Page 114 - DMGT501_OPERATIONS_MANAGEMENT

Operations Management

Notes 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 4.3, 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 4.3. TAMS decided to balance the assembly line.

4.6.2 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.

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 4.3 - 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.
For the example of the contact breaker facility, we have already taken the first step, defining
tasks, shown in Table 4.3. The second step requires identifying a specific sequence. These sequence
requirements are also listed in Table 4.3 in column 4.
Once the desired output is specified, we can calculate the theoretical minimum number of
stations required. This is done by contrasting the time required to produce one unit with the
time we can allow, given the daily output requirements. We have already calculated the time
required, as the sum of the task times in Table 4.3 and we have calculated the time allowable, as
the maximum allowable cycle time.

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