ppt. presentation on assembly line balancing

1. Abrity Bhattacharya
Hariharan Ramanathan

2. LINE BALANCING
 This is an analysis process which tries to equally divide
work to be carried out in a production process among
workstations.
 In production line workstations and work centers are
arranged in a sequence of task to be done along a
straight or curved line.

3. GOAL AND OBJECTIVE
Goal of production line analysis:
 Number of workstations needed.
 Type of task should be assigned to each workstation.
 To know the minimum number of workers, tools and
machines that can be used to provide the required amount
of capacity.
Objective of line balancing:
 Assigning task to each workstation in such a way that there
is only a little idle time.

4. TERMINOLOGIES RELATED TO
PRODUCTION LINE ANALYSIS
 TASKS: All the elements of work.
 TASK PRECEDENCE: The sequence in which tasks are
performed.
 TASK TIMES: Time required by a well-trained worker or
unattended machine to perform a task. This is usually
expressed in minutes.
 CYCLE TIME: The time expressed in minutes between
two simultaneous products coming off the end of a
production line.

5. Continued…
 PRODUCTIVE TIME PER HOUR: The average
number of minutes a workstation is working in an hour.
 WORKSTATION: A physical area where a worker with
tools/ one or more machines, or an unattended machines
like a robot performs a particular set of task in a
production line.
 WORK CENTER: A small group of identical
workstations, where each workstation performs the same
set of task.
 NUMBER OF WORKSTATIONS WORKING: The
amount of work done at a work center expressed in
number of workstations.

6. Continued…
 MINIMUM NUMBER OF WORKSTATIONS: The
least number of workstation that provides the required
production.
 ACTUAL NUMBER OF WORKSTATIONS: This is
the total number of workstations required on the entire
production line. It is calculated as the next higher integer
of the number of workstations working.
 UTILIZATION: The percentage of time a production
line is working.

7. LINE BALANCING PROCEDURE
1.
2.
3.
4.
5.
6.
7.
Determination of tasks that must be performed to
complete one unit of a product.
Determining the order or sequence of performing
the whole set of tasks.
Drawing precedence diagram. In this flowchart
circles represents task and joining arrows represents
precedence.
Estimation of task time.
Calculation of cycle time.
Determination of minimum number of workstation
required.
Using one of the heuristics to assign tasks to
workstations for balancing production line.

8. COMPUTERIZED LINE BALANCING
 Line balancing by hand becomes unwieldy as the problems grow
in size.
 There are software packages that will balance large lines quickly.
IBM's COMSOAL (Computer Method for Sequencing
Operations for Assembly Lines) and GE's ASYBL (Assembly Line
Configuration Program) can assign hundreds of work elements
to workstations on an assembly line.
 They use various heuristics, to balance the line at an acceptable
level of efficiency.
 The POM for Windows software lets the user select from five
different heuristics: ranked positional weight, longest operation
time, shortest operation time, most number of following
tasks, and least number of following tasks. These heuristics
specify the order in which work elements are considered for
allocation to workstations.

9. Line Balancing Heuristics
Two types
 Incremental Utilization Heuristic
 Longest Task Time Heuristic

10. Incremental Heuristic
 Tasks are added to each workstation in order of task
precedence one at a time until utilization is 100
percent or is observed to fall.
 Used when one or more task time is equal to or greater
than the cycle time.

11. Incremental Heuristics

12. Example
Textech, a large electronics manufacturer, assembles model
AT7S handheld calculators at its Midland , Texas, plant.
The assembly tasks that must be performed on each
calculator are shown below.
The parts used in this assembly line are supplied by
materials-handling personnel to parts bins used in each
task. The assemblies are moved along by belt conveyors
between workstations.
Textech wants this assembly line to produce 540
calculators per hour.
a. Compute the cycle time per calculator in minutes.
b. Compute the minimum number of workstations.
c. How would you combine the tasks into workstations to
minimize idle time? Evaluate your proposal.

14. SOLUTION

15. Precedence
Diagram

18. Longest-Task-Time Heuristic
 Add tasks to a workstation one at a time in the order
of task precedence.
 If a choice must be made between two or more
tasks, the one with the longest task time is added.
 This has the effect of assigning as quickly as possible
the tasks that are the most difficult to fit into a station.
 Tasks with shorter times are then saved for finetuning the solution.

19. Conditions
It can be used only when each and every task time is
less than or equal to the cycle time.
2. There can be no duplicate work stations.
1.
 If each and every task time is less than or equal to the
cycle time, and if the primary focus of the analysis of
production lines is minimizing the number of
workstations and the amount of tools and equipment
required, then this heuristic would be appropriate.

20. Steps in the Longest-Task-Time
Heuristic
1.
2.
3.
4.
Lei i = I. where i is the number of the workstation being formed.
Make a list of all the tasks that are to be assigned to a workstation.
Have to satisfy the following conditions
a. It cannot have been previously assigned to this or any previous
workstation.
b. Its immediate predecessors must have been assigned to this or a
previous workstation.
c. The sum of its task time and all other times of tasks are already
assigned to work station must be less than or equal to the cycle time
. If no such tasks are found. Go to step 4.
Assign the from the list with the longest task time to the
workstation. Go back to the step 2.
Close the assignment of tasks to Workstation i. This can occur in
two ways. If there are no tasks on the list for the work station but
there are still tasks to be assigned, set i=i+1 and go back to step 2. If
there are no more tasks, the procedure is completed.

21. PROBLEM
Using the above information in the table
a.
Draw a precedence diagram
b. Assuming that 55 minutes per hour are productive, compute the
cycle time needed to obtain 50 units per hour.

22. SOLUTION

26. LINE BALANCING ISSUES
 Earlier conveyor belts are paced with the speed of the
employees work.
 Now they are paced with the machine speed.

27. APPLICATIONS
 The classic example is Henry Ford’s auto chassis line.
• Before the “assembly line Balancing” was
introduced in 1913, each chassis was
assembled by one worker and required
12.5 hours.
• Once the new technology was
installed, this time was reduced to 93
minutes.