• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.1 s.173
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• pp.1-6
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• 2000

As dies and molds have become more and more complicated in the recent years, the demand for lower cost and shorter production time is also growing stronger. Rapid prototyping and Tooling technologies are expected to be used for more rapid and lower cost tool fabrication. However the rapid tooling methods have not yet reached the level of application to the manufacturing of metallic dies and molds which require high dimensional accuracy. As the rapid tooling technology, there are the slurry casting, the powder casting, the direct laser sintering, and so on. Generally, in the slurry casting, the alumina powder and the water soluble phenol were mainly used. However, the mechanical properties of the phenol were not good enough to apply to molds directly. In this study, pure epoxy and two types of aluminium powder reinforced resin are applied to the slurry casting. The mechanical and thermal properties are better than phenol because the epoxy is the thermosetting resin. And mechanical characteristics such as shrinkage rate, hardness, surface roughness are measured for the sake of comparison. Metal powder reinforced resin molds are better than the resin tool form the viewpoint of shrinkage rate and hardness. Finally, it has been shown that the application possibility of this process is high, because the manufacturing time and cost savings are significant.

• Journal of Dental Rehabilitation and Applied Science
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• v.36 no.3
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• pp.168-175
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• 2020

Purpose: The purpose is to test and evaluate the physical properties of commonly used temporary restoration materials and newly emerged materials. Materials and Methods: Four groups of polymer materials were evaluated: Polymethyl methacrylate (PMMA) 2 groups, Polyetheretherketone (PEEK), Polycarbonate. Four physical properties were tested: surface hardness, bending strength, abrasion resistance during wear, wear behavior. The 3-axis bending strength and Vickers hardness test were measured using a universal testing machines respectively. The microstructure was observed with a scanning electron microscope and weight comparison was evaluated after 100,000 chewing tests using a chewing simulator. Kruskal wallis test was performed to evaluate statistical significance. Results: The four groups showed the highest flexural strength and Vickers hardness of PEEK, followed by PC, PMMA-H, PMMA-T. Microstructure observation also showed the least surface roughness in the PEEK group, followed by PC, PMMA-H, PMMA-T. Conclusion: PC is considered to have sufficient mechanical properties that can be applied to the manufacture of temporary teeth. However, further studies, such as biocompatibility, are considered to be necessary for practical clinical applications.

• Journal of the Korean Vacuum Society
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• v.21 no.4
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• pp.193-198
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• 2012

In this study, we have fabricated the polymer insulator and diamond-like carbon (DLC) thin films by using plasma enhanced chemical vapor deposition methods. we fabricated the DLC films with various thicknesses as the passivation layer on plasma polymer and investigated the structural, physical, and electrical properties of DLC/plasma polymer films. The plasma polymer synthesized in this work had the low leakage current and low dielectric constant. The values of hardness and elastic modulus in DLC/plasma polymer films are increased, and the value of rms surface roughness is decreased, and contact angle value is increased with increasing DLC film thickness. In the electrical properties of DLC/plasma polymer, the value of the dielectric constant is increased, however the leakage current property of the DLC/plasma polymer is improved than that of plasma polymer film with increasing DLC film thickness.

• Korean Journal of Materials Research
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• v.22 no.10
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• pp.552-561
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• 2012

Diamond-like carbon (DLC) films have been widely used in many industrial applications because of their outstanding mechanical and chemical properties like hardness, wear resistance, lubricous property, chemical stability, and uniformity of deposition. Also, DLC films coated on paper, polymer, and metal substrates have been extensively used. In this work, in order to improve the printing quality and plate wear of polymer printing plates, different deposition conditions were used for depositing DLC on the polymer printing plates using the Pulsed DC PECVD method. The deposition temperature of the DLC films was under $100^{\circ}C$, in order to prevent the deformation of the polymer plates. The properties of each DLC coating on the polymer concave printing plate were analyzed by measuring properties such as the roughness, surface morphology, chemical bonding, hardness, plate wear resistance, contact angle, and printing quality of DLC films. From the results of the analysis of the properties of each of the different DLC deposition conditions, the deposition conditions of DLC + F and DLC + Si + F were found to have been successful at improving the printing quality and plate wear of polymer printing plates because the properties were improved compared to those of polymer concave printing plates.

• Tribology and Lubricants
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• v.37 no.3
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• pp.83-90
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• 2021

