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REFERENCE LINKING PLATFORM OF KOREA S&T JOURNALS
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Transactions of Materials Processing
Journal Basic Information
Journal DOI :
The Korean Society for Technology of Plasticity
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Volume & Issues
Volume 21, Issue 8 - Dec 2012
Volume 21, Issue 7 - Nov 2012
Volume 21, Issue 6 - Oct 2012
Volume 21, Issue 5 - Aug 2012
Volume 21, Issue 4 - Jul 2012
Volume 21, Issue 3 - Jun 2012
Volume 21, Issue 2 - Apr 2012
Volume 21, Issue 1 - Feb 2012
Selecting the target year
Forming of Metallic Bipolar Plates by Dynamic Loading
Koo, J.Y. ; Kang, C.G. ;
Transactions of Materials Processing, volume 21, issue 1, 2012, Pages 5~12
DOI : 10.5228/KSTP.2012.21.1.5
The weight of the bipolar plate is one of the crucial aspects of improving power density in PEMFC stacks. Aluminum alloys have good mechanical properties such as density, electrical resistivity, and thermal conductivity. Furthermore, using aluminum in a bipolar plate instead of graphite reduces the bipolar plate cost and makes machining easier. Therefore in this study, an aluminum alloy was selected as the appropriate material for a bipolar plate. Results from feasibility experiments with the aim of developing fuel cells consisting of Al bipolar plates with multiple channels are presented. Dynamic loading was applied and the formability of micro channels was estimated as a function of punch pressure and die radius. Sheets of Al5052 with a thickness of 0.3mm were used. For a die radius of 0.1mm the formability was optimized with a sine wave dynamic load of 90kN at maximum pressure and 5 cycles of a sine wave punch travel. The experimental results demonstrate the feasibility of the proposed manufacturing technique for producing bipolar plates.
Friction Characteristics of Warm a Forging Lubricant Containing Nano Graphite Powder
Kim, D.W. ; Kim, Y.R. ; Lee, G.A. ; Choi, H.J. ; Yun, D.J. ; Shin, Y.C. ; Lee, J.K. ; Lim, S.J. ;
Transactions of Materials Processing, volume 21, issue 1, 2012, Pages 13~18
DOI : 10.5228/KSTP.2012.21.1.13
During warm forging, materials are formed in the temperature range of
. In this temperature range, the friction between the forging die and the material is very high and has a negative effect on the forming process causing severe die wear and possible defects in the component because of stick-slip. Thus, lubrication characteristics are a very important factor for productivity during warm forging. In this paper, ring compression experiments were conducted to estimate the friction factor between the die and the materials as the main factor in characterizing the lubricant. Also, ring tests using normal graphite power as a lubricant coating system were compared with tests using nano graphite powder. The results confirm that the nano graphite is superior to the normal graphite in view of its lubricating effect. In addition, the friction factor (m) was estimated with respect to the amount of the nano graphite content in the lubricant. With 10 % nano graphite the friction factor had the lowest value as compared to other amounts. It can be concluded that the amount of the nano graphite in the coating system can be optimized to obtain the best lubrication condition between the die and the material using ring test experiments.
Finite Element Analysis of a Roll Piercing Process Equipped with Diecher`s Guiding Discs
Shim, S.H. ; Cho, J.M. ; Lee, M.C. ; Joun, M.S. ;
Transactions of Materials Processing, volume 21, issue 1, 2012, Pages 19~23
DOI : 10.5228/KSTP.2012.21.1.19
In this paper, a Mannesmann roll piercing process equipped with Diecher`s guiding discs is investigated using a rigid-thermoviscoplastic finite elements method with intelligent remeshing capability and tetrahedral elements. The analysis model is presented and the approach is applied to a Mannesmann roll piercing process found in the literature. Details about the remeshing criterion as well as mesh density control are given. The present predictions are compared with the predictions found in the literature, showing that the two predictions are in close agreement in terms of the deformed shape. However, it is emphasized that the present approach has the distinct strength in predicting details of final shape.
