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In‐Mold Electronics (IME) is an innovative technology that allows the creation of 3D‐shaped electronic surfaces by combining printed electronics and In‐Mold Decoration (IMD). During the manufacturing process, the materials that integrate these devices, such as adhesive, must endure the transformation conditions of thermoforming. However, the adhesive rigidity may influence the deformation of the film during this process. In this study, both printed and hybridized samples are compared regarding their stretching and thickness reduction during the thermoforming process. The results indicate that the deformation of the hybridized samples differs from the printed ones, resulting in less stretching in areas near the adhesive, with stretching increasing as it steps away from where it is deposited. Thickness values are also affected, being greater around the adhesive and decreasing farther away. Therefore, the presence of the adhesive significantly impacts the behavior of the film during processing, a factor that must be considered in the design of IME devices to maximize the number of functional devices. [ABSTRACT FROM AUTHOR]

Background: To compare and investigate the effects of intraoral ageing on the thickness of one group of directly printed and two groups of thermoformed aligners on the labial surface of maxillary central incisors. Materials and Methods: Six groups (12 samples per group) were included in this prospective in vivo experiment. Groups DP‐Clin, INV‐Clin and CA‐Clin consisted of directly printed (Tera Harz TC‐85 DAC resin), thermoformed (Invisalign, PU based polymer) and in house thermoformed (CA‐Pro, PET‐G based polymer) aligners, retrieved after 1 week of intraoral service. Groups DP‐Ctr, INV‐Ctr and CA‐Ctr included unused aligners samples. Thickness measurements were conducted using confocal laser scanning microscopy (CLSM). Data that underwent log‐10 transformation was analysed by multiple linear regression analysis (p <.05). Results: Statistically significant differences were found between the materials in both Clin and Ctr categories (p <.001). Group DP had the highest thickness among the groups and the least thickness was observed in the CA group (p <.001). However, intraoral ageing did not significantly affect the aligner thickness of any groups. Conclusions: Both thermoforming and direct printing of clear aligners led to thickness deviations in terms of increase for printed aligners and decrease for thermoformed aligners. Intraoral ageing did not affect the aligner thickness in any of the groups. [ABSTRACT FROM AUTHOR]

The increasing concern over environmental sustainability has prompted various industries to reassess their practices and explore greener alternatives. Dentistry, as a significant contributor to waste generation, is actively seeking methods to minimize its environmental footprint. This paper examines the environmental implications of clear aligner therapy (CAT) in orthodontics and explores strategies to prioritize sustainability in aligner manufacturing and usage. CAT has gained popularity as a viable alternative to traditional fixed appliances due to advancements in biomaterials and computer-aided design (CAD) and manufacturing (CAM) technologies. The global market for clear aligners is expanding rapidly, with significant growth projected in the coming years. To address these challenges, this paper proposes adopting the principles of reduce, reuse, recycle, and rethink (4Rs) in orthodontic practices. Strategies such as minimizing resource consumption, incorporating recycled materials, and promoting proper aligner disposal and recycling can significantly reduce environmental harm. This paper explores emerging technologies and materials to mitigate the environmental impacts of CAT. Additionally, initiatives promoting aligner recycling and repurposing offer promising avenues for reducing plastic waste and fostering a circular economy. In conclusion, while CAT offers numerous benefits in orthodontic treatment, its environmental impact cannot be overlooked. By implementing sustainable practices and embracing innovative solutions, the orthodontic community can contribute to a more environmentally conscious future while continuing to provide quality care to patients. [ABSTRACT FROM AUTHOR]

This study proposed two designs of padded patient specific wrist cast as an alternative using the 3D printing thermoforming production technique. These designs were printed as a flat structure with and without hinge joints. The casts were 3D printed with polylactic acid (PLA) filament as the main structure and thermoplastic polyurethane (TPU) as the padding material. The casts were fitted to the subject's wrist by thermoforming the printed structure. The strength of the proposed structure was analyzed using finite element analysis (FEA) during the design stage to estimate the mechanical properties of the proposed cast such as local displacement under a specific load, stress and safety factor. The thermoforming tests of the proposed designs at various temperatures were conducted experimentally to observe any crack and delamination after thermoforming. The design with hinge joint was selected based on its proper post-thermoforming fit as a functional wrist cast. [ABSTRACT FROM AUTHOR]

Plastic recycling, waste minimization such as process outfall valorization promotes a circular economy. Herein, food trays have been produced in the moulded pulp thermoforming process. To this end, high-density polyethylene (HDPE) outfall has been dispersed in water via Poly vinyl alcohol (PVA) addition in a Northern Bleached Softwood Kraft Pulp (NBSKP) slurry. Samples physical and mechanical properties have been evaluated. With an increasing HDPE content, parts air permeability was drastically reduced to a minimum of 2.4 ± 0.8 mL min−1. In addition, water and grease hold out properties have been increased with minimum water Cobb1800 value of 10.9 ± 5.4 gm−2 and oil Cobb1800 value of 13.18 ± 6.5 gm−2. Samples with high HDPE content demonstrated hydrophobic surface with water contact angle value above 90°. HDPE melting and binding to wood pulp fibers was monitored by SEM images. Regarding the mechanical properties, HDPE induced plastic deformation with a reduced Young modulus by 17 %. Moreover, the addition of HDPE increased wet strength by 81 %. However, the produced food tray composites with high HDPE content demonstrated low repulpability index. [ABSTRACT FROM AUTHOR]

