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REFERENCE LINKING PLATFORM OF KOREA S&T JOURNALS
> Journal Vol & Issue
Transactions of Materials Processing
Journal Basic Information
Journal DOI :
The Korean Society for Technology of Plasticity
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Volume & Issues
Volume 12, Issue 8 - Dec 2003
Volume 12, Issue 7 - Nov 2003
Volume 12, Issue 6 - Oct 2003
Volume 12, Issue 5 - Aug 2003
Volume 12, Issue 4 - Jul 2003
Volume 12, Issue 3 - Jun 2003
Volume 12, Issue 2 - Apr 2003
Volume 12, Issue 1 - Feb 2003
Selecting the target year
Investigation of the Jetting Phenomena in Injection Molding for Various Injection Speeds, Resins and Mold Shapes
Transactions of Materials Processing, volume 12, issue 1, 2003, Pages 3~10
DOI : 10.5228/KSPP.2003.12.1.003
The formation of surface defects associated with Jotting in injection molding is related to the geometries of cavity and fate, operational conditions and the rheological properties of polymer. In this study we have examined jetting phenomena in injection molding process for the throe kinds of PCs which have different molecular weights and structures, PBT and PC/ABS alloy with several injection speeds. We have used various cavity shapes those are tensile, flexural and impact test specimens with various gates and cavity thicknesses. Through this study we have observed that the jetting is related to the dic swell of material. This means that the jotting is strongly affected by the elastic flow property rather than the viscous flow property in viscoelastic characteristics of molten polymer. Different resins have different elastic properties, and elastic flow behavior depends on the shear rate of flow, i.e. injection speed. Large die swell would eliminate jetting however, the retardation of die swell would stimulate jetting. In the point of mole design, reducing the thickness ratio of cavity to gate can reduce or eliminate jetting regardless of amount of elasticity of polymer melt.
A Study on the Drawing of Strip by Upper Bound Elemental Technique
Transactions of Materials Processing, volume 12, issue 1, 2003, Pages 11~17
DOI : 10.5228/KSPP.2003.12.1.011
For metal forming analysis, upper-bound solution is a practical method because the solution is overestimated. However it is not easy to determine the stresses on dies by using upper-bound solution. In this study, new scheme to calculate the stresses on dies based on upper bound solution is proposed. In the velocity fields, imaginary velocity is adapted to analyze the normal pressure on die surfaces. To verify the proposed scheme. plane strain drawing has been considered. The stresses on dies obtained by the proposed scheme are compared with the results of rigid plastic FEM and the experimental results. In the experiments, pressure film is used to measure the normal pressure on dies.
Process Design for Improving Tool Life in Hot Forging Process
Transactions of Materials Processing, volume 12, issue 1, 2003, Pages 18~25
DOI : 10.5228/KSPP.2003.12.1.018
This paper explains the process design for improving tool life in the conventional hot forging process. The thermal load and the thermal softening are happened by contact between the hotter billet and the cooler tools in hot forging process. Tool life decreases considerably due to the softening of the surface layer of a tool was caused by a high thermal load and long contact time between the tools and the billet. Also, tool life is to a large extent limited by wear, heat crack and plastic deformation in hot forging process. Above all, the main factors which affect die accuracy and tool life we wear and the plastic deformation of a tool. The newly developed techniques for predicting tool life are applied to estimate the production quantity for a spindle component and these techniques can be applied to improve the tool life in hot forging process.
Finite Element Analysis for Frictional Contact Problems of Axisymmetric Deforming Bodies
Transactions of Materials Processing, volume 12, issue 1, 2003, Pages 26~33
DOI : 10.5228/KSPP.2003.12.1.026
This paper is concerned with the numerical analysis of frictional contact problems in axisymmetric bodies using the rigid-plastic finite element method. A contact finite element method, based on a penalty function, are derived from variational formulations. The contact boundary condition between two deformable bodies is prescribed by the proposed algorithm. The program which can handle frictional contact problem is developed by using pre-existing rigid-plastic finite element code. Some examples used in this paper illustrate the effectiveness of the proposed formulations and algorithms. Efforts focus on the deformation patterns, contact force, and velocity gradient through the various simulations.
