Increasing the geometric accuracy of flange walls when flanging holes by using profiled sheet metal workpieces

Problem. Flanging of holes to produce flanges in sheet metal blanks and profiles is widely used in the manufacture of parts in many industries, including aircraft and instrumentation. Significant disadvantages of flanging holes are the low geometric accuracy of the flanges obtained due to the presence of significant wall thinning along the length of the flanges and the deviation of the flange wall from the cylindrical surface of the hole of the flanging die. The wall deviation occurs due to elastic deformation after the punch is removed from the deformed workpiece. To eliminate such deficiencies, flange calibration operations are used by performing additional thinning of the cylindrical part of the flange wall. Additional thinning is also used to increase the height of the flanges to be flanged. The use of thinning leads to certain limitations when connecting the flanged parts to other products using threads. Therefore, research aimed at improving the geometric accuracy of flanges in the direction of reducing wall thinning along the length and reducing wall curvature during flanging is relevant. One way to solve this problem is to use a pre-profiled workpiese.Objective. To increase the geometric accuracy of the walls of the resulting flanges after flanging the holes by using a pre-profiled sheet blank.Method of realization. The use of a pre-profiled sheet workpiese with the largest profile thickness near the hole with a gradual decrease in thickness to the original thickness at the beginning of the rounding radius of the flanging die will significantly reduce the thinning and curvature of the flange wall after flanging the hole. Results. Using the finite element method (FEM), the processes of profiling the workpiece by extrusion to obtain a bridge and punching the bridge, as well as the subsequent flanging of holes with flat, conical and spherical punches were modeled. The dependence of the flanging forces and the forces for removing the punches from the deformed workpieces on the displacement of the punches was determined. For a spherical punch with a minimum flanging force, the dimensions of the flange were determined and compared with those of a traditional workpiece. The stress state of the metal at the maximum flanging force of a profiled workpiese with a spherical punch and the final deformed state after the punch is removed were determined. The design of the punch with a set of parts for profiling and flanging was developed and manufactured. Experimental studies were conducted, the results of which showed good agreement with the modeling data on the forces of extrusion and flanging and the dimensions of the resulting flanges.Conclusions. By using a profiled workpiese made of aluminum alloy D16, the geometric accuracy of the flanges obtained after flanging the hole was increased. The wall thickness of the resulting flange in length is almost the same as the thickness of the original workpiese and the deviation of the wall from the cylindrical surface of the hole of the flanging die is significantly reduced.