Glass Mold Research Articles

Prediction of Profile Deviation during Glass Molding of Double-Aspheric Lens

Prediction of Profile Deviation during Glass Molding of Double-Aspheric Lens

Study on α-Al2O3 anti-adhesion coating for molds in precision glass molding

Precision glass molding is a significant approach for mass production of high precision glass lenses. However, the adhesion problem, which occurs between glass and mold, seriously affects the lenses quality and mold life. Thus, there is an urgent need to develop an anti-adhesion coating for the mold inserts. With the continuous demand for glass lenses, it is essential to develop an anti-adhesive coating that can be adapted to both visible optical glass and infrared glass. In this study, an α-Al2O3 multilayer coating is deposited on tungsten carbide substrate by chemical vapor deposition and the surface roughness of the coating is improved from 100 nm to 10 nm in Ra by ultra-precision grinding with optimized machining parameters. Two currently used coatings of the rare metal Ta multilayer coating and diamond-like carbon coating are compared with the newly developed coating. Typical dense barium crown optical glass D-ZK3 and chalcogenide glass IRG206 are chosen as testing materials for wettability tests and practical precision glass molding experiments. The experimental results show that α-Al2O3 coating exhibits good anti-adhesion property for both glass materials, while Ta coating is not proper for IRG206 chalcogenide glass and diamond-like carbon coating is not suitable for D-ZK3 optical glass. Considering its excellent properties in oxidation resistance and service life, the α-Al2O3 multilayer coating would be a highly potential anti-adhesion coating for precision glass molding.

Structural investigation of the Plasma Transferred Arc hardfaced glass mold after operation

The paper presents the results of research aimed at detecting the causes of premature wear of molds for glass shaping, manifesting the formation of pits in the Plasma Transferred Arc pad-welds in which the working surface of the mold was shaped. The weld microstructure was tested, the chemical composition was determined in the pad-weld’s cross-section, linear and surface chemical distributions were made in the pad-weld’s cross-section, the surface morphology in damaged areas, and the chemical composition of surface inclusions were examined. The too high temperature of formed glass associated with wettability of the glass of the mold was indicated as the primary cause of premature mold wear.

Study on the physico-mechanical properties of treated baobab fiber (Adansonia Digitata) nano-filler/epoxy composite

In this research, the physico-mechanical properties of epoxy/baobab nano-composite were studied. The fiber was treated with sodium hydroxide and the effect of fiber loading; 0 wt%, 10 wt%, 20 wt%, 30 wt%, 40 wt% and 50 wt% has been reported. 95.58% of the baobab fiber had particle distribution of falling between 10 and 100 nm. The fabrication of the composite was by casting on a glass mould and cold curing for 24 h at 25 °C. The result showed optimum mechanical properties with 10 wt% filler loading. Hardness and water absorption increased as the filler loading increases from 10 to 50 wt%. Abrasion resistance also improved with filler loading up to 30 wt%, and then dwindled significantly with 40 wt% and 50 wt% of the filler. Consequently, the sample with 10 wt% filler had the highest tensile strength of 48 MPa; while, sample with 50 wt% of filler had least tensile strength of 20.9 MPa. Again, impact strength result showed that the sample with 10% wt had superior impact strength of 0.45 J/mm. Scanning electron microscopy image of the fractured tensile specimen further highlighted the reason for the improved mechanical properties recorded at 10 wt%. The results suggest that the baobab fiber nano-composite had adequate properties for application in the automotive industry and building construction.

Preparation and Characterization of Micro-Graphite Filled Poly(Lactic Acid) Composites: Part 1 - Rheological and Thermal Properties

