• Journal of the Korean Society of Manufacturing Process Engineers
• /
• v.9 no.1
• /
• pp.87-92
• /
• 2010

Micromachining technology using a ultra-precision micromachining system is widely applied in the fields of optics, biotechnology and analytical chemistry, etc. specially in microfabrication of fresnel lens, light guide panels of TFT-LED and PDP ribs with micro-patterns, machining errors have an effect on the performance of those products. The deflection of tool and tool holder is known to be one of the very important factors that is due to machining errors in micromachining. The deflections of diamond tool and tool holder used in micro-grooving are analysed by FEM. We analysed by FEM. With an linearity valuation of FEM, deflection of tool and tool holder is calculated by using the data of cutting force which is acquired from micro-V groove machining experiments in micromachining system.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
• /
• 2000.10a
• /
• pp.206-210
• /
• 2000

금형 및 자동차 산업에 널리 사용되는 앤드밀 가공에서 종종 소비자가 요구하는 가공 정밀도를 충족시켜 주지 못하는 경우가 발생한다. 이것은 열 변형, 공구 마모, 공작 기계 자체의 오차, 공구 처짐 등 다양한 원인이 존재한다. 본 연구에서는 공구 처짐으로 발생되는 가공 오차를 줄임으로써 가공 정밀도를 향상하기 위한 시스템을 개발하고자 한다. 이를 위해 3차원 볼 앤드밀의 절삭력 모델을 개발하고 시뮬레이션한다. 또한, 상용 CAD 시스템의 형상 및 가공 정보를 이용함으로써 모델링에서부터 가공 경로 생성, 그리고 경로 보정이라는 과정을 일괄적으로 수행할 수 있도록 한다. 이를 통해 사용자는 가공 전 시뮬레이션을 통해 가공 오차를 줄일 수 있는 기회를 제공 받는다. 따라서, 실제 가공에서 보다 높은 가공 정밀도를 얻을 수 있을 것이다.

• Nuclear Engineering and Technology
• /
• v.8 no.3
• /
• pp.151-157
• /
• 1976

The strain ageing behavior of cold-worked Zircaloy-4 in vacuum was studied as a function of deformation temperature and oxygen content from 1143 ppm to 3500 ppm 0. Strain ageing occured in the temperature range between 200 and 45$0^{\circ}C$ for the 0 to 10% cold-worked Zircaloy-4, decreasing with increasing amount of cold work. This suppression of strain ageing by cold work is considered to be due to the trapping of oxygen atoms by cold work-produced defects. It has been found that the maximum strain ageing stress in cold-worked Zircaloy-4 is proportional to the square root of oxygen content.

• Journal of the Korea Concrete Institute
• /
• v.24 no.2
• /
• pp.195-204
• /
• 2012

In the construction of high-rise buildings, bent re-bars are manually straightened to connect slabs to core-walls, which are usually cast before floor structures. During cold bending and straightening of re-bars, plastic deformation causing work hardening, Bauschinger effect and aging hardening is unavoidable. Tensile tests of coldly bent and straightened re-bars were conducted with test parameters of grade, diameter, and bend radius of re-bars as well as age between bending and straightening. Test results showed that proportional limits were lower and strain hardening occurred without yield plateaus. Inside and outside of re-bars with compression and tension deformations, respectively, during bending showed lower yield points due to Bauschinger effect and no yield plateaus due to work hardening, respectively. When re-bar grade was higher, yield point became significantly lower where Grade 400 re-bars had yield strengths lower than specified yield strength of 400 MPa. Because the surface of re-bar has higher strength than the core of re-bar, Bauschinger effect was more obvious for higher-grade re-bars. When age between bending and straightening was greater, yield strength increased and elongation decreased (i.e. embrittlement occurs). Using measured data, stress-strain relationship for straightened re-bars was developed based on Ramberg-Osgood model, which can be used to evaluate stiffness of joints when straightened re-bars are applied.

• Proceedings of the Korean Nuclear Society Conference
• /
• 1995.05a
• /
• pp.729-734
• /
• 1995

원자력용 316L강에 질소를 첨가한 경우의 고온 인장성질을 조사하였다. 온도가 증가하면 인장강도는 감소하다가 온도범위가 30$0^{\circ}C$~50$0^{\circ}C$에서는 일정한 값을 나타낸 후 급격한 감소를 나타내었고 연신율은 감소하다가 40$0^{\circ}C$에서 최소값을 나타낸 후 다시 증가하는 경향을 나타내었다. 질소를 첨가하면 인장강도증가와 함께 연신율도 증가하였다. 동적변형시효 온도구간에서 변형속도변화에 따른 인장강도 및 연신율의 변화는 매우 작다. 동적변형시효를 위한 활성화에너지를 구해본 결과 동적변형시효를 일으키는 원소는 Cr이다. 질소를 첨가하면 동적변형시효가 발생되는 온도가 고온 쪽으로 이동되었는데 이것은 질소가 Cr과의 상호작용에 의해 Cr의 확산속도를 낮추기 때문이다. 가공경화지수는 동적변형시효와 회복의 영향으로 40$0^{\circ}C$에서 최대값을 나타내었으며 이 온도는 연신율이 최소값을 나타내는 온도와 인장강도가 일정하게되는 온도와 일치하므로 강도강화기구는 동적변형시효로 판명되었다.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2008.11a
• /
• pp.333-334
• /
• 2008

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2009.10a
• /
• pp.478-478
• /
• 2009

• Transactions of Materials Processing
• /
• v.14 no.4 s.76
• /
• pp.310-318
• /
• 2005

판금 성형성의 대표평가기준인 디프드로잉성과 성형한계도에 미치는 재료의 인장성질, 특히 소성변형비는 재료의 집합조직과 밀접한 관계가 있다. 따라서 성형성 향상을 위해서는 집합조직을 제어하는 것이 중요하다.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 1997.03a
• /
• pp.117-120
• /
• 1997

Microstructure and pole figure through thickness in cold rolled sheet steel were investigated. The calculated plastic strain ratio in surface is greatly different with that in center layer and measured value in tensile test.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2006.06a
• /
• pp.86-86
• /
• 2006