Aluminum Mold Research Articles

Repeatable replication method with liquid infiltration to fabricate robust, flexible, and transparent, anti-reflective superhydrophobic polymer films on a large scale

Flexible superhydrophobic films that can be adapted to any target object for practical applications have drawn much attention in recent years. In this paper, we propose a simple method to fabricating highly flexible superhydrophobic polydimethylsiloxane (PDMS) films, via a repeatable replication and nondestructive detachment from a superhydrophobic aluminum mold. Due to the hierarchical surface structures and intrinsic hydrophobicity of PDMS, the fabricated films exhibited superior water repellency without any further modifications using low surface energy materials. Moreover, these water repellent films exhibited excellent mechanical durability and flexibility without losing the anti-wetting property under harsh conditions. The use of a robust superhydrophobic mold and the easy detachment of the film using a solution with a low surface tension allow for the clean release of large-area replicas without any damages to the mold. This enables the repeated fabrication of superhydrophobic PDMS films without the deterioration of their wettability using a single mold. Furthermore, the superhydrophobic PDMS film exhibited an efficient anti-reflection property and high transparency, which allows an enhanced light collection and efficiency when applied to solar cells. Consequently, this simple and inexpensive method is appropriate for diverse applications that require films with superior mechanical and optical properties, and a special wetting behavior.

Injection molding of magneto-sensitive polymer composites

Magneto sensitive parts made of a thermoplastic elastomer reinforced with iron microparticles were prepared by imposing a magnetic field during injection molding. In particular, an aluminum mold was designed to host an electro-magnet able to apply a magnetic field during the injection of the material into the mold and its subsequent solidification. Samples obtained in the presence of magnetic field were characterized by a peculiar, aligned distribution of iron particles along the magnetic field lines, and columnar structures of variable length were obtained. The mechanical characterization showed that the samples in which the iron particles were aligned had higher modulus compared to samples in which the particles were randomly dispersed. The magnetic field induced an anisotropic structural reinforcement that imparted to composite samples a magnetostrictive feature, namely the capability to sense the magnetic field and to react with a shape change under the application of the magnetic field.

Preparation of renewable antireflection moth-eye surfaces by nanoimprinting using anodic porous alumina molds

Renewable antireflection surfaces were formed by the lamination of polymer thin films with moth-eye structured surfaces. Moth-eye structures were prepared by nanoimprinting using an anodic porous alumina mold. Thin-film lamination was performed using a photocurable monomer as an adhesive. A renewed low-reflectance moth-eye structured surface could be exposed by peeling the uppermost film from the sample.

Prosthetic Hip Joint Infection: An Aluminium Mold for Intraoperative Production of Antibiotic-loaded Cement Hip Prostheses: 3 Cases Report

Introduction: To treat hip prosthetic infection, 2-stage revision, including removal and reimplantation, remains the standard treatment for prosthetic infection. Articulating cement spacer has been shown to provide better functional results after reimplantation. However, its cost as a manufactured product is not cheap and the choice of antibiotics is not flexible either. We designed an aluminium mold to make an antibiotic impregnated cement spacer, and replaced it between the first and the second stage. The current study was conducted to test their clinical efficacy.Case report: We report 3 cases of hip prosthetic infection treatment by using antibiotic impregnated cement spacer made by an aluminium mold. All patients presented to us in first 2-years postoperation and all had a deep infection. Three patients with infected total hip arthroplasties were treated with 2-stage revision using articulating spacers made by an aluminium mold and had a good result.Conclusion: Treating hip prosthetic infection with these articulating spacers eradicates infection effectively, improves the life quality before reimplantation and provides good final results without significant complications.

Preparation of superhydrophobic surfaces with micro/nano alumina molds.

Polymer micro/nano hierarchical structures were successfully formed by photo-nanoimprinting using anodic porous alumina molds. Anodic porous alumina molds with hierarchical structures were prepared by the anodization of an Al substrate with a micro-concave array. The obtained surfaces with hierarchical structures exhibited superhydrophobicity. The hydrophobic properties of the obtained samples were dependent on the surface structures and could be optimized by changing the micro- and nanopatterns in the hierarchical structure.

