• 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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• 2002.05a
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• pp.112-116
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• 2002

In cold forging, the elastic behavior of the die has a direct influence on the accuracy of the forging part. And the die dimension is continuously changed during the loading, unloading, and ejecting stage. In this paper, we evaluated the elastic deflections of cold forging die during loading, unloading, and ejecting stage. Uni-axial strain gauges are used to measure elastic strain of die during each forging stage. Strain gauges are attached on the surface of die. A commercial F.E.M code, DEFORM-2D$\^$TM/ is used to predict elastic strain of die. Two method of F.E.M. analysis are used to compare with measured and calculated elastic strain. One is to regard the die as rigid body over forging cycle. And then, the die sass is analyzed by loading the die with pressure from the forging part. The other is to regard the die as elastic body from forging cycle. The elastic strain of die is calculated and the die is elastically deformed at each strop. The calculated results under the elastic die assumption are well agreed with experimental data using strain gauges.

• Transactions of Materials Processing
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• v.27 no.3
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• pp.165-170
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• 2018

In order to increase the lifetimes of cold forging dies, insert rings are generally used. In this study, an insert ring and shrunk ring of the flange upsetting die were designed for the cold forging of an automotive wheel nut. The Stress distribution occurring in the die during forging was simulated using a commercial finite element analyzing program. The effects of the fitting interference and inclined angle of the insert ring on the compressive stress of the die inside were also investigated. The simulated data were compared with the real lifetimes of the forging dies. The maximum compressive stress acting on the edge of a forging die should have the most influence on die lifetime, an idea which could help develop the die design with the longest lifetime. The design of the most optimal forging die with the longest lifetime is made possible by analyzing the maximum inner pressure and principal stress between the shrunk ring and insert ring.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1997.10a
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• pp.164-167
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• 1997

The die wear is one of the main factors affecting die accuracy and tool lifetime. It is desired to reduce die wear by developing simulation method to predict wear based on process parameters, and then optimize the process. Therefore, this paper describes disign methodology of preform for minimizing wear of finisher die in multi-stage cold forging processes. The finite element method is combined with the routine of wear prediction and the cold forging processes. The finite element method is combined with the routine of wear prediction and the cold forging process is analyzed. In order to obtain preform to minimize die wear, the FPS algorithm is applied and the optimal preform shape is found from iterative deformation analysis and wear calculation.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.9 no.2
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• pp.281-285
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• 2008

Die hobbing is one of the dieblock manufacturing methods of cold forging die, which makes the upper side of dieblock indented using master punch, hobb to produce impression not using cutting work. SKD11, alloy tool steel was used as the material of dieblock and stainless sheet metal was used as product material in cold forging work. The life span of the die was 6,000 strokes. In this research, the material of dieblock was changed into SKH51, the high speed tool steel and the product material was S45C, the carbon steel in the cold forging work. The life span of the die was 21,000 strokes, which is 350% of the life span of the die using the former method.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1998.06b
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• pp.43-53
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• 1998

Heat - affected zones degenerated in cold forging die have been investigated to improve the tool life. There are many cases of heat-affected zone which are degenerated in manufacturing die and using the cold forging process. In order to define amounts of grinding inmanufacturing the toolfor cold forging, we have investigated the hardness and microstructure of surface layer after EDM. Considering the results of T.R.S. and compression test, it is likely that mechanical properties of tool have been decreased sharply if the heat-affected zones degenerated by EDM were not machined properly. also analyzed the tool surfac which is fractured during the cold forging. According to the microstructures and hardness distribution, surface of many tools have been degenerated in cold forging and fractured due to the heat-affected zone.

• Transactions of Materials Processing
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• v.11 no.2
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• pp.171-178
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• 2002

The elastic deflections of the cold forging die influence the dimensional accuracy of forged parts. The die dimension is continuously changed during the loading, unloading, and ejecting stage. In this paper, we evaluated the elastic deflections of cold forging die during the loading, unloding and ejecting stage with experimental and FEM analysis. Uni-axial strain gages are used to measure elastic strain of die during each forging stage. Strain gages are attached un the upper surface of die. A commercial F.E.M. code, DEFORM$-2D^{TM}$ is used to predict the elastic strains of die, to be compared those by experiments. Two modelling approaches are used to define the reasonable analysis method. The first of the two modelling approaches is to regard the die as rigid body over forging cycle. And then, the die stress is analyzed by loading the die with pressure from the deformed part. The other is to regard the die as elastic body from forging cycle. The elastic strain of tool is calculated and the tool is elastically deformed at each strep. The calculated results under the elastic die assumption are well agreed wish experimental data using the strain gages.

• Transactions of Materials Processing
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• v.16 no.6
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• pp.452-456
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• 2007

Cold forging technology of a gear product is being interested in the dimensional accuracy, high stiffness and reduction of stress concentration. Especially it is needed to avoid the damage due to extremely high local pressure. Therefore it is important to reduce the high pressure in die design of cold forging. In this study, single die insert type and splitted die insert type are considered to recognize the notch effects in the die of sprocket forming. The stress concentration has been released at the notch area by the cushion effect in the splitted die insert.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2004.05a
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• pp.135-138
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• 2004

Since the upsetting type is superior to an extrusion type to get the dimensional accuracy of cold forged spur gear, the upsetting type process far spur gear cold forging has been studied. FE analysis of upsetting type process fur spur gear cold forging was performed to investigate about flow pattern of workpiece and die stress. To analyze the elastic characteristics of die, both rigid and elastic material model were used during loading stage. Under-filled defects were detected In lower portions of spur gear forged by upsetting type in experimental. When the elastic material model for die was used, the under-filled defects could be predicted. On the other hand, if the material model of die was rigid, the defects could not been presented because the die deflection was not considered.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2003.10b
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• pp.63-66
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• 2003

Forged gears have the obvious advantages with the greater utilisation of raw material and high productivity over the machined gears. The forged bevel gear has been used in differential gear for automotive with a high reliance. On the other hand, the studies have been continued to improve the accuracy and expand the applying areas. In this paper, a whole manufacturing process for forged gear from die design and cold forging to heat-treatment was introduced. The stress and elastic deformation for forging die have been analysed by the 3D-FEM-package. The real elastic deformation of die was measured by the strain-gages. The elastic deformation of die was reached to 1mm, in terms of the present study. The analysed quantitative dimension of die was taken into consideration into the CAD/CAM data for forging die.