• 한국재료학회지
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• 제16권8호
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• pp.516-523
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• 2006

In recent years, Magnesium (Mg) and its alloys have become a center of special interest in the automobile industry. Due to their high specific mechanical properties, they offer a significant weight saving potential in modern vehicle constructions. Most Mg alloys show very good machinability and processability, and even the most complicated die-casting parts can be easily produced. The die casting process is a fast production method capable of a high degree of automation for which certain Mg alloys are ideally suited. In this study, step-dies and flowability tests for AM50 were performed by die-casting process according to various combination of casting pressure and plunger velocity. We were discussed to velocity effect of forming conditions followed by results of microstructure, FESEM-EDX, hardness and tensile strength. Experimental results represented that the conditions of complete filling measured die-casting pressure 400 bar, 1st plunger velocity 1.0 m/s and 2nd plunger velocity 6.0 m/s. The increasing of 2nd plunger velocity 4.0 to 7.0 m/s decreased average grain size of $\alpha$ phase and pore. It was due to rapid filling of molten metal, increasing of cooling rate and pressure followed by increased 2nd plunger velocity. The pressure should maintain until complete solidification to make castings of good quality, however, the cracks were appeared at pressure 800bar over.

• 한국공작기계학회논문집
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• 제17권4호
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• pp.104-111
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• 2008

The objective of this study is to evaluate micro end-milling characteristics and tool wear behavior of AlN-hBN composites. First, AlN based composites with hBN contents in the range of 10 to 20vol% were prepared by hot-pressing. Vickers hardness and flexural strength of the prepared composite specimens were measured and compared according to the vol% of hBN variations. Then, cutting force variations were measured and analyzed using a tool dynamometer during the micro end-milling experiments; and machined surface shapes and roughness were investigated using a 3D non-contact type surface profiler. After micro end-milling, worn tools were investigated using a tool microscope and SEM images. From the experimental results, it can be observed that the cutting forces decreased, and surface qualities were improved with increasing hBN contents. At low content of hBN, tool chipping was observed; and tool wear rate decreased with increasing hBN contents. The results of this study insist that proper machining conditions, including tool wear behavior investigation, should be determined for the micro end-milling of AlN-hBN composites for its further application.

• 대한치과기공학회지
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• 제35권4호
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• pp.295-302
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• 2013

Purpose: The grindability of Ti-10%Zr-X%Cr(X=0,1,3) alloys in order to develop Ti alloys for dental applications with better machinability than unalloyed titanium has been evaluated. Methods: Experimental Ti-10%Zr-X%Cr(X=0,1,3) alloys were made in an argon-arc melting furnace. Slabs of experimental alloys were ground using a SiC abrasive wheel on an electric handpiece at one of the four rotational speeds of the wheel (12000, 18000, 25000 or 30000rpm) by applying a force(100gf). Grindability was evaluated by measuring the amount of metal volume removed per minute(grinding rate) and the volume ratio of metal removed compared to the wheel material lost, which was calculated from the diameter loss (grinding ratio). Experimental datas were compared the results with those of cp-Ti(commercially pure titanium) Results: It was observed that the grindability of Ti-10%Zr-X%Cr(X=0,1,3) alloys increased with an increase in the Cr concentration. More, they are higher than cp-Ti, particularly the Ti-10%Zr-3%Cr alloy exhibited the highest grindability at all rotational speeds except 12000rpm. There was significant difference in the grinding rate and grinding ratio between Ti-10%Zr-3%Cr alloy and cp-Ti at all rotational speeds(p<0.05). Conclusion: The Ti-10%Zr-3%Cr alloy exhibited better grindability at high rotational speeds, great potential for use as a dental machining alloy.

