Byung-Ohk Rhee

Pyrrolic molecular rotors acting as viscosity sensors with high fluorescence contrast.

New pyrrolic viscosity sensors exhibit one order of magnitude higher fluorescence contrast compared to that of the conventional phenolic analogues due to the viscosity-sensitive rotation of the asymmetric pyrrole group and successfully demonstrate mapping of intracellular viscosity by fluorescence lifetime imaging microscopy.

A Study on the Void Formation in Residual Wall Thickness of Fluid-Assisted Injection Molding Parts

In fluid-assisted injection molding, the distribution of the residual wall thickness on the inside and outside of the curved area is different, and void is formed due to the effect of the shrinkage on the outside where the residual wall thickness is thicker. The shrinkage that takes place in the residual wall is affected by the rheological changes in the polymer caused by temperature change and also by the thermal properties of the penetration fluid. In this study, the different effects on void formation in residual wall during fluid-assisted injection molding were analyzed, and water and silicone oil that had different thermal properties were used for the fluids. For this, heat transfer analysis and injection molding analysis were conducted. The void formation occurred due to the different temperature distribution and volumetric shrinkage in the direction of the residual wall in the curved area with a hollow section. It was also found that the void formation in the curved area decreased in the case of silicone oil compared to the case of water from simulation and experiments.

A Study on the Design of Electromagnetic Valve Actuator for VVT Engine

Electromagnetic valve (EMV) actuation system is a new technology for improving fuel efficiency and at the same time reducing emissions in internal combustion engines. It can provide more flexibility in valve event control compared with conventional variable valve actuation devices. The electromagnetic valve actuator must be designed by taking the operating conditions and engine geometry limits of the internal combustion engine into account. To help develop a simple design method, this paper presents a procedure for determine the basic design parameters and dimensions of the actuator from the relations of the valve dynamics, electromagnetic circuit and thermal loading condition based on the lumped method. To verify the accuracy of the lumped method analysis, experimental study is also carried out on a prototype actuator. It is found that there is a relatively good agreement between the experimental data and the results of the proposed design procedure. Through the whole speed range, the actuator maintains proper performances in valve timing and event control.

Development of Metal Plate with Internal Structure Utilizing the Metal Injection Molding (MIM) Process

In this study, we focus on making a double-sided metal plate with an internal structure, such as honeycomb. The stainless steel powder was used in the metal injection molding (MIM) process. The preliminary studies were carried out for the measurement of the viscosity of the stainless steel feedstock and for the prediction of the filling behavior through Computer Aided Engineering (CAE) simulation. PE (high density polyethylene (HDPE) and low density polyethylene (LDPE)) and polypropylene (PP) resins were used to make the sacrificed insert with a honeycomb structure using a plastic injection molding process. Additionally, these sacrificed insert parts were inserted in the metal injection mold, and the metal injection molding process was carried out to build a green part with rectangular shape. Subsequently, debinding and sintering processes were adopted to remove the sacrificed polymer insert. The insert had a suitable rigidity that was able to endure the filling pressure. The core shift analysis was conducted to predict the deformation of the insert part. The 17-4PH feedstock with a low melting temperature was applied. The glass transition temperature of the sacrificed polymer insert would be of a high grade, and this insert should be maintained during the MIM process. Through these processes, a square metal plate with a honeycomb structure was made.

Multi-objective Optimization of an Injection Mold Cooling Circuit for Uniform Cooling

An injection mold cooling circuit for an automotive front bumper was optimally designed in order to simultaneously minimize the average of the standard deviations of the temperature and the difference in mean temperatures of the upper and lower molds for uniform cooling. The temperature distribution for a specified design was evaluated by Moldflow Insight 2010, a commercial injection molding analysis tool. For efficient design, PIAnO (Process Integration, Automation and Optimization), a commercial PIDO tool, was used to integrate and automate injection molding analysis procedure. The weighted-sum method was used to handle the multi-objective optimization problem and PQRSM, a function-based sequential approximate optimizer equipped in PIAnO, to handle numerically noisy responses with respect to the variation of design variables. The optimal average of the standard deviations and difference in mean temperatures were found to be reduced by 9.2% and 56.52%, respectively, compared to the initial ones.