Dimensional Analysis of Edge Rolling for the Prediction of the Dog-bone Shape
Yun, D.J. ; Hwang, S.M. ;
Transactions of Materials Processing, volume 21, issue 1, 2012, Pages 24~29
DOI : 10.5228/KSTP.2012.21.1.24
Precision control of the width of slabs is vital for product quality and production economy in steel rolling mills. However, the formation of so called `dog-bone` at the edge of the slab would affect the final width during the horizontal rolling that follows. Therefore, it is essential to predict and control the dog-bone shape. In this paper, a model is derived by using a number of finite element simulations for edge rolling and a least square regression analysis. The prediction accuracy of the proposed model is examined by comparing the predictions from finite element simulation with experiment results in the literature.
An Experimental Study on the Warpage of a Film Insert Molded Plate
Yoo, Y.G. ; Lee, H.S. ;
Transactions of Materials Processing, volume 21, issue 1, 2012, Pages 30~35
DOI : 10.5228/KSTP.2012.21.1.30
FIM(Film Insert Molding) is an innovative method of producing decorated parts for a wide range of products. Because it requires fewer steps when compared to conventional production methods, the time and cost of manufacturing high quality components can be reduced considerably. In this paper, the effects of processing conditions on the warpage of film-insert molded plate were investigated by using a design of experiments. The dominant factors affecting warpage were mold temperature and holding pressure. Warpage increased with the temperature difference between stationary mold and fixed one. Even when the mold temperature difference was zero, the plate with a film was bent after ejection such that the film side protruded. As holding pressure increased, warpage decreased significantly. In addition warpage increased with time increment for the film-insert molded plates.
Development of a Gas Assisted Injection Molding Process for Exterior Display Panels
Choi, D.S. ; Kim, H.S. ;
Transactions of Materials Processing, volume 21, issue 1, 2012, Pages 36~41
DOI : 10.5228/KSTP.2012.21.1.36
Gas Assisted Injection Molding is a relatively new low-pressure injection molding technique that provides benefits such as reduced part warpage, excellent surface quality without shrink marks, greater design flexibility, etc. In the gas assisted injection molding process, the injected pressurized nitrogen gas flows through designed gas channels and forms hollow sections within the part. However, due to the characteristics of the gas, the design of the gas channels which are the paths for the injected gas is important in order to avoid defects such as gas blowout, fingering, etc. Therefore, in this study, the gas channel design for gas assisted injection molding of exterior display panels was conducted by examining the results of three CAE analyses. The designed gas channel was verified by conducting tryouts using a 450 ton injection molding machine with 3-stage pressure controlled gas kit. In addition, the hollow shapes which were formed by the gas with the installed gas channels were examined by examining the cross sections of the prototypes that were produced. As a result, it was found that exterior display panels can be produced without any defect by applying the gas assisted injection molding technique.
Effect of Process Parameters on Hydroforming Characteristics of a Rectangular Shape Flange
Kim, S.H. ; Kim, S.Y. ; Jeon, C.H. ; Joo, B.D. ; Moon, Y.H. ;
Transactions of Materials Processing, volume 21, issue 1, 2012, Pages 42~48
DOI : 10.5228/KSTP.2012.21.1.42
Hydroforming has attracted the attention of manufacturing industries for vehicles and transportation systems. A wide range of products such as subframes, camshafts, radiator frames, axles and crankshafts are made by the hydroforming process. Hydroformed parts often need to be structurally joined to other components during assembly. Therefore it is useful if the hydroformed automotive parts can be attached with a localized flange. In this study, a hydroforming process to produce a rectangular shape flange is proposed. FE analysis to form the flanged rectangular shape was performed by Dynaform 5.5. The hydroforming characteristics at various die aspect ratios and feeding conditions were analyzed and optimal process conditions which can avoid defects are suggested. For validation purposes, hydroforming experiments to form the flange were conducted with the optimized conditions. The results show that the flanged parts can be successfully formed with a hydroforming process without additional processing steps.
