Now showing 1 - 10 of 18
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Replication of micro/nano-scale features by micro injection molding with a bulk metallic glass mold insert

2012-05-17, Zhang, Nan, Chu, J. S., Byrne, Cormac J., et al.

The development of MEMS and Microsystems needs a reliable mass production process to fabricate micro components with micro/nano scale features. In our study, we used the micro injection molding process to replicate micro/nano scale channels and ridges from a Bulk Metallic Glass (BMG) cavity insert. High density polyethylene (HDPE) was used as the molding material and Design of Experiment (DOE) was adopted to systematically and statistically investigate the relationship between machine parameters, real process conditions and replication quality. The peak cavity pressure and temperature were selected as process characteristic values to describe the real process conditions that material experienced during the filling process. The experiments revealed that the replication of ridges, including feature edge, profile and filling height, was sensitive to the flow direction; cavity pressure and temperature both increased with holding pressure and mold temperature; replication quality can be improved by increasing cavity pressure and temperature within a certain range. The replication quality of micro/nano features is tightly related to the thermomechanical history of material experienced during the molding process. In addition, the longevity and roughness of the BMG insert was also evaluated based on the number of injection molding cycles.

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Vacuum venting enhances the replication of nano/micro-features in microinjection molding process

2016-03-24, Choi, Seong Ying, Zhang, Nan, Toner, J. P., Gilchrist, M. D.

Vacuum venting is a method proposed to improve feature replication in microparts that are fabricated using micro injection molding (MIM). A qualitative and quantitative study has been carried out to investigate the effect of vacuum venting on nano/micro feature replication in MIM. Anodized aluminium oxide containing nanofeatures and a bulk metallic glass tool mold containing micro features were used as mold inserts. The effect of vacuum pressure at constant vacuum time, and of vacuum time at constant vacuum pressure on the replication of these features is investigated. It is found that vacuum venting qualitatively enhances the nano-scale feature definition as well as increases the area of feature replication. In the quantitative study, higher aspect ratio features can be replicated more effectively using vacuum venting. Increasing both vacuum pressure and vacuum time are found to improve the depth of replication, with the vacuum pressure having more influence. Feature orientation and final sample shape could affect the absolute depth of replication of a particular feature within the sample.

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Towards nano-injection molding

2012-05, Zhang, Nan, Byrne, Cormac J., Browne, David J., Gilchrist, M. D.

Bulk metallic glasses (BMGs), having no limiting microstructure, can be machined or thermoplastically-formed with sub-micron precision while still retaining often-desirable metallic properties such as high compressive strength. These novel materials thus have enormous potential for use as multi-scale tools for high-volume manufacturing of polymeric MEMS and information storage devices. Here we show the manufacture of a prototype BMG injection molding tool capable of producing cm-long polymeric components, with sub-micron surface features.

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Characterization of microinjection molding process for milligram polymer microparts

2013-08-02, Zhang, Nan, Gilchrist, M. D.

Injection molding small milligram components requires precise metering and high-speed injection. Industrially, metering can be maintained either by using small injection screws (≤14 mm in diameter) or plungers as small as 3 mm diameter and/or by having very large sprues and runners. Although large sprues and runners increase metering volume, they hide the effect of process parameters on microcomponents. Consequently, knowledge of conventional injection molding is not transferable to microinjection molding, making quality control and optimization difficult. We investigated the filling and postfilling behavior of 25 mm3 microdumbbell specimens with 289 mm3 sprue and runner by in-line process monitoring. Design of Experiments were carried out to characterize the effects of process parameters on cavity filling and postfilling behavior. Process characterization indicated that the machine transition from velocity control to pressure control (V-P transition) was around 10 ms: this was comparable to cavity filling time and had a significant effect on cavity filling behavior. Traditional short shot trials cannot provide the correct shot size for small parts, but introduce the effect of holding pressure into cavity filling. Based on a shot size optimization method using only cavity pressure and screw velocity, we eliminated the effect of holding parameters on cavity filling.

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Piezoelectric Tensor of Collagen Fibrils Determined at the Nanoscale

2017-05-03, Denning, Denise, Kilpatrick, J. I., Fukada, Eiichi, Zhang, Nan, Gilchrist, M. D., Rodriguez, Brian J., et al.

Piezoelectric properties of rat tail tendons, sectioned at angles of 0, 59, and 90° relative to the plane orthogonal to the major axis, were measured using piezoresponse force microscopy. The piezoelectric tensor at the length scale of an individual fibril was determined from angle-dependent in-plane and out-of-plane piezoelectric measurements. The longitudinal piezoelectric coefficient for individual fibrils at the nanoscale was found to be roughly an order of magnitude greater than that reported for macroscopic measurements of tendon, the low response of which stems from the presence of oppositely oriented fibrils, as confirmed here.

