• Journal of the Korean Society for Precision Engineering
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• v.21 no.1
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• pp.32-39
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• 2004

Traditional forging of a hollow T-shaped part has been applied to forge a solid T-shaped product from a solid billet and then to machine the hollow in that. In a case, a hollow T-shaped part can be forged by backward-extruding from a solid billet. In this study, four types of forging were suggested for manufacture of hollow T-shaped parts. Forging simulations for each of these forging methods were carried out to investigate folding defect, metal flow pattern, effective strain, and forging loads. Experimental works were carried out to be compared with the simulation results. Here, the ratio of the thickness of the hollow tube to that of the flange was selected to investigate a forging defect like folding.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1995.04b
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• pp.204-208
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• 1995

Copper magnetron anode of a microwave-oven consists of an cylindrical outer-tube and various inner-vanes. The magnetron anode is produced by the complex process ; vane blanking, pipe cutting and sliver-alloy brazing of vanes. Recently, the backward extrusion process for forming vanes has been developed to avoid the complex procedures. The developed process is analyzed by using upper-bound elemental technique(UBET). In the UBET analysis, the upper-bound load, the configuration and the vane-height of final extruded product are determined by minimizing the total power consumption with respect to chosen parameters. To verify theoretical analysis, experiments have been carried out with pure plasticine billets at room temperature, using different web-thickness and number of vanes. The theoretical predictions both for forming load and vane-height are in reasonable agreement with the experimental results.

• Transactions of the Korean Society of Automotive Engineers
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• v.9 no.6
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• pp.160-169
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• 2001

To predict busting failure in tubular hydroforming, the criteria for ductile fracture proposed by Oyane is combined with the finite element method. From the histories of stress and strain in each element obtained from finite element analysis, the fracture initiation site is predicted by mean of the criterion. The prediction by the ductile fracture criterion is applied to three hydroforming processes such as a tee extrusion, an automobile rear axle housing and lower am. For these products, the ductile fracture integral I is not only affected by the process parameters, but also by preforming processes. All the simulation results show the combination of the finite element analysis and the ductile fracture criteria is useful in the prediction of farming limit in hydroforming processes.

• Journal of the Korean Society for Heat Treatment
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• v.17 no.3
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• pp.165-172
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• 2004

Compared with the hydroforming technology for steel, the hydroforming technology for aluminum has not been actively investigated. Recently, the hydroforming of high strength aluminum tubes has attracted great interest because of its good strength to weight ratio. In this study, front side member (FSM) is fabricated with the hydroforming of aluminum tube and the mechanical properties and dimensional accuracy of the hydroformed FSM is investigated. For hydroforming process, extruded aluminum tubes with ribs to improve the structural rigidity are used. To ensure the mechanical properties, the aluminum tubes are T6 heat-treated before hydroforming.

• Journal of the Korean institute of surface engineering
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• v.34 no.6
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• pp.575-584
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• 2001

Erosion due to abrasive particles contained in gas streams from boilers has been emerged as a significant problem in the coal fired power plants. Particle erosion accounted for approximately 50% of boiler failures and especially flyash erosion was responsible for 20~30% of emergency boiler shutdowns. Particularly, because of the high ash loading and high velocity, most erosion occurs in the boiler tubes and economiser tube bank where the direction of the gas stream changes to $180^{\circ}$ .In this study, a high temperature particle erosion tester was used to evaluate erosion rate in a simulated environment. The erosion parameters such as erosion temperature, particle impact angle, particle velocity and various particle size were changed. Flyash is the combustion product of the pulverized coal, where size is ranging from 1 to $200\mu\textrm{m}$. Flyash composed of mainly SiO$_2$, $A1_2$$_O3$, and $Fe_2$$O_3$has dense spherical particles and irregular particles containing numerous pores and cavities. From the erosion tests at various conditions, the maximum erosion was experienced at impact angles of $30^{\circ}$ to $60^{\circ}$ In addition, erosion rate increased in proportional to velocity and temperature. And from the observation of the eroded surfaces, it was also concluded that 304 stainless steel was mainly eroded by extrusion-forging at high impact angle ($90^{\circ}$) and by microcutting mechanism at low impact angles ($30^{\circ}$ and $45^{\circ}$).

• Journal of Korea Foundry Society
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• v.43 no.5
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• pp.223-229
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• 2023

In this study, STS316L produced by a double-melting process involving vacuum induction melting (VIM) and vacuum arc remelting (VAR) was subjected to extrusion and drawing to form a tube and was subsequently electrolytic polished (EP). The grain size of the obtained STS316L without EP was approximately 55 ㎛, with no difference found after EP. The thickness of the EP layer was measured by AES and TEM, showing values of approximately 10 nm and 15 nm, respectively. After EP, the Cr/Fe and CrO/FeO ratios of the passive layer increased from 1.48 to 1.62 and from 2.15 to 2.26, respectively, while the surface roughness decreased significantly from 0.255 to 0.024 ㎛. Consequently, the corrosion rate decreased in both NaCl and HCl solutions after the EP process. Additionally, the amounts of eluted Cr and Fe ions were reduced from 1.2 to 0.8 ppb and 10.3 to 0.8 ppb, respectively. Furthermore, polarization tests revealed that STS316L treated with EP required a lower current density to reach a passive state, indicating that corrosion behavior was retarded.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.30 no.2
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• pp.153-162
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• 2020

