• ETRI Journal
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• 제33권6호
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• pp.904-913
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• 2011

Three-dimensional (3D) memories using through-silicon vias (TSVs) as vertical buses across memory layers will likely be the first commercial application of 3D integrated circuit technology. The memory dies to stack together in a 3D memory are selected by a die-selection method. The conventional die-selection methods do not result in a high-enough yields of 3D memories because 3D memories are typically composed of known-good-dies (KGDs), which are repaired using self-contained redundancies. In 3D memory, redundancy sharing between neighboring vertical memory dies using TSVs is an effective strategy for yield enhancement. With the redundancy sharing strategy, a known-bad-die (KBD) possibly becomes a KGD after bonding. In this paper, we propose a novel die-selection method using KBDs as well as KGDs for yield enhancement in 3D memory. The proposed die-selection method uses three search-space conditions, which can reduce the search space for selecting memory dies to manufacture 3D memories. Simulation results show that the proposed die-selection method can significantly improve the yield of 3D memories in various fault distributions.

• ETRI Journal
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• 제34권3호
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• pp.388-398
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• 2012

Three-dimensional (3D) memories using through-silicon vias (TSVs) will likely be the first commercial applications of 3D integrated circuit technology. A 3D memory yield can be enhanced by vertical redundancy sharing strategies. The methods used to select memory dies to form 3D memories have a great effect on the 3D memory yield. Since previous die-selection methods share redundancies only between neighboring memory dies, the opportunity to achieve significant yield enhancement is limited. In this paper, a novel die-selection method is proposed for multilayer 3D memories that shares redundancies among all of the memory dies by using additional TSVs. The proposed method uses three selection conditions to form a good multi-layer 3D memory. Furthermore, the proposed method considers memory fault characteristics, newly detected faults after bonding, and multiple memory blocks in each memory die. Simulation results show that the proposed method can significantly improve the multilayer 3D memory yield in a variety of situations. The TSV overhead for the proposed method is almost the same as that for the previous methods.

• 한국정밀공학회지
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• 제18권3호
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• pp.158-168
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• 2001

Die design of die casting is composed of selection of cast alloy, design of die casting product, runner design and gate design, etc. In reality, however, die design of die casting has been performed by trial and error method, which cause economic and financial loss. Nowadays, several FEM(finite element method) and FDM(finite difference method) codes have been developed to analyze process of die casting, but this is just confined to an offer of limited information for die design of die casting. In this study, die design system for gate of die casting process has been developed to present algorithm for automation of die design, especially runner-gate system. In addition, specific rules for runner-gate system have been presented to avoid too many trials and errors with expensive equipment. It is possible for engineers to make automatic and efficient die design of die casting and it will result in reduction of expense and time to be required.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2000년도 추계학술대회 논문집
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• pp.316-321
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• 2000

Die Casting is one of the forming methods to manufacture large number of products with short period time and clean surface by high forming pressure and temperature of cast alloy. Die design is composed of selection of cast alloy, design of die casting product, runner and gate design etc. In reality, however, die design of die casting has been performed by trial and error method, which cause economic and time loss. This paper describes a research work of developing computer-aided design of die casting product and die design. Approach to the CAD system has been written in AutoLISP on the AutoCAD with personal computer. In this study, die design system for gate of die casting process has been developed to present algorithm for automation of die design, especially runner-gate system. As forming process and die design system using 3-D geometry handling are integrated with technology of process planning, die design is possible to set. In addition, specific rules and equations for the runner-gate system have been presented to avoid too many trails and errors with expensive equipment. It is possible for engineers to make automatic and efficient die design of die casting and it will result in reduction of expense and time to be required. An example is applied to cap-shaped casting using proposed algorithm.

• 한국산학기술학회논문지
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• 제11권1호
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• pp.49-54
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• 2010

자동차의 A.C 제너레이터(alternating current generator) 부품으로 사용되는 로터폴(rotor pole)을 가공할 때는 트랜스퍼온간단조금형(transfer warm forging die)으로 성형한다. 소재를 온간가공 영역으로 가열한 후 즉시 금형안으로 이송시켜 제1스테이지(1st stage)에서 업세팅가공(upsetting work)하고 제2스테이지(2nd stage)로 이송하여 측방압출(lateral extrusion)가공을 한다. 이때 측방압출 스테이지의 금형에서 다이블록(die block), 다이부싱(die bushing), 센터펀치(center punch), 사이드펀치(side punch)의 접촉면이 압출시의 과혹(過酷)한 조건에 견디지 못하여 쉽게 마멸(abrasion)되어 금형수명(die life)을 단축시키고 있다. 이 때문에 생산량 감소로 인한 납기지연, 금형의 수리보수시간 과다, 제품의 정밀도 저하 등의 문제점이 발생되고 있다. 이러한 문제점을 해결하기 위하여 금형재질 선정과 열처리 작업 싸이클 개선, 방전가공시의 트러블 해소, 핵심부품의 구조변경 등을 연구하여 금형수명을 40~50% 연장 하고자 하였다.

