Micro-injection moulding (micro-moulding) is a process which enables the mass production of polymer micro-products. In order to produce high-quality injection moulded micro-parts, a crucial aspect to be fully understood and optimised is the filling of the cavity by the molten polymer. As a result, the relationships between the filling pattern and the different process parameter settings have to be established. In this paper, a novel approach based on the use of weld lines as flow markers to trace the development of the flow front during the filling is proposed. The effects on the filling stage of process parameters such as temperature of the melt, temperature of the mould, injection speed and packing pressure have been investigated. An optical coordinate measuring machine has been employed for the investigation. The micro-cavity, which presents micro-features ranging from 600 mu m down to 150 mu m, has been manufactured by micro-electrodischarge machining. A commercially available polystyrene grade polymer has been moulded using a high-speed injection moulding machine. The design of experiment technique was employed to determine the effect of the process parameters on the filling phase of the micro-cavity. In addition, extensive measuring uncertainty analysis was performed to validate the experimental plan. Results show that the temperature of the mould and the injection speed are the most influencing process parameters during the injection moulding of a micro-component
In actual hot runner systems for the injection moulding process, the control of polymers in gate is passive, which means that the melt temperature distribution and associated flow conductance is governed by a balance of heat convection by the flowing melt with heat conduction from the hot melt to the cold mould. This paper examines the rheological and thermal behaviour of a PA66 during freeze-off and melt flow activation. Numerical simulations were carried out according to the Finite Volume Method as implemented in the Ansys CFX® code. Rheological and thermal data were obtained from a careful material characterization conducted on a capillary rheometer and a differential scanning calorimetry (DSC). The analyses indicated that relatively small changes in melt temperature and injection pressure can substantially increase the flow conductance and dynamically control both the gate freezing and the onset of melt flow in the subsequent cycle. Therefore, simple gate thermal actuators were designed and numerically implemented to active control the plastic melt flow. This numerical approach can be used to design and optimize the active control of hot runners gate when the use of mechanical actuation (i.e. valve gates) is not suitable due to excessive cost, critical maintenance or miniaturization of the entire system
Abstract. The numerical simulation of the injection moulding process involving microstructures presents several challenges, mainly due to the surface effects that dominate the flow behaviour at the microscale. In this paper a new approach, which employs weld lines as flow markers, is used to evaluate whether the numerical codes that are normally used to simulate the conventional injection moulding process, are suitable to characterize the melt flow patterns in the filling of micro features. The Cross-WLF viscous model and the Giesekus viscoelastic model were evaluated using 3D models of a micro part implemented in two different numerical codes. A micro cavity was designed in order to compare the results of numerical simulations and experiments. While the viscous simulations were found to be inappropriate for multi-scale structures, the accuracy of micro filling predictions was significantly improved by implementing a viscoelastic material model.
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