3D-printed sensors
3D-printing is becoming increasingly important in industrial manufacturing. It not
only makes it possible to produce very complex shapes that would otherwise be
virtually impossible to generate using conventional processes, but also enables
small batch numbers to be produced on a cost-effective basis. However, up to
now, the integration of electronic components and consequently, the production
of customized sensors has presented a challenge. Now, together with the BadenWürttemberg-based companies ARBURG and Balluff, Fraunhofer IPA has achieved
a breakthrough.
Sensors in individualized form are interesting for tasks in automation technology, as
they can be used flexibly for a variety of applications. Inductive proximity sensors are
available in cylindrical metal casings in which a coil, a circuit board and a plug are
installed in a fixed configuration – a standard component with a fixed geometry. In
automation technology, inductive proximity sensors are used in great numbers for
non-contact detection of metal objects. In industrial applications they can not only
register the proximity of a component, but also at what distance it is located. However,
due to the shape of the casings, inductive proximity sensors for integration in specific
environments – robotic arm gripper fingers, for example – had not yet been developed
until now.
A casing of any shape
The question therefore arose: Why not print the sensor casing in plastic so that it can
be manufactured in any shape? This is exactly what a research team from the Centre
for Additive Production at the Fraunhofer Institute for Manufacturing Engineering and
Automation IPA has now achieved. The team was supported by colleagues from the
plastics processing machine manufacturer ARBURG GmbH & Co. KG and the sensor
and automation specialist Balluff GmbH. A plastic with high dielectric strength and
flame-retardant properties was required for the sensor casing. The experts opted for
semi-crystalline plastic polybutylene terephthalate (PBT), which is used as standard
injection molding material for the production of electronic casings. However, this type
of material had not yet been used for 3D printing, necessitating work of a pioneering
nature.
Conductor tracks in 3D printing
The plastic was fed in granulate form into a “freeformer”, ARBURG’s industrial additive
manufacturing system, which uses a material preparation unit with a special plasticizing
screw. After melting the standard granulate, the freeforming process, which uses no
FRAUNHOFER INSTITUTE FOR MANUFACTURING ENGINEERING AND AUTOMATION IPA
molds, followed: A high frequency nozzle closure discharged tiny plastic droplets,
which could be precisely positioned with the aid of a movable part carrier.
In this way, the freeformer created three-dimensional components with cavities layer by
layer, into which components could be inserted during the printing process. To make
this possible, the freeformer automatically interrupted the process at each respective
layer, so that the coil, circuit board and plug could be integrated very precisely. In a
separate process, a dispenser was then used to produce the silver conductor tracks
inside the casing. To complete the process, all that was needed was to overprint the
cavities and then pot them in polyurethane.
The team produced more than 30 demonstration models of customized sensors in this
way and then put them through their paces: the components had to be able to withstand temperature changes and vibrations, they had to be waterproof and pass an
electrical insulation test. By optimizing the design and manufacturing process, the tests
were ultimately completed successfully.
The “Electronic Function Integration in Additively Manufactured Components” research
project ran for eighteen months. Stefan Pfeffer, who led the project at Fraunhofer IPA,
is currently working with ARBURG on research into how conductive plastics can also be
used in the future to tap into additional application areas.
