Precision compression molding of glass microlenses and microlens arrays--an experimental study

An innovative manufacturing process utilizing high-temperature compression molding to fabricate aspherical microlenses by using optical glasses, such as BK7, K-PG325, and soda-lime glass, is investigated. In a departure from conventional approaches, a unique hollow contactless mold design is adopted. Polished glass substrates and the mold assembly are heated above the glass transition temperature first, followed by initial forming, then annealing. The forming rate is controlled in real time to ensure mold position accuracy. Mold materials used include tungsten carbides, 316 stainless steel, 715 copper nickel, and aluminum alloys. The geometric control of the microlenses or microlens arrays can be precisely controlled by the forming temperature, forming speed, mold design, and annealing time.     

Refractive index variation in compression molding of precision glass optical components

Compression molding of glass optical components is a high volume near net-shape precision fabrication method. In a compression molding process, a variation of the refractive index occurs along the radial direction of the glass component due to thermal treatment. The variation of refractive index is an important parameter that can affect the performance of optical lenses, especially lenses used for high precision optical systems. Refractive index variations in molded glass lenses under different cooling conditions were investigated using both an experimental approach and a numerical simulation. Specifically, refractive index variations inside molded glass lenses were evaluated by measuring optical wavefront variations with a Shack-Hartmann sensor system. The measured refractive index variations of the molded glass lenses were compared with the numerical simulation as a validation of the modeling approach.     

Simulation of the three-dimensional non-isothermal mold filling process in resin transfer molding

Numerical simulation of resin transfer molding (RTM) is known as a useful method to analyze the process before the mold is actually built. In thick parts, the resin flow is no longer two-dimensional and must be simulated in a fully three-dimensional space. This article presents numerical simulations of three-dimensional non-isothermal mold filling of the RTM process. The control volume/finite element method (CV/FEM) is used in this study. Numerical formulation for resin flow is based on the concept of nodal partial saturation at the flow front. This approach permits to include a transient term in the working equation, removing the need for calculation of time step to track the flow front in conventional scheme. In order to compare the results of the nodal partial saturation concept with the conventional method, a numerical scheme based on the quasi-steady state formulation is also presented. The computer codes developed based on both numerical formulations, allow the prediction of flow front positions; and pressure, temperature and conversion distributions in three-dimensional molds with complicated geometries. The validity of the two schemes is evaluated by comparison with analytical solutions of simple geometries. In all instances excellent agreement is observed. Numerical case studies are provided to demonstrate the effectiveness of the developed computer codes. The results show that the numerical procedure based on the nodal partial saturation concept, developed in this study, provides numerically valid and reasonably accurate predictions.     

Ion-exchanged diffractive elements in glass for substrate-mode optics

We recently demonstrated the use of continuous-phase ion-exchanged diffractive elements in glass for free-space optics. We extend our design methods to substrate-mode optics, which permits compact packing of miniature-sized free-space optical systems. We designed one-dimensional gratings for equal-intensity 1 ? 3 and 1 ? 5 beam splitting, assuming both planar and conical incidence angles. An experimental demonstration of a 1 ? 3 beam splitter with a uniformity error of 3.4% is presented.     

Nanofibrous glass tailored with apatite-fibronectin interface for bone cell stimulation

Exploring a material with smart and biomimetic interface has great potential in the biomaterials and tissue engineering field. This paper reports a novel nanofibrous bone matrix that was developed to retain a cell-stimulating and bone-mimetic biointerface. The bone mineral, apatite, and the cell adhesive protein, fibronectin (FN), were hybridized on the interface of a bioactive glass nanofibrous mesh, through the dissolution-and-reprecipitation process. The hybridized nanofibrous mesh showed significant improvement in the initial responses of the bone-derived cells. It is believed that this biomimetic and cell-stimulating nanofibrous mesh can be used as a potential bone regeneration matrix.     

