• Transactions of Materials Processing
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• v.8 no.6
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• pp.612-619
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• 1999

Internal and external defects of an inner pulley for automobile air conditioner are investigated in this study. Inner pulley is a part of compressor clutch assembly of automobile air conditioner. In cold forging of inner pulley, the design requirement are to keep the same height of the inner rib and outer one and to make uniform distribution of hardness in the forged product. At the end of the forging of inner pulley, the piping defect as an external defect begins to form at the back center of the billet. The internal crack as an internal defect also occur at the adiabatic shear band which usually has maximum ductile fracture value. It is important to predict when the internal and external defects occur during the deformation process, in order to minimize the amount of discard that is generated. The finite element simulations are applied to analyze the defects. The validity of the computational results are examined by experiments. These computational results are in good agreement with the experimental ones.

• Transactions of Materials Processing
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• v.20 no.4
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• pp.291-295
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• 2011

The injector housing has two functions, namely, positioning the injector and protecting it from coolant. The conventional manufacturing process of the injector housing by machining has some drawbacks such as considerable loss of material and environmental pollution caused by excessive use of cutting oil. In this paper, precision cold forging is proposed as a new manufacturing process in order to improve these issues. A numerical study was conducted to compute the metal flow, strain, load and other process variables using DEFORM-2D, a finite element analysis(FEA) code for metal forming. Two process methods were investigated and optimal conditions were computed with the FEA code. A prototype was manufactured from the optimal process method and the metal flow and hardness were obtained from the prototype.

• Transactions of Materials Processing
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• v.12 no.5
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• pp.473-478
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• 2003

This study presents the enhancement of forgeability of SNCM522H materials. Target parts are output shaft(OP shaft) used as components of power train for automobiles. To carry out cold forging process of OP shaft by 1 pass instead of existing 2 pass process, studies in terms of process design and heat treatment were performed. To introduce the new process, the finite element method was accomplished, and to assess the validity of proposed heat treatment cycle, several experiments(hardness test, observation of optical microstructures, tensile test) were carried out. The 2Pass forging process could be reduced as lPass process through improvement of process and heat treatment technology and that would give cost reduction.

• Transactions of Materials Processing
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• v.7 no.6
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• pp.530-538
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• 1998

Elimination of the heat treatment process is very important in automation of metal forming since controlling heat treatment by computer has many difficulties and it has bottle neck problem. non-heat-treated steels materials which are not in need of heat treatment have been developed for cold forging. However to apply non-heat-treated steel to structural parts. it is necessary to prove reliability of mechanical properties. In order to define the reliability of mechanical properties we have investigated microstructure, hardness, the tensile strength compressive strength and tensile fatigue strength for both steels. Considering the results of high cycle fatigue test for both specimen the characteristics of non-heat-treated steel are decided on the yield strength, It has same tendency for heat-treated steel. Therefore non-heat-treated steel which has the appropriate yield strength may be applied in cold forging.

• Journal of Welding and Joining
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• v.5 no.3
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• pp.19-27
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• 1987

This paper presents the weldability for cold pressure but welding method in junction of dissimilar metals each other. Although the weldability between the same aluminium metal plate welding has been studied, the study of itthe rod of aluminium and coper has not fully been investigated. The purpose is to suggest the optimal conditions on the rod of those under above method. To obtain the optimal conditions, associated experiments were performed in a various welding parameters. Consequently, it was proved that the mechanical properties such as tensile strength, hardness and bending strength could be obtained excellent particularly under the welding conditions; pressure is $(32~39) {\times} 10^3/kg/cm^2$, time is beyond 70 seconds, stage is higher than fifth stage.

• Korean Journal of Metals and Materials
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• v.47 no.9
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• pp.550-557
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• 2009

In this study, bronze or SUS304 powders blended with 10 wt.% diamond particles were used to prepare metal/diamond composite materials deposited by cold spraying. The effects of matrix metal, diamond partical size, and the thickness of the Ni coating on the diamond were studied on Al 6061 substrate. The results showed that the hardness of the metal/diamond composite coating layers was higher than that of the same composite materials when using the sintering method. The fraction of diamond content in the coated layer increased when the metal matrix was soft. When the size of the diamond particles was reduced, the fraction of the diamond particles increased. In addition, in the case of diamond with a thicker Ni-coated layer, the fracturing of diamonds was mitigated in the composite coating layers.