Conductive polymer composites (CPCs) have attracted great attention of researchers due to their enhanced properties such as an adjustable electrical conductivity, good processability, good mechanical and thermal properties, etc. CPCs had many potencies for wider application in electronic devices. Poly (lactic acid) or PLA is one of the interesting polymers used in the developing of these new important materials. PLA properties are comparable to the synthetic petroleum-based polymers such as polyethylene terephthalate (PET), polypropylene (PP), etc. This research focuses on studying the rheological and thermal properties of PLA/micro-graphite as a conductive polymer composite which adjustable its electrical conductivity. In this study, the PLA/micro-graphite was prepared through solvent blending method using chloroform. The micro-graphite composition was varied from 0%, 5%, and 10 % (w/w) with different stirring time (30 and 60 minutes) and then, poured in glass mould. In the melt rheology study, the frequency sweep test showed that the complex viscosity (|η*|) of the bio-composite increased with the micro-graphite loading. The same tendency was also found in thermal property and stability. The melting temperature and thermal degradation were slightly increasing. The crystallinity of PLA was influenced by the presence of micro-graphite. In this solvent blending method, the homogeneous distribution of micro-graphite in the bio-composite required at least 60 minutes (stirred at 650 rpm and 60 °C).

Robust and reproducible fabrication of large area aluminum (Al) micro/nanorods arrays by superplastic nanomolding at room temperature

Large-scale preparation of aluminum (Al) micro/nanorods is reported by directly nanomolding of pure Al with bulk metallic glass (BMG) molds at room temperature. Combined with experiments and theoretical modeling, the critical dislocation nucleation stress in Al is determined, which is generally challenge to decouple from the propagation of dislocations. Benefited from the excellent mechanical properties of BMGs, the BMG molds are found to be used repeatedly. Therefore, the proposed method is intrinsically a low-cost process and could guide the high-throughput fabrication of metal nanostructures, as well as facilitate their applications such as in plasmons and wear-resisting superhydrophobic surfaces.

Thermal Stability of CrWN Glass Molding Coatings after Vacuum Annealing

CrWN glass molding coatings were deposited by plasma enhanced magnetron sputtering (PEMS). The microstructure and thermal stability of these coatings were investigated by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscope, transmission electron microscope, atomic force microscope and nanoindentation tests. The as-deposited coating exhibited an aggravated lattice expansion resulting in a constant hardness enhancement. The vacuum annealing induced surface coarsening and the spinodal decomposition of the coating accompanied by the formation of nm-sized c-CrN, c-W2N, and h-WN domains. The annealed coating with low W content had mainly a face-centered cubic (f.c.c) matrix, strain fields caused by lattice mismatch caused hardness enhancement. Following an increase in W content, the annealed coating showed a mixed face-centered cubic (f.c.c) and hexagonal close-packed (h.c.p) matrix. The large volume fraction of h-WN phases seriously weakened the coating strengthening effect and caused an obvious drop in hardness.

PtIr protective coating system for precision glass molding tools: Design, evaluation and mechanism of degradation

During Precision Glass Molding (PGM), the molding tools have to withstand severe thermo-chemical and thermo-mechanical loads cyclically. To protect their high-quality surface against degradation and increase their service lifetime, protective coatings are applied on the molding tools. In this work, we designed four different PtIr protective coating systems, where the thickness of the PtIr layer and the adhesion layer were varied. Their lifetimes were evaluated and compared using an in-house built testing bench. Among all the studied coating systems, the protective coating, which consists of a 600-nm-thick PtIr layer and a 20-nm-thick Cr adhesion layer, showed the best durability. To understand the degradation mechanism of the coating during actual engineering production, an industrial PGM machine was used and emulation PGM tests were conducted. Detailed sample characterization was performed using an array of complementary techniques including white light interferometry (WLI), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), scanning transmission electron microscopy (STEM) and atom probe tomography (APT). Phenomena such as interdiffusion, oxidation, coating spallation and glass sticking on the coating were observed and are discussed in the context of optimization of the coating's performance and durability.

Thermo-viscoelastic Modeling of Nonequilibrium Material Behavior of Glass in Nonisothermal Glass Molding

Nonisothermal Glass Molding (NGM) has become a viable replicative manufacturing technology for the cost-efficient production of complex precision optical components made of glass. During the pressing stage in NGM, glass materials undergo a huge temperature change in the glass transition range. In this range, glass exhibits thermo-viscoelastic responses, and the temperature drop through the glass transition leads glass structure to depart from an equilibrium to a nonequilibrium state. Thermo-viscoelastic properties of the nonequilibrium glass material greatly depend on temperature and thermal history. This paper presents a phenomenological constitutive model developed for modeling the thermo-viscoelastic responses of nonequilibrium glass. We propose a direct incorporation of the temperature -and thermal history effects into each parameter of the phenomenological model. This novelty allows the model to describe the nonequilibrium phenomena and to study temperature-dependent viscoelasticity of glass without assuming thermo-rheologically simple characteristics. Furthermore, the phenomenological model enables the coupling of structural -and stress relaxation phenomena. The model validation conducted for creep experiments demonstrates an enhancement in numerical predictions of the nonequilibrium material behaviors of glass over wide ranges of temperature and thermal history.

