This paper presented a fundamental investigation on the exit-chipping formation mechanisms involved in rotary ultrasonic drilling (RUD) and conventional drilling (CD) of glass BK7. It was found that the mutual tool-material extrusion initially activated the subsurface crack with the maximum depth (incipient crack) at the margin of the machined surface, and its penetration of the undrilled thickness brought about the emergence of the exit-chipping at Region I. Subsequently, the opposite propagations of two ring-cracks along the circumferential direction of the drilled hole were conducive to the collapse of the machined cylinder, thus leading to the appearance of the exit-chipping at Region II. Ultrasonic superposition significantly decreased the actual undrilled thickness of the machined surface, while slightly increased the exit-chipping width. All the exit-chippings, generated with and without ultrasonic, exhibited the elliptic and symmetrical morphologies accompanied by the corrugated stripes winding the entire chipping surfaces. The quantitative relationship between the instantaneous extrusion pressure and the propagation direction of the incipient crack was proposed, revealing that the propagation angle was inversely proportional to the extrusion pressure. Ultrasonic superimposition augmented the extrusion pressure exerted the machined surface, which reduced the propagation angle of the incipient crack. The elliptic morphology characteristics of the exit-chipping were attributed to the parabolic variation of the additional bending moment with the circumferential spreading of the ring-crack. Ultrasonic superposition increased the propagation angle of the ring-crack, thus deteriorating the exit quality of the drilled hole.

In this paper, we present a new approach of combining point-by-point selective powder delivery with powder bed fusion for multiple material (metal/glass) components printing. Dual ultrasonic vibration was used to achieve stable flowrates of both 316 L steel and soda-lime glass powders which were dispensed selectively and separately. The effects of the stand-off distance and the scanning speeds on the quality of the formed layers were investigated. The results showed that the ratio between the stand-off distance and the powder size (h/d) should be lower than 3 for accurate selective material deposition. However, in practical processing, for preventing the nozzle from being damaged by the parts, the stand-off distance was larger than three times of the powder size. Different laser processing parameters were developed for processing the metal and glass due to material property differences. The interfaces between 316 L and soda-lime glass were examined. A number of 3D objects consisting of metal and glass were printed using this method.

A three-dimensional (3D) inner surface inspection system is developed in this research based on circle-structured light, which is an improved laser triangulation method. A conical reflector is used to reflect the laser and generate radial laser plane that is called circle-structured light, and a CCD camera is used to capture the light stripe on the inner surface. Then, the 3D coordinates of points on the light stripe are calculated through laser triangulation algorithm. Compared with existing inner surface measurement systems, this research takes assembly errors and refraction distortion into consideration and proposes a laser plane mathematical model with four degrees-of-freedom along with corresponding flexible laser plane calibration technique based on binocular vision that is easy to operate. The proposed inspection system calibrated by proposed algorithm performs well in diameter measurement experiment, in which the absolute error is superior to 3 μm, and defect detecting experiment, in which the defect resolution is superior to 0.02 mm. Moreover, the system also performs well in straightness and roundness evaluation. Experiments indicate that this system is applicable in inner surface measurement and inspection, and the calibration method is accurate and easy to operate.

Direct thermal imprinting of nanostructures on glass substrates is reliable when manufacturing net-shaped glass devices with various surface functions. However, several problems are recognized, including a long thermal cycle, tedious optimization, difficulties in ensuring high level replication fidelity, and unnecessary thermal deformation of the glass substrate. Here, we describe a more sustainable and energy efficient method for direct thermal imprinting of nanostructures onto glass substrates; we use silicon mold transparent to infrared between 2.5 and 25 μ m in wavelength combined with CO 2 laser scanning irradiation. The glass strongly absorbed the 10.6 μ m wavelength irradiation, triggering substantial heating of a thin layer on the glass surface, which significantly enhanced the filling of pressed glass material into nanostructured silicon mold cavities. For comparison, we conducted conventional direct glass thermal imprinting experiments, further emphasizing the advantages of our new method, which outperformed conventional methods. The thermal mass cycle was shorter and the imprint pattern quality and yield, higher. Our method is sustainable, allowing more rapid scalable fabrication of glass nanostructures using less energy without sacrificing the quality and productivity of the fabricated devices.

