Page 270 - DMGT206_PRODUCTION_AND_OPERATIONS_MANAGEMENT

Unit 13: Production Planning and Control

Notes
Example: The moldings have to be assembled prior to subsequent assembly steps to
ensure that the four moldings can be connected together. Finally, the contact breaker cannot be
assembled until the moldings have been riveted together.
This sequence must be observed because the contact breaker cannot be assembled correctly in
any other way. On the other hand, it makes no difference whether the contacts are placed before
the plastic lever or after the springs are assembled in the molding. Similarly, the order of the
riveting is irrelevant.
In general, the assembly tasks, listed in the table, are broken down into the smallest whole
activity. For each task, we note in column 4 of Table 13.1, the task or tasks that must
immediately precede it. However, job simplification is possible even within the requirement of
precedence.
Is the Line Efficient? The revised layout had six stations manned by 12 operators. All workers are
paid for 8 hours daily. How much of their time was spent productively? This assignment to
revise the layout was given to Technology and Management Systems (TAMS).
ABC Electricals, due to the traditional approach, believed that the assembly was very labour
intensive. Even with parallel processing they were utilizing up to twelve operators as is shown
in column 6 of Table above. TAMS decided to balance the assembly line.

13.6.1 Assembly Line Balancing

Given a capacity or production rate requirement, we can meet that requirement with a single
line with a cycle time ‘c’, or with two parallel lines with a cycle time ‘2c’, and so forth. Line
balancing programs have been developed that enable the most efficient use of the assembly
line.

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Caution In multiple parallel lines, as the number of parallel lines increases, so does the
scope of job.
We can also increase output by horizontal job enlargement, as has been demonstrated in the
example of ABC Electricals. The point is that alternatives do exist.
How can the cost of idle time of man and machine be reduced? Perhaps the ten tasks (A to M in
Table above – exclude tasks either at station 1 or station 2) can be reassigned so that more
available employee time is used.
An ideal assembly line would be one where tasks are assigned to different workstations in such
a way that the total processing times at each workstation is equal. If every station used up an
equal amount of task time, no time would be idle time. Though this is seldom true, an
approximation of this condition can be achieved by effective assembly line balancing. The
problem of equalizing stations is solved using six steps:

1. Define tasks.
2. Identify precedence requirements.
3. Calculate the minimum number of work stations required to produce desired output.
4. Apply an assignment heuristic to assign tasks to each station.
5. Evaluate effectiveness and efficiency.

6. Seek further improvement.

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