• Journal of the Korean Society for Precision Engineering
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• v.28 no.2
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• pp.219-225
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• 2011

Silicone resin is recently used as encapsulant for high-power LED module due to its excellent thermal and optical properties. In the present investigation, finite element analysis of cure process was attempted to examine residual stress evolution behavior during silicone resin cure process which is composed of chemical curing and post-cooling. To model chemical curing of silicone, a cure kinetics equation was evaluated based on the measurement by differential scanning calorimeter. The evolutions of elastic modulus and chemical shrinkage during cure process were assumed as a function of the degree of cure to examine their effect on residual stress evolution. Finite element predictions showed how residual stress in cured silicone resin can be affected by elastic modulus and chemical shrinkage behavior. Finite element analysis is supposed to be utilized to select appropriate silicone resin or to design optimum cure process which brings about a minimum residual stress in encapsulant silicone resin.

• Transactions of Materials Processing
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• v.21 no.2
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• pp.101-106
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• 2012

Generally, rapid cure reaction of LED encapsulation silicone resin causes serious defects in cured resin products such as warpage, residual bubbles, and reduced wettablility. In order to prevent residual bubbles in silicone resin, the step cure process was examined in the present paper. Three kinds of step cure processes were applied, and bubble-free phenomenon was observed. Most of the bubbles were removed under $70^{\circ}C$, the minimum temperature for activating cure reaction. In addition, degree of cure(DOC) and temperature distribution were predicted by using FEM analysis of heat transfer. It was concluded that maintaining cure temperature which provide a DOC under 0.5~0.6 effectively reduces residual bubbles.

• Composites Research
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• v.31 no.6
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• pp.404-411
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• 2018

As the autoclave process progresses in a given cure cycle, residual stress in the composite product is induced by cure shrinkage of the resin. As a result, It generates the thermal deformation such as spring-in and warpage, and the inaccuracy of the final product increases. It is important to predict thermal deformation in aerospace parts which require precise fabrication. The research has been done on predicting and grasping curing process of composite material. In this study, the cure mechanism of composite materials according to the process is predicted through finite element analysis, and the effect of cure shrinkage on thermal deformation generated by the process is analyzed.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2001.04a
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• pp.1089-1092
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• 2001

In the stereolithography process, build parameters are laser power, scan velocity, scan width, bean diameter, layer thickness and so on. These values are determined according to product accuracy and build time. Build time can be reduced by improving of scan velocity, laser power, layer thickness, hatching space and so on. But variation of these parameters influence part accuracy, surface roughness, strength. This paper observed cure properties in various beam diameter. In order to examine these, relationships of scan velocity and cure depth, scan velocity and cure width according to various beam diameter in one scan line are measured. And cure thickness is measured according to beam diameter and scan velocity in scan surface of one layer. For reduction of build time, beam diameter and scan velocity is proposed in stereolithography process.

• Elastomers and Composites
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• v.34 no.4
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• pp.321-331
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• 1999

The curing process is the final step in tire manufacturing whereby a green tire built from layers of rubber compounds is formed to the desired shape and the compounds are converted to a strong, elastic materials to meet tire performance needs under elevated pressure and temperature in a press. A numerical optimization procedure was developed to improve product quality in a tire curing process. First, a dynamic constrained optimization problem was formulated to determine the optimal condition of the supplied cure media during a curing process. The objective function is subject to an equality constraint representing the process model that describes the heat transfer and cures kinetic phenomena in a cure press and is subject to inequality constraints representing temperature limits imposed on cure media. Then, the optimization problem was solved to determine optimal condition of the supplied cure media for a tire using the complex algorithm along with a finite element model solver.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2001.04a
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• pp.32-36
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• 2001

Recently, reaction injection molding has been used broadly for rapid prototyping, because of its convenience and versatility. Since the properties of molded products are dependent on the process variables and the production is very short(less than 2minutes), the control of process variables is important. Generally, the two significant process variables are degree of cure and temperature of the reactants. In this paper, the relation between the degree of cure and the temperature of reactants was investigated to find the optimal curing condition of reaction injection molding for rapid prototyping. The degree of cure during reaction injection molding was measured by the Lacomtech sensor and dielectrometry equipment employing Wheatstone bridge type circuit.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.10a
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• pp.714-719
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• 2004

