Jo Jul 21, 2025
The multi-point forming (MPF) technology is a flexible forming method for three-dimensional sheet metal parts. In multi-point forming, the conventional stamping dies are replaced by a pair of matrices of elements (punches) and the relative positions of the elements can be varied to suit the requirements.
In the multi-point forming (MPF) for sheet metal, precisely constructing the die surface according to the geometry of parts is important for improving the dimensional accuracy and shape accuracy of products.
Today, a method based on NURBS surface is one of the generating methods of die surface using multi-point elements. This method can freely describe various curves and surfaces by using a general mathematical model. However, the NURBS method tends to lose data when the surface information (boundary information and shearing information, etc.) of product is obtained.
The method of representing complex geometry and location using triangular mesh data files (STL) is being widely used in the fields of high speed forming, inverse forming, finite element analysis, etc., and it is now widely accepted as the data exchange files of CAD/CAM/CAE systems. The triangular mesh model is convenient for processing and display on a computer, and it can represent any complex surface shape. Using the file of the triangular mesh data in a multi-point forming process can overcome the shortcomings of the NURBS method and solve the problem of data loss.
Paek Kuk Song, a researcher at the Faculty of Materials Science and Technology, has introduced the finite element theory into the construction of multi-point forming die surface to calculate the height of the elements according to the product geometry given by the triangular mesh data file (STL), and optimized the multi-point forming die surface by simulation analysis.
He performed the simulation analysis using ABAQUS software, and a full-scale experiment for the product that underwent the simulation analysis. The maximum absolute error between the target surface and the formed product was 0.09mm.
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Jo Jul 20, 2025
SiC whisker reinforced aluminum composites are fabricated by vacuum hot pressing. The whisker is a kind of fine needle-like fibrous material that exists in the form of a single crystal without defects. Its internal structure is absolutely complete and defect-free. The whisker-reinforced composites have many excellent properties. SiC whiskers are widely used in metallic matrix composites as whisker reinforcements with excellent properties. Among them, SiC whisker reinforced aluminum composites have been widely used in aerospace, automotive and other industries due to their high specific strength and hardness and good dimensional stability.
The key to fabricating SiC whisker reinforced aluminum composites lies in the uniform distribution of whiskers in the matrix, and the strong bonding between whiskers and aluminum. Now, the most important techniques for preparing SiC whisker reinforced aluminum composites are die-casting and powder metallurgy. Recently, powder metallurgy has become one of the main processes for fabricating high-performance aluminum-based composites.
In the hot-pressing sintering process, the thermal conductivity values of the aluminum powder and SiC whiskers that constitute the raw mixture change with increasing sintering temperature, while the relative density of the raw mixture changes with increasing sintering pressure. When the sintering temperature is too high, the grain growth occurs, which decreases the relative density of sintered compacts. As a result, the mechanical properties decrease. It is also difficult to separate the sintered compacts from dies after sintering because of the melting of sintered compact into dies. Therefore, some process problems arise, such as the difficulty of repeated use of dies.
Kim Kuk Il, a researcher at the Faculty of Materials Science and Technology, conducted a simulation analysis of the temperature distribution in the die and the raw mixture during sintering, and experimentally confirmed it. On this basis, he has presented a new question for determining the sintering conditions such as sintering temperature, heating rate and holding time, and investigated it.
As a result, he has confirmed the optimum sintering temperature (600℃), heating rate (15℃/min) and holding time (15min).
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Jo Jul 18, 2025
Humic acid is an organic substance that is produced by a series of decomposition and transformation processes of the remains of dead animals and plants. The oxidative polymerization of polyphenols in soils is regarded as one of the main processes in the formation of humic substances.
There have been many studies to find industrial applications of humification processes. However, there are few reports on the properties of humic acids in their use as binders for coal briquette.
O Chan Sok, a researcher at the Faculty of Metal Engineering, has conducted some experiments to improve the thermal stability and aromatization of humic acid in oxidized lignite with low humic acid content, and determined the optimum conditions.
He set ferric oxide content, caustic soda content, heating temperature and heating time as experimental parameters, and varied them at three levels, respectively. The optimum conditions are as follows. The ferric oxide and caustic soda oxide were 5% and 8% of the humic acid feed, respectively, and the reaction temperature and the reaction time were 80℃ and 60min, respectively.
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Jo Jul 17, 2025
Incline hoist skips are classified into dumping and non-dumping ones. Non-dumping skips are of two types―rear discharging and bottom discharging. They are mainly used on the slopes of 40° or more. The dumping skips are used at inclination angles below 40°, and an auxiliary rail is installed to increase the inclination of the skip for a sufficient discharging angle.
