• 한국소성가공학회:학술대회논문집
• /
• 한국소성가공학회 2003년도 제4회 박판성형 심포지엄
• /
• pp.53-57
• /
• 2003

In order to make a doubly curved sheet metal effectively, a sheet metal farming process has been developed by adopting the flexibility of the incremental forming process and the principle of bending deformation which causes slight deformation to thickness. The developed process is an unconstrained forming process with no holder. For this study, the experimental equipment is set up with the roll set which consists of two pairs of support rolls and one center roll. In the experiments using aluminum sheets, it is found that the curvature of the formed sheet metal is determined by controlling the distance between supporting rolls in pairs and the forming depth of the center roll and it also depends on the thickness of the sheet metal. In order to check the effect of process parameters on the generation of sheet metal curvatures in this process, the orthogonal array is adopted. From the experimental results, among the process parameters, the distance between supporting rolls in pairs along the same direction of one principle radius of curvature as well as the forming depth and the thickness of the material is shown to influence the generation of curvature in the same direction significantly. That is, the other distance between supporting rolls in pairs which are not located in the same direction of one principle radius of curvature, does not have an significant effect on the generation of the curvature in that direction. It just affects the generation of curvature in its own direction mainly with the forming depth and the thickness of the material.

• 소성∙가공
• /
• 제17권6호
• /
• pp.412-419
• /
• 2008

Using lightweight materials in vehicle manufacturing in order to reduce energy consumption is one of the most effective approach to decrease pollutant emissions. As a lightweight material, magnesium is increasingly employed in automotive parts. However, because of its hexagonal closed-packed(HCP) crystal structure, in which only the basal plane can move, the magnesium alloy sheets show low ductility and formability at room temperature. Thus the press forming of magnesium alloy sheets has been performed at elevated temperature within range of $200^{\circ}C{\sim}250^{\circ}C$. Here we try the possibility of sheet metal forming at room temperature by adopting incremental forming technique with rotating tool, which is so called as rotational-incremental sheet forming(RISF). In this rotational-incremental sheet forming the spindle tool rotates on the surface of the sheet metal and moves incrementally with small pitch to fit the sheet metal on the desired shape. There are various variables defining the formability of sheet metals in the incremental forming such as speed of spindle, pitch size, lubricants, etc. In this study, we clarified the effects of spindle speed and pitch size upon formability of magnesium alloy sheets at room temperature. In case of 0.2, 0.3 and 0.4mm of pitch size with hemispherical rotating tool of 6.0mm radius, the maximum temperature at contact area between rotating tool and sheet metal were $119.2^{\circ}C,\;130.8^{\circ}C,\;and\;177.3^{\circ}C$. Also in case of 300, 500, and 700rpm of spindle speed, the maximum temperature at the contact area were $109.7^{\circ}C,\;130.8^{\circ}C\;and\;189.8^{\circ}C$.

• Computers and Concrete
• /
• 제26권3호
• /
• pp.213-226
• /
• 2020

The present study covenants with the static and free vibration behavior of nanocomposite sandwich plates reinforced by carbon nanotubes resting on Pasternak elastic foundation. Uniformly distributed (UD-CNT) and functionally graded (FG-CNT) distributions of aligned carbon nanotube are considered for two types of sandwich plates such as, the face sheet reinforced and homogeneous core and the homogeneous face sheet and reinforced core. Based on the first shear deformation theory (FSDT), the Hamilton's principle is employed to derive the mathematical models. The obtained solutions are numerically validated by comparison with some available cases in the literature. The elastic foundation model is assumed as one parameter Winkler - Pasternak foundation. A parametric study is conducted to study the effects of aspect ratios, foundation parameters, carbon nanotube volume fraction, types of reinforcement, core-to-face sheet thickness ratio and types of loads acting on the bending and free vibration analyses. It is explicitly shown that the (FG-CNT) face sheet reinforced sandwich plate has a high resistance against deflections compared to other types of reinforcement. It is also revealed that the reduction in the dimensionless natural frequency is most pronounced in core reinforced sandwich plate.

• 한국소성가공학회:학술대회논문집
• /
• 한국소성가공학회 2001년도 추계학술대회 논문집
• /
• pp.358-363
• /
• 2001

In sheet metal forming, material cost and die process number are very important manufacturing process for an economic die-making. In this report on implemention of a computer aided sheet-metal nesting program for nesting of irregular shaped blank on ae coil strip of limit width. The result of the computing in the nesting program reduced material cost and die process number.

