Replication Of Micro Features Research Articles

Characterisation of microneedle replication and flow behaviour in ultrasonic micro-injection moulding through design of experiments

This research investigates the impact of process parameters on ultrasonic micro-injection moulding (u-μIM) by studying microneedle replication efficiency, temperature evolution during moulding, melt flow consistency and sonication behaviour. The experimentation comprises of a full-factorial design of experiments using three process variables: sonication time, mould temperature and injection force. The current study presents that; (i) mould temperature was found to be the most influential parameter to tune and optimise micro-feature replication, (ii) consistent ultrasonic micromoulding flows can be achieved using higher mould temperatures, (iii) injection force is a key parameter influencing sonication frequency, a critical aspect of the ultrasonic method to obtain a repeatable manufacturing process. These outcomes will be a datum during development of the manufacturing processes for specific products using the ultrasonic method. The research presented here takes a unique approach to characterise the ultrasonic method for the development of this novel technique, particularly for microneedle patch and medical device production. With this increased level of understanding of u-μIM process characteristics, the method can become an energy efficient and cost-effective alternative to conventional micro-injection moulding processes for delivering high-quality, miniature components.

Rapid microfluidics prototyping through variotherm desktop injection molding for multiplex diagnostics.

In this work, we demonstrate an inexpensive method of prototyping microfluidics using a desktop injection molding machine. A centrifugal microfluidic device with a novel central filling mechanism was developed to demonstrate the technique. We overcame the limitations of desktop machines in replicating microfluidic features by variotherm heating and cooling the mold between 50 °C and 110 °C within two minutes. Variotherm heating enabled good replication of microfeatures, with a coefficient of variation averaging only 3.6% attained for the measured widths of 100 μm wide molded channels. Using this methodology, we produced functional polystyrene centrifugal microfluidic chips, capable of aliquoting fluids into 5.0 μL reaction chambers with 97.5% accuracy. We performed allele-specific loop-mediated isothermal amplification (AS-LAMP) reactions for genotyping CYP2C19 alleles on these chips. Readouts were generated using optical pH sensors integrated onto chips, by drop-casting sensor precursor solutions into reaction chambers before final chip assembly. Positive reactions could be discerned by decreases in pH sensor fluorescence, thresholded against negative control reactions lacking the primers for nucleic acid amplification and with time-to-results averaging 38 minutes. Variotherm desktop injection molding can enable researchers to prototype microfluidic devices more cost-effectively, in an iterative fashion, due to reduced costs of smaller, in-house molds. Designs prototyped this way can be directly translated to mass production, enhancing their commercialization potential and positive impacts.

Experimental Validation of Injection Molding Simulations of 3D Microparts and Microstructured Components Using Virtual Design of Experiments and Multi-Scale Modeling.

The increasing demand for micro-injection molding process technology and the corresponding micro-molded products have materialized in the need for models and simulation capabilities for the establishment of a digital twin of the manufacturing process. The opportunities enabled by the correct process simulation include the possibility of forecasting the part quality and finding optimal process conditions for a given product. The present work displays further use of micro-injection molding process simulation for the prediction of feature dimensions and its optimization and microfeature replication behavior due to geometrical boundary effects. The current work focused on the micro-injection molding of three-dimensional microparts and of single components featuring microstructures. First, two virtual a studies were performed to predict the outer diameter of a micro-ring within an accuracy of 10 µm and the flash formation on a micro-component with mass a 0.1 mg. In the second part of the study, the influence of microstructure orientation on the filling time of a microcavity design section was investigated for a component featuring micro grooves with a 15 µm nominal height. Multiscale meshing was employed to model the replication of microfeatures in a range of 17–346 µm in a Fresnel lens product, allowing the prediction of the replication behavior of a microfeature at 91% accuracy. The simulations were performed using 3D modeling and generalized Navier–Stokes equations using a single multi-scale simulation approach. The current work shows the current potential and limitations in the use of micro-injection molding process simulations for the optimization of micro 3D-part and microstructured components.

