Hemispherical Mould Research Articles

Bioinspired Lubricity from Surface Gel Layers.

Surface gel layers on commercially available contact lenses have been shown to reduce frictional shear stresses and mitigate damage during sliding contact with fragile epithelial cell layers in vitro. Spencer and co-workers recently demonstrated that surface gel layers could arise from oxygen-inhibited free-radical polymerization. In this study, polyacrylamide hydrogel shell probes (7.5 wt % acrylamide, 0.3 wt % N,N'-methylenebisacrylamide) were polymerized in three hemispherical molds listed in order of decreasing surface energy and increasing oxygen permeability: borosilicate glass, polyether ether ketone (PEEK), and polytetrafluoroethylene (PTFE). Hydrogel probes polymerized in PEEK and PTFE molds exhibited 100× lower elastic moduli at the surface ( = 80 ± 31 and = 106 ± 26 Pa, respectively) than those polymerized in glass molds ( = 31,560 ± 1,570 Pa), in agreement with previous investigations by Spencer and co-workers. Biotribological experiments revealed that hydrogel probes with surface gel layers reduced frictional shear stresses against cells (τPEEK = 35 ± 15 and τPTFE = 22 ± 16 Pa) more than those without (τglass = 68 ± 15 Pa) and offered greater protection against cell damage when sliding against human telomerase-immortalized corneal epithelial (hTCEpi) cell monolayers. Our work demonstrates that the "mold effect" resulting in oxygen-inhibition polymerization creates hydrogels with surface gel layers that reduce shear stresses in sliding contact with cell monolayers, similar to the protection offered by gradient mucin gel networks across epithelial cell layers.

Numerical simulation analysis of forming of continuous fiber reinforced polypropylene composites: Relaxation, creep, and hot stamping

In this study, the viscoelastic constitutive equation of continuous glass fiber reinforced polypropylene composites based on the generalized Maxwell model and SCFM model was constructed by combining genetic algorithm. Based on this, a multi-scale numerical model for describing material relaxation and creep is proposed, and the accuracy of different scale models was compared through experiments. The forming state of the workpiece under various stamping speeds and preheating temperatures was also examined using a hot stamping numerical model. The independent design of the hot stamping hemispherical mold was used to confirm the hot stamping model's accuracy. The study's findings demonstrate that the macroscopic model can accurately simulate the relaxation and creep of composite materials. The hot stamping simulation results are match up well with experimental results. Composite molding defects appeared at the waist of the part, and defects were accompanied by resin loss.

A 3D bioprinted hydrogel multilevel arc vascular channel combined with an isomaltol core sacrificial process

This study presents a novel approach for the rapid and efficient fabrication of arc vascular channels. A hydrogel matrix preparation and a vascular core 3D printing method are proposed for the construction of multilevel vascular channels. In this method, an SA (sodium alginate)-PAM (acrylamide) hydrogel was used as the matrix for vascular core embedding, and a “sugar” (isomaltol) was used as the vascular core sacrificial material in combination with hemispherical mold deformation. After the vascular core was embedded, solidified, and dissolved in the hydrogel at 70 °C, a 3D multilevel hydrogel vascular channel was obtained. The test results of the HUVEC culture showed that the cells were triangular or spindle-shaped and were evenly attached to the inner wall of the channels. The prepared vascular channels can be used as research models for vascular diseases, drug delivery, targeted therapy, and microenvironment simulation.

Processing Optimization of Shear Thickening Fluid Assisted Micro-Ultrasonic Machining Method for Hemispherical Mold Based on Integrated CatBoost-GA Model.

