• Polymer(Korea)
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• 제38권6호
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• pp.708-713
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• 2014

Most plastics products are being produced by injection molding process. However, mold shrinkage is inevitable in injection molding process and it deteriorates dimensional quality through deflections and warpages. Mold shrinkage depends upon the material property of resin as well as injection molding condition. In this study, material property of resin has been predicted for glass fiber reinforced polycarbonate to control the warpage, and computer simulation of injection molding has been performed using predicted property. It was observed that the deflection of part decreased by the glass fiber reinforced resin. In order to verify the validity of this method and confidence of results, experiments of injection molding were performed. The results of experiments and computer simulations showed good agreement in their tendency of deflections. Consequently, it was concluded that the method of designing the material property of resin conducted in this study can be utilized to control the dimensional accuracy of injection molded products.

• Journal of the Korean Recycled Construction Resources Institute
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• 제10권1호
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• pp.48-55
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• 2022

This study uses the recovered water as mixing water and artificial lightweight aggregate pre-wetting water as part of a study to increase the recycling rate and reduce greenhouse gas of the ready-mixed concrete recovered during the concrete transport process, and cement fine powder of blast furnace slag(BFS) and fly ash(FA). The engineering characteristics of the three-component lightweight aggregate mortar used as a substitute were reviewed. For this purpose, the flow, dry unit mass, compressive strength, drying shrinkage, neutralization depth, and chloride ion penetration resistance of the three-component lightweight aggregate mortar were measured. When used together with the formulation, when 15 % of BFS and 5 % of FA were used, it was found to be positive in improving the compressive strength and durability of the mortar.

• Journal of the Korea Concrete Institute
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• 제19권5호
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• pp.623-630
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• 2007

Grouting materials are used for the unification of superstructural and substructural body like bridge seat (shoe) or machinery pedestal and e.t.c by filling their intercalary voids. Accordingly, grouting materials have been developed and used mainly with products of high strength because those materials are constructed specially in a part receiving large or impact load. In this situation, the structural body constructed by grouting materials with high stiffness-centered (caused by high strength) products is apt to cause brittle failure when receiving over a limit stress and to cause cracks according to cumulative fatigue by continuous and cyclic load. In addition, grouting materials are apt to cause cracks by using too much rapid hardening agents that give rise to high heat of hydration to maintain high strength at early age. In this study, to overcome these problems, cement type grouting materials including powder of waste tire and resin as elastic materials which aim to be more stable construction and to be improvement of mother-body's unification are developed and endowed with properties of high toughness and high durability add to existing properties of high flowability, non-shrinkage and high strength. Besides, this study contribute to of for green construction materials for being possible recycling industrial waste like waste tire and flyash. On the whole, seven type mixing conditions are tested and investigated to choose the best mixing condition.

• Journal of the Korea Concrete Institute
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• 제13권4호
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• pp.314-320
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• 2001

In this paper, the properties of an expansive agent (CaO-CaS $O_4$) for dry shrinkage compensation were investigated by a series of experimental program, which might be used at On-Dol heating system as mortar type. The expansion principle of the CaO-CaS $O_4$ was mainly verified. As a result of this study, the correlation between the content of the expansive agent and the compressive strength was obtained in the form of exponential function(Y = A $e^{-x}$), showing that as the content of expansive agent increased as the expansion performance with the compressive strength increased by only a certain amount. Also, as a results of the analysis of a correlation between the expansive performance and the chemical properties which generally accompanied a part of quality management in manufacturing the expensive cement, the expansive performance was relative to only the contents of the F-CaO among chemical properties(Blaine, +44$\mu\textrm{m}$R, F-CaO, S $O_3$,L.O.I). And it was clarified that the results were relative to the second order function, showing that if the contents of the F-CaO increased the expansive performance Increased.d.

• Journal of Welding and Joining
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• 제34권5호
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• pp.61-69
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• 2016

A numerical simulation of the solid/liquid coexistence temperature range, using solidification segregation model linked with the Kurz-Giovanola-Trivedi model, explained the mechanism of the BTR shrinkage (with an increase in welding speed) in type 310 stainless steel welds by reduction of the solid/liquid coexistence temperature range of the weld metal due to the inhibited solidification segregation of solute elements and promoted dendrite tip supercooling attributed to rapid solidification of laser beam welding. The reason why the BTR enlarged in type 316 series stainless welds could be clarified by the enhanced solidification segregation of impurity elements (S and P), corresponding to the decrement in ${\delta}-ferrite$ crystallization amount at the solidification completion stage in the laser welds. Furthermore, the greater increase in BTR with type 316-B steel was determined to be due to a larger decrease in ${\delta}-ferrite$ amount during welding solidification than with type 316-A steel. This, in turn, greatly increases the segregation of impurities, which is responsible for the greater temperature range of solid/liquid coexistence when using type 316-B steel.

