• Journal of Korea Foundry Society
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• v.15 no.3
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• pp.283-290
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• 1995

Molybdenum ingot of 50mm in diameter were obtained from sintered Mo bars by EB drip melting technique. Macroscopic observation of EB remelted ingot indicates that coarse and columnar grains grow in the direction parallel to ingot pulling direction. This can be explained by slow solidification (3mm/min), large temperature gradient and heat flow to this direction. The orientation of columnar structure was found to be <110>, <200> and <211> by the analysis of X-ray diffraction patterns. The contents of typical metallic impurities in Mo sintered bar are 1.2ppm Cr, 3ppm Fe, 44ppm Zr, 150ppm W. Most of metallic impurities were reduced below the order of ppm except zirconium and tungsten by the selective evaporation. In the removal of nonmetallic impurities, oxygen and carbon impurities were lowered from 120 to 6ppm and from 157 to 106ppm, respectively, after first melting. Although the purification effect was not significant with the number of remelting, Vickers hardness was reduced from 217 to 195 and 184 in sequence with increasing the number of remelting.

• International Journal of Industrial Entomology and Biomaterials
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• v.26 no.1
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• pp.54-60
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• 2013

The partial degumming of silk has recently attracted researchers' attention because of its ability to produce silk textiles with new tactile properties, intermediate between the softness of fully degummed silk and the hardness of raw silk. However, it is difficult to obtain partially degummed silk in a homogenously degummed state due to the heterogeneous character of sericin removal. It is also difficult to examine the homogeneity of degumming. In the present study, Fourier transform infrared (FTIR) spectroscopy with attenuated total reflection (ATR) geometry was used to evaluate the effect of processing conditions on the degumming of silk yarns. The crystallinity index, calculated from FTIR spectra, showed an increase with the degumming ratio. Therefore, the homogeneity of degumming could be evaluated by the variation of crystallinity index for 30 different spots in silk yarns. The homogeneity of degumming was influenced by the total degumming time, the content of surfactant, and the liquor rate. No effect was observed upon changing the number of degumming cycles at the same total degumming time.

• Journal of Ocean Engineering and Technology
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• v.19 no.6 s.67
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• pp.64-71
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• 2005

The welding methods have been applied to the most structural products used in the automobile, ship construction, and construction. The structure steel must have sufficient strength of structure; However, the mechanical properties of the welded part changes when it is welded. Therefore, the stability or life of the structure may be affected by the changed mechanical properties. The mechanical properties of the welded part must be examined in order to ensure the safety of structure. In this research, the SS400 steel and the STS304 steel were used to estimate the mechanical properties of the HAZ by weld thermal cycle simulation. In this study, the materials were used to examine the weld thermal cycle simulation characteristic, under two conditions: the drawing with diameter of $\Phi$10 and the residual stress removal treatment. To examine the mechanical properties by the weld thermal cycle simulation, the tensile test was carried out in room temperature. The crosshead speed was lmm/min.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.17 no.1
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• pp.16-22
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• 2018

Silicon carbide (SiC) is used in various semiconductor processes because it has superior thermal, mechanical, and electrical characteristics as well as higher chemical and corrosion resistance than existing materials. Due to these characteristics, various manufacturing technologies have been developed for SiC. A recent development among these technologies is Chemical Vapor Deposition SiC (CVD-SiC). Many studies have been carried out on the processing and manufacturing of CVD-SiC due to its different material characteristics compared to existing materials like RB-SiC or Sintered-SiC. CVD-SiC is physically stable and has excellent chemical and corrosion resistance. However, there is a problem with increasing the thickness, because it is manufactured through a deposition process. Additionally, due to its high strength and hardness, it is difficult to subject to machining.

• Transactions of Materials Processing
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• v.15 no.1 s.82
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• pp.57-64
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• 2006

High speed milling experiment on the hardened mold steel (CALMAX at hardness of HRC 55) is carried out using small diameter ball endmills. Tool lift and wear characteristics under the various machining parameters are investigated Effect of dynamic runout on the wear of the tool is also studied. For most of the cases, catastrophic chipping of tool edge is not observed and uniformly distributed wear on the flank surface of the tool is obtained. It is found that lower rate of tool wear is obtained as the cutting speed is increased. Also, high pick feed rate is found to be more favorable in terms of the tool wear and material removal rate.

• Journal of the Korean Society for Precision Engineering
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• v.21 no.1
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• pp.61-70
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• 2004

Generally, ceramics are very difficult-to-cut materials because of its high strength and hardness. The machining process of ceramics can be characterized by cracking and brittle fracture. In the machining of ceramics, edge chipping and crack propagation are the principal reasons to cause surface integrity deterioration. Such phenomenon can cause not only poor dimensional and geometric accuracy, but also possible failure of the ceramic parts. Ceramics can be machined with traditional method such as grinding and polishing. However, such processes are generally cost-expensive and have low material removal rate. Thus, in this paper, to overcome these problems. BN powder, which gives good cutting property, is added for the fabrication of machinable ceramics by volume of 5,10,15,20,25 and 30%. And, mechanical properties, R-curve behavior and machining tests are carried out to evaluate the machining properties of the manufactured machinable ceramics.

