Page 113 - DMGT501_OPERATIONS_MANAGEMENT

Unit 4: Process Selection and Facility Layout

The method of assembly was on a series of benches with the sub-assemblies being placed in Notes
boxes for transfer to the riveting press. The rivet operation involved the manual placing of four
long tubular rivets, pressing a 5 tonne press and securing the assembly. The product was again
boxed for transfer to testing.
The demand for this was 3000 units per month. However, due to the high rate of rejection and the
highly labour intensive process, they were unable to meet the demand. Table 4.3 gives the
assembly line details for the product.

Is capacity adequate? The number of units this layout permits the company to produce each day
depends on the station whose tasks take the longest time to perform. From Table 4.3 we know
that:
1. The task assigned to station1 requires 0.010 hours,
2. Station 2 and station 3 are parallel paths and the tasks assigned take 0.080 hours,
3. Station 4 requires 0.50 hours,

4. The longest time is needed at station 6 that is 0.098 hours, and so on.
Since every unit passes through all stations, station 3 is the bottleneck operation. This station
restricts the rate of flow of the line. With this layout, a finished contact breaker will flow to the
end of the line every 0.098 hours. This time is called the cycle time of the line.
The cycle time is, in fact, also the time after which the conveyor moves in a moving assembly
line. Cycle time is defined as the time period after which completed units come off the assembly
line. Completed units are available after each movement of the conveyor, as the basic structure
worked upon at the last workstation will become a completed unit in that time.
With a cycle time of 0.098 hours, how many contact breakers are produced daily? If the operation
runs for one 8-hour shift each day, the available productive time each day is 8 hours. Therefore,
maximum daily output can be as follows:
Maximum daily output = Available time/(Cycle time/unit)
= 8.0/0.098 = 81.63 units

Since this assembly line can generate 81 units daily, and the requirement is 3000 units per
month, capacity is inadequate,
An alternative method for determining whether capacity is adequate is to calculate the maximum
allowable cycle time give a desired capacity 3000 units/month.
Maximum allowable cycle time = Time available/Desired number of units
= (8 × 24)/3000 = 0.064 hours/unit

This calculation shows that a layout whose cycle time is 0.064 hours or less will yield the desired
capacity.
Is the sequence of tasks feasible? For now, we will assume that the proposed sequence of tasks is
feasible. By examining the product, we can see the sequence restrictions that must be observed
in its assembly.

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.

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