PRUEBAS AL CANAL DE TRANSMISIÓN

Eventually, all four models (the base model, the MRP-model, the ConWIP model, and the bottleneck control model) have been run. The results are summarized in the following table:

69

Table 15: Results of KPI's for the models of the four planning approaches.

Average internal WIP (pc.) Total output (pc.) Internal throughput time (DD:HH:MM:SS) Total throughput time (DD:HH:MM:SS) Base model 167,4 12703,6 44:03:46:57 65:02:21:54 ConWIP model 108,0 12759,5 22:06:50:45 41:22:31:37 MRP-model 107,0 12764,7 21:23:07:28 41:14:41:39

Bottleneck control model 107,4 12803,5 _21:23:20:47 41:14:09:58

As shown in the table, the throughput times and WIP levels are much lower while a similar output is acquired. For all models, the average weekly output was close to 6 AC-types and 12 B-types, as shown in table 16:

Table 16: Output numbers for the models of the four planning approaches.

Avg. Weekly output B (pc.)

Avg. Weekly output AC (pc.)

Avg. total weekly output (pc.) Confidence interval (sign. 95%) Base model 6,00 12,00 18,00 (17,99, 18,00) ConWIP model 6,01 12,01 18,02 (17,99, 18,06) MRP-model 6,00 12,00 18,00 (18,00, 18,00) Bottleneck control model 5,98 12,09 18,07 (18,03, 18,11)

The output for bottleneck control is slightly higher but based on these numbers, the systems can be compared. The confidence intervals (confidence level 95%) are displayed in figure 4, for the ConWIP, MRP and bottleneck control model:

Figure 4: Confidence intervals for the average total throughput time, for the planning approach experiments.

This figure will be recurring for all other experimental levels. Therefore, it will be shortly explained in this section. The right interval bound (orange) displays the maximum of the confidence interval, whereas the left interval bound (blue) displays the minimum of the confidence interval. The average (grey) displays the average of the observations from the simulation model. With a confidence level of 95%, it can be stated that the average of the total throughput time is within this interval. The

confidence level refers to the amount of confidence with which can be stated that the average is within this interval. So, preferably, the confidence interval (and its average) needs to lay as low as possible in this graph. The confidence interval of the total throughput time of the ConWIP lays higher than the confidence interval of the MRP and bottleneck control approaches. The average of the

3570000 3580000 3590000 3600000 3610000 3620000 3630000 3640000

Conwip MRP Bottleneck control

Av era ge T o ta l T T (s ec) Planning Approach Left interval bound Right interval bound Average

70 MRP-approach and bottleneck control approach are close together. Though, the confidence interval of the MRP-approach is larger than the others. As an addition to this comparison, comparing the systems was done with a confidence interval of the difference in the average total throughput time (in seconds), with the paired-t approach. The confidence level is again equal to 95%.

Table 17: Paired-T approach for comparing the planning approaches on average total throughput time (sec).

MRP model ConWIP model Bottleneck control model

Base model

Paired-T test result (2022395, 2036035) (1990863, 2011172) (2020896, 2041337)

Statist. conclusion Base model > MRP Base model > ConWIP Base model > Bttlnck ctrl.

MRP model

Paired-T test result -- --

(-38534, -17862) (-7377, 11180)

Statist. conclusion MRP < ConWIP No sign. difference

ConWIP model

Paired-T test result -- --

-- --

(27661, 32537)

Statist. conclusion ConWIP > Bttlnck ctrl.

Based on the confidence intervals of the difference in the average total throughput time, it can be concluded that the throughput time in the base model (sign. 95%) is much longer than in all other approaches. Any other approach will at least improve the total throughput time with approximately 23 days and one hour (minimum of the confidence interval of ConWIP) and perhaps even with 23 days and 15 hours (maximum of the confidence interval of Bottleneck control), with a significant level of 95%. Moreover, it can be concluded (sign. 95%) that total throughput time in the MRP model and the bottleneck control model is shorter than the total throughput time in the ConWIP model. Lastly, there is no significant difference (sign. 95%) that the total throughput time in the MRP-model is longer than in the bottleneck control model. The same conclusions can be drawn (95% sign.) regarding average internal throughput time:

Table 18: Paired-T approach for comparing the planning approaches on average internal throughput time (sec).

MRP ConWIP model Bottleneck control model

Base model

Paired-T test result (1911014, 1924123) (1879740, 1899804) (1906014, 1927525)

Statist. conclusion Base model > MRP Base model > ConWIP Base model > Bttlnck ctrl.

MRP model

Paired-T test result -- --

(-37427, -18166) (-10206, 8608)

Statist. conclusion MRP < ConWIP No difference

ConWIP model

Paired-T test result -- --

-- (24766, 29230)

Statist. conclusion -- ConWIP > Bttlnck ctrl.

The results of the two best approaches will be summarized. These are displayed in table 19 for the MRP-model:

Table 19: Confidence interval for average internal and total throughput time in the MRP-model.

Internal TT Total TT

Mean (DD:HH:MM:SS) 21:23:07:28 41:14:41:39

95% Confidence interval min 21:19:30:29 41:10:49:28

71 And the bottleneck control model in table 20:

Table 20: Confidence interval for average internal and total throughput time in the bottleneck control model.

Internal TT Total TT

Mean (DD:HH:MM:SS) 22:06:50:45 41:22:31:37

95% Confidence interval min 22:05:10:04 41:20:43:15

95% Confidence interval max 22:08:31:26 42:00:19:59

Based on the paired-t approach (95%), the following table can be made regarding the total average throughput time. In addition, the means of the WIP and WIP values (€5000*WIP) will be compared, on request of the project supervisor. The comparison of the WIP is not based on a statistical test (a confidence interval).

Table 21: Comparing the planning approaches based on time gains, WIP, and WIP value

Planning approach

Approximate time gain in average total throughput time regarding the base model

Difference in mean WIP

Difference in mean WIP value

Base model 0 0 0

MRP model 23 days and 10 hours to 23

days and 14 hours.

59,4 €297000

ConWIP model 23 days and 1 hour to 23 days and 7 hours.

60,4 €302000

Bottleneck control model

23 days and 9 hours to 23 days and 15 hours.

60 €300000

As shown in table 21, different planning approaches result in much lower average total throughput times, mean WIP levels, and WIP values.