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The use of variotherm systems for microinjection molding

2016-11-14, Su, Quanliang, Zhang, Nan, Gilchrist, M. D.

Microinjection molding (μIM) is a fast-developing technology which is used to produce polymeric microcomponents or components with micro/nanoscale features, such as are used in many fields including microfluidic diagnostics, microneedle drug delivery devices, microgears, and microswitches. The capabilities and performance of the microinjection molding process can be improved by incorporating a variotherm system. This leads to improved component quality, especially for high aspect ratio features. It can also help to increase the polymer flow path, improve feature replication, reduce residual stresses and molecular orientations, and also can eliminate weld lines. This article reviews the use of different variotherm systems in μIM, and describes how simulation of its use can provide insight when designing a mold cavity or a component with challenging microfeatures. The article highlights important problems, challenges and areas for further research. An increased understanding of these issues will provide opportunities to enhance further developments in the μIM process.

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Manufacturing microstructured tool inserts for the production of polymeric microfluidic devices

2015-08-10, Zhang, Nan, Srivastava, Amit P., Kirwan, Brendan, Byrne, Richard, Fang, Fengzhou, Browne, David J., Gilchrist, M. D.

Tooling is critical in defining multi-scale patterns for mass production of polymeric microfluidic devices using the microinjection molding process. In the present work, fabrication of various microstructured tool inserts using stainless steel, nickel and bulk metallic glasses (BMGs) is discussed based on die-sinking EDM (electrical discharge machining), electroforming, focused ion beam milling and thermoplastic forming processes. Tool performance is evaluated in terms of surface roughness, hardness and tool life. Compared to stainless steel, nickel and BMGs are capable of integrating length scales from 100 to 10−8 m and are good candidates for producing polymeric microfluidics. Selection of tool materials and manufacturing technologies should consider the end-user requirements of actual applications.

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Characterization of thermo-rheological behavior of polymer melts during the micro injection moulding process

2012-09, Zhang, Nan, Gilchrist, M. D.

In-line process monitoring and rheological characterization can help to understand the behaviour of polymer melt flows during manufacture and to make injection moulding a measurable process for manufacturing high quality parts. This work developed an in-line rheology measurement system using a slit die attached to a micro injection moulding machine. A series of dumbbell mould inserts was used to form the slit die with thickness ranging from 600 μm to 200 μm. Two combined pressure and temperature sensors were embedded into the slit die to measure the pressure drop. Based on the slit flow model, it was found that the viscosity of Pebax melts depends on the slit thickness in the actual injection moulding process. The competing effects of wall slip and non-isothermal conditions will determine the melt viscosity. The plastication induced thermo-mechanical history can also influence polymer viscosity, although it is neglected in conventional rheology measurements.

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Flow Induced Crystallization of Poly(ether-block-amide) from the Microinjection Molding Process and its Effect on Mechanical Properties

2014-11, Zhang, Nan, Choi, Seong Ying, Gilchrist, M. D.

Crystallization during microinjection molding is investigated relative to process conditions. Modulus and hardness of the skin layer are higher than the core layer, regardless of core structure. Young's modulus, strain at break and yield stress all increase with an increase of skin ratio. The relationship between process, morphology and mechanical properties is studied for micro products. By using in-line process monitoring, flow induced crystallization is characterized by shear stress and apparent specific work. Shear stress is shown to be a good candidate to characterize the formation of highly oriented structures under actual microinjection molding processes. This may provide a method for in-line control of morphology development, and then final properties, by controlling the flow conditions.

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Large-area sub-micron structured surfaces using micro injection moulding templates of nanoporous anodized Aluminum Oxide

2012, Zhang, Nan, Harrison, S., Meagher, Philip, et al.

This study demonstrates a mass production method using nanoporous Anodized Aluminum Oxide (AAO) templates as mould insert tools that are used to structure large area polymer surfaces by a micro injection moulding process. SEM and water contact angle measurements served to evaluate the effect of nanostructures on surface properties. Human umbilical vein endothelial cells were cultured on nano-structured and ultra-smooth surfaces of polymer parts. Experimental results indicated that nano-pillar features sized from ~100nm to 250nm were easily replicated on these same polymer surfaces. The contact angles varied from 3o to 9o. The nanoporous AAO templates were able to retain their pore integrity very well for ~80 injection moulding cycles: this suggests they they could be a potential mould tool for large area patterning of polymer surfaces. The endothelial cell culture analysis indicates that cell growth was not significantly affected by nano-topography compared to the smooth surfaces (baseline RA ~6nm) and both surfaces had equally good cell adhesion.