Seok Kwan Hong

Simulation of an Aspheric Glass Lens Forming Behavior in Progressive GMP Process

Recently, GMP(Glass Molding Press) process is mainly used to produce aspheric glass lenses. Because glass lens is heated at high temperature above Tg (Transformation Temperature) for forming the glass, the quality of aspheric glass lens is deteriorated by residual stresses which are generated in a aspheric glass lens after forming. In this study, as a fundamental study to develop the mold for progressive GMP process, we conducted a aspheric glass lens forming simulation. Prior to a aspheric glass lens forming simulation, compression and thermal conductivity tests were carried out to obtain mechanical and thermal properties of K‐PBK40 which is newly developed material for precision molding, and flow characteristics of K‐PBK40 were obtained at high temperature. Then, using the flow characteristics obtained, compression simulation was carried out and compared with the experimental result for the purpose of verifying the obtained flow characteristics. Finally, a glass lens press simulation in progressive GMP process was carried out and we could forecast the shape of deformed glass lenses and residual stresses contribution in the structure of deformed glass lenses after forming.

Simulation-Based Optimization of Cure Cycle of Large Area Compression Molding for LED Silicone Lens

Three-dimensional heat transfer-curing simulation was performed for the curing process by introducing a large area compression molding for simultaneous forming and mass production for the lens and encapsulants in the LED molding process. A dynamic cure kinetics model for the silicone resin was adopted and cure model and analysis result were validated and compared through a temperature measurement experiment for cylinder geometry with cure model. The temperature deviation between each lens cavity could be reduced by implementing a simulation model on the large area compression mold and by optimizing the location of heat source. A two-step cure cycle was constructed to reduce excessive reaction peak at the initial stage and cycle time. An optimum cure cycle that could reduce cycle time by more than 29% compared to a one-step cure cycle by adjusting dwell temperature, heating rate, and dwell time was proposed. It was thus confirmed that an optimization of large area LED lens molding process was possible by using the present experiment and the finite element method.

Thermal characterisation of high-aspect-ratio nanoheaters using IR thermography

Recently, micro/nanoheater have been used and studied in various fields such as sensors. In particular, they have become important in biology and medicine. In this paper, we propose a novel measurement method which can indirectly measure the temperature distribution of a nanoheater’s surface from side temperature measurements using infrared microscopes. Two different types of nanoheaters are fabricated and their thermal behaviours are analysed and characterised. They are fabricated in a top-down approach using silicon-on-insulator wafers and basic MEMS processes. Nanoheaters with a high-aspect-ratio are fabricated: a width of 200 nm, length of 100 μm and height of 30 μm. The nanoheater’s surface is doped with boron by ion implantation for joule heating. Their thermal profile depending on their heat sink type was investigated. In conclusions, it is expected that a nanoheater with exact temperature control and thermally efficient structural design can be applied for bio-molecule manipulation.

Finite Element Analysis for the Tube Sinking Process of the Micro Ti-0.2Pd Tube

In this study, the tube sinking process for manufacturing the micro Ti-0.2Pd tube (2.4 mm external diameter, 0.4 mm thickness) was simulated by finite element analysis. The external diameter of the initial tube was 5.0 mm. In order to simulate the tube sinking process, the flow stress equation was deducted from the result of the tensile test and friction coefficient was indirectly obtained through the parameter studies. The simulation results showed the simulation error according to the change of diameter predicted to be less than 2%. The defect of the internal surface by stress was found through the experiment result.

Effect of Process Conditions on Hydrophobic Characteristics of Injection Molded Silicone Rubber Surface Replicated from Electric Discharge Machined Surface

In recent years, a lot of effort has gone into many researchers making components of specific functions, mimicking various microstructures in nature. In this study, a super hydrophobic surface on injection-molded liquid silicone rubber was fabricated, mimicking micro-bumps on a lotus leaf. Original patterns were machined by electric discharge machining and liquid silicone rubber was injection-molded by using the original patterns as molds. The hydrophobic characteristics of injection-molded liquid silicone rubber surface replicated from the original electric discharge machined surface were studied. According to variations of injection molding process parameters like mold temperature, injection speed, injection pressure, vacuum, etc. the variations of water contact angles, as a hydrophobic index, measured on the injection-molded surfaces were examined. The liquid silicone rubber surface molded from wire-cutting electric discharge machined surface at mold temperature 120°C, injection speed 5 mm/sec, injection pressure 70 bar and in a vacuum cavity showed water contact angle of 148°, which is close to super-hydrophobic level.

Finite Element Analysis and Optimization for the Multi‐stage Deep Drawing of Molybdenum Sheet

Molybdenum, a bcc refractory metal with a melting point of about 2600°C, has a high heat and electrical conductivity. In addition, it remains strong mechanically at high temperatures as well as at low temperatures. Therefore it is a technologically very important material for the applications operating at high temperatures. However, a multi‐stage process is required due to the low drawability for making a deep drawn part from the molybdenum sheet. In this study, a multi‐stage deep drawing process for a molybdenum circular cup was designed by combining the drawing with the ironing, which was effective for the low drawability materials. A parametric study by FE analysis for the multi‐stage deep drawing was conducted for evaluation of the design variables effect. Based on the FE analysis result, the multi‐stage deep drawing process was parameterized by the design variables, and an optimum process design was obtained by the process optimization based on the FE simulation at each stage.