Vacuum level effects on gas porosity in vibro-vacuum degassing of a viscous metal–polymer composite for hybrid am tool bodies

Metal–composite technology (MCT) for hybrid additively manufactured tool bodies based on an ‘SLM shell + metal–polymer composite material (MPCM) infill’ architecture increases functionality by enabling complex internal coolant/lubricant channels while reducing the additively manufactured metal volume. In practice, the deployment of such tool bodies is strongly constrained by MPCM gas porosity, particularly in critical regions adjacent to the SLM shell wall and near internal channels, where defects reduce thermal transport and load-bearing capacity and increase the likelihood of unstable filling in thin-walled cavities. This study experimentally quantifies vacuum level (residual pressure) effects on MPCM gas porosity during vibro-vacuum degassing and defines a practical processing window for MCT tool bodies. Experiments were conducted using a two-stage vibro-vacuum setup comprising a preliminary degassing chamber and a casting chamber with low-frequency vibration. Standard MPCM specimens were produced at each vacuum level, and porosity was evaluated via a microscopy-based scoring method (pore distribution, clustering, and characteristic defect size). A stable nonlinear (V-shaped) response was observed: as pressure decreased from atmospheric to approximately 450 Pa, the average porosity score monotonically declined and reached a minimum within 400–350 Pa (1–2 points), whereas further vacuum intensification below 300 Pa triggered vigorous gas evolution and foaming (‘boiling’), resulting in a sharp rise in defect severity (up to 3–5 points). The identified 400–350 Pa range is recommended as a practical window for low-porosity MPCM filling of SLM shells, improving infill repeatability and supporting reliable hybrid AM tool-body manufacturing under import-substitution driven production constraints.