Application of the core-shell-type granulation process for the preparation of compression molding granules containing fibrous material and powders

Acore-shell granulation process has been investigated using a bottom agitaton-type mixer in order to control the segregation of fine powders and improve the flowability of irregular-shaped composite granules containing fibrous materials. Following the mixing of powdery components (matrix and thermosetting resin) with the fiber, the mixture was granulated so as to obtain a relatively napped granule (core) surface. The optimum operating conditions for the formation of the soft powder layer (shell) onto the core granules without damaging the napped fibers is discussed on the basis of changes in the physical properties of the granules and the mechanical strength of the sintered test pieces. The experimental results show the effectiveness of the formation of a network among granules during the molding operation using the proposed granulation process.     

A numerical study of filling process through multilayer preforms in resin injection/compression molding

In resin injection/compression molding (RI/CM), a preform often comprises layers of different fiber reinforcements. Each fiber reinforcement has unique through thickness and in-plane permeabilities as well as compressibility, creating a heterogeneous porous medium in the mold cavity. In the present article, numerical simulation is utilized to investigate the filling process of RI/CM in such a heterogeneous porous medium. The filling stage is simulated in a full three-dimensional space by using control volume/finite element method and based upon an appropriate filling algorithm. The flow in the open gap which may be present in the mold cavity is modeled by Darcy’s law using an equivalent permeability. Numerical simulations of filling process for preforms containing two and three layers of different reinforcements in various stacking sequences are conducted with the aid of computer code developed in this study. Results show that the injection time as well as flow front progression depends on fiber types in the whole preform, fiber stacking sequence and open gap provided in the mold cavity. Simulated results also suggest that the presence of open gap at top of reinforcement can lead to both low injection time and uniform flow pattern.     

空心玻璃微珠/环氧树脂固体浮力材料模压成型工艺及性能

借鉴陶瓷材料模压成型工艺提出了适用于环氧树脂基固体浮力材料制备的真空辅助模压成型自由固化方法,实现了固体浮力材料制备过程中成型与固化环节的分离,为高性能固体浮力材料的制备提供了新方法。以环氧树脂(E-4221)为基体,空心玻璃微珠(Hollow glass microsphere, HGMS)做填充材料,采用模压成型自由固化方法制备高HGMS体积分数的HGMS/E-4221固体浮力材料,研究了HGMS体积分数、成型压力对HGMS/E-4221固体浮力材料密度、抗压强度、吸水率等性能的影响。结果表明,真空辅助模压成型自由固化方法适用于HGMS体积分数为65%~67%的HGMS/E-4221固体浮力材料制备,所获得的HGMS/E-4221固体浮力材料密度为0.621~0.655 g/cm3,适用深度可达到8 000~10 000 m。      

Terahertz lenses made by compression molding of micropowders

We present a simple and versatile approach for fabricating terahertz lenses based on compression molding of micropowder polymer materials in a tabletop hydraulic press. To demonstrate the feasibility of this approach, a biconvex lens shape is calculated using a ray-tracing algorithm and lenses based on two different micropowders are fabricated. As the powder materials have different refractive indices, the resulting lenses share the same geometric shape but differ in their respective focal length. The focusing properties of the lenses are evaluated by transversal and sagittal beam profile measurements in a fiber-coupled terahertz time-domain spectroscopy system, confirming the excellent imaging qualities of the compression molded lenses.     

模压法制备微孔发泡聚碳酸酯片材

为制备采用微孔挤出法、微孔注射法及常规发泡方法难以制备的薄型微孔发泡聚碳酸酯(PC)片材,首次采用具有制备周期短、工艺简单、操作容易、制备价格低廉等优点的模压法,通过快速降温降压制备了薄型微孔发泡PC片材,并探讨了加工参数对泡孔结构的影响,利用显微镜对泡孔结构进行了表征.实验结果表明:随着发泡时间的增加,泡孔尺寸先增加后恒定不变,泡孔密度先增加后降低;随发泡压力的增加,泡孔尺寸快速减小后变化不大,泡孔密度先快速增加后变化较小;随着发泡温度的增加,泡孔尺寸快速增加,泡孔密度快速降低;随活化比的增加,泡孔尺寸先减小后增加,泡孔密度则先增加后降低.通过控制发泡时间、发泡压力、发泡温度、活化比等加工参数可以控制微孔发泡PC的泡孔结构.     

