• 소성∙가공
• /
• 제20권3호
• /
• pp.193-205
• /
• 2011

Because of its rustproof property, stainless steel is widely used in kitchen appliances, building materials, electronics, chemical plants and automobile exhausts. In addition, the utilization of stainless steel for fuel cell application is growing. As the demand for this material increases, it is necessary to study the basic properties of stainless steel such as corrosion resistance, heat transfer, formability, cutting or shearing ability and weldability. In this article, the mechanical properties, formability and press forming performance of stainless steel are reviewed. Since temperature and strain rate affect the press forming performance of STS304(austenitic) stainless steel, the influence of these parameters on the plastic behavior should be investigated. Moreover, measures for the prevention of ridging of STS430(ferritic) and delayed fracture of STS430, which respectively appear during and after press forming, should be considered. Recently, stainless steel sheets with a thickness lower than 0.2 mm have been widely used in applications for mobile phone, digital camera and fuel cell separator. Therefore, there is a growing interest of studying the grain size effect and plasticity at the crystal scale in order to understand the anisotropic behavior and micro forming ability of thin sheets. This review paper was written with the objective of helping engineers and researchers to understand the forming characteristics of stainless steel and to establish standards in plastic forming techniques.

• 펄프종이기술
• /
• 제45권3호
• /
• pp.52-58
• /
• 2013

To evaluate the anisotropic characteristics of Korean traditional paper-Hanji, the physical and mechanical characteristics of hand-made hanji, and machine-made hanji were investigated in this research. The densities of copying paper and newsprint paper appeared to be two times higher than the densities of hand-made hanji using Ssangbal sheet forming and hanji made of paper mulberry fiber. The breaking length, and tear index of both Hanji using Owangbal sheet forming, and hand-made Hanji using Ssangbal sheet forming appeared to be different according to the directions in paper. The breaking lengths of Hanji using Owangbal sheet forming showed little differences according to the directions. Breaking length of Hanji using Ssangbal sheet were slightly higher than those of Hanji using Owangbla sheet forming. The breaking lengths of machine-made hanji, copying paper, and newsprint paper were two to four times higher than those of hand-made Hanji. The breaking length showed higher differences according to the direction than the tear index. The tensile strength according to the directions in paper showed significant differences (${\alpha}$=0.05) in all papers used in this research.

• 대한기계학회논문집A
• /
• 제37권7호
• /
• pp.913-919
• /
• 2013

본 연구에서는 마그네슘 합금 AZ31을 적용한 배터리 팩 케이스를 개발하여 자체 진동 및 외부 충격으로부터 배터리를 보호하도록 하며, 기존 스틸 소재 대비 50% 이상 경량화하여 친환경 기술개발을 목적으로 한다. 또한, 제품의 복잡한 형상 및 마그네슘 소재의 특성으로 제품을 성형하기에는 힘든 측면이 많으므로 이를 해결하기 위해 마그네슘 합금소재의 온도별 최적성형조건을 제시하고자 한다. 즉 AZ31의 성형방법에 따라 상온, $230^{\circ}C$, $250^{\circ}C$ 및 $270^{\circ}C$의 4가지 조건하의 시험편으로 인장시험, 경도시험, 부식시험 및 피로시험 등을 실시하여 기계적 특성을 정량적으로 분석하였고, 또 FEM해석을 통하여 자동차 부품 배터리 팩 케이스 개발에 적용토록 하였다.

• 소성∙가공
• /
• 제13권8호
• /
• pp.696-703
• /
• 2004

The purpose of this study is to examine the bulk/sheet forming characteristics of bulk amorphous alloys in the super cooled liquid state. Recently it is reported that amorphous alloys exhibit stress overshoot/undershoot and non-Newtonian behaviors even in the super cooled liquid state. The stress-strain curves with the temperature-dependences as well as strain-rate dependence of Newtonian/non-Newtonian viscosities of amorphous alloys are obtained based on the previous experimental works. Then, those curves are directly used in the thermo-mechanical finite element analyses. Upsetting and deep drawing of amorphous alloys are simulated to examine the effects of process parameters such as friction coefficient, forming speed and temperature. It could be concluded that the superior formability of an amorphous alloy can be obtained by taking the proper forming conditions.