An approach to calculate master curve for glass moulding press based on finite element simulation

A new approach is proposed to calculate the master curve (MC) of glass. It can solve the problem: when the temperature is higher than Tt,l (defined later), the measured shear relaxation modulus cannot describe the mechanical response of the annealing stage during glass moulding press (GMP) through the thermal rheological simple (TRS) theory. Based on the temperature dependent Yang's modulus and TRS theory, the MC with a reference temperature less than Tt,l is calculated by an iterative process. In order to verify the suitability of MC at high temperature, the MC and shear relaxation moduli are used in the finite element (FE) simulation at the isothermal compression stage. Similar von Mises stresses are shown and the usability of the MC at moulding temperature is proved by the simulation results. In order to predict residual stress within the formed glass lens, the MC is used to conduct FE simulation for the whole GMP process.

An approach to calculate master curve for glass moulding press based on finite element simulation

A new approach is proposed to calculate the master curve (MC) of glass. It can solve the problem: when the temperature is higher than Tt,l (defined later), the measured shear relaxation modulus cannot describe the mechanical response of the annealing stage during glass moulding press (GMP) through the thermal rheological simple (TRS) theory. Based on the temperature dependent Yang's modulus and TRS theory, the MC with a reference temperature less than Tt,l is calculated by an iterative process. In order to verify the suitability of MC at high temperature, the MC and shear relaxation moduli are used in the finite element (FE) simulation at the isothermal compression stage. Similar von Mises stresses are shown and the usability of the MC at moulding temperature is proved by the simulation results. In order to predict residual stress within the formed glass lens, the MC is used to conduct FE simulation for the whole GMP process.

Development of shrinkage model of micro structured vitreous carbon mold for glass molding

Carbonization of replicated furan precursors has been proposed as a low-cost large-area method for fabricating microstructured vitreous carbon (VC) molds to glass micromolding. During the carbonization of furan precursors, large anisotropic shrinkage occurs inherently owing to thermal decomposition of the material, and this anisotropic shrinkage should be compensated to obtain the designed profiles of microcavities on the VC mold. In this study, a linear gradual shrinkage ratio model (LGSRM) was developed to predict the anisotropic shrinkage characteristics associated with the fabrication of microstructured VC molds. To verify the shrinkage model, the shape change of the VC mold according to the LGSRM was simulated with ANSYS and compared with the experimental results. To determine the coefficients of LGSRM, a finite element analysis code, in which a gradual shrinkage ratio can be assigned to each individual mesh, was developed, and the coefficients of LGSRM were selected to minimize the errors between the simulated and measured geometrical properties of the VC mold.

Effect of Elastic Modulus on the Accuracy of the Finite Element Method in Simulating Precision Glass Molding.

Precision glass molding is a revolutionary technology for achieving high precision and efficient manufacturing of glass aspheric lenses. The material properties of glass, including elastic modulus and viscosity, are highly dependent on temperature fluctuations. This paper aims to investigate the effect of elastic modulus on the high-temperature viscoelasticity of glass and the accuracy of the finite element simulation of the molding process for glass aspheric lenses. The high-temperature elastic modulus of D-ZK3L glass is experimentally measured and combined with the glass cylinder compression creep curve to calculate the high temperature viscoelasticity of D-ZK3L. Three groups of viscoelastic parameters are obtained. Based on this, the molding process of the molded aspheric lens is simulated by the nonlinear finite element method (FEM). The surface curves of lenses obtained by simulation and theoretical analyses are consistent. The simulation results obtained at different initial elastic modulus values indicate that the elastic modulus has a great influence on the precision of the FEM-based molding process of glass aspheric lenses.

