• Proceedings of the Korean Society of Precision Engineering Conference
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• 1997.04a
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• pp.1049-1052
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• 1997

The pupose of this study on the surface finishing is to examine the performance of brushing as a means of reducing the surface roughness of the precision theaded shafts in ball screw assemblies. Ball screws provide superior performance compared to other types of screw feeds in terms of static and dynamic rolling resistance,backlash,and wear characteristics. The Reduction of the surface roughness of the lead shaft in ball screw assembiles is essential for precision movement,high speed/low noise tracel, and for low wear/long life. To reduce machine dependent errors that would influence the surface roughness compared with other lapping or polishing techniques,experiments will be performed using special wire brushes to polish precision ground shafts. The best results were obtained using the Al /sab 2/O /sab3/ brushes, with the Al /sab 2/O /sab3/ #500 grit brush producing a surface finish of approximately 0.7 .mu.m, and the Al /sab 2/O /sab3/ #600 grit producing a surface finish of approximately 0.8 .mu.m. Both of these results were produced at the highest wheel polishing speed of 3520 rpm. The SiC #500 brush produced a surface roughness of approximately 1 .mu.m at 3520 rpm.

• Tribology and Lubricants
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• v.30 no.6
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• pp.350-355
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• 2014

This study proposes a sustainable bearing remanufacturing process using the ultrasonic nanocrystal surface modification (UNSM) technique. The UNSM technique is a newly developed and sophisticated surface modification technique that can increase the mechanical properties and improve the friction and wear performance of materials. Taking advantage of the bearing manufacturing process is the most significant way of optimizing the life of a bearing. The proper maintenance and usage of repaired bearings can increase their life to be equal to or greater than that of new bearings. This paper discusses the restoration of certain mechanical properties of worn, damaged, and discarded bearings, and suggests a remanufacturing process for used bearings, which can impart them with a lifespan equivalent to that of new bearings. The most damaged part of the discarded bearings is the raceway, which is the site of accumulated fatigue. The existing polishing or barrel finishing processes can recover the accumulated fatigue only partially. Rolling contact fatigue tests performed on UNSM-treated new and used specimens polished after $4{\times}10^6$ cycles reveal that UNSM-treated new specimens exhibit the longest fatigue life compared to other specimens. This study verifies the proposed complete fatigue recovery process, which can increase the fatigue life of used bearings to a level greater than that of new bearings.

• Journal of the Korean Society of Industry Convergence
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• v.26 no.4_2
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• pp.591-598
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• 2023

In this study, the corrosion resistance by salt spray was evaluated using A6061-T6 for an electric vehicle battery pack case coated with an organic/inorganic hybrid solution. The lowest curing temperature of 190 ℃ resulted in significant corrosion and pitting. Meanwhile, no corrosion was observed in the coated specimens at 210 ℃ and 230 ℃ except at 210 ℃ - 6 min and 8 min. The surface of the as-received coating specimen observed by FE-SEM exhibited streaks and dents in the rolling direction, but the coating surface was clean. On the 190 ℃ - 6 min coating specimen, which had a lot of corrosion, rolling streaks spread, and dents were caused by corrosion. The 200 ℃ - 12 min coating specimen did not show corrosion, but it showed an etched surface. In the line profile, Si, the main component of the coating solution, was detected the most, and Ti was also detected. In the coating specimens with salt spray, O increased and Si decreased, regardless of corrosion. The peeling rate by adhesion evaluation was 26 - 87% for the 190 ℃ coating specimen, 4 - 83% for the 210 ℃ coating specimen, and 94 - 100% for the 230 ℃ coating specimen. The optimal curing conditions for the coating solution used in this study were 210 ℃ for 10 min.

• Journal of the Korean Society for Precision Engineering
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• v.26 no.10
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• pp.47-55
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• 2009

In this study, a robot foot having toes for firm stepping on uneven surface is proposed. The toes are connected to the lower leg by parallel links so that the lower leg can rotate in the rolling and pitching directions during stance phase without ankle joint. The landing performance of the foot on uneven surface was evaluated by relative comparison with that of the most common foot making point contact with the walking surface, since the test conditions considering real uneven surface could be hardly defined for its objective evaluation. Anti-slip margin(ASM) was defined in this study to express the slip resistance of a robot foot when it lands on a projection with half circular-, triangular- or rectangular cross section, assuming that uneven surface consists of projections having these kind of cross sections in different sizes. Based on the ASM analysis, the slip conditions for the two feet were experimentally confirmed. The results showed that the slip resistance of the new foot is not only higher than that of the conventional point contact type foot but also less sensitive to the surface friction coefficient.