• 한국산학기술학회논문지
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• 제16권11호
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• pp.7917-7924
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• 2015

본 연구에서는 친환경 제설제로 사용이 증가되고 있는 CMA를 바탕으로 고성능흡습제로 사용되어지고 있는 SAP와 sodium carbonate, $MgCl_2$/MgO (M/M)에 대하여 제습MB를 제조하고 필름으로서의 흡습율 및 제습성능을 분석하고, 제습필름 적용물질에 대한 Data를 확보하고자 한다. CMA와 SAP를 혼합한 제습MB의 경우 발포현상과 수분문제로 필름가공성이 어려웠으나, Bentonite와 calcium carbonate 첨가로 해결할 수 있었다. 필름가공시 물질들 간의 표면적 공간을 넓히는 역할로서 발포제를 첨가한 경우, CMA와 M/M의 경우 큰 차이성은 없었지만, 발포제가 첨가된 SC의 제습성은 3.15 g/g로 높은 결과를 알 수 있었다. 또한 방청성 테스트의 결과 CMA 제습필름 경우 부식발생은 없었으며, SC의 경우 점 부식 발생, M/M의 경우 부식발생이 일어났다.

• 한국주조공학회지
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• 제17권4호
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• pp.347-355
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• 1997

It is well known that the coarse primary Si in hypereutectic Al-Si alloys deteriorate castability, machinability, and mechanical properties. So, many treatment has been tried to refine the primary Si increasing cooling rate and adding refinement agent. Therefore. the purpose of our work was the observation of the effect on the refinement of primary Si and the analysis of the trend to apply to the casting process by changing the amount of P addition and the cooling rate while fixing the temperature at $750^{\circ}C$ of P addition and the type of AlCuP. In the condition of amount of P addition was fixed, primary Si was finer as cooling rate increased but in case of cooling rate was fixed, the effect of refinement was resisted as incersed the amount of P addition. At a relatively slow cooling rate of $22^{\circ}C/sec$, refinement was governed by the amount of P addition rather than cooling rate. At elevated cooling rate of $51^{\circ}C/sec$ and $99^{\circ}C/sec$, the undercooling due to faster cooling rate promoted nucleation of primary Si rather than P addition more significantly.

• 한국융합학회논문지
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• 제12권1호
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• pp.105-110
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• 2021

의료기관에서 최근 많이 사용되고 있는 친환경 소재 방사선 차폐체는 시트 형태로 제작되어 Apron의 재료로 활용되고 있다. 친환경 Apron의 차폐성능은 납당량을 기준으로 제시되고 있으며, 납당량은 0.25~0.50mmPb로 제시되고 있다. 납이 주재료 사용되는 차폐체인 경우 납의 우수한 가공성으로 인해 두께로 차폐성능을 조절할 수 있다. 그러나 친환경 차폐시트는 차폐재료의 함량, 베이스 재료인 고분자 물질의 물성, 공정과정의 기술적 차이에 따라 차폐성능이 변화되어 두께 기준의 차폐성능을 제어하기가 어렵다. 본 연구에서는 이러한 문제점을 해결하고자 두께를 기준으로 차폐시트를 제작하여 차폐성능을 평가, 비교하였다. 동일한 시트 제작공정을 제시하여 두께를 제어할 수 있는 캘린더 공정의 압연 기술을 적용하였고 여러층의 적층 구조와 단일 구조로 제작된 두 시트의 두께별 차폐성능을 비교하여 5%대의 차이를 관찰하였다. 그 결과 여러 층으로 차폐한 적층 구조 차폐시트가 더 효과적임을 증명하는 동시에 두께 중심의 차폐성능의 가능성을 제시하였다.

• 박물관보존과학
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• 제26권
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• pp.1-12
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• 2021

석조 문화재 보존처리 시 사용되고 있는 Bisphenol A계 Epoxy 수지의 Yellowing 현상개선과 재료의 다양성 확보를 위해 hydrogenated Bisphenol A계 주제 기반의 석조 문화재 보존용 Epoxy 수지를 제조하여 물성 비교 실험을 진행하였다. 실험 결과 제조한 Epoxy 수지가 인장강도, 접착 강도, 가공성에서 기존 재료보다 향상된 물성을 확인할 수 있었으며, 황변성은 약 5 ~ 8배 개선되었다. 이러한 결과는 대부분이 야외에 위치한 석조 문화재의 특성상 안정적인 보존 재료로서의 적용이 가능할 것으로 판단된다.

