• Journal of the Korean Society of Industry Convergence
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• v.25 no.5
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• pp.799-810
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• 2022

Welding work is a production work method widely used throughout the industry, and various types of welding technologies exist. In addition, many methods are being studied to automate these welding operations using robots, but in the ship manufacturing field, welding such as painting, cutting, and grinding is also the most common operation, but the manual operation ratio is higher than in other industries. Such a high manual labor ratio in the field of ship manufacturing not only causes quality problems and production delays according to the skill of workers, but also causes problems in the supply and demand of manpower. Therefore, this paper analyzed the reason why the automation rate is low in welding work at ship manufacturing sites compared to other industries, and analyzed the production process and field environment for small and medium-sized ship manufacturing companies that repeatedly manufactured with a small quantity production method. Based on the analysis results, it is intended to propose a robot system that can easily move between workplaces and secure uniform welding quality and productivity by collaborating simple welding tasks with humans. Finally, the simulation environment is constructed and analyzed to secure the suitability of robot system application to current production site environment, work process, and productivity, rather than to develop and apply the proposed robot system. Through such pre-simulation and robot system suitability analysis, it is expected to reduce trial and error that may occur in actual field installation and operation, and to improve the possibility of robot application and positive perception of robot system at ship manufacturing sites.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.10 no.10
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• pp.2596-2601
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• 2009

Gouging is defined as the removal of weld metal and base metal from the opposite of a partially welded joint to facilitate complete joint penetration. Since the work by current method needs skillful welding and grinding, there is a limit on the increase of operation efficiency. Noise and dust from the weld gouging also deteriorate the work place and cause environmental problems. In this study, the gouging work by cutting method is proposed to overcome the defects from weld gouging such as low productivity, severe noise, dense dust, and so on. The developed cutting gouging system removes material as much as $13,565mm^3/min$, and enlarge the labor productivity as three times compared to that by weld gouging method.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.29 no.10 s.241
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• pp.1416-1429
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• 2005

In order to meet the increasing competitive pressures coupled with higher demands for component quality, whirling machines have been at the cutting edge of the automobile industry for more than 25 years. The hard whirling process can save on machining time and operation elimination. Hard whirling is done dry, without coolant. The chips carry away nearly all of the heat during cutting, leaving the workpiece cool and minimizing any thermal geometry variations. The surface finish and profile accuracy are close to grinding quality. Whirling machines usually consist of four major parts; 1) loading system that requires the necessary axial speeds, 2) head stock that needs high precision clamping and positioning system at the chuck and tailstock, 3) whirling unit that demands the high cutting speeds and cutting power fer cutting deep thread profiles and 4) unloading system that requires an easy workpiece unloading. Also, capabilities of the whirling machine can be improved by attaching a vision system to the machine. Most of whirling machines in Korean automobile industry are imported from the Leistritz company, Germany and the Hasegawa company, Japan. Tn this paper, a basic research will be performed to improve and enhance the existing whirling machines. Finally, a new Korean whirling machine will be proposed and developed.

• Journal of the Korean Society for Railway
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• v.18 no.6
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• pp.578-585
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• 2015

Track elastic components can be technically and economically efficient when integrated well into track superstructure of a railway network. In such cases, the elastic rail pad is larger than a 800m radius curve provides smooth rail branching and allows for high-speed operation ($V{\geq}160km/h$). High track resistance causes the tamping intervals to stand out because the constantly increasing share of the sleeper pad further extends the increase of the tamping interval and the long grinding period; the engineering and construction of the small curve radius track provides some measures for reducing the solid sounds. Installation of elastic mats under the ballast can have a good effect, particularly in the context of protection against dust during construction or extensive renovation measures when laying new lines. However, such a process requires special attention and proper installation.

• Plant Journal
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• v.18 no.3
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• pp.28-40
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• 2022

As the proportion of renewable energy generation is expected to increase, public power generation businesses need to actively consider implementing the expansion of biomass mixing, In this study, the biomass co-firing rate is being changed from 0wt.% to 5.0wt.% at 500MW coal-fired power plant, measuring the major operation characteristics of the pulverizer. First, the composition analysis and grinding characteristics of lignocelluosic biomass were examined, and the effect of volume increase on dirrerential bowl pressure difference, motor current, coal spillage, outlet temperature, and internal fire count was analyzed. As the co-firing rate increased, it was confirmed that the difference in the differential bowl pressure, motor current, and coal spillage treated increased, and the outlet temperature was minimal. The number of internal fires is difficult to find a clear correlation, but it has been confirmed that it is highly likely to occur in combination with other driving factors.

