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bioplasticsMAGAZINE_1406

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bioplasticsMAGAZINE_1406

3D printing Low cost

3D printing Low cost extruder Specifications of the low cost extruder Plastics (tested) Production rate Motor Heating Total performance Producing affordable bio filaments for 3D printing PLA, ABS 0.5 kg / h 60 rpm, 14 Nm Up to 300 °C, 48 V, 230 W 0.2 kWh In recent years the use of low cost 3D printing has become a significant factor. A student project at the Institute of Plastics Processing (IKV) in Industry and the Skilled Crafts at RWTH Aachen University deals with the design and the engineering of an extruder that produces 3D printer compatible filaments. Central aspects are low costs and the use of easily available components. The result is an extruder which manages the challenge of uniting functional performance and the minimization of costs. It has the ability to produce customized plastics filaments in a fast and easy way. The personal low cost 3D printer market grew between 2008 and 2011 at an average of 346 % per year. [1] In the context of Fused Deposition Modelling (FDM), there are different requirements that need to be fulfilled by the extruded filament. The filament should be highly customizable and available at comparatively low volumes and low cost. To meet the requirements of small businesses and individuals, a small and very cheap extruder is needed, which is able to produce filament with appropriate technology. The engineering of a low cost extruder The popular, low cost versions of 3D printers are designed to be working with thermoplastics (usually PLA or ABS) in filament shape. These filaments are, compared to pellet costs, relatively high priced. Especially in the case of using multiple colours or material properties the user needs to purchase larger amounts of filament. From this situation, the idea to produce cheap filament from pellets emerged. Colours should be individually mixable and produced in small quantities. From the beginning, the project was sponsored by the IKV. Beside the financial grant and the provision of laboratory extruders, premises as well as professional skill led to the successful preparation of the theoretical foundations for single-screw extruders. Hereby, the scientific approach for designing and engineering the low cost extruder was ensured. Since the goal was a low cost implementation, the core components of an extruder should be replaced by simple, products commercially available in any hardware- or DIY-store. Components of the low cost extruder From a cost-perspective point of view it is obvious that one cannot fall back to complicated screw geometries like threezone screws used in conventional extruders. Therefore a screw with a simple geometry has to be used. In this case 24 bioplastics MAGAZINE [06/14] Vol. 9

3D printing an SDS-hammer drill for concrete is installed, working as a conveying screw. For the cylinder a commercially available precision stainless steel tube is used. Requirements posed on the motor are a high torque transmission at a low rotational speed as well as a constant rotational speed even with fluctuating torque. The implemented DC motor is commonly used as a garage door motor, but meets exactly those requirements. For its cooling a computer CPU fan ventilates cooling ribs. An aluminium frame functions as an absorber for direct agent forces. Laser cut MDF panels serve to conduct the cooling flow, to protect from external impacts as well as to cover components. Their stability is achieved by joining the parts with the help of tongue and groove joints. Advantageous in this case are the low material cost, the manufacturing quality of the panels and the easy installation. To melt the pellets during the conveying process, the extruder has to be heated over a large part of the tube. The basic requirement is a constant, high-power and well controlled heating. Therefore approximately 85 cm of heating wire was wound around the extruder tube and is supplied with 48 V AC, resulting in a heat output of 230 W. The heating is controlled by a PID controller. The extruder is connected to a conventional 230 V AV household outlet. The input voltage is transformed to 24 V DC by a power supply to drive the motor. Additionally, a transformer converts the 230 V AC to 48 V AC to run the heating. Cost analysis The total costs of an extruder are estimated at about 375 Euros. Relevant cost units are power supply, transformer, drill and motor, which together add up to about 50 % of the total. A reduction of 20 % can be achieved by a higher batch size which decreases the manufacturing costs of a singl extruder to approx. 300 Euros. Electrical current costs occur from the total power per hour, 0.2 kWh. Conclusion In the project’s context a low cost extruder was successfully designed, built and tested. As a result of this it is shown that the processing of plastic granules to 3D printable filaments is possible with very simple means and at very low costs. With the extruder a homogenous (after adding a masterbatch) even a coloured filament can be produced. Tests have shown that the filament can be processed on open-source 3D printers with hardly any differences to be observed compared to commercial filament. The deviation in the filament diameter was found to be with in the given tolerances. However, a follow-up project targets optimising a constant diameter by developing a haul-off unit controlled by a cross-section measuring device. This project provides a basic introduction to the development of solutions for a low-budget extrusion. The low cost extruder and its performance data, determined in experiments, conclude with instructions for its use and development and can serve as a guide for future projects. Thus low cost applications open up new perspectives for small businesses in developing and emerging countries. Further members of the student team are M. El‐Mahgary and J. Klose) Literature: [1] Wohlers, T.: Wohlers Report. Fort Collins: Wohlers Associates, 2013 By: Christian Hopmann Head of the Institute Martin Kimm, Yannick Ostad Student Project Workers (Authors) Christian Windeck Head of department extrusion and rubber technology Institute of Plastics Processing (IKV) at RWTH Aachen University Aachen, Germany bioplastics MAGAZINE [06/14] Vol. 9 25

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