• Journal of the Semiconductor & Display Technology
• /
• v.10 no.3
• /
• pp.35-42
• /
• 2011

This paper describes the characteristics of high speed grinding and the influence of wheel surface speed V and a grindability of the grinding materials. The various fine ceramics pieces was ground by metal and vitrified bonded diamond wheel. The surface roughness of fine ceramics(Zirconia($ZrO_2$), Silicon Carbide(SiC), Silicon Nitride($Si_3N_4$), Alumina($Al_2O_3$)) decreases from $0.05{\mu}m(R_{max})$ to $0.025{\mu}m(R_{max})$ when the wheel speed at grinding point increases the wheel speed. Relation between the temperature at grinding point and surface roughness was linear. Abrasive jet machining(AJM), a specialized from of shot blasting, is considered one of the most helpful micro machining methods for hard and brittle materials such as glasses and ceramics by constant pressure grinding.

• Journal of the Korean Society for Precision Engineering
• /
• v.27 no.7
• /
• pp.117-122
• /
• 2010

Recently, aspheric glass lens molding core is fabricated with tungsten carbide(WC). If molding core is fabricated with silicon carbide(SiC), SiC coating process, which must be carried out before the Diamond-Like Carbon(DLC) coating can be eliminated and thus, manufacturing time and cost can be reduced. Diamond Like Carbon(DLC) is being researched in various fields because of its high hardness, high elasticity, high durability, and chemical stability and is used extensively in several industrial fields. Especially, the DLC coating of the molding core surface used in the fabrication of a glass lens is an important technical field, which affects the improvement of the demolding performance between the lens and molding core during the molding process and the molding core lifetime. Because SiC is a material of high hardness and high brittleness, it can crack or chip during grinding. It is, however, widely used in many fields because of its superior mechanical properties. In this paper, the grinding condition for silicon carbide(SiC) was developed under the grinding condition of tungsten carbide. A silicon carbide molding core was fabricated under this grinding condition. The measurement results of the SiC molding core were as follows: PV of 0.155 ${\mu}m$(apheric surface) and 0.094 ${\mu}m$(plane surface), Ra of 5.3 nm(aspheric surface) and 5.5 nm(plane surface).

• Journal of Powder Materials
• /
• v.8 no.3
• /
• pp.210-213
• /
• 2001

$Si_3N_4$/TiN nano/nano-type composites were successfully fabricated by the combination of a mechano-chemical grinding (MCG) method and a short time sintering process, and their wear resistance was evaluated. Powder mixtures of $\alpha-Si_3N_4$and Ti were prepared using mechano-chemical grinding process and the resulting nanocomposite powder mixtures were consolidated using pulsed electric current sintering (PECS). TEM observation showed that the nano/nano-type composites consisted of homogeneous and very fine matrix grains with the size less than 100 nm. The obtained $Si_3N_4$-based nano/nano-type showed high wear resistance and electric discharge machinability.

• Journal of the Korean Ceramic Society
• /
• v.51 no.2
• /
• pp.121-126
• /
• 2014

The influence of a liquid medium duringa wet-milling process in the grinding and oxidation of silicon powder was investigated. Distilled water, dehydrated ethanol and diethylene glycol were used as the liquid media. The applied grinding times were 0.5, 3, and 12 h. Ground silicon powder samples were characterized by means of aparticle size analysis, scanning electron microscopy(SEM), x-ray powder diffraction (XRD), FT-IR spectroscopy and by a chemical composition analysis. From the results of the characterization process, we found that diethylene glycol is the most efficient liquid medium when silicon powder is ground using a wet-milling process. The FT-IR results show that the Si-O band intensity in an unground silicon powder is quite strongbecause oxygen becomes incorporated with silicon to form $SiO_2$ in air. By applying deionized water as a liquid medium for the grinding of silicon, the $SiO_2$ content increased from 4.12% to 31.7%. However, in the cases of dehydrated ethanol and diethylene glycol, it was found that the $SiO_2$ contents after grinding only changed insignificantly, from 4.12% to 5.91% and 5.28%, respectively.

