Mold Surface Research Articles

Laser-assisted direct roller imprinting of large-area microstructured optical surfaces

In this study, a high-throughput fabrication method called laser-assisted direct roller imprinting (LADRI) was developed to lower the cost of nanoimprinting large-area polymer films and to address problems associated with nanoimprinting, namely, microstructural damage and precision in flatness of entire film. With LADRI, the laser directly heats the microstructured surface of the roller mold, which heats and melts the surface of a polymethyl methacrylate (PMMA) film to replicate the microstructures on the mold rapidly. In this study, the effects of laser power density, scanning speed, size of the microstructures, and contact pressure on the replication speed were investigated experimentally. The replication speed increased as the power and scanning speed increased. However, because the film required heating until it filled the entire depth of the microstructure, an appropriate replication speed was necessary. This result was supported by simulation of the temperature distribution inside the mold and the PMMA using transient heat conduction analyses. To demonstrate the applications of LADRI, two different optical surfaces were replicated: an antireflection (AR) structure with conical structures sized several hundred nanometers and a light-extraction structure with a microlens array (MLA) comprising 10 μm lenses, for display and illumination, respectively. The replication degree of the MLA was governed by the contact pressure. Polymer flow simulation indicated that the heat conduction and flow speeds of the melted PMMA surface were comparable within several tens of micrometers. In addition, the reflectivity of the AR structure decreased from 4 to 0.5%, and the light intensity of the light-extraction structure increased by a factor of 1.47.

The Start-Up Phase of Aluminum Billet Production Using Direct Chill Casting

Direct chill (DC) casting has been considered as one of the promising casting methods that can be used to produce aluminum alloys billet. The process is conducted by pouring aluminum metal into a water-cooled mold. The billet shell begins to form when molten aluminum contact directly with the mold (this is also known as primary cooling). Afterward, the starting block is pulled downwards at a specified casting speed to achieve desired aluminum billet. The start-up phase during the DC casting process is considered a crucial step since it may determine the formation of defects in the casting products. This research aims to investigate the casting defects on the aluminum alloy that were formed during the start-up process of DC casting. The results show that the billet failed to form following the downward movement of starting block. Meanwhile, the billet tended to stick to the mold wall due to several factors, such as too low a pouring temperature, a less-round mold shape, the poor quality of the hot top and graphite ring, and the water that entered the mold during the casting process. It also noted several markers of the casting defects that occurred during the DC casting process such as liquation or bleeding, cold folding, billet stuck in the mold, butt structure, and rough billet surface.

The Implementation of Neural Networks for Polymer Mold Surface Evaluation.

This paper presents the measurement and evaluation of the surfaces of molds produced using additive technologies. This is an emerging trend in mold production. The surfaces of such molds must be treated, usually using laser-based alternative machining methods. Regular evaluation is necessary because of the gradually deteriorating quality of the mold surface. However, owing to the difficulty in scanning the original surface of the injection mold, it is necessary to perform surface replication. Therefore, this study aims to describe the production of surface replicas for in-house developed polymer molds together with the determination of suitable descriptive parameters, the method of comparing variances, and the mean values for the surface evaluation. Overall, this study presents a new summary of the evaluation process of replicas of the surfaces of polymer molds. The nonlinear regression methodology provides the corresponding functional dependencies between the relevant parameters. The statistical significance of a neural network with two hidden layers based on the principle of Rosenblatt's perceptron has been proposed and verified. Additionally, machine learning was utilized to better compare the original surface and its replica.

Optimal Sensor Placement for Mold Level in Continuous Casting

For high product quality in the continuous casting of steel, it is important that the liquid steel level in the mold remains constant and that its surface is fat. A slag layer on top of the liquid steel surface prevents direct optical measurement of the surface. However, knowing the mold level and surface shape is essential for quality monitoring and feedback control. The current paper addresses the optimal placement of mold-level sensors, given that their number is limited. The actual estimation of the surface shape is performed by an observer that receives mold-level measurements as input. The computed optimal sensor positions are validated based on experimental data from a full-scale laboratory water model of the continuous caster.