The quality of woven carbon fiber fabric/polycarbonate thermoplastic composites after thermoforming and demolding was investigated using finite element simulation and the Taguchi orthogonal array. The simulation utilized a discrete approach with a micro-mechanical model to describe the deformation of woven carbon fabric, combined with a resin model. This simulation was validated with bias extension tests at five temperatures. The thermoforming process parameters considered were blank temperature, mold temperature, and blank holding pressure, with three levels for each factor. Optimal values for the fiber-enclosed angle, spring-back angle, mold shape fitness, and the strain of the U-shaped workpiece were desired. The results indicated that the comparison of the stress-displacement curve of bias extension tests verified the application of the discrete finite element method. Results from the Taguchi array indicated that blank holding pressure was the dominant parameter, with the optimal value being 1.18 kPa. Blank temperature was the second most significant factor, effective in the range of 160 °C to 230 °C, while mold temperature had a minor effect. Furthermore, the four quality values are dependent and have a similar trend. The best combination was identified as a blank holding press of 1.18 kPa, a blank temperature of 230 °C, and a mold temperature of 190 °C. [ABSTRACT FROM AUTHOR]

This paper examined the mechanical properties of wrist–hand orthoses made from polylactic acid (PLA) and polyethylene terephthalate glycol (PETG), produced through material extrusion with infill densities of 55% and 80%. These orthoses, commonly prescribed for wrist injuries, were 3D-printed flat and subsequently thermoformed to fit the user's hand. Experimental and numerical analyses assessed their mechanical resistance to flexion after typical wear conditions, including moisture and long-term aging, as well as their moldability. Digital Imaging Correlation investigations were performed on PLA and PETG specimens for determining the characteristics required for running numerical analysis of the mechanical behavior of the orthoses. The results indicated that even the orthoses with the lower infill density maintained suitable rigidity for wrist immobilization, despite a decrease in their mechanical properties after over one year of shelf life. PLA orthoses with 55% infill density failed at a mean load of 336 N (before aging) and 215 N (after aging), while PETG orthoses did not break during tests. Interestingly, PLA and PETG orthoses with 55% infill density were less influenced by aging compared to their 80% density counterparts. Additionally, moisture and aging affected the PLA orthoses more, with thermoforming, ongoing curing, and stress relaxation as possible explanations related to PETG behavior. Both materials proved viable for daily use, with PETG offering better flexural resistance but posing greater thermoforming challenges. [ABSTRACT FROM AUTHOR]

Spring‐back is a forming defect in thermoplastic fiber‐metal‐laminate (FML) structures that is influenced by all steps of the forming process. Here, we propose a complete CAE chain to predict spring‐back in a FML parts during one‐step hot stamping by fully considering the material properties, latent heat, thermal mismatch, and modulus mismatch during forming and cooling. Then, constitutive models of the aluminum sheet, a visco‐hyperelastic constitutive model, and an elastic model of the UD CF/PEEK prepregs during hot‐stamping and cooling are introduced to describe the deformation behavior. A Coulombic friction model, latent heat model, and contact resistance model are also proposed to describe the interfacial flow, heat generation, and thermal conductivity. The proposed models and CAE chain are validated by the experimentally determined punching force, geometric shape, temperature, and spring‐back angle. The S‐shaped feature of the FML greatly increases the spring‐back of the FML specimens, and lower punching speeds and higher forming temperatures decreases the S‐shaped feature, thereby reducing the spring‐back angle. Highlights: A complete CAE chain was proposed to predict spring‐back in a FML curved beam.A new visco‐hyperelastic constitutive model of the CF/PEEK was applied.The latent heat and thermal mismatch were considered in cooling simulation.The S‐shaped feature of the FML greatly increases the spring‐back.The thermal mismatch increased the S‐shaped feature of the FML. [ABSTRACT FROM AUTHOR]

The thermoforming process is a widely utilized manufacturing technique for shaping thermoplastic materials into various products. Achieving uniform and controlled thermal distribution within the material during thermoforming is crucial to ensure high-quality products and minimize defects. This study investigates and enhances the understanding of thermal distribution in thermoforming processes through simulation analysis before it is done via experiment. This research investigates the thermal distribution in the thermoforming process of Polyphenylene Sulfide composites. The heating element distances were varied during the simulations of the thermoforming process of Polyphenylene Sulfide (PPS) composites, focusing on understanding how different distances affect the material's deformability, dimensional accuracy, and overall quality. Three heater temperatures with three heater distances are tested. The distance between two heated surfaces is 200, 300 and 500 mm for 320℃, 360℃ and 400℃ heated surfaces. The desired PPS temperature (320℃) and maximum heater temperature (400℃) are parameters. The test result shows that to achieve 320℃ thermoplastic temperature, we can use 385℃ IR heater temperature with a heater distance of 200 mm. However, this 200 mm distance might be too close for the operation, and a larger distance might be needed. Using 300 mm or 500 mm can achieve close to 320℃ if the heater temperature is set to 400℃. In conclusion, this value is a reference for the distance of the material between the heater during the fabrication process. [ABSTRACT FROM AUTHOR]

One of the evaluative criteria utilized to ascertain the quality of a thermoformed product is the ultimate thickness of the sheet achieved through the processing. In determining the visual performance of optical products such as aircraft canopy, windscreens, etc., thickness distribution is crucial. Consequently, precise thickness measurement is the most essential aspect of quality control. To measure thickness, a variety of mechanical and optical measurement systems, in addition to several manual systems, are available. The manual intervention restricts the measurement system to lesser measurements and simplifies the system to simple geometries. Furthermore, post-processing of the image or point data is necessary to obtain thickness distribution using an optical measurement system. However, manual intervention is exceptionally time-consuming and may result in inaccurate outcomes. As a result, the current investigation put forth an algorithm based on machine learning to measure the precise thickness distributions from point data obtained through the measuring system. The algorithm's functionality is illustrated through the thermoforming of a PMMA hemispherical dome at various forming pressures. Point data for thickness measurements of the hemispherical domes were acquired using the Rapid-I system of measurement. Utilizing the proposed algorithm, the thickness distribution of the hemispherical domes was measured accurately and efficiently. [ABSTRACT FROM AUTHOR]