• 한국소성가공학회:학술대회논문집
• /
• 한국소성가공학회 1997년도 춘계학술대회논문집
• /
• pp.183-187
• /
• 1997

A membrane element is regarded as more preferable rather than other elements in the sense of its computing efficiency and the merit with respect to contact treatment. However, it cannot consider the bending effect during the deformation. Moreover, due to the characteristics of rolling process, sheet metal has anisotropy with respect to the direction in the plane. To take the bending effect into account, a modified membrane element was introduced and improved to consider planar anisotropic characteristics with the aid of Hill's quadratic criterion.

• 한국정밀공학회지
• /
• 제18권6호
• /
• pp.109-114
• /
• 2001

Forming pressure of the rupture disc has been analyzed theoretically and verified by experiments. Final shape of the rupture disc after forming process is assumed to be hemi-ellipsoid for small height of the rupture disc. The predicted forming pressures are in good agreement with those by experiment. A new simple model has been proposed to predict the burst pressure of the rupture disc. Experimental results show that the proposed model of burst pressure describes the bursting characteristics of the rupture disc very well.

• 한국지반공학회지:지반
• /
• 제14권5호
• /
• pp.53-66
• /
• 1998

풍화토는 암석이 풍화되어 생성되기 때문에 모암과 풍화과정에 따라 그 특성이 결정된다. 따라서, 풍화토의 특성을 고찰하기 위해서는 먼저 모암에 대한 고찰과 풍화과정을 지배하는 풍화환경에 대한 고찰이 이루어져야 한다. 이번 연구에서는 모암과 풍화정도에 따른 풍화의 특성을 고찰하기 위해 화강암 풍화토와 편마암 풍과토를 불교란 또는 교란상태로 채취한 후. 기본 물성시험, 암석학적 시험 그리고 다양한 전단시험을 실시하였다. 여러 가지 시험의 결과에서 암석의 풍화는 모암의 조암광물 분포 및 생성특성과 밀접한 관계가 있음을 확인하였다. 화강암 풍화토의 경우 모암의 비방향적인 성격 때문에 현장응력 상태화 전단특성이 등방적으로 나타났으며, 편마암 풍과토는 그 내부에 존재하는 불연속면이 역학적 거동을 지배하는 방향적 특성을 갖는 것으로 나타났다. 또한 식영이 장석 또는 운모보다 풍화저항력이 크다는 사실의 확인과 함께 풍화대의 두께가 구성 조암광물에 크게 영향을 받는다는 결론을 얻었다.

• 한국정밀공학회:학술대회논문집
• /
• 한국정밀공학회 2002년도 추계학술대회 논문집
• /
• pp.663-666
• /
• 2002

Originally, the thermoforming method has been developed to produce the plastic parts which have simple geometric characteristics such as door trims and wrapping materials within the short time. But the thermoformed parts have non-uniform thickness distributions over the surface according to the material characteristics, set-up angle and geometry of the parts. But, only few analysis methods have been developed so far, due to the difficulties of the selection of important factors, and contribution of each factor in the simulation. So, to guarantee the dimensional accuracy and mechanical properties of crucial points in the thermoformed parts, it is necessary to develop the thickness prediction method. This research suggests a new approaching methodology to predict the thermoformed parts by modulating the control points of the NURBS curve. The newly developed method makes it possible not only to choose the suitable thickness of polymer sheets but also to induce data modification for vacuum forming.

• 대한기계학회논문집A
• /
• 제20권7호
• /
• pp.2182-2195
• /
• 1996

Densification characteristics and behavior of tool steel powder compact during high temperature forming processes were investigated under pressure less sintering, sinter forging and hot isostastic pressing. In pressureless sintering, full density was obtained at a closely controlled temperature near the solidus of the material. Finite element calculations from constitutive model for densification by power law creep and diffusional flow were compared with experimental data. Agreements between theoretical calculations and experimental data were good in hot isostatic pressing but not as good in sinter forging.

• 한국정밀공학회지
• /
• 제28권5호
• /
• pp.578-584
• /
• 2011

In mechanical cutting process, burr was generated at workpiece by cutting tool generally. It is working disturbance during manufacturing process. Besides burr was taken shape relatively large size more micro scale machining than macro scale machining. Many researches have been studied to remove micro burr(de-burring), because it was negative effect for accuracy of machining shape. However, micro de-burring was constrained by burr height, micro feature and so on. In this paper, experimental research was carried out to compare de-burring characteristics of $Al_2O_3$ abrasive and polymer.