Evaluation of Vacuum Venting for Micro-injection Molding

Abstract

While the effect of vacuum venting has been reported for injection molding of micro and nanoscale features, the limited research has produced conflicting results. To clarify the positive effect of vacuum venting on replication of microscale features, this work focused on the interactions between vacuum venting and (1) feature size, (2) material type in terms of melt viscosity and wettability, and (3) injection velocity and mold temperature. A metal-polymer hybrid tooling with a range of positive microscale features was employed to mold polystyrene and polymethylmethacrylate parts. Overall, vacuum venting always effective in feature definition (sharpness of edges) enhancement, but provided increases in depth ratio that depended on material (melt viscosity and wettability) and processing conditions (i. e., injection velocity, and mold temperature).

Investigation of the influence of vacuum venting on mould surface temperature in micro injection moulding

“…This research work is focused on the influence of the cavity air evacuation on the flow front temperature during the µIM process. The application of vacuum venting for the evacuation of air from the cavity has been introduced in injection moulding with the intent to further enhance feature replication and accuracy (sharpness of edges) by removing air pockets trapped in the micro features, which can resist the melt filling flow [10]. At the macro scale, air entrapment inside the moulds is usually avoided by evacuating the air through vents, that are machined on the interior surfaces of the mould plates, in the parting plane, and the air is expelled as the melt fills up the mould.…”

“…While the beneficial effect of applying a vacuum venting in µIM has been proven to derive from the removal of air trapped inside the narrow cavities, which obstacolate the polymer flow [4], [10], the supposed negative effect of this auxiliary technology on the mould temperature [15] has not been experimentally demonstrated. The aim of this work is the direct measurement of the effect of cavity air evacuation on the mould/polymer temperature, using a novel experimental setup.…”

Vacuum Venting Enhances the Replication of Nano/Microfeatures in Micro-Injection Molding Process

“…Inadequate venting in conventional injection molding has caused some common defects such as short-shot, poor appearance, burn marks and even permanent mold damage, and it is believed that the defects could be accentuated in MIM since the process involves high injection velocity and pressure, and rapid cooling [1][2][3]8]. The interactions between vacuum venting and (1) feature size, (2) material type, i.e.…”

“…Yoon et al [8] summarized a list of studies on the effect of vacuum venting for micro injection molding. Most studies used positive mold features, with the feature size being mainly in tens of microns in size and not smaller than 5micron or at the sub-micron scale.…”

“…The efficiency of vacuum venting in feature replication often can be quantified in terms of depth ratio (DR), i.e. ratio of the feature height in the molded part to the feature height in the tooling, which can also be expressed in percentage terms [6,8].…”