Precision replication of micro features using micro injection moulding: Process simulation and validation

Commercial software for injection moulding is available to optimise the mould design for macroscale products, but such software cannot accurately simulate the moulding process and defects for micro features, which are critical for the performance of polymeric micro/nano devices. In the present work, essential micro features with an aspect ratio of 3:1 on a microfluidic flow cytometer chip were used as typical models to develop a feasible approach to describe the filling of the micro features using commercial simulation software. Factors including the heat transfer coefficient, venting, wall slip and freeze temperature that were critical for micro injection moulding but not of primary importance for conventional injection moulding were specifically investigated. Based on process monitoring and a series of experiments and validation, the insufficient filling of micro features was successfully predicted. The heat transfer coefficient showed a significant impact on the filling of micro features. Venting and wall slip were both critical in simulating the filling process. This paper provides a reasonable approach that can be used to predict defects when injection moulding micro features, while the simulation accuracy still needs to be further improved.

Investigation of Product and Process Fingerprints for Fast Quality Assurance in Injection Molding of Micro-Structured Components.

Injection molding is increasingly gaining favor in the manufacturing of polymer components since it can ensure a cost-efficient production with short cycle times. To ensure the quality of the finished parts and the stability of the process, it is essential to perform frequent metrological inspections. In contrast to the short cycle time of injection molding itself, a metrological quality control can require a significant amount of time and the late detection of a problem may then result in increased wastage. This paper presents an alternative approach to process monitoring and the quality control of injection molded parts with the concept of “Product and Process Fingerprints” that use direct and indirect quality indicators extracted from part quality data in-mold and machine processed data. The proposed approach is based on the concept of product and process fingerprints in the form of calculated indices that are correlated to the quality of the molded parts. A statistically designed set of experiments was undertaken to map the experimental space and quantify the replication of micro-features depending on their position and on combinations of processing parameters with their main effects to discover to what extent the effects of process variation were dependent on feature shape, size, and position. The results show that a number of product and process fingerprints correlate well with the quality of the micro features of the manufactured part depending on their geometry and location and can be used as indirect indicators of part quality. The concept can, thus, support the creation of a rapid quality monitoring system that has the potential to decrease the use of off-line, time-consuming, and detailed metrology for part approval and can thus act as an early warning system during manufacturing.

Geometric Replication Integrity of Micro Features Fabricated Using Variotherm Assisted Micro Injection Moulding

The geometric surface integrity of micro patterns is critical for functionality of polymeric micro devices, e.g. replication accuracy for micro channels and individual lens for the element of a compound eye lens. Micro injection moulding has been used widely for mass production of these devices. However, achieving high replication integrity is a critical challenge. In the present work, we developed a variotherm assisted micro injection moulding process to replicate a micro droplet and ellipse feature arrays in order to study the deformation behaviour of sickled blood cells. The effects of warm circuit temperature and cold circuit temperature on replication integrity, including filling depth, profile and morphology, were characterized based on moulding process monitoring, measurement and imaging. We have found that the warm circuit temperature is critical for feature filling due to its influence on the polymer-mould interface temperature, and that too high a warm circuit temperature can cause significant adhesion of polymer to a micro cavity. The cold circuit temperature controls shrinkage of polymer melts and the mould, and subsequently influences demoulding. Both temperatures need to be optimized to achieve the best replication of micro features.

Analysis of the influence of part thickness on the replication of micro-structured surfaces by injection molding

The achievement of an adequate accuracy of the microinjection molding process applied to the replication of micro-features is a complex task. The selection of process parameters and the geometry of the molded part influences the filling flow of the melt inside the mold cavity as well as the final quality of the replicated micro-features. In this work, the replication of a micro-structured surface is studied in relation to the thickness of the molded part. In particular, the effects of a rapid heat cycle molding process, cavity air evacuation, part thickness are experimentally evaluated. The analysis of the experimental data showed that the thickness of the main flow region and the molding temperature are significant factor affecting the replication quality. In particular, a combination of small cavity thickness and a high mold temperature (above Tg) can be effective in increasing the replicated height of micro-features. Experimental results also point out the correlation between the holding pressure and the distance from the injection location.An effective approach to the design of both the part and the process, should consider that the selection of process parameters must be related to design of the mold cavity.

INJECTION MOLDING OF THERMOPLASTIC ELASTOMERS FOR MICROSTRUCTURED SUBSTRATES

ABSTRACT Microstructured surfaces injection molded from thermoplastic elastomers have emerging applications as superhydrobic surfaces and patterned adhesives, but there is a limited understanding of the factors affecting replication with these materials. This work investigates the interactions of the tooling aspect ratio and feature orientation (negative and positive tooling) and thermoplastic elastomer hard segment content on microfeature replication. Electroformed nickel tooling having positive and negative features with different geometries and aspect ratios of 0.02:1 to 2:1 were molded from three copolyester thermoplastic elastomers with similar chemistry and different hardness values. The tooling and part features were characterized for feature depth and height as well as feature definition using scanning electron microscopy and optical profilometry. Results were correlated with elastomer properties.