TPP-Based Microfluidic Chip Design and Fabrication Method for Optimized Nerve Cells Directed Growth

Microfluidic chips offer high customizability and excellent biocompatibility, holding important promise for the precise control of biological growth at the microscale. However, the microfluidic chips employed in the studies of regulating cell growth are typically fabricated through 2D photolithography. This approach partially restricts the diversity of cell growth platform designs and manufacturing efficiency. This paper presents a method for designing and manufacturing neural cell culture microfluidic chips (NCMC) using two-photon polymerization (TPP), where the discrete and directional cell growth is optimized through studying the associated geometric parameters of on-chip microchannels. This study involves simulations and discussions regarding the effects of different hatching distances on the mold surface topography and printing time in the Describe print preview module, which determines the appropriate printing accuracy corresponding to the desired mold structure. With the assistance of the 3D maskless lithography system, micron-level rapid printing of target molds with different dimensions were achieved. For NCMC with different geometric parameters, COMSOL software was used to simulate the local flow velocity and shear stress characteristics within the microchannels. SH-SY5Y cells were selected for directional differentiation experiments on NCMC with different geometric parameters. The results demonstrate that the TPP-based manufacturing method efficiently constructs neural microfluidic chips with high precision, optimizing the discrete and directional cell growth. We anticipate that our method for designing and manufacturing NCMC will hold great promise in construction and application of microscale 3D drug models.

Study on the influence of injection molding parameters on the warpage using simulation and Taguchi method

Injection moulding (IM) is a processing technique produced from polymeric products. Warpage defect (WD) is the defect that generally occurs during the IM process due to the inappropriate processing parameters of the melt temperature, mould surface temperature, packing pressure, injection pressure, and packing pressure time. This paper investigates the IM parameters that influence product warpage by combining the simulation, analysis of variance, signal-to-noise analysis, and Taguchi method. The simulation process was performed by Moldflow software. The product material is high-density polyethylene. The WD has been predicted and optimized to enhance product quality. Melt temperature and packing pressure time are the factors that acrimoniously influenced the warpage of the product. The results show that the packing pressure time and melt temperature have the highest effects on the WD by the contributions of 48.94% and 37.48%, respectively. The optimal IM parameters are scanned again with the WD abated at about 1.2%. The mathematical formula has been constructed to predict the WD with the reflection of acceptable values of 86.29%. The research hopes that the results have been applied to designing and fabricating the plastic product in the near future.

Air-through-precursor suction-augmented replica molding for fabrication of anisotropic microparticles in gas-impermeable molds.

Replica molding (REM) is a powerful technique for fabricating anisotropic microparticles. Current REM methods rely on the use of gas-permeable molds for defect-free castings and facile particle recovery. However, they often encounter limitations on either technical accessibility or producible particle diversity. While the use of gas-impermeable molds presents a promising solution to these challenges, particle production within such molds necessitates addressing two critical issues: precursor loading and particle recovery. This study introduces a REM methodology specifically tailored to enable the production of anisotropic microparticles within gas-impermeable molds. To address the issue of precursor loading, our approach incorporates the air-through-precursor suction method, employing a degassed polydimethylsiloxane block to effectively eliminate air bubbles trapped in microwells. Additionally, fluorosilane pretreatment of the mold surface, along with the polyvinyl alcohol film formation, significantly enhances particle recovery up to 249-fold while ensuring particle homogeneity. This methodology demonstrates high adaptability to various gas-impermeable molds and curing techniques. The practical feasibility is illustrated through the successful production of functional composite microparticles that can be effectively utilized for oxygen sensing and self-assembly, challenging in conventional REM.