This study aims to establish and optimize a process for the fabrication of 3D microstructures of the biocompatible polymer Parylene C using hot embossing techniques. The different process parameters such as embossing temperature, embossing force, demolding temperature and speed, and the usage of a release agent were optimized, utilizing adhesive micropillars as a use case. To enhance compatibility with conventional semiconductor fabrication techniques, hot embossing of Parylene C was adapted from conventional stainless steel substrates to silicon chip platforms. Furthermore, this adaptation included an investigation of the effects of the hot embossing process on metal layers embedded in the Parylene C, ensuring compatibility with the ultra-thin Parylene printed circuit board (PCB) demonstrated previously. To evaluate the produced microstructures, a combination of characterization methods was employed, including light microscopy (LM) and scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Fourier-transform infrared spectroscopy (FTIR). These methods provided comprehensive insights into the morphological, chemical, and structural properties of the embossed Parylene C. Considering the improved results compared to existing patterning techniques for Parylene C like plasma etching or laser ablation, the developed hot embossing approach yields a superior structural integrity, characterized by increased feature resolution and enhanced sidewall smoothness. These advancements render the method particularly suitable for diverse applications, including but not limited to, sensor optical components, adhesive interfaces for medical wearables, and microfluidic systems. [ABSTRACT FROM AUTHOR]

A comprehensive modeling framework for the thermoforming of polymer matrix woven laminate composite was developed. Two numerical indicators, the slip path length and traction magnitude, have been identified to be positively correlated to matrix smearing and wrinkling defects. The material model has been calibrated with picture-frame experimental results, and the prediction accuracy for intra-ply shear and thickness distribution was examined with measurements of the physically formed parts. Specifically, thickness prediction for most locations on the formed parts was accurate within an 11.6% error margin. However, at two points with significant intra-ply shear, the prediction errors increased to around 20%. Finally, a parametric study was conducted to determine the relationship between various process parameters and the quality of the formed part. For the trapezoidal part, orienting the laminate at 45 degrees to the mold axis reduces the likelihood of matrix smear and wrinkling defects. Although this laminate orientation yielded a greater spatial variation in part thickness, the thickness deviation is lower than that for the 0-degree orientation case. Two forming analyses were conducted with ramp rates of 25 mm/s and 80 mm/s to match the equipment's operational limits. It was observed that higher forming rates led to a greater likelihood of defects, as evidenced by a 15% and 10% increase in the formed part areas with longer slip paths and higher traction magnitudes, respectively. It was discovered that shallower molds benefit from faster ramp rates, while deeper molds require slower rates to manage extensive shearing, stretching and bending. Faster forming rates lead to smaller thickness increases at high intra-ply shear regions, indicating a shift from intra-ply shear to out-of-plane bending due to the visco-plastic effect of the molten laminate and can negatively impact part quality. Lastly, it was shown that a well-conceived strategy using darts could improve the part quality by reducing the magnitude of the defect indicators. [ABSTRACT FROM AUTHOR]

Screen printing is an interesting technique for the high‐volume production of printed conductive electronic devices on flexible substrates. In this study, silver conductive lines have been produced by screen‐printing technique on flexible PEN substrates and optimized in order to provide maximum electrical conduction. The geometry of the obtained conductive samples has been modified by performing thermoforming tests in a mold with complex geometry, replicating a significant section of dashboard coating. The functionality of the shape‐deformed substrates has been assessed. [ABSTRACT FROM AUTHOR]

Highly loaded complex parts are machined from a solid block of metal by removing material through cutting, boring, drilling, and grinding to obtain the three-dimensional shape. Most cases, this involves removing as much as 80 percent of the material from a billet, which is time-consuming and inefficient considering the cost of the materials. Alternatively, these complex parts can be manufactured using hybrid overmolding process which involves injecting plastics over a reinforced substrate with continuous fiber-reinforcement eliminating subtractive machining or joining of multiple parts. The substrate is typically heated using an infrared (IR) oven and preformed over a solid mold to a three-dimensional shape using thermoforming. Injection overmolding material can also be reinforced with discontinuous fibers based on the design requirements. Both thermoforming and injection molding are matured automotive ultra-high-rate manufacturing processes. Adopting these technologies to aerospace requires advanced aerospace-grade thermoplastic material systems and developing the hybrid overmolding process that combines both thermoforming and injection molding processes. Material compatibility is one of the key enablers for the fusion across the overmolded interfaces. To demonstrate the overmolding technology for an aerospace application, Victrex AE250 lowmelt polyaryletherketone (LM-PAEK) system reinforced with AS4 fibers and a 30% carbon fiber-reinforced polyetheretherketone (PEEK) were used to overmold aircraft window plugs to be used for cargo conversion of passenger aircraft. The fully automated overmolding process was demonstrated using KraussMaffei multirobotic thermoforming and injection molding system. Thermal and mechanical test evaluations were employed to assess the material compatibility and overall part quality. Photomicrographs and flexure tests conducted on test samples extracted from the window plugs indicated satisfactory fusion across the overmolded interface and optimized holding of PEEK materials. [ABSTRACT FROM AUTHOR]

We present a novel technique for designing molds suitable for desktop thermoforming, specifically for creating packaging such as blister packs. Our molds, PackMolds, feature neither undercuts nor negative draft angles, facilitating their easy release from thermoformed plastic sheets. In this study, we optimize the geometry of PackMolds to comply with user-specified draft angle constraints. Instead of simulating the traditional thermoforming process, which necessitates time discretization and specifying detailed parameters for both material properties and machine configuration to achieve an accurate simulation result, we formulate our problem as a constrained geometric optimization problem and solve it using a gradient-based solver. Additionally, in contrast to industrial thermoforming, which benefits from advanced tools, desktop thermoforming lacks such sophisticated resources. Therefore, we introduce a suite of assistive tools to enhance the success of desktop thermoforming. Furthermore, we demonstrate its wide applicability by showcasing its use in not only designing blister packs but also in creating double-sided blister packs and model stands. [ABSTRACT FROM AUTHOR]

