Balancing Production Lines

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Facilities Planning - Unit 06Balancing
Production Lines
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Factors Affecting Capacity
External Factors Government regulations Union agreements Supplier capabilities Technology Internal Factors Product and service design Personnel jobs Equipment Capabilities Materials management Q.C. Systems Management capabilities Plant layout flow
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Process Selection and System Design
Facilities andEquipment
Forecasting
CapacityPlanning
Layout
Product andService Design
ProcessSelection
WorkDesign
TechnologicalChange
Capacity is significantly impacted by process
selection and facility layout.
4
Basic Layout Types

• Product layout
• Process layouts
• Fixed-Position layout
• Group Technology / Combination layouts

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Product Layout

• Facility organized around product
• Design minimizes line imbalance
• Delay between work stations
• Types Fabrication line assembly line

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Product Layout
Fabrication Line
Assembly Line

• Assembles fabricated parts
• Uses workstation
• Repetitive process
• Paced by tasks
• Balanced by moving tasks

• Builds components
• Uses series of machines
• Repetitive process
• Machine paced
• Balanced by physical redesign

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Product Type Layout - Requirements

• Standardized product
• High production volume
• Stable production quantities
• Uniform quality of raw materials components

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Product Layout - Flow Diagram Showing the
Production Process for Harley Davidson, York, PA.
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Product Layout
Raw materials or customer
Station 2
Station 3
Station 4
Finished item
Station 1
Material and/or labor
Material and/or labor
Material and/or labor
Material and/or labor
Used for Repetitive or Continuous Processing
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Product Layout More Examples
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Line Balancing Problem

• Work stations are arranged so that the output of
  one is an input to the next, i.e., a series
  connection
• Layout design involves assigning one or more of
  the tasks required to make a product to work
  stations
• The objective is to assign tasks to minimize the
  workers idle time, therefore idle time costs,
  and meet the required production rate for the
  line

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Line Balancing Problem

• In a perfectly balanced line, all workers would
  complete their assigned tasks at the same time
  (assuming they start their work simultaneously)
• This would result in no idle time
• Unfortunately there are a number of conditions
  that prevent the achievement of a perfectly
  balanced line
• The estimated times for tasks
• The precedence relationships for the tasks
• The combinatorial nature of the problem

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Assembly Line Balancing Steps

• 1. Determine tasks (operations)
• 2. Determine sequence
• 3. Draw precedence diagram
• 4. Estimate task times
• 5. Calculate cycle time
• 6. Calculate number of work stations
• 7. Assign tasks
• 8. Calculate efficiency

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Assembly Lines Balancing Concepts
Question Suppose you load work into the three
work stations below such that each will take the
corresponding number of minutes as shown. What
is the cycle time of this line?
Answer The cycle time of the line is always
determined by the work station taking the longest
time. In this problem, the cycle time of the
line is 7 minutes. There is also going to be
idle time at the other two work stations.
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Assembly Lines Balancing Example 1

• Youve just been assigned the job a setting up an
  electric fan assembly line with the following
  tasks

Total Task Times 11.35 Minutes
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Assembly Lines Balancing Example 1Structuring
the Precedence Diagram

• Question Which process step defines the maximum
  rate of production?

Answer Task C is the cycle time of the line and
therefore, the maximum rate of production.
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Assembly Lines Balancing Example 1The
Bottleneck
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Assembly Lines Balancing Example 1Cycle Time
Determination

• Question Suppose we want to assemble 100 fans
  per day. What would our cycle time have to be?

Answer
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Assembly Lines Balancing Example 1Theoretical
Minimum Number of Workstations

• Question What is the theoretical minimum number
  of workstations for this problem?

