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

Table 4.7 listed the simulation results due to different number of machines that
participate in the production in station 8 of the main assembly line (MA 8) and station 2
in the preassembly line (PA 2). In order to get more precise results, each condition has
been taken fifteen times’ simulations. And at last calculate the average value. Take the
average value as the measurement of the solution.
When add more machines in the assembly line, a problem in the simulation process
occurred. As the production rate increased, blocks happened in station 10 of the main
assembly line. According to the animation around the block point, it is inferred that the
causes of the block are the stochastic split stream in station 10 and the small queue
length between station 10 and station 11.
The stochastic choice of the direction of each incoming item in station 10 may cause the
disorder and block in the system. In the reality, products in different operating time
(TID) in station 10 are in batches. Therefore, not each item chooses the different
streams stochastically. In order to investigate whether this block problem would happen
in the batch production or not, simulate the system with one stream only for the two
situations. The results came out to be no block for each single stream. So the block in
station 10 only happens in simulation model, while in the real production line it will not
happen. Thus, it is feasible to smooth the model by increasing queue length between
station 10 and station 11.
In order to find out the ideal queue length, several tests are operated. When the queue
length increased to three or four items, the block rate is reduced but not eliminated. If
the value increases to 5, most of the simulations can run well. So the queue length can
be set to 5 items between station 10 and station 11 in the model. However, since the
change of queue length is only in the model to keep simulation smooth, set the value to
a bigger one to get a stable simulation environment. Based on this point, the queue
length increased to 10 when run the simulation model.
As mentioned above, comparing station 2 in preassembly line and station 8 in main
assembly line, station 8 is the main bottleneck. So at first, the author tries to only insert
one machine at station 8 to improve the current situation. From the last raw of Table 4.7,
which shows the average output of the assembly line, it is can not satisfy the market
requirement. If increase machines both at station 8 and station 2, the production volume
will hit the market in 2008.
4.3.2 Cutting down the Time to Repair in bottlenecks
As mentioned earlier, current production is too far away to the ideal situation because
of the frequent shut down and long TTR. The TTF is greatly relating to the technical
parameter of the machine, thus it is not easy to change the value. Nevertheless, TTR can
be reduced by effort of the company.
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