Flexible Mold Research Articles

Development of Connection Technology between Multi-Point Press and Flexible Mold for Manufacturing Free-Form Concrete Panel

Many studies have been conducted for the accuracy of free-form concrete panel fabrication, but there still are errors in the process of fabrication. This study developed a connection technology of detachable shape part that can be applied to the existing multi-point Computer Numerical Control (CNC) to enhance the accuracy of fabrication. The detachable type can place a silicone plate on top of the rod without additional fixtures. The accuracy of the technology was verified by curvature test and free-form concrete panel fabrication test. Three curves were created to compare the discrepancies between the designed shapes and the fabricated shapes through quality test. As a result, the detachable type decreased the error by up to 2 mm. In addition, a panel was fabricated to analyze the error to verify the rigidity of the developed molds. The error caused by concrete deflection under load or the error caused by repeated fabrication was about 0.5 mm. The shape error was within 3.5 mm. This small error proved greater accuracy compared to the existing technology.

Flexible metallic mold based precision compression molding for replication of micro-optical components onto non-planar surfaces

Replication of micro/nano-scale optical components onto non-planar substrates is considered technically challenging and excessively expensive via existing manufacturing approaches. A low-cost, large-volume and high-precision fabrication approach is thus highly desirable. In this paper, a novel precision compression molding approach that enables large-volume and high-resolution replication of micro/nano-scale optical features from planar to non-planar substrates is proposed. A micro-lens array is demonstrated to be transferred from a planar master mold to a non-planar substrate. In such process, a micro-lens array mold is initially fabricated by single-point diamond turning on a planar mold surface and then replicated by micro-injection molding. After that, the optical structures are transferred from micro-injected polymeric samples to a nickel foil by electro-plating, which is employed as a critical transition medium. To obtain sufficient flexibility with considerable strength, the thickness of the electro-plating mold is controlled to be around 75 μm, which is further integrated with precision molding tools to replicate micro/nano-scale optical features onto cylindrical substrates. Geometrical profile and surface roughness of the fabricated optical components in each processing step are characterized experimentally. The results indicate that the replication of the micro-lens array successfully demonstrates the process to transfer micro-optical components from planar surfaces to non-planar thermo-plastic polymeric substrates with high fidelity and optical-level surface quality. Compared with conventional precision compression molding, this novel proposed method in this research could achieve much higher flexibility and comparable fidelity with low cost on transferring optical structures from planar to non-planar surfaces. The application of this method might be widely extended to numerous replication methods, such as precision glass molding, roll-to-roll and roll-to-plane imprinting.

Fabrication and oxidation of amorphous Zr-based alloy for imprint lithography

As nanoimprint lithography provides promising potential in industrial manufacture, it is highly desirable to fabricate a flexible mold with good surface hardness and corrosion resistance. In this work, a nano-patterned template with amorphous surface was fabricated by magnetron sputtering and electrodeposition. The glassy structure imparted high affinity to oxygen with selective oxidation of Zr, Cu, and Al atoms in ambient atmosphere. These nanoimprint templates, having excellent flexibility, surface hardness, and environmental stability, combined with strong capability for constructing nanopatterns, are advantageous for high-resolution imprint lithography with good industrialization prospects.

Preparation of Ideally Ordered Anodic Porous Alumina by Prepatterning Process Using a Flexible Mold

Ideally ordered anodic porous alumina with controlled interpore distances was formed by fabricating a resist mask using a flexible mold and subsequent anodization. Prior to forming the resist pattern on the surface of an Al substrate, Al was pre-anodized at 10 V to prepare the fine porous structure, which acts as a resist adhesive layer. After the formation of the resist mask using a flexible mold, an arranged array of cavities with Al exposed at the bottom was formed by the selective dissolution of the oxide layer at resist openings. The subsequent anodization of the sample with the cavity array generated ideally ordered anodic porous alumina because alumina holes were formed at the bottom of cavities during anodization. This process allows the preparation of ideally ordered anodic porous alumina even on a curved Al surface owing to the flexibility of the mold. In addition, this process can also be applied to the preparation of an ideally ordered anodic porous alumina with a large sample area because the Al substrate can be patterned without high pressure. The obtained sample can be used for various applications requiring an ideally ordered hole array structure.