Development and testing of Pine Apple and Glass Fiber Reinforced Epoxy Hybrid Composites

Usage of Natural Fiber Composites (NFC) is increased rapidly due to the bio degradability nature of the fibers. These natural fibers are mixed with synthetic fibers to obtain better mechanical properties. In this study, pine apple and glass fiber reinforced epoxy composites are developed and their mechanical properties were evaluated. Composites were prepared by varying the fibers content and by using hand layup process with glass moulds of size 160 x 160 x 3 mm3. The obtained laminates were sliced as per the ASTM criterion to test the properties. Higher glass fiber content in the composite specimen obtained higher mechanical properties. The composites can be utilized for the purpose of manufacturing components like doors panels, desks, roof tops etc.

Temperature effect on the deformation and optical quality of moulded glass lenses in precision glass moulding

AbstractThe aim of this study was to thoroughly investigate the effect of temperature on the deformation behavior and optical performance of moulded glass in a nonuniform temperature field. Experiments and numerical simulations were used to analyze how different temperature gradients distributed across a glass cylinder affected the deformation behavior of the moulded glass. Additionally, the imaging quality of the moulded glass lens was detected using the optical measurement system. The results show that the overall shape of the moulded glass cylinder was mainly determined by the value of the temperature gradient. The larger temperature gradient led to smaller deformation angle θ in the moulded glass cylinder. Temperature difference inside the glass dominantly affected the deformation behavior and surface morphology in the nonuniform temperature field, which greatly determines the imaging quality of glass lenses. The results of this study are significant for glass lens fabrication.

Modeling and experimental investigation of polymer micropart demolding from a Zr‐based bulk metallic glass mold

Demolding is a necessary process in polymer micro molding, which requires energy for fracture of the bonds between the mold and the polymer. This often leads to structural defects due to an inappropriate combination of process parameters, including demolding temperature, embossing force or injection pressure, separation rate, and separation mode. In this article, we focus on the theoretical analysis and experimental optimization of the process parameters for polymer micro‐part demolding from a zirconium (Zr)‐based bulk metallic glass mold. We developed a theoretical model to predict the demolding work, in which we considered the effects of sidewall friction combined with deformation and adhesion. We also optimized the parameters for the demolding process based on the Taguchi method. The experimental results showed that the embossing force and the separation mode had significant effects on the demolding work of hot embossing. We determined the optimum process parameters and found that with these parameters the demolding work could be decreased to 10.36 mJ in this case. POLYM. ENG. SCI., 59:2202–2210, 2019. © 2019 Society of Plastics Engineers

Hybrid refractive-diffractive microlenses in glass by focused Xe ion beam

The combination of refractive and diffractive components in a single optical element provides miniaturization of optical systems and enhancement of their performance. Thus, hybrid singlet lenses with diffractive structures added on top of the refractive curved surface were shown to have reduced chromatic and spherical aberration. Optical systems based on such hybrid lenses have reduced dimensions as they require fewer lenses for aberrations-correction. Diffractive elements provide additional possibilities of light manipulation and enable the realization of miniaturized multifocal systems, spectrometers, and other devices. Glass hybrid lenses are typically realized by diamond turning or glass moulding. These techniques, however, are not applicable for the fabrication of lenses in brittle materials or microlenses (hundreds of micrometers in diameter or less). On the other hand, direct writing techniques, such as focused ion beam (FIB) milling (typically Ga), offer a high resolution and flexibility of patterning on curved lens surfaces made of a great variety of materials. The disadvantages of FIB milling are its slow speed and Ga implantation that may alter or degrade the optical performance of fabricated components. FIB systems based on high brightness plasma ion sources provide more than an order of magnitude increase in milling rates with noble gas ions (e.g., Xe) compared with Ga FIBs. Here, the authors demonstrate the feasibility of rapid, direct milling of hybrid refractive-diffractive microlenses in glass using >60 nA of Xe ion current. Microlenses with up to 300-μm diameter were milled and diffraction gratings were realized on top of their curved surfaces. The performance of the lenses was characterized by mapping the transmitted intensity at different positions. Due to the introduction of diffraction gratings on the surface of the lenses, their optical performance is modified with the emergence of additional focal spots spatially separated by distances consistent with the theoretical and simulated values. The results indicate the applicability of the plasma focused ion beam systems for rapid fabrication of high-quality hybrid optical elements directly in hard substrates.

