Parametric assessment of injection dynamics for metal and polymer rapid-tooling using in-line process measurements and modelling of micro-injection moulding

Optimising injection dynamics in micro-injection moulding (μIM) enhances efficiency, reduces defects, and improves repeatability. The current study examines the injection dynamics of μIM using both rapid-tooling, fabricated via material jetting, and conventional aluminium metal tooling. A 20 mg micro-moulding cavity was used to assess injection behaviour, injection pressure profiles, and process variation through in-line process monitoring and computational modelling. Results reveal significant differences between rapid and metal tooling in terms of drag, pressure build-up during injection and mechanical properties of the final products. The low thermal conductivity of rapid-tooling has led to prolonged low melt viscosity retention, resulting in significantly reduced peak injection pressures and dampened pressure overshoots, improving process repeatability. Metal tooling in contrast showed increased pressure fluctuations, making the injection dynamics more complex and affecting process repeatability. Computational modelling captured the major trends and exhibited deviations in pressure profiles, particularly for rapid-tooling, where accurate heat transfer coefficient estimation remains a challenge. Mechanical property correlations with injection dynamics further highlight the data-rich nature of μIM, with shear stress effects at higher injection rates influencing part performance. This study provides new insights into μIM process dynamics, emphasising the role of thermal properties and the challenges in modelling heat transfer effects in rapid-tooling. The findings support the optimisation of μIM for improved process control, predictive modelling, and data-driven quality monitoring for both industrial and rapid prototyping settings.