• Journal of the Korean Society for Precision Engineering
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• v.29 no.4
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• pp.395-408
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• 2012

An experimental investigation with 2.8kW Nd:YAG laser system was carried out to study the effects of different laser process parameters on the microstructure and hardness of STD11. The optical lens with the elliptical profile are designed to obtain a wide surface hardening area with uniform hardness. The Laser beam is allowed to scan on the surface of the work piece varying the power (1600, 1800 and 1900kW) and traverse speed (200, 400, 600, 800 and 1000mm/min) at three different F-numbers of lens. After laser surface treatment three zones, In the microstructure have been observed : melted zone(decarburization), heat affected zone(martensite), and the substrate.

• Food Science of Animal Resources
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• v.20 no.2
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• pp.139-145
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• 2000

This study was conducted to investigate the storage and quality characteristics of vegetable hot dog. The b-value of sausage was increased significantly, but the color of bread was not changed during storage. The hardness, springiness, cohesiveness and chewiness of sausage were not changed, but the gumminess was increased during storage. The hardness, springiness, cohesiveness and gumminess of bread were not changed, but the chewiness was decreased during storage. The moisture content of sausage was not changed, but that of bread was decreased during storage. The pH of vegetable hot dog showed 5.67~5.71 during storage. The TBA of sausage was increased from 0.13 to 0.29mg/kg, the VBN was increased from 4.24 to 5.46mg% during storage. The total plate counts showed $3.5\times$104 CFU/g 8 days of storage. The coliform group, Staphylococcus aureus. Salmonella and Vibrio parahaemolyticus were not detected during storage. The vegetable hot dog was found to be fresh by sensory scores such as taste, aroma, color, texture and palatability, and the appearance of mold and slime was not detected during storage.

• Korean Journal of Materials Research
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• v.33 no.11
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• pp.482-490
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• 2023

The purpose of this study was to analyze microstructural changes and evaluate the mechanical properties of TWIP steel subjected to variations in heat treatment, in order to identify optimal process conditions for enhancing the performance of TWIP steel. For this purpose, a homogenization heat treatment was conducted at 1,200 ℃ for 2 h, followed by hot rolling at temperature exceeding 1,100 ℃ and cold rolling. Annealing heat treatment is achieved using a muffle furnace in the range of 600 ℃ to 1,000 ℃. The microstructure characterization was performed with an optical microscope and X-ray diffraction. Mechanical properties are evaluated using micro Vickers hardness, tensile test, and ECO index (UTS × Elongation). The specimens annealed at 900 ℃ and 1,000 ℃ experienced a significant decrease in hardness and strength due to decarburization. Consequently, the decarburization phenomenon is closely related to the heat treatment process and mechanical properties of TWIP steel, and the effect of the microstructure change during annealing heat treatment.

• Journal of Power System Engineering
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• v.20 no.5
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• pp.29-36
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• 2016

Aluminum alloys have been widely used in engine materials, cold & hot-water storage vessels and piping etc., Furthermore, the aluminum alloy of AC8A have been widely used in mold casting material of engine piston for various vehicles because of its properties of temperature, wear and corrosion resistance. Therefore, it is considered that evaluation of corrosion resistance as well as wear resistance of AC8A material is also important to improve its property and to prolong its lifetime. In previous paper, the effect of solution($510^{\circ}C$:4hrs) and tempering($190^{\circ}C$: 16, 24, and 36 hrs)heat treatments to corrosion resistance and hardness were investigated using electrochemical method. In this study, in order to examine completely the effect of the tempering hours to hardness variation and corrosion resistance, the results of solution($510^{\circ}C$:4hrs) and tempering($190^{\circ}C$: 2, 4, 8 and 12hrs)heat treatments to hardness and corrosion resistance were investigated using electrochemical method. The hardness decreased with solution heat treatment compared to mold casting condition, but its value increased with tempering heat treatment. Furthermore, the corrosion resistance increased with decreasing of the hardness, and decreased with increasing of the hardness reversely. And the tempering heat treatment temperature at $190^{\circ}C$ for 8 hrs exhibited the highest value of the hardness and also indicated the highest corrosion current density. However, the values of hardness and corrosion current density was again increasingly decreased with increasing of tempering hours than 8 hrs, Consequently, it is suggested that decision of the optimum. tempering hours is very important to improve the corrosion or wear resistance.