Now showing 1 - 10 of 18
  • Publication
    Large-area sub-micron structured surfaces using micro injection moulding templates of nanoporous anodized Aluminum Oxide
    (Research Publishing Services, 2012) ; ; ;
    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.
  • Publication
    The effects of miniaturization and processing on microinjection moldings
    (Dr. Gupta Verlag, 2015) ;
    Product miniaturization and high shear/cooling rates during microinjection molding increase the volume of the highly oriented skin layer, thereby modifying the mechanical properties of the fabricated product.
  • Publication
    Effect of design on the replication of micro/nano scale features by micro injection moulding
    (Research Publishing Services, 2011) ; ;
    The replication of micro/nano scale features is of great interest for MEMS and Microsystems. However, the flow behaviour of melts into a micro/nano cavity is still not well understood. In this work, we used the micro injection moulding 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 moulding material. The influence of feature configuration, length, width, gap distance between features, location on substrate, and substrate thickness on the quality of replication was investigated. The experiments revealed that the replication of ridges, including feature edge, profile and filling distance, was sensitive to the flow direction; a critical feature length was found below which the filling of features was significantly reduced. Both the feature location and the substrate thickness had an influence on the filling of micro/nano features while the gap distance had a negligible effect on the replication of features.
  • Publication
    Miniaturization/process dependent mechanical properties of microinjection moldings
    Product miniaturization and high shear/cooling rates in microinjection molding increase the volume of highly oriented skin layer, which modifies a product’s mechanical properties and needs careful consideration for product design.
  • Publication
    Characterisation of micro injection moulding process for replication of micro/nano features and micro components
    (University College Dublin. School of Mechanical and Materials Engineering, 2013)
    Polymeric micro parts and micro/nano scale features, as typically found on miniature medical devices and microfluidic chips, are mainly produced by the micro injection moulding process, because of its mass production capability. Because of high surface to volume ratios, filling small cavities and tiny features requires high temperature and high speed in order to prevent short shots from premature solidification. The polymer melts are consequently subject to high shear rates and thermal gradients. This thesis has characterized the micro injection moulding process, polymer rheological behaviour at the micro scale, micro/nano feature replication, and morphology development and mechanical properties of micro parts and micro features.An in-line process monitoring system was developed to characterize filling, packing, and cooling of a typical micro component having a large sprue and runner. A shot size optimization method was proposed, which successfully eliminates the effect of machine switchover and holding pressure on the cavity filling process. Using a slit flow model, polymer melt viscosity at the micro scale was found to be dependent on cavity thickness and was lower than conventional viscosity, which is attributed to wall slip and non-isothermal flow. Replication of multi-scale features, ranging from hundreds of microns to as small as 100nm, has been successfully achieved by micro injection moulding using Bulk Metallic Glass tool inserts. Feature replication is characterized with respect to the moulding process and to the material, design, and feature configuration. Bulk Metallic Glass tools can successfully retain mould patterns for ~20,000 moulding cycles. Poly (ether block amide) micro parts exhibit some unique morphological features: spherulite-free core, larger spherulites between a skin layer and fine-grained layer/core layer. Shear stress was shown to be a successful threshold for the onset of an orientated structure by comparing the micro injection moulding process to a "short-term shear protocol". The morphology of the micro features was found to be similar to that of the core region, and the skin layer deformed into micro feature cavities depending on local pressure. Process-morphology-mechanical properties are correlated for micro parts.
  • Publication
    Characterization of Micro Injection Molding Process for the Replication of Micro/Nano Features Using Bulk Metallic Glass Insert
    Microsytems are motivating the development of complex, net-shape products weighing a few milligrams or having micro/nano features. Such small components or micro/nano features are subject to extreme shear rates and thermal gradients in the micro injection molding process due to their large surface to volume ratio. Detailed process monitoring and characterization are desirable to create a viable manufacturing process with acceptable part quality for MEMS and Microsystems. This work covers the replication of micro/nano scale features using Bulk Metallic Glass (BMG), implementation of a suite of PT (pressure and temperature) sensors on a commercial reciprocating micro injection molding machine, and detailed analysis of the relationship between process-rheology-replication. The results indicate that injection velocity dominates the average viscosity of polymer melts; holding pressure can adjust the input pressure history for micro/nano features and mold temperature can enhance feature filling by elevating the po-mold interface temperature. Tailored strategies to set machine parameters for different molds and plastics can be developed to meet the quality requirement for both small components and micro/nano features.