• Fashion & Textile Research Journal
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• 제17권6호
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• pp.1020-1029
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• 2015

This paper investigated the wearing performance of knitted fabrics made of air vortex yarns using PTT/tencel/cotton fibres in comparison with ring and compact yarns for emotional garment. Wicking property of knitted fabric made of MVS yarns was worse than those by ring and compact yarns, however, drying property of knitted fabric made of MVS yarns was better than those by ring and compact yarns, which was explained as more water vapor transport due to larger openness between fibres in the MVS yarns than those in the ring and compact yarns. Thermal conductivity of knitted fabric made of MVS was lower than those of ring and compact yarns and maximum heat flow(Q_max) at the transient state of MVS knitted fabric was lower than those of ring and compact yarns, which may be attributed to MVS yarn structure that has parallel fibres in the core part of the yarn and fasciated fibre bundles on the sheath part with roughness on the yarn surface. However, pilling of MVS knitted fabric was better than those by ring and compact yarns, which was caused by less and shorter hairy fibres protruded from MVS yarn surface than those of ring and compact yarns. It was observed that tactile hand of MVS yarn knitted fabrics was stiffer than those of ring and compact yarns knitted fabrics. It was explained by low extensibility and compressibility and high bending and shear rigidities of the MVS yarn knitted fabrics, which resulted in bad wearing performance of MVS knitted fabric.

• Journal of Advanced Navigation Technology
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• 제18권4호
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• pp.364-370
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• 2014

In this paper, high reliable trench formation technique and a novel fabrication techniques for trench gate MOSFET is proposed which is a key to expend application of power MOSFET in the future. Trench structure has been employed device to improve Ron characteristics by shrinkage cell pitch size in DMOSFET and to isolate power device part from another CMOS device part in some power integrated circuit. A new process method for fabricating very high density trench MOSFETs using mask layers with oxide spacers and self-align technique is realized. This technique reduces the process steps, trench width and source and p=body region with a resulting increase in cell density and current driving capability and decrease in on resistance.

• Design & Manufacturing
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• 제18권3호
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• pp.71-80
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• 2024

Sink marks are a common defect that occurs due to differences in shrinkage in areas with significant thickness variations in injection-molded parts. In this paper, we investigated the reduction of sink marks and the improvement of gas venting in injection molding processes using External Gas Injection (EGI). A mold was designed with considerations for EGI core pins, O-ring grooves to prevent gas leakage, and ejector-pin sealing. The sink marks were then examined through a series of experiments. When the delay time for injecting compressed air was set to 2.2 seconds, the depth of the sink marks was minimized. However, when the delay time was either too short or too long, the depth of the sink marks increased. There was almost no difference in the depth of the sink marks at discharge pressures of 30 and 50 bar of compressed air, but the sink marks were significantly reduced at a discharge pressure of 70 bar. Under the conditions of a 2.2-second delay time and a supply pressure of 70 bar, the smallest depth, 0.594 ㎛, was observed when the supply time was between 6 and 7 seconds. This represents a reduction of approximately 94% compared to the sink mark depth of 10.078 ㎛ observed with conventional injection molding. To verify the gas venting effect of compressed air injection, an experiment was conducted using non-dried PC. The silver streaks that appeared on the exterior of the molded part were completely eliminated when the air supply pressure was set to 20 bar. This indicates that by injecting compressed air into the mold cavity before injecting the resin, the appearance quality of the injection-molded part can be improved without the need to dry the resin in advance.

• Elastomers and Composites
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• 제52권4호
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• pp.317-325
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• 2017

Molding conditions can be described as factors that determine the quality of a product obtained from injection molding. Many studies have been performed on the injection molding pressure, injection temperature, packing pressure and other molding conditions related to part quality. However, the most accessible factor among the adjustable molding conditions during actual injection is the injection speed. In this study, we simulated the variation of the physical quantity according to injection speed and performed experiments to understand the effect of injection speed on the actual product. A CAE analysis program (Moldflow) was used to simulate and analyze the results using PC and PBT for two models. In order to compare these results with the experimental results, an actual injection molding was performed for each injection speed, and the correlation between simulation and injection molding, especially for the shrinkage of the molded article, was discussed.

• Journal of the Korean Society of Manufacturing Process Engineers
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• 제19권9호
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• pp.93-99
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• 2020

Recently, as the weight reduction of vehicles has been actively progressed, parts developed using aluminum 60XX series from existing steel materials are increasing. In this paper, the bushing used for the front frame rail, which is one of the parts for fixing engines and other parts in automobiles, was changed to an aluminum material of the Al60XX series, and it was intended to be produced by applying of cold forging method. The bushing is a part that secures the engine frame, and in order to produce it by cold forging, the molding limit is predicted through process design, and a multi-stage process is designed through finite element analysis. In addition, in order to verify the feasibility of the designed forging process, the limits of the multi-step process were verified based on the Cockcroft Latham theory, and the crack and overlap of the actual forging work were predicted and improved.