The application of vacuum venting for the evacuation of air from the mould cavity has been introduced in injection molding with the intent to further enhance micro/nano feature replication and definition. The technique is adopted to remove air pockets trapped in the micro-features (which are difficult or impossible to reach using conventional venting technologies), which can create considerable pressure that resist the melt filling flow. Nonetheless, several studies have revealed a negative effect that could possibly arise from the application of vacuum venting. It is proposed that air evacuation removes a mold surface heating effect caused by adiabatic compression of the air ahead of the flow front and subsequent conduction of that heat into the mold surface. Hence, with the increase of the surface-to volume ratio in micro-cavities, air evacuation could have a detrimental effect on the melt fill for polymers that are sensitive to changes of the mold temperature. Although incomplete filling of micro-scale features has often been attributed to poor venting, the limited research examining the application of vacuum venting has produced mixed results. In this work, the effect of air evacuation on the mold/polymer temperature was experimentally investigated. A novel experimental setup is demonstrated to monitor the mold and polymer temperature during the micro injection molding process using a high speed infrared camera system, Ircam Equus 81k SM, and sapphire window in the mold. A design of experiments (DoE) approach was applied to design and analyze of the experimental campaign. The factor investigated were: the mold temperature (Tm), the injection velocity (Vinj) and the presence of air evacuation (Ea). The choices of the upper and lower levels for the factors derived from a literature review, recommendations of the material supplier and the technological limits of the available experimental setup. The response variable for this analysis was chosen to be the average temperature of the flow front inside the mold cavity. The results provide empirical evidence about the effect of the air evacuation on the mold/polymer temperature that is more evident at high values of process parameters setting. In fact, as shown in Fig.1, at a Tm of 140°C and Vinj of 800 mm/s, the presence of air evacuation from the mold, imply a decrease on the flow front temperature of 39 °C (-12%) while at a Tm of 80°C and Vinj of 300 mm/s this decrease is about the 4%. In conclusion, the empirical findings in this study provide a new understanding of the effect of cavity air evacuation in microinjection molding process.

Investigation of the Influence of Vacuum Venting on Mold Surface Temperature in Micro Injection Molding

SORGATO, MARCO;LUCCHETTA, GIOVANNI;
2015

Abstract

The application of vacuum venting for the evacuation of air from the mould cavity has been introduced in injection molding with the intent to further enhance micro/nano feature replication and definition. The technique is adopted to remove air pockets trapped in the micro-features (which are difficult or impossible to reach using conventional venting technologies), which can create considerable pressure that resist the melt filling flow. Nonetheless, several studies have revealed a negative effect that could possibly arise from the application of vacuum venting. It is proposed that air evacuation removes a mold surface heating effect caused by adiabatic compression of the air ahead of the flow front and subsequent conduction of that heat into the mold surface. Hence, with the increase of the surface-to volume ratio in micro-cavities, air evacuation could have a detrimental effect on the melt fill for polymers that are sensitive to changes of the mold temperature. Although incomplete filling of micro-scale features has often been attributed to poor venting, the limited research examining the application of vacuum venting has produced mixed results. In this work, the effect of air evacuation on the mold/polymer temperature was experimentally investigated. A novel experimental setup is demonstrated to monitor the mold and polymer temperature during the micro injection molding process using a high speed infrared camera system, Ircam Equus 81k SM, and sapphire window in the mold. A design of experiments (DoE) approach was applied to design and analyze of the experimental campaign. The factor investigated were: the mold temperature (Tm), the injection velocity (Vinj) and the presence of air evacuation (Ea). The choices of the upper and lower levels for the factors derived from a literature review, recommendations of the material supplier and the technological limits of the available experimental setup. The response variable for this analysis was chosen to be the average temperature of the flow front inside the mold cavity. The results provide empirical evidence about the effect of the air evacuation on the mold/polymer temperature that is more evident at high values of process parameters setting. In fact, as shown in Fig.1, at a Tm of 140°C and Vinj of 800 mm/s, the presence of air evacuation from the mold, imply a decrease on the flow front temperature of 39 °C (-12%) while at a Tm of 80°C and Vinj of 300 mm/s this decrease is about the 4%. In conclusion, the empirical findings in this study provide a new understanding of the effect of cavity air evacuation in microinjection molding process.
Proceedings of the Polymer Processing Society Conference 2015
File in questo prodotto:
Non ci sono file associati a questo prodotto.
Pubblicazioni consigliate

Caricamento pubblicazioni consigliate

I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.

Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11577/3162899
Citazioni
  • ???jsp.display-item.citation.pmc??? ND
  • Scopus ND
  • ???jsp.display-item.citation.isi??? ND
social impact