Characterization of microinjection molding process for milligram polymer microparts

Abstract

Injection molding small milligram components requires precise metering and high speed injection. Industrially, metering can be maintained either by using small injection screws (≤14mm in diameter) or plungers as small as 3mm diameter and/or by having very large sprues and runners. While large sprues and runners increase metering volume, they hide the effect of process parameters on micro components. Consequently, knowledge of conventional injection molding is not transferable to micro injection molding, making quality control and optimization difficult.We investigated the filling and post-filling behavior of 25mm 3 micro dumbbell specimens with 289 mm 3 sprue and runner by in-line process monitoring. Design of Experiments were carried out to characterize the effects of process parameters on cavity filling and post-filling behavior. Process characterization indicated that the machine transition from velocity control to pressure control (V-P transition) was around 10ms: this was comparable to cavity filling time and had a significant effect on cavity filling behavior. Traditional short shot trials cannot provide the correct shot size for small parts, but introduce the effect of holding pressure into cavity filling. Based on a shot size optimization method using only cavity pressure and screw velocity, we eliminated the effect of holding parameters on cavity filling.

Flow Induced Crystallization of Poly(ether‐block‐amide) from the Microinjection Molding Process and its Effect on Mechanical Properties

“…Thermomechanical history during plasticization is kept consistent for all processing conditions. More details on process monitoring and characterization can be found in our previous work …”

Microinjection molding of multiwalled carbon nanotubes (CNT)–filled polycarbonate nanocomposites and comparison with electrical and morphological properties of various other CNT‐filled thermoplastic micromoldings

“…Metering size is also an important process parameter, which could be influenced by the average material temperature . Similarly, Zhang and Gilchrist reported that the metering size could be determined by injection speed, melt temperature, and mold temperature.…”

The Influence of Processing Conditions on the Polypropylene Apparent Viscosity Measured Directly in the Mold Cavity

“…This solution resembled the action of a capillary rheometer powered by the plasticizing system of the injection molding machine. Similar tools were used by other researchers . Differences were in geometry and dimensions of flow channels and sensors placement.…”