An affordable injection-molded precision hybrid glass–polymer achromatic lens

This paper describes the development of an affordable precision hybrid glass–polymer achromatic doublet fabricated by microinjection molding. This hybrid lens can be used to correct chromatic aberration by combining a flint and a crown glass. Specifically, polycarbonate was selected as the flint glass with higher dispersion and N-BK7 was selected for lower dispersion crown glass. Microinjection molding was utilized to apply the aspherical polycarbonate layer directly onto the N-BK7 glass lens’ surface in this study for its capabilities of precision microfeature replication and mass production. In addition, finite element-based numerical simulation for molding process was employed to assist the design to improve the manufacturability. To ensure high precision in the fabricated hybrid lens, mechanical alignment features were created on the mold inserts to position the finished polymer lens along with the insert that housed the glass lens. The mold inserts’ surfaces were diamond-turned to optically finished without polishing. It was demonstrated in this study that with properly designed manufacturing processes, an integrated hybrid glass–polymer lens could be fabricated without further mechanical alignment. Lastly, the optical performance of the hybrid lens was verified by focal shift evaluation.

Replication of Micro Features in Injection Molding

Replication of Micro Features in Injection Molding

Molding and Optical Performance Simulations of a New Plastic Grating Lens for an Asymmetric LED Fog Lamp

This research focuses on the effect manufacture factors about the brightness and uniformity of multi-stage reflector. Trace-pro and 3D CAD model were used for optical simulations. The optical simulation results of grating lens and reflector were done as well as successfully developed the LED fog lamp. The results meet the regulations, R19 CLASS F3, of Economic Commission for Europe (ECE) at the test distance of 25 meters, and central zone under line6 achieves average over 3200cd. The optimal design of reflector is of third-order paraboloidal one to improve the brightness and uniformity. The acuter the microstructure’s tip is(R below 0.1mm), the better the apparent improving of eliminating stray light. In accordance with microstructure of grating lens, Moldex-3D is used to help the mold flow filling simulation and mold design. The mold cavity with microstructure was manufactured by the wire cutting and polishing processing. And the molding plastic was optics level PC (Polycarbonate). Both Taguchi’s method applied in Moldex-3D and real injection molding experiments showed that high melt temperature, low injection speed and suitable holding time can reduce warpage; in addition, using higher melt temperature, mold temperature and injection pressure can achieve higher degree of replication of micro features.

Continuous infrared‐assisted double‐sided roll‐to‐roll embossing of flexible polymer substrates

AbstractThis article reports a novel infrared (IR)‐assisted roll‐to‐roll embossing method, which enables the replication of microfeatures onto the surfaces of flexible polymer substrates. An IR‐assisted roll‐to‐roll embossing facility was designed and built in our laboratory especially for this study. Metallic rollers bearing micropatterns of two different feature sizes, namely 150 and 20 μm in depth, were employed. The former one was prepared by microelectric discharge machining the roller, whereas the latter was fabricated by electroplating a thin layer of nickel on the surface of the roller, followed by a diamond turning process to create the microstructures. The embossing facility was used to replicate the microstructure onto polyethylene terephthalate and polycarbonate films in the experiments. During roller embossing, the IR radiation shed on the rollers, and the energy was converted into heat to melt the polymer substrates and to replicate the microstructures. The influence of various processing parameters on the replicability of microfeatures was investigated. Under the proper processing conditions, double‐sided flexible polymer substrates with microstructures could be successfully fabricated. The proposed method shows great potential for fabrication of micro‐optical components due to its simplicity and versatility. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers

Injection molding and injection compression molding of thin‐walled light‐guided plates with V‐grooved microfeatures