Objectives: 3D printing technologies have become widely developed and are increasingly being used for a variety of purposes. Recently, the evaluation of 3D printing operations has been conducted through chamber test studies, and actual workplace studies have yet to be completed. Therefore, the objective of this study was to determine the emission of volatile organic compounds(VOCs), metals, and particles from printing operations at a workplace. This included monitoring conducted at a commercial 3D printing service workplace where the processes involved material extrusion, material jetting, binder jetting, vat photo polymerization, and powder bed fusion. Methods: Area samples were collected with using a Tenax TA tube for VOC emission and MCE filter for metals in the workplace. For particle monitoring, Mini Particle Samplers(MPS) were also placed in the printer, indoor work area, and outdoor area. The objective was to analyze and identify particles' size, morphology, and chemical composition using transmission electron microscopy with energy dispersive spectroscopy(TEM-EDS) in the workplace. Results: The monitoring revealed that the concentration of VOCs and metals generated during the 3D printing process was low. However, it also revealed that within the 3D printing area, the highest concentration of total volatile organic compounds(TVOC) was 4,164 ppb at the vat photopolymerization 3D printing workplace, and the lowest was 148 ppb at the material extrusion 3D printing workplace. For the metals monitoring, chromium, which, is carcinogenic for humans, was detected in the workplace. As a characteristic of the particles, nano-sized particles were also found during the monitoring, but most of them were agglomerated with large and small particles. Conclusions: Based on the monitoring conducted at the commercial 3D printing operation, the results revealed that the concentration of VOCs and metals in the workplace were within Korea's occupational exposure limits. However, due to the emission of nano-sized particles during 3D printing operations, it was recommended that the exposure to VOCs and metals in the workplace should be minimized out of concern for workers' health. It was also shown that the characteristics of particles emitted from 3D printing operations may spread widely within an indoor workplace.

• Journal of the Korean Electrochemical Society
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• v.7 no.2
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• pp.94-99
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• 2004

Anode-supported flat tubular solid oxide fuel cell (SOFC) was investigated to increase the cell power density. The anode-supported flat tube was fabricated by extrusion process. The porosity and pore size of Ni/YSZ ($8mol\%$ yttria-stabilized zirconia) cermet anode were $50.6\%\;and\;0.23{\mu}m$, respectively. The Ni particles in the anode were distributed uniformly and connected well to each other particles in the cermet anode. YSZ electrolyte layer and multilayered cathode composed of $LSM(La_{0.85}Sr_{0.15})_{0.9}MnO_3)/YSZ$ composite, LSM, and $LSCF(La_{0.6}Sr_{0.4}Co_{0.2}Fe_{0.7}O_3)$ were coated onto the anode substrate by slurry dip coating, subsequently. The anode-supported flat tubular cell showed a performance of $300mW/cm^2 (0.6V,\; 500 mA/cm^2)\;at\;500^{\circ}C$. The electrochemical characteristics of the flat tubular cell were examined by ac impedance method and the humidified fuel enhanced the cell performance. Areal specific resistance of the LSM-coated SUS430 by slurry dipping process as metallic interconnect was $148m{\Omega}cm^2\;at\;750^{\circ}C$ and then decreased to $148m{\Omega}cm^2$ after 450hr. On the other hand, the LSM-coated Fecralloy by slurry dipping process showed a high area specific resistance.

• The korean journal of orthodontics
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• v.44 no.5
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• pp.236-245
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• 2014

Objective: To evaluate the therapeutic effects of a preformed assembly of nickel-titanium (NiTi) and stainless steel (SS) archwires (preformed C-wire) combined with temporary skeletal anchorage devices (TSADs) as the sole source of anchorage and to compare these effects with those of a SS version of C-wire (conventional C-wire) for en-masse retraction. Methods: Thirty-one adult female patients with skeletal Class I or II dentoalveolar protrusion, mild-to-moderate anterior crowding (3.0-6.0 mm), and stable Class I posterior occlusion were divided into conventional (n = 15) and preformed (n = 16) C-wire groups. All subjects underwent first premolar extractions and en-masse retraction with preadjusted edgewise anterior brackets, the assigned C-wire, and maxillary C-tubes or C-implants; bonded mesh-tube appliances were used in the mandibular dentition. Differences in pretreatment and post-retraction measurements of skeletal, dental, and soft-tissue cephalometric variables were statistically analyzed. Results: Both groups showed full retraction of the maxillary anterior teeth by controlled tipping and space closure without altered posterior occlusion. However, the preformed C-wire group had a shorter retraction period (by 3.2 months). Furthermore, the maxillary molars in this group showed no significant mesialization, mesial tipping, or extrusion; some mesialization and mesial tipping occurred in the conventional C-wire group. Conclusions: Preformed C-wires combined with maxillary TSADs enable simultaneous leveling and space closure from the beginning of the treatment without maxillary posterior bonding. This allows for faster treatment of dentoalveolar protrusion without unwanted side effects, when compared with conventional C-wire, evidencing its clinical expediency.

• Transactions of the Korean Society of Automotive Engineers
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• v.25 no.1
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• pp.42-50
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• 2017

A study has been conducted to develop an aluminum EGR cooler for the LPL EGR system of a diesel engine. Aluminum has a much lower density and thermal conductivity that is about 12 times or more than that of stainless steel, so it is advantageous for use in an EGR cooler for weight reduction and cooling performance effects. A design process has been carried out to ensure heat dissipation performance in a restricted space to investigate the geometric parameters and satisfy the requirements for pressure drops at both fluid sides. The tubes of exhaust gas have been designed as extruded tubes. An aluminum EGR cooler consisting of extruded tubes entails a simpler manufacturing process compared to a stainless steel EGR cooler with conventional heat transfer fins. A prototype has been manufactured from the final model selected through the design process. The performance of the aluminum EGR cooler was evaluated and compared with that of the conventional one. The weight of the aluminum EGR cooler is reduced by 22.9%, while performance is significantly improved.