• 한국분말재료학회지
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• 제29권4호
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• pp.291-296
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• 2022

The green body of WC-Co cemented carbides containing polymeric binders such as paraffin, polyethylene glycol (PEG), and polyvinyl acetate (PVA) are prepared. The green density of the WC-Co cemented carbides increases with the addition of binders, with the exception of PVA, which is known to be a polar polymeric substance. The green strength of the WC-Co cemented carbides improves with the addition of paraffin and a mixture of PEG400 and PEG4000. In contrast, the green strength of the WC-Co does not increase when PEG400 and PEG4000 is added individually. The compressive strength of the green body increases to 14 MPa, and the machinability of the green body improves when more than 4-6 wt% paraffin and a mixture of PEG400 and PEG4000 is used. Simultaneously, the sintered density of WC-Co is as high as 99% relative density, similar to a low binder addition of 1-2 wt%.

• Structural Engineering and Mechanics
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• 제86권1호
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• pp.119-137
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• 2023

The purpose of this research is to assess the performance of CBN and ceramic tools during the dry turning of gray cast iron EN GJL-350. During the turning operation, the variable machining parameters are cutting speed, feed rate, depth of cut and type of the cutting material. This contribution consists of two sections, the first one deals with the performance evaluation of four materials in terms of evolution of flank wear, surface roughness (2D and 3D) and cutting forces. The focus of the second section is on statistical analysis, followed by modeling and optimization. The experiments are conducted according to the Taguchi design L₃₂ and based on ANOVA approach to quantify the impact of input factors on the output parameters, namely, the surface roughness (Ra), the cutting force (Fz), the cutting power (Pc), specific cutting energy (Ecs). The RSM method was used to create prediction models of several technical factors (Ra, Fz, Pc, Ecs and MRR). Subsequently, the desirability function approach was used to achieve a multi-objective optimization that encompasses the output parameters simultaneously. The aim is to obtain optimal cutting regimes, following several cases of optimization often encountered in industry. The results found show that the CBN tool is the most efficient cutting material compared to the three ceramics. The optimal combination for the first case where the importance is the same for the different outputs is Vc=660 m/min, f=0.116 mm/rev, ap=0.232 mm and the material CBN. The optimization results have been verified by carrying out confirmation tests.

• Composites Research
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• 제20권5호
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• pp.49-55
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• 2007

반도체 쿼츠 웨이퍼 다이싱용 블레이드는 마이크로/나노 디바이스와 부품을 제조하기 위해 고정밀도의 가공성을 요구한다. 따라서 균일한 마이크로/나노 선폭의 가공을 위해서는 블레이드의 제작 단계에서 균일한 두께와 밀도를 유지하는 것이 중요하다. 기존의 실리콘웨이퍼 가공을 위해서는 금속의 블레이드가 사용되고 있지만 쿼츠 웨이퍼 가공을 위해서는 고분자 복합재가 사용된다. 이러한 복합재는 가공성, 전기전도성, 그리고 적절한 강도와 연성 및 마모저항성이 있어야 한다. 그러나 기존의 건식성형 공정으로는 균일성을 유지하기 위해 많은 공정과 비용이 소비되고 있다. 본 연구에서는 도전성 나노 세라믹스 분말, 연마재 세라믹스 분말에 열경화성 수지, 전도성 고분자를 혼합한 복합재 분말을 습식성형 공정에 의해 제조, 평가하는 연구를 수행하였다. 먼저 복합재 분말을 액상과 혼합하여 블레이드를 제작하였으며, 액상의 종류, 액상 건조공정의 영향을 고찰하였다. 평가는 마이크로미터 측정기와 현미경을 이용하여 두께를 측정하였다. 두께편차와 기공률, 밀도, 경도, 등의 특성을 비교, 평가하였다. 그 결과 습식성형에 의해 블레이드의 두께편차를 감소시킬 수 있었으며, 경도 등의 특성을 향상시킬 수 있었다.