Evaluation of the Functional Impression Technique with Various Impression Materials on the Surface Topography of Dental Stone Casts and Their Effect on Retention

Background: The accuracy of the final prosthesis is affected by the final impression technique and master cast production. The aim of the present study was to evaluate the effect of the functional impression technique with various impression materials on the surface characteristic of dental stone casts and their clinical effect on the retention of complete dentures. Method: Specimens of three impression materials/stone casts were fabricated. The specimens of the impression materials/stone casts were divided into three equal groups (I, II, and III). The impression materials used were as follows: tissue conditioner group (I), zinc oxide (ZEO) (group II) and poly (vinyl siloxane) (PVS) (group III). Cylindrical split aluminium moulds were designed to receive the impression materials and the stone mixture. The surface roughness of the stone cast specimens of the three groups (I, II, and III) was measured with a surface profilometer and analyzed by a scanning electron microscope. A clinical study included five severely resorbed mandibular edentulous alveolar ridges and edentulous maxillary arches. Each subject received three heat-cured acrylic resin dentures, fabricated using the functional impression technique. The three dentures were identical except for the different impression materials used from Groups I, II and III. The retentive force of each denture for each subject was measured. Result: The results of this study revealed that the mean value of surface roughness of the stone cast surface of group I was higher than group II and group III. A statistically significant difference was observed in surface roughness and the retentive dislodging force between the three studied groups. Although using a tissue conditioner as a functional impression material led to a high level of surface roughness and good retention, it could not produce the same smooth surface quality of PVS or ZEO. These data were supported by SEM analysis. The complete dentures for these patients require important oral and denture hygiene care. Conclusion: Complete dentures made using functional impression technique with PVC as a final impression material are more comfortable, retentive and stable.

A Comparative Evaluation of Time-dependent Changes on the Surface Hardness of Bulk Cure Composites: Anin vitroStudy

ObjectivesThe objective of this in vitro study was to assess the surface hardness through Vickers hardness (VH) test of one conventional hybrid resin composites (Filtek Z350), compared with that of two bulk cure resin composites (SDR™, Tetric N Ceram®).Materials and methodsTwenty specimens of each material were prepared in cylindrical aluminum molds with an internal diameter of 5 mm and depth of 4 mm, 10 (incremental curing) and 10 (bulk curing).The surface of each specimen was covered with a transparent plastic matrix strip before light curing with conventional visible light for 40 seconds. The specimens thus obtained were stored in deionized water and transferred to an incubator at 37°C for 24 hours to simulate clinical conditions. After 24 hours, the microhardness of each specimen was measured using a Vickers indenter, with a load of 100 gm and dwell time of 15 seconds (HV 0.2/40).The specimens were further subjected to VH test in an interval of 7, 30, and 90 days. The data were subjected to statistical analysis—Student’s t test, analysis of variance, and post hoc Tukey’s test.ResultsThe present study showed that SDR™ in bulk curing showed consistently greater value of hardness and was comparable to traditional incremental cured Filtek Z350, highlighting the advantages of the new SDR technology.How to cite this article: Sarma A, Nagar P. A Comparative Evaluation of Time-dependent Changes on the Surface Hardness of Bulk Cure Composites: An in vitro Study. Int J Clin Pediatr Dent 2018;11(3):183-187.

Application of Conjugate Simulation for Determination of Temperature and Stress Distributions During Curing Process of Pre-Impregnated Composite Fibers

AbstractThe composites made of continuous fibers in the form of unidirectional and fabric prepregs are widely used in many fields of engineering for the production of lightweight and durable parts or whole structures. To achieve this, we not only need to possess knowledge of the composite mechanics, but also have to master the technology. In most cases, particularly for parts with advanced geometric shapes, autoclaving technique is used. The success of the carried out process occurs when the prepreg reaches the proper temperature throughout its volume in the specified time, where there are no overheated or unheated zones as well as when the prepreg is correctly pressed against the mold. In order to ensure adequate stiffness, the mold has much greater thickness than formed composite and the stiffening ribs. The result is that the time required for prepreg heating is greatly extended. To prevent this, the appropriate electric heaters embedded in the silicone grips are used.The paper presents problems related to the mold structures and application of numerical methods aiming at early verification of the temperature and stress distribution. The coupled analysis of CFD (computational fluid dynamic) and heat transfer structural simulations were performed in Abaqus program. The studies were carried out for the airfoil fragment. A total of 12 simulations were conducted, 6 cases in which heat was supplied only from air flowing through the autoclave and 6 cases which included heaters inside the silicone grips. In the result the inhomogeneity of prepreg heating for each of the mold geometry was compared, and the average temperature was obtained after 60 seconds from the process initiation. Both the pressure inside the silicone grips (before inserting the mold into the autoclave) and the non-uniform temperature distribution result in the formation of stresses whose values were analyzed for molds made of aluminum. For this purpose the temperature dependent elastic – plastic material model was used for aluminum molds.