This article deals with the thermoforming process, in which the plastic sheet is heated to a suitable temperature and stretched through a single-sided mould. This paper focuses on the study of thickness distribution along the final part through numerical simulation with T-SIM software and optical characterization of the practical process. PC LEXAN™ 8A13E films, with different initial thickness, were moulded by two types of moulding (positive and negative). It was intended to evaluate, characterize and correlate the effect of the process on the optical properties of the films. The findings of the study suggest that films formed with a negative mould exhibit more pronounced thickness variations compared to those formed with a positive mould, resulting in lower final thicknesses. Additionally, thicker films exhibit higher thickness variations after thermoforming, as supported by the experimental data. Regarding the optical characterization of the films, transmittance and reflectance tests were performed. In the case of transmittance, a significant increase in this property is observed after thermoforming, while a decrease in the reflectance values was observed. This paper is then focused on the study through numerical simulation and optical characterization of the thermoformed films, elucidating the dynamics inherent in the thermoforming process with transparent polycarbonate films, providing valuable insights for optimization and application across various industrial sectors. [ABSTRACT FROM AUTHOR]

This research aims to investigate the influence of model height employed in the deep drawing of orthodontic aligner sheets on force transmission and aligner thickness. Forty aligner sheets (Zendura FLX) were thermoformed over four models of varying heights (15, 20, 25, and 30 mm). Normal contact force generated on the facial surface of the upper right central incisor (Tooth 11) was measured using pressure-sensitive films. Aligner thickness around Tooth 11 was measured at five points. A digital caliper and a micro-computed tomography (µ-CT) were employed for thickness measurements. The normal contact force exhibited an uneven distribution across the facial surface of Tooth 11. Model 15 displayed the highest force (88.9 ± 23.2 N), while Model 30 exhibited the lowest (45.7 ± 15.8 N). The force distribution was more favorable for bodily movement with Model 15. Thickness measurements revealed substantial thinning of the aligner after thermoforming. This thinning was most pronounced at the incisal edge (50% of the original thickness) and least at the gingivo-facial part (85%). Additionally, there was a progressive reduction in aligner thickness with increasing model height, which was most significant on the facial tooth surfaces. We conclude that the thermoplastic aligner sheets undergo substantial thinning during the thermoforming process, which becomes more pronounced as the height of the model increases. As a result, there is a decrease in both overall and localized force transmission, which could lead to increased tipping by the aligner and a diminished ability to achieve bodily movement. [ABSTRACT FROM AUTHOR]

A series of experimental and numerical studies were carried out on the mechanical and geometric performance of an aerostructural part produced by a material out-of-autoclave stamp forming process using unidirectional (UD) carbon fiber (CF) reinforced polyetherketoneketone (PEKK), which provides advantages like reshaping, recycling, welding, and low serial manufacturing costs. As a novelty, initial part geometry, different types of springs, and their attachment type were examined experimentally and compared with simulations. Compression tests were performed to determine mechanical strengths which reach levels up to 550 MPa. In addition, differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were conducted to determine the crystallinity which occurs depending on the cooling regimes of the material. The crystallinity has been observed to vary regionally ranging from 16 to 21%. However, the crystallinity of the part towards the cold mold region decreased from 20 to 17%. In addition, simulations were performed to observe and control the occurrence of wrinkles and other defects. [ABSTRACT FROM AUTHOR]

Thermoformed fossil‐based disposable packaging is widely used in everyday life but it represents a serious environmental problem, as it is often incorrectly dispersed or destined to landfills. Bio‐based and biodegradable materials can constitute and effective solution to this issue. Two different blends of poly(butylene succinate‐co‐butylene adipate) (PBSA) and Poly (3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate) (PHBH) were studied as constituents for disposable packaging production. The blends were produced via twin screw extrusion. Sheets were cast extruded and then thermoformed into trays. A rheological, thermal and mechanical characterization was performed on compounds and manufacts. Both blends presented a good processability and interesting properties for packaging application, which can be tailored by varying the percentage of constituent polymers. [ABSTRACT FROM AUTHOR]

The quest to reduce global plastic consumption has led to the emergence of biodegradable fiber-based composites as a promising sustainable replacement to conventional plastics in the food packaging industry. As the packaging sector is shifting more towards fiber-centric materials, thermoforming techniques for the 3D forming of the fiber-based materials, especially using complex mold designs, should be thoroughly researched to replace the conventional plastics in the industry. Finite element analysis of the deformation behavior of the paperboard during the thermoforming process and the factors that trigger the fracture of the composite layers were studied in the present work. The results show that 90° fiber orientation, 0.3 mm sheet thicknesses, and specific mold geometries can result in better forming results, thereby maximizing the potential of fiber-based materials in thermoforming.

This article provides a concise insight into the thermoforming of airlaid CTMP pulp. First, the airlaid process was studied, showing that fiber fractionation and the retention of fines occurred in the forming head. Then, the effect of temperature and pressure during thermoforming was investigated. Harsher conditions, i.e. higher temperature and pressure, yielded greater densification of the substrate and higher tensile strength. The maximum strength was found at the highest settings tested, that is, 100 MPa and 200°C. The screening of thermoforming conditions was also compared to previously published results on wetforming. Next, the effect of softwood CTMP pulp was delineated, which on average showed the best mechanical properties at elevated freeness and high degrees of bleaching. At last, a comparison between dry forming and wetforming was made for one selected pulp quality. Here, the dryformed substrates were stiffer at low elongation, yet the wetformed substrates yielded a greater extensibility and higher tensile strength. In conclusion, dryformed pulp mostly relies on temperature and pressure for bond formation during thermoforming, which produces materials that are distinctly different from wetformed molded pulp.