The purpose of this study was to investigate the advantages of laser surface melting for improving wetting over the traditional approach. For comparison, kovar alloy was preoxidized in atmosphere at 700 °C for 10 min, and then wetted with borosilicate glass powder at 1100 °C with different holding time in atmosphere. The proposed approach used a Nd:YAG laser to melt the surface of the kovar alloy sample in atmosphere, then wetted with borosilicate glass powder at 1100 °C with the same holding time. The laser melted surface shows a decrease in contact angle (CA) from 47.5 deg to 38 deg after 100 min. X-ray photoelectron spectroscopy (XPS) analysis shows that the surface and adjacent depth have higher concentration of FeO for laser treated kovar (Kovar(L)) than that on traditional thermal treated kovar (kovar(P)). This is attributed to the following improved wetting and diffusion process. The adhesive oxide layer formed on kovar (L) may enhance the oxygen diffusion into the substrate and iron diffusion outward to form an outside layer. This is an another way to enhance the wetting and diffusion process when compared to the delaminated oxide scales formed on kovar (P) surface. The diffusion mechanisms were discussed for both approaches. Scanning electron microscope (SEM) revealed that an iron oxide interlayer in the joint existed under both conditions. Fayalite nucleated on the iron oxide layer alloy and grew into the glass. In both cases, neither Co nor Ni were involved in the chemical bonding during wetting process. The work has shown that laser surface melting can be used to alter the wetting and diffusion characteristics of kovar alloy onto borosilicate glass.

There are many scientific and engineering applications of transparent glass including optics, communications, electronics, and hermetic seals. However, there has been minimal research toward the additive manufacturing (AM) of transparent glass parts. This paper describes and demonstrates a filament-fed technique for AM of transparent glass. A transparent glass filament is melted by a CO 2 laser and solidifies as the workpiece is translated relative to the stationary laser beam. To prevent thermal shock, the workpiece rests on a heated build platform. In order to obtain optically transparent parts, several challenges must be overcome, notably producing index homogeneity and avoiding bubble formation. The effects of key process parameters on the morphology and transparency of the printed glass are explored experimentally. These results are compared to a low-order model relating the process parameters to the temperature of the molten region, which is critical to the quality of the deposited glass. At lower temperatures, the glass is not fully melted, resulting in index variations in the final part, while at higher temperatures, phase separation introduces bubbles and other defects into the part. The correct process avoids these issues and deposits optically transparent glass.

Interlaminar crack initiation and propagation are a major mode of failure in laminate fiber reinforced composites. A laser reinforcement process is developed to bond layers of glass fabric prior to the vacuum-assisted transfer molding of laminate composites. Glass fabric layers are bonded by fusing a dense glass bead to fibers within the laser focal volume, forming a 3D reinforcement architecture. Coupled heat transfer and viscous flow modeling is used to capture the temperature and morphology evolution of glass during the reinforcement process under experimentally observed conditions. Mode I double cantilever beam (DCB) testing is performed to quantify the effects of laser interlaminar reinforcements on composite delamination resistance. Postmortem high-resolution imaging of the fracture surface is used to characterize the toughening mechanism of the interlaminar reinforcements. Improved delamination resistance of laser reinforced composites derives from crack arrest and deflection mechanisms, showing a positive correlation to the reinforcement thickness.

Alumina ceramics, due to their excellent properties of high hardness, corrosion resistance, and low thermal expansion coefficient, are important industrial materials with a wide range of applications, but these materials also present difficulty in machining with low material removal rates and high tool wear. This study is concerned with laser-assisted machining (LAM) of high weight percentage of alumina ceramics to improve the machinability by a single point cutting tool while reducing the cutting forces. A multiscale model is developed for simulating the machining of alumina ceramics. In the polycrystalline form, the properties of alumina ceramics are strongly related to the glass interface existing in their microstructure, particularly at high temperatures. The interface is characterized by a cohesive zone model (CZM) with the traction–separation law while the alumina grains are modeled as continuum elements with isotropic properties separated by the interface. Bulk deformation and brittle failure are considered for the alumina grains. Molecular dynamics (MD) simulations are carried out to obtain the atomistic structures and parameterize traction–separation laws for the interfaces of different compositions of alumina ceramics at high temperatures. The generated parameterized traction–separation laws are then incorporated into a finite element model in Abaqus to simulate the intergranular cracks. For validation purposes, simulated results of the multiscale approach are compared with the experimental measurements of the cutting forces. The model is successful in predicting cutting forces with respect to the different weight percentage and composition of alumina ceramics at high temperatures in LAM processes.

