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Assembly Line Balancing

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Assembly Line Balancing Jaime Joo MBA 530 Section 1 Brigham Young University * Step 2: Production time per must be expressed in seconds since Task times are in ... – PowerPoint PPT presentation

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Title: Assembly Line Balancing


1
Assembly Line Balancing
  • Jaime Joo
  • MBA 530 Section 1
  • Brigham Young University

2
Outline
  • What is Assembly Line Balancing?
  • How can Assembly Line Balancing benefit your
    operations?
  • Classic approach to ALB
  • Lets practice!
  • ALB in the real world
  • Conclusions

3
What is Assembly Line Balancing (ALB)?
  • ALB is the procedure to assign tasks to
    workstations so that
  • Precedence relationship is complied with
  • No workstation takes more than the cycle time to
    complete
  • Operational idle time is minimized

4
How can Assembly Line Balancing benefit your
operations?
  • A balanced line
  • Promotes one piece flow
  • Avoids excessive work load in some stages
    (overburden)
  • Minimizes wastes (over-processing, inventory,
    waiting, rework, transportation, motion)
  • Reduces variation

5
Unbalanced Line
!?
Zzz
Zzz
?
10 sec
40 sec!
20 sec
15 sec
Overproduction! Generates waste
Undesirable waiting
6
Balanced Line
?
?
?
?
25 sec
25 sec
20 sec
15 sec
  • Promotes one piece flow
  • Avoids overburden
  • Minimizes wastes
  • Reduces variation

7
Line Balancing prerequisites
  • Prior to balancing a line we must
  • Determine the required workstation cycle time (or
    TAKT time), matching the pace of the
    manufacturing process to customer demand
  • Standardize the process

8
Classic approach to ALB
  • Also known as SALBP (Simple Assembly Line
    Balancing Problem), the classic approach to ALB
    is an heuristic process to optimize assembly
    lines simplifying the problem to a basic level of
    complexity

Dubbed SALBP by Becker and Scholl (2004)
9
Example
  • The next table shows the tasks performed in a
    production line. Our goal is to combine them into
    workstations. The assembly line operates 8 hours
    per day and the expected customer demand is 1000
    units per day. Balance the line and calculate the
    efficiency and theoretical minimum number of
    workstations.

10
Example (cont.)
Task Task Time (sec) Preceding Task
A 13 -
B 11 A
C 15 A
D 20 B
E 12 B
F 13 C
G 13 C
H 18 D, E
I 17 F, G
J 15 H, I
K 9 J
Total Time 156
11
Example (cont.)
  • Step 1 Draw a precedence diagram according to
    the given sequential relationship

20 sec
D
11 sec
18 sec
B
H
12 sec
13 sec
9 sec
15 sec
E
A
K
J
13 sec
17 sec
F
15 sec
I
C
13 sec
G
12
Example (cont.)
  • Step 2 Determine Takt time or Workstation Cycle
    Time
  • CProduction time per day / Customer demand (or
    output per day)
  • C 28800 sec (8 hours) / 1000 units 28.8
  • Step 3 Determine the theoretical number of
    workstations required
  • N Total Task Time / Takt time
  • N 156 / 28.8 5.42 (6 workstations)

13
Example (cont.)
  • Step 4 Define your assignment rules. For this
    example our primary rule will be number of
    following tasks and the secondary rule will be
    longest operation time

14
Example (cont.)
  • Step 5 Assign tasks to workstations following
    the assignment rules and meeting precedence and
    cycle time requirements
  • To form Workstation 1

11 sec
13 sec
B
Following tasks 5
A
Lot 15gt11!
15 sec
C
Following tasks 5
WS1 AC28 sec Cycle Time met!
15
Example (cont.)
  • Forming Workstation 2

BDgtCycle time!
11 sec
13 sec
B
LOT_FGgtE
A
15 sec
C
WS2 Operation time24 sec (ltC)
Arbitrarily choose F
16
Example (cont.)
  • Following the same criteria we achieve our
    balancing with 7 workstations

17
Example (cont.)
  • Step 6 Calculate Efficiency
  • Efficiency Total Task Time / (Actual number of
    workstations Takt Time)
  • Efficiency 156 / (728.8) 77
  • How to interpret this efficiency?
  • Is this the best efficiency achievable?

18
Lets Practice
  • We have found a new market for our product. This
    market is less demanding so we have decided not
    to include a particular feature, specifically the
    feature added by task I. As a consequence, task
    time in F drops to 5 seconds and task time in G
    drops to 8 seconds. Balance the line according to
    the other conditions.

19
Lets practice (cont.)
Task Task Time (sec) Preceding Task
A 13 -
B 11 A
C 15 A
D 20 B
E 12 B
F 13 5 C
G 13 8 C
H 18 D, E
I 17 F, G
J (new I) 15 H, F, G
K (new J) 9 I
Total Time 156 126
20
Lets practice (cont.)
  • Lets take some time to solve this new problem.
    This time we will calculate keeping the primary
    and secondary rules as in the original problem.

21
Lets practice (solution)
  • Precedence diagram

20 sec
D
11 sec
18 sec
B
H
12 sec
13 sec
9 sec
15 sec
E
A
J
I
5 sec
F
15 sec
C
8 sec
Previously J K respectively
G
22
Lets practice (solution)
  • Takt time
  • C 28,800 sec / 1000 units 28.8
  • Theoretical number of workstations
  • N 126/28.8 4.38 (5 workstations)
  • Primary rule number of following tasks
  • Secondary rule longest operation time

23
Lets practice (solution)
  • Following the rules and observing cycle time and
    precedence we obtain

24
Lets practice (solution)
  • Efficiency 126/(628.8) 73
  • Challenge Is this the best efficiency
    achievable? Try to solve with LOT as the primary
    rule and you will obtain a 5 workstations
    balance, increasing efficiency to 87

25
ALB in the real world
  • The simple ALB problem approach is limited by
    some constraints
  • Balance on existing and operating lines
  • Workstations have spatial constraints
  • Some workstations cannot be eliminated
  • Need to smooth workload among workstations
  • Multiple operators per workstation
  • Different paces among operators, different lead
    times within the same workstation

26
ALB in the real world (cont.)
  • Operator spatial constraints
  • Different workstation imposed working positions
  • More than one task to be performed in what should
    be the space for one task
  • Multiple Products
  • Coping with different products, some operations
    are needed for some products but not for others
  • Some products can introduce peak times in some
    workstations
  • Different task times performed in different
    shifts
  • Particularly when introducing new employees or
    workers with some degree of incapacity

27
Conclusion
  • Simply Assembly Line Balancing is a valid method
    to optimize assembly lines. However, many
    variables found in real operating lines increase
    the complexity of the problem. More complex
    algorithms have been developed to solve the
    difficult task of balancing large scale
    industrial lines. Some of them are commercially
    available in software.

28
References
  • F. Robert Jacobs Richard B. Chase Operations
    and Supply Management, The Core
    McGraw-Hill/Irwin First Edition
  • Emanuel Falkenauer Line Balancing in the real
    world Optimal Design
  • Paul Swift. http//www.beyondlean.com/line-balanci
    ng.html
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