Answer
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Assembly Lines Balancing Example 1Workstations
Tasks Assignment
D (4.2 - 1.2) 3
C (4.2 - 3.25) 0.95
A (4.2 2 2.2)
E (3 - 0.5) 2.5
B (2.2 1 1.2)
F (2.5- 1) 1.5
G (1.2 -1 0.2)
H (1.5 - 1.4) 0.1
Idle 0.1
Idle 0.95
Idle 0.2
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Assembly Lines Balancing Example 1Efficiency
of Assembly Line
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Assembly Line BalancingLayout Heuristics for
Assigning Tasks

• Basic rules
• Rule 1 Pick the task with the longest required
  time. Save shorter tasks for fine-tuning
• Rule 2 Select the task with the largest number
  of followers. This preserves options for
  subsequent. stations and tends to reduce idle
  time.
• Common Practice Use rule 2. When ties exist use
  rule 1

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Assembly Lines Balancing Example 2
Vickis Pizzeria and the Precedence Diagram
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Assembly Lines Balancing Example 2

• Determine output rate
• Vicki needs to produce 60 pizzas per hour
• Determine cycle time
• The amount of time each workstation is allowed to
  complete its tasks
• Limited by the bottleneck task (the longest task
  in a process)

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Assembly Lines Balancing Example 2

• Compute the theoretical minimum number of
  stations
• Number of stations needed to achieve 100
  efficiency (every second is used)
• Always round up (no partial workstations)
• Serves as a lower bound for our analysis

(
)
å
task times
seconds

165



stations

3
or

2.75,
Stations

of
Number
sec/station

60
time
cycle
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Assembly Lines Balancing Example 2

• Assign tasks to workstations
• Start at the first station choose the longest
  eligible task following precedence relationships
• Continue adding the longest eligible task that
  fits without going over the desired cycle time
• When no additional tasks can be added within the
  desired cycle time, begin assigning tasks to the
  next workstation until finished

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Assembly Lines Balancing Example 2

• Compute efficiency and balance delay
• Efficiency () is the ratio of total productive
  time divided by total time
• Balance delay () is the amount by which the line
  falls short of 100

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Assembly Lines Balancing Example 3

• Total Work Content, ?t 306 decimal min.
• Need 450 dolls/day, one shift per day
• Available time 420 minutes
• a. Precedence diagram
• b. Maximum cycle time (c) 420 min x 100 / 450
  dolls 93
• c. Minimum number of stations (n) 306/93 3.3
  ? 4
• d. Assigning work elements to workstations (next
  page)
• e. Balance delay (nc-?t)/nc (4 x 91) 306
  / (4 x 91) 0.159
• or 15.9
  idleness among the four stations

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Assembly Lines Balancing Example 3
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Assembly Lines Balancing Example 3
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Assembly Lines Balancing Example 3
Station 3
Station 2
Station 4
Station 1
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Assembly Lines Balancing Example 4 Precedence
Graph for Credit Applications
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Assembly Lines BalancingBalancing the Work
Through Better Work Flow Design
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Assembly Lines Balancing - Layout Design
U-Shaped or horseshoe arrangements better enable
workers communications and task sharing
Connections of subassembly islands S feed
parts/components to end-assembly E islands -
each island functions as a separate team
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Line Balancing Procedure Summarized

• Determine the cycle time and the minimum number
  of workstations.
• Make assignments to workstations in order,
  beginning with Station 1. Tasks are assigned to
  workstations moving from left to right through
  the precedence diagram.
• Before each assignment, use the following
  criteria to determine which tasks are eligible to
  be assigned to a workstation
• All preceding tasks in the sequence have been
  assigned.
• The task time does not exceed the time remaining
  at the workstation.
• If no tasks are eligible, move on to the next
  workstation

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Line Balancing Procedure Summarized

• After each task assignment, determine the time
  remaining at the current workstation by
  subtracting the sum of times for tasks already
  assigned to it from the cycle time
• Break ties that occur using one of these rules
• Assign the task with the longest task time.
• Assign the task with greatest number of
  followings.
• Continue until all tasks have been assigned to
  workstations.
• Compute appropriate measures (e.g., percent idle
  time, efficiency) for the set of assignments.