Laser scribing is an important manufacturing process used to reduce photocurrent and resistance losses and increase solar cell efficiency through the formation of serial interconnections in large-area solar cells. High-quality scribing is crucial since the main impediment to large-scale adoption of solar power is its high-production cost (price-per-watt) compared to competing energy sources such as wind and fossil fuels. In recent years, the use of glass-side laser scribing processes has led to increased scribe quality and solar cell efficiencies; however, defects introduced during the process such as thermal effect, microcracks, film delamination, and removal uncleanliness keep the modules from reaching their theoretical efficiencies. Moreover, limited numerical work has been performed in predicting thin-film laser removal processes. In this study, a nanosecond (ns) laser with a wavelength at 532 nm is employed for pattern 2 (P2) scribing on CdTe (cadmium telluride) based thin-film solar cells. The film removal mechanism and defects caused by laser-induced micro-explosion process are studied. The relationship between those defects, removal geometry, laser fluences, and scribing speeds are also investigated. Thermal and mechanical numerical models are developed to analyze the laser-induced spatiotemporal temperature and pressure responsible for film removal. The simulation can well-predict the film removal geometries, transparent conducting oxide (TCO) layer thermal damage, generation of microcracks, film delamination, and residual materials. The characterization of removal qualities will enable the process optimization and design required to enhance solar module efficiency.

Functionally graded bioactive glass coatings on bioinert metallic substrates were produced by using continuous-wave (CW) laser irradiation. The aim is to achieve strong adhesion on the substrates and high bioactivity on the top surface of a coating material for load-bearing implants in biomedical applications. The morphology and microstructure of the bioactive glass from the laser coating process were investigated as functions of processing parameters. Laser sintering mechanisms were discussed with respect to the resulting morphology and microstructure. It has been shown that double layer laser coating results in a dense bond coat layer and a porous top coat layer with lower degree of crystallinity than an enameling coating sample. The dense bond coat strongly attached to the titanium substrate with a 10 μm wide mixed interfacial layer. A highly bioactive porous structure of the top coat layer is beneficial for early formation of a bone-bonding hydroxycarbonate apatite (HCA) layer. The numerical model developed in this work also allows for prediction of porosity and crystallinity in top coat layers of bioactive glass developed through laser induced sintering and crystallization.

Selective laser melting (SLM) is a technique for the additive manufacturing (AM) of metals, plastics, and even ceramics. This paper explores using SLM for depositing glass structures. A CO2 laser is used to locally melt portions of a powder bed to study the effects of process parameters on stationary particle formation as well as continuous line quality. Numerical modeling is also applied to gain insight into the physical process. The experimental and numerical results indicate that the absorptivity of the glass powder is nearly constant with respect to the processing parameters. These results are used to deposit layered single-track wide walls to demonstrate the potential of using the SLM process for building transparent parts. Finally, the powder bed process is compared to a wire-fed approach. AM of glass is relevant for gradient index optics, systems with embedded optics, and the formation of hermetic seals.

The compression molding of precision glass lens is a near net-shape forming process for optical components fabrication. The final profile curve accuracy is one of the most crucial criterions for evaluating the quality of the molded lens. In this research, our purpose was focused on the evaluation of the molded lens curve deviation. By incorporating stress relaxation and structural relaxation model of glass, numerical simulations of the whole molding process for fabricating a planoconvex lens were conducted by utilizing the commercial software msc Marc. The relationship of the three variables, i.e., the lens curve deviation, the mold curve deviation, the gap between the lens and the lower mold, was discussed and the evolution plots with time of the three variables were obtained. Details of the thermal boundary conditions were discussed by considering the contact heat transfer behavior. Then the essentiality of a small gap between the molds and the molded lens after releasing the upper mold was demonstrated. In details, the sensitivity analysis of the processing parameters was conducted, such as the releasing temperature, the cooling rate in the annealing and fast cooling stage, respectively, and the magnitude of the hold-up force. The results showed that the glass lens curve deviation was not sensitive to the choices of the releasing temperature and the cooling rate. What's more, the results indicated that the curve deviation decreased with the hold-up force increasing. Finally, with all the details considered, the final simulation results were presented accurately with good reason.

