• Transactions of Materials Processing
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• v.8 no.2
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• pp.178-187
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• 1999

The Cross rolling between flat jaws, as a kind of hot forging, is the forming method to make the axisymmetric multi-step shaft by its rotation and pressure between flat jaws which move in opposite direction. The purpose of this study is to propose the optimal geometric data for shape development of the forward forming region. All data described on this paper are quantified by experiment from initial shape design to final shape development. As the result, proper geometric data are proved that lenth of the first forming area in the forward forming region is 1.5 times larger than circumference of work-piece and the progress angle changes 3 times smoothly.

• Transactions of Materials Processing
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• v.8 no.6
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• pp.563-568
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• 1999

The study has been performed for the relation between die and product in closed die upsetting by the experiment. The strain of die has been given by the simple experiment using the strain gauge located at the outer surface of die and the deformation history of die and product has been given by the experiment and Lame's formula. The inner pressure of die causes the deformation of die that affects the accuracy of dimension and shape of product. The product with accurate dimension and shape can be obtained by analysing elastic deformation of die during upsetting process. The deformation of die during metal forming process has been usually predicted by the experience of industrial engineers or finite element analysis. But it is difficult to predict the dimension of product at unloading and ejected states. The study has given useful result for the deformation history of die and product through the experiment and Lame's formula at closed die upsetting, and can be applied in the die design for product with accurate dimension.

• Design & Manufacturing
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• v.2 no.2
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• pp.43-47
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• 2008

This paper is concerned with the analysis of material flow characteristics of stepped rod forming. The analysis in this paper concentrated on the evaluation of the design parameters for deformation patterns of tube forming, load characteristics, extruded length, and die pressure. The design factors such as punch nose radius, die corner radius, friction factor, and punch face angle are involved in the simulation. The stepped rod forming is analyzed by using a commercial finite element code. This simulation makes use of stepped rod material and punch geometry on the basis of punch geometry recommended by International Cold Forging Group. As radius ratio is large, forming load was reduced but extruded length ratio was increased.

• Journal of the Korean Society for Precision Engineering
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• v.18 no.12
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• pp.145-151
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• 2001

The dimensional accuracy of the cold forged part is depended on the elastic characteristics of the die. To increase the stiffness of the prestressed die, the first stress ring of the tungsten carbide alloy (WC) is considered. For the design, Lame's equation is used. Diameter ratios and interferences have been determinated by maximum inner pressure without yielding of materials. The design of the prestressed die has been compared with the conventional one. For the comparison, the FE-analysis using ANSYS has been performed. The results indicate that the prestressed die with the high stiffness can be obtained by the using the high stiffness material as the first stress ring.

• Journal of Welding and Joining
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• v.32 no.3
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• pp.95-101
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• 2014

Joining of grey cast iron by fusion welding has much difficulties for its extremely low ductility and low toughness because of the flake form of the graphite. And the brittle microstructure, i.e. ledeburite may be formed during fusion welding by its rapid cooling rates. By these kinds of welding problem, preheat and post heat treatment temperature must be increased to avoid weld crack or welding problems. In order to avoid these fusion welding problem, friction welding of cast iron was carried out for improving joint soundness, establishing friction welding variables. There is no factor for evaluating friction weldability in continuous drive type friction welding. In this point of view, this study proposed the parameters for calculating friction weld heat input. The results obtained are as follows ; 1. There was a close relationship between tensile strength and flash appearance of friction welded joint. 2. Tensile strength was decreased and flash was severely oxidized as increasing frictional heating time. 3. As increased forging pressure $P_2$, flash had a large crack and tensile strength was decreased. 4. As powdered graphite by rotational frictional force induced flat surface and hindered plastic flow of metal, tensile strength of welded joint was decreased. 5. Heat input for continuous drive type friction welding could be calculated by the factors of $P_1$, $P_2$ and upset distance(${\delta}$).

