Milan — Silicones Europe (CES) trade association Secretary General Pierre Germain gave an update on 3D printing of liquid silicone rubber at the Silicone Elastomers World Summit in Milan in November.
In one example, a high-temperature vulcanizing solid silicone rubber prosthetic foot made by Stamos + Braun Prothesenwerk GmbH in Dresden, Germany, has been enhanced with a soft, fast printing 3D printed UV-curing LSR lattice structure inlay for enhanced comfort.
The project was developed at Dresden Technical University's IFD institute for fine mechanics and electronic design.
Stamos + Braun was established in 2013 by Managing Director Alex Stamos and CEO Christoph Braun, with the former focusing on aesthetic aspects and the latter on technical functioning aspects.
IFD says the new insert reduced the weight of the cushion function by 70 percent over non-latticed silicone gel previously used. Initial tests have been successful, opening opportunities to develop artificial hands and fingers with integrated bone structures directly in a single printing process.
The researchers also see potential for 3D printed hearts, kidneys, intestines and spleens. As Germain pointed out, ETH University in Zurich, Switzerland, has already made a 3D printed silicone heart.
Rick Ziebell of Cerritos, Calif.-based based R.D. Abbott Co. Inc. also addressed LSR 3D printing: "Silicones — and more specifically liquid silicone rubber — is uniquely suited for its flowable viscosity at room temperature and fast heat-activated cure system."
Ziebell described how a printer lays down a continuous bead for each layer and that "directional, bead thickness, bead separation and layer-to-layer overlap are important considerations for optimal printing."
The best adhesion of beads and layers is obtained, Ziebell stressed, "when materials flow together."
He revealed that beads have been found to adhere better when successive layers are laid down parallel with offset orientation, with all beads aligned with each other, so that the following layer can "infill" the trough between the beads of the preceding layer.
Extrusion at a rate greater than the linear travel of the dispensing head results in overflow for a higher degree of infilling. These approaches "provide best print configuration by producing best looking and functional performance," Ziebell said.
Ziebell said printing in a programmed direction creates anisotropy rather like flow lines from an injection molding gate. R.D. Abbott made 3D printing and injection molding comparisons of Evolv3D LC 3335 from Dow Silicones, a type of LSR that is analogous to commercial injection molding grades, yet with curing behavior adapted for 3D printing.
Ziebell concluded that although printed properties do not exactly match molded ones, test bar values obtained were similar and that compression set values did not differ by more than 5 percent.
R.D. Abbott and Dow Silicones work closely with 3D printing machinery producer German RepRap GmbH in Feldkirchen, which in November commercially launched its new L280 printer, dedicated to printing the Dow halogen lamp heat-curing Evolve3D LC 3335 grade. That launch happened at the Formnext 2018 trade show.
Also at Formnext 2018, Wacker ACEO launched a new 3D printable electrically conductive LSR, developed with Duderstadt, Germany-based Cinogy GmbH for the conductive area of its PlasmaDerm silicone cold plasma wound care dressing device.