Experimental investigation and numerical simulation of injection molding with micro-features

Injection molding of thin plates of micro sized features was studied in order to manufacture micro-fluidic devices for bioMEMS applications. Various types of mold inserts-CNC-machined steel, epoxy photoresist, and photolithography and electroplating produced nickel molds-were fabricated and tested in injection molding. The feature size covers a range of 5 microns to several hundred microns. Issues such as surface roughness and sidewall draft angle of the mold insert were considered. Two optically clear thermoplastics, PMMA and optical quality polycarbonate, were processed at different mold and melt temperatures, injection speeds, shot sizes, and holding pressures. It was found that the injection speed and mold temperature in injection molding greatly affect the replication accuracy of microstructures on the metal mold inserts. The LTV-LIGA produced nickel mold with positive draft angles enabled successful demolding. Numerical simulation based on the 2D software C-MOLD was performed on two types of cavity fillings: the radial flow and the unidirectional flow. The simulation and experimental data were compared, showing correct qualitative predictions but discrepancies in the flow front profile and filled depth.