• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.15 no.7
• /
• pp.4057-4064
• /
• 2014

In this paper, attempts were made to design a preform for a final punch inexpensively using the proposed approximate optimization method or metamodel-based simulation optimization. The design objective of this work is to achieve a uniform distribution of effective strains, the angle dimension of the preformed punch is chosen as a design variable, and maximum underfill ratio is used as a constraint. For this optimization, a computer simulation of a practical punch forging process is run using DEFORM software, in which a preformed punch(workpiece), a master punch(upper die), and a bottom die are dealt with. A validation method is introduced to determine if the simulation results match the actual forging process. In addition, this work presents the detailed design optimization procedure consisting of (i) generation of an initial metamodel, (ii) metamodel optimization, (iii) validation of metamodel-predicted optimum, and (iv) metamodel improvement.

• Journal of Korean Academy of Fundamentals of Nursing
• /
• v.11 no.2
• /
• pp.203-212
• /
• 2004

Purpose: This study was done to determine whether providing auditory and vestibular stimulation to preform infants would have an effect on stress hormones. Methods: The design was a nonequivalent control group protest-posttest design in a quasi-experimental study Seventy-nine preform infants were assigned either one of two experimental groups or to a control group: 27 in the auditory stimulation group, 25 in the vestibular stimulation group and 27 in the control group. The criteria for inclusion in this study were 1) gestational age of less than 37 weeks, 2) birth weight of less than 2,500g, 3) the absence of congenital anomalies or specific diseases, 4) recovering physiological weight loss, and 5) weaned from ventilatory assistance or oxygen. The data were collected from March 2002 to May 2003. The auditory stimulation, a music audiotape, was provided 20 minutes twice a day for 10 days and the vestibular stimulation, an infant waterbed, was provided for 10 days. On day 1 and day 10 of the study, 24 hour urine sample was collected for norepinephrine, epinephrine, and cortisol assays. In the data analysis SPSSWIN 10.0 program was utilized for descriptive statistics, ANOVA and t-test. Results: General characteristics of the three groups showed no significant differences, thus three groups were found to be homogenous. The 24 hour urine cortisol for the auditory (t=3.489, p=.001) and for the vestibular (t=2.638, p=.013) stimulation group were significantly reduced compared to the control group after 10 days. Conclusions: The results suggest that auditory and vestibular stimulation can be used to reduce 24 hour urine cortisol in preform infants. Therefore, music audiotapes and waterbeds provided in incubator are be recommended for reduction of the stress in preform infants who are hospitalized in neonatal intensive care units.

• Composites Research
• /
• v.30 no.5
• /
• pp.297-302
• /
• 2017

Finite element analysis of T-beam laminate structure under bending-torsional loading was conducted to prevent the delamination which is the major failure behavior on laminated composites. Three-dimensional preform, which is that fabric is braided through thickness direction, is suggested from the laminate analysis. The analysis aimed to optimize the fiber ratio in laminated composites. After it is suggested that guideline for design of T-beam structure using commercial software ANSYS Composites PrePost. The results show that strength of T-beam structure is increased 21.6% when the fiber density along with beam length direction is two times bigger than transverse direction. It is expected that development of high strength T-beam structure using designed three-dimensional preform.

• Korean Journal of Materials Research
• /
• v.2 no.6
• /
• pp.461-467
• /
• 1992

A fabrication process for SiC whisker preform reinforced AC4A Al composites is being developed. The Al alloy used as the matrix in this study is AC4A. SiC whisker preform made by Tokai Carbon Co. Ltd. Shizuoka, Japan were used. These consisted of $\beta$-type single crystals 0.1 ~ 10${\mu}$m in diameter and 20~10${\mu}$m in length. The most adequate fabrication condition was that whisker preform was preheated up to 750~80$0^{\circ}C$, set into a mould preheated to ~40$0^{\circ}C$, molten Al alloy heated to ~80$0^{\circ}C$ and applied pressure 75MPa. And Si$C_w$reinforced AC4A composite was advanced above twice than AC4AI/M. Also it was not large effect by pressure at Si$C_w$ 20v/o.