Quantification and design of jumping-ski characteristics:

Elastic and dynamic characteristics of jumping-skis affect ski performance at all four ski jumping phases. Compared with the number of studies on alpine-skis, there have been few studies on the characteristics of jumping-skis. This article identifies design parameters that have the most influence on jumping-ski characteristics. To identify the elastic and dynamic characteristics of jumping-skis, previous research and testing methods for alpine-skis were modified. Spring constants and bending stiffness distributions for three jumping-skis were measured. Natural frequencies, modal shapes, and damping ratios were also measured. From these results, the bending stiffness distribution was identified as a more elastic characteristic of jumping-skis than the spring constant. The natural frequency and damping ratio were selected as the relevant dynamic characteristics. To determine the effective design parameter for elastic and dynamic characteristics of jumping-skis, a jumping-ski was modeled by finite element method, and the inner structures and material properties of components of a jumping-ski were measured and analyzed. By comparing the simulation with actual test results, the reliability of the finite element method simulation was verified. The geometrical feature of the ski thickness profile is the most significant design parameter for elastic characteristics of jumping-skis. A mechanical property of the face material and wood at the sidewall is a highly influencing design parameter for dynamic characteristics of jumping-skis.

Characterization of curing behavior of UV-curable LSR for LED embedded injection mold

For many applications, liquid silicone rubber (LSR) injection molding is widely used for their great design flexibility and high productivity. In particular, a sealing part for a mobile device such as smartphone and watch has been produced by injection molding. While thermally curable LSR causes deformation problem due to a high mold temperature, UV-curable LSR can be molded at room temperature, which has advantages for over-molding with inserts of temperature-sensitive materials. Ultraviolet light-emitting diodes (UV LEDs) have advantages such as a longer service life, a lower heat dissipation, and smaller size to equip into the mold than conventional halogen or mercury UV lamps. In this work, rheological behavior of UV-curable LSR during curing process was analyzed by UV LEDs available in the market. UV-LEDs of various wave lengths and intensities were tested. The steady shear test was applied to find the starting time of curing and the SAOS was applied to find the ending time of curing to estimate processing time. In addition, the hardness change with irradiation energy was compared with the rheological data to confirm the reliability of the rheological test.

The 15th International Symposium on Applied Rheology (ISAR)

The 15th International Symposium on Applied Rheology (ISAR) organized by the Korean Society of Rheology (KSR) was held successfully at the International Convention Center at Jeju Island, on June 9, 2015. The ISAR of this year was held together with The 31st International Conference of the POLYMER PROCESSING SOCIETY (PPS_31) at the same place. It’s always been a rewarding experience to invite the Korean audience to the annual ISAR. The reason is obviously the same all the time: introduce the coveted lectures in various subfields of rheology by world-renowned rheologists to Korean audience so that each and every participant can leap-frog their competitiveness by increasing contribution to the added-value production, utilizing their much-enhanced knowledge of rheology acquired through this symposium.

Experimental and Numerical Investigation of the Effect of Process Conditions on Residual Wall Thickness and Cooling and Surface Characteristics of Water-Assisted Injection Molded Hollow Products

Recently, water-assisted injection molding was employed in the automobile industry to manufacture three-dimensional hollow tube-type products with functionalities. However, process optimization is difficult in the case of water-assisted injection molding because of the various rheological interactions between the injected water and the polymer. In this study, the boiling phenomenon that occurs because of the high melt temperature when injecting water and the molding characteristics of the hollow section during the water-assisted injection process were analyzed by a water-assisted injection molding analysis. In addition, the changes in the residual wall thickness accompanying changes in the process conditions were compared with the analysis results by considering water-assisted injection molding based on gas-assisted injection molding. Furthermore, by comparing the cooling characteristics and inner wall surface qualities corresponding to the formation of the hollow section by gas and water injections, a water-assisted injection molding technique was proposed for manufacturing hollow products with functionality.

Optimization of Valve Gates Locations Using Automated Runner System Modeling and Metamodels

Abstract : Injection pressure is one of factors that influence part quality. In this paper, injection pressure was minimized by optimizing valve gate locations. In order to perform design optimization, MAPS-3DTM (Mold Analysis and Plastic Solution-3D) was used for injection mold analysis and PIAnOTM (Process Integration, Automation and Optimization) was used as process integration and design optimization. Also we adapted meta models based on design of experiments for efficiency. By using introduced methodology, we were able to obtain a result so that maximum injection pressure reduced by 28% compared to the initial design. And the validity of the proposed method could also be demonstrated. Key words : Automotive door trim( 자동차용 도어트림), Injection molding( 사출성형), Runner system( 런너 시스템), Valve gate(밸브 게이트), Pressure(압력), Design of experiments(실험계획법), Metamodel(근사모델), Optimization (최적설계), Evolutionary algorithm( 진화알고리즘) Nomenclature 1) P : pressure, MPa Subscripts x : design variable 