The objective of the research was to identify the optimized thread tensile values for the setup of Model D – We 1218-55 computerized 18-needles sewing machine in order to minimize a number of times the machine halts. The cause of the sewing machine halting which reduced the efficiencies of the machine was found to be torn threads. In order to maximize the efficiencies the experimental design technique was utilized to find the optimal values for five types of cloth: polo tc-cool cotton jacket and shirt. The method involved three nested designs which are the type of thread number of sewing layers and thread-hole size. The three thread tensile levels experimented were low (2 oz.) medium (5 oz.) and high (8 oz.) and the response was the number of times the machine halted in the span of 30 minutes. The ANOVA (Analysis of Variance) used for the experimental design showed that the three factors significantly affected the machine’s halt. The number of times the machine halted was used to create Surface Plot with polynomial trend-lines and the quadratic equation was applied to determine the optimal value for each type of thread number of sewing layers and thread-hole size. The values obtained were then set for another experiment the results of which were that the sewing machine halted less frequently and the efficiencies thus increased about by 77.01%.

The purpose of this research is to determine the optimal factors existing in the aluminum riveting process. First a 25 full-factorial design was used to screen five factors and two levels by selecting a lapping-joint method using only one rivet which exhibited significant riveting shear. The five riveting parameters used were press force 5000 and 8000 newtons a thickness of material of 2.5 and 4mm a size of hole of 4.7 and 5.2 mm over long rivets of 4.7 and 5.2 mm and press times of 5 and 15 seconds. There were three parameter levels: thickness of the metal (2.5 3.2 and 4.0 mm) size of the hole (2.5 3.2 and 4.0 mm) and size of the over-long rivet (4.5 5.6 and 6.7mm) then a Box-Behnken design was used in order to analyze the data and find the optimization point. The experiment found that a standard rivet has a shear strength resistance of 1113.30 newtons. The study methodology was to prepare the riveting specimens use by selecting a lapping joint per one rivet to test the mechanical quality and shear. The results of the experiment show that the optimal conditions (to a statistically significant degree) were to use a 5.2 mm hole a 2.8 mm level of thickness and a 6.3 mm over-long rivet. The optimal point for the shear test was 1417.55 newtons and an over-shear strength of 303 newtons could be increased by 27.32 percent.