Development is moving forward for 3D printing of liquid silicone rubber

Among the latest materials-related business developments in liquid silicone rubber, ACEO is launching new fluorosilicone versions of its LSR 3D printing materials.

The ACEO business unit of Burghausen, Germany-based silicone materials producer Wacker Chemie AG makes drop-on-demand 3D printed LSR materials. The company participated in two 3D printing fairs in May.

At the 3D Print exhibition in Lyon, France, ACEO launched a new fluorosilicone version of its LSR 3D printing materials, displaying the first fluorosilicone sample parts at the fair.

Bernd Pachaly, who heads up the ACEO unit, said: “This is only the beginning of a series of novel materials for ACEO silicone 3D printing, as we will introduce functional silicones enabling unprecedented functionalities of silicone product designs in the next couple of months.”

While exhibiting at 3D Print 2018 in France, ACEO simultaneously also had a booth at Rapid.tech 2018 in Erfurt, Germany, where it showed 3D printed soft robotic grippers, as customized designs in LSR with hardnesses between Shore 20A to 60A.

ACEO said the digitally fabricated pneumatic silicone actuators “exhibit unprecedented programmable bio-inspired architectures and motions.”

The material was already available in Shore 30A, 40A and 60A hardnesses prior to Rapid.tech, in RAL 5010 gentian blue, Pantone 7513C “skin,” RAL 9011 graphite black, translucent, RAL 3000 flame red, RAL 9010 pure white and RAL 7001 silver gray versions. The new, even softer 20A material comes in the same colors, but not as a translucent material.

The formulations combine LSR with reinforcing filler, cross-linking agents and addition-cure catalyst as used in conventional LSR. The LSR cure is triggered off by UV light activation of the catalyst and ends by post-cure of the printed part.

Within an overall Bahsys plastics development and solutions business unit, the Protosys rapid tooling, prototyping and mold insert department of Overath, Germany-based engineering plastics compounds producer and solutions provider Barlog Plastics GmbH introduced injection molding LSR into its activities in 2016. It has focused here on optimizing the bond strength between LSR and polybutylene terephthalate.

In February 2018, Bahsys announced that it had started also using LSR 3D printing as well for prototyping and small-series production without revealing details, however, of the exact type of LSR materials and 3D printers used.

In justification of its move into LSR processing, the company stated that silicone prototypes were generally being made available on the market by use of silicone rubber vacuum casting. It added, obviously referring here to advantages of both LSR injection molding and 3D printing, “this [vacuum casting] process clearly requires only low investment but has the disadvantage that neither LSR as a material for serial production, nor the later production process, can be used.”

Bahsys said its LSR processing capabilities now offer the possibility of producing cost-effective LSR prototypes and low prosecution series parts, whether by liquid injection molding or 3D printing.

The focus among Dow Silicones exhibits at the July DKT German Rubber Conference in Nuremberg was on its 5Shore 50A hardness Silastic LC 3335 grade of LSR for 3D printing, now marketed under the Evolv3d LC 3335 brand name.

Dow introduced the material at K 2016 and has been working on it together with Feldkirchen, Germany-based 3D printer manufacturer German RepRap GmbH, using its LAM liquid additive manufacturing printing machines to print footwear midsole cores.

Dow revealed more details on the midsoles work in April, pointing out that it has been using it to “leverage” in-store 3D printed customized footwear with LSR midsole cores by working together with the ILE innovation laboratory of Bredebro, Denmark-based footwear company ECCO Sko A/S in its Quant-U customized footwear pilot project.

Customers should get their customized footwear printed “within only a few hours,” Dow said, once the structure and gait of the feet have been established with use of wearable 3D sensors and foot scans.

ECCO stated separately that its Quant-U pilot project was going to be available initially for public use for a limited period in April at ECCO's W-21 experimental store in Amsterdam. The company produces its shoes, into which the midsole cores are later fitted, in factories located in China, Indonesia, Portugal, Slovakia, Thailand and Vietnam.

Aside from needing midsole cores, ECCO shoes are made with a DIP direct injection of polyurethane process for the undersoles.

Having launched 3D printed LSR capability at Fakuma 2017, Feldkirchen, Germany-based prototyping company Proto Labs GmbH has meanwhile revealed that it is using the UV-curing 3DP Silicone 3D printing material with Shore 35A (AR-G1L) and 65A (AR-G1H) hardness and the Agilista 3200W 3D inkjet printing machine, both from Keyence.

Keyence first launched its first 3D printing machines with acrylate monomer and urethane-acrylate oligomer materials in 2015. The LSR material was introduced later, in November 2016, along with its AR-S1 aqueous support material.

The Agilista 3200W machine used by Proto Labs has build volume of 297 by 210 by 200 millimeters and prints layers in 20 or 30 µm, depending on the resolution selected. The machine has a footprint of 1,360 by 94 by 700 mm.