Studying the new modes of deposition of plasma coatings

Problem. This paper considers using ion-plasma spraying of mold surfaces. This makes it possible to replace scarce and expensive tungsten-containing steels with other materials. Purpose. The purpose is to study the possibility of using the KIB method to increase the stability of die-casting molds, to establish the possibility of replacing scarce, expensive tungsten-containing steels with other materials. Materials and methods. 4Х5МФС and 5ХНМ steel grades were chosen as materials for copper alloy die-casting molds in this work. The choice of these steel grades is due to the fact that these steels do not contain tungsten due to its sharply increased scarcity and limited molybdenum content, and they also meet the requirements for the substrate material on which the titanium nitride coating is applied. Coatings were applied to samples for laboratory tests and die-casting mold parts by the condensation method with ion bombardment. Titanium nitride is applied at different partial nitrogen pressures – from 3×10-3 to 1 Pa to determine the required nitrogen pressure, which ensures that the working surfaces of mold parts receive coatings with the best performance characteristics. The coatings obtained at different nitrogen pressures differ in the amount and size of the droplet phase. Results of experiments. The largest amount of the droplet phase containing α-Ti is observed in coatings obtained at nitrogen pressures of 3×10-3 Pa, 3×10-2 Pa. An increase in nitrogen pressure (4×10-1 Pa, 1 Pa) significantly reduces the level of microdistortions of the crystal lattice in the coating, and its plasticity increases. In this regard, the coating's brittleness is reduced at a sufficiently high hardness. Results. The titanium nitride coating obtained at a nitrogen pressure of 1 Pa is the most effective in protecting the working surfaces of mold parts from destruction. Laboratory tests have shown that the titanium nitride coating applied under optimal process parameters increases the corrosion resistance of mold parts to which it is applied by 3 times and the scale resistance by 2-4 times.

Polymer/mold interfacial heat transfer during injection molding

AbstractAn experimental injection molding setup was designed and fabricated. The purpose of the setup is to cast polymer components and estimate the polymer/mold interfacial heat flux transients during injection molding. The mold plate is instrumented with K‐type thermocouples to record its thermal history continuously during the cyclic process. Experiments were performed at a melt injection temperature of 280°C. Velocity and shear rate profiles were determined to assess the flow behavior of the melt. The spatiotemporal heat flux transients at the interface and the mold surface temperature were estimated using measured temperature data inside the mold as input to an inverse heat conduction problem. The estimated boundary heat flux transients were used to numerically simulate the polymer melt's cooling behavior. From the estimated heat flux and surface temperatures, heat transfer coefficients (HTC) were determined. The peak value of the HTC was 5775 W/m2K and occurred at a mold surface temperature of 35.7°C and polymer surface temperature of 47.4°C. The evolution of the air gap at the interface was quantified using an exponential fit. The estimated air gap width corresponding to peak HTC was about 4 μm and increased to about 100 μm towards the end of the solidification. While the peak heat flux is associated with the start of the formation of polymer skin on the mold surface, the peak HTC corresponds to the onset of nucleation of the air gap or a nonconforming contact.Highlights An experimental setup to study heat transfer during injection molding. Spatiotemporal heat flux transients (q) were estimated during injection molding. Polymer temperatures were simulated using q, and HTC was determined. The peak HTC indicated the onset of nucleation of an air gap. Evolution of air gap at the interface was modeled using an exponential fit.

Finite Element Formulation and Computation of Superplastic Metal Forming Processes with Optimized Rate of Deformation Control

Superplastic forming (SPF) is a material forming technique that uses superplastic exceptional elongations and deformation characteristics to form superplastic materials into certain shapes. The combination of superplastic forming with diffusion bonding (SPF/DB) gives rise to an almost unlimited extension of superplastic forming since more integral lightweight cellular structural components can be manufactured. This paper discusses numerical modelling of the mechanism of superplasticity in metallic materials. The SPF computational method based on the finite element technique augmented with the controlling rate of deformations is developed to examine a range of design or operating conditions leading to more economical forming processes. The non-Newtonian ‘viscous flow’ material is used to model the constitutive of superplastic material during the forming period. The contact mechanics between the sheet material and the mold surface and the intersheet material contact mechanics are imposed using the penalty control method, in which the sticking contact boundary conditions are employed. The space discretization is carried out using the membrane element under plane strain and axisymmetric flow stress conditions, while the implicit time integration technique is utilized to follow the shape changes of the formed sheet material. The validation of the SPF finite element formulation was performed by comparing it with the available analytical solution of Hydraulic Free Bulging of Thin strips. The SPF of a hemispherical dome made of 7475 aluminum sheet alloy was performed to demonstrate the forming process as well as to validate the results obtained between the SPF finite element numerical simulation and the experimental results. The SPF/DB of the multicell component section is considered in the final part.

Fabrication of Polymethyl Methacrylate (PMMA) Hydrophilic Surfaces Using Combined Offset-Tool-Servo Flycutting and Hot Embossing Methods.

