BUS606: Operations and Supply Chain Management

In this second stage of results analysis the type of layout was included as a control factor with three levels: job shop, traditional cell, and virtual cell. It was verified how the response variables behaved in relation to the type of layout. This analysis of statistical significance was based on the value of P using ANOVA. It is noticed in Table 9 that the type of layout has statistical significance ("s") for all response variables to the significance level of 0.05.

Table 9 Comparison between control factors and response variables.

Figure 7 Main effects plot of the final time in the layouts.

The cells highlighted in Table 10 shows the three factors in which the confidence intervals do not intersect between the virtual cell and the traditional cellular layouts.

Table 10 Confidence intervals for the three layouts.

Figure 8 Main effects plot of the layouts for throughput.

Figure 9 shows how the layouts behaved in relation to the average work in process. In this response variable, the job shop and virtual cell layouts again present better performance, and the virtual cell layout was still better than the job shop. The virtual cell layout was better in approximately 27% in relation to the traditional cell layout, while for the job shop layout the superiority was 10%. This shows that the virtual cell layout can be located between job shop and traditional cell layouts, having advantages of both. However, observing the confidence interval (confidence level of 95%) ( Table 6 ), statistically it cannot be stated that these values are different.

Figure 9 Main effects plot of the average WIP in the layouts.

Figure 10 illustrates the behavior of the type of layout with respect to the response variable referred to as average resource utilization. Once again, the job shop and virtual cell layouts outperformed the traditional cell layout. The virtual cell layout had a resource utilization 20% higher than the traditional cell layout. Observing the confidence interval (confidence level equal to 95%) ( Table 6 ), it can be stated that the values between the virtual cell and traditional cell systems are different.

Figure 10 Main effects plot of the resource use in the layouts.

Figures 11 and 12 show the behavior of the layouts with respect to the waiting total time and lead time variables, respectively. It is noticed a very similar behavior for both cases, where again the virtual cell and job shop layouts performed better.

Figure 11 Main effects plot of the waiting time in the layouts.

Figure 12 Main effects plot of the lead time in the layouts.

With regard to the waiting time, the performance of the virtual cell layout was again better than the others, about 10% in the average with respect to the job shop layout, and far better than the traditional cell layout (about 50%). Observing the confidence interval (confidence level of 95%) ( Table 6 ), it can be stated that the values between the virtual cell and traditional cell layouts are different.

Regarding lead time, on average the virtual cell layout had a good result, approximately 7% shorter than the job shop, and 50% shorter than the traditional cell layout. Observing the confidence interval ( Table 6 ) (confidence level equal to 95%), it can be affirmed that the values between the virtual cell and traditional cell layouts are different. In summary, Table 11 presents the performance of each layout for the response variables, always having the virtual cellular layout as the reference of the comparison. The minus sign indicates a worse result when compared to the virtual cell, and the plus signal indicates a better result compared to the virtual cell.

Table 11 Summary of comparison percentages.