Inspection and improvement studies of tears occurred during the flange forming process of bushings used in vehicle suspension systems

Bushings constitute one of the most important parts of the suspension system of vehicles. Control arms are connected to the vehicle chassis thanks to bushings, and the rubber inside the bushings absorbs vibration and sudden loads from the road, making vehicle driving comfortable and reliable. In rubber bushings, flange forming is usually done at the end of the outer pipe. During the manufacturing, ruptures may occur in the pipes, especially during the flaring process. In this context, in the thesis a part manufactured from welded steel pipe of S355JR-N standards with a diameter of 40.3 mm and a wall thickness of 2 mm, with a flange diameter of 59 mm, was selected. It is aimed to prevent tearing by determining the factors that cause tearing, optimizing the process and improving the die design through metallographic examinations, mechanical tests applied to the pipes and Finite Element Analysis (FEA) of the forming process. The mechanical properties of the teared pipes were determined by the tensile test. Normalization was performed on the pipes and their internal structures were obtained by metallographic examinations. In order to examine the process and parameters, SEAs of the flange forming process were performed, and the thickness reduction and flange diameter were predicted accurately with a rate of more than 90%. Optimization studies on the process and die geometry have been carried out for the part currently produced in two stages with a thinning rate of 16,1%. Thus, the targeted part could be obtained in a single step with a thinning rate of 9,5%. Trial production of more than 100 parts was made with optimized dies and no tear damage was encountered in any of the parts. Thus, the aim of the thesis to prevent tearing that occurs during the flange forming process of bushings used in vehicle suspension systems has been fully achieved.