Polymethyl methacrylate (PMMA) is a material with good surface wettability and has unique and widespread applications in industrial fields. However, fabricating this material in an environmentally friendly way while maintaining its mechanical robustness remains a challenging task. One effective way is through the rational design of microstructure surfaces. The current study fabricated a pyramid microstructure array on a mold surface using offset-tool-servo flycutting, which was then combined with hot embossing to replicate an inverted pyramid microstructure array on a PMMA surface. Firstly, a toolpath compensation algorithm was developed to linearize the arc toolpath and reduce the cost of ultra-precision lathe. Then, the algorithm was further developed to achieve automatic linear toolpath intersection, aiming to ensure the machining accuracy and improve machining efficiency. An experiment testing the linear toolpath intersecting at 90° was conducted, fabricating a pyramid microstructure array with nanoscale roughness on the mold surface. This surface was then employed for replicating an inverted pyramid microstructure array on the PMMA surface using hot embossing. Furthermore, the accuracy of replication was evaluated, and the experimental results demonstrated excellent replication fidelity, exceeding 98%. The microstructural surface of the PMMA exhibited a change in surface wettability. The wettability test showed a water-droplet contact angle reduction from 84.8° ± 0.1° to 56.2° ± 0.1°, demonstrating a good hydrophilic effect. This study introduces a novel, environmentally friendly and high-precision method to fabricate a functional PMMA surface with an inverted pyramid microstructure array. The results of this study also provide strong technical support and theoretical guidance for micro-nanostructure functional surface machining and replicating.

Effect of fiber entanglement in chopped glass fiber reinforced composite manufactured via long fiber spray-up molding

Long Fiber Spray-up Molding (LFSM) deviates from the conventional approach in liquid composite molding (LCM) processes by utilizing extremely long chopped strands of fibers as the primary reinforcement material in its fabrication process. In LFSM, chopped fibers are impregnated with resin that is sprayed vertically downwards before reaching the mold surface. The spraying mechanism is mounted on an actuator, which is capable of spraying freely in any specified pattern or direction. Under LFSM, it is extremely difficult to fabricate a composite part with uniformly distributed fiber content throughout its volume. The consequences of the non-uniform fiber volume distribution arise from the fiber entanglement as the length of the fiber reaches up to 100 mm in LFSM. In this study, the effect of fiber entanglement during LFSM was analyzed through various approaches. This included measuring the coefficient of friction between fibers in contact and examining the correlation between fiber lengths and the number of intersections. Furthermore, the viscoelastic properties of the uncured composite part were assessed by experimenting with the influence of viscosity on fiber length during compression molding. The results were then computed, modeled, and visualized in MATLAB, considering variations in viscosity and fiber length, both before and after compression molding.

Exploring the effect of mold fermentation on the taste and flavor properties of traditional Japanese smoked-dried bonito (katsuobushi)

The present study aimed to investigate the differences in the physicochemical properties, taste characteristics, and flavor compounds of Katsuobushi, a traditional Japanese smoked-dried bonito product, including Arabushi (unfermented) and Karebushi (mold-fermented), as well as the effects of surface fermentation on the internal, middle, and external of Karebushi products. The findings showed that mold fermentation could be an effective method for improving the color characteristics of Katsuobushi. Karebushi possessed the highest content of flavorful amino acids and nucleotides, which synergistically enhanced the level of umami taste profiles. Notably, the EUC value of the exterior (12.51 g MSG/100 g) is significantly higher than that of the interior (8.81 g MSG/100 g), which means that the surface fermentation imparts a stronger umami taste to the exterior. In addition, the abundance of organic acids in the Karebushi helped to improve the umami and sweet tastes. The electronic nose and fingerprint profiles revealed that Karebushi was found to have higher types and contents of flavor compounds than Arabushi. 3-Methyl-1-butanol, 2,5-dimethylpyrazine, and α-pinene are the characteristic volatile aroma components of Karebushi, contributing to the exceptional malty, nutty, and roasted aroma. This study may be conducive to a better understanding of the effect of mold surface fermentation on the flavor characteristics of Katsuobushi, and provide a theoretical basis for the development of appropriate start cultures.

