Laser welding is a novel method for direct joining of metals and polymers, which leads to a mechanical and chemical bond between metal and polymer. In this study, feasibility of dissimilar joining between St12 and polycarbonate is studied theoretically. Then, the ND: YAG laser is implemented to join St12 and Polycarbonate. Empirical results indicate creation of a joint between St12 and polycarbonate. In order to conduct thermomechanical analysis of the welding process, the finite element model has been developed by Abaqus software. In addition, the cylindricalinvolution-normal (CIN) heat source model was used to describe the laser power distribution and FORTRAN software has been used to define the thermal model in welding simulation. Comparison of experimental and simulation results shows that the finite element model is capable of predicting weld width, and therefore the results of the finite element model are verified. Therefore, the finite element model is used to predict residual stresses. The results disclose that dissimilar bonding creates residual tension stresses on the metal surface and compressive residual stresses on the polymer surface.

Two points incremental forming is divided into two categories, negative and positive, and the process investigated in this research is Two points incremental forming. Today, in the forming industry, the production of parts with Dimensional accuracy and proper thickness distribution is very important. The aim of this research is to improve the dimensional accuracy and thickness distribution of the sample produced by the negative two-points incremental forming process. For this purpose, thickness distribution and dimensional accuracy of conical parts have been investigated by making changes in process parameters such as tool diameter, step down, type of lubricant and deformation strategy. To do this research, a numerically controlled milling machine, a complete set of negative die, St12 steel sheet with a thickness of 0.9 mm, spherical tool and SAE 10W oil lubricant were used The analysis of the results of the tests shows that due to the increase in the diameter of the tool at a constant step down, the minimum thickness increases from 0.24 to 0.5 mm, which has caused a decrease in thinning and ultimately the possibility of tearing in the sheet. Reducing the diameter of the tool in a constant step down has led to better shaping in the sharp corners of the production parts, and by applying a new shaping strategy and increasing the number of stages from one stage to two stages, the minimum thickness has increased. This state has improved the thickness distribution of the sample and reduced the possibility of tearing in the sample, and according to the investigations carried out in this research, the lubricant did not have a significant effect on the thickness distribution and dimensional accuracy of the production sample, and the use of the lubricant in this research only reduced the surface roughness.

Metal oxides have a wide industrial application and are an important component of engineered nanocomposites that can improve the surface properties of metals by applying them to a variety of substrates through coating methods. In the present study, the Ni-Cr nano-oxide (NiO/NiCr2O4) was synthesized by co-precipitation to increase the durability of St12 carbon steel in harsh environments against corrosive and abrasive materials. Subsequently, the surface of St12 carbon steel sheets was coated by electrophoretic deposition (EPD) at 110V-3min. The properties of the synthesized nanocomposite and coatings were investigated by XRD, FTIR, FESEM and optical microscope (OM). The results showed that NiO and NiCr2O4 form nanoscale deposits with a crystallite size of 28.8nm and an average particle size of 60-80nm. The wear and corrosion behavior of the St12 substrate and coatings was investigated using ball-on-disk wear, EIS and polarization tests. XRD analysis of the coating materials after sintering revealed Ni, NiCr2O4 and phases of NiAl2O4 and Al formed during sintering as a result of Al addition. The results showed that the Ni-Cr oxide nanocomposite was successfully deposited on the St12 surface by EPD. The average coating thickness was measured to be 10.76 µm. The improvement in wear behavior was determined by measuring 1.8 and 2.1 mg mass of worn material for the coated sample and substrate, respectively. According to the Tafel analysis, the corrosion current density (icorr) was 10.3 and 140.3 µA.cm−2 for the prepared coating and substrate, respectively, showing the considerable evolution of the corrosion behavior of bare steel by adding coatings up to 13 times. The electrochemical impedance spectroscopy (EIS) data were used to evaluate the corrosion mechanism and simulate the corresponding electrical equilibrium circuit. The charge transfer resistance (Rct) was 7934.6 and 134.49 Ω for the coated sample and the bare St12 substrate, respectively.