Rigid-Plastic FE Modeling of Frictional Contact Problems based on a Penalty Method
Transactions of Materials Processing, volume 12, issue 1, 2003, Pages 34~42
DOI : 10.5228/KSPP.2003.12.1.034
This paper presents a rigid-plastic finite element method to handle the frictional contact problem between two deformable bodies experiencing large deformation. The variational formulation combined with incremental quasi-static model is employed for treating the contact boundary condition. The frictional behavior of the model obeys Coulomb's law of friction. The proposed contact algorithms are classified into two categories, one for searching contacting nodes and the other for calculating contact forces at the contact surface. A slave node and master contact segment are defined using the geometric condition of finite elements on the contact interface. The penalty parameter is used to limit the penetration between contacting bodies, and the finite elements are coupled with contact boundary elements.us gates and cavity thicknesses. Through this study we have observed that the jetting is related to the die swell of material. This means that the jotting is strongly affected by the elastic flow property rather than the viscous flow property in viscoelastic characteristics of molten polymer. Different resins have different elastic properties, and elastic flow behavior depends on the shear rate of flow, i.e. injection speed. Large die swell would eliminate jetting however, the retardation of die swell would stimulate jetting. In the point of mole design, reducing the thickness ratio of cavity to gate can reduce or eliminate jetting regardless of amount of elasticity of polymer melt.
FEM Analysis on Deformation Inhomogeneities Developed in Aluminum Sheets During Continuous Confined Strip Shearing
Transactions of Materials Processing, volume 12, issue 1, 2003, Pages 43~48
DOI : 10.5228/KSPP.2003.12.1.043
The strain state during the continuous confined strip shearing (CCSS) based on ECAP was tackled by means of a two-dimensional FEM analysis. The deformation of AA 1100 sheet in the CCSS apparatus was composed of three distinct processes of rolling, bending and shearing. The pronounced difference in the friction conditions on the upper and lower roll surfaces led to the different variation of the strain component
throughout the thickness of the aluminum sheet. Strain accompanying bending was negligible because of a large radius of curvature. The shear deformation was concentrated at the corner of the CCSSchannel where the abrupt change in the direction of material flow occurred. The process variables involving the CCSS-die design and frictions between tools and strip influenced the evolution of shear strains during CCSS.
Spring-Back Prediction for Sheet Metal Forming Process Using Hybrid Membrane/shell Method
Transactions of Materials Processing, volume 12, issue 1, 2003, Pages 49~59
DOI : 10.5228/KSPP.2003.12.1.049
To reduce the cost of finite element analyses for sheet forming, a 3D hybrid membrane/shell method has been developed to study the springback of anisotropic sheet metals. In the hybrid method, the bending strains and stresses were analytically calculated as post-processing, using incremental shapes of the sheet obtained previously from the membrane finite element analysis. To calculate springback, a shell finite element model was used to unload the final shape of the sheet obtained from the membrane code and the stresses and strains that were calculated analytically. For verification, the hybrid method was applied to predict the springback of a 2036-T4 aluminum square blank formed into a cylindrical cup. The springback predictions obtained with the hybrid method was in good agreement with results obtained using a full shell model to simulate both loading and unloading and the experimentally measured data. The CPU time saving with the hybrid method, over the full shell model, was 75% for the punch stretching problem.
HIP Diffusion Bonding of Two Types of Superalloys for Engine Blisk Applications
Transactions of Materials Processing, volume 12, issue 1, 2003, Pages 60~65
DOI : 10.5228/KSPP.2003.12.1.060
HIP diffusion bonding of Ni-based superalloys, cast Mar-M247 (MM247) and Udimet 720 (U720) powder, was experimentally and numerically studied. Subsolvus HIP treatment was optimized by investigating the variations of high temperature tensile properties of HIP-bonded specimens with powder size, HIP'ing time, etc. While the tensile strength at high temperatures showed no detectable changes, the tensile elongation and reduction in area were slightly increased as the powder size decreased from -140 mesh to -270 mesh. While as-HIP'ed U720 showed a high tensile strength comparable to that of lorded U720 alloy, the HIP diffusion-bonded specimen showed a strength lower than the forged U720 alloy and the cast MM247 alloy The increase of HIP'ing tune from 2 hours to 3 hours resulted in a rapid risc of tensile strength and elongation due to the disappearence of microvoids in the cast MM247. FEM simulation for HIP process was conducted by applying the McMeeking micromechanical model, which uses power-law creep model as constitutive equations. ABAQUS user subroutine CREEP with an implemented microscopic model was used for the simulation. Numerical simulation was shown to be essential for the near-net shape manufacturing as well as the HIP process optimization.