Additively manufactured 3D articles of certain high-temperature polymer composites such as ULTEM 1000 reinforced with chopped carbon fibers and printed by current state-of-the-art Fused Deposition Modeling (FDM) printers, suffer significantly with high porosity due to moisture-induced cavitation during the liquefying process under high printing temperatures because the pre-fabricated feedstock filaments contain excessive moisture trapped in polymer matrix or fiber interfaces that is extremely difficult to remove. During compounding (mixing of chopped fibers with resin) and the filament extrusion process, controlling moisture absorption is extremely difficult and very costly. Furthermore, compounding and filament fabrication are two separate processes normally performed at different plants, and thus add extra costs and technical challenge of keeping the material dry. In the case of the high-temperature polymer, it is even more difficult to control the residual moisture content and is more prone to blistering during FDM printing due to higher melting temperature.
The innovation reported here deals with attachments and/or modifications to the nozzle and/or printer head of FDM 3D printers that will be capable of combined in-situ melting, mixing, degassing, decavitation, and extrusion of raw materials such as resin pellets and fillers directly, thus enabling direct printing of polymer resins and their composites with reinforcing fillers or fibers without the pre-fabricated filament that involves complicated, multi-step processes. This is particularly beneficial for developing high-temperature polymer composite systems for 3D printing since it not only eliminates development/ fabrication of filament, but also resolves the difficult technical challenges in controlling residual trapped moisture content from the compounding process and handling, resulting in blistering-induced cavitations and subsequently inferior quality of the printed products.
This innovation includes a simpler module/attachment that may only provide decavitation of melted/liquefied polymer or composite filaments that were prefabricated, but not fully optimized in terms of residual moisture content.
The anticipated process sequence of the new FDM printers developed with
this innovation includes melting, mixing, degassing, extrusion, and decavitation, and printing in serial or parallel order. New attachments will be designed to perform those processes individually, or will be connected to the printing nozzle directly or via flexible connection, depending on their size and function. The new printer will still provide the option of using the pre-made filament, but the attachment modules will be designed to take neat resin pellets or powder and fillers directly via an additional feeding mechanism(s). Melting of resin can be achieved by high-temperature air jet or heating element.
During the melting and mixing process, extensive cavitation by moisture-induced blistering will take place if the neat resin or fillers are not fully dried. A resonant acoustics mixing (RAM) mechanism equipped with high-vacuum pulling capacity will be employed for mixing, degassing, and possibly decavitation. Small-scale twin screw extruders or similar mixing mechanism(s) after various modifications also can be considered for the mixing and extrusion steps. In addition to RAM, an optimized metal mesh or sieve will be added for decavitation of the molten polymer-filler mixture. If the prefabricated filaments are used, the metal mesh/sieve and/or other geometrical modifications of the nozzle (such as narrower to wider, spiral tracks/teeth, or serrated tracks/teeth) can be the main decavitation mechanisms. The decavitated molten mixture is then printed via the nozzle tip, improving the quality of the printed articles at reduced porosity.