• 소성∙가공
• /
• 제19권3호
• /
• pp.179-184
• /
• 2010

The present study is focused on the deep drawability and product qualities of ultra thin beryllium copper sheet metal. The goal of this research is to investigate the limit drawing ratio in deep drawing of ultra thin beryllium copper metal. For the experiment, beryllium copper(C1720, $50{\mu}m$ in thickness) is used. Tensile test are also carried out to find out the material properties. Deep drawing experiments are carried out in Universal Testing Machine(UTM) to obtain limit drawing ratio. Deep drawing tests are carried out for various specimen sizes. Teflon film is used as a lubricant and constant blank holding force is imposed. Sheet thickness and surface hardness are measured along radial direction after deep drawing. Thickness is measured using optical microscope. For beryllium copper(C1720), the maximum LDR of 2.4 is obtained when the die shoulder radius is 20 or 30 times of sheet thickness.

• 한국자동차공학회논문집
• /
• 제2권1호
• /
• pp.96-105
• /
• 1994

Cup drawing tests were performed to evaluate the friction characteristics of sheet metals. The linear relationship between drawing force and blank holding force obtained from the cup drawing test was used to calculate the coefficient of friction of the sheet metal. The friction coefficient was compared to that from conventional draw bead friction test. It was clarified that the cup drawing test can be used as a simple and convenient method for evaluating the friction characteristic of the sheet metal and also lubricity of the lubricant used.

• 소성∙가공
• /
• 제16권5호통권95호
• /
• pp.364-369
• /
• 2007

The effect of temperature on the forming limit diagram was investigated for AZ31B magnesium alloy sheet through the limit dome height test in the range from room temperature to $300^{\circ}C$. The formability of AZ31B sheet was improved significantly according to the increasing temperature. Also we studied the springback characteristics through the 2D draw bending test with different blank holding forces at elevated temperatures. Springback quantity was considerably reduced as temperature went up. The blank holding force in the range used, however, had little influence on springback. Experimental results obtained in this study may provide a material database for AZ31B sheet.

• Journal of Advanced Marine Engineering and Technology
• /
• 제31권6호
• /
• pp.736-743
• /
• 2007

Laser welding has the advantage of high welding speed and Provides low heat distortion Thus laser welding is a very attractive process for joining thin steel sheet and surface treated steel sheet. And the major item in market for surface treated steel sheet is zinc coated steel. However. the laser welding of zinc coated steel is very difficult because of its low boiling point. Compared with zinc, on the other hand, aluminum has a high boiling point. Thus, laser weldability of aluminized steel is better than that of zinc coated steel. Moreover aluminized steel sheet is a material with excellent heat resistance, thermal reflection and corrosion resistance. The results of laser weldability of the aluminized steel for the full penetration welding will be described in this paper We focused on the investigation of the phenomenons caused by coating condition and behavior of aluminum in weld.

• 소성∙가공
• /
• 제10권2호
• /
• pp.91-100
• /
• 2001

A sectional FEA program is developed lot analyzing forming processes of sandwich sheets, which are intensively used recently as a lightweight material of an automobile body. The aluminum sandwich sheet consists of two aluminum skins and a polyprophylen core in between. The aluminum sandwich sheet is dominantly effected by the bending effects in small radius of curvature, so that an appropriate description of bending effects is required to analyze the forming processes. For the evaluation of bending effects, the bending equivalent forces are calculated from the bending moment computed using the curvature of the tool and are added to the membrane stretch forces. To verify the validity of the developed program the sectional FEA results in stretch/draw forming Processes of a square cup and draw forming Processes of an outer hood panel were compared with the measurements.

• 한국공작기계학회:학술대회논문집
• /
• 한국공작기계학회 2004년도 추계학술대회 논문집
• /
• pp.162-169
• /
• 2004

In press forming of sheet metals, the material sheet is usually subjected to very large plastic strain under in-plane stressing. Moreover, the sheet also very often is subjected to out-of-plane compressive force between tools such as the upper and lower dies, the blank holder and the die, and so forth. In this paper, it is clearly demonstrated theoretically that out-of-plane stress may notably raise the forming limit strain and thus it can be effectively utilized to avoid earlier fracture of the sheet in press forming.

• 멤브레인
• /
• 제3권1호
• /
• pp.22-28
• /
• 1993

Polyester, polyacrylics, nylon과 cotton을 이용해 이들의 막지지천으로의 사용가능성을 조사하였다. 압축률, membrane embossing, 유량과 물리적$\cdot$화학적 특성 등을 고려한 결과 50 번수의 polyester가 막지지천으로 적당함을 알았다. 이 polyester를 막지지천으로 사용해 압력 강하, 조업압력, 점도 등이 막지지천을 통한 유체 흐름에 미치는 영향을 조사하였는데, 이 막지지천을 통한 유체 흐름은 Darcy's law를 만족시켰다.

• Journal of the Optical Society of Korea
• /
• 제13권1호
• /
• pp.152-157
• /
• 2009

The structure of the prism sheet and the reflective polarizer sheet in the direct - illumination liquid crystal display (LCD) backlight is optimized and fabricated. The apex angle of the prism sheet was changed from 90 degree to 96.5 and 101.5 degree and the angular spread of the diffuser films attached on the reflective polarizer sheet was changed from 7 to 1.5 degrees. The measured view angle, the normal luminance, and the contrast ratio from the optimized backlight unit showed improved optical performances.

• 소성∙가공
• /
• 제13권6호
• /
• pp.528-534
• /
• 2004

In order to find the effect of lubricant viscosity, tool geometry, forming speed, and sheet material properties on the friction in the sheet metal forming, friction tests were performed. Friction test results show that as the lubricant viscosity becomes lower, the friction coefficient is higher. When surface roughness is extremely low or high, the friction coefficient is high. The bigger die corner radii and punch speed are, the smaller is the friction coefficient. From the experimental observation, the friction model which is the mathematical expression of friction coefficient in terms of lubricant viscosity, roughness and hardness of sheet surface, punch corner radius, and punch speed is constructed. By comparing the punch load found by FEM using the proposed friction model with that obtained from the experiment in 2-D stretch forming, the validity and accuracy of the friction model are demonstrated.

• 한국기계기술학회지
• /
• 제13권2호
• /
• pp.31-37
• /
• 2011

Sheet aluminum alloys have been used in manufacturing of machine structures. In fatigue crack propagation behavior of thin sheet aluminum alloys, it is important that fatigue crack growth rate is affected by crack closure phenomenon. In this work, we analyzed the characteristics of fatigue crack propagation behavior in experiment of constant stress condition for thin sheet Al 2024-T3 alloys, and identified the retardation behavior of crack growth by comparing experimental results of thin and thick plate specimen. We attempt to operate the fatigue life estimating process using the fatigue related material constants from referred fatigue crack propagation analysis. And we analyzed the experimental and prediction results of fatigue life of thin sheet aluminum alloy in order to identify the relation between retardation behavior of fatigue crack growth and crack closure phenomenon.