• Transactions of Materials Processing
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• v.30 no.4
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• pp.172-178
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• 2021

The cold forging process induces material deformation in an enclosed space, generating a very high forging load. Therefore, it is mainly designed as a multi-stage process, and fatigue failure occurs in forging die due to cyclic load. Studies have been conducted previously to quantitatively predict the fatigue limit of cold forging dies, however, there was a limit to field application due to the large error range and the need for expert intervention. To solve this problem, we conducted a study on the introduction of a real-time forging load measurement technology and an automated system for quantitative prediction of die life cycle. As a result, it was possible to reduce the error range of the quantitative prediction of die life cycle to within ±7%, and it became possible to use the die life cycle calculation algorithm into an automated system.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.10a
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• pp.326-329
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• 2005

Since the required strength of forged part is achieved by work hardening with the accumulation of plastic strain during the cold working, severe load can be exerted on die system. So, dies are liable to the early fracture for the non-heat treated steel forging in comparison with the conventional mild steels. Therefore, it is necessary to lower the flow stress of steels as much as possible during forging steps. Bauschinger effect can be utilized to lower flow stress during forging steps by giving the tensile prestrain on the forging billet during wire drawing step. In the present study, the prestrain effect on Bauschinger phenomenon is studied to avoid difficulties with application of non-heat treated cold forging steels in practice.

• Transactions of Materials Processing
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• v.23 no.4
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• pp.221-230
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• 2014

This study deals with a series of experimental investigations on multi-stage cold forging of an outer race used for a constant velocity (CV) joint with six inner ball grooves. The multi-stage cold forging, which consists of forward extrusion, upsetting, backward extrusion, and combined sizing-necking including ironing, was used to produce a prototype of the outer race. The cold forging tools such as forging punches and dies required in this multi-stage cold forging were also designed and fabricated. For the combined sizing-necking, especially, the longitudinally six-segmentallized punches were developed to easily eject from the necked inner groove of the outer race with consideration of the operating mechanism. Spheroidized SCr420H billet was used in the experimental study. To verify the suitability of the proposed process, the obtained parts were obtained from each forging operation, and the geometries were compared with the target dimensions. It was confirmed that the outer race with six inner ball grooves was well forged by adopting the proposed multi-stage cold forging, and the dimensional accuracy of the forged outer race matched well with the requirements.

• Transactions of Materials Processing
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• v.5 no.2
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• pp.105-114
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• 1996

Recently, precision forging techniques are applied to manufacture spur gears. Compared to conventional machining, they produce parts of better mechanical properties and less residual stresses with a much higher production rate. In the present investigation a rigid-plastic three dimensional finite element method was applied to analyze hot forging and cold sizing of a spur gear by closed dies. The involute curve of a tooth profile was approximated by a circle close to the curve. Results of the analyses make it possible to predict local strengths of the gear die failure and an appropriate preform for cold sizing. It was found that the preform for cold sizing. It was found that the preform for the cold sizing is the most important because it determines whether the gears especially teeth can be successfully formed.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.32 no.6
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• pp.251-261
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• 2022

This paper describes the finite element analysis and die design change of spring retainer forging process to reduce the cold forging load and plastic forming stress concentration. Plastic deformation analysis was carried out in order to understand the forming process of workpieces and elastic stress analysis of the die set was performed in order to get basic data for the die fatigue life estimation. Cold forging die design was set up to each process with different four types analysis progressing, the upper and lower dies shapes with combination of fillets and chamfers shapes of cold forging dies. This study suggested optimal cold forging die geometry to reduce cold forging load. The design parameters of fillets and chamfers are selected geometry were selected to apply optimization with the DoE (design of experiment) and Taguchi method. DoE and Taguchi method was performed to optimize the workpiece preform shape for spring retainer forging process, it was possible to expect an increase in cold forging die life due to the 20 percentage forging load reduction.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.10a
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• pp.119-123
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• 2009

In this paper, effects of major design parameters of cold forging dies on die mechanics are quantitatively investigated with emphasis on shrink fit using a thermoelastic finite element method. A ball-stud cold forging process found in a cold forging company is selected as a test process and the effects of die insert material, shrink fit, dimension of ring, partition of die inert and clamping force on effective stress and circumferential stress are analyzed.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.17 no.6
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• pp.104-110
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• 2008

A lot of straight bevel gears have been manufactured by the cold forging process in order to improve the productivity and mechanical property of the product. The die for the cold forging of the gear needs high precision and reproducibility. In the study, cold forging die has been modeled by CAD/CAM and manufactured by machining center using ball end mill coated by (Al, Ti)N for heat-treated alloy steel(STD11, HRC 60). Through the measurement of the machined die, satisfactory dimensional accuracy and surface roughness were obtained. In the future, many 3-d cold forging dies will be directly machined instead of electric discharge machining.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.10 s.181
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• pp.2610-2618
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• 2000

In this paper, the elastic deformation of cold forging die has been investigated to improve the accuracy of forged parts with FEM analysis and experiments using the strain gages. In the finite element analysis, two types of analysis are used to predict elastic deformation of die. The one is that dies are considered to be elastic body from initial stage to final one, and the other is that the dies are considered to be rigid body during forging simulation and then considered to be elastic body at elastic analysis. Considering the results of analysis and experiments, it is likely that the analytical results are in good agreement with experimental inspections. The method using the elastic assumption of die relatively takes a lot of time to simulate the forming operation. However, It is better that using an elastic die to predict not only the shape of product but also filling of die cavity.

• Journal of the Korean Society for Precision Engineering
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• v.28 no.3
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• pp.301-307
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• 2011

In this paper, effects of major design parameters of cold forging dies on die mechanics are quantitatively investigated with emphasis on shrink fit using a thermoelastic finite element method. A ball-stud cold forging process found in a cold forging company is selected as a test process and the effects of die insert material, magnitude of shrink fit, dimension of shrink ring, number of shrink rings, partition of die insert and clamping force on effective stress and circumferential stress are analyzed. It has shown that the number of shrink rings, magnitude of shrink fit, and Young's modulus of die insert material have strong influence on compressive circumferential stress in die insert but that the influence of the other design parameters is relatively weak.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.20 no.12
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• pp.8-15
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• 2021

Cold forging is a method in which molding is performed at room temperature. It has a high material recovery rate and dimensional precision and produces excellent surface quality, and it is mainly used for the production of bolted or housing products. The lifespan of cold forging molds is generally determined by the wear of the mold, plastic deformation of the mold, and fatigue strength. Cold forging molds are frequently damaged due to fatigue destruction rather than wear and plastic deformation in a high-temperature environment as it is molded at room temperature without preheating the raw material and mold. Based on the results analyzed through FEM, an effective mold structure design method was proposed by analyzing the changes in tensile and compressive stresses on molds according to the number of molds and reinforcement rings and comparing the product geometry and mold stress using three existing mold models.