• 한국정밀공학회지
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• 제34권2호
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• pp.77-81
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• 2017

CP (Commercially Pure) titanium has been widely used in various industries such as in energy plants and bio-materials because of an excellent corrosion resistance and its non-toxicity to the human body. But there are limitations for usage as structural materials due to low strength. The tensile properties of CP titanium could be improved by microstructure refinement such as in a SPD (Severe Plastic Deformation) process. However, high strengthening of CP titanium wire is impossible by SPD processes like ECAP (Equal Channel Angular Pressing), HPT (High-Pressure Torsion), and the ARB (Accumulative Roll Bonding) process. The study purposes are to increase the strength of CP titanium wire by optimization of the cold drawing process and the harmonization with mechanical properties by heat treatments for the next forming process. The optimization process was investigated with regard to the design of drawing dies and the reduction ratio of cross sections. The elongations of high strength CP titanium were controlled by heat treatment.

• 한국정밀공학회지
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• 제34권2호
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• pp.83-87
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• 2017

A multi-step warm forging process for subminiature screws is investigated. Due to the low formability of Titanium alloys, bit forming of Titanium screws is difficult by cold forging. In order to overcome this low formability of Titanium alloys, two candidate processes, i.e., multi-step forging and warm forging are introduced. First, a multi-step (two-step) forging process is investigated. The punch shape and stroke of forging during the first step is designed via various analyses. Finally, the bit formability is investigated at different forging temperatures. Analyses are carried out for two-step forging at various temperatures and the formability under these thermal conditions is compared.

• 한국정밀공학회지
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• 제19권1호
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• pp.204-211
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• 2002

Today\`s industrialized plants are required to reduce SOx emitted from stacks at factories, utility power stations, etc. For this purpose, flue gas desulfurization(FGD) system is installed in thermal power plant and gas-gas heater(GGH) is used to play a vital role to reheat the wet treated gas from FGD. The sector plates are located at cold and hot sides of gas-gas heater. They serve as sealing to prevent mixing treated and untreated gases. Therefore, the deformation of the sector plate due to its dead weight and gas pressure should be considered as major factor for the sector plate design. And finite element analysis(FEA) for rotor part in GGH is performed with original model and two weight-reduced models with different diaphragm thickness, respectively. Stress concentrations at rotor diaphragm happen due to the dead weight, pressure difference between treated and untreated gas, and thermal distribution in the rotor. As the thickness of diaphragm is decreased, the stress level is increased. The direction of treated gas and untreated gas flow may affect the stress level.

• 한국정밀공학회지
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• 제16권10호
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• pp.164-171
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• 1999

An optimum blank design technology is required for near-net of net-shape cold forming using sheets. Originally, the backward tracing scheme has been developed for preform design in bulk forming, and applied to several forming processes successfully. Its key concept is to trace backward from the final desirable configuration to an intermediate preform of initial blocker. A program for initial blank design in sheet forming which contains the capabilities of forward loading simulation by the finite element method and backward tracing simulation, has been developed and proved the effectiveness by applying to a square cup stamping process. In the blank design of square cup stamping, the backward tracing program can produce an optimum blank configuration which forms a sound net-shape cup product without machining after forming. Another general application appears in the blank design of a cup stamping with protruding flanges, one of typical automobile components. The blank configurations derived by backward tracing simulation have been confirmed by a series of loading simulations. The approach or decision of an initial blank configuration presented in this study will be a milestone in fields of sheet forming process design.

• 한국정밀공학회지
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• 제16권6호
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• pp.45-51
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• 1999

The semi-solid forging is a new forging technology in which the billet is heated to the semi-solid state coexisting liquid and solid phase for making globular microstructure and subsequently formed. As the semi-solid forging is compared with conventional casting such as die casting and squeeze casting for the characteristics of its process, the product without inner defects such as gas porosity and segregation can be obtained and its microstructure is globular grain. Simutaneously, its mechanical properties are improved by globular microstructure and the lower temperature of the slug causes the cycle time of manufacturing to be shortened and the die life to be lengthened. As it is compared with conventional cold and hot forging, it is possible to minimize the equipment of production owing to a lower forming load and reduce the number of process by a followed treatment for complex shaped product. Therefore it is needed to confirm the quality of a semi-solid forged product by defining its characteristics quantitatively under these advantages. This paper investigates the formability of a master cylinder by its forming variables. And the microstructural characteristics and mechanical property of it is also studied.