The continuous growth of additive manufacturing in worldwide industrial and research fields is driven by its main feature which allows the customization of items according to the customers' requirements and limitations. There is an expanding competitiveness in the product development sector as well as applicative research that serves special-use domains. Besides the direct use of additive manufacturing in the production of final products, 3D printing is a viable solution that can help manufacturers and researchers produce their support tooling devices (such as molds and dies) more efficiently, in terms of design complexity and flexibility, timeframe, costs, and material consumption reduction as well as functionality and quality enhancements. The compatibility of the features of 3D printing of molds with the requirements of low-volume production and individual-use customized items development makes this class of techniques extremely attractive to a multitude of areas. This review paper presents a synthesis of the use of 3D-printed polymeric molds in the main applications where molds exhibit a major role, from industrially oriented ones (injection, casting, thermoforming, vacuum forming, composite fabrication) to research or single-use oriented ones (tissue engineering, biomedicine, soft lithography), with an emphasis on the benefits of using 3D-printed polymeric molds, compared to traditional tooling. [ABSTRACT FROM AUTHOR]

The quest to reduce global plastic consumption has led to the emergence of biodegradable fiber-based composites as a promising sustainable replacement to conventional plastics in the food packaging industry. As the packaging sector is shifting more towards fiber-centric materials, thermoforming techniques for the 3D forming of the fiber-based materials, especially using complex mold designs, should be thoroughly researched to replace the conventional plastics in the industry. Finite element analysis of the deformation behavior of the paperboard during the thermoforming process and the factors that trigger the fracture of the composite layers were studied in the present work. The results show that 90° fiber orientation, 0.3 mm sheet thicknesses, and specific mold geometries can result in better forming results, thereby maximizing the potential of fiberbased materials in thermoforming. [ABSTRACT FROM AUTHOR]

This experimental study probes the dynamic behaviour of a 3 mm ABS sheet during positive mould vacuum-assisted thermoforming. In this process, the sheet undergoes large and fast deformations caused by the applied vacuum and mechanical stretching by the mould. The objective is to elucidate the complexities of these large, rapid, and non-isothermal deformations. The non-isothermal conditions are caused by the radiative heating of the sheet, convective heat loss to the surrounding air, and conductive heat transfer from the sheet to the mould. By utilizing stereo digital image correlation (DIC) in tandem with thermal imaging, the present study accurately maps the occurring displacement, strain, and strain rate field in relation to real-time temperature variation in the material. The study progresses to observe the ABS material from the moment it contacts the mould until it conforms to a positive 250 mm diameter semi-sphere cast aluminum mould. The DIC methods are validated by comparing thickness values derived from DIC's principal strain directions to ultrasonic thickness gauge readings. This knowledge not only broadens the understanding of the thermo-mechanical behaviour of the material but also aids in optimizing process parameters for improved thickness uniformity in thermoformed products. [ABSTRACT FROM AUTHOR]

In this study, the simulation of a vacuum forming process employing a micromechanical inspired viscoelastic–viscoplastic model is investigated. In the vacuum forming process, a plastic sheet is heated above the glass transition temperature and subsequently forced into a mold by applying a vacuum. The model consists of a generalized Maxwell model combined with an dissipative element in series. Each Maxwell element incorporates a hyperelastic element in series with a viscous element based on a hyperbolical law. While the generalized Maxwell model considers the relaxation due to molecular alignment, the additional viscous element is a modification based on the approach of Bergström and thus considers molecular chain reptation. The model is designed with the aim to converge to the generalized linear Maxwell model in the limit of small deformation. Furthermore, the viscous modeling is temperature activated and follows the Williams–Landel–Ferry approach in the limit of linear viscoelasticity. To simulate rheological standard experiments, a physical‐network‐based implementation into Simscape is presented. To validate the performance of the model in thermoforming, it is implemented into Fortran programming language for finite element simulation with Abaqus/Explicit. It can be shown that the simulation is able to predict the thickness in high correlation with experimental results. [ABSTRACT FROM AUTHOR]

Lightweight component design is effectively achievable through sandwich structures; many past research studies in the aerospace and racing sectors (since the 1920s) have proven it. To extend their application into the automotive and other transport industries, manufacturing cycle times must be reduced. This can be achieved by sandwich materials made of continuous fibre-reinforced thermoplastic (CFRTP) cover layers and thermoplastic honeycomb cores. To widen the application of flat thermoplastic-based sandwich panels into complex parts, a novel forming technology was developed by the Fraunhofer Institute of Microstructure of Materials and Systems (IMWS). Manufacturing defects like wrinkling and surface waviness should be minimised to achieve high reproducibility of the sandwich components. Studying different manufacturing parameters and their influence on the final part is complex and challenging to analyse through experiments, as it is time-consuming. Therefore, a finite element (FE) modelling approach is implemented to reduce such efforts. Initially, a thermoforming model is developed and validated with experimental results to check its reliability. Further, different simulations are performed to optimise the novel sandwich-forming process. In this study, a thermoplastic sandwich made of polypropylene (PP) honeycomb core and polypropylene glass fibre (PP/GF) cross-ply as cover layers was used, and its numerical model was executed in LS-DYNA software release R11.2.1. [ABSTRACT FROM AUTHOR]

Thermoforming of continuous fiber-reinforced plastics made of semi-crystalline thermoplastics has gained significant interest due to its potential for producing lightweight and high-strength components for various applications. Before thermoforming, a laminate is heated to a temperature beyond the melting point of the thermoplastic. During the subsequent forming process, the laminate is continuously cooled, which triggers non-isothermal crystallization in the semi-crystalline matrix material. In this context, the study of crystallization kinetics is crucial in identifying phase transition, analyzing exothermic latent heat during crystallization and determining inhomogeneous crystallinity distribution caused by uneven cooling in the laminate's thickness direction. This contribution primarily deals with experimental investigations, modeling and finite element simulations for characterizing the crystallization kinetics in the matrix material, Polyamide 6 and investigating the aforementioned factors. To model the crystallization kinetics, an extended form of the Avrami model, known as the modified Nakamura–Ziabicki model, is adopted. The parameters for the modified Nakamura–Ziabicki model, which depend on the local cooling rates, are identified based on fitting the model to flash DSC (differential scanning calorimetry with high cooling rates) and standard DSC non-isothermal cooling experiments. Finally, the model is implemented into the commercial FE software COMSOL Multiphysics® and the crystallinity evolution in the laminate is simulated for the process-relevant die and laminate temperatures and laminate thicknesses. [ABSTRACT FROM AUTHOR]

