• Journal of the Korean Society for Precision Engineering
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• v.26 no.9
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• pp.58-63
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• 2009

Silicon carbide (SiC) has been used for many engineering applications because of their high strength at high temperatures and high resistances to chemical degradation. SiC is very useful especially for a glass lens mold whose components demanded to the machining with good surface finish and low surface damage. The performance and reliability of optical components are strongly influenced by the surface damage of SiC during grinding process. Therefore, the severe process condition optimization shall be necessary for the highly qualified SiC glass lens mold. Usually the major form of damage in grinding of SiC is a crack occurs at surface and subsurface. The energy introduced in the layers close to the surface leads to the formation of these cracks. The experimental studies have been carried out to get optimum conditions for grinding of silicon carbide. To get the required qualified surface finish in grinding of SiC, the selection of type of the wheel is also important. Grinding processes of sintered SiC work-pieces is carried out with varying wheel type, depth of cut and feed using diamond wheel. The machining result of the surface roughness and the number of flaws, have been analyzed by use of surface profilers and SEM.

• Journal of the Korean Society of Industry Convergence
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• v.5 no.4
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• pp.367-372
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• 2002

Experimental study was conducted for lapping process after WEDMed specimen. In order to decide the lapping depth of the specimen, the number of the grain size was increased from 400, 600 to 800 to obtain the better surface. Observation of scanning electron microscope, hardness test, surface roughness test and energy dispersive spectrum(EDS) analysis were used for this experimental study. From the comparison and analyses of the results of between the wire-cut electrical discharge machining and the lapping, the following results were obtained. The surface roughness after lapping was found to be improved as increasing the number of lapping process like 1st, 2nd, 3rd lapping and the number of grain size such as 400, 600, 800. The surface hardness after increasing the lapping depth of the specimen was slowly increased. It was found that after 3rd lapping process the hardness was reached the hardness of original base material. It was found that the small amount of coating components within 3% was remained after the 1st lapping process, compared to that approximately 16% after WEDM process.

• Journal of Advanced Navigation Technology
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• v.17 no.5
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• pp.574-580
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• 2013

In this paper, The process of thin-film coating technology was applied to improve adhesion of the hardness thin film and nitride layer. This thin-film coating technology have formed composite thin-film to gain hardness and toughness used in press mold. The thin-film coating manufacturing technology increased vacuum present in the vacuum chamber and improved the throw ratio of the gun power using physical vapor deposition coating technology. Ti alloys target improved performance and surface material through the development of a composite film coating technology for various precision machining parts.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2012.05a
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• pp.180-186
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• 2012

A water-flow test for acceptance verification is carried out for a nonimpinging-type injector prior to the design-performance verification of 70 N-class liquid-rocket engine under development. It is observed that there exist varying characteristics of atomization among the injector-orifices caused by a fabrication crudeness of orifice holes which can be judged from a microscopic standpoint. The flow shedding phenomenon and ruffle on the surface of liquid column (or droplet) could be caught from the instantaneous spray images.

• Tribology and Lubricants
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• v.34 no.6
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• pp.262-269
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• 2018

In this work the friction and wear characteristics of the gray cast iron surface processed by broaching method, which is widely used in the machinery industry, were investigated. The broaching process is mainly used for mass production because it has high dimensional accuracy and processing speed, but the defects on surface can be easily generated. In order to improve the tribological characteristics, the approach was to reduce the roughness and hardness of the surface by adding a machining process to the broaching specimen. The secondary machining process using abrasive grains produces low roughness and hardness than broaching because it has high tool accuracy and removes the work hardened surface. The friction coefficient and the wear rate were assessed using a reciprocating-type tribotester to analyze the effects of surface finishing on the tribological properties. The friction tests were conducted under dry and lubricated conditions. The test results showed that the reduction of surface roughness and hardness through secondary machining process in lubricated condition improved the friction and wear characteristics. The reason why the same results did not appear in a dry condition was that wear occurred more rapidly than in lubricated condition. Thus, the positive effect of roughness and hardness of the surface obtained through the secondary machining process was not observed.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.45 no.4
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• pp.61-69
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• 2022

The function of coolant in machining is to reduce the frictional force in the contact area in between the tool and the material, and to increase the precision by cooling the work-piece and the tool, to make the machining surface uniform, and to extend the tool life. However, cutting oil is harmful to the human body because it uses chlorine-based extreme pressure additives to cause environmental pollutants. In this study, the effect of cutting temperature and surface roughness of titanium alloy for medical purpose (Ti-6Al-7Nb) in eco-friendly ADL slot shape machining was investigated using the response surface analysis method. As the design of the experiment, three levels of cutting speed, feed rate, and depth of cut were designed and the experiment was conducted using the central composite planning method. The regression expressions of cutting temperature and surface roughness were respectively obtained as quadratic functions to obtain the minimum value and optimal cutting conditions. The values from this formula and the experimental values were compared. As a result, this study makes and establishes the basis to prevent environmental pollution caused by the use of coolant and to replace it with ADL (Aerosol Dry Lubricant) machining that uses a very small amount of vegetable oil with high pressure.