• 한국전기전자재료학회:학술대회논문집
• /
• 한국전기전자재료학회 2001년도 하계학술대회 논문집
• /
• pp.1100-1103
• /
• 2001

(1) By comparing and analyzing the distribution of brightness as domestic lamps and Japanese products go thinner and lighter, we set an effective design standard. (2) By comparing and analyzing the feature, brightness, chromaticity and uniformity of domestic LGPs and Japanese products, early home-manufacturing and stabilization in home-manufacturing are possible. (3) By comparing and analyzing the distribution of brightness as sheets are varied, we can design an ideal sheet composition.

• 한국소성가공학회:학술대회논문집
• /
• 한국소성가공학회 1999년도 추계학술대회논문집
• /
• pp.18-21
• /
• 1999

The wrinkling of thin sheet metal induced by compressive instability is one of major defects in sheet metal forming processes. compressive instability is influence by many factors such as mechanical properties of the sheet material geometry of the sheet contact conditions and plastic anisotropy. The analysis of compressive instability in a plastically deforming body is rather difficult because the effects of the above-mentioned factors are rather complex and the instability behavior may show swide variations even for small deviations of the factors. in this work the bifurcation theory is introduced for the finite elemental analysis of the instability behavior of a thin sheet with initially sound geometry and property. All the above-mentioned factors are conveniently considered by the finite element method. The instability limit is found by introducing a criterion scheme into the incremental analysis and the post-bifurcation behavior is analyzed by introducing the branching scheme. Wrinkling initiation and growth in the deep drawing process are analyzed.

• 한국정밀공학회지
• /
• 제24권2호
• /
• pp.103-109
• /
• 2007

In fatigue life prediction, it is important that fatigue life is affected by crack closure phenomenon in thin sheet Al alloy. In this research, we attempt to (1)analyze the characteristics of fatigue crack propagation in constant loading condition for thin sheet Al 2024-T3 alloy which is generally used in transportation structures, (2)identify the crack closure phenomenon in thin sheet comparing experimental results of thin and thick sheet specimen under same fatigue loading condition. In using the fatigue related material constants from these fatigue crack propagation analysis, we attempt to (3)operate the fatigue life estimating process with considering crack closure phenomenon and (4)analyze the experimental and prediction results of fatigue life in thin sheet Al alloy.

• 한국건축시공학회:학술대회논문집
• /
• 한국건축시공학회 2008년도 춘계 학술논문 발표대회
• /
• pp.73-77
• /
• 2008

In this study, we would like to study on the application of roof exposure waterproofing method of joint stability through shiplap rubberized asphalt color sheet to complement problem of fracture, exfoliation and water leakage by existing roof exposure sheet waterproofing material joint weakness. Accordingly, examined basis performance and stability for joint that shiplap rubberized asphalt color sheet through test of that tensile strength, bonding strength, water permeability after bonding, peel resistance after bonding, lengthen resistance after bonding and hang resistance after bonding. The results of this study, waterproofing method to using shiplap rubberized asphalt color sheet is judged to solved fracture, exfoliation and water leakage problems happened in joint by problem was joint of exposure sheet by minimizing gap of joint being integration by shiplap.

• 소성∙가공
• /
• 제16권4호
• /
• pp.317-322
• /
• 2007

In order to investigate the cause and condition of fluting in tangential bending of low carbon steel sheet, an analytic analysis, an experiment and a series of finite element analysis for bending process were done. The fluting in bended sheet was related with the yield point elongation of material. Due to the yield point elongation, unstable plastic hinge was occurred in course of bending of elastic perfectly plastic sheet. According to the analysis and computational results, lower yield point elongation than 5% was required to prevent fluting in 0.5-0.6t sheet in $15{\sim}25mm$ radius bending. The tendency of fluting occurrence was reduced as decreasing the radius of bending, increasing thickness of bended sheet, and removing irregularity in sheet and bending processes.

• 한국소성가공학회:학술대회논문집
• /
• 한국소성가공학회 2009년도 춘계학술대회 논문집
• /
• pp.164-167
• /
• 2009

The applications of the aluminum alloy sheets to the auto-body panels are dramatically increasing for weight reduction of the automobiles. However, low formability of the aluminum alloy sheet compare to the steel sheet can be obstacles in tool manufacturing process. Therefore, much of yield criteria for the anisotropic material such as the aluminum alloy sheet have been observed. In this study, the biaxial tensile test and FLD test for the aluminum alloy sheet are performed. The results are compared with Hill's 1948 and Hill's 1990 model by means of theoretical predictions. Finite element analysis also performed using the proposed method for the real panel.