Effect of mold temperature on properties of hybrid biocomposites from semicrystalline polymers and agro-industrial by-products

The surface temperature of the mold is a critical processing parameter that significantly influences the quality of composites during injection molding. Therefore, this study aimed to investigate the effect of mold surface temperature on the properties of hybrid biocomposite materials prepared by incorporating polypropylene-PP with agro-industrial by-products such as rice husks-RH and fique powder-FP using co-rotating twin-screw extrusion and injection molding. While this article focuses on PP as the polymeric matrix, the methodology employed in this study can also be applied to investigate the effect of mold surface temperature on the properties of other polymers used in the production of hybrid composites via injection molding as biobased or biodegradable plastics. The mechanical characterization reveals that the utilization of higher mold temperatures and the hybridization of RH and FP result in an increase in the elastic modulus of up to 30% compared to PP. Also, thermal, viscoelastic, morphological, and HDT characterization revealed that higher surface mold temperature led to changes in PP crystallinity, and a better hybrid biocomposites performance. This study highlights the potential of mold surface temperature controlling and agro-industrial by-products hybridization for the design and production of higher quality and sustainable products using injection molding.

A study of Ru–Cr protective coatings for precision glass molding

This study evaluates the performance of Ru–Cr nanolayers used as protective coatings for precision glass molding (PGM) applications. Because the direct growth of Cr-oxide from Cr at high temperatures does not yield a dense oxide scale, Ru is employed as a diffusion barrier to stabilize the growth process. The fabricated coatings were subjected to annealing at 750 °C for different durations, with the coverage of aluminosilicate glass (ASG) pieces. During the annealing process, the outward diffusion of Cr resulted in the formation of thin and stable chromium oxide (Cr2O3) films, which remained unadhered to the glass pieces. Therefore, the Ru–Cr bilayer is a cost-effective coating design to protect mold surfaces in PGM. Detailed analysis using transmission electron microscopy (TEM) revealed that while columnar grains with vertical grain boundaries facilitate the outward diffusion of Cr, a thick Ru layer can effectively hinder Cr diffusion leading to a stable oxide film at a high temperature. A diffusion-oxidation phase-field model quantitatively elucidates oxide film thickness dependence on Ru thickness (>600 nm). Thinner Ru layers (<600 nm) display limited Ru thickness influence and some metallic Cr content in the scales, causing incomplete densification.

In vitro formation and extended culture of highly metabolically active and contractile tissues.

3D cell culture models have gained popularity in recent years as an alternative to animal and 2D cell culture models for pharmaceutical testing and disease modeling. Polydimethylsiloxane (PDMS) is a cost-effective and accessible molding material for 3D cultures; however, routine PDMS molding may not be appropriate for extended culture of contractile and metabolically active tissues. Failures can include loss of culture adhesion to the PDMS mold and limited culture surfaces for nutrient and waste diffusion. In this study, we evaluated PDMS molding materials and surface treatments for highly contractile and metabolically active 3D cell cultures. PDMS functionalized with polydopamine allowed for extended culture duration (14.8 ± 3.97 days) when compared to polyethylamine/glutaraldehyde functionalization (6.94 ± 2.74 days); Additionally, porous PDMS extended culture duration (16.7 ± 3.51 days) compared to smooth PDMS (6.33 ± 2.05 days) after treatment with TGF-β2 to increase culture contraction. Porous PDMS additionally allowed for large (13 mm tall × 8 mm diameter) constructs to be fed by diffusion through the mold, resulting in increased cell density (0.0210 ± 0.0049 mean nuclear fraction) compared to controls (0.0045 ± 0.0016 mean nuclear fraction). As a practical demonstration of the flexibility of porous PDMS, we engineered a vascular bioartificial muscle model (VBAM) and demonstrated extended culture of VBAMs anchored with porous PDMS posts. Using this model, we assessed the effect of feeding frequency on VBAM cellularity. Feeding 3×/week significantly increased nuclear fraction at multiple tissue depths relative to 2×/day. VBAM maturation was similarly improved in 3×/week feeding as measured by nuclear alignment (23.49° ± 3.644) and nuclear aspect ratio (2.274 ± 0.0643) relative to 2x/day (35.93° ± 2.942) and (1.371 ± 0.1127), respectively. The described techniques are designed to be simple and easy to implement with minimal training or expense, improving access to dense and/or metabolically active 3D cell culture models.