• Composites Research
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• v.36 no.4
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• pp.241-245
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• 2023

Aluminum (Al) and copper(Cu) are non-ferrous alloys with excellent electrical and thermal conductivity but have relatively lower mechanical properties than iron alloys. Stainless steel(STS), an iron alloy, is a high-strength industrial material due to its excellent mechanical properties and corrosion resistance compared to non-ferrous Al and Cu. In this research combined Al, Cu, and STS to fabricate as a functionally graded material (FGM) through a powder metallurgical process. The produced FGM exhibited lightweight and excellent surface hardness compared to copper and iron alloys and also showed higher thermal conductivity than single Al and STS materials.

• Korean Journal of Materials Research
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• v.33 no.2
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• pp.71-76
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• 2023

The electroconvection generated on the surface of an ion exchange membrane (IEM) is closely related to the electrical/chemical characteristics or topology of the IEM. In particular, when non-conductive regions are mixed on the surface of the IEM, it can have a great influence on the transfer of ions and the formation of nonlinear electroconvective vortices, so more theoretical and experimental studies are necessary. Here, we present a novel method for creating microscale non-conductive patterns on the IEM surface by laser ablation, and successfully visualize microscale vortices on the surface modified IEM. Microscale (~300 ㎛) patterns were fabricated by applying UV nanosecond laser processing to the non-conductive film, and were transferred to the surface of the IEM. In addition, UV nanosecond laser process parameters were investigated for obvious micro-pattern production, and operating conditions were optimized, such as minimizing the heat-affected zone. Through this study, we found that non-conductive patterns on the IEM surface could affect the generation and growth of electroconvective vortices. The experimental results provided in our study are expected to be a good reference for research related to the surface modification of IEMs, and are expected to be helpful for new engineering applications of electroconvective vortices using a non-conductive patterned IEM.

• Journal of the Korean Society for Precision Engineering
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• v.12 no.11
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• pp.52-62
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• 1995

In the laser surface hardening process the geometrical parameters, especially the depth, of the hardened layer are utilized to assess the integrity of the hardening layer quality. Monitoring of this geometrical parameter ofr on-line process control as well as for on-line quality evaluation, however, is an extremely difficult problem because the hardening layer is formed beneath a material surface. Moreover, the uncertainties in monitoring the depth can be raised by the inevitable use of a surface coating to enhance the processing efficiency and the insufficient knowledge on the effects of coating materials and its thicknesses. The paper describes the extimation results using neural network to estimate the hardening layer depth from measured surface temperanture and process variables (laser beam power and feeding velocity) under various situations. To evaluate the effec- tiveness of the measured temperature in estimating the harding layer depth, estimation was performed with or without temperature informations. Also to investigate the effects of coating thickness variations in the real industry situations, in which the coating thickness cannot be controlled uniform with good precision, estimation was done over only uniformly coated specimen or various thickness-coated specimens. A series of hardening experiments were performed to find the relationships between the hardening layer depth, temperature and process variables. The estimation results show the temperature informations greatly improve the estimation accuracy over various thickness-coated specimens.

• Journal of Korean Society of Steel Construction
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• v.22 no.5
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• pp.399-409
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• 2010

Steel structures are threatened to reduce load-carrying capacity as the cross section is decreased by corrosion. However, there has been no method in definitely evaluating residual load-carrying capacity and the effect of corrosion to the load-carrying capacity of steel. This study evaluated tensile residual load-carrying capacity of corroded steel plates by using tensile tests of specimens, which were selected from the web of temporary structure's main beam. After the surface shapes were measured and tensile tests were examined, the rust of 21 corroded specimens was, first of all, removed using a chemical method. From the tensile test result, which of reference specimens that was picked off at the flange of the same main 13-mm-thick beam and corroded specimens were based, surface geometry and correlation with the reduction of corroded thickness and strain, yield strength or tensile strength was established as constant numbers. Effective thickness of corroded steel with irregular cross sections could be calculated using average residual thickness and standard deviation. The irregular cross sections could be the evaluated tensile strength that is equalized to non-corroded uniform steel's regardless of corrosion. Also, reasonable measuring intervals of residual thickness could be proposed by using this result to apply for executive work.