Micro-electro-mechanical systems (MEMS) hemispherical resonant gyroscopes are used in a wide range of applications in defense technology, electronics, aerospace, etc. The surface roughness of the silicon micro-hemisphere concave molds (CMs) inside the MEMS hemispherical resonant gyroscope is the main factor affecting the performance of the gyroscope. Therefore, a new method for reducing the surface roughness of the micro-CM needs to be developed. Micro-ultrasonic machining (MUM) has proven to be an excellent method for machining micro-CMs; shear thickening fluids (STFs) have also been used in the ultra-precision polishing field due to their perfect processing performance. Ultimately, an STF-MUM polishing method that combines STF with MUM is proposed to improve the surface roughness of the micro-CM. In order to achieve the excellent processing performance of the new technology, a Categorical Boosting (CatBoost)-genetic algorithm (GA) optimization model was developed to optimize the processing parameters. The results of optimizing the processing parameters via the CatBoost-GA model were verified by five groups of independent repeated experiments. The maximum absolute error of CatBoost-GA is 7.21%, the average absolute error is 4.69%, and the minimum surface roughness is reduced by 28.72% compared to the minimum value of the experimental results without optimization.

Evolution of etch profile of silicon in HNA solution

In purpose of building highly symmetric hemispherical molds for 3D shell resonator fabrication, the evolution of etch profile of 〈111〉 silicon in HNA (HF/HNO 3 /CH 3 COOH) solution has been reported. According to experimental data, the etch profile first evolves into an annular groove and returns to smooth surface as the etching period increases. The duration of the annular groove phase could last from seconds to minutes, depending on the etching configurations and mask window dimensions. It is suggested that the hemispherical molds can only be formed after the annular groove phase, where the etch is considered as isotropic. Based on the experimental conditions used in this study, hemispherical molds have been fabricated with etch window radii lower than 10 μm. The fluorophore-assisted confocal laser measurement shows that the molds possess an average radius of 38.93 μm with a variance of 0.79 μm, which builds the basis to fabricate 3D shell resonators with high structure symmetry. • Highly symmetric hemispherical molds for 3D shell resonator has been fabricated on <111> silicon by isotropic wet etching(HNA). • The evolution of etch profile has been studied which evolved first into an annular groove and returned to smooth surface as the etching period increased. • It is suggested that the hemispherical molds can only be formed after the annular groove phase, where the etch is considered as isotropic.

Deep isotropic chemical etching (DICE) process for fabricating highly symmetric hemispherical silicon molds

This paper introduces the deep isotropic chemical etching (DICE) process developed for wafer-scale manufacturing of highly symmetric hemispherical silicon molds. The DICE process uses silicon nitride concentric rings as a masking layer during hydrofluoric, nitric, acetic etching of silicon substrate. These concentric rings pop up and widen the etch aperture as etch depth increases, thereby allowing control of vertical and lateral etch rates until reaching the desired mold dimensions. Our comparative experiments demonstrate that the pop-up rings are remarkable at creating molds with enhanced symmetry compared to the conventional pinhole masks. We have demonstrated the effectiveness of our approach compared to single pinholes by producing a super-symmetric 0.1 mm hemispherical mold () using two concentric rings surrounding a pinhole. We have then shown how the DICE process can be used to fabricate larger silicon molds and presented the results of a single concentric ring that achieves fabrication of a 0.25 mm-deep mold with an aspect ratio of .

Micro ultrasonic machining hemispherical mold for MEMS resonator gyroscope using a novel ultraprecise ceramic entire-ball tool

The manufacture of inertial-grade and tactical-grade diamond micro electro mechanical systems (MEMS) hemispherical resonator gyroscopes is limited by the manufacturing accuracy of the monocrystalline silicon hemispherical concave mold, on which the gyroscope shell is formed. To solve this problem, this paper presents a new method for micro-ultrasonic machining of microhemispherical molds for resonator gyroscopes using an ultraprecise ceramic entire-ball tool (UCET). To study the wear mechanism of the UCET and the influence of tool wear on the surface integrity and form accuracy of the microhemispherical mold, a mathematical model for the tool wear of micro-ultrasonic machining of microhemispherical molds with UCET is established and verified by experiments. The micro-ultrasonic amplitude, the abrasive material and the abrasive size is found to have significant influences on the tool wear of the UCET. The wear rates of tungsten carbide and silicon nitride ceramic tools are 2.22% and 3.64%, respectively, which are far less than the wear rate of 8.03% of bearing steel. The wear condition agrees with the theoretical model. The machining experiment shows that the radius change, ΔR, is 6.47 µm of the microhemispherical mold processed by UCET, which is much better than 32 µm of the micromold processed by micro-electro discharge machining at one time. After 10 continuous machining runs, the deviation rate of the form accuracy of the micromold is 1.71%, 3.71% and 24.21%, due to the wear of tungsten carbide, silicon nitride and bearing steel, respectively. It can be seen that micro-ultrasonic machining of microhemispherical molds using UCET has the characteristics of a high initial form accuracy, low wear rate, high integrity and form accuracy. This is a potentially effective method to obtain micromolds with high accuracy and surface integrity.

