Microcellular injection moulding (MuCell^®) is a polymer processing technology that uses a supercritical fluid inert gas, CO₂ or N₂, to produce light-weight products. Due to environmental pressures and the requirement of light-weight parts with good mechanical properties, this technology recently gained significant attention. However, poor surface appearance and limited mechanical properties still prevent the wide applications of this technique. This paper reviews the microcellular injection moulding process, main characteristics of the process, bubble nucleation and growth, and major recent developments in the field. Strategies to improve both the surface quality and mechanical properties are discussed in detail as well as the relationships between processing parameters, morphology, and surface and mechanical properties. Modelling approaches to simulate microcellular injection moulding and the mathematical models behind Moldex 3D and Moldflow, the two most commonly used software tools by industry and academia, are reviewed, and the main limitations are highlighted. Finally, future research perspectives to further develop this technology are also discussed.

Microcellular injection moulding is an important injection moulding technique to create foaming plastic parts. However, there are no consistent conclusions on the impact of processing parameters on the cell morphology of microcellular injection moulded parts. This paper investigates the influence of the main processing parameters, such as melt temperature, mould temperature, injection pressure, flow rate, shot volume and gas dosage amount, on the average cell size and weight reduction of a talc-reinforced polypropylene square part (165 mm × 165 mm × 3.2 mm), using the commercial software Moldex 3D. The effect of each parameter is investigated considering a range of values and the simulation results were compared with published experimental results. The differences between numerical and experimental trends are discussed.

Crystallization, as a physical transformation process, plays an important role on the final properties of a plastic part. Similar to other injection moulding processes, injection and cooling conditions in microcellular injection moulding (e.g. MuCell^® process) determine the phase change transformation of the material (molten to solid) and consequently, nucleation, crystal growth and crystallinity. The crystallization process of microcellular injection moulded parts has been mainly investigated using laborious and time-consuming experimental characterization techniques, but no studies reported the use of numerical methods to estimate the crystallization process. This paper presents a mathematical model successfully used to simulate the crystallization process of microcellular injection moulded parts. Microcellular injection moulding was simulated using Moldex 3D, and the crystallization process was investigated using the Hoffman nucleation theory for the crystal nucleation rate, the Lauritzen-Hoffman growth theory for the crystal growth rate, and the Avrami model to calculate the relative crystallinity. Numerical simulations allowed to investigate the effect of key processing parameters (melt temperature, mould temperature, flow rate, gas dosage amount and shot volume) on the crystallization process. Moreover, the numerical model was validated considering published experimental data.