Unlike conventional welding methods, joining titanium alloys to steels using ultrasonic welding does not result in the formation of brittle intermetallic compounds and high torsion, causing a reduction in the mechanical properties of the joint. Ultrasonic welding of the St12-CP.Ti samples was performed at constant parameters of 7 bars, 2 s and 1 kW and variable parameter of interlayer material (Cu, 70B and Zn). The investigation of samples by OM, SEM, shear-tensile and microhardness tests revealed that Zn and Cu samples had the lowest and highest bond densities, with 42.2 and 80.6 percent, respectively. The bond density and the strength of the sample with greater interlayer deformability have higher values. Due to the high plastic deformation capability of copper, the Cu sample has generated more heat and deformation at the joint interface than in the other samples. As a result, the microstructure underwent recrystallization and grain growth after enduring severe plastic deformation. Also, the highest hardness of the steel side equal to 201 HV was for the Cu sample, followed by 70B and Zn, respectively.

Incremental sheet forming is a flexible forming technology in which the sheet metal is gradually formed by the movement of tools in specified path. Due to the progressively localized deformation of the sheet and concentration of the forces on contact area of tool and sheet metal, the formability of the sheet increases compared with other common forming methods. In this study, numerical simulation of the incremental forming of AA3105-St12 twolayer sheet has been performed to calculate forming force and final thicknesses of the layers. The validity of the simulation results is evaluated by comparing them with those obtained from experiments. Numerical models for estimating the vertical force applied on the tool and the final thicknesses of the layers in terms of the process variables have been obtained using artificial neural network. Multi-objective optimization has been conducted to achieve the minimum force and the minimum thickness reduction of layers using obtained numerical models based on genetic algorithm method. Optimum thickness of the two-layer sheet and the thickness ratio the layers in different states of contact of the aluminum or the steel layers with the forming tool have been determined.

Incremental forming is considered as one of the rapid prototyping methods and has a high degree of flexibility and cost-effectiveness at low production volume. Meanwhile, the lack of technical knowledge has challenged the use of this method in the industry. One of the things that can help the actual usage of this process is the suitable process window; a window used to determine maximum tearing depth of the sheet with respect to the material, thickness and wall angle. In this study, firstly, the formability of low-carbon steel sheet, St12, with the thicknesses of 1. 25 and 1. 50 mm in single point incremental forming of a truncated pyramid with different constant wall angles has been investigated experimentally. Then, it is compared with the formability of the truncated pyramid with variable wall angles under two different wall geometries. Based on the experimental results, the process windows are presented in terms of the maximum depth and wall angle and compared to each other under different circumstances. The results showed that the critical wall angle for St12 sheet in incremental forming of a truncated pyramid with a fixed wall angle differs from the pyramid with variable wall angle, but doesn’ t depend on the size of the pyramid base. The critical wall angle for the fixed and variable wall angle pyramids was obtained 67⁰ and 75⁰ , respectively. For a pyramid with a fixed wall angle, the thickness distribution of the wall is almost constant, while for a pyramid with a variable wall, it varies along the path.

Single point incremental sheet forming is a die-less forming technology in which the sheet metal is formed progressively by the movement of a tool in the specified path. In this paper, the single point incremental forming of the AA3105-St12 two-layer sheet is studied through numerical and experimental approaches. Numerical simulation of the process is done based on the finite element method. The validity of the numerical model is evaluated via a comparison between the obtained numerical and experimental results. The force applied to the forming tool, the thickness distribution of formed sheets, and the maximum thinning that occurred in aluminum and steel layers were studied. The effects of the parameters of the two-layer sheet including total thickness, thickness ratio of layers, and arrangement of layers were investigated as well. The results showed that regardless of the contact of the steel or aluminum layer with the tool, increasing the ratio of the thickness of the steel layer to the thickness of the aluminum layer reduces the thinning in the aluminum layer and increases it in the steel layer. Hence, thinning becomes more severe in each layer when it is in contact with the forming tool.

In the present research, similar and dissimilar resistance spot welding (RSW) process of St12 and galvanized steel sheets with thickness of 0.9 mm was investigated. The experiments were carried out based on the statistical design of experiments (DOE) approach to investigate the effect of RSW parameters on the welding quality, achieving the mathematical regression equations and predicting the new results. Welding time and electrode force were considered as the input process variables while the tensile-shear strength of the joints was considered as the process response. By comparing three RSW types, galvanized steel has the highest tensile-shear strength. Statistical analysis shows that tensile-shear strength is increased with increasing electrode force and welding time. Good agreement between the verification tests and the optimization results revealed that the statistical modelling would be appropriate for RSW process. Welding time (T) =5 s and electrode force (P) =925 N, welding time (T) =5 s and electrode force (P) =1100 N and welding time (T) =3 s and electrode force (P) =925 N were obtained as the optimum settings for similar RSW of St12, dissimilar RSW of St12 to galvanized steel and similar RSW of galvanized steel, respectively.