# An Analysis of Mechanical Properties for Ultrasonically Welded Multiple C1220-Al1050 Layers
## 3 Results of the Experiment
### The Optimization of Welding Conditions  
Based on the S/N ratio analysis for each factor level designed in the experiment to determine the optimal welding conditions, the highest S/N ratio was measured at level 5 (80%) in factor A, level 4 (3.5 sec) in factor B (welding time), and level 0 (1.0 bar) in factor C (pressure load), so the optimal welding conditions were obtained at level A\({}_{5}\)B\({}_{4}\)C\({}_{0}\). The S/N ratio calculated should be examined to ensure the reliability of the optimal welding conditions derived. As such, it is necessary to perform a variance analysis for the S/N ratio of the larger-the-better characteristics and to verify the significance of the welding variables that affect the strength of the weld. The variance analysis general linear model tool of the commonly used statistical program Minitab was used to perform the variance analysis of the S/N ratio of the larger-the-better characteristics, and the results are as shown in Table 3. The tensile strengths used for the S/N ratio calculations were taken from the simultaneous tensile strength results. Simultaneous tensile strength represents the strength of each weld joint, and the strengths of weld zones 1, 2, and 3 are combined to represent the maximum tensile strength. The variance analysis found that the F-test is possible for all of the factors because the sum of the degrees of freedom of factors A, B, and C is 12, and the are a total of 24 degrees of freedom. Since there are no factors with an F-value less than 1, the significance level (\(p\)-value) of each factor was evaluated without a separate pooling process. Factors B and C were significant at the significance level of 5% (95% confidence interval) with \(p\)-values of 0.004 and 0.056, respectively, and A was not significant at the significance level of 5% with a \(p\)-value of 0.343, but the difference in the level is not negligible. Therefore, to obtain the optimal welding conditions, it is necessary to calculate the estimated value of the S/N ratio average for each factor level, and the highest S/N ratio average value according to each  
Figure 13: Average strength values according to fracture location. factor level should be determined as the optimal welding condition. The average value of the S/N ratio for each factor level is calculated using the S/N ratio value of orthogonal arrays shown in Table 4, and Table 5 shows the S/N ratio average estimated value for each factor level. Through calculating the S/N ratio average estimated value for each level, it was determined that the levels with the highest S/N ratio average estimated value were level 4 for factor A, level 3 for factor B, and level 0 for factor C. Table 5 summarizes the values corresponding to the welding experiment variables and welding conditions corresponding to each factor and level. Weld strength, the characteristic value of this study, is a larger-the-better characteristic, which is considered to be good if the S/N ratio is high, so the S/N ratio was calculated based on a combination of factors and levels corresponding to the optimal welding conditions using the Taguchi result prediction tool of the Minitab program. The S/N ratio calculated by applying the optimal welding conditions resulted in a high value of 64.4985, shown in Table 6. Weld strength, the characteristic value of this study, is a larger-the-better characteristic, which is considered to be good if the S/N ratio is high; therefore, when compared to the S/N ratio value according to the experiment number in the L25(53) table of orthogonal arrays, the weld strength, as a larger-the-better characteristic, was determined to be the best, as the S/N ratio is highest under the optimized welding conditions. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Amplitude (\%)** & **Welding Time (sec.)** & **Pressure Load (bar)** & **S/N Ratio** \\ \hline
80 & 3.5 & 1.0 & 64.4895 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Optimal welding conditions and S/N ratio.