• 소성∙가공
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• 제8권5호
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• pp.498-506
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• 1999

The metal forming processes of aluminum alloy wheel forging at elevated temperature are analyzed by the finite element method. A coupled thermo-mechanical model for analysis of plastic deformation and geat transfer is adapted in the finite element formulation. In order to consider the strain-rate effects on material properties and the flow stress dependence on temperatures, rigid-viscoplasticity is introduced in this formation. In this paper, several process conditions were applied to the dimulation such as die speed, rib thickness, and depth of die cavity. Simulation results are compared, and discussed with each case. Metal flow, die pressure distributions, temperature distributions, velocity fields and forging loads are summarized as basic data for process design and selection of a proper press equipment.

• 한국산학기술학회논문지
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• 제18권9호
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• pp.61-67
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• 2017

프레스금형 제작 시 사용목적에 맞는 적합한 소재선택과 빠른 가공방법에 대한 연구는 금형제작시간을 줄이고 금형원가를 절감하는데 절대적으로 필요한 연구분야이다. 특히 장수명 프레스금형을 개발하기 위해선 열에 대한 고찰이 반드시 이루어져야 한다. 일반적으로 프레스금형의 주요부품 소재로는 Cr, W계 저합금 공구강, 고탄소 고크롬강, 고속도강 등 냉간 금형용 합금공구강이 많이 쓰이고 있다. 프레스금형부품을 가공하는 데는 주로 공작기계와 와이어 컷 방전가공을 사용하고 있다. 가공공정에 따라 금형부품의 가공시간 및 수명이 많은 차이가 난다. 밀링가공과 연삭가공으로 제작된 부품의 경우 제작시간과 비용은 많이 드는데 비해 금형의 수명이 길고 밀링가공과 와이어 컷 방전가공을 사용하면 제작시간과 비용은 절감되는 반면 금형수명은 줄어드는 현상이 나타난다. 따라서 본 연구에선 가공시간과 비용이 절감되는 가공방법으로 열처리를 사용하여 금형의 사용수명을 향상시키는 방법에 대해 고찰하고자 한다. 밀링가공-연삭가공, 밀링가공-와이어 컷 방전가공, 밀링가공-와이어 컷-고온템퍼링, 3가지 가공방법으로 시편을 제작하여 가공표면과 중심부를 SEM, EDS분석 및 표면조도분석으로 문제점을 고찰하였고 밀링가공-와이어 컷 방전가공-고온템퍼링의 가공방법으로 밀링가공-연삭가공과 동일한 금형의 수명을 만드는 방법을 도출하였다.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2003년도 춘계학술대회 논문집
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• pp.1784-1788
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• 2003

For the improvement of geometrical accuracy in end milling, cutting method and cutting condition selection are investigated in this paper. As machining processes are composed of several steps such as roughing, semi-finishing. and finishing, cutting forces and tool deflection are calculated considering surface shape generated by the previous cutting. The effects of tool teeth numbers, tool geometry, and cutting conditions on the form error are analyzed. Using the from error prediction method from tool deflection, cutting condition for geometrical accuracy improvement is discussed. The characteristics and the difference of generated surface shape in up and down milling are dealt with and over-cut free condition in up milling is presented. The form error reduction method by alternating up and down milling is also suggested. The effectiveness of the presented method is examined from a set of cutting tests under various cutting conditions. This research contributes to cutting process optimization for the geometrical accuracy improvement in die and mold manufacture.

• 한국기계가공학회지
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• 제14권6호
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• pp.136-141
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• 2015

Laser surface polishing is a polishing method for improving surface roughness using an integrated laser beam. Using a laser for surface polishing can improve the surface condition without physical contact or chemical action. Laser polishing has mainly been used to polish the surface of diamond or optical articles, such as lenses and glasses. Recently, diverse studies on laser polishing for metals have been conducted. The analytic study of laser surface polishing has been conducted with experimental trials for comparison, so that the proper conditions for laser polishing can be recommended. In this study, laser surface polishing was simulated in order to predict the heat-affected zone on the die steel depending on the power of the pulsed laser. The simulated results were verified by comparing them to those of the experimental trials. Through this study, therefore, the application of FEM to the selection of appropriate laser conditions could be possible.

• 한국생산제조학회지
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• 제21권4호
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• pp.593-600
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• 2012

Thixomolding of Mg-alloy is a semi-solid injection molding process utilizing thixotropic phenomenon. Using this process, higher strength, thinner wall section and tighter tolerance without porosity are obtained. It has been applied for production of near-net-shape magnesium component. To design optimal thixomolding process of Mg-alloy part, molding conditions such as slurry temperature, mold temperature and injection time should be determined properly. Selection of these parameters has been dependent upon engineers' experience and intuitiveness. In this paper, to improve mechanical properties of the thixomolded product, optimal selection of process variables such as injection velocity, barrel temperature and die temperature in the process has been studied through microstructural analysis and Taguchi method. Performance of the process is verified through experiments.