• Korean Journal of Materials Research
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• v.16 no.8
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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.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.17 no.4
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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.

• Journal of Technologic Dentistry
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• v.35 no.4
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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.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.11
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• pp.7917-7924
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• 2015

In this study, based on CMA which is increasingly used for eco-friendly deicing materials, dehumidification MB made of sodium carbonate, $MgCl_2$/MgO (M/M), and SAP is to be produced. And its moisture absorption rate and dehumidification performance of the film are to be analyzed. And the data on the materials used for the dehumidification film are to be acquired. In case of the dehumidification MB, in which CMA and SAP are mixed, had poor film machinability due to foaming and moisture issues, but adding bentonite and calcium carbonate solved the problem. When a foaming agent was added to extend surface area between substances, CMA and M/M showed no remarkable difference, but SC showed large increase to 3.15 g/g. As the result of anti-corrosive test, CMA dehumidification film showed no corrosion while SC showed pitting corrosion and M/M showed corrosion.

• Journal of Korea Foundry Society
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• v.17 no.4
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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.

• Journal of the Korea Convergence Society
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• v.12 no.1
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• pp.105-110
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• 2021

Radiation shielding of affinity material, which is widely used in medical institutions, is made in sheet form and is mainly applied to apron. Shielding performance is presented based on lead equivalent, and is presented as 0.25-0.50mmPb. In the case of shielding materials where lead is used as the main material, the shielding performance can be adjusted by thickness due to the excellent machinability of lead. However, eco-friendly shielding sheets are difficult to control shielding performance based on thickness criteria as shielding performance varies depending on the content of shielding materials, the properties of polymeric materials that are base materials, and the technical differences in the process. In this study, shielding sheets were manufactured based on thickness to solve these problems and the shielding performance was compared in this study. As a result, it was shown that the laminated structure shielding sheet was more effective.

• Conservation Science in Museum
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• v.26
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• pp.1-12
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• 2021

The bisphenol A epoxy resin currently used for the conservation of stone cultural heritage items is known to suffer from yellowing discoloration. In order to mitigate this yellowing and explore the availability of more diverse materials for the conservation of stone cultural heritage items, a hydrogenated Bisphenol A-based epoxy resin was prepared and compared with the epoxy resin currently used in the conservation treatment of stone cultural heritage items. The newly prepared epoxy resin showed improved physical properties relative to the existing materials, especially in terms of tensile strength, adhesion, and machinability, while the yellowing discoloration was reduced by a factor of roughly five to eight. The results suggest that epoxy resin could be used as a stable material for the conservation treatment of stone cultural heritage items, most of which are located outdoors.

• Journal of Powder Materials
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• v.29 no.4
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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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• v.86 no.1
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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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• v.20 no.5
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• pp.49-55
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• 2007

Nanocomposite blade for dicing semiconductor wafer is investigated for micro/nano-device and micro/nano-fabrication. While metal blade has been used for dicing of silicon wafer, polymer composite blades are used for machining of quartz wafer in semiconductor and cellular phone industry in these days. Organic-inorganic material selection is important to provide the blade with machinability, electrical conductivity, strength, ductility and wear resistance. Maintaining constant thickness with micro-dimension during shaping is one of the important technologies fer machining micro/nano fabrication. In this study the fabrication of blade by wet processing of mixing conducting nano ceramic powder, abrasive powder phenol resin and polyimide has been investigated using an experimental approach in which the thickness differential as the primary design criterion. The effect of drying conduction and post pressure are investigated. As a result wet processing techniques reveal that reliable results are achievable with improved dimension tolerance.