Identification and validation of a hyperelastic model for self-reinforced polypropylene draping

Self-reinforced polypropylene (SRPP) is a composite in which the reinforcement and the matrix consist of the same polymer, namely polypropylene. The present work focuses on the development and experimental validation of an FE model for thermoforming of SRPP. The constitutive model of SRPP sheet is based on the Boisse-Charmetant hyperelastic law. Material properties required to fit the model were obtained from the tensile and picture frame shear tests performed at forming temperatures and bending test of a non-consolidated fabric at room temperature. The model is validated in comparison with the experimental draping data, with special attention to parameters and patterns of wrinkles. Samples, preheated to a surface temperature of 170-175°C, were deformed up to 1-4 cm heights using a hemispherical mould with a 4.5 cm diameter. Overall, good qualitative correlation between experimental and modelling results is observed, which justifies use of the proposed model with the experimentally identified parameters for prediction of SRPP draping and subsequent analysis of the mechanical response of the consolidated part to loading.

Improved HNA isotropic etching for large-scale highly symmetric toroidal silicon molds with &lt;10-nm roughness

Microsystem technology is well suited to batch fabricate microhemispherical resonator gyroscopes (HRG) to reduce cost and volume. In the processing of micro-HRG, a crucial step is to get a 3-D hemispherical mold with the large-scale, high-symmetry, and smooth surface. Compared with the hemispherical resonator, the toroidal resonator has the smaller frequency split and larger effective resonance mass under the same processing accuracy. A wafer-scale etching method for the toroidal resonator mold was presented, which is based on the deep reactive ion etching and improved HNA isotropic etching. The advantages of this method include low cost, time savings, and easy operation. With this method, toroidal molds with an average diameter over 1900 μm, asymmetry

Draping Behavior of Carbon Non-Crimp Fabrics and Its Effects on Mechanical Performance of the Hemispherical Composites

In order to investigate the draping behavior of non-crimp fabrics (NCFs), two types of carbon NCFs with tricot-chain stitches or chain stitches were formed on a hemispherical mould via a stretch forming process. The shear angle and forming defects of the fabrics were measured on the hemisphere, under different blank holder forces (BHFs). The results showed that increasing BHF could enhance the shear angle slightly, reduce the asymmetry for the deformation of the fabrics, and change the main type of the process-induced defects. Besides, compression tests were performed on the corresponding composite components. By analyzing the change of fiber volume fraction and structural parameters of the textile reinforcements, the effects of draping behavior of NCFs on the mechanical performance of the composites were studied. The results reveal that draping process has distinguishable impacts on the mechanical properties of the final components, which is closely related to the stitching pattern of the NCFs.