Fabrication of ordered submicrometer-scale convex lens array via nanoimprint lithography using an anodized aluminum mold

The fabrication of submicrometer-scale ordered convex lens array was demonstrated through nanoimprint lithography using an aluminum dimple array mold fabricated by etidronic acid anodizing and selective oxide dissolution. Highly-pure aluminum plates were anodized in a 0.2M etidronic acid solution at 260V for the formation of ordered porous alumina. The anodized specimens were immersed in a 0.2M CrO3/0.51M H3PO4 solution to dissolve the porous alumina, and an ordered dimple array measuring approximately 670nm in dimple diameter was obtained on the aluminum surface. Phosphonic acid-based self-assembled monolayers (SAMs) were coated on the aluminum dimple array as a release agent for nanoimprint lithography. The shape of the aluminum dimple array mold was transferred to a UV curable photopolymer by nanoimprint lithography. An ordered convex lens array, which corresponded to the negative shape of the dimple array, was successfully obtained by the removal of curable polymer. However, the polymer surface was contaminated with phosphonate molecules due to the multilayered phosphonate films being formed on the aluminum mold. This contamination can be avoided by ultrasonication of the aluminum mold before nanoimprint lithography.

Phase transition characterization based on acoustic reverberation time

Non-destructive monitoring of a material’s state during its physicochemical transformations is of interest for several industrial fields including food processing, such as milk-derived products, or cosmetics. The use of ultrasound to provide reliable information about physicochemical properties is becoming increasingly popular. Indeed, ultrasonic techniques have the main advantage of being rapid and non-invasive methods that allow parameters such as product composition, structure, and physical state to be obtained. Yet, classical techniques are limited to the characterization of the medium along the propagation path using the first wave packets. Here, we propose an alternative technique based on the study of the reverberated waves, classically used in room acoustics. In previous works, this method has shown its capability to characterize materials as well, with the advantage over classical techniques to address a medium in its whole structure. In this context, the determination of sol-gel phase transition time of Salol using this method is presented. Measurements are performed in an aluminum mold using five piezoelectric (PZT) patches, one being used as emitter and the others as receivers. The mean reverberation time over four receivers has been studied and its evolution is shown to lead to a good estimation of the phase transition time.

Analyzing polymeric matrix for fabrication of a biodegradable microneedle array to enhance transdermal delivery.

Traditional drug delivery systems, using invasive, transdermal, and oral routes, are limited by various factors, such as the digestive system environment, skin protection, and sensory nerve stimulation. To improve the drug delivery system, we fabricated a polysaccharide-based, dissolvable microneedle-based array, which combines the advantages of both invasive and transdermal delivery systems, and promises to be an innovative solution for minimally invasive drug delivery. In this study, we designed a reusable aluminum mold that greatly improved the efficiency and convenience of microneedle fabrication. Physical characterization of the polysaccharides, individual or mixed at different ratios, was performed to identify a suitable molecule to fabricate the dissolvable microneedle. We used a vacuum deposition-based micro-molding method at low temperature to fabricate the model. Using a series of checkpoints from material into product, a systematic feedback mechanism was built into the "all-in-one" fabrication step, which helped to improve production yields. The physical properties of the fabricated microneedle were assessed. The cytotoxicity analysis and animal testing of the microneedle demonstrated the safety and compatibility of the microneedle, and the successful penetration and effective release of a model protein.

Study on the Optimum Cutting Parameters of an Aluminum Mold for Effective Bonding Strength of a PDMS Microfluidic Device.

Master mold fabricated using micro milling is an easy way to develop the polydimethylsiloxane (PDMS) based microfluidic device. Achieving high-quality micro-milled surface is important for excellent bonding strength between PDMS and glass slide. The aim of our experiment is to study the optimal cutting parameters for micro milling an aluminum mold insert for the production of a fine resolution microstructure with the minimum surface roughness using conventional computer numerical control (CNC) machine systems; we also aim to measure the bonding strength of PDMS with different surface roughnesses. Response surface methodology was employed to optimize the cutting parameters in order to obtain high surface smoothness. The cutting parameters were demonstrated with the following combinations: 20,000 rpm spindle speed, 50 mm/min feed rate, depth of cut 5 µm with tool size 200 µm or less; this gives a fine resolution microstructure with the minimum surface roughness and strong bonding strength between PDMS–PDMS and PDMS–glass.

