Now showing 1 - 10 of 19
  • 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
    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
    Characterization of microinjection molding process for milligram polymer microparts
    (Wiley Blackwell (John Wiley & Sons), 2013-08-02) ;
    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.
      840Scopus© Citations 16
  • Publication
    Replication of micro/nano-scale features by micro injection molding with a bulk metallic glass mold insert
    (IOP Publishing, 2012-05-17) ; ; ;
    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.
      1100Scopus© Citations 85
  • 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.
      680Scopus© Citations 24
  • Publication
    Towards nano-injection molding
    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.
      622Scopus© Citations 55
  • Publication
    Flow Induced Crystallization of Poly(ether-block-amide) from the Microinjection Molding Process and its Effect on Mechanical Properties
    (Wiley Blackwell (John Wiley & Sons), 2014-11) ; ;
    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.
      947Scopus© Citations 31
  • Publication
    Manufacturing microstructured tool inserts for the production of polymeric microfluidic devices
    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.
      1590Scopus© Citations 31
  • Publication
    The use of variotherm systems for microinjection molding
    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.
      1745Scopus© Citations 43
  • Publication
    Characterization of thermo-rheological behavior of polymer melts during the micro injection moulding process
    (Elsevier, 2012-09) ;
    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.
      2299Scopus© Citations 71