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Line Balancing and Facility Layout

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Line Balancing and Facility Layout Powered By Docstoc
					           Today’s Agenda
• Line Balancing

• Facility Layout




                            © Wenge Zhu
Line Balancing
   Line Balancing
• Line Balancing is the
  process of assigning tasks
  to workstations in such a
  way that the workstations
  (operations) have
  approximately equal time
  requirements.
• For Product Layouts
  (Sequence of tasks!)
• Multiple tasks can be
  assigned to one
  workstation.

                               © Wenge Zhu
             One Important Term
Cycle Time of Workstation
• The time a workstation needs to complete its set of assigned
  tasks once.

Example: Workstation A is assigned 2 tasks, task one
  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)



                                                          © Wenge Zhu
                   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?

                                                   © Wenge Zhu
     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



                                                       © Wenge Zhu
   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?)




                                           © Wenge Zhu
           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
                                                           © Wenge Zhu
  Minimum Number of Workstations Required

                                    (D)( t)
                              N =
         Sum of Task Times             OT
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 =???



                                                         © Wenge Zhu
              Line Efficiency

                     Sum of task times
  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%

                                                     © Wenge Zhu
  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
        tasks where all preceding tasks CT been assigned and
   b.              times that do not exceed the only
        tasks with 2. Sequence: we canremaining time at the work
        station.
                 assign a task when
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.
   b.   Assign the task with the longest task time.
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.

                                                                        © Wenge Zhu
          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
Station      Remaining     Tasks      Task              Time
  1                 1.2     a, b       a
                          a. Assign the task with the
                    1.1   greatest number of tasks following it.
                            c, b       c
                          b. Assign the task with
                    0.1    None                 0.1
                          the longest task time.
  2                 1.2      b         b

                    0.5      d         d                  0

  3                 0.2      e         e                 1.0


                                                                    © Wenge Zhu
 0.1 min     1 min

   Assign the task the longest task time.
a. a            c
b. Assign the task with the greatest
                           0.2 min
number of tasks following it.
      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



                                                   © Wenge Zhu
    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.


                                       © Wenge Zhu
    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

                                       © Wenge Zhu
          Toy Wagon Assembly Line Balance Example
Task   Performance Time (sec.)   Tasks that must precede
 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


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




                        195
              N min         4
                        50.4

                                  © Wenge Zhu
                    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




                                              © Wenge Zhu
                Balance the Line Using Most Followers Rule
                Task       Remaining    Feasible       Task @             Task@
        Task   time(sec)     time       Rem. Tasks   most followers   longest opr. time

St. 1    A      45           5.4 idle    none




                                                                             © Wenge Zhu
                Balance the Line Using Most Followers Rule
                Task       Remaining    Feasible       Task @             Task@
        Task   time(sec)     time       Rem. Tasks   most followers   longest opr. time

St. 1    A      45           5.4 idle    none

St. 2 D          50          0.4 idle    none




                                                                             © Wenge Zhu
                Balance the Line Using Most Followers Rule
                Task       Remaining      Feasible       Task @             Task@
        Task   time(sec)     time         Rem. Tasks   most followers   longest opr. time

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




                                                                               © Wenge Zhu
                Balance the Line Using Most Followers Rule
                Task       Remaining      Feasible       Task @             Task@
        Task   time(sec)     time         Rem. Tasks   most followers   longest opr. time

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

                                                                               © Wenge Zhu
                Balance the Line Using Most Followers Rule
                Task       Remaining      Feasible      Task @             Task@
        Task   time(sec)     time        Rem. Tasks   most followers   longest opr. time

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
                                                                        © Wenge Zhu
see that efficiency goes up to about 97%, i.e. BD goes down to 3%.
Solve Example Again With
     Reversed Rule




                           © Wenge Zhu
         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

                                     © Wenge Zhu
      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
                                               © Wenge Zhu
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




                                         © Wenge Zhu
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
                                            © Wenge Zhu
  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


                                        © Wenge Zhu
             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



                                                          © Wenge Zhu
         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

                                             © Wenge Zhu
           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

                                                 © Wenge Zhu
                                                                  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
                               author.                                                © Wenge Zhu

				
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