Residual stresses and refractive index of molded glass lenses are important quality indicators of their optical performance. In this research, the control of residual stresses and refractive index variation of molded glass lenses were experimentally investigated by postmolding annealing. Residual stresses were quantitatively measured using a circular polariscope. Refractive index was reconstructed and calculated by an optical setup based on Mach–Zehnder interferometer. In addition, geometry of the aspherical surface of lens was also evaluated before and after annealing. The comparison between the measured results before and after annealing showed that residual stresses and refractive index variation were well controlled and the shape of the aspherical surface was largely retained. This comprehensive experimental study demonstrated a suggestion to improve quality of the compression molded glass lens by postmolding annealing for high-precision optical applications.

Laser scribing of multilayer-thin-film solar cells is an important process for producing integrated serial interconnection of mini-modules, used to reduce photocurrent and resistance losses in a large-area solar cell. Quality of such scribing contributes to the overall quality and efficiency of the solar cell, and therefore predictive capabilities of the process are essential. Limited numerical work has been performed in predicting the thin film laser removal processes. In this study, a fully-coupled multilayer thermal and mechanical finite element model is developed to analyze the laser-induced spatio-temporal temperature and thermal stress responsible for SnO2:F film removal. A plasma expansion induced pressure model is also investigated to simulate the nonthermal film removal of CdTe due to the micro-explosion process. Corresponding experiments of SnO2:F films on glass substrates by 1064 nm ns laser irradiation show a similar removal process to that predicted in the simulation. Differences between the model and experimental results are discussed and future model refinements are proposed. Both simulation and experimental results from glass-side laser scribing show clean film removal with minimum thermal effects indicating minimal changes to material electrical properties.

A laser fusion joining method is investigated for the purpose of through thickness strengthening of glass fiber reinforced laminate composites. Laser fusion joining is evaluated as a potential process to replace mechanical reinforcements used in conventional laminate composite fabrication. A two step laser process is developed to form fusion bonds between fibers within a single bundle and between adjacent fiber bundles. Coupled heat transfer and viscous flow modeling is carried out to investigate the temperature and dynamics of the joining process under three experimentally observed conditions. Linear elastic finite element analysis is used to investigate the effect of joint morphology on stress concentrations and strength. Joint strength is found to be a function of the fiber contact angle and packing density at the joint interface. Tensile tests show that laser joined fiber bundle strength is on the same order of magnitude as the raw fiber bundles. The challenges to laser processing of three dimensional fiber reinforcements in laminate composite fabrication are discussed.

Femtosecond laser pulses were focused on the interface of two glass specimens. Proper use of optical and laser processing parameters enables transmission welding. The morphology of the weld cross section was studied using differential interference contrast optical microscopy. In addition, a numerical model was developed to predict the absorption volumes of femtosecond laser pulses inside a transparent material. The model takes into account the temporal and spatial characteristics and propagation properties of the laser beam, and the transmission welding widths were subsequently compared with the absorption widths predicted by the model. The model can lead to the achievement of a desirable weld shape through understanding the effects of laser pulse energy and numerical aperture on the shape of the absorption volume. The changes in mechanical properties of the weld seams were studied through spatially resolved nanoindentation, and indentation fracture analysis was used to investigate the strength of the weld seams.

