Improvement of Material Flow in the Production and Supply Chain of ...

line. In order to simplify the model and bring the keystones to the front, the two lines
are joined together and working simultaneously. The detail situation about the
preassembly line and main assembly line has described in chapter three.
During the process of setting up model, there is a problem when associating the
preassembly line to the main assembly line. As shown in Figure 3.1, there are five
stations before insert the preassembly line at station 5b. According to the data of
process time shown in Table 4.1 below, from the beginning to output the first product,
the working time of first five stations in main assembly line is 105s, which is shorter
than the working time of preassembly line that is 179s. As a result, for the early period
preassembly line is behind the main assembly line. So a buffer with the products of the
preassembly line is needed. By setting another “Stock” block between station 5b and
station 5, the two assembly lines join together at station 5 of the main production line to
smooth the simulation. This solution is not discrete form the reality since in the virtual
assembly process, there is a small holding area used to store the magnetism parts from
the preassembly line, which can satisfied the requirement of main assembly line. The
“Stock” block in the model has the same function as the holding area. There are several
reasons lead to the necessary of a holding area; one of them is that the cycle time of the
main assembly is longer than the cycle time of the preassembly line, which can be
confirmed by the data shown in Table 4.1. Calculated the delayed time, the model can
work smoothly as long as more than three items are held in the stock.
Table 4.1* Working Parameters of Each Station
Station/Main TID Queue Station/Pre. TID Queue
Capacity
Capacity
1&2 1
3 2
4 3
5b
5
6
4
7
*Because of the different
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configurations, TID of station 10 in
9
10
11
main assembly line is variation. 7/30
of the products cost 55s at this station
and the rests cost 35s.
In the model, each buffer before the stations is to simulate the length of the queue. All
the stations indicate the actual working times in the assembly line. The detailed
information of processing time (TID) and queue length for each station are listed in
Table 4.1 above.
Generally speaking, scraps occur in station 5b, 6, 8, 10 and 11 of main assembly line.
Statistical analysis work focus on these five stations. First time pass rates of the five
stations are shown in Table 4.2 separately. “Select DE Output” blocks are added after
these stations to simulate the pass rates.
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