• Korean Journal of Metals and Materials
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• v.48 no.3
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• pp.194-202
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• 2010

Application of a stronger and more durable material for reactor pressure vessels (RPVs) might be an effective way to insure the integrity and increase the efficiency of nuclear power plants. A series of research projects to apply the SA508 Gr.4 steel in ASME code to RPVs are in progress because of its excellent strength and durability compared to commercial RPV steel (SA508 Gr.3 steel). In this study, the microstructural characteristics and mechanical properties of SA508 Gr.3 Mn-Mo-Ni low alloy steel and SA508 Gr.4N Ni-Mo-Cr low alloy steel were investigated. The differences in the stable phases between these two low alloy steels were evaluated by means of a thermodynamic calculation using ThermoCalc. They were then compared to microstructural features and correlated with mechanical properties. Mn-Mo-Ni low alloy steel shows the upper bainite structure that has coarse cementite in the lath boundaries. However, Ni-Mo-Cr low alloy steel shows the mixture of lower bainite and tempered martensite structure that homogeneously precipitates the small carbides such as $M_{23}C_6$ and $M_7C_3$ due to an increase of hardenability and Cr addition. In the mechanical properties, Ni-Mo-Cr low alloy steel has higher strength and toughness than Mn-Mo-Ni low alloy steel. Ni and Cr additions increase the strength by solid solution hardening. In addition, microstructural changes from upper bainite to tempered martensite improve the strength of the low alloy steel by grain refining effect, and the changes in the precipitation behavior by Cr addition improve the ductile-brittle transition behavior along with a toughening effect of Ni addition.

• Journal of Power System Engineering
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• v.17 no.3
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• pp.44-49
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• 2013

The refrigerating system are high efficiency and comfortable due to the automation of the system as well as enhance energy saving are contributing to driving system. Previous study the rotational frequency of the compressor was confined to the fixed condition have changed load of evaporator and condenser related about the refrigerator performance characteristic according to the evaporation load and condensation load change tries to be analyze through the experiment. The useful data for the economic driving of the freezing apparatus tries to be drawn. Consequently, it confirmed that refrigerant in the compressor overheated and as the evaporation load increased the specific volume was increased and the coolant circulation rate decreased. In confirmed that condensation load increased the compression ratio and discharge gas temperature increased. It reduced the low-temperature efficiency and condensation calorie and the quality factor was decreased.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.19 no.9
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• pp.15-23
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• 2020

Spline is a machine component using transmits rotating energy with grooves on internal of boss and external periphery of shaft. Internal spline is generally produced by machining process. However, to reduce manufacturing cost and save time, plastic deformation process such as backward extrusion is gradually adapted for spline production. In plastic deformation process, forming load, stress on tools and flow flaws should be taken into account to have sound products. For this purpose, kinematically admissible velocity fields for Upper Bound Method in backward extrusion of internal spline has been suggested, then forming load and relative pressure have been calculated. Internal spline forming experiments have been con-ucted under hydraulic press and the calculated forming load well predicts the load of experiment.

• Journal of Powder Materials
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• v.14 no.6
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• pp.362-366
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• 2007

Magnesium and magnesium alloys are promising materials for light weight and high strength applications. In order to obtain homogeneous and high quality products in powder compaction and powder forging processes, it is very important to control density and density distributions in powder compacts. In this study, a model for densification of metallic powder is proposed for pure magnesium. The mode] considers the effect of powder characteristics using a pressure-dependent critical density yield criterion. Also with the new model, it was possible to obtain reasonable physical properties of pure magnesium powder using cold iso-state pressing. The proposed densification model was implemented into the finite element method code. The finite element analysis was applied to simulating die compaction of pure magnesium powders in order to investigate the density and effective strain distributions at room temperature.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.05a
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• pp.219-222
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• 2005

The temperature difference between die and workpiece has frequently caused various surface defects. The non-homogeneous temperature distribution of forged part should be analyzed to prevent the generation of various defects related with the temperature. The surface temperatures were mainly affected by the coefficient of thermal contact conductance. The precise coefficient is necessary to predict accurately the temperature changes of die and workpiece. The experiment is preformed to measure the temperature distribution of die and workpiece in closed die upsetting. And then, the coefficient is classified into function of pressure and confirmed by the comparison between experiments and FE analyses using the other model. The FE analysis to predict the temperature distribution is performed by commercial software $DEFORM-3D^{TM}$. However, it might be impossible to measure directly the temperature distribution of forged part. Therefore, the comparisons between measured temperature and predicted values are performed with the hardness of Al6061-forged part.