Large aspect ratio microscale 1–3 piezoelectric arrays prepared by soft mold combined with UV curing

1-3 piezoelectric composites, as materials with integrated structural/functional characteristics, are typically used to manufacture ultrasonic transducers. As a core sensitive element, the structural dimensions as well as the molding quality of the 1–3 piezoelectric array, will directly affect the transducer's operating performance. In this paper, an improved soft mold process is proposed to prepare lead zirconate titanate (PZT) microscale 1–3 piezoelectric arrays by a soft mold combined with UV curing process. Firstly, the rheological behavior of PZT ceramic suspension and the preparation process of polydimethylsiloxane (PDMS) soft mold were studied. The surface contact angle of the Si master mold modified by trimethylchlorosilane (TMCS) was significantly increased, facilitating the peeling of the PDMS soft mold from the Si master mold surface, thus improving the surface quality of the PDMS soft mold. Then, the sintering process, microstructure, and electrical properties of microscale 1–3 piezoelectric arrays were systematically investigated. The perpendicularity and integrity of the piezoelectric arrays were improved by an optimized sintering process, and the arrays had micropillar diameters as small as 8 μm and aspect ratios over 7.5. The electrical properties of the piezoelectric composites with thicknesses of 55 μm and 42 μm were analyzed to obtain their resonant frequencies fs of 33.8 MHz and 41.3 MHz, respectively. The developed novel soft mold process can realize the preparation of microscale 1–3 piezoelectric arrays with fine structure and large aspect ratios, which are expected to fabricate high-frequency ultrasonic transducers.

Storage stability evaluation of conventional and reduced calorie peda (a dairy dessert) under different packaging conditions

Peda is a calorie dense heat desiccated dairy dessert popular in the Indian subcontinent. Reduced calorie peda (RCP) was developed in previous research for diabetic and calorie conscious populace using low fat khoa, high intensity sweetener and bulking agents. Peda is conventionally packaged in cardboard boxes; however, it possesses inferior barrier properties leading to rapid deterioration of the product. Therefore, in the present study, conventional peda packaged in cardboard box was compared with RCP packaged in cardboard box, laminated plastic tray with and without modified atmospheric packaging (MAP). The samples were stored at 30 ± 1 °C and analysed for physico-chemical, instrumental colour and texture, microbiological and sensory attributes. Samples having ambient air in their head space were spoiled by surface mold growth and those having MAP were spoiled by the development of off (sour) flavour. Quality attributes of RCP deteriorated rapidly than conventional peda in cardboard box. Laminated plastic trays in combination with MAP significantly (p < 0.05) delayed product's deterioration and led to three-fold increase in shelf life as compared to cardboard packaging.

Optimization of Port Angle for Narrow‐Width Mold Flow Field under High Casting Speed Based on Large Eddy Simulation and High‐Temperature Measurement of Velocity

Herein, the flow field of the mold through numerical simulation and high‐temperature measurement is studied, and discussed the effects of casting speed and port angle on the flow field of the 880 mm wide mold. The velocities near the mold surface of the numerical simulation are in good agreement with those of the high‐temperature measurement. As the casting speed continues to increase, the surface flow velocity of the mold also increases. When the casting speed increases to 1.8 m min−1, the flow pattern of the mold exhibits a strong double‐roll flow, the strong jet increases the risk of argon bubbles being captured by the solidification front inside the mold. As the port angle of the submerged entry nozzle (SEN) gradually increases, the surface flow velocity of the mold gradually decreases. By appropriately increasing the port angle of the SEN to 20°, the surface flow velocity of the mold decreases, and the stability of the molten steel–slag interface improves. At the same time, there is no significant change in the distribution of argon bubbles, and the removal rate of inclusions is the highest.

Quasistatic deflection analysis of slender ball-end milling cutter

In this study, a quasistatic force-deflection interaction model considering cutting and elastic force was proposed to analyze and compensate for the quasistatic deflection of slender ball-end milling cutter. The theoretical waveforms and peaks of cutting force considering the force-deflection interactions were consistent with the experimental results. The deflection of slender ball-end milling cutter significantly reduces the cutting force, and the Pearson's correlation coefficient between the difference in the peak cutting force and maximum deflection in radial is larger than that of in feed directions. An analysis of the machining error of a cylindrical surface revealed that the deflection of slender ball-end milling cutter had a considerable effect on the machining error, and the compensation of slender cutter deflection effectively reduced the amplitude and fluctuation of the machining error. This work can provide a useful guidance for machining error control in the ball-end milling process of mold surfaces with deep cavities.