502. Biomaterial-Mediated Lentiviral Delivery of Anti-Inflammatory Genes in Cartilage-Derived Matrix Hemispheres

Objectives: Cartilage tissue engineering seeks to provide a functional replacement for damaged or degenerated articular surfaces that develop in osteoarthritis (OA). Human bone marrow-derived mesenchymal stem cells (MSCs) seeded within cartilage-derived matrix (CDM) hemispherical scaffolds exhibit robust chondrogenic differentiation and extracellular matrix (ECM) deposition without evidence of a hypertrophic phenotype. However, inflammation within an OA joint may inhibit chondrogenesis of MSCs and induce degradation of both native and engineered cartilage, particularly through the action of interleukin-1 (IL-1). The goal of this study was to develop an anatomically-shaped, tissue-engineered cartilage capable of tunable and inducible expression of IL-1 receptor antagonist (IL-1Ra) in MSCs via biomaterial-mediated lentiviral gene delivery. Methods: IL-1Ra or eGFP coding sequences were cloned into doxycycline(dox)-inducible lentiviral vectors. Hemispherical scaffolds were fabricated from resuspended cartilage powder in hemispherical molds (outer radius 4.76 mm, inner radius 3.175 mm). Scaffolds were crosslinked and sterilized via dehydrothermal treatment. Dox-inducible eGFP or IL-1Ra lentivirus was immobilized to PLL-coated CDM scaffolds to transduce MSCs upon seeding. Non-transduced (NT), eGFP-expressing, or IL-1Ra-expressing constructs were treated with 0 or 0.1 ng/mL IL-1 during 28 days of chondrogenesis (+10 ng/mL TGF-s3) with 1 µg/mL dox. Results: Transduction of MSCs occurred throughout the CDM hemispheres (Fig 1AFig 1A) and the transduction efficiency of MSCs isolated from the construct was 57±5% eGFP+ by flow cytometry. Hemispherical constructs maintained their anatomical shape throughout chondrogenic culture (Fig 1BFig 1B). IL-1Ra-expressing constructs produced over 200 ng/mL of IL-1Ra, a concentration expected to inhibit pathologic IL-1 concentrations, and IL-1 treatment did not affect IL-1Ra production (Fig 1CFig 1C). IL-1 treatment reduced ECM deposition by NT and eGFP-expressing MSCs but not IL-1Ra-expressing MSCs, as evidenced by safranin-O/fast green staining for glycosaminoglycans and total collagen, respectively (Fig 1DFig 1D). After 28 days of chondrogenesis, IL-1 treatment significantly increased matrix metalloproteinase (MMP) activity in the conditioned media of NT and eGFP-expressing constructs but not in IL-1Ra-expressing constructs (p<0.05) (Fig 1EFig 1E). Significance: We engineered an anatomically and compositionally mimetic cartilage hemisphere that is inflammation-resistant and shows promise for total articular resurfacing in an arthritic environment.Tunable production of IL-1Ra from an IL-1-resistant cartilage tissue may provide therapeutic effects to other joint tissues, such as the synovium or subchondral bone.View Large Image | Download PowerPoint Slide

Experimental measurement of wrinkle formation during draping of non-crimp fabric

A rig and image analysis methodology is described to characterise wrinkle formation during draping of non-crimp fabrics. The circular fabric blank is draped over a male hemispherical mould, partly constrained by a circular clamping ring around the periphery of the blank. The three-dimensional shape of the fabric is derived from a shape-from-focus analysis of a stack of photographs of the deformed blank. Wrinkles are identified from the deviation of the shape from a smoothed shape. Wrinkle formation is strongly dependent on the fabric architecture and increases progressively with increased punch displacement. Triaxial fabrics have the highest wrinkle amplitude, unidirectional and 0/90° biaxial fabrics the lowest amplitude. The clamping force reduces the wrinkling for some fabrics but, for the maximum force applied, is not effective at eliminating wrinkling.

Hemispherical micro-resonators from atomic layer deposition

Hemispherical shell micro-resonators may be used as gyroscopes to potentially enable precision inertial navigation and guidance at low cost and size. Such devices require a high degree of symmetry and large quality factors (Q). Fabricating the devices from atomic layer deposition (ALD) facilitates symmetry through ALD’s high conformality and low surface roughness. To maximize Q, the shells’ geometry is optimized using finite element method (FEM) studies to reduce thermoelastic dissipation and anchor loss. The shells are fabricated by etching hemispherical molds in Si (1 1 1) substrates with a 2:7:1 volumetric ratio of hydrofluoric:nitric:acetic acids, and conformally coating and patterning the molds with ALD Al2O3. The Al2O3 shells are then released from the surrounding Si substrate with an SF6 plasma. The resulting shells typically have radii around 50 µm and thicknesses close to 50 nm. The shells are highly symmetric, with radial deviations between 0.22 and 0.49%, and robust enough to be driven on resonance at amplitudes 10 × their thickness, sufficient to visualize the resonance mode shapes in an SEM. Resonance frequencies are around 60 kHz, with Q values between 1000 and 2000. This Q is lower than the 106 predicted by FEM, implying that Q is being limited by unmodeled sources of energy loss, most likely from surface effects or material defects.

