Page 268 - DMGT206_PRODUCTION_AND_OPERATIONS_MANAGEMENT

Unit 13: Production Planning and Control

13.6 Defining the Layout Problem Notes

The layout-planning problem for assembly lines, is to determine the minimum number of
stations (workers) and assign tasks to each station, so that a desired level of output is achieved.
The design must consider the following aspects:

1. It should focus on achieving a desired level of output capacity.
2. The tasks assigned to stations and the sequence in which tasks must be carried out.

3. The output should be attained efficiently, without using minimum input resources.
How this is achieved can be best understood with an example.

Example: ABC Electricals is a medium-sized firm in Delhi. It has an established design of
a contact breaker assembly, used industry-wide to protect all electrical circuits. The company
has established an assembly line to manufacture the product.
The operator starts the assembly process with a molding half. Into this molding he puts the
contacts, springs, plastic levers, etc. The assembly is closed off with a similar molding half. The
final assembly, comprised up to four of these units, is secured with four rivets passing through
the sandwich. The assembly is then tested. Testing is a critical operation, as the contact breaker
assembly carries up to 415 volts. If the unit is found acceptable, it is labeled and packed for
despatch.
The method of assembly was on a series of benches with the sub-assemblies being placed in
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 13.1 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 the Table we know
that:

1. The task assigned to station 1 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.

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