bioplasticsMAGAZINE_1406

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