• 한국생산제조학회지
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• 제22권1호
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• pp.173-177
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• 2013

The purpose of this paper is to investigate the influences on mechanical properties of two-stroke cycle motor pistons manufactured by casting, conventional forging and powder forging, through the comparison of characteristics, merits and disadvantages of each forming technology. For each forming technology, the optimal process parameters were determined through the experiments for several conditions, and microstructure, hardness, tensile strength and elongation of pistons are compared and analyzed. In conventional forging process, material temperature was $460^{\circ}C$ and the die temperature was $210^{\circ}C$ for the Al 4032. The optimal condition was found as solution treatment under $520^{\circ}C$ for 5 hours, quenching with $23^{\circ}C$ water, and aging under $190^{\circ}C$ for 5 hours. In powder forging process, the proper composition of material was determined and optimal sintering conditions were examined. From the experiment, 1.5% of Si contents on the total weight, $580^{\circ}C$ of sintering temperature, and 25 minutes of sintering time were determined as the optimal process condition. For the optimal condition, the pistons had 76.4~78.3 [HRB] of hardness, and 500 [MPa] of tensile strength after T6 heat treatment.

• 한국정밀공학회지
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• 제2권2호
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• pp.31-42
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• 1985

The metal flow and the strain distribution is investigated for the steady state and non-steady state bulk deformation processes by using an improved visioplasticity method which includes the effective smoothing scheme. The comparison of various smoothing schemes leads to the selection of the five- point least square smoothing method which is employed to reduce the measurement errors. As a steady state forming process experiments are carried out for axisy- mmetric forward extrusion through conical and curved dies of various area reduc- tions using Aluminum and steel billets. Axisymmetric backward extrusion is chosen for a nonsteady state forming process. In axisymmetric forward extrusion the results from visioplasticity show that the curved die of a fourth-order polynomial renders more uniform distribution of strain rates and strains. Higher reduction leads to greater strain rates at the outer side of the billet. The visioplastic observation for axisymmetric backward extrusion as a non-steady state deformation process shows the concentration of higher strain at the inner wall of the extruded product. The visioplastic results in forward extrusion are in agreement with the computed results by the finite element method. It is thus shown that the visio- plasticity combined with a smoothing technique is an effective method to determine the pattern and the distribution of strain rates and strains.

• 한국정밀공학회지
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• 제16권12호
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• pp.168-173
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• 1999

It is investigated that internal defect of planetary gear which consists of two gears with different number of teeth on both side. The internal defect, central burst, begin to form at the place of adiabatic shear band which usually has maximum ductile fracture value during the forming operation, forward and backward extrusion. It makes the plastic forming of planetary gear difficult. The prediction of defect to minimize the cost to produce the planetary gear. The finite element simulation code DEFORM is applied to analyze the defects. In the analysis, the toothed gears are assumed as axisymmetric cylinders whose diameters are equal to those of pitch circles of the each gears. Experiments were carried out with the SCM415 alloy steel as billet material and AIDA 630-ton knuckle-joint press. The calculated results and experimental inspections are compared to design a die and blank without defects and the results are useful to predict the internal defect.

• 소성∙가공
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• 제22권3호
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• pp.123-132
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• 2013

Hot stamping, which is the hot pressing of special steel sheet using a cold die, can combine ease of shaping with high strength mechanical properties due to the hardening effect of rapid quenching. In this paper, a thermo-mechanical analysis of hot stamping using the finite element method in conjunction with phase transformations was performed in order to investigate the plastic deformation behavior, temperature history, and mechanical properties of the stamped car part. We also conducted a fully coupled thermo-mechanical analysis during the stamping and rapid quenching process to obtain the mechanical properties with the consideration of the effects of plastic deformation and phase transformation on the temperature histories at each point in the part. The finite element analysis could provide key information concerning the temperature histories and the sheet mechanical properties when the phase transformation is properly considered. Such an analysis can also be used to determine the effect of cyclic cooling on the tooling.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1996년도 춘계학술대회 논문집
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• pp.819-823
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• 1996

In the large steel ingosts, void defects exhibiting microvoid shapes are inevitably formed in the V-segregation zone of the ingots during solidification. In the hot open-die forging process, material properties are improved by eliminating internal porosity. The void size is practically very small as compared with the huge large ingot. Thus, for deformation analysis of a large ingot, a massive number of elements are needed in order to describe a void surface and to uniform mesh sturcture. In the present work the Global/Local scheme has been introduced in order to reduce the computational time and to easily generate the mesh system as a void module of local mesh for obtaining the accurate solution around a void. The procedure of the global- local method consists of two steps. In the first step global analysis is carried out which seeks a reasonably good solution with a cpurse mesh system without describing a void. Then, a local analysis is performed locally with a fine mesh system under the size-criterion of a local region. The computational time has been greatly reduced. Though the work it has been shown that large ingot forging incorporation small voids can be effectively analyzed by using the proposed Global/Local scheme.

