• 한국소성가공학회:학술대회논문집
• /
• 한국소성가공학회 2002년도 춘계학술대회 논문집
• /
• pp.66-69
• /
• 2002

In the ideal forming theory(1), which has been deviously developed as a direct method for optimizing forming process, material elements are required to deform following the minimum plastic work path (or the proportional true strain path). Besides the general theory(2,3), specific ideal forming theories have been developed for membrane sheet forming(4) as well as two-dimensional steady bulk forming(5-7). In this work, the ideal forming theory was successfully applied for non-steady bulk forming under the plane strain condition. Here, the shape change complying with the minimum plastic work path, was effectively described by developing a numerical code based on the characteristic method. Numerical results obtained for a specific industrial part also include the optimum pre-forming shape and its evolving shape change to the final shape as well as the boundary traction history.

• 한국소성가공학회:학술대회논문집
• /
• 한국소성가공학회 2004년도 춘계학술대회 논문집
• /
• pp.190-193
• /
• 2004

Ever since the ideal forming theory has been developed fur process design purposes, application has been limited to sheet forming and, for bulk forming, to two-dimensional steady flow. Here, application for the non-steady case was performed under the plane-strain condition based on the theory previously developed. In the ideal flow, material elements deform following the minimum plastic work path (or mostly proportional true strain path) so that the ideal plane-strain flow can be effectively described using the two-dimensional orthogonal convective coordinate system. Besides kinematics, for a prescribed final part shape, schemes to optimize a preform shape out of a class of initial configurations and also to define the evolution of shapes and boundary tractions were developed. Discussions include the two problematic issues on internal tractions and the non-monotonous straining. For demonstration purposes, numerical calculations were made for a bulk part under forging.

• 소성∙가공
• /
• 제13권6호
• /
• pp.540-545
• /
• 2004

Ever since the ideal forming theory has been developed for process design purposes, application has been limited to sheet forming and, fur bulk forming, to two-dimensional steady flow. Here, application for the non-steady case was performed under the plane-strain condition based on the theory previously developed. In the ideal flow, material elements deform following the minimum plastic work path (or mostly proportional true strain path) so that the ideal plane-stram flow can be effectively described using the two-dimensional orthogonal convective coordinate system. Besides kinematics, fur a prescribed final part shape, schemes to optimize a preform shape out of a class of initial configurations and also to define the evolution of shapes and boundary tractions were developed. Discussions include the two problematic issues on internal tractions and the non-monotonous straining. For demonstration purposes, numerical calculations were made for a bulk part under forging.

• Fibers and Polymers
• /
• 제3권3호
• /
• pp.120-127
• /
• 2002

Ever since the ideal forming theory has been developed for process design purposes, application has been limited to sheet forming and, for bulk forming, to two-dimensional steady flow. Here, application for the non-steady case was made under the plane-strain condition. In the ideal flow, material elements deform fellowing the minimum plastic work path (or mostly proportional true strain path) so that the ideal plane-strain flow can be effectively described using the two-dimensional orthogonal convective coordinate system. Besides kinematics, schemes to optimize preform shapes for a prescribed final part shape and also to define the evolution of shapes and frictionless boundary tractions were developed. Discussions include numerical calculations made for a real automotive part under forging.

• 한국소성가공학회:학술대회논문집
• /
• 한국소성가공학회 2004년도 춘계학술대회 논문집
• /
• pp.233-236
• /
• 2004

The major objective of this paper is to clarify the effect of constitutive laws on bulk forming design based on the ideal flow theory. The latter theory is in general applicable for perfectly/plastic materials. However, its kinematics equations constitute a closed-form system, which are valid for any incompressible materials, therefore enabling us to extend design solutions based on the perfectly/plastic constitutive law to more realistic laws with rate sensitive hardening behavior. In the present paper, several constitutive laws commonly accepted for the modeling of cold and hot metal forming processes are considered and the effect of these laws on one particular plane-strain design is demonstrated. The closed form solution obtained describes a non-trivial nonsteady ideal process. The design solutions based on the ideal flow theory are not unique. To achieve the uniqueness, the criterion that the plastic work required to deform the initial shape of a given class of shapes into a prescribed final shape attains its minimum is adopted. Comparison with a non-ideal process is also made.

• 소성∙가공
• /
• 제20권5호
• /
• pp.377-386
• /
• 2011

During stamping processes, the air trapped between sheet metal and the die cavity can be highly compressed and ultimately reduce the shape accuracy of formed panels. To prevent this problem, vent holes and passages are sometimes drilled into the based on expert experience and know-how. CAE can be also used for analyzing the air behavior in die cavity during stamping process, incorporating both elasto-plastic behavior of sheet metal and the fluid dynamic behavior of air. This study presents sheet metal forming simulation combined simultaneously with simulation of air behavior in the die cavity. There are three approaches in modeling of air behavior. One is a simple assumption of the bulk modulus having a constant pressure depending on volume change. The next is the use of the ideal gas law having uniform pressure and temperature in air domain. The third is FPM (Finite point method) having non-uniform pressure in air domain. This approach enables direct coupling of mechanical behavior of solid sheet metal and the fluid behavior of air in sheet metal forming simulation, and its result provides the first-hand idea for the location, size and number of the vent holes. In this study, commercial software, PAM-$STAMP^{TM}$ and PAM-$SAFE^{TM}$, were used.

• 한국미생물·생명공학회지
• /
• 제9권3호
• /
• pp.145-152
• /
• 1981

산업폐수로부터 강력한 $\alpha$-amylase 생성능력을 가진 미생물을 분리하여 검토한 곁과 Bacillus속 (Bacillus Y-124)으로 판명되었으며, Bacillus Y-l24로부터 $\alpha$-amylase의 생산성을 최적화하기 위해 배양조건 및 생성된 효소의 안정성을 유지하기 위한 제반 영향들을 검토하였다. 기본 배지내의 casein 및 Ca-pantothenate의 첨가는 본 효소의 생산에 좋은 인자로 작용하였으며 calcium이온 역시 효소합성에 관여하는 것으로 나타났다. 또한 (NH$_4$)$_2$HPO$_4$는 본 미생물의 효소생성 에 중요한 유기 질소원으로 작용하였다. 생성된 본 효소의 보존에 대한 안정성의 유지에는 calcium 및 sodium염의 영향이 컸으며 특히 CaCO$_3$ 및 $Na_2$SO$_4$의 첨가는 이 효소의 변성요인을 제거하는데 효과적인 보존제의 하나로 인식되 었다.