Vol.:(0123456789) 1 3 Progress in Additive Manufacturing https://doi.org/10.1007/s40964-019-00088-4 FULL RESEARCH ARTICLE Direct coupling of fxed screw extruders using fexible heated hoses for FDM printing of extremely soft thermoplastic elastomers Mohammad Abu Hasan Khondoker 1  · Dan Sameoto 1 Received: 25 June 2018 / Accepted: 20 June 2019 © Springer Nature Switzerland AG 2019 Abstract We present a new method—fused pellets printing—to print any thermoplastic materials by converting a screw extruder into a direct source for feeding material into fused deposition modeling (FDM) style 3D printer. We achieve this by feeding thermoplastic pellets into a stand-alone single screw system that melts and pushes the material through a fexible heated hose to the print head. The material is fnally deposited through the print head onto the print bed to construct the 3D object. This heated hose decouples the large mass extruder from an FDM print head which can then move with high speed and precision. The result is a very simple 3D printing tool that can take raw input pellets or even recycled thermoplastic scrap, and directly print parts without the need to produce an intermediate, high-quality flament. This technique has been suc- cessfully used for pellets of both soft and hard thermoplastics. Using pellets of styrene–ethylene–butylene–styrene, airtight pneumatic soft robotic actuators have been printed in a single process. In theory, this technique should be suitable for any thermoplastic material regardless of their fexibility, stretchability, and hardness which is not possible with currently avail- able commercial FDM systems. Keywords Fused deposition modeling · Additive manufacturing · Fused pellet printing · Thermoplastic elastomer · Pellet extruder 1 Introduction Fused deposition modeling (FDM) is an additive manufac- turing (AM) technique where a molten material is extruded through a nozzle to develop two-dimensional (2D) layers. Each layer is deposited onto the previously deposited layer, thus constructing the whole three-dimensional (3D) object [1]. In general, in FDM, the feed material is provided as a previously formed flament from a roll, with full control over the feed rate by virtue of a motor-roller feeder assem- bly. Then, the flament is liquefed inside a melt chamber and then extruded through a nozzle. The melt chamber and the nozzle assembly are commonly known as the hot end. The flament between the spool and roller assembly is in tension, whereas, between the roller and melt chamber, the flament is in compression [2]. Three major factors control the operation of a motor-roller feeder assembly—the maxi- mum torque supplied by the feeder motor, the amount of force transferred from the motor shaft to the solid flament, and the column strength of the flament before entering the melt chamber [3]. The main driving force is the torque (τ) supplied by the feeder stepper motor. Here, the solid flament acts as a piston to push the highly viscous polymer melt through the print nozzle. The required motor power ( P motor ) can be estimated from Eq. 1 [4–6]: where ΔP is the pressure drop in the melt chamber, A is the cross-sectional area of the flament, and  r and R r are the angular speed and radius of the toothed gear of the driving motor. The coefcient of friction (f) between counter-rotat- ing wheels and the flament determines how much force can be transferred to the flament from the motor shaft. Elkins (1) P motor = 1 2 ΔPA r R r , Electronic supplementary material The online version of this article (https://doi.org/10.1007/s40964-019-00088-4) contains supplementary material, which is available to authorized users. * Mohammad Abu Hasan Khondoker khondoke@ualberta.ca 1 Department of Mechanical Engineering, University of Alberta, 10-390, Donadeo Innovation Centre for Engineering, Edmonton T6G 1H9, Canada