Abstarct: Nowadays, concerns regarding reducing the weight of automobiles to reduce fuel consumption has made the automotive industry more inclined to use high strength steel sheets. Joining these types of steel sheets to similar and dissimilar steel sheets is a challenge for their application. Sheet mextal clinching process is a forming-baxsed method for mechanical joining of mextal sheet parts. In this dissertation, first, clinching of DX51D galvanized steel sheets of 1.5 and 2 mm in thickness (DX51D/DX51D joint), as an alternative for spot welding process in a special application for car manufacturing industry, using a grooved die was studied. Then, a new method for hole clinching of 1 mm thick Docol sheet to 1.5 mm thick DX51D sheet (Docol/DX51D joint) using a conical die was presented. In order to make sure about the strength of the joint, the tooling should have optimum design. Consequently, after characterizing the mechanical properties of raw materials, baxsed on orthogonal experimental design (OED), and finite element analysis, most influencing parameters of the forming tool were optimized for achieving maximum joint strength F. Nine tests for clinching process of DX51D/DX51D sheets and 27 experiments for hole clinching process of DX51D/DOCOL sheets were designed using minitab software. Parametric studies tool and explicit solver of Abaqus software were used to analyze the designed experiments. Parametric input files were generated and used to change the process parameters in the simulations. After running the experiments designed baxsed on the OED in computer, optimal values of the important parameters affecting the tool design were obtained for both methods of clinching. The maximum tensile strengths of 2319 N and 3509 N were obtained for clinching of DX51D / DX51D and DX51D / DOCOL, respectively. Next, clinching tools were designed and fabricated baxsed on these optimum geometric parameters. The clinching and hole clinching process were successfully done using the fabricated tooling. Tensile strength and geometry profiles of clinched samples were measured. Comparison of the experimental and simulation results shows a good agreement between them. baxsed on the demands of car manufacturing standards, DX51D/DX51D clinch joint using grooved die, can replace the conventional spot welding method in the particular case studied. Further, the results showed that using conical fixed die as a new design, for hole clinching DX51D/DOCOL, the joint strength can increase by 18% compared to the hole clinching using cylindrical die.