Statical assessment of multi process parameters' effects on the microstructure and mechanical properties in the cold pressure welding process

In this study, multiple quality characteristics for two different numbers of upsets (4 and 12), welding time (0 and 5s), and welding pressure (4 and 6 bar) were statistically researched in the joining of pure copper rods (Cu-ETP, Diameter Ø8 mm). Resistance, diameter, microhardness, and tensile (Rm-MPa) strength test results based on Taguchi's L8 orthogonal array were evaluated by variance and regression analysis. According to microhardness examinations, no significant results were obtained according to regression analysis and ANOVA in the first three regions (KB1, KB2, and KB3). For KB4, KB5, and KB6, the effects of the main and binary interactions of factors on hardness were modeled at coefficients of determination of 99.92%, 99.93%, and 99.71%, respectively, and were quite satisfactory. The optimum hardness values for KB4, KB5, and KB6 were obtained as 96, 90.1, and 84.1 HV at the first level of upset number (A=4), second welding time (B=5sec), and welding pressure (C=6 bar) respectively. According to the tensile strength studies, the effects of the main and binary interactions of the factors on the tensile strength were modeled with high accuracy at a determination coefficient of 99.84%. The optimum tensile strength was obtained as 233.6 MPa at the first level of impact number (A=4), first impact time (B=0 sec), and second level of welding pressure (C=6 bar). According to the electrical resistance analysis, the effects of the main and binary interactions of the factors on the resistance were modeled at a coefficient of determination of 99.99% and were close to perfect. The lowest resistance value was determined as 49.13 µΩ at the first level (A=4) of the number of upsets (A=4), the second (B=5sec) of the welding time, and the first level of the welding pressure (C= 4 bar).