Prediction for Thickness and Fracture of Stainless Steel-Aluminum-Magnesium Multilayered Sheet during Warm Deep Drawing
Lee, Y.S. ; Lee, K.S. ; Kim, D. ;
Transactions of Materials Processing, volume 21, issue 1, 2012, Pages 49~57
DOI : 10.5228/KSTP.2012.21.1.49
It is difficult to estimate the properties of multilayered sheet because they are composed of one or more different materials. Plastic deformation behavior of the multilayered sheet is quite different as compared to each material individually. The deformation behavior of multilayered sheet should be investigated in order to prevent forming defects and to predict the properties of the formed part. In this study, the mechanical properties and formability of stainless steel-aluminum-magnesium multilayered sheet were investigated. The multilayered sheet needs to be deformed at an elevated temperature because of its poor formability at room temperature. Uniaxial tensile tests were performed at various temperatures and strain rates. Fracture patterns changed mainly at a temperature of
. Uniform and total elongation of multilayered sheet increased to values greater than those of each material when deformed at
. The limiting drawing ratio (LDR) was obtained using a circular cup deep drawing test to measure the formability of the multilayered sheet. A maximum value for the LDR of about 2 was achieved at
, which is the appropriate forming temperature for the Mg alloy. Fracture patterns on a circular cup and thickness of formed part were predicted by a rigid-viscoplastic FEM analysis. Two kinds of modeling techniques were used to simulate deep drawing process of multilayered sheet. A single-layer FE-model, which combines the three different layers into a macroscopic single layer, predicted well the thickness distribution of the drawn cup. In contrast, the location and the time of fracture were estimated better with a multi-layer FE model, which used different material properties for each of the three layers.
A Cooling Method which Reduces the Tangential Tensile Stresses on a Work Roll Surface during Hot Slab Rolling
Na, D.H. ; Lee, Y. ;
Transactions of Materials Processing, volume 21, issue 1, 2012, Pages 58~66
DOI : 10.5228/KSTP.2012.21.1.58
The work roll surface temperature rises and falls repetitively during hot slab rolling because the work roll surface is cooled continuously by water. This study focused on Std. No. 7 to determine a cooling method which significantly reduces the tangential tensile stresses on the work roll surface of the hot slab mill at Hyundai Steel Co. in Korea. A series of finite element analyses were performed to compute the temperature distribution and the tensile stresses in the circumferential direction of the work roll. The virtual slab model was used to reduce the run time considerably by assigning a high temperature to the virtual slab. Except for the heat generated by plastic deformation, this is equivalent to the hot rolling condition that a high temperature slab (material) would experience when in contact with the work rolls. Results showed that when the virtual slab model was coupled with FE analysis, the run time was found to be reduced from 2000 hours to 70 hours. When the work roll surface cooled with a certain on-off patter of water spray, the magnitude of the tangential stresses on the work rolls were decreased by 54.1%, in comparison with those cooled by continuous water spraying. Savings of up to 83.3% in water usage are possible if the proposed water cooling method is adopted.
Properties of a Helical Gear Due to the Manufacturing Process - Forged versus Machined Product
Jung, H.C. ; Kang, B.S. ; Lee, I.H. ; Choi, S.T. ; Sin, S.J. ; Kang, S.H. ; Lee, Y.S. ;
Transactions of Materials Processing, volume 21, issue 1, 2012, Pages 67~74
DOI : 10.5228/KSTP.2012.21.1.67
Although high productivity is possible, cold forged helical gears have not been widely used due to difficulty in achieving mechanical properties as well as dimensional accuracy of the product. Confidence in the gear characteristics also is very important in heavy-duty gear applications. Therefore, the properties of forged gears must be compared to the properties of conventional machined gears. The properties might be different due to the different fabrication processes. In this study, machined and forged products both before and after heat-treated have been compared by measuring the residual stress and involute curve of the tooth. Characteristics of hardness and microstructure were also compared. Additionally, tooth fracture strength was compared for the heat-treated products. Moreover, the tooth strength and the fracture pattern were compared between the machined and forged gears. The forged gear showed decreased changes in residual stress and decreased changes in dimensions when compared to the machined gear before and after heat treatment. The forged gear was over 10% better than the machined gear in tooth strength.