• Transactions of the Korean Society of Automotive Engineers
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• v.22 no.5
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• pp.20-28
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• 2014

The high velocity oxygen fuel spraying (HVOF) is a kind of surface modification process technology to form the sprayed coating layer after spraying the powder to molten or semi-molten state by the ultra-high speed at the high-temperature heat source and conflicting with a substrate. It is desirable to melt completely the thermal spray powder in order to produce the coating layer with an optimal adhesion, however, because a semi-molten powder in a spray process has the low efficiency and become a factor that degrades the mechanical property by the inducement of pore-forming within the coating layer. To improve the wear resistance, corrosion resistance and heat resistance, in this study, the plungers of high-speed and ultra-high pressure reciprocating hydraulic pumps for oil and water used in ironwork are produced with $420J_2$ and the coating layers of plungers are formed by the powders of WC-Co-Cr and WC-Cr-Ni including the high hardness WC. The surface of these plungers is modified by the super-mirror face grinding machine using variable air pressure developed in this laboratory, and then the characteristics of cross-sectional microstructure, and surface roughness and hardness values between no operation and 100 days-operation are examined and made a comparison. The fine tops and bottoms on surface roughness curve of oil-hydraulic pump plunger sprayed by WC-Cr-Ni are molded more and higher than those of water-hydraulic pump sprayed by WC-Co-Cr because the plunger diameter of oil-hydraulic pump is 0.4 times smaller than that of water-hydraulic pump and the pressure of oil-hydraulic pump exerted on the plunger is operated with the 70 bars higher than that of water-hydraulic pump. As a result, it is found that the values of centerline average surface roughness and maximum height for oil-hydraulic pump plunger are bigger than those of water-hydraulic pump plunger.

• The korean journal of orthodontics
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• v.36 no.2 s.115
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• pp.103-113
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• 2006

Most elderly women experience a decrease in their bone density due to a deficiency of calcium intake, ovariectomy, or menopause. This study evaluated the usability of the microscrew as a skeletal anchorage system in these orthodontic treatment cases, using rats as a research group. The 4 month old sprague-dawley species rats were divided into two groups, the OS (Ovariectomy Screw), and the SS (Sham operation Screw) group. In both the OS and SS groups, microscrews were implanted into the palatal bone between the upper molar teeth and two upper incisors were retracted using NETE coil spring with 75 g of force. After 3days, the again after 7 days, 7 rats in each group were sacrificed. Three days before they were sacrificed, Alizarin red S was intraperitoneally injected, and their maxillary bone, tibia and blood from their hearts were taken. The components of the extracted blood were biochemically analyzed and non-decalcified grinding resin sections for maxillary bone and tibia were made. The sections were examined with a polarization microscope, and fluorescent microscope. Smaller concentrations of Ca and P, the inorganic substances closely related to bone density, were found in the extracted blood of the OS group. Both OS and SS groups showed a possibility of bone remodeling with a high concentration of ALP after 7 days. An increase in bone density on the tension and compression sides of the microscrew and the tension side of the tooth for both OS and SS groups was confirmed with a polarization microscope. However, the bone density of the pressure side of the tooth and apical side was decreased. More deposits of Alizarin red S in the bone after 7 days rather than 3 days seen with a fluorescent microscope suggested the existence of new bone formation.

• Resources Recycling
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• v.23 no.6
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• pp.3-11
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• 2014

Bottom ash from coal fired power plants is not widely used due to a broad range of particle sizes and a high carbon content for producing geopolymers. The effect of mechanical activation on compressive strength of bottom ash- based geopolymers was examined by rod and planetary-ball milling to encourage full-fledged recycling of bottom ash, the main component of pond ash. The amount of amorphous component in the milled ash samples did not change significantly after the mechanical activation. It is presumably because needle-shaped mullite crystals, which is a major crystalline phase and grown in a glassy matrix, possess high strength and toughness, and therefore, they could endure external shocks and remain almost intact. Milling operation, however, decreased the particle size and improved the homogeneity of ash, thereby leading to increase reactivity of milled ash with alkali activators. Rod milling produced a relatively narrow particle size distribution of the milled ash particles; however, it was less effective in reducing the particle size. Nevertheless, it was interesting to observe that rod milling had equal effect on improving the compressive strength of geopolymers up to about 37%, as that of planetary ball milling. Rod milling is believed to be suitable process for enhancing the reactivity of bottom ash for large-scale recycling of bottom ash and producing geopolymers.