Parameters design and optimisation of concave and convex hemispherical roundness-surface millings

In this paper, we utilise Taguchi experimental approaches to study the optimal machining parameters for the roundness of the hemispherical mould processed by the five-axis NC milling machine with a rotatable-tilting table. Four machining parameters, tool’s tilt angle, surface-cutting speed, feeding per tooth, and depth in axial cutting, are considered. The experimental results indicate that the optimal parameters setting of the material NAK80 is the tool’s tilt angle at 35°, surface-cutting speed at 150 m min−1, feeding per tooth at 0·05 mm min−1, and depth in axial cutting at 0·02 mm, where the optimal measurements of roundness for the concave and the convex hemispherical moulds are 0·022 and 0·026 mm respectively.

Parameters Optimization for Roundness of Hemispherical Surface Milling

The hemispherical surface has been widely implicated in design of products. Its precise roundness, a key quality characteristic of smaller-the-better, highly depends on the milling quality of the hemispherical mold. In this paper, we study the optimal machining parameters for the roundness of the hemispherical mold processed by the five-axis NC milling machine with a rotatable-tilting table. Four machining parameters, tool’s tilt angle, surface-cutting speed, feeding per tooth, and depth in axial cutting, are considered with their three varied levels selected on the basis of the onsite professional knowledge acquired from weighing the effect of tool interference and the milling capability of machine tools. The material NAK80, one type of plastic mold steels, possessing excellent resistance and dimensional stability is used as experimental test specimens. The experimental results conclude that the optimal measurements of roundness for the concave and the convex hemispherical molds are 0.022 mm and 0.026 mm, respectively.

Investigation into thermoformability of hot compacted polypropylene sheet

This paper describes an investigation into the thermoformability of a new class of oriented polymeric material recently developed, namely hot compacted polypropylene sheet. Exploitation of any new material requires an intimate understanding of a whole range of factors, amongst which thermoformability is pre-eminent. This is particularly true for oriented polymeric materials, for while the preferred molecular alignment gives enhanced properties such as stiffness, strength, and resistance to impact, the downside is that the stretched molecular chains tend to limit further flow under stress, making thermoforming difficult. The aim of the present study was to establish the critical parameters for successful thermoforming of hot compacted polypropylene sheet.Elevated temperature tensile tests were used to investigate the stress–strain behaviour of the compacted materials. The crucial parameters were found to be the post-yield modulus, which gives a measure of the resistance of the material to large scale deformation, and the strain to failure, which gives the upper limit on deformation. The post-yield modulus was found to be significantly affected by the test temperature and the high strain hardening behaviour of the material confirmed that significant force is required to thermoform the compacted polypropylene sheets. A hemispherical mould, with built-in gripping plate, was used to carry out a study of the thermoforming behaviour of the compacted sheets, and the results were found broadly to confirm the conclusions of the tensile tests. A linear relationship was found between the tensile force and the postforming force, reinforcing the synergy between the two tests. In addition the forming tests showed that the best temperatures to use were either side of the melting point of the melted and recrystallised phase, depending on the amount of postforming deformation required. Different gripping arrangements were investigated both in which the sheet was fully gripped and in which the sheet was allowed to flow into the mould during forming. The different schemes were found to control whether a successful component could be produced under different conditions and at different ultimate strains. Finally, the tests with the hemispherical mould showed that thermoforming this shape requires significant interlaminar shear deformation, and above 15% strain this resulted in destruction of the interlayer bond. For strains greater than this, successful thermoforming could only be achieved by allowing the material to flow into the mould.

