The application of innovative injection molding methodologies – Injection Compression Molding (ICM) and
Vacuum Injection Molding (VIM) – for the mass replication of optical miscroscale plastic components was
compared to conventional injection molding. Injection compression moulding process can be performed only on
dedicated machines, whereas vacuum injection moulding process can be applied to conventional injection moulding
machine with minor set-up and mould modifications. Vacuum injection molding implies an increase in cycle time
due to the time needed to reach the vacuum condition inside the cavity.
The analysis of the transcription ratio data derived from experiments evidenced that ICM is most precise and
repeatable of the three injection molding methodologies, whereas VIM is a minor process improvement. However
the maximum transcription ratio was strongly dependent on the optical prism geometry. Specifically, high levels of
transcription ratio were reached only when the prism angle was large. There was no evidence of a strong effect of
the height of the prism Hm on the transcription ratio.
Holding pressure was the main factor influencing all injection molding processes and producing variations of the
TR up to 9% for IM, 3.5% for ICM and 5.5% for VIM. The transcription ratio obtained by IM was also influenced
by the mould temperature and injection speed. Injection speed was also the second most relevant factor influencing
the VIM process.
It would be of further interest to continue the research on this topic by combining the ICM and VIM
methodologies and extending the investigation to other prism geometries.