Papers by Keyword: Forming Load

Abstract: The Tooth Impact Factor was defined and introduced into the formula of forming load of closed-upsetting. Thus the formula for calculating the forming load of hot precision forging of cylindrical gears was put forward. The equation for the Tooth Impact Factor was fitted using the data from FE simulation of forging process in which gears with different modules were forged. Some forging tests for gears were conducted and the forming load was measured to ensure the validity of the formula. The tests also revealed that the formula is suitable for forming load calculation of hot precision forging of both spur and helical gears in a wide size range.

Abstract: Low formation loads are desirable in metal stamping industries as it reduces the press capacity of the machine and the tooling cost. In the previous study, the author had successfully developed a 2-stage end formation process of a round tube into a square section having small corner radii. However, the formation load in this process increased linearly with the punch stroke in the 1st stage due to the continuous expansion of the tube end by the conical die. Hence, buckling and cracks occurred at the circular section and the bottom end of the square section respectively when the punch stroke was excessive. In this study, the author proposes a circular die having a conical bottom replacing the conical die for the expansion of the tube end. Although the formation load increases when the tube end is expanded at the conical bottom, the amount of increase becomes small when the tube end reaches the circular section of the die due to its constant diameter. At the circular section, the tube end curls and wraps over the die when the punch stroke is increased. In the 2nd stage, the squaring process is performed with a conical bottom square punch and a taper square die for the two different expanded tubes i.e. the one formed with the conical die and the one formed with the conical bottom circular die. Both Finite Element Method (FEM) simulation and experiment were performed to evaluate these two processes. The distribution of plastic strains, forming loads and product appearances are investigated. With the circular die, the maximum forming loads are successfully reduced by 20% and 33% in the 1st and the 2nd stages respectively in the experiment when compared to the ones formed with the conical die. No buckling and cracks are observed for the tube formed with the circular die.

Abstract: Oxidation in hot stamping of ultra high strength steel sheets was prevented by coating the sheets with an oxidation preventive oil. For four types of oxidation preventive oil, the degree of oxidation under natural cooling of the heated sheets without forming was first evaluated. The oil that forms a liquefied film at elevated temperatures exhibited high oxidation prevention, and this oil was chosen for a hot bending experiment. Hot hat-shaped bending of the coated sheets using resistance heating was carried out to examine the properties of the products. The bending load was markedly decreased, the shape accuracy of bent products was very high, the surface roughness was similar to that of the sheet, and the hardness was about 1.5 times larger than that of the sheet before the bending due the die quenching. In addition, the layer remaining on the surface of the formed product could be removed using phosphoric acid. It was found that the hot stamping operation using the oxidation preventive oil is effective in the precision forming of ultra high strength steel sheets.

Abstract: This paper is concerned with the analysis of the forming load characteristics of a forward-backward can extrusion in both combined and sequence operation. A commercially available finite element program, which is coded in the rigid-plastic finite element method, has been employed to investigate the forming load characteristics. AA 2024 aluminum alloy is selected as a model material. The analysis in the present study is extended to the selection of press frame capacity for producing efficiently final product at low cost. The possible extrusion processes to shape a forward-backward can component with different outer diameters are categorized to estimate quantitatively the force requirement for forming forward-backward can part, forming energy, and maximum pressure exerted on the die-material interfaces, respectively. The categorized processes are composed of combined and/or some basic extrusion processes such as sequence operation. Based on the simulation results about forming load characteristics, the frame capacity of a mechanical press of crank-drive type suitable for a selected process could be determined along with securing the load capacity and with considering productivity. In addition, it is suggested that different load capacities be selected for different dimensions of a part such as wall thickness in forward direction and etc. It is concluded quantitatively from the simulation results that the combined operation is superior to sequence operation in terms of relatively low forming load and thus it leads to low cost for forming equipments. However, it is also known from the simulation results that the precise control of dimensional accuracy is not so easy in combined operation. The results in this paper could be a good reference for analysis of forming process for complex parts and selection of proper frame capacity of a mechanical press to achieve low production cost and thus high productivity.