Micro-nano hierarchical pillar array structures prepared on curved surfaces by nanoimprinting using flexible molds from anodic porous alumina and their application to superhydrophobic surfaces.

Flexible molds with micro-nano hierarchical structures on the surface were fabricated by a two-step template process using anodic porous alumina as a starting material. The obtained flexible molds could be used to form micro-nano hierarchical pillar arrays on the surface of glass tubes and convex lenses by photo-nanoimprinting. The contact angle characteristics of the surfaces with hierarchical pillar arrays were measured, and it was confirmed that they exhibit superhydrophobic properties with a water-droplet contact angle exceeding 150°. The flexible molds obtained in this study can be used repeatedly and efficiently to form micro-nano hierarchical surfaces with superhydrophobic properties on the surfaces of substrates with various curvatures.

Fabrication of transparent quartz roll mold using a roll-to-plate wrapping process for flexible electronics

In this study, we numerically simulated the equivalent stress and deformation of a brittle quartz roll with the aim of optimizing its structure and conditions of use in roll-to-plate (R2P) wrapping with a transparent quartz roll. Initially, we analyzed the equivalent stress and contact phenomena between the quartz rolls and the flexible mold by varying the structural parameters of two differently structured quartz rolls to optimize the structure of the R2P system. The results of our analysis enabled us to determine the structure of the R2P system with a polydimethylsiloxane (PDMS) wrapped quartz roll. Further, we analyzed the effects of the thickness of the PDMS cushion and the E-modulus on the stress experienced by the quartz roll and optimized these parameters for the R2P wrapping process. Finally, we applied the optimized quartz roll structure and condition to the actual R2P wrapping process. In addition, we used our wrapped transparent quartz roll mold for the R2R imprint lithography of a micropattern.

AFM-Based nanofabrication and quality inspection of three-dimensional nanotemplates for soft lithography

Soft lithography is one of the most promising nanofabrication technologies for scalable nanomanufacturing. It uses flexible molds or stamps to fabricate extremely high-resolution nanopatterns in a low cost and rapid fashion on both flat and curved surfaces. Although two-dimensional soft lithography has been widely investigated and applied for some applications, there is a lack of quantitative research on using nanometer scale 3D patterns fabricated by atomic force microscope (AFM) for 3D soft lithography. In this paper, we demonstrated the effectiveness of ultrasonic vibration assisted AFM-based nanomachining in fabricating 3D master nanotemplates for 3D soft lithography. We successfully applied Polydimethylsiloxane (PDMS) daughter molds, casted from a nanometer scale 3D master template, using a soft lithography technique solvent-assisted micromolding. In addition, we investigated the quality and reusability of the master nanotemplates, and the quality of the PDMS patterns by quantifying the volume differences using an automatic imaging registration algorithm. Results show that there are zero or little PDMS residuals in the polymethyl methacrylate (PMMA) master nanotemplate with a simple contour for the first and second daughter mold casting, but 7% residuals for the third casting. And a more complex master nanotemplate shows slightly higher residual levels.

Feasibility of Customised Polymethyl Methacrylate Implants Fabricated Using 3D Printed Flexible Moulds for Correction of Facial Skeletal Deformities.