• Tribology and Lubricants
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• v.35 no.4
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• pp.237-243
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• 2019

Through this study, we investigate the effects of ultrasonic nanocrystal surface modification (UNSM) technology on the fatigue life of needle roller bearings. The fatigue life of untreated and UNSM-treated needle roller bearings is evaluated using a roller fatigue tester at various contact stress levels under oil-lubricated conditions. We can ascertain that the fatigue life of an UNSM-treated needle roller bearing was extended by approximately 34.3% in comparison with an untreated one, where the effectiveness of UNSM technology diminishes with increasing contact stress. The surface roughness and surface hardness of needle roller bearings before and after being treated by UNSM technology are compared and discussed to understand the role of UNSM technology in improving the fatigue life of needle roller bearings. In addition, a fractograph of the damaged bearings is observed using a scanning electron microscopy to shed light on the fracture mechanisms of bearings under different contact stress levels. We can therefore conclude that the application of UNSM technology to the needle roller bearings improves the fatigue life by reducing the friction coefficient and increasing the wear resistance; this may be attributed to a reduction in surface roughness from 0.5 to $0.149{\mu}m$ and an increase in surface hardness from 58 to 62 HRc.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1991.06a
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• pp.1-30
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• 1991

The lubrication state between contacting bodies with rolling and sliding under loaded condition is generally understood by the conception shown in Figure 1. When the lubricating oil film formation between facing bodies is good enough to separate these bodies by the hydrodynamic pressure, this state is called by the expression of "hydrodynamic lubrication". The thickness of oil film is so large that the lubricating oil between facing bodies behaves as fluid and metal-to-metal contact between surface roughness asperities on facing bodies does not occur. When the oil film thickness becomes thinner or when the surface roughness height becomes larger, top of surface roughness asperities on facing bodies reaches very near to each other and there the oil or absorbed oil molecules on the surface of facing bodies behave no more as fluid. Partly metal-to-metal contact of surface roughness asperities occurs. Such lubrication state is called by the expression "mixed-lubrication". When the oil film thickness becomes more thinner or surface roughness height becomes larger, metal-tometal contact or contact via absorbed oil molecules dominate at most of the part in contact zone. Such state is called by the expression "boundary lubrication". Schematic representation of these three regimes of lubrication is shown in Figure 1.rication is shown in Figure 1.

• Journal of Electrical Engineering and Technology
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• v.11 no.6
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• pp.1729-1734
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• 2016

The surface inspection of a steel billet is a common practice in the steel manufacturing process prior to hot rolling to produce steel wire for tire cord. This billet surface inspection is an important process because flaws on the surface may cause major failures during the product manufacturing phase. This paper presents a computer simulation based on a finite element method for a magnetic flaw detector with a function of the current intensity, the number of coil turns, and the billet proceeding speed during the production phase based on the typical condition of conventional apparatus. Based on the simulation result, the magnitude of the electromagnetic field on the surface diminished with distance from the electromagnet. In addition, the increased current intensity and the increased number of coil turns actually induced a stronger electromagnetic field on the billet surface. On the other hand, the proceeding speed of a billet in its production line had no significant effects. The result in this study may assist to reduce trial and error and to minimize the opportunity costs during the optimization process by applying the findings of this study into the operation condition in the steel billet production line.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2002.10b
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• pp.199-200
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• 2002

Three-body abrasive wear resistance of mild steel, low alloy steel (Bisalloy) and 27%Cr white cast iron was investigated using a ball-cratering test. Glass beads, silica sand, quartz and alumina abrasive particles with sizes larger than $100{\mu}m$ were used to make slurries. It was found that the wear rates of all three materials tested increased with time when angular abrasive particles were used and were rather constant when round particles were used. This increase in wear rates was mainly due to the gradual increase in ball surface roughness with testing time. Abrasive particles with higher angularity caused higher ball surface roughness. Mild steel and Bisalloy were more affected by this ball surface roughness changes than the hard white cast iron. Generally, three-body rolling wear dominated. The contribution of two-body grooving wear increased when the ball roughness was significant. More grooves were found when round particles were used or the size of the particles was decreased.

• Transactions of the Korean Society of Automotive Engineers
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• v.18 no.3
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• pp.43-52
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• 2010

In this study, the shapes of the wheel and rail are represented by using 3-dimensional surface functions with surface parameters and a 3-dimensional wheel-rail contact analysis is presented. A whole numerical solution of wheel-rail contact at tread and flange including 2-point contacts can be achieved with the proposed numerical algorithm. Kinematic characteristics such as variances of vertical displacement and roll angle, and variance of wheel radius difference for arbitrary yaw and lateral displacement of wheelset, are determined for the KTX wheel-rail pair as an example. The condition of yaw and lateral displacement occurring 2-point contacts to analyze derailment are compared between standard and worn wheels. Differences of contact characteristics between curved and straight rails are also analyzed.

• Journal of the Korean Society for Precision Engineering
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• v.15 no.5
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• pp.167-175
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• 1998

A mathematical formulation is presented to model anisotropy from the deformation textures developed in a forming process. In this work, a micro-mechanical-based polycrystalline analysis is implemented into a consistent finite element method for the anisotropic, viscoplastic deformation of polycrystalline metals. As suggested by Taylor, the deformation of each grain in an aggregate is assumed to be same as the macroscopic deformation of an aggregate or a macro-continuum point. Algorithms are developed to represent the plastic anisotropy, such as the anisotropic yield surface and R-value, from the predicted deformation texture. As applications, the evolution of texture in rolling, upsetting and drawing/extrusion processes are simulated and the corresponding changes of mechanical properties such as yield surface and R-value are predicted.