• Korean Journal of Materials Research
• /
• v.28 no.1
• /
• pp.6-11
• /
• 2018

There are various manufacturing processes for pure $SiO_2$ that is used as abrasives, chemicals, filters, and glasses, and in metallurgy and optical industries. In the optical fiber industry, to produce $SiO_2$ preform, $SiCl_4$ is utilized as a raw material. However, the combustion reaction of $SiCl_4$ has caused critical environmental issues, such as ozone deficiency by chlorine compounds, the greenhouse effect by carbon dioxide and corrosive gas such as hydrochloric acid. Thus, finding an alternative source that does not have those environmental issues is important for the future. Octamethylcyclotetrasiloxane (OMCTS or D4) as a chlorine free source is recently promising candidate for the $SiO_2$ preform formation. In this study, we first conducted a vaporizer design to vaporize the OMCTS. The vaporizer for the OMCTS vaporization was produced on the basis of the results of the vaporizer design. The size of the primary particle of the $SiO_2$ formed by OMCTS was less than 100 nm. X-ray diffraction patterns of the $SiO_2$ indicated an amorphous phase. Fourier-transform infrared spectroscopy analysis revealed the Si-O-Si bond without the -OH group.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.38 no.1
• /
• pp.65-70
• /
• 2014

This paper introduces a preform design method for a ring rolling process with an outer step. Underfilling is one of the general defects of the profile ring rolling process. It occurs when the deformation amount is small or step depth of the profiled region is large. To prevent underfilling, increasing the deformation amount or using a preform of size similar to that of the final product are required. Furthermore, the filling limit equation is suggested based on the shape factor and deformation ratio for preventing defects in the products. The filling limit equation has been derived through finite element analyses and production tests for four different cases. For verifying the suggested method, realsized profile rolling tests were performed, and test results were compared with the predictions of the equation.

• Composites Research
• /
• v.28 no.6
• /
• pp.340-347
• /
• 2015

As resin impregnates through the fiber preform in vacuum assisted resin transfer molding process, the volume of fibers is changed by expansion of fiber mat according to filling time. It causes not only the change in dimension but also the decrease of mechanical properties of the composite product. Moreover, it results in the economic loss by increase of the used amount of resin especially in the large product such as wind turbine blade. In this study, the ways to control fiber volume fraction were investigated by both the experimental and theoretical analyses on the expansion of fiber preform as the preform was impregnated by resin in the VARTM process. Two kinds of swelling stage were observed as flow front progressed, which was analyzed by comparing the experimental and simulation results. The process parameters are expected to be optimized by investigating the swelling behavior of fiber preform in the manufacturing process of the composite product.

• Journal of the Korean Society of Manufacturing Process Engineers
• /
• v.16 no.6
• /
• pp.63-68
• /
• 2017

The purpose of this study is to improve the whitening phenomenon around the PET preform gate for blow molding. CAE analysis of plastic injection molding has been applied to design of preform shape and select the injection molding conditions. A ceramic insulation gate with lower thermal conductivity than metal is applied to improve the whitening phenomenon created around the gate in the injection molding process. According to the results of CAE analysis, the warpage deformation at the square corner was estimated to be about 0.34 mm at the bottom. From the results of the temperature history analysis, it was confirmed that the resin near the gate cooled more rapidly than the cavity. Ceramic insulated gates were fabricated to reduce the cooling rate and experiments were conducted to confirm the effectiveness of the whitening phenomenon improvement. As a result of the ceramic insulation gate experiment, it was confirmed that the whitening phenomenon was significantly reduced around the gate.

• Composites Research
• /
• v.34 no.4
• /
• pp.249-256
• /
• 2021

In this paper, the densification of a carbon/carbon composite during a chemical vapor infiltration (CVI) process is studied using a chemo-mechanical model. The multi-physics numerical model, developed in the previous research, couples computational fluid dynamics and major chemical reactions in the reactor. The model is especially utilized to study the effect of flow behavior around the preform on the densification. Four different types of "flow-guide" structures are placed to alter the gas flow around the preform. It is shown that the flow pattern and speed around the preform can be controlled by the guide structures. The process simulations demonstrate that the average density and/or density distribution of the preform can be improved by controlling the gas flow around the perform. In this study, a full industrial-scale reactor and process parameter were used.

• Journal of the Korean Society for Precision Engineering
• /
• v.27 no.1
• /
• pp.25-32
• /
• 2010

With the latest automobile technology, though the third generation common rail system requires high injection pressures up to 1,800bar, the next generation diesel engine is expected to require more higher pressures than the third generation. The common rail pipe requires higher strength because it is one of the parts in the common rail system, which is influenced directly by fuel under high pressure. Preform design is very important for preventing head of the common rail pipe from folding in the heading process. In this study, die angle, curvature, outer diameter of die and length of trapped part are selected as main parameters to obtain best preform shape minimizing radius of folding. Therefore optimal design is carried out by finite element analysis and Taguchi method through main parameters. Results of the finite element analysis have good agreements with those of the experiments in the actual field.