Controlling the cure depth of the Fa1260T photopolymer enhances the quality of a microstructure and minimizes its size in microstereolithography. In this work, variation of cure depth of the Fa1260T photopolymer is investigated while the concentration of a photopolymerization inhibitor as a radical quencher was varied. The energy source inducing photopolymerization was a He-Cd laser and a motorized stage controled the laser beam path accurately. The effects of process variables such as laser beam power and scan speed on the cure depth were examined. Optimum conditions for the minimum cure depth were determined as laser power of 230 W and scan speed of 40-50 m/s at the concentration of the radical quencher of 5％. The minimum cure depth at the optimal condition was 14 m. The feasibility of the fabrication of microstructures such as a microcup, microfunnel, and microgrid of 100 m size is demonstrated using Super IH process.

• Composites Research
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• v.33 no.5
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• pp.302-308
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• 2020

We measured the thermal conductivity of composite materials manufactured by the autoclave and vacuum bag only processes and predicted the cure behavior of the external and internal of composite parts with a cure kinetics model. The temperature difference between the external and internal depends on the processes because of the change of thermal conductivity. In the autoclave process, the temperature and cure behavior of the internal were similar to those of the external because of the high thermal conductivity. However, the temperature of the internal of the vacuum bag only process was different from that of the external. The difference can influence the part quality and evacuation of air. Compression tests were performed to find the mechanical property using 0° unidirectional specimens. The composite of the vacuum bag only process was found to have a lower compressive strength than that of the autoclave process.

• Macromolecular Research
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• v.10 no.5
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• pp.259-265
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• 2002

The cure kinetics of blends of epoxy (DGEBA, diglycidyl ether of bisphenol A)/anhydride resin with polyamide copolymer, poly(dimmer acid-co-alkyl polyamine), were studied using differential scanning calorimetry (DSC) under isothermal condition. On increasing the amount of polyamide copolymer in the blends, the reaction rate was increased and the final cure conversion was decreased. Lower values of final cure conversions in the epoxy/(polyamide copolymer) blends indicate that polyamide hinders the cure reaction between the epoxy and the curing agent. The value of the reaction order, m, for the initial autocatalytic reaction was not affected by blending polyamide copolymer with epoxy resin, and the value was approximately 1.3, whereas the reaction order, n, for the general n-th order of reaction was increased by increasing the amount of polyamide copolymer in the blends, and the value increased from 1.6 to 4.0. A diffusion-controlled reaction was observed as the cure conversion increased and the rate equation was successfully analyzed by incorporating the diffusion control term for the epoxy/anhydride/(polyamide copolymer) blends. Complete miscibility was observed in the uncured blends of epoxy/(polyamide copolymer) up to 120 $^{\circ}C$, but phase separations occurred in the early stages of the curing process at higher temperatures than 120 "C. During the curing process, the cure reaction involving the functional group in polyamide copolymer was detected on a DSC thermogram.gram.

• Composites Research
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• v.30 no.3
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• pp.202-208
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• 2017

Resin transfer molding (RTM) is a mass production process that allows the fabrication of composites ranging in size from small to large. Recently, fast curing resins with a curing time of less than about 10 minutes have been used in the automotive and aerospace industries. The viscosity of resin is bound up with the degree of cure, and it can be changed rapidly in the fast-cure resin system during the mold filling process. Therefore, it is advantageous to experimentally measure and evaluate the degree of cure because it requires much effort to predict the flow characteristics and cure of the fast curing resin. DMA and dielectric technique are the typical methods to measure the degree of cure of composite materials. In this paper, the resin flow and degree of cure were measured through the multi-channel dielectric system. A total of 8 channels of dielectric sensors were used and resin flow and degree of cure were measured and compared with each other under various pressure conditions.