(a) Pellet extruder with an integrated drip feeder and hopper. (b) CAD model showing the internal structure of the extruder and important dimensions.

Filament-based extrusion is a very common practice in the 3D printing community, but it’s not necessary for extrusion to only work with filament, at least as far as FFF 3D printers go. In order to successfully deposit layers of material to 3D print an object, an FFF system only needs a material flow that can be easily controlled, whether it’s with a ram or syringe style printer or a pellet extruder system.

With pellet extrusion, a screw is used as a feeding mechanism to move and melt the material inside the barrel, before forcing it out of a heated die. Pellet extrusion is a stable process, and offers more flexibility and choice in 3D printable materials, but screw-based pellet extruder designs, while offering many benefits, are more complex than other methods. But this type of system is what a research team from Massey University in Auckland, New Zealand is working to create.

The researchers, from the Center for Additive Manufacturing within the university’s School of Engineering and Advanced Technology, have been developing and characterizing a micro pellet extruder, along with an accompanying 3D printing system.

Khalid Mahmood Arif, PhD, Senior Lecturer in Mechatronics and Robotics from the Center for Additive Manufacturing, told 3DPrint.com, “This pellet extruder is designed from the first principles to meet the size, speed, and requirements of a small scale system. As far we know, this is the first time a pellet printer has not only been developed but also scientifically characterized for strength, surface quality and consistency of the printed parts.”

The research team published a paper on their work, titled “Design and development of an extrusion system for 3D printing biopolymer pellets,” in the International Journal of Advanced Manufacturing Technology; co-authors include Sean Whyman, Dr. Arif, and Professor Johan Potgieter, Professor of Robotics within the Massey Agritech Partnership Research Centre.

Custom built biopolymer pellet printer.

According to the abstract, “The extrusion system is an integral part of any fused deposition style 3D printing technique. However, the extruder designs found in commercial and hobbyist printers are mostly suitable for materials in filament form. While printing with a filament is not a problem per se, the printing of materials that may not be readily available in the filament form or not commercially viable remains untapped, e.g., biopolymers and material blends. This is particularly an issue in the research and hobbyist space where the capability of printing a variety of materials or materials recycled from already printed parts may be of utmost importance. This paper presents a pellet-based extrusion system for the 3D printing of biopolymers. The system has been designed from the first principles and therefore can be extended to other materials with parameter adjustments or slight hardware modifications. A robust mechatronic design has been realized using an unconventional yet simplistic approach. The extrusion system uses a series of control factors to generate a consistent output of material over the course of a print. The platform and surrounding processes are set up so that software can be used to define the printing parameters; this allows a simpler adaption to different materials. The utility of the extruder is demonstrated through extensive printing and testing of the printed parts.”

Comparison of three extruder screw designs. (a) A common three-section screw with its pressure profile, (b) rubber extrusion screw, and (c) an auger drill bit with its pressure profile.

In the paper, the researchers discuss the design and development of their pellet extruder, which can extrude mixes of biopolymers and more common 3D printing polymers, such as PLA, at pellet sizes from 1 – 3 mm in length and diameter.

The team designed the lightweight system from the ground up, relying heavily on basic extrusion theory to make everything work the way it should. The pellet extruder has advanced features such as temperature control, liquid cooling, and controlled pellet feeding, and also includes a drive motor, an extrusion die for shaping material output, a hopper system for feeding the right amount of material, and an extrusion screw for transporting the pellets.

The design of our pellet extruder is very similar in many ways to a conventional pellet extrusion process,” the paper reads. “It is simple full-sized single-screw extruder miniaturized to work with a consumer-sized 3D printing platform. The extruder is vertically mounted with a drip feeder controlling the polymer input, a hopper to guide and hold the material, heating band to heat the polymer, and a liquid cooling loop around the neck of the extruder.”

A variety of 3D printed parts demonstrating the capability of the designed pellet extrusion system.

The goal of the extrusion system is to be able to consistently print, without burning, Harakeke flax fiber that’s been mixed with PLA polymer.

The team put their new system through its paces by printing out a variety of items, using two different extruder designs, and then testing the mechanical properties of the 3D printed parts to see if there were any noticeable differences in print quality between the two designs.

The conclusion reads, “The innovative design of the extruder resulted in a compact and light-weight unit that can be mounted on an open-source scanning system and used for printing just like the filament-based counterparts.”

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