Use of patient specific Polymethyl methacrylate (PMMA) implants for the reconstruction of cranial defects has become a standard practice with excellent long-term results. However, for the reconstruction of midface and mandibular osseous defects other alloplastic materials are preferred but their use is limited due to high cost. This is a report of our experience with the use of low-cost patient specific PMMA implants fabricated using 3D printed moulds in the reconstruction of osseous defects involving different areas of the facial skeleton not limited to cranium. The 25 consecutive patients with craniofacial osseous defects who underwent reconstruction using customized PMMA implants were analyzed. All PMMA implants were fabricated intraoperatively with the use of 3D printed flexible moulds or templates. A total of 34 implants were used in 25 consecutive patients. Out of 34 implants 25 were used for midface and mandibular osseous defects. Most common etiology was post-traumatic deformity (n = 19) followed by tumor (n = 3), craniofacial anomalies (n = 2) and post-craniotomy (n = 1). One patient out of 25 (n = 1) had postoperative implant exposure. The follow-up was ranged from 3 to 19 months with an average of 12 months. The aesthetic outcome was found to be good to excellent with mean visual analogue score of 4.08. Polymethyl methacrylate implants fabricated intraoperatively using 3D printed moulds provide accurate and precise reconstruction at an exceptionally low cost. PMMA has an excellent moulding property with low infection rates. As shown in our study its application may be easily extended to all areas of the craniofacial skeleton.

Flexible gypsum mould applied in the mechanical system for blank of grouted ceramic handicrafts based on the radial movement of the sphere and connection by the principle of six‐point positioning

In order to solve the problems of low production efficiency, poor quality of blanks, high labour intensity and inability to meet the market demand with the manual gypsum mould, a novel design of the gypsum mould to be applied into the automatic production of the planks was developed for ceramic handicrafts. This mould inherits the advantages of the manual mould with tenon–mortise connection and adopts six-piece combination. According to the spherical radial movement, the new mould opens and closes, mostly avoiding movement interference and significantly improving service life. The connection technique of ‘six-point positioning principle’ was proposed and adopted to embed the connection device of four side die pieces with manipulator, so as to realise the strength of gypsum die pieces and effectively connect with the manipulator. Based on the group technique, the standard eigenvector and norm for the grouping of geometric elements of target blanks were proposed to realise the grouping of many different kinds of blanks into a few number of groups with all the blanks. Within a group, the gypsum mould keeps the external geometric features and tenon–mortise connection unchanged, while the working cavity of different blanks only alters, for the flexibility of gypsum mould. Thus, the universality of the mould is gained, and the design and manufacturing efficiency is greatly improved, with the considerable reduction of the cost, and the digitisation of design, manufacturing and management processes is realised. The gypsum mould provides a new technological method and technical guarantee for changing the labour-intensive production mode of ceramic handicraft blank cast and forming, realising the intellectualisation and automation of the main production link of ceramic handicraft blank cast and efficiency automatic and intellectualised production of ceramic handicraft blank with high identity.

Ultrahigh emissivity of grating-patterned PDMS film from 8 to 13 μ m wavelength regime

Polydimethylsiloxane (PDMS) is a prominent material for radiative cooling due to its promising optical properties in the mid-infrared spectral region as well as its fabrication easiness. Even though several works have reported that the mid-infrared emissivity of a PDMS film can be increased by surface modification, there is still room for further enhancement through global optimization. Here, we designed and fabricated the thin PDMS film patterned with two-dimensional gratings to obtain the highest emissivity in the wavelength range from 8 to 13 μm. A surrogate-model-based optimization was performed, and the optimum structure exhibited the averaged emissivity value of 0.99 in the wavelength of 8–13 μm, which is the highest value reported to date among polymer-based radiative coolers. For real-world applications, we also developed the fabrication method that is repeatable and applicable for various surfaces using a flexible master mold.

DEVELOPMENT OF AN AUTOMATED VACUUM CHAMBER FOR SMALL-SCALE CASTING OF PLASTIC PARTS

The results of developing the optimal technology for manufacturing plastic parts for small-scale production are presented. Methods for improving the quality of reactive plastics casting have been identified. Designed and manufactured automated equipment that support developed by the technology of casting thermosetting plastics in flexible molds.

