rationale for the RPWT is that the positional weight is a measure of
the task´s importance. Tasks with a high positional weight imply much
subsequent work and tasks depending on them.
Also…
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Longest work element first
• 
Shortest work element first
• 
Etc…
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Designing Product Layouts
Ranked Positional Weight Technique (RPWT)
1.  Construct a diagram of precedence relationships among the tasks (arrows indicate
which tasks must proceed others)
2.  For each task, add up the task times for that task and ALL tasks that must follow it
directly and indirectly. This value is called positional weight for the task.
3.  Select the task with the largest positional weight and assign it to the first work
station.
4.  Select the task with the next largest positional weight and assign it to the earliest
possible work station that exists, as long as:
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• 
The maximum cycle time is not exceeded
• 
All the task´s predecessors must be assign to the same or earlier work stations
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“Largest work-element time” rule
Same procedure as RPWT, but instead of choosing the work-element
with the highest RPW, choose the work-element with the largest time
(as long as the precedence requirements are fulfilled).
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EXAMPLE
4
Designing product layouts
(Line balancing)
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Find a line balancing solution for Green Grass Inc.
using the RPWT technique
Work
Element
Description
Time (sec)
Immediate
Predecessor(s)
D
40
A
Bolt leg frame to hopper
40
None
B
Insert impeller shaft
30
A
C
Attach axle
50
A
D
Attach agitator
40
B
E
Attach drive wheel
6
B
A
F
Attach free wheel
25
C
40
G
Mount lower post
15
C
H
Attach controls
20
D, E
I
Mount nameplate
18
F, G
B
E
30
F
C
25
50
I
G
Theoretical minimum no of stations = 5
Cycle time = 60 sec
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6
Total 244
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H
18
15
32
Find a line balancing solution for Green Grass Inc.
using the RPWT technique
Work
Element
Description
Time (sec)
Immediate
Predecessor(s)
A
Bolt leg frame to hopper
40
None
B
Insert impeller shaft
30
A
C
Attach axle
50
A
D
Attach agitator
40
B
E
Attach drive wheel
6
B
F
Attach free wheel
25
C
G
Mount lower post
15
C
H
Attach controls
20
D, E
I
Mount nameplate
18
F, G
Total 244
D
B
E
30
20
6
A
40
H
40
C
50
F
25
I
G
Theoretical minimum no of stations = 5
Cycle time = 60 sec
18
15
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Solution:
Station
Candidates
Choice
Cumulative
time
Idle time
S1
A
A
40
20
S2
B,C
C
50
10
S3
B, F, G
B
30
30
E, F, G
F
55
5
D, E, G
D
40
20
E, G
G
55
5
E, I
I
18
42
E
E
24
36
H
H
44
16
S4
S5
When implementing this solution, we must observe precedence requirements within each station.
For example, the worker at station S5 can do element I at any time but cannot start element H until
element E is finnished.
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D
B
E
30
20
6
A
40
H
40
F
C
25
50
I
G
18
15
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The manager of a computer assembly line plans to produce 100 assembled computers per 10-hour
workday. Work element data for the assembly is shown in the table below.
Work
element
Time
(minutes)
Immediate
predecessors
A
2
None
B
3
A
C
1
B
D
5
B
E
5
C, D
F
4
E
G
1
D, E
H
2
F
I
6
G
J
4
H
K
2
I, J
L
6
K
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a)  Draw a precedence diagram.
b)  What cycle time (in minutes) results in the
desired output rate?
c)  What is the theoretical minimum number of
work stations?
d)  Using trial and error, balance the line as best
as you can.
e)  What is the efficiency of your solution?
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C
A
B
E
D
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F
G
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J
K
L
I
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C
A
B
E
D
Work
element
Time
(minutes)
RPW
A
2
41
B
3
39
C
1
31
D
5
35
E
5
30
F
4
18
G
1
15
H
2
14
I
6
14
J
4
12
K
2
8
L
6
6
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F
H
J
G
K
L
I
WS
Candidates
CT
1
A, B, C
6
2
D
5
3
E, G
6
4
F, H
6
5
I
6
6
J, K
6
7
L
6
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C
WS1
A
B
E
D
WS2
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WS6
WS4
F
G
WS3
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J
WS7
K
L
I
WS5
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Improving line efficiency
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Parallel workstations
Bottlenecks may be the result of difficult or very long tasks and
may disrupt the flow of products down the line.
In these situations, parallel workstations increase the work flow
and provide flexibility.
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Mixed model lines
Still another approach is to design the line to handle multiple
products, often referred to as mixed model lines. This implies that
the products have to be similar with similar work elements.
This approach offers great flexibility in varying the amount of output
of the products.
One example is found in the automotive industry where cars are
often made on the same platform.
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Workers
Another approach to achieving a balanced line is to cross train
workers to be able to perform multiple tasks.
This implies that a worker with temporarily increased idle time can
assist other workers to maintain the flow of the line, so called
dynamic line balancing.
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Improving job shop efficiency
A job shop has the least efficiency…
⇒  Creating a line flow in parts of the job shop will increase efficiency!
•  One worker – multiple machines
•  Cell/Group technology
These are called hybrid layouts!
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One worker – multiple machines
•  One worker operates several machines
simultaneously to achieve line flow (moves
from one machine to the next)
•  The machine set-up can be changed to
produce different products or parts
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Cell/Group technology
•  This manufacturing technique groups parts or products with similar
characteristics into families and sets aside groups of machines for
their production => A line within the job shop.
•  Based on shape, size, manufacturing requirements etc.
•  Goal: efficient production with minimal change-over and set-up times
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EXAMPLE
5
Cell/Group technology
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Lathing
L
L
Milling
L
L
M
Drilling
M
M
D
D
D
D
M
Grinding
L
L
L
L
Receiving and
shipping
M
M
Assembly
A
A
A
A
G
G
G
G
G
G
(a) Jumbled flows in a job shop without GT cells
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L
L
M
L
G
M
Assembly
area
A
Cell 2
Cell 1
Receiving
D
G
A
G
Cell 3
L
M
D
Shipping
(b) Line flows in a job shop with three GT cells
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Volvo CE, CS-09
After:
Before:
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Storage layouts
The design of storage facilities present a different set of factors
than the design of factory layouts.
Frequency of order is an important consideration:
•  Items that are ordered frequently should be placed near the entrance of
the facility
•  Items that are ordered infrequently should be placed in the rear of the
facility.
The goal is to minimize picking time and transportation (distance of
movement and travel time)!
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Storage layouts
If items are ordered/sold together it is beneficial to store them
close to each other.
Other considerations:
•  Width and length of aisles
•  Height of storage racks
•  Need to periodically make a physical count of stored items
•  Modes of internal transport
•  Level of automation
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EXAMPLE
6
Storage Layout
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Office layouts
Office layouts are undergoing transformations
as the flow of paperwork is replaced by
electronic communications.
This implies that there is less need to place
office workers in a layout that optimizes a
physical flow.
However, providing efficient use of space and
possibilities for cooperation between
colleagues are of course important issues.
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Relevant book chapters
•  Chapter: “Developing a process strategy”
–  Layout
•  Chapter: “Managing process constraints”
•  Chapter: “Designing lean systems”
–  Designing lean systems layouts
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Questions?
antti.salonen@mdh.se
Next lecture on Tuesday 2015-12-01
Aggregate planning
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