Glass molding is as an effective approach to produce precision micro optical elements with complex shapes at high production efficiency. Since glass is deformed at a high temperature where the mechanical and optical properties depend strongly on temperature, modeling the heat transfer and high-temperature deformation behavior of glass is an important issue. In this paper, a two-step pressing process is proposed according to the non-linear thermal expansion characteristics of glass. Heat transfer phenomenon was modeled by considering the temperature dependence of specific heat and thermal conductivity of glass. Viscosity of glass near the softening point was measured by uniaxially pressing cylindrical glass preforms between a pair of flat molds using an ultraprecision glass molding machine. Based on the numerical models and experimentally measured glass property, thermo-mechanical finite element method simulation of temperature rise during heating and material flow during pressing was carried out. The minimum heating time and pressing load changes were successfully predicted.

Modeling high-temperature glass molding process by coupling heat transfer and viscous deformation analysis

Investigation on the viscoelasticity of optical glass in ultraprecision lens molding process

Coupled thermomechanical finite element models were developed in ABAQUS to simulate the precision glass lens molding process, including the stages of heating, soaking, pressing, cooling and release The aim of the models was the prediction of the deviation of the final lens profile from that of the mold, which was accomplished to within one-half of a micron The molding glass was modeled as viscoelastic in shear and volume using an n-term, prony series; temperature dependence of the material behavior was taken into account using the assumption of thermal rheological simplicity (TRS); structural relaxation as described by the Tool-Narayanaswamy-Moynihan (TNM)-model was used to account for temperature history dependent expansion and contraction, and the molds were modeled as elastic taking into account both mechanical and thermal strain In Part I of this two-part series, the computational approach and material definitions are presented Furthermore, in preparation for the sensitivity analysis presented in 

/pdf/final-shape-of-precision-molded-optics-part-1-computational-178exs2pn1.pdf

Final Shape of Precision Molded Optics: Part 1 - Computational Approach, Material Definitions and the Effect of Lens Shape

This paper reports a novel hot embossing technique using rapid heating and uniform pressure for replication of microstructures on polymeric substrates. The rapid heating is made possible by a graphene–polymer composite heater that makes use of the exceptional thermal and electrical properties of graphene. The uniform embossing pressure is achieved by using gas as the pressing medium. A heating rate of 14 °C s−1 can be achieved by applying a voltage of 44 V to a heating area of 30 mm × 30 mm. A facility that integrates graphene-based heating and gas-assisted embossing is designed and implemented. Three microstructures, namely, microlens array, V-groove, and microcylinder array, are successfully replicated on three polymeric substrates. The accuracy and uniformity of replication over the area of 50 mm × 50 mm is also confirmed. Furthermore, the thermal cycle time is reduced to less than 30 s. This study proves the great potential of using graphene–polymer composite heaters in gas-assisted micro hot embossing for replication of microstructures for various applications.

/pdf/application-of-graphene-polymer-composite-heaters-in-gas-4lol58wrsj.pdf

Application of graphene–polymer composite heaters in gas-assisted micro hot embossing

Metallic tubular micro-components play an important role in a broad range of products, 
from industrial microsystem technology, such as medical engineering, electronics and optoelectronics, to sensor technology or microfluidics. The demand for such components is increasing, and forming processes can present a number of advantages for industrial manufacturing. These include, for example, a high productivity, enhanced shaping possibilities, applicability of a wide spectrum of materials and the possibility to produce parts with a high stiffness and strength. However, certain difficulties arise as a result of scaling down conventional tube forming processes to the microscale. These include not only the influence of the known size effects on material and friction behavior, but also constraints in the feasible miniaturization of forming tools. Extensive research work has been conducted over the past few years on micro-tube forming techniques, which deal with the development of novel and optimized processes, to counteract these restrictions. This paper reviews the relevant advances in micro-tube fabrication and shaping. A particular focus is enhancement in forming possibilities, accuracy and obtained component characteristics, presented in the reviewed research work. Furthermore, achievements in severe plastic deformation for micro-tube generation and in micro-tube testing methods are discussed.

https://www.mdpi.com/2075-4701/9/5/542/pdf

Review on Advances in Metal Micro-Tube Forming

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 of an Aspheric Glass Lens Forming Behavior in Progressive GMP Process

Silicon (Si) nanowires have been widely used as sensor and heater in various fields such as biology and chemistry due to its high sensitivity and fast responsivity. In this paper, we measured the temporal response property of Si nanowire-heater through infrared microscopy. Nanowire-heaters were fabricated using silicon-on-insulator (SOI) wafer with Si heights of 15 μm and 30 μm, respectively. In order to compare the change of the temporal response property according to the structural shape, four different types of nanowire-heater were fabricated using the basic MEMS processes. To measure the transient temperature change of nanowireheaters, the voltage of square wave with constant pulse duration was applied using a function generator. According to the pulse duration, the transient temperature distribution for four different types of Si nanowire-heater was measured using infrared (IR) microscope. Consequently, regardless of the structural shape and width difference of Si nanowire-heaters, they showed a fast response time less than 1 ms when the voltage with 500 Hz pulse duration was repeatedly applied. Also, the simulated results using COMSOL multiphysics showed that they had around 100 μs response time which is around 10 times faster than the maximum time resolution of the IR microscope.

Fast thermal response of silicon nanowire-heater for heat shock generation

Hot embossing, one of nanoimprint lithography(NIL) techniques, has been getting attention as an alternative candidate of next generation patterning technologies by the advantages of simplicity and low cost compared to conventional photolithographies. A typical hot embossing usually, however, takes more than ten minutes for one cycle of the process because of a long thermal cycling. Over the last few years a number of studies have been made to reduce the cycle time for hot embossing or similar patterning processes. The target of this research is to develop an induction heating apparatus for heating a micro patterning mold at high speed with the uniformity of temperature distribution. It was found that a 0.5 mm-thick nickel mold can be heated from 25degC to 150degC within 1.8 seconds with the temperature variation of plusmn10degC in 4-inch diameter area, using the induction heating apparatus. Micro patterns of 120 mum line width and 25 mum height were successfully replicated on a plastic sheet under the pressure of about 0.09 MPa within 60 seconds.

Replication of polymeric micro patterns by rapid thermal pressing with induction heating apparatus

Disclosed herein is a method of manufacturing a touch screen panel, including the steps of: forming a spacer array and a mold having a shape corresponding to that of a horizontal groove array or a vertical groove array; fabricating a transparent upper plate having a horizontal groove array including two or more horizontal grooves and a transparent lower plate having a vertical groove array including two or more vertical grooves using the mold; charging a predetermined amount of conductive ink in the horizontal groove array and the vertical groove array; and drying the conductive ink to form a conductive array and then attaching the upper plate to the lower plate.

Jeong Jin Kang

Papers

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

Fast thermal response of silicon nanowire-heater for heat shock generation

Replication of polymeric micro patterns by rapid thermal pressing with induction heating apparatus

Touch screen panel for multi-touching and method of manufacturing the same

Method for manufacturing a micro multi-layer lens