Molding of strength testing samples using modern PDCPD material for purpose of automotive industry

The casting of metal materials is widely known but the molding of composite polymer materials is not well-known method still. The initial choice of method for producing composite bodies was the method of casting of PDCPD material. For purpose of performing casting of polymer composite material, a special mold was made. Firstly, the 3D printed, using PLA material, mold was used. After several attempts of casting PDCPD many problems were encountered. The second step was to use mold milled from a firm and dense isocyanate foam. After several attempts research shown that this solution is more resistant to high-temperature peak, but this material is too fragile to use it several times. This solution also prevents mold from using external heating, which can be necessary for performing correct molding process. The last process was to use the aluminum mold, which is dedicated to PDCPD polymer composite, because of low adhesiveness. This solution leads to perform correct PDCPD polymer composite material injection.After performing casting operation every PDCPD testing samples were tested. These results were compared together. The result of performed work was to archive correct properties of injection of composite material. Research and results were described in detail in this paper.

IMPACTS OF NANOSCALE INCLUSIONS ON FIRE RETARDANCY, THERMAL STABILITY, AND MECHANICAL PROPERTIES OF POLYMERIC PVC NANOCOMPOSITES

A number of different nanoscale inclusions including nanoclay, nanotalc, and graphene were incorporated with polyvinyl chloride (PVC), dispersed in N,N-Dimethylacetmide (DMAC) and cast in rectangular aluminum (Al) molds prior to the testing. The fire retardancy, thermal stability, and mechanical properties of the PVC nanocomposites were determined using the ASTM UL 94 standard, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and microtensile test units. Surface morphology studies of the resultant materials were also carried out using scanning electron microscopy (SEM). Test results showed that the fire retardancy, thermal stability, and mechanical properties of the PVC nanocomposites were significantly enhanced in the presence of nanoscale inclusions. Among the inclusions, graphene had the major impact on improving the physical properties, which may be because of its higher thermal conductivity, mechanical strength, size, and shape. Polymers have a wide range of applications in daily life, but they are highly flammable and mechanically not stable for different applications. This study has shown that the weakness of the PVC could be significantly enhanced by incorporating nanoscale inclusions for various industrial purposes.

Effect of susceptor and mold material on microstructure of in-situ microwave casts of Al-Zn-Mg alloy

In-situ microwave casting is a novel technique; it is based on the principles of microwave hybrid heating. The dynamics of the process and the cast quality are significantly influenced by the materials used in the microwave irradiation. In the present work, role of susceptor and mold on exposure time, melting time, mold preheating and cast properties is studied. Physics of the process in the context of exposure time and mold materials is discussed. The aluminum alloy 7039 casts were developed in ambient atmosphere inside an applicator using microwaves at 2.45GHz and 1400W. Charge was hybrid heated using susceptors – SiC and ceramic crucible to melt and cast in-situ in the preplaced alumina and graphite molds. Characterization reveals that grain structures of the casts were influenced by mold preheating and mold material. Finer grains with higher micro-pores were observed in the casts developed in alumina mold with SiC susceptor. The casts contain MgZn2, Mg2Si, Al3Fe and Al8Fe2Si as intermetallics; however, their distribution and size depend upon the cooling pattern of the melt. Microindentation hardness of the casts developed in alumina mold with SiC susceptor was observed to be the highest (146±10HV) among the developed casts.

Aerodynamic design methodology for wind tunnel tests of wind turbine rotors

This paper illustrates the methodology and the experimental verification of the design of a 1/75 aero-elastic scaled rotor of the DTU 10 MW reference wind turbine for wind tunnel tests. The aerodynamic design was focused on the minimization of the difference, in terms of thrust coefficient, with respect to the full scale reference. From the Selig low-Reynolds airfoils database, the SD7032 one was chosen for this purpose and a corresponding constant section wing was tested at DTU red wind tunnel, providing force and distributed pressure coefficients for the design, in the Reynolds range 30−250×103 and for different angles of attack. The aero-elastic design algorithm was set to define the optimal spanwise thickness over chord ratio (t/c), the chord length and the twist, in order to match at least the first flapwise scaled natural frequency. An aluminium mould for the carbon fibre autoclave process was CNC manufactured based on B-Splines CAD definition of the external geometry given as an output of the design procedure. Wind tunnel tests at were carried out Politecnico di Milano on the whole 1/75 wind turbine scale model, confirming the successful aerodynamic design and manufacturing approaches. The experimental modal analysis carried out to verify the structural consistency of the scaled blade is also reported.

