# Line Balancing and Facility Layout

Document Sample

```					           Today’s Agenda
• Line Balancing

• Facility Layout

Line Balancing
Line Balancing
• Line Balancing is the
to workstations in such a
way that the workstations
(operations) have
approximately equal time
requirements.
• For Product Layouts
assigned to one
workstation.

One Important Term
Cycle Time of Workstation
• The time a workstation needs to complete its set of assigned

needs 0.5 minute and task two 1 minute. So the Cycle
Time (CT) of Workstation A is?

• The CT of a product line containing multiple workstations is
the longest CT of the workstations. (Line CT)

1 minute      10 minute     3 minute
Example
Five Tasks to be assigned to ??? workstations

a         b           c         d         e

0.1min   1.0min    0.7min       0.5min    0.2min

1. What is the maximum number of workstations
(assuming the tasks are not sub-divisible)
2. What are the minimum number of workstations
3. What number of workstations would yield the minimum
line cycle time?
4. What number of workstations would yield the maximum
line cycle time?

Precedence Diagram
• Task assignments must respect precedence
relationships and other technological constraints.
• Precedence diagram: Tool used in line balancing to
display elemental tasks and sequence requirements

0.1 min       1 min

a              c

0.2 min

b                  d          e
0.7 min        0.5 min

Number of Workstations
Question: How does one determine the
number of workstations to use?

Answer: By specifying a desired line cycle time
or, equivalently by specifying an output rate.
(How are cycle time and output related?)

Desired Cycle Time
Operating Time per Day (OT)
Desired Line CT 
Desired Output per Day (D)

Example (continued): Suppose OT = 8 hours per day (480
minutes per day) and D = 400 units per day. Then CT = ??

0.1 min        1 min

a               c

0.2 min

b                   d           e
0.7 min         0.5 min
Minimum Number of Workstations Required

(D)( t)
N =
N m in 
Cycle Time
 t = sum of task times
Example (continued): CT = 480/400= 1.2 minutes
per unit per workstation, Sum of task times = 2.5
minutes per unit. Nmin =???

Line Efficiency

Line Ef f iciency                   x100%
(Nactual )(CT)

Can we find the Line Efficiency of the example?

CT = 1.2 minutes per unit per workstation
Sum of task times = 2.5 minutes per unit.
Line Efficiency = 2.5/(3*1.2) =69.4%

Line Balancing Procedure (Heuristic)
1. Calculate CT and NMin.
to Total task time for a
2. Assign tasks 1. workstations moving from left to right through the
precedence diagram.
workstation should be
3. Tasks eligible for assignment are
a.               less than Line have
b.              times that do not exceed the only
tasks with 2. Sequence: we canremaining time at the work
station.
4. Select an eligible task for assignment using one or more of the
all
following rules: its predecessors are
assigned
a. Assign the task with the greatest number of tasks following it.
5. After each task assignment calculate time remaining at the current
work station.
6. Continue this until all tasks have been assigned to workstations.
7. Compute appropriate measures (e.g., line percent idle time and line
efficiency) for the set of assignments.

0.1 min         1 min

a                c

0.2 min

b                    d            e
0.7 min          0.5 min

Work          Time       Eligible   Assign          Station Idle
1                 1.2     a, b       a
a. Assign the task with the
1.1   greatest number of tasks following it.
c, b       c
0.1    None                 0.1
2                 1.2      b         b

0.5      d         d                  0

3                 0.2      e         e                 1.0

0.1 min     1 min

a. a            c
b. Assign the task with the greatest
0.2 min
b                d          e
0.7 min       0.5 min

0.1 min     1 min
I.    Even more
a            c                            balanced

0.2 min
II.   Hopefully shorter
CT (More output)
b                d          e
0.7 min      0.5 min

Line balancing Examples
• P253, Example 1
• P252, Example 2
• P264, Solved Problem #1. They use a
positional weight to break tie. You can
follow their method, or you can try-and-
error work out any feasible solution
satisfies CT and sequence requirements.

Toy Wagon Assembly Line
Balance Example
• For a 8 hour production day, Toy wagon
assembly line need to produce 571
wagons, how many work stations do you
need?

