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

TLDR

Injection molding of thin plates with micro‑sized features was investigated to produce micro‑fluidic devices for bioMEMS applications. The study used CNC‑machined steel, epoxy photoresist, and UV‑LIGA nickel molds of 5–hundreds‑micron features, processed PMMA and polycarbonate at varied temperatures, speeds, shot sizes, and pressures, and performed 2‑D C‑MOLD simulations of radial and undirectional cavity filling. Higher injection speed and mold temperature improved micro‑structure replication accuracy, UV‑LIGA nickel molds with positive draft angles allowed successful demolding, and simulations qualitatively matched experiments but differed in flow front profile and fill depth.

Abstract

Abstract 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 UV‐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 undirectional flow. The simulation and experimental data were compared, showing correct qualitative predictions but discrepancies in the flow front profile and filled depth.