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Replication of surface micro-features using variothermal injection molding: Application to micro-fluidics

P. G. Wlodarski, J. F. T. Pittman, John Pittman, Patrick Wlodarski

Polymer Engineering & Science

Swansea University Authors: John Pittman, Patrick Wlodarski

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DOI (Published version): 10.1002/pen.24772

Abstract

We study injection molding of mesoscale items with µm-scale surface features, namely micro-fluidic channels, relating replication quality to process conditions. Using variothermal molding, the variables are the pre-heat temperature of the cavity insert surface before melt injection and the mold cool...

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Published in: Polymer Engineering & Science
ISSN: 0032-3888
Published: 2017
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URI: https://cronfa.swan.ac.uk/Record/cronfa37783
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Abstract: We study injection molding of mesoscale items with µm-scale surface features, namely micro-fluidic channels, relating replication quality to process conditions. Using variothermal molding, the variables are the pre-heat temperature of the cavity insert surface before melt injection and the mold cooling start time. Surface temperatures and in-cavity melt pressures are continuously measured. Rounded upper corners of the micro-channels are used as an index of replication quality. For polymethylmethacrylate the thickness of a layer with solid-like properties (below 124°C) is calculated and used with pressures to interpret results. It is shown how improved replication correlates with low layer thickness at the end of the compression phase when pressures are at a maximum, and the necessity of properly timed cooling to lock in replication before melt pressures fall. Results show how the inter-relationship of layer thickness and melt pressure is controlled by pre-heat temperature and cooling switch-on time. Delayed cooling can result in poorer replication, due to a retraction effect of the plastic. Too early cooling also reduces replication of parallel-to-flow features downstream of transverse features, and of the replication of transverse features on their downstream side. Good replication of 100 and 70 µm channels requires lower pre-heat than 400 µm ones.
College: Faculty of Science and Engineering

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