• 한국자동차공학회논문집
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• 제15권4호
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• pp.108-114
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• 2007

This research represents the catalytic converter for application in the motorcycle. We have to consider about catalytic converter for reducing exhaust gas strength regarding the displacement volume enlargement. The catalytic converter has been widely used to satisfy the regulations of pollutant emissions from automobiles. Recently, all catalytic converter researches are about automobile. Study about motorcycle catalytic converter has not been conducted yet. In this study, flow uniformity and pressure distribution were simulated in the monolithic inlet of catalytic converter for motorcycle. Exhaust pulsation pressure was set as transient condition about. It was found that flow uniformity shown in base model (0.85) was lower than megaphone model (0.98).

• 한국자동차공학회논문집
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• 제15권4호
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• pp.132-138
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• 2007

Experimental results of pulsating pressure behavior inside a chamber have been confirmed by computational work. Inside-cylinder pressure shows unstable condition at low rpm. This is caused by plate-type suction valve. It has effect up to inlet of the chamber. But trembling phenomenon is reduced as the pressure is enlarged by increasing the rpm. Result comparison between experimental and numerical analysis shows pulsation reduction is affected by the chamber. We can confirm that compressible effect of the working flow is shown at chamber inlet by increasing rpm. On the other side, this effect is declined at chamber outlet by increasing rpm. It means outlet pressure is going on balance with atmosphere pressure. Buffer plate-type chamber has efficiency of pulsation flow reduction.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2007년도 추계학술대회 논문집
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• pp.173-176
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• 2007

The characteristics of the tool system give many effects into the costs and qualities for the finished components. This study proposes a new method for manufacturing of high manufacturing productivity, production process reduction and low cost through back pressure forming. The Lock-up hub is manufactured through many processes, such as upsetting($1^{st}$ Forming), piercing, direct extrusion($2^{nd}$ Forming), final sizing process($3^{rd}$ Forming). In this study, process design for closed-die forging of a Lock-up hub used for a component of automobile transmission was made using three-dimensional finite element simulations, and the strain distributions and velocity distributions are investigated through the post processor. The rigid-plastic finite-element method for back pressure forging has been used in order to reduce development time and die cost. Using the FEM simulation, we found the optimum value of back pressure. The prototypes of Lock-up hub parts were forged into the net-shape. In the experiment, lead precision of tooth are measured by the CCMM(Contact Coordinate Measuring Machine). The dimensional accuracy of forged part was improved up to the 40% when back press was applied.

• 한국정밀공학회지
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• 제21권7호
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• pp.153-162
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• 2004

This paper describes a research work on the die design for the deep drawing ＆ ironing(D.D.I.) of high pressure gas cylinder. D.D.I die set is large-sized die used in horizontal press, which is usually composed of drawing, and ironing die. Design method of D.D.I. die set is very different from those of conventional cold forging die set.. Out diameter of the die set is fixed because of press specification and out diameter of the insert should be as small as possible for saving cost of material. In this study, D.D.I die set has been designed to consider those characteristics and the feasibility of the designed die has been verified by FE-analysis. In addition, the automated system of die design has been developed in AutoCAD R14 by formulating the applied methods to the regular rules.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2005년도 추계학술대회 논문집
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• pp.627-631
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• 2005

In this study, low fatigue behavior of laser welded sheet metal were investigated. Before welding, the cross section of butt joint was prepared only by fine shearing without milling process. Specimens were same sheet metal and welding condition that using automobile manufacturing company at present. Butt joint of cold rolled sheet metal was welded by $CO_2$ laser. It is used that welding condition such as laser welding speed was 5.5m/sec and laser output power was 5kW for 0.8mm and 1.2mm sheet metal. The laser weldments were machined same or different thickness and same or different material. In order to mechanical properties of around welding zone, hardness test was performed. Hardness of welding bead is about 2 times greater than base material. We performed the low cycle fatigue tests for obtaining fatigue properties about thickness and the weld line direction of specimen. The results of strain controlled low cycle fatigue test indicate that all specimens occur cyclic softening, as indicated by the decrease in stress to reach a prescribed strain.