• Journal of the Korean Society for Precision Engineering
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• v.21 no.1
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• pp.133-139
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• 2004

High speed machining (HSM) can reduce machining time with the high metal removal rate by high speed spindle and feedrate. This paper supports HSM technology using the small size tool with the optimal tool path generation and modification of tool change. The optimum tool path is generated to reduce cutting length of cavity pattern and change the cutting tool for preventing the tool breakage by wear. The tool path is modified with the experiment data of tool wear and breakage to support tool change on reasonable time. The result can contribute to HSM technology of high hardness materials using the small size end-mill.

• Journal of the Korean Society of Safety
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• v.24 no.1
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• pp.1-6
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• 2009

In machining of ceramic materials, they are very difficult-to cut materials because of there high strength and hardness. Machining of ceramics are characterized by cracking and brittle fracture. Generally, ceramics are machined using conventional method such as grinding and polishing. However these processes are generally costly and have low MRR(material removal rate). This paper focuses on machinability evaluation of machinable ceramics for products with CNC machining center. Thus, in this paper, experiment applying cutting parameters is performed based on experimental design method. A design and analysis of experiments is conducted to study the effects of these parameters on the surface roughness by using the S/N ratio, analysis of ANOVA, and F-test. And multiple linear regression analysis is applied to compare experimental with predicted data in consideration of surface roughness. Cutting parameters, namely, feed, cutting speed and depth of cut are used to accomplish purpose of this paper. Required experiments are performed, and the results are investigated.

• The Journal of Korean Academy of Prosthodontics
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• v.41 no.2
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• pp.128-135
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• 2003

Statement of problem : Implant screw loosening remains a problem in implant prosthodontics. Some abutment screws with treated surfaces were introduced to prevent screw loosening and to increase preload. DLC(Diamond Like Carbon) film has similar properties on hardness, wear resistance, chemical stability, biocompatibility as real diamond materials. Purpose : The purpose of this study was to investigate the effect of lubricant layer on abutment screw and to discriminate more effective method between soft lubricant and hard lubricant to prevent screw loosening. Material and method : In this study, $1{\mu}m$ thickness DLC was used as protective, lubricating layer of titanium screws and 3 times removal torque was measured on the abutment screws to investigate the difference in 10 coated and 10 non-coated abutment screws. Results : The results indicated that the implants with DLC coating group were not more resistant to the applied force in screw loosening. At 32Ncm, the 3 times removal torque in DLC group were $27.75{\pm}2.89,\;25.85{\pm}2.35$ and $26.2{\pm}2.57$. The removal torque in no-coated abutment screws were $27.85{\pm}4.23,\;27.35{\pm}2.81$ and $27.9{\pm}2.31$, respectively. Conclusion : The lubricant layer used in this study was Diamond Like Carbon(DLC) and it have a properties of hard and stable layer. The DLC coating layer was hard enough to prevent distortion of screws in the repeated unscrewing procedure in clinical situation. The reduced friction coefficient in hard DLC layer was not effective to prevent screw loosening.

• Journal of Surface Science and Engineering
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• v.53 no.6
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• pp.271-279
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• 2020

Non-ferrous metals, widely used in the mechanical industry, are difficult to machine, particularly by drilling and tapping. Since non-ferrous metals have a strong tendency to adhere to the cutting tool, the tool life is greatly deteriorated. Diamond-like carbon (DLC) is one of the promising candidates to improve the performance and life of cutting tool due to their low frictional property. In this study, a sacrificial DLC layer is applied on the hard nitride coated drill tool to improve the durability. The DLC coatings are fabricated by controlling the acceleration voltage of the linear ion source in the range of 0.6~1.8 kV. As a result, the optimized hardness(20 GPa) and wear resistance(1.4 x 10-8 ㎣/N·m) were obtained at the 1.4 kV. Then, the optimized DLC coating is applied as an sacrificial layer on the hard nitride coating to evaluate the performance and life of cutting tool. The Vickers hardness of the composite coatings were similar to those of the nitride coatings (AlCrN, AlTiSiN), but the friction coefficients were significantly reduced to 0.13 compared to 0.63 of nitride coatings. The drilling test were performed on S55C plate using a drilling machine at rotation speed of 2,500 rpm and penetration rate of 0.25 m/rev. The result showed that the wear width of the composite coated drills were 200 % lower than those of the AlCrN, AlTiSiN coated drills. In addition, the cutting forces of the composite coated drills were 13 and 15 % lower than that of AlCrN, AlTiSiN coated drills, respectively, as it reduced the aluminum clogging. Finally, the application of the DLC sacrificial layer prevents initial chipping through its low friction property and improves drilling quality with efficient chip removal.