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Authors: H.S. Koo, B.D. Ko, D.H. Jang, Jung Min Seo, Beong Bok Hwang
Authors: Geun An Lee, Seo Gou Choi, Dong Jin Yoon, Hee Woong Lee, Kyoung Hoan Na
Abstract: A microalloyed (MA) forging steel is non-heat-treated materials that have been replacing for conventional quenched and tempered (Q/T) structural steels since the MA forging steels are very cost-effective compared with Q/T steels for the production of automotive parts. However, due to a high strength and low elongation, it has been difficult to apply the MA cold forging steel to the ball stud for automobile. In this study, finite element analyses were carried out to investigate the forming loads, the stress and strain distributions of the workpiece in the cold forging processes of the ball stud using the MA cold forging steel. Compression test at room temperature and fatigue test were also performed to obtain the flow stress and fatigue life, respectively. From these results, it was found that the fatigue life was greatly affected by the strength in the neck region of the ball stud and the cold forging processes should be designed to improve the fatigue life of the ball stud used the MA cold forging steel.
Authors: Joong Yeon Lim, Jung Min Seo, Beong Bok Hwang
Abstract: A finite element method for the compaction process of metallic powder is introduced in the present work. Basic equations for the finite element formulation are summarized. A yield criterion, which is modified by describing asymmetric behavior of powder metal compacts, is introduced and applied to a certain class of powdered metal compaction processes. Two-level flanged solid cylindrical components are analyzed in three different compacting methods with three different compact geometries. The simulation results are summarized in terms of relative density distribution within compacts, pressure distributions along the die-wall interfaces, load-stroke relationships of each punch, average densities as functions of height and radius of the compact, respectively, and average densities of pin and head. For each compact from different compacting method, the best pressing method is chosen for uniform density distributions within the compact.
Authors: D.H. Jang, Beong Bok Hwang, Sun Keun Hwang, Kyung Hoon Min, Hyoung Jin Choi
Abstract: A frictional contact model is adopted for the analysis of conventional solid rivet setting. Material properties for the selected plates and rivets are obtained from analytical method using elastic constants and tensile strengths for each material. Rigid- and elasto-plastic models are selected for process analysis in this paper. Process variables are selected to investigate the effect of variables on the successful rivet setting and servicing in any structure as force transmitting member. Major variables in riveting process are material variables such as material properties and geometrical variables, which are dimensions of head, shank, and blank diameters. Analysis in this study is concentrated on the influence of variety of materials and of shank dimensions on the contact area after rivet setting, i.e. after forming process of rivet head. Soft and hard materials are selected as mother materials to investigate how the selection of material influences on the riveting process in quantitative manner. The geometry of head is closely investigated through simulation in terms of contact status, i.e. contact area between rivet head and mother material, which would affect the snap fit joint by riveting.
Authors: Jin Yong Zhang, Zheng Yi Fu, Wei Min Wang, Qing Jie Zhang
Abstract: Recently research shows that heterogeneous model is needed to explain some complex combustion behaviors in SHS. However, more heterogeneous details be considered more difficulties will be faced. A micro-heterogeneous & macro-homogeneous model is proposed in this paper based on some previous works for this problem. Combustion compact is divided into lots of little units, which are composed of a large number of small particles. Considering a well-mixed situation, properties of every unit must be almost the same, so the compact can be treated as a macro-homogeneous system on the scale of these little units. During the combustion, every unit will have a heterogeneous properties and change; it can be gotten by a micro-heterogeneous model. Therefore, the micro-heterogeneous characters are connected with the Marco-combustion behaviors. Combustion dynamics of Ti-C-Fe system was studied to certify this model. Results show well consistency with experiments results.