• Journal of the Korean Ceramic Society
• /
• v.34 no.2
• /
• pp.195-201
• /
• 1997

The present paper describes the effect of dry mixed grinding on kaolinite-aluminum trihydroxide mixture with a planetary ball mill before sintering and its influence on mullite formation during sintering. The size reduction of the mixture is market in the early stage of grinding and the obtained fine particles agglomerate subsequently with an increase of grinding time. The crystal structure of the mixture is collapsed easily into an amorphous one by planetary ball milling, of which amount increases with an increase of grinding time. Only mullite phase except for anatase as an inherent impurity in kaolinite appeared in the sintered body of the mixtures with mixed grinding as relatively lower temperature 1523K, while corundum, cristobalite, and Al-Si spinel phases, besides mullite were formed in the sintered body of the mixture without mixed grinding. Therefore, the mixed grinding treatment is very effective to improve the homogeneous mixing and disp-ersion of the mixture of raw materials on a micro scale and to decrease the thermal decomposition tem-perature by crystal structure change of them so as to obatin direct preparation of mullite with high purity at relatively low temperature.

• Transactions of the Korean Society of Machine Tool Engineers
• /
• v.12 no.4
• /
• pp.9-16
• /
• 2003

In this study, the decision of dressing time for diamond wheel was analyzed by observing with acoustic emission signals and surface roughness, and also obtained the machining characteristics by weibull distribution plot for the values of bending strength. From the experimental study, it was possible to predict the time of re-dressing for the diamond grinding wheel with the analysis of acoustic emission signals and surface roughness values, and following conclusions were obtained. The root-mem-square values of acoustic emission signals were obtained low as the increased of table speed for different abrasive grain size. This is caused by the lack of grinding power which is not able to get rid of all real grinding mass of depth as the table speed is increased. The values of bending strength for ground $Si_3 N_4$ specimens were decreased for gain size of #400 than that of #60, but it was found that the surface roughness values for gain size of #60 were better than that of #400. As compared the shape parameter of weibull distribution plot for the values of bending strength, it was found that the reliability of bending strength for grain size of #60 increased than that of #400.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 1995.10a
• /
• pp.14-18
• /
• 1995

Although structural ceramics have excellent mectanical properties, it is very difficult to grind with high efficiency and high quality because of their high strength, hardness, and brittleness. Unfortunately machined ceramics often contain surface damages such as micro fracture and crack on account of brittle fracture. Therefore, is is important to minimize the brittle fracture. The present paper examines grinding characteristics of representative structural ceramics,such as Al /sab 2/O /sab 3/, SiC, Si /sab 3/ N /sab 4/. Effects of grinding variables including table speed and depth of cut on the grinding performance were investigated. Experimental results show that the surface quality is related to the specific grindings energy. The higher specific energy results in the better surface quality.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2002.10a
• /
• pp.155-159
• /
• 2002

This paper has studied to obtain the grinding characteristics and optimal grinding conditions of ceramics in the grinding with diamond wheel by Taguchi method. Feed rate was most important factor to the surface roughness. In the case of 4{Si_3}{N_4}$ and ${A1_2}{O_3}$, surface roughness value were small at 3m/min of feed rate. In the case of $ZrO_2$. surface roughness value was small at 4m/min of feed rate. Surface roughness have much influenced by major load for the :ii3N4 and $ZrO_2$. On the other hand, ${A1_2}{O_3}$ have more influenced by grain shedding of brittle fracture phenomenon. The major factors affecting the surface roughness and the optimum grinding conditions were obtained with minimum experiment using Taguchi method.

• Journal of the Korean Society for Precision Engineering
• /
• v.16 no.10
• /
• pp.182-186
• /
• 1999

Structural ceramics such as $Al_2O_3$, SIC, and $Si_3N_4$ are difficult to grind materials because of their high hardness and brittleness. They are normally ground in brittle mode, but it is possible to be ground in ductile mode depending upon the grinding conditions. In this paper an experimental investigation has been carried out to see the relationship between the grinding energy and grinding mode. It has been found that the ductile mode grinding consumes more grinding energy than the brittle mode grinding. Thus, the grinding conditions of the higher specific grinding energy leads to the plastic deformation in the ground surface of workpiece and results in the better surface finish.

• Journal of the Korean Society for Precision Engineering
• /
• v.19 no.8
• /
• pp.141-146
• /
• 2002

This paper has studied to obtain the grinding characteristics and optimal grinding conditions of ceramic materials in the grinding with diamond wheel by design of experiments. The load on wheel by varying the feed rate was related with the surface roughness due to the minute destruction phenomenon of grains for the $Si_3\;N_4\;and\;ZrO_2$. The depth of cut is related with the surface roughness because the grinding is carried out by grain shedding process due to the brittle fracture phenomenon for the $A1_2\;O_3$. The major factors affecting the surface roughness and the optimum grinding conditions were obtained with minimum experiments using design of experiments.