• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.10a
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• pp.406-409
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• 2005

In the forging operation of large ingot two break-down process are upsetting and cogging. The first purpose of upsetting is to ensure sufficient forging ratio for subsequent cogging operations and consolidate the voids along the centerline. The second purpose is related to improve the physical properties for a final product. Voids which are generated during the casting process can be one of the decisive defects of materials. So it is necessary to know the standard of Judgment for void-closure in upsetting operation. In practical conditions, FEM analysis(DEFORM 2D 8.1) was carried out to decide how much effective strain has influence on void-closure. It is finally suggested that the function consists of the effective strain of analysis data and the area rate of void.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1999.05a
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• pp.20-23
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• 1999

The current three-stage cold extrusion process including upsetting to produce a flange is investigated for the purpose of improvement of manufacturing process. The main goal of this study is to obtain an appropriate process sequence which can produce the required part most economically without overloading of tools and select an appropriate process for reducing manufacturing cost. The current process sequence is simulated and design criteria are examined. Based on the results of simulation of the current three-stage process, a design strategy for improving the process sequence is developed using the thick-wall pipes. Based on the results of simulation of the one-stage processes, the forming processes of a flange for improving the conventional process are proposed.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2003.05a
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• pp.216-220
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• 2003

Most important for meaningful forging simulation is the determination of correct process parameters. In addition a check and a compensation of the data base after the comparison between experiments and the computation of the developed process is necessary. The existence of a systematic process parameter data bank for special kinds of forming process in combination with forging specific simulation lifts the value of the products. Finite volume method is applied to simulate the hot forging process to investigate the defects for the automobile product. Three typical forging processes have been investigated; Extrusion by hydrolic press, Upsetting by crank press and Inclined upsetting by hammer press. Simulated result has compared with the experiment and provided a direction to improve the process.

• Design & Manufacturing
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• v.7 no.1
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• pp.28-33
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• 2013

During the cold forming, due to high working pressure acting on the die surface, failure mechanics must be considered before die design. One of the main reasons of die failure in industrial application of metal forming technologies is wear. The mechanisms of wear are consisted of adhesion, abrasion, erosion and so on. Die wear affects the tolerances of formed parts, metal flow, and costs of process. The only way to control these failures is to develop a prediction method on die wear suitable in the design state in order to optimize the process. The wear system is used to analyse 'operating variables' and 'system structure'. In this study, with AISI D2, AISI 1020, AISI 304SS materials, a series of the wear experiments of pin-on-disk type to obtain the wear coefficients from Archard's wear model and the upsetting processes are carried out to observe the wear phenomenon during the cold forming process. The analysis of upsetting processes are performed by the rigid-plastic finite element method. The result of the analysis is used to investigate the die wear the processes, and the analysis simulated die wear profiles are compared with the experimental measured die wear profiles.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1996.03b
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• pp.7-15
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• 1996

A Manufacturing process of the power steering worm blank is analyzed by FEM aimulation. The process includes mainly three operations such as indentation, extrusion, and upsetting, which was designed bya forming equipment expert. The results of simulation are summarized in terms of load-stroke relationships, die pressure distributions, effective strain distribution, and deforming patterns for each forming operation. Also, Efforts are focused to get the reason that the tool expert designed the forming process in three operations. The results of the simulation are to be useful for the next advanced process planning in terms of good dimesional accuracy, savings in material and machining, no deforaming defects and imporvements in mechanical properties.

• Journal of the Korean Society for Precision Engineering
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• v.17 no.11
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• pp.213-219
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• 2000

A impeller hub is usually made through three forging processes : forward extrustion, upsetting and finishing. The finishing process is closed die forging in which the load increases abruptly at the final stage, resulting in underfilling in the finished product due to insufficient load capacity of the press. In this study, the rigid-plastic finite element analysis was applied to the impeller hub forging process in order to optimize process and to estimate required load. As a result, two kind of improvements for the process were suggested to reduce the load requirement in the finishing process.

• Transactions of Materials Processing
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• v.22 no.8
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• pp.463-469
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• 2013

In the previous work, a new forging process design, which included incremental upsetting, diffusion bonding and cogging, was suggested as a method to manufacture 1.9wt%C ultrahigh carbon workrolls. The previous study showed that incremental upsetting and diffusion bonding are effective in closing voids and healing of the closed void. In addition, compression tests of the 1.9wt%C ultrahigh carbon steel revealed that new microvoids form within the blocky cementite at temperatures of less than $900^{\circ}C$ and that local melting can occur at temperatures over $1120^{\circ}C$. Thus, the forging temperature should be controlled between 900 and $1120^{\circ}C$. Based on these results, incremental upsetting and diffusion bonding were used to check whether they are effective in closing and healing voids in a 1.9wt%C ultrahigh carbon steel. The incremental upsetting and diffusion bonding were performed using sub-sized specimens of 1.9wt%C ultrahigh carbon steel. The specimen was deformed only in the radial direction during the incremental upsetting until the reduction ratio reached about 45~50%. After deformation the specimens were kept at $1100^{\circ}C$ for the 1 hour in order to obtain a high bonding strength for the closed void. Finally, microstructural observations and tensile tests were conducted to investigate void closure behavior and bonding strength.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.12 no.1
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• pp.90-96
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• 2013

During the cold forming, due to high working pressure acting on the die surface, failure mechanics must be considered before die design. One of the main reasons of die failure in industrial application of metal forming technologies is wear. Die wear affects the tolerances of formed parts, metal flow and costs of process etc. The only way to control these failures is to develop methods which allow prediction of die wear and which are suited to be used in the design state in order to optimize the process. In this paper, the wear experiments to obtain the wear coefficients and the upsetting processes was accomplished to observe the wear phenomenon during the cold forming process. The analysis of upsetting processes was accomplished by the rigid-plastic finite element method. The result from the deformation analysis was used to analyse the die wear during the processes and the predicted die wear profiles were compared with the measured die wear profiles.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1996.11a
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• pp.105-109
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• 1996

The calculation of the total power required at the Continuous Extrusion Forming(CONFORM) has been performed by the theoretical analysis of three transformation regions(primary grip length and extrusion grip length, flashing). In this study, that was performed by five transformation regions(biting, upsetting, filling, extruding, flashing)and four transformation regions(biting, upsetting and filling, extruding, flashing) and then results of theoretical analyses were compared with experimental results. Results of analysis by four and five transformation regions than that of three transformation regions in the CONFORM showed in a good agreement with experimental results.

• Transactions of Materials Processing
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• v.16 no.2 s.92
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• pp.126-131
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• 2007

Voids in a large rotor are formed in solidification process of a cast ingot. The voids have to be eliminated from the rotor by a forming process, because they would became stress-intensity factors which suddenly fracture the rotor in the operation. Previous studies on void-elimination of a large rotor have mainly focused on finding the process variables affecting the void-closure. But the study on the amount of void closure in a large rotor has been very rare. This study was performed to obtain an equation which predicts the amount of void-closure in a forging process of a large rotor and to evaluate the availability of the void-closure equation through finite element analyses. Firstly, 2D FE analysis was carried out to find effects of time integral of hydrostatic stress and effective strain on void volume rate of a large rotor in the upsetting process for various diameters and shapes of void, and material temperature. From the 2D FE analysis, we found that effective strain was suitable for predicting the void-closure of a large rotor, because there was a constant relationship between void volume rate and effective strain. And a void-closure equation was proposed fur predicting void-closure of a large rotor in the upsetting process. Finally, ken the 3D FE analysis, the proposed void-closure equation was verified to be useful for upsetting and cogging processes.