The fundamental problem of layout planning for assembly is to determine the minimum number of stations (workers) and assign tasks to each station so that a desired level of output is achieved.

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Defining the Layout Problem

The fundamental problem of layout planning for assembly is to determine the minimum number of stations  (workers) and assign tasks to each station so that a desired level of output is achieved.

Notice several implications in this statement.

First, the design focuses on achieving a desired level of productive capability.(output capacity).

Second, if tasks are to be assigned to stations, the sequence of tasks must be considered. Which tasks must be done first, and which ones may follow?

Finally, our concern is attaining desired output efficiently, without using unnecessary input resources.

Capacity, Sequencing and Efficiency

Let’s illustrate these ideas with an example.

A manufacturer is developing plans for a facility to make 320 aluminum storm windows. The desired minimum daily output capacity is 320 windows. Figure-I and Table-I show the tentative assembly line layout. The operations manager wants to know if this is a good design and if better designs are possible.

                       A              B        C          D   E        F          G                    H                

Figure-I : Diagram for storm window assembly line

 

Table – I: Initial assembly line layout for aluminum storm windows

This is a good design if the sequence and assignments meet the following criteria:

  • They produce the desired output capacity
  • They are feasible
  • They are efficient

Is Capacity Adequate?

The number of units this layout allows the company to produce each day depends on the station whose tasks take the longest time to perform. From Table-I we know that the tasks assigned to station 1 require 70 seconds, and to station 2, 80 seconds. Station 3 comprises two tasks: inserting frame screws © and installing the frame latch (D). Thus station 3 tasks require 60 (40+20) seconds. Tasks at stations 4, 5, and 6 require 70, 50, and 50 seconds, respectively. The longest time , then is needed at station 2, 80 seconds. Since every unit passes through all stations, and each must spend 80 seconds at station 2, station is the bottleneck operation, the station restricts the rate of flow off the line. A finished window will flow off the end of the line every 80 seconds, no less, with this layout. The time is called the cycle time of the line.

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With a cycle time of 80 seconds, how many windows are produced daily? If the operation runs for one 8-hour shift each day, the available productive time each day is 28,800 seconds (8 hours * 3600 seconds/hour). Therefore maximum daily output can be as follows: (available time)/(cycle time/unit) = 28800 seconds / 80 seconds/unit = 360 units.

Since this assembly line can generate more than the required 320 units daily, capacity is adequate.

An alternative method for determining whether capacity is adequate calculates the maximum allowable cycle time given a desired capacity (320 units/day).

Maximum allowable cycle time ...

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