Additive Manufacturing of Gun Propellants based on GAP-ETPE by Material Extrusion

Due to their ability to produce parts with little geometric limitations which may also be comprised of multiple different materials, additive manufacturing (AM) techniques have seen a wide spread in various industries in recent years. In the field of gun propellants, the burning behaviour is governed by geometry and material composition. Scope of design of these characteristics are limited by state-of-the-art production techniques (e.g. ram extrusion) which makes AM a promising way to overcome these limitations and to further improve the performance of gun propellants. For this purpose, Fraunhofer ICT is investigating the feasibility of additively manufactured gun propellants by material extrusion, which is a particular AM technique where molten or pasty material is extruded through a fine nozzle to create the desired shape. A suitable 3D printer with a screw-type print head has been adapted for processing energetic materials. General processing parameters have been adjusted with a non-energetic material system before continuing to print the energetic material system which contains solely energetic components and features a high solid loading with excellent energetic performance. The processing parameters have been further adjusted to improve the resolution of the printed geometry. The resulting single-perforated cylindrical propellant grains have been characterized in various ways with a focus on the microstructure which differs greatly from conventionally produced grains. The results show that propellant grains can be additively manufactured with good precision and in a reproducible manner with the adapted printing set-up. This paves the way for realizing complex grain geometries which are hardly producible by other techniques and propellant grains comprised of different formulations resulting in locally adjustable burning properties.