AbstractIn this study, we investigated the feasibility of injection molding (IM) and injection compression molding (ICM) for fabricating 3.5‐in. light‐guided plates (LGPs). The LGP was 0.4 mm thick with v‐grooved microfeatures (10 μm wide and 5 μm deep). A mold was designed to fabricate LGPs by IM and ICM. Micromachining was used to make the mold insert. The Taguchi method and parametric analysis were applied to examine the effects of the process parameters on the molding quality. The following parameters were considered: barrel temperature, mold temperature, packing pressure, and packing time. Mold temperature in this investigation was in the conventional range. Increasing the barrel temperature and mold temperature generally improved the polymer melt fill in the cavities with microdimensions. The experimental results for the replication of microfeatures by IM and ICM are presented and compared. The height of the v‐grooved microfeatures replicated by ICM was more accurate than those replicated by IM. Additionally, the flatness of the fabricated LGPs showed that ICM was better than IM for thin‐walled molding. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

New deformation phenomenon for micro-formability of polycrystalline materials

The accepted mechanism in metallic micro-forming is grain boundary sliding and grain rotation, with feature size limited by grain size. However, contrary to this belief, by employing a silicon master, excellent replication of micro-features much smaller than grain size was achieved by hot embossing near the solidus temperature of AA6061.

Mold temperature variation for assisting micro-molding of DVD micro-featured substrate and dummy using pulsed cooling

Variable mold temperature for micro-molding has been a new trend, assisting in both the micro-feature replication accuracy and in holding cycle time increases down. Although various mold temperature controls have been proposed and proven useful in improving micro-feature dimensional accuracy, the required increases in cycle time hinder commercial application. Cycle time is particularly important in molding thin-wall parts such as cellular phone housings, CDs, and DVD substrates, for which the cycle times range from less than 10 s to about 4 s. In this study, pulsed cooling is evaluated and employed in the injection molding of DVD-R substrate and dummy. For pulsed cooling, coolant circulation is usually stopped during the melt-filling process and the opening and closing period of the mold. This may lead to additional cavity surface temperature increases of 10–15 °C in the melt-filling stage, depending on the overall cycle time and cooling circuit design. It helps to improve the microgroove replication accuracy by about 6% in molding micro-featured substrate and results in a 4–6% reduction in radial and tangential deviation in the molding dummy. If pulsed cooling is employed with original coolant temperature lowered by 8–10 °C, cycle times can be reduced from 4 s to 3.5 s and from 4 s to 3.2 s, respectively, for substrate and dummy molding, while holding microgroove accuracy and geometry deflection properties at their previous levels. Pulsed cooling technology has been successfully employed in low cycle time molding cases to either reduce cycle time or improve part qualities without a cycle time increase, or both.

Rapid mold temperature variation for assisting the micro injection of high aspect ratio micro-feature parts using induction heating technology

Hot embossing and injection molding are popular methods to duplicate micro features formed during polymer micro-fabrication of MEMS devices. However, both methods face challenges in filling the polymer melt completely into a micro-featured geometry of a high aspect ratio. In this study, electromagnetic induction heating combined with water cooling is used to achieve rapid mold surface temperature control during the micro-feature injection molding process. A CAE simulation was also developed through integration of both thermal and electromagnetic analysis modules of ANSYS, and its capability and accuracy were verified experimentally. Efficiency evaluations of induction heating and the uniformity of mold temperature control were conducted on a micro-featured mold. This mold was designed with a micro channel array of 30–50 µm in width and 120 and 600 µm in depth, corresponding to aspect ratios ranging from about 2.4 to 12. The accuracies of the micro channels in molded PMMA parts can be used to evaluate the effect of mold temperature on replication accuracy. It was found that rapid mold surface heating with temperature rising from 60 °C to between 100 °C and 140 °C by induction heating requires 2–3.5 s, while the mold temperature returns to 60 °C in about 70–110 s. The simulated mold surface temperature results are consistent with measured results. Achieving the same temperature variation by switching circulation coolants of different temperatures requires at least 7 min. The simulation also reveals that the electromagnetic wave can penetrate into the bottom of the micro channel and results in only about a 2 °C difference in temperature uniformity. For mold temperatures of 100 °C, 120 °C and 140 °C, the molded channel depths were 94.9 µm, 105.4 µm and 116.0 µm, respectively, when the ideal channel depth was 120 µm. When the channel depth is 600 µm, the mold temperature must exceed 120 °C, so that reasonable accuracy in micro-feature replication can be achieved. Our results to date indicate that the aspect ratio for molded PMMA micro channels can be as high as 12. Efficient mold temperature variation by induction heating to improve the replication accuracy in molding micro features is successfully illustrated.