8*60*60
Desired CT           50.4(sec)
571

Toy Wagon Assembly Line Balance Example
A              45                         ---
B              11                          A
C               9                          B
D              50                          ---
E              15                           D
F              12                           C
G             12                            C
H             12                            E
I            12                            E
J             8                         F,G,H,I
K             9                                J

Toy Wagon Assembly Line
Balance Example
• Sum of task time = 195

195
N min         4
50.4

Precedence Diagram
12
11         9
45 sec.                              F    8                 9
B          C
12
A                                        J                 K
G
15              12
50
D                        H
E
12
I

Balance the Line Using Most Followers Rule

St. 1    A      45           5.4 idle    none

Balance the Line Using Most Followers Rule

St. 1    A      45           5.4 idle    none

St. 2 D          50          0.4 idle    none

Balance the Line Using Most Followers Rule

St. 1    A      45           5.4 idle      none

St. 2 D          50          0.4 idle      none

St. 3 B           11          39.4         C, E            C, E                E
E        15          24.4          C,H,I            C
C         9          15.4         F,G,H,I        F,G,H,I          F,G,H,I
F*        12          3.4 idle      none

Balance the Line Using Most Followers Rule

St. 1    A      45           5.4 idle      none

St. 2 D          50          0.4 idle      none

St. 3 B          11          39.4          C, E            C, E               E
E       15          24.4          C,H,I             C
C        9          15.4          F,G,H,I         F,G,H,I          F,G,H,I
F*        12          3.4 idle      none
St.4    G*        12         38.4           H, I           H, I               H, I

H        12          26.4            I
I        12          14.4            J
J        8            6.4 idle      none

Balance the Line Using Most Followers Rule

St. 1    A      45           5.4 idle      none

St. 2 D          50          0.4 idle      none

St. 3 B          11          39.4          C, E           C, E               E
E       15          24.4          C,H,I            C
C        9          15.4          F,G,H,I        F,G,H,I          F,G,H,I
F*       12          3.4 idle      none
St. 4    G*       12          38.4          H, I           H, I              H, I

H        12           26.4            I
I        12          14.4             J
J           8         6.4 idle      none
St. 5    K            9       41.4 idle      none                             © Wenge Zhu
Efficiency and Balance Delay Calculations

195
Efficiency =                              = 0.78 or 78%
(5) 50
57
Balance Delay =                                = 0.22 or 22%
(5) 50

Check, Total =                      100%

Notice that BD = 1.0 – Eff.
• Also if we switch the primary rule with the secondary and rebalance the line we
see that efficiency goes up to about 97%, i.e. BD goes down to 3%.
Solve Example Again With
Reversed Rule

Facilities Layout
• Layout: the configuration of
departments, work centers, and
equipment, with particular emphasis on
movement of work (customers or
materials) through the system
• Product layouts
• Process layouts
• Fixed-Position layout
• Combination layouts

Objective of Layout Design
1. Facilitate attainment of product or service quality
2. Use workers and space efficiently
3. Avoid bottlenecks
4. Minimize unnecessary material handling costs
5. Eliminate unnecessary movement of workers or
materials
6. Minimize production time or customer service
time
7. Design for safety
Importance of Layout Decisions
• Requires substantial investments of
money and effort
• Involves long-term commitments
• Has significant impact on cost and
efficiency of short-term operations

The Need for Layout Decisions
Inefficient operations
For Example:              Changes in the design
High Cost                 of products or services
Bottlenecks

Accidents
The introduction of new
products or services

Safety hazards
The Need for Layout Design
(Cont’d)
Changes in
environmental         Changes in volume of
or other legal          output or mix of
requirements               products

Morale problems
Changes in methods
and equipment

Types of Layout

• Product Layout:
• Here equipment is arranged according to the
progressive steps by which the product is made.
• Assembly line is a good example of a narrow
production line such as car assembly.

Machine type A   Machine type B   Machine type A

Basic Layout Types
• Product layout
–   Layout that uses standardized processing
operations to achieve smooth, rapid, high-
volume flow
• Process layout
–   Layout that can handle varied processing
requirements
• Fixed Position layout
–   Layout in which the product or project
remains stationary, and workers, materials,
and equipment are moved as needed

Cellular Layouts

• Cellular Production
–   Layout in which machines are grouped
into a cell that can process items that
have similar processing requirements
• Group Technology
–   The grouping into part families of items
with similar design or manufacturing
characteristics

Cellular Manufacturing Layout

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