• Steel and Composite Structures
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• v.34 no.5
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• pp.681-698
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• 2020

The paper addresses contribution to the modeling and optimization of major machinability parameters (cutting force, surface roughness, and tool wear) in finish dry hard turning (FDHT) for machinability evaluation of hardened AISI grade die steel D₃ with PVD-TiN coated (Al₂O₃-TiCN) mixed ceramic tool insert. The turning trials are performed based on Taguchi's L₁₈ orthogonal array design of experiments for the development of regression model as well as adequate model prediction by considering tool approach angle, nose radius, cutting speed, feed rate, and depth of cut as major machining parameters. The models or correlations are developed by employing multiple regression analysis (MRA). In addition, statistical technique (response surface methodology) followed by computational approaches (genetic algorithm and particle swarm optimization) have been employed for multiple response optimization. Thereafter, the effectiveness of proposed three (RSM, GA, PSO) optimization techniques are evaluated by confirmation test and subsequently the best optimization results have been used for estimation of energy consumption which includes savings of carbon footprint towards green machining and for tool life estimation followed by cost analysis to justify the economic feasibility of PVD-TiN coated Al₂O₃+TiCN mixed ceramic tool in FDHT operation. Finally, estimation of energy savings, economic analysis, and sustainability assessment are performed by employing carbon footprint analysis, Gilbert approach, and Pugh matrix, respectively. Novelty aspects, the present work: (i) contributes to practical industrial application of finish hard turning for the shaft and die makers to select the optimum cutting conditions in a range of hardness of 45-60 HRC, (ii) demonstrates the replacement of expensive, time-consuming conventional cylindrical grinding process and proposes the alternative of costlier CBN tool by utilizing ceramic tool in hard turning processes considering technological, economical and ecological aspects, which are helpful and efficient from industrial point of view, (iii) provides environment friendliness, cleaner production for machining of hardened steels, (iv) helps to improve the desirable machinability characteristics, and (v) serves as a knowledge for the development of a common language for sustainable manufacturing in both research field and industrial practice.

• Journal of Technologic Dentistry
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• v.37 no.3
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• pp.131-144
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• 2015

Purpose: This study set out to propose plans for more efficient and effective clinical practice by investigating the current state of clinical practice in the field of dental technology and thus provide basic data to develop pre- and post-education programs for clinical practice. Methods: The subjects include dental technicians at dental technical laboratories that were appointed as the place of clinical practice by the Department of Dental Technology of G University. The survey period spanned from December 22, 2014 to January 20, 2015. Total 250 questionnaires were distributed to them, and 190(76.0%) were returned. After excluding 23 whose answers were uncertain or seemed to lack reliability, total 167(66.8%) were used in final analysis. Results: 1. The most frequent practice the student did during clinical practice was articulator attachment, which was followed by pin operation or model making, one's own task and practice, sand and crow sculpturing, burying, casting, and grinding. 2. In case of going through the entire process, porcelain had the most students at 39(23.4%), being followed by crown & bridge at 28(16.8%), clinical model at 23(13.8%), full denture at 17(10.2%), and partial denture at 17(10.2%) in the order. 3. Of the students, 59.8%(30.5% for reinforced basic practice; 29.3% for intensive practice education) said that intensive practice education should be reinforced in school; and 22.3% said that intensive theory and practice education was needed, which indicates that 82.6% voiced their opinion of reinforcing education around practice. 4. The students felt that they lacked diligence, passion, and theoretical knowledge somewhat and were relatively good at clinical adaptation and operational skills. Conclusion: The findings show that the students felt an absolute lack of practice education as the school education was focused on theory and national exams in the field of dental technology, thus raising a need to reinforce practice education. Of all the respondents, 62.9% said there was a need to improve the current education with a focus on jobs. In future, education of dental technology should work to bring up able dental technicians that can perform in clinical dental technology right after graduation by reinforcing job-based practice education.