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인크리멘탈 성형을 이용한 마그네슘 합금 판재의 성형변수에 관한 연구
박진기(J. G. Park),유봉선(B. S. You),김영석(Y. S. Kim) 한국소성·가공학회 2008 소성가공 : 한국소성가공학회지 Vol.17 No.6
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°C~250°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°C, 130.8°C, and 177.3°C. Also in case of 300, 500, and 700rpm of spindle speed, the maximum temperature at the contact area were 109.7°C, 130.8°C and 189.8°C.
티타늄 합금판재(Ti-6Al-4V)의 고온 소성변형특성(1)
박진기(J. G. Park),김정한(J. H. Kim),박노광(N. K. Park),김영석(Y. S. Kim) 한국소성가공학회 2009 한국소성가공학회 학술대회 논문집 Vol.2009 No.5
Titanium alloy sheets have excellent specific strength and corrosion resistance as well as good performance at high temperature. Recently, titanium alloys are widely employed not only aerospace parts but also bio prothesis and motorcycle However, due to the low formability and large spring back at room temperature, titanium alloy sheets were usually formed by slow forming or hot forming with heating die and specimen. in the sheet metal forming area, FE simulation technique to optimize forming process is widely used. To achieve high accuracy FE simulation results, Identification of material properties and deformation characteristic such as yield function are very important. In this study, uniaxial tensile and biaxial tensile test of Ti-6Al-4V alloy sheet with thickness of 1.0mm were performed at elevated temperature of 873K. Biaxial tensile tests with cruciform specimen were performed until the specimen was breakdown to characterize the yield locus of Ti-6Al-4V alloy sheet. The experimental results for yield locus are compared with the theoretical predictions based on Von Mises, Hill, Logan-Hosford, and Balat’s model. Among these Logan-Hosford’s yield criterion well predicts the experimental results.
박진기(J. G. Park),안덕찬(D. C. Ahn),남재복(J. B. Nam),김영석(Y. S. Kim) 한국소성가공학회 2010 한국소성가공학회 학술대회 논문집 Vol.2010 No.10
This paper includes a review of biaxial tensile test equipment and specimen. Biaxial testing of metal is becoming prevalent in sheet metal industry to evaluate mechanical properties for tested materials. Because light and high strength materials as aluminum, magnesium, titanium, and ultra high strength steel are largely anisotropic, biaxial tensile test i: used as opposed to the common uniaxial test. Also, the stresses acting on a component in service are generally multi-axial in nature. Therefore, it is necessary to consider the mechanical properties not only under uniaxial stress states but also under these multi-axial states of stress. In this paper, the several kinds of biaxial tensile test were introduced and it: limitation and challenge were discussed.
티타늄 합금판재(Ti-6Al-4V)의 온간 소성변형특성(2)
박진기(J. G. Park),박노광(N. K. Park),김영석(Y. S. Kim),J. H. Kim 한국소성가공학회 2010 한국소성가공학회 학술대회 논문집 Vol.2010 No.10
Titanium alloy sheets have excellent specific strength and corrosion resistance as well as good performance at high temperature. Recently, titanium alloys are widely employed not only aerospace parts but also bio prothesis and motorcycle However, due to the low formability and large spring back at room temperature, titanium alloy sheets were usually formed by slow forming or hot forming with heating die and specimen. In the sheet metal forming area, FE simulation technique to optimize forming process is widely used. To achieve high accuracy FE simulation results, Identification of material properties and deformation characteristic such as yield function are very important. In this study, uniaxial tensile of Ti-6Al-4V alloy sheet with thickness of 1.0㎜ were performed at elevated temperature of 400℃~600℃. Also, uniaxial compression tests with special jig were performed characterize the yield locus of Ti-6AI-4V alloy sheet at 600℃. The experimental results for yield locus are compared with new yield function which was proposed in this study. The new yield function can describe not only the anisotropic of material but also asymmetry behavior between tension and compression.