A. Almalki, A. Rajhi, A. Kundu, J. Coulter
Lehigh University,
United States
Keywords: microinjection molding, Bulk Metallic Glass, tooling, lifetime, Focused Ion Beam
Summary:
The growing demand for large-scale manufacturing of polymeric products with micro and sub micro features requires robust tooling with a high lifetime. Unlike steel and other metals, Bulk Metallic Glasses (BMGs) demonstrate superior mechanical properties and the ability to incorporate such features. Therefore, BMGs, especially Zr-based BMGs can be a good material candidate for tooling inserts in microinjection molding. This paper investigated numerically and experimentally BMG insert lifetime for microinjection molding to further understand the effect of polymer melt on the BMG tooling life. In this research, commercially available Zr-based BMGs alloy; Vitreloy-1b, were utilized using Focused Ion Beam (FIB) for milling circular microfeatures of 5 μm in diameter and 10 μm edge to edge spacing with an aspect ratio of 1. The milling process parameters were optimized using different ion beam currents to achieve the desired geometry with faster milling time. It was observed that an ion beam current of 50 nA at 30 KeV with a dwell time of 1 μs could provide the intended features. In addition, optimal processing parameters were obtained using Autodesk MoldFlow Insight simulation, and thermoplastic polyurethane (TPU) material that is widely used in healthcare applications for molding polymeric parts was selected. 3D flow simulations were performed to optimally conduct molding parameters such as melt and mold temperatures, packing and injection pressures, filling velocity, and cooling time then used as input for molding experimentations. The BMG insert with molded parts were characterized periodically throughout the molding cycles using Scanning Electron Microscope (SEM) to investigate the features’ capability for replication. It was observed that the absence of anti-stiction coating was critical for the fidelity of molded parts after couple hundred cycles which hinders the BMG tooling lifetime. Moreover, Ansys was used to perform fatigue life analysis of the BMG insert to examine BMG insert fatigue regions under cyclic loading.