The paper presents a technology for the out-of-autoclave consolidation of thermoplastic composite material based on the polypropylene and fiberglass. The temperature-time regimes of consolidation and thermoforming were optimized using the differential scanning calorimetry and rheometry methods. A technique for carrying out the vacuum-thermal consolidation and press molding is described making it possible to obtain consolidated plates, which are blanks for thermoforming. [ABSTRACT FROM AUTHOR]

In this work, the thermoforming potential of PS/perlite composites was investigated. Compositions with amounts of 10% and 20% of the mineral filler were processed in a twin-screw extruder with two different screw configuration profiles, followed by compression molding. The influence of perlite content and screw configuration profiles on the flow behavior and heat capacity of the composites was evaluated through morphological, rheological, and thermal properties. The micrographs indicated that most of the perlite broke during the processing and the ones that remained intact were not bigger than 50 µm. The rheological assessment and the evaluation were decisive for the thermoforming properties characterization. The most pronounced elastic behavior identified for the composite processed in low shear conditions and with higher perlite content (P(20%wt)2:2), even in the fragments form, indicated that this composite was the one with the highest potential thermoforming. The low heat capacity value identified for P(20%wt)2:2 composite when compared to the neat-PS:2:2 reinforced that this was the most suitable composite for thermoforming considering its rapid cooling capability after molded. [ABSTRACT FROM AUTHOR]

Highlights: The influence of temperature parameters in two thermal cycles on the self-nucleation (SN) behavior was revealed. The heating rate and processing melt temperature during the first thermal cycle exhibited a synergistic effect on the SN behavior. Under appropriate conditions, both the first and second thermal cycles can generate SN behavior, but the mechanisms were different. During the secondary thermoforming of carbon fiber-reinforced polyphenylene sulfide (CF/PPS) composites, a vital material for the aerospace field, varied thermal parameters profoundly influence the crystallization behavior of the PPS matrix. Notably, PPS exhibits a distinctive self-nucleation (SN) behavior during repeated thermal cycles. This behavior not only affects its crystallization but also impacts the processing and mechanical properties of PPS and CF/PPS composites. In this article, the effects of various parameters on the SN and non-isothermal crystallization behavior of PPS during two thermal cycles were systematically investigated by differential scanning calorimetry. It was found that the SN behavior was not affected by the cooling rate in the second thermal cycle. Furthermore, the lamellar annealing resulting from the heating process in both thermal cycles affected the temperature range for forming the special SN domain, because of the refined lamellar structure, and expelled various defects. Finally, this study indicated that to control the strong melt memory effect in the first thermal cycle, both the heating rate and processing melt temperature need to be controlled simultaneously. This work reveals that through collaborative control of these parameters, the crystalline morphology, crystallization temperature and crystallization rate in two thermal cycles are controlled. Furthermore, it presents a new perspective for controlling the crystallization behavior of the thermoplastic composite matrix during the secondary thermoforming process. [ABSTRACT FROM AUTHOR]

The present work presents a new approach to the parameters of the thermoforming process for jute fiber commingled thermoplastic composites based on pressure control. Effect of gradual pressure on the microstructures of jute fiber and their mechanical properties has been investigated. The singeing of Jute yarn and subsequent co-twisting with Polypropylene (PP) was done to make reinforcement. Jute/PP composites were developed using Jute/PP commingled reinforcement. Flexural and Charpy impact tests were conducted to analyze the mechanical performance of composites made using gradual and instant loading on the compression hot press. It is found that application of gradual pressure not only decreases fiber damages, but also increase flexural strength by 82%, impact strength by 43% and impact energy by 93% as compared to composite fabricated using instant pressure. Further, the complete analysis of microstructure of fibers of both type of composites is done to compare the effect of both fabrication techniques. [ABSTRACT FROM AUTHOR]

The aim of this study was to investigate new materials from organosolv fibers, organosolv lignin, kraft fibers, and their blends. The organosolv fibers showed reprecipitated lignin on the surface, a comparably low fiber length of 0.565 mm on average, and a high fines content of 82.3%. Handsheets were formed and thermopressed at 175 °C and 50 MPa, yielding dense materials (1050–1100 kg/m3) with properties different to that of regular paper products. The thermopressing of organosolv fibers alone produced materials with similar or better tensile strength (σb = 18.6 MPa) and stiffness (E* = 2.8 GPa) to the softwood Kraft reference pulp (σb = 14.8 MPa, E* = 1.8 GPa). The surface morphology was also smoother with fewer cavities. As a result, the thermopressed organosolv fibers exhibited higher hydrophobicity (contact angle > 95°) and had the lowest overall water uptake. Combinations of Kraft fibers with organosolv fibers or organosolv lignin showed reduced wetting and a higher density than the Kraft fibers alone. Furthermore, the addition of organosolv lignin to Kraft fibers greatly improved tensile stiffness and strength (σb = 23.8 MPa, E* = 10.5 GPa), likely due to the lignin acting as a binder to the fiber network. In conclusion, new thermopressed materials were developed and tested, which show promising potential for sustainable fiber materials with improved water resistance. [ABSTRACT FROM AUTHOR]

The thermoforming process is commonly used in industry for the manufacturing of lightweight, thin-walled products from a pre-extruded polymer sheet. Many simulations have been developed to simulate the process and optimize it with computer tools. The development of testing machines has simplified the simulation of this type of process, allowing researchers to characterize the behavior of the material at different temperatures and for large deformation to be closer to the real conditions of the process. This paper presents the results of a study on the modeling of the thermoforming process for an industrial demonstrator made from a high-impact polystyrene (HIPS) polymer. The HIPS shows a mechanical behavior that depends on the temperature and strain rate. In such conditions, a thermo-hyper-viscoelastic constitutive model is used to replicate the thermoforming process of the industrial demonstrator using ABAQUS/Explicit. Its behavior is determined via various experimental tests: uniaxial tensile tests at different temperatures and strain rates and Dynamic Mechanical Analysis (DMA). A comparison between the numerical and experimental results is carried out for the evolution of film thickness. The paper concludes with a discussion of possible improvements to be considered for future simulations of the thermoforming process using Abaqus, which presents complex challenges in terms of contact and material modeling. [ABSTRACT FROM AUTHOR]