Surface finish determines service life of glass workpieces. Therefore, an extensive polishing phase is usually performed to limit the local irregularities. In this paper, we propose to investigate the influence of the grinding parameters on the surface finish of glass samples in order to limit the damages at the earlier stage of the machining process. A central composite design of experiments has been used to define experimental tries that consist of up-grinding or down-grinding glass samples with various feed rate, depth of cut, and wheel speed values. Roughness parameters derived from the Abbott–Firestone curve R k , R vk , and the material ratio 100–Mr2 have been used to characterize the surface finishes of the ground glass samples. Using the design of experiments, surface responses have been modeled for each roughness parameter to investigate the influence of the cutting parameters. Abbott–Firestone parameters allow a relevant characterization of the glass samples surface finishes. Feed rate increase led to deeper valleys, thus providing a rough surface finish that could potentially shorten workpieces service life. On the contrary, increasing depth of cut tend to reduce valley depth. Wheel speed has shown minor influence on the surface finish. Up-grinding could help obtain less deep valleys than with a down-grinding. However, up-grinding also increases the cutting forces and induces vibrations that led to an increase of the core roughness and eventually to the fracture of the glass sample during the machining. In a material removal context—in opposition with polishing—feed rate should be carefully chosen since it is the most influential parameter on the surface finish. To maximize productivity while obtaining low-valleys surface finishes, an appropriate strategy would consist in down-grinding with a low feed rate, a high depth of cut, and a high wheel speed.

Industrial glass blowing is an essential stage of manufacturing glass containers, i.e., bottles or jars. An initial glass preform is brought into a mold and subsequently blown into the mold shape. Over the past few decades, a wide range of numerical models for forward glass blow process simulation has been developed. A considerable challenge is the inverse problem: to determine an optimal preform from the desired container shape. A simulation model for blowing glass containers based on finite element methods has previously been developed ( Giannopapa, 2008, “Development of a Computer Simulation Model for Blowing Glass Containers,” ASME J. Manuf. Sci. Eng., 130, p. 041003 ; Giannopapa and Groot, 2007, “A Computer Simulation Model for the Blow-Blow Forming Process of Glass Containers,” 2007 ASME Pressure Vessels and Piping Conference and 8th International Conference on CREEP and Fatigue at Elevated Temperature ). This model uses level set methods to track the glass-air interfaces. The model described in a previous paper of the authors showed how to perform the forward computation of a final bottle from the given initial preform without using optimization. This paper introduces a method to optimize the shape of the preform combined with the existing simulation model. In particular, the new optimization method presented aims at minimizing the error in the level set representing the glass-air interfaces of the desired container. The number of parameters used for the optimization is restricted to a number of control points for describing the interfaces of the preform by parametric curves, from which the preform level set function can be reconstructed. Numerical applications used for the preform optimization method presented are the blowing of an axisymmetrical ellipsoidal container and an axisymmetrical jar.

Femtosecond laser pulses were focused in the interior of a single fused silica piece. Proper use of optical and laser processing parameters generated structural rearrangement of the material through a thermal accumulation mechanism, which could be potentially used for the transmission welding process. The morphology of generated features was studied using differential interference contrast optical microscopy. In addition, the predictive capability of the morphology is developed via a finite element analysis. The change in mechanical properties was studied through employment of spatially resolved nanoindentation. The specimen was sectioned and nanoindents were applied at the cross section to examine mechanical responses of the laser-modified region. Fracture toughness measurements are carried out to investigate the effects of the laser treatment on strength of the glass.

In this work, we demonstrate the plausibility of integrating two-photon polymerization (TPP) with nanoimprinting for direct, digital nanomanufacturing. TPP offers manufacturing of nanomolds at a low cost, while the nanoimprinting process using the nanomolds enables massively parallel printing of nanostructures. A Ti:sapphire femtosecond laser (800 nm wavelength, 100 fs pulse width, at a repetition rate of 80 MHz) was used to induce TPP in dipentaerythritol pentaacrylate to fabricate the nanoimprinting mold with 400 nm wide line array on a glass substrate. The mold surface was silanized by tridecafuoro-1,1,2,2-tetrahydrooctyl-1 trichlorosilane to facilitate the detachment of the mold from the imprinted material. This mold was then used to imprint poly(ethylene glycol) diacrylate (PEGDA). PEGDA is an important biomaterial for many applications such as tissue scaffolds for cell growth. A spectrophotometer and a scanning electron microscope were used to characterize the materials and nanostructures.