Stamp forming of continuous glass fibre reinforced polypropylene

Abstract A thermoforming technique, known as stamp forming, has been used to process unidirectional glass fibre reinforced polypropylene (PP). A novel hemispherical mould with built-in hold-down arrangement was designed. This mould was used at room temperature to form parts from pre-heated flat pre-consolidated laminates. Pre-consolidated laminates are heated by contact heating in an external heater above the melting temperature of the PP polymer matrix; they are then formed in the cold matched metal tool. Typical cycle times to process the pre-consolidated laminates (including pre-heating time of the pre-consolidated laminates) are in the range of 2 min. Useful processing conditions, such as stamping temperature, stamping velocity and hold-down pressure required for the stamp forming of this composite are determined. The effects of die geometries and laminate dimension on the `fibre buckling' are studied. Finally, the thickness distribution in stamped parts is investigated in relation to different directions of fibre orientation.

Underwater sound radiation from a spherical bubble cloud encapsulated by a thin spherical shell

Measurements of sound transmission versus frequency are performed (in the Rickover Hall Hydrodynamics Tow Tank Facility) for a submerged spherical bubble cloud that is encapsulated by a thin spherical shell. The bubble cloud is driven by a miniature spherical PZT transducer unit that is suspended in the center. A theoretical model has been developed which predicts the resonant frequencies for the case where the shell thickness has negligible effect. Therefore, the resonances will depend on the radius of the cloud and the sound speed in the bubbly media (which is a function of the air volume void fraction). A shell of urethane elastomer is molded as a single piece by using the ‘‘lost wax technique.’’ Hemispherical molds are used. The first set is for making the ‘‘inner’’ spherical wax ball. The second set forms the ‘‘outer’’ boundary of the casting for the spherical shell with filling ports on the north and south poles. The shell’s inner wax material is then melted out to complete the process. The shell is nearly acoustically transparent since ρ=1.03 g/cm3, clong∼1450 m/s and ctran∼70 m/s. The bubbly fluid consists of castor oil that has been whipped in a microblender.

Stamp forming of fabric‐reinforced thermoplastic composites

AbstractA stamp forming technique has been used to process a fabric woven composite made of glass fibers (GF) and polyetherimide (PEI). A hemispherical mold with a built‐in hold‐down arrangement was designed and used at room temperature to stamp parts from preheated flat preconsolidated laminates. Tensile properties of the material were measured under similar heating conditions as in the relevant stamp‐forming process. Stretch in the fiber direction was found to be smaller than the maximum elastic extension of the glass fibers. Reduction of the angle between the crossing fibers was quite large when the satin woven fabric composite was pulled in the 45° direction. The effect of die geometries and original laminate dimensions on the “shear‐buckling” were studied. The results described the correlations between processing parameters and fiber buckling. Finally, the local strain of fiber bundles was investigated in relation to different directions of fiber orientation.

The Effect of Diaphragm Stiffness on the Quality of Diaphragm Formed Thermoplastic Composite Components

An experimental autoclave with a forming rate control system and sophisticated data acquisition facilities has been employed for polymeric diaphragm form ing of carbon fibre reinforced polyetheretherketone (PEEK). Central displacement mea surements were recorded using a high temperature linear variable differential transformer (LVDT), while forming into a hemispherical mould. Using this facility the pressure versus displacement relationships were established for Upilex-R, Upilex-S, and Kapton-H and superplastic aluminium (Supral) diaphragms. Both Upilex-S and Kapton-H were found to have similar stiffness values, about eight times greater than Upilex-R, while the Supral is about sixteen times stiffer than Upilex-R. Pressure versus displacement characteristics are reported for (0°)8, (0°)16, (0°/90°) 2 s, (0°/90°)4 s and (0°/+45°/-45°/90°) s carbon fibre reinforced PEEK (APC-2) layups, which show that the laminate stiffness at forming tem perature is very low relative to the diaphragm stiffness of Upilex-S, Kapton or Supral. The effect of diaphragm stiffness on squeeze flow is clearly demonstrated as the stiffer di aphragms, Upilex-S and Supral, require higher pressures to complete the forming and consequently cause increased squeeze flow over that shown when using Upilex-R. How ever, it has also been demonstrated that the use of these stiffer diaphragms reduces the risk of laminate buckling. When forming with Upilex-R diaphragms, out of plane buckling was eliminated for a (0°/+45°/-45°/90°), APC-2 layup by reducing the forming rate to 6 mm/mm