Authors: Shao Qing Guo, Wen Li Xu, Hong Yuan, Wei Hua Gu, Xi Tang Tian
Abstract: Residual distortion is a serious problem associated with welding thin aluminum alloy plates. As a distortion control technique static thermal tensioning has been used for many years. Owing to the insufficient understanding of its control mechanism and parameter influence, its application cannot always yield ideal results. So finite element analysis was performed. Based on the simulation results, presetting a saddle-shaped temperature field during welding can significantly reduce longitudinal inherent shrinkage strain in the weld and its adjacent zones, which will then reduce residual stresses and distortion. Temperature difference between the side and central zones is a key parameter and with its increase distortion reduction can be improved. Postweld thermal tensioning can cause certain plastic tensioning, but its effect cannot compare to that of a preset one. These numerical simulation findings were verified finally by experimental investigation.
Authors: Beong Bok Hwang, B.S. Ham, Kyung Hoon Min, Hyoung Jin Choi, Joong Yeon Lim
Abstract: The manufacturing process sequence of a power steering worm gear blank is analyzed. The conventional process sequence for manufacturing power assisted steering (PAS) part contains three distinctive operational stages such as indentation, extrusion, and upsetting, which were originally designed by forming equipment experts. Process conditions such as reduction in area, semi die angle and upsetting ratio are carefully considered to prevent from internal or geometrical defects. The simulation results of the conventional forging process are summarized in terms of deformation patterns, load-stroke relationships and die pressures along the interface for each operational stage. Close investigation of simulation results for current forming process leads to a new process sequence in which the number of operation are reduced into just one operation. Comparisons between the existing and proposed processes are made in terms of maximum force requirement, required forming energy, and process time, respectively. Experiment has been performed to confirm that the proposed process could be applied to replace the existing conventional process sequence and proved the new process to be a safe process sequence for manufacturing PAS part.
Authors: B.D. Ko, Hyoung Jin Choi, Beong Bok Hwang, S.H. Kim, Sun Keun Hwang
Abstract: New manufacturing processes for a valve-spring retainer (VSR) are proposed by replacing the initial solid billet for commercially available thick-walled pipes. The rigid-plastic FEM has been applied to simulate the conventional five-stage manufacturing process for VSR component. The existing process includes mainly backward extrusion and heading operations. A process design methodology is proposed and applied for the analysis. The process design criteria are the maximum force requirement within the available press limit, and the material saving by reducing the wastes from the process. As a result, several simulations of one-step process from selected stocks to the final product shape are performed for a possibly better process than the conventional one. Statistics among different processes are summarized and compared each other in terms of number of required operations for final product, forging load, material waste, number of individual die, process time, and even the possibility of fracture during service. Experiment also has been conducted to ensure that the proposed one-step process is safe operation without geometrical defects.
Authors: Hoon Jae Park, Seung Soo Kim, Sang Mok Lee, Tae Hoon Choi, Hee Woong Lee, Seong Joo Lim, E.Z. Kim, Kyoung Hoan Na, C.S. Han
Abstract: The optimum design of a die shape for Pilger mill process was carried out using FEM analyses considering various processing factors. The important design parameters of the Pilger mill machine are feed rate and profile of the grooved die. Optimum design procedure was conducted in order to investigate effects on forming load and the deformed shape of a material depending on the die surface profiles. Profiles of the die surface for the optimum design were testified with linear, cosine and quadratic curves considering physical forming process. The results of the analyses provided that the model of the quadratic profile gave the lowest forming load and the proper deformed shape.
Authors: Xia Huang, Yuan Song Zeng, Zhi Qiang Li, Xin Hua Zhang
Abstract: In this paper, a new cold bending process is presented to form the titanium alloy tubular part with small relative bend radius, that is, its centerline bending radius is less than 2 times the outside diameter of the tube. FEM is applied to simulate the forming process, and at the same time the results, such as the distribution of the stress and the wall thickness, prediction of defects area, the effects of the internal pressure and friction condition on the tube deformation, are also analyzed. Finally, experimental research was preformed. It is found that the numerical results are in good agreement with the experimental values.

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