Variation of a Triangular Pattern Shape due to Shrinkage in the Repeated UV Imprint Process

Shrinkage is inevitable in the curing of resins during the nanoimprint process. The degree of shrinkage that occurs as the resin transforms from a viscous liquid to solid differs depending on the type of resin. However, if the cured material is repeatedly cured using the same material, constant shrinkage can be confirmed. In this study, the pattern of change was observed by repeatedly performing the nanoimprint process using a resin with a constant shrinkage rate. The observed pattern for the change of shape was made using a triangular pyramid-shaped aluminum master mold and a flexible replica mold made from the master. Shrinkage that results from the nanoimprint process occurs linearly in the longitudinal direction of the pattern and can be predicted by simple calculations. The change of the pattern due to shrinkage occurred as expected. If the shrinkage rate remains constant, various patterns can be manufactured with high accuracy by correcting these changes before producing a specific shape. This study confirms that the pattern of the desired angle can be obtained by performing the repeated imprint without having to manufacture a master mold.

Investigation of Nonwoven Geotextiles for Full Contact Flexible Mould Used in Preparation of MICP-treated Geomaterial

This study is concerned with needle-punched, nonwoven geotextile materials that have been used to develop full contact flexible moulds (FCFM) to treat soil specimens through microbial calcite precipitation (MICP) process by immersing method. MICP was induced through bacteria-urea reactions. The objective of this study was to figure out how different geotextiles influence the preparation of MICP-treated specimens. Five types of geotextiles were selected to prepare FCFM used for MICP treatment in this study. There is one singeing geotextile with the sintered side during these five geotextiles. Unconfined compression tests, four-point bending tests, and direct shear tests were conducted on MICP-treated specimens prepared by different geotextiles. The experimental results indicated that the mechanical properties of MICP-treated soil specimen prepared in FCFM made by G2 geotextile and G3 geotextile were similar. The unconfined compressive strength of the MICP-treated specimen reached 1.12 MPa (G2) and 0.90 MPa (G3), and MICP-treated specimens prepared by singeing geotextile had better performance than original geotextiles.

Study of integral hat-stiffened composite structures manufactured by automated fiber placement and co-curing process

Integrated and automated manufacturing processes of advanced composites have attracted extensive attention, aiming at the improvement of mechanical performance and cost efficiency of composites. This experimental study investigated the feasibility of a manufacturing process for co-cured integral hat-stiffened panels based on automated fiber placement. To achieve desirable manufacturing quality and simplify manufacturing process, a novel flexible inner mold was designed for the enclosed cavity between stringers and skin, which was suitable for curved and large hat-stiffened panels. Influences of flexible mold and processing parameters on dimensional accuracy were studied by both finite element analysis and experimental methods. Moreover, fiber distribution around the transition region between skin and stringer were obtained through microscopy observation. With the optimum inner mold and layup processing parameters, hat-stiffened composites can be manufactured integrally with improved surface quality and geometric accuracy, based on co-curing process and automated fiber placement.

Shear behaviour of fabric formed T beams reinforced using W-FRP

A combination of flexible moulds as external formwork and bespoke robotically fabricated fibre reinforced polymer cages as tensile reinforcement offers a new opportunity for the manufacture of structural concrete components that have been optimised to minimise material use. This technology could potentially help in our quest to reduce carbon emissions in the construction industry, yet there remain technical issues to overcome if such flexibly formed concrete structures are to become a reality. This paper presents experimental research on fabric-formed T beams reinforced with wound fibre-reinforced polymer (W-FRP) to quantify the shear contribution of this novel system. It is shown that, depending on the geometry of the beam, carefully chosen flexural and shear reinforcement can resist shear in a predictable manner. Because of geometric variation along the length of the beam, shear resistance is found to move from being provided by both the W-FRP reinforcement and the sloping longitudinal reinforcement to being provided predominantly by the longitudinal FRP reinforcement as the W-FRP gradually ruptures. In turn, this demands higher anchorage capacity of the longitudinal bars than that might have been expected by design codes of practice. By overcoming such issues, this paper shows that savings in concrete of up to 64% can be made in the webs in such structures, compared with conventional T-beams.

