• 소성∙가공
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• 제6권5호
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• pp.446-455
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• 1997

A Combined extrusion operation consists of forward and backward extrusion forming and it is possible to make the process be simple by employing it. But the metal flow pattern induced by the operation is hard to analyze accurately because the flows are non-steady, which have at least two directions dependent upon each other. So engineers in the industrial factories had conducted the two extrusion operations separately. A new process was designed by the industrial expert for forming of an alu-minum preform using the combined extrusion operation. In this study, experiments and finite element analysis was carried out to determine the process parameters. Through the preliminary experiment, it was shown that warm forming condition was more desirable than cold or hot ones. And optimal shape of initial billet could be also determined. From the compatibility test, bonde-lube was chosen as the optimal lubricant and 20$0^{\circ}C$ as the material temperature by the inspection of micro-structure. The operation was simulated by the rigid-plastic finite element method to examine the metal flow. Disap-pearing of dead metal zone was observed as the punch fell down and desirable shape was obtained from the one operation. As a result of this study, 7 operations could be reduced and 225% of material saved.

• 대한기계학회논문집A
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• 제21권12호
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• pp.2055-2067
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• 1997

Values of process parameters in sheet metal forming can be estimated by various one-step inverse methods. One-step inverse methods based on deformation theory, however, cause some amount of error. The amount of error is generally increased as the deformation path becomes more complex. As a remedy, a new three dimensional multi-step inverse method is introduced for optimum design of blank shapes and strain distributions from desired final shapes. The approach extends a one-step inverse method to a multi-step inverse method in order to reduce the amount of error. The algorithm developed is applied to square cup drawing to confirm its validity by demonstrating reasonably accurate numerical results. Rapid calculation with this algorithm enables easy determination of an initial blank of sheet metal forming.

• 소성∙가공
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• 제17권4호
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• pp.278-283
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• 2008

This paper concerns the die face design for a heat protect panel aided by the finite element forming analysis in order to eliminate the surface defect and to improve the surface quality. The CAE procedure of the stamping process is introduced in order to reveal the reason of surface inferiorities and to improve surface quality. Complicated shape of the product induces the surface inferiorities such as wrinkling due to the insufficient restraining force of the forming blank and the non-uniform contact of the blank with the tools. This paper proposes a new guideline for the die design which includes the modification of tool shapes and addition of the draw-beads on the tool surface for ensuring the increased the restraining force with the uniform contact condition. The effectiveness of the proposed design is verified by the forming analysis and is confirmed by the tryout operation in the press shop. The analysis and test results show that the modified process parameters such as tool shapes and draw-beads can reduce the tendency of wrinkling and improve surface quality.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2009년도 춘계학술대회 논문집
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• pp.207-212
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• 2009

In order to optimize the press formability of incremental sheet forming for complex shape (e.g human face), a combination of both CAM and FEM simulation, is implemented and evaluated from the histories of stress and strain value by means of finite element analysis. Here, the results, using ABAQUS/Explicit finite element code, are compared with fracture limit curve (FLC) in order to predict and optimize the press formability by changing parameters of tool radius and tool down-step according to the orthogonal array of Taguchi's method. Firstly, The CAM simulation is used to create cutter location data (CL data). This data are then calculated, modified and exported to the input file format required by ABAQUS through using MATLAB programming. The FEM results are implemented for negative incremental sheet forming and then investigate by experiment.

• 대한기계학회논문집A
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• 제33권7호
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• pp.681-686
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• 2009

Direct laser metal forming technology was applied to restore the damaged mold surface. In order to estimate melting characteristics of the $20{\mu}m$ Fe-Cr-Ni powder, single layer experiments were performed at various levels of heat input. The process window of the $20{\mu}m$ Fe-Cr-Ni powder provided feasible process parameters for the smooth regular surface. The cross hatching scanning strategy on the multiple layer experiment was performed to reduce the thickness non-uniformity of edge portions compared with the one direction scanning. To estimate the coherence between the melted powder and the basematal, the tendency of hardness distribution has been observed. The hardness of the melted and the remelted zone was distributed from 400HV to 600HV. It is over 2 times compared of the hardness of the basemetal. Experimental results show that the mold restoring process using direct laser metal forming can be successfully applied in the mold repair industry.

• 대한화학회지
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• 제10권2호
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• pp.103-108
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• 1966

The effect of temperature on the critical micelle concentration of dodecylpyridinium chloride has been determined by electrical conductance method over the range from $5^{\circ}C\;to\;50^{\circ}C$. The values of the change in heat content, ${\Delta}H_m$, and the other thermodynamic parameters have been estimated using the equation of temperature dependence on the critical micelle concentration for the same temperature range. The significance of these thermodynamic quantities and their relations to the various current theories of micelle forming processes were discussed.

• 산업기술연구
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• 제18권
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• pp.217-223
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• 1998

The springback characteristics of some sheet metals such as commercially pure aluminium, mild steel and stainless steel in a forming process are investigated experimentally. Three geometrical parameters for evaluating springback in the plane-strain draw-bending, which was a benchmark model of NUMISHEET '93 conference, are defined. The measurement of the springback parameters is carried out accurately and easily by using an image analysis system developed in this study. The effects of the blank holding pressure and tensile strength of the material on the springback are also examined.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2000년도 하계학술대회 논문집
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• pp.9-16
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• 2000

A survey over the role of sol-gel processing and metal alkoxides in the thin film preparation is given. The basic chemistry of the sol-gel process is complex due to the different reactivities of the network forming and the wide variety of reaction parameters. Despite the important progress in the investigations of the mechanisms of thin film formation, a direct relation of reaction parameters to functional oxide properties is still very difficult.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2007년도 추계학술대회 논문집
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• pp.11-12
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• 2007

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part 1
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• pp.128-129
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• 2006