A multi-stage cold forging process was developed and complemented with finite element analysis (FEA) to manufacture a high-strength one-body input shaft with a long length body and no separate parts. FEA showed that the one-body input shaft was manufactured without any defects or fractures. Experiments, such as tensile, hardness, torsion, and fatigue tests, and microstructural characterization, were performed to compare the properties of the input shaft produced by the proposed method with those produced using the machining process. The ultimate tensile strength showed a 50% increase and the torque showed a 100 Nm increase, confirming that the input shaft manufactured using the proposed process is superior to that processed using the machining process. Thus, this study provides a proof-of-concept for the design and development of a multi-stage cold forging process to manufacture a one-body input shaft with improved mechanical properties and material recovery rate.

Residual stress may influence the mechanical behavior and durability of drawn materials. Thus, this study develops a multiple reduction die (MRD) that can reduce residual stress during the drawing process. The MRD set consists of several die tips, die cases, and lubricating equipment. All the die tips of the MRD were disposed of simultaneously. Finite element analysis of the drawing process was performed according to the reduction ratio of each die tip, and the variables in drawing process with the MRD were optimized using a deep neural network to minimize the residual stress. Experiments on the drawing process with the conventional die and MRD were performed to evaluate the residual stress and verify the effectiveness of the MRD. The results of X-ray diffraction measurements indicated that the axial and hoop residual stresses on the surface were dramatically reduced.

Rha SW, et al. Korean Circ J. 2016 Sep;48:e98. https://doi.org/10.4070/kcj.2017.0340

In the multi-pass wire drawing process, the diameter of a wire is decreased by continuously passing it through progressively smaller drawing dies. Although the deformation depends on the process variables, in most wire drawing processes, the wire deformation is concentrated on the surface by its direct contact with the drawing dies, causing a nonlinear distribution of radial direction effective strain from the center to the surface. In this study, a new model for predicting this effective strain in two-pass drawn wire was derived based on the upper bound method, and a finite element analysis and drawing experiment were conducted to validate its effectiveness. The proposed model offers a promising approach to determining and thus controlling the strain in multi-pass drawn wire.