# Numerical Simulation and Experimental Study of the Extrusion Process in Additive Manufacturing for High-Viscosity and High-Solid-Content Multi-Component Energetic Materials

## TL;DR

This paper studies how to improve 3D printing of high-viscosity, high-solid-content explosive materials by combining simulations and experiments to optimize equipment design and extrusion parameters.

## Contribution

A novel combined numerical and experimental approach to optimize extrusion equipment and parameters for printing high-viscosity energetic materials.

## Key findings

- Cylindrical screws outperformed conical screws with a 3mm clearance being optimal.
- A 1.55 mm nozzle with specific screw speeds enabled stable extrusion of high-solid-content slurry.
- Uniform slurry with 70% solid content was achieved after 3 hours of kneading at 25 rpm.

## Abstract

A combined numerical simulation and experimental validation approach was employed to investigate the phenomena of screw adhesion and nozzle clogging, which occur frequently during material conveying and extrusion of high-viscosity, high-solid-content multi-component energetic materials in additive manufacturing. First, conical and cylindrical screws were designed. Through simulation calculations of the energetic material extrusion process, patterns in the variation in internal pressure and shear rate within the screw were analyzed, providing guidance for the design of the printing equipment. Second, a Z-shaped stirring paddle kneading device and a dual-nozzle printing device featuring horizontally and vertically arranged two-stage screws were designed. Through extrusion experiments with PBX (polymer-bonded explosive) slurry, the optimal matching relationship between the kneading rate and the extrusion rates of the horizontal and vertical screws was obtained. Finally, additive manufacturing of complex-shaped PBX charges using high-viscosity energetic materials was successfully accomplished. This confirms the further optimization of the additive manufacturing equipment in terms of safety control, precision control, and adaptability to complex structures under extreme operating conditions. The results indicate that the cylindrical screw outperforms the conical screw, and with a screw clearance of 3mm, it represents the optimal design solution. During the kneading process, a screw rotational speed of 25 rpm was used. After kneading for 3 h, the slurry exhibited good uniformity, with a solid content of approximately 70% and relatively small deviation. During the extrusion process, a nozzle diameter of 1.55 mm combined with a rotational speed of 5 rpm for the horizontal screw (feeding screw) and 7 rpm for the vertical screw (extrusion screw) can satisfy the requirements of the “starved feeding” mode, thus achieving continuous and stable filament formation of the slurry.