In this study, an ultrasonic nanocrystal surface modification (UNSM) was used to improve the mechanical properties, scratch resistance and tribological performance of Cu-based bimetals, which are usually used to manufacture sliding bearings and bushings for internal combustion engines (ICEs). Two different Cu-based bimetals, namely CuPb10Sn10 and CuSn10Bi7, were sintered onto a low carbon steel substrate. The mechanical properties and dry tribological performance using a tensile tester and micro-tribo tester were evaluated, respectively. The scratch resistance was assessed using a micro-scratch tester at an incremental load. The tensile test results showed that the yield strength (YS) and ultimate tensile strength (UTS) of both Cu-based bimetals increased after UNSM. Furthermore, the scratch and tribological tests results revealed that the scratch resistance and tribological performance of both Cu-based bimetals were improved by the application of UNSM. These improvements were mainly attributed to the eliminated pores, increased hardness and reduced roughness after UNSM. CuSn10Bi7 demonstrated better mechanical properties, scratch resistance and tribological performance than CuPb10Sn10. It was found that the presence of Bi in CuSn10Bi7 formed a Cu₁₁Bi₇ intermetallic phase, which is harder than Cu₃Sn. Hence, CuSn10Bi7 demonstrated higher strength and wear resistance than CuPb10Sn10. In addition, a CuSn10Bi7 formed both SnO₂ and Bi₂O₃ that prevented adhesion and improved the tribological performance. It can be expected that under dry tribological conditions, ICEs can utilize UNSM bearings and bushings made of CuSn10Bi7 instead of CuPb10Sn10 under oil-lubricated conditions.

• Proceedings of the Korean Geotechical Society Conference
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• 2002.03a
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• pp.237-244
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• 2002

Televiewer is a logging tool capable of scanning the borehole wall. The tool uses a rotating acoustic beam generator that acts as both a transmitter and receiver. The beams are sent toward the wall. The amplitude of a returning signal from the wall has nearly a linear relationship with the reflection coefficient R of the borehole wall, when the wall is smooth. As R depends only on rock impedance for fixed water impedance, the amplitude is directly associated with mass density and seismic velocity of rock. Meanwhile, the amplitude can be further reduced by wall roughness that may be caused by drilling procedures, differences in rock hardness, because the rough surface can easily scatter the acoustic energy and sometimes the hole becomes elongated in all directions according to the degree of weathering. In this sense, the amplitude is related to the hardness of rocks. For convenience of analysis, the measured amplitude image(2-D data(azimuth ${\times}$ depth)) is converted, with an appropriate algorithm, to the 1-D data(depth), where the amplitude image values along a predetermined fracture signature(sinusoid) are summed up and averaged. The resulting values are subsequently scaled simply by a scalar factor that is possibly consistent with a known strength. This scaled Televiewer reflectivity is named, as a matter of convenience,“Televiewer rock strength”. This paper shows, based on abundant representative case studies from about 8 years of Televiewer surveys, that Televiewer rock strength might be regarded, on a continuous basis with depth, as a quitely robust indicator of rock classification and in most cases as an approximate uniaxial strength that is comparable to the rebound value from Schmidt hammer test.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.21 no.2
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• pp.123-129
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• 2022

Quartz (SiO2) has high abrasion and heat resistances and excellent chemical and mechanical properties; therefore, it is used in various industries, such as machinery, chemistry, optics, and medicine. Quartz is a high-hardness and brittle material and is classified as the topmost difficult-to-cut material, which is because of the cracking or chipping at the edge during processing. Corner wear, such as cracks and chippings that occur during cutting, is a major cause for the deterioration in the machining quality. Therefore, many researchers are investigating various techniques to process quartz effectively. However, owing to the mechanical properties of quartz, most studies have been conducted on grinding, micromachining, and microdrilling. Few studies have been conducted on quartz processing. The purpose of this study was to analyze the machining characteristics according to the machining factors during the slot machining of quartz using a cubic boron nitride (CBN) tool and to select the optimal machining conditions using the Taguchi method. The machining experiment was performed considering three process variables: the spindle speed, feed rate, and depth of cut. The cutting force and surface roughness were analyzed according to the processing conditions.

• 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 the Korean Society for Precision Engineering
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• v.28 no.6
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• pp.694-700
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• 2011

Since polycrystalline diamond (PCD) has high hardness like diamond, it has been used as tool material for lathe and milling of non-ferrite material. A micro tool fabricated from PCD material can be used for micro machining of hard material such as tungsten carbide, glass, and ceramics. In this paper, micro PCD tools were fabricated by micro EDM (electrical discharge machining) and used for micro grinding of glass. Craters generated on the tool surface by EDM spark work as like grits in grinding process. The effects of tool shapes, tool roughness and PCD grain size were investigated. Also studied was a hybrid process combining electrochemical discharge machining (ECDM) and micro grinding for micro-structuring of glass.

• Journal of the Korean Society for Precision Engineering
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• v.30 no.3
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• pp.324-330
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• 2013

This paper describes a novel method to surface large optics mirror with an extremely high hardness, which could replace the high cost of the repetitive off-line measurement steps and the large ultra-precision grinding machine with ultra-positioning control of 10 nm resolution. A lot of diamond pellet to be attached on the convex aluminum base consists of a grinding tool for the concave large mirror, and the tool was pressured down on the large mirror blank. The tool motion at an interval on the spiral path was controlled with each feed rate as the dwell time in the conventional computer-controlled polishing. The shape to be surfaced was measured directly by a touch probe on the machine without any separation of the mirror blank. Total 40 iterative steps of the surfacing and measurement could demonstrate the form error of RMS $7.8{\mu}m$, surface roughness of Ra $0.2{\mu}m$ for the mirror blank with diameter of 1 m and spherical radius of curvature of 5400 mm.