Investigation on replication of microfluidic channels by hot embossing

ABSTRACTIn this study, effects of embossing temperature, time, and force on production of a microfluidic device were investigated. Polymethyl methacrylate (PMMA) substrates were hot embossed by using a micromilled aluminum mold. The process parameters were altered to observe the variation of replication rate in width and depth as well as symmetry of the replicated microfluidic channels. Analysis of variance (ANOVA) on the experimental results indicated that embossing temperature was the most important process parameter, whereas embossing time and force have less impact. One distinguishing aspect of this study is that, the channels were observed to be skewed to either side of the channel depending on the location of the protrusions on the mold. The mechanism of the skewness was investigated by finite element analysis and discussed in detail. Results showed that the skewness depends on the flow characteristics of the material and could be reduced by increasing the embossing temperature. The best replication rates were obtained at parameter settings of 115°C, 10 kN, and 8 min for the molds with minimum 56 µm wide features of 120 µm depth. We also showed that the fabricated channels could be successfully sealed by solvent-assisted thermo-compressive bonding at 85°C under 5.5 kN force.

Optimization and continuous fabrication of moth-eye nanostructure array on flexible polyethylene terephthalate substrate towards broadband antireflection.

Reflection loss can cause harmful effects on the performance of optoelectronic devices, such as cell phones, notebooks, displays, solar cells, and light-emitting diode (LED) devices. In order to obtain broadband antireflection (AR) properties, many researchers have utilized surface texture techniques to produce AR subwavelength structures on the interfaces. Among the AR subwavelength structures, the moth-eye nanostructure is one of the most promising structures, with the potential for commercialization in the near future. In this research, to obtain broadband AR performance, the optimization of moth-eye nanostructures was first carried out using the finite difference time domain method within the spectral ranges of 400-800nm, including the optimization of shape, height, pitch, and residual layer thickness. In addition, the continuous production of moth-eye nanostructure array upon a flexible polyethylene terephthalate substrate was demonstrated by using the roll-to-roll ultraviolet nanoimprint lithography (R2R UV-NIL) process and anodic aluminum oxide mold, which provided a solution for the cost-effective fabrication of moth-eye nanostructure array. The AR performance of moth-eye nanostructure array obtained by the R2R UV-NIL process was also investigated experimentally, and good consistence was shown with the simulated results. This research can provide a beneficial direction for the optimization and cost-effective production of the moth-eye nanostructure array.

Surface profiling of an aspherical liquid lens with a varied thickness membrane.

Inspired by crystalline lenses in human eyes, liquid lenses have a simple yet elegant working principle, and result in compact optical systems. Recent numerical studies showed that membranes with variable thicknesses could affect the lens profile. However, fabrication and assembly of a liquid lens with an inhomogeneous membrane is difficult. There is also a lack of experimental studies about the changes of a lens profile during deformation. In this paper, we provided a new experimental approach for characterizing the performance of a liquid lens with an inhomogeneous membrane. A 2D axisymmetric lens model was built in finite element analysis software to theoretically study the non-linear deformation behavior of the inhomogeneous membrane. Then we provided a new approach to fabricate inhomogeneous membranes using a pre-machined aluminum mold. An optical coherence tomography (OCT) system was used to dynamically measure the changes of a lens profile without contact. Both simulation and the experiments indicated that the variation of the thickness of the membrane could affect the lens profile in a predictable manner. A negative conic constant was achieved when a plano-concave membrane was adopted in a liquid lens. Larger increments of the thickness of the membrane in the radial direction resulted in a larger contribution of a conic constant to the lens profile. The presented study offers guidance for image-quality analysis and optimization of a liquid-lens-based optical system.

Design and fabrication of Si-HDPE hybrid Fresnel lenses for infrared imaging systems.

In this work, novel hybrid Fresnel lenses for infrared (IR) optical applications were designed and fabricated. The Fresnel structures were replicated from an ultraprecision diamond-turned aluminum mold to an extremely thin layer (tens of microns) of high-density polyethylene polymer, which was directly bonded onto a flat single-crystal silicon wafer by press molding without using adhesives. Night mode imaging results showed that the fabricated lenses were able to visualize objects in dark fields with acceptable image quality. The capability of the lenses for thermography imaging was also demonstrated. This research provides a cost-effective method for fabricating ultrathin IR optical components.