Hemp hurd fiber, a low-value waste stream from the hemp industry, has potential downstream applications as an alternative to non-renewable plastics for single-use food service ware and packaging applications. Packaging paper substrates made from chemically pulped hemp hurd, mixed in varying ratios with bleached thermomechanical radiata pine pulp were developed and tested. Handsheets were characterized using several mechanical property tests including tensile strength, tearing resistance, burst strength, short-span compression, ring crush, together with Gurley air resistance, contact angle, and Cobb60 tests. Generally, addition of hemp hurd fibers significantly improved handsheet mechanical properties. Hot-pressing of the handsheets so as to approximate molded fiber thermoforming further enhanced their performance, with pure hemp hurd handsheets having the highest mechanical properties and barrier performance. A prototype was successfully thermoformed from hemp fiber, demonstrating overall feasibility of this fibre source for molded fibre objects.

In this study, the influence of thermoforming conditions on the resulting material properties was investigated, which aimed at developing advanced wood-fiber-based materials for the replacement of fossil plastics. Two bleached softwood pulps were studied, i.e., northern bleached softwood Kraft pulp (NBSK) and chemi-thermomechanical softwood pulp (CTMP). The thermoforming conditions were varied between 2–100 MPa and 150–200 °C, while pressing sheets of 500 g/m² for 10 min to represent thin-walled packaging more closely. As our results showed, the temperature had a more pronounced effect on the CTMP substrates than on the Kraft pulp. This was explained by the greater abundance of lignin and hemicelluloses, while fibrillar dimensions and the fines content may play a role in addition. Moreover, the CTMP exhibited an optimum in terms of tensile strength at intermediate thermoforming pressure. This effect was attributed to two counteracting effects: 1) Improved fiber adhesion due to enhanced densification, and 2) embrittlement caused by the loss of extensibility. High temperatures likely softened the lignin, enabling fiber collapse and a tighter packing. For the Kraft substrates, the tensile strength increased linearly with density. Both pulps showed reduced wetting at elevated thermoforming temperature and pressure, which was attributed to hornification and densification effects. Here, the effect of temperature was again more pronounced for CTMP than for the Kraft fibers. It was concluded that the thermoforming temperature and pressure strongly affected the properties of the final material. The chemical composition of the pulps will distinctly affect their response to thermoforming, which could be useful for tailoring cellulose-based replacements for packaging products.

The increasing concern over environmental sustainability has prompted various industries to reassess their practices and explore greener alternatives. Dentistry, as a significant contributor to waste generation, is actively seeking methods to minimize its environmental footprint. This paper examines the environmental implications of clear aligner therapy (CAT) in orthodontics and explores strategies to prioritize sustainability in aligner manufacturing and usage. CAT has gained popularity as a viable alternative to traditional fixed appliances due to advancements in biomaterials and computer-aided design (CAD) and manufacturing (CAM) technologies. The global market for clear aligners is expanding rapidly, with significant growth projected in the coming years. To address these challenges, this paper proposes adopting the principles of reduce, reuse, recycle, and rethink (4Rs) in orthodontic practices. Strategies such as minimizing resource consumption, incorporating recycled materials, and promoting proper aligner disposal and recycling can significantly reduce environmental harm. This paper explores emerging technologies and materials to mitigate the environmental impacts of CAT. Additionally, initiatives promoting aligner recycling and repurposing offer promising avenues for reducing plastic waste and fostering a circular economy. In conclusion, while CAT offers numerous benefits in orthodontic treatment, its environmental impact cannot be overlooked. By implementing sustainable practices and embracing innovative solutions, the orthodontic community can contribute to a more environmentally conscious future while continuing to provide quality care to patients.

The quality of woven carbon fiber fabric/polycarbonate thermoplastic composites after thermoforming and demolding was investigated using finite element simulation and the Taguchi orthogonal array. The simulation utilized a discrete approach with a micro-mechanical model to describe the deformation of woven carbon fabric, combined with a resin model. This simulation was validated with bias extension tests at five temperatures. The thermoforming process parameters considered were blank temperature, mold temperature, and blank holding pressure, with three levels for each factor. Optimal values for the fiber-enclosed angle, spring-back angle, mold shape fitness, and the strain of the U-shaped workpiece were desired. The results indicated that the comparison of the stress-displacement curve of bias extension tests verified the application of the discrete finite element method. Results from the Taguchi array indicated that blank holding pressure was the dominant parameter, with the optimal value being 1.18 kPa. Blank temperature was the second most significant factor, effective in the range of 160 °C to 230 °C, while mold temperature had a minor effect. Furthermore, the four quality values are dependent and have a similar trend. The best combination was identified as a blank holding press of 1.18 kPa, a blank temperature of 230 °C, and a mold temperature of 190 °C.

This paper examined the mechanical properties of wrist–hand orthoses made from polylactic acid (PLA) and polyethylene terephthalate glycol (PETG), produced through material extrusion with infill densities of 55% and 80%. These orthoses, commonly prescribed for wrist injuries, were 3D-printed flat and subsequently thermoformed to fit the user’s hand. Experimental and numerical analyses assessed their mechanical resistance to flexion after typical wear conditions, including moisture and long-term aging, as well as their moldability. Digital Imaging Correlation investigations were performed on PLA and PETG specimens for determining the characteristics required for running numerical analysis of the mechanical behavior of the orthoses. The results indicated that even the orthoses with the lower infill density maintained suitable rigidity for wrist immobilization, despite a decrease in their mechanical properties after over one year of shelf life. PLA orthoses with 55% infill density failed at a mean load of 336 N (before aging) and 215 N (after aging), while PETG orthoses did not break during tests. Interestingly, PLA and PETG orthoses with 55% infill density were less influenced by aging compared to their 80% density counterparts. Additionally, moisture and aging affected the PLA orthoses more, with thermoforming, ongoing curing, and stress relaxation as possible explanations related to PETG behavior. Both materials proved viable for daily use, with PETG offering better flexural resistance but posing greater thermoforming challenges.