Optimization of Microstructural Evolution during Laser Cladding of Ni Based Powder on GCI Glass Molds

In glass industry, laser cladding is an innovative surfacing technique allowing to deposit a layer of nickel to protect glass mold against corrosion, abrasion and thermal fatigue. This method (powder fusion by projection), well known in additive manufacturing represents a real technological leap for the glass industry. But during laser cladding of Ni-based powder on gray cast iron, cracks can be observed for some process conditions. These cracks are often due to the Heat Affected Zone that creates structural stresses linked to the development of a martensitic structure in the ferritic matrix of the lamellar graphite cast iron. The aim of this work is to observe the impact of laser cladding (without substrate pre-heating usually employed to limit cracking) on the coating behavior but also on the flake-graphite cast iron substrates. The microstructure and the mechanical properties were studied (SEM and microanalysis, microhardness) around the interface cladding/substrate. Also, the impact of the processing parameters (power P (1500-2300 W), scanning speed v (2.5-10 mm/s) and powder feeding rate PFR (24.5-32.5 g/min) was studied by using the ANOVA (ANalysis Of VAriance) technique. It has been observed that laser cladding on graphite cast iron is possible without cracks by limiting the linear energy induced by the process. Also, an optimization of the processing parameters (P, v, PFR) in order to obtain the industrial expected geometry of the coating has been proposed.

Alternative for fine pure silica in kiln-casting glass molds

Silicon dioxide, also known as silica, is the most abundant mineral in the Earth’s crust. Mixed with gypsum plaster, kaolin and water, they form the main components used in the composition of Kiln-casting glass molds. However, the silica used for these types of molds has very fine granulometry (37–74 µm), which can lead to health problems and, in addition, it goes through purification processes, generating additional costs. Thus, aiming to propose a healthier and cheaper alternative for fine pure silica in molds composition, this work proposes the use of sea and river sand (300–700 µm) in substitution of it. The raw materials and compositions used in this study were analyzed and tested by Optical Microscopy, X-ray Fluorescence, Scanning Electron Microscopy and Compression Tests. The compositions with fine pure silica and river sand proved to be more resistant, both before and after being subjected to a heat treatment. On the other hand, the composition with sea sand presented lower resistance, and this was regarded as a desirable feature for complex pieces, making easier their demolding.

Manufacture and Determination of Absorbent in Bolus Radiotherapy Based On Alginate Using of 8 MeV and 10 MeV Energy

Bolus radiotherapy have been created by using material of mixture a silicone rubber as matrix and alginate powder as a filler through chemical solution deposition methods with variation of composition silicone rubber: alginate powder: catalyst (99 : 0 : 1)%wt, (80: 19: 1)%wt, (80: 18: 2)%wt, (80: 17: 3)%wt, (80:16: 4)%wt and (80: 15: 5)%wt. The sample fabrication was done in two steps. The first step of alginate powder is mixed with a solution of rubber and catalyst silicon until homogeneous for 5 minutes with the wet mixing method. The second step of the powder which was homogeneously mixed was printed with glass mould measuring 11 x 11 x 1 cm3 with variations in thickness of 5 mm, 10 mm and 15 mm then dried at 300. Each bolus sample is already to be characterized which includes: physical properties (density, porosity, and water absorption), mechanical properties (tensile strength, elongation and modulus young) and performance (CT Number and absorbency dose). The characterization results showed that alginate powder: optimum rubber silicon ie (80: 19) wt% at a thickness of 15 mm resulted in a density value of 2.091 x 103 kg/m3, porosity of 9.82% and water absorption of 1.66%. Mechanical properties with tensile strength 3.37 MPa, elongation at 45.28% and modulus of elasticity of 0.816 MPa. Bolus radiotherapy performance properties relative electron density (RED) values or CT numbers of 1.25 resulted in surface absorbance doses of 8 MeV of 101% and 10 MeV of 108.01%. The results of bolus radiotherapy based on composite alginate powder reinforced by silicone rubber can be applied as a cancer therapy material to replace bolus from wax, and paraffin.