Optimal design criteria for form-finding of double-curved surfaces

The development of new digital design tools and fabrication technologies stimulated a large research interest in the design and construction of free-form architecture. Free-form architecture indicates the symbolic act of freeing architecture from the limitations of pure form. During the form-finding process, the priority is on identifying the geometry that enables the optimum force flow within the structure.This study focuses on the problem of the form-finding problem of concrete double-curved surfaces. First, a suitable form-finding optimization framework to optimize shell surfaces based on the surface Stress Density method is established. This framework is based on the use of different software such as Rhinoceros, Grasshopper, and Matlab. The stress density method is chosen because it allows obtaining an optimized shape starting by few parameters: the geometric characteristics of the model, the surface density factor and the magnitude of the load. In a second step, the study is focused on a single panel of the structure. Structural analyses of this panel are carried out using the commercial finite element software SAP2000 to demonstrate that it is a shape resistant structure. Finally, a new production process for concrete double-curved surfaces is presented showing a prototype at a small scale. This process is trying to satisfy the needs of new shapes within architectural design. The proposed solution is the improvement of an existing flexible mould formwork technology and represents the first attempt to reach a reusable, reconfigurable and affordable procedure.

Flexible tools in mould and formwork making: a review

The rigid and one-off moulds are quite insufficient to fabricate differentiated and non-standard building components due to the low adaptation capability of mass production to changing demands of the market. Aligning with mass customisation, flexible tools are developed to solve time, cost and waste problems in moulding and casting of variable building components in the architecture, engineering, and construction. This study guides architects and engineers in the development of flexible moulds and tooling for building components. This paper aims to review the latest research trends by analysing the publications from 2004 to 2019. The systematic mapping method was adopted from software engineering to determine the-state-of-the-art technologies in flexible tools. The review study shows that flexible tools can be used to cast variable and non-standard building components by further researching on large-scale implementation, process capability and control. A survey of future trends in this promising field concludes this paper.

Effects of Imprinting Pressure on the Damage of Flexible Composite Mould and Pattern Quality during UV Nanoimprinting.

Imprinting pressure is the significant factor for composite mould durability and pattern quality during UV nanoimprinting on complex surfaces. To solve these problems, the effects of imprinting pressure on the damage of flexible composite mould and pattern quality-encountering particles were investigated through experiment and simulation. It was found that increasing the pressure could improve the pattern quality, but it will damage the mould and reduce the durability. Moreover, too small pressure could lead to serious pattern defects. Therefore, the imprint pressure of 30 kPa was suitable for use in the imprinting process from the viewpoints of protecting the mould and reducing pattern defects. These findings will be useful for improving the pattern quality and mould durability.

Forming of Dynamic Microstructure of Flexible Polymer.

This study focuses on the forming of dynamic microstructure of flexible polymer. The dynamic tensile control microstructure of the polymer mold, along with the gasbag, was used to exert pressure to achieve forming. This study simulated the dynamic control of the flexible mold, and proposed four mechanical models of material viscoelastic response for modeling and evaluation. MATLAB software was used to calculate the imprint prediction calculation theory construction according to the imprint result of curved surface and asymmetric imprint forming. This study designed and developed a gasbag-assisted dynamic forming system, and tested the proposed system for verification. The test results showed that the mechanical stability, curved surface, and asymmetric imprint prediction calculation of the mechanical model of the viscoelastic response of flexible mold material, as proposed in this study, can display the geometric features of the imprinted microstructure. The dynamic mold microstructure control process can accurately transfer a bifacial microstructure and construct the confidence interval for transfer printing forming.

Sandy Soil Improvement through Microbially Induced Calcite Precipitation (MICP) by Immersion.

The goal of this article is to develop an immersion method to improve the microbially induced calcite precipitation (MICP) treated samples. A batch reactor was assembled to immerse soil samples into cementation media. The cementation media can freely diffuse into the soil samples in the batch reactor instead of cementation media being injected. A full contact flexible mold, a rigid full contact mold, and a cored brick mold were used to prepare different soil sample holders. Synthetic fibers and natural fibers were selected to reinforce the MICP-treated soil samples. The precipitated CaCO3 in different areas of the MICP-treated samples was measured. The CaCO3 distribution results demonstrated that the precipitated CaCO3 was distributed uniformly in the soil sample by the immersion method.