This study aims to establish and optimize a process for the fabrication of 3D microstructures of the biocompatible polymer Parylene C using hot embossing techniques. The different process parameters such as embossing temperature, embossing force, demolding temperature and speed, and the usage of a release agent were optimized, utilizing adhesive micropillars as a use case. To enhance compatibility with conventional semiconductor fabrication techniques, hot embossing of Parylene C was adapted from conventional stainless steel substrates to silicon chip platforms. Furthermore, this adaptation included an investigation of the effects of the hot embossing process on metal layers embedded in the Parylene C, ensuring compatibility with the ultra-thin Parylene printed circuit board (PCB) demonstrated previously. To evaluate the produced microstructures, a combination of characterization methods was employed, including light microscopy (LM) and scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Fourier-transform infrared spectroscopy (FTIR). These methods provided comprehensive insights into the morphological, chemical, and structural properties of the embossed Parylene C. Considering the improved results compared to existing patterning techniques for Parylene C like plasma etching or laser ablation, the developed hot embossing approach yields a superior structural integrity, characterized by increased feature resolution and enhanced sidewall smoothness. These advancements render the method particularly suitable for diverse applications, including but not limited to, sensor optical components, adhesive interfaces for medical wearables, and microfluidic systems.

Process-induced defects during thermoforming are widespread problems in laminate manufacturing. The aim of this study is to describe the effects of holding time and pressure on several properties of the manufactured laminate. A design of experiments is performed, followed by an analysis of variance to examine significant effects. Subsequently, a regression model is created to predict the laminate's properties, which is also validated. A significant interaction between holding time and pressure is determined for the resulting tensile strength and elongation at break with a p-value of 1.52 · 10 − 16 and 0.02 , respectively. The highest values of tensile strength and elongation at break are found for low settings of holding time and pressure. The fibre volume fraction is not affected by the process parameters. As holding time and pressure increase, significant fibre misalignment takes place, leading to a decrease of the mechanical properties. The regression model corresponds well with the validation and a tensile strength of 1049 MPa with an elongation at break of 2.3 % is reached. [ABSTRACT FROM AUTHOR]

The effectiveness of clear aligners in correcting malocclusions is closely linked to the properties of the materials used to make them. The polymers used in the manufacture of clear aligners have well-established properties. However, the process of manufacturing clear aligners, known as thermoforming, involves thermal and mechanical shocks that may alter these properties. The objective of this study was to evaluate the effects of thermoforming on the mechanical, optical, chemical, and morphological properties of sixty PET-G specimens. The study compared the thickness, weight, absorbance, chemical structure, surface roughness, elastic modulus, yield strength, and breaking load of thirty thermoformed specimens with thirty non-thermoformed specimens. The study introduces a new approach by using standardized samples to analyze both chemical and physical properties. The results showed statistically significant differences in thickness (−15%), weight (−11%), and surface roughness (+1233% in roughness average; +1129% in RMS roughness) of the material. Additionally, a correlation was found between reduction in thickness and increase in opalescence. There was no significant change in the functionality of the aligners after thermoforming, as no significant mechanical changes were found. However, the increase in surface roughness may lead to plaque and fluid accumulation and worsen the fit of the aligners. [ABSTRACT FROM AUTHOR]

The spring-in behavior of woven carbon fiber/polycarbonate thermoplastic composite is investigated by both the experiment and simulation ways. These thermoplastic composite plates are thermoformed into V-shaped structures, and the final bending angle is measured after demolding. In the finite element simulation to describe the thermoforming and spring-in behavior of the composite, the discrete approach is adopted to simulate the behavior of woven carbon fabric and combined with a resin model. The results from both the experiment and the simulation indicate the spring-in behavior of this thermoplastic composite. For [(±45)]6 blanks, the spring-in angle is around 2.60° for a 60-degree V-shape and around 1.72° for a 90-degree V-shape. For [(0/90)]6 blanks, the spring-in angle is around 2.38° and 1.19° for 60-degree and 90-degree V-shapes, respectively. The [(±45)]6 blank always has a slightly higher spring-in angle than the [(0/90)]6 blank, even though the difference is small. The finite element results show 6% to 12% differences with the experimental values if the spring-in angle is used, and the error is less than 0.6% when the bending angle is compared. By using the present finite element analysis, the results indicate that the stacking sequence could have an evident effect on the spring-in angle, and symmetric laminates have less spring-in effect as compared to their unsymmetric counterparts. [ABSTRACT FROM AUTHOR]

Dual-component epoxy resins are widely used for bonding different materials in automotive interior processing. However, due to the complexity and variability of automotive interior parts, uneven temperature distribution on curved surfaces during the thermoforming process can lead to uneven thermal stress distribution, damaging the interior components. This study focuses on addressing the damage issues caused by uneven thermal stress distribution during the thermoforming of automotive interior components. By monitoring the temperature and strain on the adhesive surface of the interior components during processing, using sensors and combining the readings with a finite element simulation, damage to the adhesive during processing was simulated. Based on this, a segmented thermoforming method for the model surface was employed, but it was found that this method did not significantly reduce the level of damage to the adhesive during application. Building upon the segmented simulation, significant results were achieved by applying temperature modulation at a certain frequency to adjust the damage of the interior components during processing. The techniques used in this study successfully reduced the unevenness of the adhesive surface temperature, improved the performance of the adhesive during application through segmented optimization and the application of ultrasound-assisted techniques, and markedly reduced the manufacturing process's energy consumption. [ABSTRACT FROM AUTHOR]