  • Publication
    Micro injection molding: characterisation of cavity filling process
    (Society of Plastics Engineering, 2011) ; ;
    Based on reciprocating micro injection molding machine, this paper characterizes the influence of machine process parameters and its transition response from velocity control to pressure control (V-P transition) on the micro cavity filling process. The method of Design of Experiment was employed to systematically and statistically investigate the effect of machine parameters on actual cavity filling process, which was described by the defined process characteristic values (PCVs). The statistical analysis of the experiments indicated that injection speed was dominated factor affecting all PCVs in cavity filling process. It was also found that the machine V-P transition have significant effects on cavity filling.
  • Publication
    Piezoelectric Tensor of Collagen Fibrils Determined at the Nanoscale
    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.
      724Scopus© Citations 51
  • Publication
    Effect of gate design and cavity thickness on filling, morphology and mechanical properties of microinjection moldings
    Miniaturized parts weighing up to tens of milligrams represent a large category of microinjection moulded products. Both miniaturization and extreme processing under microinjection moulding cause material to experience high shear rates and high cooling rates, and to have different morphology and final properties from conventional injection moulding. It also makes mould design quite challenging. This study investigates micro gate design (opening and thickness) and cavity thickness (100–500 μm) on filling, morphology and mechanical properties of Poly(ether-block-amide) miniaturized dumbbell parts. It is found that a reduction of gate size has two conflicting effects: increased shear heating increases flow length; increased cooling rate reduces flow length. Filling increases significantly with an increase of cavity thickness. In addition, skin ratio reduces from ∼70% to ∼10%, when part thickness increases from 100 μm to 500 μm. Such oriented skin layer determines molecular orientation and broadly influences Young’s modulus, elongation and yield stress. Natural aging at room temperature induces an increase of modulus and yield stress, and a decrease of strain at break. Mechanical properties of microinjection mouldings are significantly different from conventional injection mouldings and measurement at the microscale is required for successful miniaturized product design.
      250Scopus© Citations 21
  • Publication
    Performance of nickel and bulk metallic glass as tool inserts for the microinjection molding of polymeric microfluidic devices
    Electroformed nickel and bulk metallic glasses (BMGs) can be designed to incorporate features withlength scales ranging from millimeters to nanometers. This, combined with their good mechanical prop-erties relative to other materials, makes them competitive candidates for manufacturing multi-scalemolds to produce high volumes of polymeric microfluidics components and other micro/nano devices.Despite this attractiveness, BMGs are newly developed engineering materials and their capabilities asa mold material have not been evaluated. This paper compares the performance of nickel tools madeby an electroforming process and BMG tools made by a thermoplastic forming process, specifically withregard to typical microfluidics patterns and features. Ni shows excellent capabilities for good featurereplication. BMG thermoplastic forming is highly dependent on the choice of alloy composition, whichrestricts the achievable feature size and aspect ratio. Compared to Ni, BMG has hardness values that areclose to those of stainless steel and shows the superior mechanical strength that is required for massproduction applications. However, oxidation in BMG tool manufacturing process affects the tool surfacefinish significantly and reduces the tool¿s corrosion resistance. Future development of BMG tools includepreventing the formation of oxidation layers or developing BMGs with an anti-oxidation composition,and further reducing their overall cost and widening its processing window parameters. Despite thesechallenges, however, BMGs are shown to combine excellent mechanical properties and capabilities formulti-scale forming; this makes them significantly more attractive than relatively soft Ni tools.
      484Scopus© Citations 22