Micromoulding: process characteristics and product properties

Abstract

Key aspects of the technology and challenges associated with the micromoulding process are discussed. The apparent shear and extensional viscosity behaviour of a polyacetal at high wall shear rates have been measured using inline capillary rheometry on a commercial micromoulding machine and a larger servoelectric injection moulding machine; the polymer behaved predictably at shear rates in excess of 106 s -1. Initial moulding trials indicated that a stepped plaque and 0·25 mm thick rectangular plaque mouldings lled in a satisfactory manner, but a thicker plaque cavity exhibited a jetting ow into the cavity. A data capture system capable of measuring multiple process dynamics at high sampling rates (up to 50 kHz per channel) allowed detailed process measurements taken during moulding of the stepped plaque moulding. Atomic force microscopy of the moulded products showed diVerent surface nishes on each step of the stepped plaque moulding. Topography scans of the 0·25 mm thick rectangular plaque moulding showed that mould surface features with length scales of the order of a few micrometres were well replicated on the moulded product and the quality of the surface nish is dependent on the melt pressure during moulding.PRC/2020

The Micro Injection Moulding Process for Polymeric Components Manufacturing

“…A product manufactured by micro-injection moulding process can be defined [2] as reported below [2]::…”

“…In literature there are different methods proposed to measure the cavity pressure as for example a piezoelectric force trasducer located behind the injection pin [2] or a miniaturized quartz sensor to direct measure the pressure in the micro mould cavity applied at the end of the sprue channel [17].…”

“…The high shear rates occurring in the micro processes encourage the use of materials that exhibit high shear thinning rheology, allowing cavity filling at the lowest possible injection pressure [2]. The interaction between the type of used polymer and the quality of the moulded part makes a challenging task to define the useful material for each application without testing it under different conditions.…”

“…The use of filler materials can improve the mechanical performance of the resins, but the small feature dimensions present in micro mould cavities deny the use of conventional fillers, such as glass or carbon fibres. Nano fillers such as exfoliated clay platelets, polyhedral oligosilesquioxanes (POSS) and carbon nano tubes show potential for use in the micro moulding environment [2]. The addition of montmorillonite nano clays to polymer systems has emerged as a viable method to improve mechanical, barrier and flameretarding properties [38].…”

Microinjection Molding of Enhanced Thermoplastics

“…However, for the sake of accuracy and repeatability of the process, higher precision of plastic metering and clamping may be achieved by the servo mechanisms of the electrically driven machine allowing for more accurate process control along with low noise level and energy efficiency. (Whiteside et al, 2003;Chang et al, 2007) …”