• 열처리공학회지
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• 제18권3호
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• pp.172-176
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• 2005

Modern automobiles are built with a steadily increasing variety of materials and semifinished products. The traditional composition of steel sheet and cast iron is being replaced with other materials such as aluminum and magnesium. But low formability of these materials has prevented the application of the automotive components. The formability can be enhanced by conducting the warm hydroforming using induction heating device which can raise the temperature of the specimen very quickly. The specimen applied to the test is A6061, A7075 extruded tubes which belong to the age-hardenable aluminum alloys. But in the case of A6061 age hardening occurs at room temperature or at elevated temperatures before and after the forming process. In this study the effects of the heating condition such as heating time, preset temperature, holding time during die closing and forming time on the hydroformability are analyzed to evaluate the phenomena such as dynamic strain hardening and ageing hardening at high temperatures after the hydroforming process.

• 한국정밀공학회지
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• 제19권3호
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• pp.101-106
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• 2002

This paper presents an experimental investigation of high speed machining of dies and molds. Several critical issues involved with the high speed machining of QRO90 tool steel of hardness up to HRc62, have been studied and explained from a detail analysis of experimental observations. The experiments were performed using ball end mills. The effect of different process parameters on tool life and surface finish produced was also investigated. The cutting parameters involved were; cutting speeds in the range of 100 to 40 / m/min, axial depth of cut from 0.1 to 0.5mm, pick feed of 0.1 to 0.5mm. Run out and acceleration signals were observed during the experiment to investigate cutting slates. Compressed air and flood coolant were used and the effect of coolant on tool life was also determined.

• 소성∙가공
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• 제12권8호
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• pp.702-709
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• 2003

In the automotive industry hydroforming of sheet metal pairs have received special attention because materials for various sheet metal components of vehicles have changed into the high strength steel, aluminum, and titanium blank having low formability. Uniform deformation over the whole region is a main advantage in the sheet hydroforming process. Because upper and lower parts could be produced simultaneously with one tool, hydroforming of sheet metal pairs is competitive in reducing the lead-time and development cost. In this paper, the multi-stage hydroforming process of sheet pair is proposed in order to increase the formability of a structural part like the oil pan shape. The upper die for forming oil pan shape is divided into two parts which can move separately. By the finite element simulation, the design parameters such as geometry of the tool and detailed specification of hydraulic pump were calculated and verified. For the strict comparison of the proposed process, the blank holding force is kept to a constant value during deformation by hydraulic valve. The deformed shape and strain distribution of the manufactured parts with the proposed process are compared with the results of simulation. In the multi-stage hydroforming process, maximum thickness strain was improved by more than 30 percent.

• 소성∙가공
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• 제27권3호
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• pp.139-144
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• 2018

Many studies have been conducted on the process of forming magnesium alloy sheets to reduce the body weights of vehicles. Magnesium has a lower specific gravity than steel and also has a higher specific strength. Mg alloy sheets have low formability and a lot of springback due to their limited ductility and low young's modulus. As the temperature increases, the yield strength of the material decreases. Warm forming increases the formability and minimizes the springback of a material by heating it and the die to reduce the required load at forming. In this study, the temperature of the AZ31B sheet was controlled in order to reduce springback and increase formability. However, as the temperature increased, the deformation characteristics of the material changed and the radius of curvature of the material increased. The load and springback amount required for forming were analyzed according to the temperature and the bottoming force in the bending deformation.

• 산업기술연구
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• 제19권
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• pp.67-74
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• 1999

The mechanical properties including forming limit and deep-drawability of commercially-used sheet metals were experimentally estimated in this study. Uniaxial tensile test to obtain basic mechanical properties was carried out, followed by limiting dome height (LDH) test and forming limit diagram (FLD) test to quantitatively evaluate the sheet-formability. Deep drawing and reverse drawing tests were also performed to find out the critical values of the blank holding force and the gap between the die and the blank holder which enabled the deep drawing and reverse drawing of a successful cop without any wrinkle or fracture. The thickness of the cup wall along the rolling-, transeverse- and $45^{\circ}$-directions was measured and compared with one another. And the punch force-stroke curve and the critical punch force expected from the theory coincided with the experimental result very well for mild steel while not for aluminium alloy.