The dumping skips are of two types―rear-discharging and front-discharging. The latter is widely used. The rear wheel of a front-discharging skip is bigger in width than the front wheel. When approaching the emptying point, the front wheel tilts forward along the main rail, while the rear wheel is lifted along the profile of the unloading curve to increase the discharge angle.
The main rails on which the front wheels are placed are generally straight, which often causes complete overturning of the skip. Skip winching facilities are subjected to overwinding in unloading sections for several reasons. If the skip is out of its unloading section by overturning, the skip will be completely overturned in the direction of movement due to the increase in the angle of inclination of the skip, which causes the forward movement of the center of gravity, and the increase in the drag force exerted on the front wheels. There is also a disadvantage of poor skip restoration due to the presence of the center of gravity in the front side of the skip.
To prevent such phenomena, the main rails can be set to be curved. The curved shape of the main rails can prevent complete overturning of skips and increase the possibility of restoration. There have been many studies on dumping skips with big dip angles used in manufacturing lines of factories and enterprises in the construction and building materials industry. However, they failed to consider the unloading properties of bulk materials in the skips.
Hong Ryo Myong, a researcher at the Faculty of Mining Engineering, has analyzed the unloading properties of the front-discharging skips by combining the analysis of bulk materials and motion. He proposed that the curved shape of main rails for front wheels can eliminate full overturning of skips, and proved it by analyzing the behavior of bulk materials and motion.
He proposed a method of evaluating the overturning possibility of skips. The overturning possibility of skips can be estimated by measuring the force acting on hoisting wire ropes. If the force on hoisting wire ropes remains unchanged at zero for a while, the skips can be completely overturned.
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Jo Jul 14, 2025
Impregnated diamond bits are widely used in drilling work for geological prospecting, petroleum production and civil construction.
The most difficult problem in the application of diamond bit is the rate of penetration of diamond bit in the slipping formation. The very low rate of penetration in these slipping formations which are often encountered during drilling, is related to the mechanical characteristics of the slipping formation. The slipping formation usually has three characteristics. First, rock hardness is relatively high because of the high quartz content. Second, rock strength is high because the rock-forming mineral grains are very small and have local siliceous cementation. Third, rock abrasiveness is weak.
To overcome these shortcomings, a researcher designed a sandwich impregnated diamond bit to maintain concentric circular shape of the bottom surface of bit during drilling, remarkably improving the drilling efficiency in the slipping formation. The shortcomings of preceding studies on SIDB (sandwich impregnated diamond bit) can be found as follows. First, the effect of structural parameters (width of non-working layer) on the drilling performance of SIDB in the slipping formation is not clearly clarified. Second, the effect of sandwich structural parameters on the rock failure mode of SIDB is not clearly clarified.
Kim Il Jin, a researcher at the Faculty of Earth Science and Technology, in order to investigate the effect of structural parameters on the drilling performance of SIDB and determine suitable structural parameters, has fabricated the SIDB of ϕ59mm/41mm with different structural parameters (0, 0.5, 1, 1.5, 2, 2.5mm) and conducted a field-drilling test.
In addition, through a particle size analysis of the rock debris produced during drilling, he demonstrated that the reasonable structural parameters changed the rock breakage mode of SIDB from micro cutting to micro cutting-micro volume breakage.
The results of his study are very important to effectively overcome the slipping formation which is a challenge in the application of a diamond bit and to improve overall drilling efficiency.
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Jo Jul 13, 2025
Inverse hyperbolic problems appear in underwater sound search, geophysics, electrodynamics, etc.
In most practical applications, most of the physical phenomena are modeled by multidimensional equations. Therefore, considerable attention has been devoted to the analysis of multidimensional inverse problems. However, to the best of our knowledge, the solvability of the hyperbolic inverse source problems has only been studied for one-dimensional linear equations.
Ryom Su Jong, a post-graduate student of the Faculty of Applied Mathematics, has investigated the unique solvability of an inverse problem of determining a solely time-dependent source in a multidimensional semilinear hyperbolic equation.
This inverse problem models the identification of underwater sound source when its position is known. She addressed a numerical scheme together with the existence and uniqueness of the weak solution by means of Rothe’s time-discretization method. Moreover, she evaluated the error of the semi-discretization scheme.
The time-discretization method she applied is a powerful and efficient tool for solving a wide range of evolution equations.
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