• Transactions of Materials Processing
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• v.22 no.6
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• pp.328-333
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• 2013

The current study aims to determine the limit strains more accurately and reasonably when producing a forming limit curve (FLC) from experiments. The international standard ISO 12004-2 in its recent version (2008) states that the limit major strain should be determined by using the best-fit inverse second-order parabola through the experimental strain distribution. However, in cases where fracture does not occur at the center of the specimen, due to insufficient lubrication, the inverse parabola does not give a realistic fit because of its intrinsic symmetry in shape. In this study it is demonstrated that an inverse quartic function can give a much better fit than an inverse parabola in almost all FLC test samples showing asymmetric strain distributions. Using a quartic fit creates more reliable FLCs.

• Journal of Institute of Convergence Technology
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• v.3 no.2
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• pp.17-21
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• 2013

Hot cross wedge rolling process as an incremental forming has many advantages such as the material usage, the short process time, the automatic equipment line and the low forming load. However, it occurs some defects such as the surface groove, the axis warping and the Mannesmann hole. In this paper, the defect of the Mannesmann hole was carried out. Finite element analysis was utilized to reveal the stress distribution, the rotation of the specimen and the change of section profile. Cross wedge rolling experiment was also conducted on the generation of the Mannesmann hole. It was demonstrated according to the spreading angle with respect to the various types of material. In the view point of metal flow, the smaller forming angle and the larger spreading angle increase opportunities of the defect hole generations.

• Journal of the Korean Society for Precision Engineering
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• v.31 no.12
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• pp.1093-1100
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• 2014

The goal of this paper is to investigate preliminary the applicability of 3D printing technologies for the development of the hot bulk forming process and die. 3D printing technology based on the plastic material was applied to the preform design of the hot forging process. Plastic hot forging dies were fabricated by Polyjet process for the physical simulation of the workpiece deformation. The feasibility of application of Laser-aided Direct Metal Rapid Tooling (DMT) process to the fabrication of the hot bulk metal forming die was investigated. The SKD61 hot-working tool steel was deposited on the heat treated SKD61 using the DMT process. Fundamental characteristics of SKD 61 hot-working tool steel deposited specimen were examined via hardness and wear experiments as well as the observation of the morphology. Using the results of the examination of fundamental characteristics, the applicability of the DMT process to manufacture hot bulk forming die was discussed.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.5
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• pp.1119-1128
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• 1990

A numerical method for analyzing non-isothermal, rigid-viscoplastic deformation problems has been presented. As an application, a stretch forming of sheet metals, including temperature effect, has been analyzed by a three-dimensional finite element method. Bishop`s step-wise decoupled method is adopted to solve thermomechanical coupling between deformation and heat transfer. Using the method, the effect of temperature on strain distribution during stretch forming is investigated. By comparison of the non-isothermal results with isothermal analysis, the importance of including temperature effects in the analysis of metal forming problems is emphasized. The predicted results were in good agreement with the existing experimental measurements at the different punch temperatures and dome heights investigated. It is also found that any increase of the punch temperature appeared to postpone the strain localization process by lowering the peak strain in the critical punch-sheet contact region and by normalizing strain distribution within the specimen.

• Design & Manufacturing
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• v.15 no.4
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• pp.1-7
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• 2021

A study on in-mold punching technology for hole piercing during molding of hollow plastic parts was conducted. Considering the non-linearity of the HDPE plastic material, mechanical properties were obtained according to the change in temperature and load speed. A standard specimen for the in-mold punching test was designed to implement the in-mold punching process, and the specimen was obtained through injection molding. In order to analyze the influence of process variables during in-mold punching, an in-mold punching mold capable of controlling variables such as temperature and support pressure of the specimen was designed and manufactured. Mold heating characteristics were confirmed through finite element analysis, and punching simulations for changes in process conditions were performed to analyze punching characteristics and reflected in the experiment. Through simulations and experiments, it was found that the heating temperature, punch shape, punching speed, and pressure of the back side of the specimen were very important during in-mold punching of HDPE materials, and optimal conditions were acquired within a given range.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.14 no.7
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• pp.606-610
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• 2001

Bi-2212 HTS tube was fabricated by centrifugal forming and partial melting processes. Bi-2212 bulk tube has been optimized to achieve smooth surface and uniform thickness. The slurry was prepared in the mixing ratio of 10:1 between Bi-2212 powder and binder and initially charged into the rotating mold under the speed of 300~450 rpm. Heat-treatment was performed at the temperature ranges of 860~89$0^{\circ}C$ in air for partial melting. the HTS tube fabricated by centrifugal forming process at 89$0^{\circ}C$ under the rotating speed of 450 rpm was highly densified and the plate-like grains with more than 20${\mu}{\textrm}{m}$ were well oriented along the rotating axis. The measured Tc and J$_{c}$ at 10K on specimen heat treated at 89$0^{\circ}C$ was around 85 K and 1,200 A/$\textrm{cm}^2$ respectively.y.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2000.11a
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• pp.261-264
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• 2000

The objective of this work was to characterize mechanical properties of thermoplastic composites for various forming condition in compression molding. Randomly oriented long glass fiber reinforced polypropylene(PP) was used in the work. The composite materials contained 20%, 30%, and 40% glass fiber by weight. Compression molding was conducted to make the test specimen. Dimensional stability was measured on each forming condition with the spring-forward angle. Tensile test was conducted to characterize mechanical properties of formed parts in various forming conditions.

• Transactions of Materials Processing
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• v.12 no.2
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• pp.94-101
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• 2003

For the optimal net shape forging of S semi-solid materials (SSM), it is important to predict the deformation behavior and defects of materials. Among these defects, liquid segregation is detrimental to produce products with good mechanical properties. Moreover, to apply a numerical method to thixoforging, it is very important to prevent a liquid segregation during forming process. The liquid segregation phenomena in deformation behavior of semi-solid material with variation of test specimen size were studied. The SSM compression tests were performed by dynamic material test system with a furnace. Stress-strain curves and microstructures of SSM were investigated, and Porosities were analyzed to evaluate the effects of experiment parameters on liquid segregation.

• Journal of the korean Society of Automotive Engineers
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• v.15 no.2
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• pp.121-129
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• 1993

Plane strain punch stretching test (PSST) was developed to evaluate stamping formability of sheet materials. In this test, the rectangular specimen of sheet material is uniformly stretched up to fracture by raising a specially designed punch to certainly assure plane strain stretching deformation along the longitudinal direction of the specimen. The stamping formability was evaluated by limit punch height(LPH) in plane strain punch stretching test compared to limit dome height(LDH) in hemispherical punch stretching test. LPH-value in PSST well ranks the stamping formability of various material and correlates with press performance. Moreover by using ultrasonic thickness gauge the plane strain intercept-limit plane strain(FLCo)-in forming limit curve can be accurately determined from thickness measurement around the fracture area. The FLCo derived from thickness measurement well correlates with the results from circle grid analysis for the deformed circle grid marked on the surface of the specimen.

• Korean Journal of Ichthyology
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• v.26 no.4
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• pp.331-335
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• 2014

A single specimen of the stone cockscomb, Alectrias alectrolophus (Pallas, 1811) was collected from off Gangneung-si, East Sea, Korea. The present Korean specimen is characterized in having a dermal crest on dorsal median line of head, LXIII dorsal fin rays, I, 44 anal fin rays, 68 vertebrae, slender and flexible dorsal spines in its anterior parts, and scales on the posterior portion of body, and fused gill membranes forming a free fold across the isthmus. We report A. alectrolophus based on a single specimen collected from the Korean water as the first record from Korea.