Well tailored compressive stress-strain relations for elastomeric foams in uni-axial stress compression

Well tailored compressive stress-strain relations for elastomeric open and closed cell foams under a uni-axial stress compression were developed. These sets are aimed at replacing those presented by Gibson and Ashby (1988) [1] since they are mismatched and cannot be used. The proposed set of compressible stress-strain relations for elastomeric open cell foams was compared with experimental results. Good agreement was seen.     

Beam-array combination with planar integrated optics for three-dimensional multistage interconnection networks

We propose a configuration of planar integrated optics for three-dimensional multistage interconnection networks. To show the feasibility of cascading operations in the planar integrated optics, we present experimental results on the beam combination of signal- and power-beam arrays at a node stage. The beam-combination efficiency measured in the experiment is ~42% of the theoretical limit.     

Optimization of plastic injection molding process parameters for manufacturing a brake booster valve body

The plastic injection molding (PIM) process parameters have been investigated for manufacturing a brake booster valve body. The optimal PIM process parameters is determined with the application of computer-aided engineering integrating with the Taguchi method to improve the compressive property of the valve body. The parameters considered for optimization are the following: number of gates, gate size, molding temperature, resin temperature, switch over by volume filled, switch over by injection pressure, and curing time. An orthogonal array of L₁₈ is created for the statistical design of experiments based on the Taguchi method. Then, Mold-Flow analyses are performed by using the designed process parameters based on the L₁₈ orthogonal array. The signal-to-noise (S/N) ratio and the analysis of variance (ANOVA) are used to find the optimal PIM process parameters and to figure out the impact of the viscosity of resin, curing percentage, and compressive strength on a brake booster valve body. When compared with the average compression strength out of the 18 design experiments, the compression strength of the valve body produced using the optimal PIM process parameters showed a nearly 12% improvement.     

Processing of cardanol resin with CSP using compression molding technique

This paper exhibits the synthesis of a cardanol-based polymeric resin (CR) from cashew nut shell liquid as a composite matrix along with coconut shell (CS) as reinforcement utilizing poly-condensation technique. In the proposed method, the provincially gathered CSs are dried in an oven in order to expel dampness content. With an average diameter ranging from 25 to 75 µm, the dried CSs are then grated into small particles and in the compression molding method these particles are made into two sets for untreated and treated (5% NaOH) biocomposites with varying concentration of 0%, 10%, 20%, 30%, and 40%. The thermal properties are assessed by thermo gravimetric analysis (TGA) and differential thermal analysis (DTA) whereas the chemical formulation is reckoned by the assistance of Fourier transforms infrared spectroscopy. The microstructures of the composites are portrayed by scanning electron microscopy to scrutinize the morphological and surface characteristics of CR and CS. The TGA and DTA results revealed that the treated CS particle at 25 and 75 µm thermal stability (484° and 459°) with untreated CS particle (466°C and 449°C) at 30% particle loading condition. The 25-µm CS particles are thermally more stable than 75 µm particles. Veritably it is unveiled that, a polymeric matrix composite combined with untreated and treated CS particles might be a good alternative remembering the ultimate goal to nab an eco-friendly product.     

Numerical simulation of injection/compression liquid composite molding. Part 2: preform compression

In the injection/compression liquid composite molding process (I/C-LCM), a liquid polymer resin is injected into a partially open mold, which contains a preform of reinforcing fibers. After some or all of the resin has been injected, the mold is closed, compressing the preform and causing additional resin flow. This paper addresses compression of the preform, with particular emphasis on modeling three-dimensional mold geometries and multi-layer preforms in which the layers have different mechanical responses. First, a new constitutive relation is developed to model the mechanical response of fiber mats during compression. We introduce a new form of nonlinear elasticity for transversely isotropic materials. A special case of this form is chosen that includes the compressive stress generated by changes in mat thickness, but suppresses all other responses. This avoids the need to model slip of the preform along the mold surface. Second, a finite element method, based on the principle of virtual displacement, is developed to solve for the deformation of the preform at any stage of mold closing. The formulation includes both geometric and material nonlinearities, and uses a full Newton–Raphson iteration in the solution. An open gap above the preform can be incorporated by treating the gap as a distinct material layer with a very small stiffness. Examples show that this approach successfully predicts compression in dry preforms for three-dimensional I/C-LCM molds.