A. Rajhi, I.H. Jaafar, J.P. Coulter
Keywords: injection molding, nano/micro-manufacturing, bulk metal glass, microfabrication
Summary:This paper describes current efforts to numerically and experimentally investigate micro and nanoscale features replication using the injection molding process. A silicon (Si) insert with micro–features is fabricated via photolithography followed by deep reactive ion etching (DRIE) to achieve the required depth, which is validated using a scanning electron microscope (SEM). The Si insert serves as the mold for injection molding. The study finds that Si tooling may not be an optimal method for this purpose due to its brittle nature, whereas in high volume manufacturing such as injection molding, the demand for extended tooling life is necessary. Bulk metallic glass (BMG) alloys may be an alternative as it provides exceptional material properties with high strength, high elastic limit, formability, corrosion, and wear resistance. It has also been found to exhibit low viscosity Newtonian flow characteristics and excellent micro/nanoscale formabililty with low stress levels. A BMG-based mold insert is fabricated via controlled low-pressure (approximately 20 MPa) superplastic forming, using an inverse pattern on a micro-featured Si template. Once the BMG insert is formed, the Si template is removed via dissolution in KOH. Both Si and BMG molds are tested for mold life expectancy for injection molding. Moldflow simulation is also performed to study the filling process of a micro-structured mold cavity. The cavity is 0.5 in. in diameter, with different micro-structured patterns that include oval (15 µm diameter and height) and circular (5 µm diameter and 2 µm height) shapes. Experimental parameters will be based on 3D flow simulation outputs. The polymers selected for micro-molding investigation are polystyrene (PS), cyclic olefin copolymer (COC), and polyethylene (PE). The processing parameters that are investigated to optimize the micro-feature replication are melt and mold temperature, filling velocity, and cooling time.