What is silicone 3D printing?
Silicones are polymers based on polymerized siloxanes and are known for their rubber-like properties, as well as good thermal stability and chemical resistance, biocompatibility, water tightness, environmental hardiness, and electrical insulation. This roster of properties has led to silicones being used for a wide variety of applications, from cooking utensils, to aircraft seals, to electrical coatings, to medical implants.
Despite their widespread adoption using more conventional manufacturing processes, silicones are notoriously challenging materials to 3D print. This is largely due to the fact that silicone is an elastomer. Unlike thermoplastics which can be melted and returned to a solid state, elastomers cannot be melted down once they are solidified. This has excluded many forms of 3D printing—such as fused filament fabrication (FFF)—from the possibility of 3D printing silicones.
Even so, it is possible to 3D print silicone-based materials and there are a number of solutions that exist on the market today for silicone 3D printing. We’ll explore the topic in further detail below, discussing how silicone 3D printing works, applications for the technology, and the pros and cons of silicone 3D printing.
How does silicone 3D printing work?
In recent years, a handful of additive manufacturing technologies compatible with silicone materials have been developed. Interestingly, because the material group has not fit well with any existing 3D printing process, companies and research groups have had to create specialized additive manufacturing solutions tailored to silicone.
Within this subgroup of AM technologies, there are a few different approaches to printing silicone. The first is based on deposition technologies. Unlike FFF, which uses a heated printhead to extrude layers of melted thermoplastics onto a print bed—which then solidify as they cool—silicone deposition 3D printing does not involve any heating process. Instead, a print head is used to deposit droplets of liquid silicone onto a print bed and a curing method is used to harden the droplets.
ACEO, a company owned by Wacker Chemie AG, has pioneered a deposition-based 3D printer that uses a print head to dose single droplets of a silicone-based 3D printing material onto a build platform. These droplets are then cured using UV light (when it comes to silicones, the curing process is also called vulcanization), which solidifies the droplets by creating crosslinks. Parts are built up in this fashion—dosing and curing—layer by layer. ACEO’s 3D printer technology integrates several printheads, enabling multi-material silicone printing as well as the use of removable supports for achieving more complex geometries.
Another deposition approach was introduced by InnovatiQ (formerly German RepRap). The technology, called Liquid Additive Manufacturing (LAM), is described as “an additive manufacturing process in which liquids (or low-strength materials) can be additively processed, such as liquid silicone rubber (LSR).” The LSR material compatible with this process is produced by chemical company Dow. The LAM process uses volumetric extrusion to precisely deposit the liquid silicone material. Curing takes place directly in the build space after every printed layer of material. Using this technology, the curing is achieved using a high-temperature halogen lamp.
3D printing company Carbon also offers a silicone 3D printing capability based on its Digital Light Synthesis (DLS) technology. In 2017, the company launched SIL 30, a silicone urethane material with good tear resistance and biocompatibility that is compatible with DLS. This process uses UV light projections to cure layers of liquid polymer resin. In this technique, the silicone resin material is held in a vat, with layers solidifying as the build platform is raised.
Swiss startup Spectroplast is also an emerging player in the silicone 3D printing area. The company’s patented Silicone Additive Manufacturing (SAM) technology is capable of printing 100% pure silicone materials and is offered through a dedicated 3D printing service. Little more is known about how the process works but Spectroplast has also brought to market TrueSil, a series of ISO-certified silicone materials for 3D printing with a range of Shore A hardnesses.
Of course, these are not all of the companies that provide silicone 3D printing capabilities. In general, however, silicone 3D printing requires some form of liquid material dosing (whether it’s using droplets or a vat of resin) and curing or vulcanizing to solidify the printed layers. In some cases, support material removal and additional curing to further solidify the silicone part may be necessary, but extensive post-processing is not generally required because of good surface finish quality.
There is also another way 3D printing is used in the production of silicone parts. While we will not dive into this process in detail because it is an indirect 3D printing technique, it involves printing masters for producing silicone molds. Molds themselves can also be 3D printed.
Silicone 3D printing advantages and disadvantages
Like any material, there are pros and cons to 3D printing silicone elastomers. Some of the main advantages of silicone in 3D printing are related to the material’s mechanical properties, including its unique combination of strength and flexibility, temperature and chemical resistance, biocompatibility, and electrical insulation. Of course, these advantages are available using traditional production methods.
3D printing unlocks a whole other set of advantages for silicone manufacturing, including greater design freedom, customization, and agile production. Silicone 3D printing also enhances the product development process by enabling rapid prototyping and cutting back on prototyping costs. In other words, product developers and engineers can rapidly iterate silicone prototypes, test them, make necessary adjustments, and reiterate until the design is perfect.
Silicone’s main disadvantages when looking at 3D printing are its processability and accessibility. Because the material is tricky to process using many conventional additive techniques—such as FFF/FDM—it requires specialty hardware which can be expensive. Moreover, because silicone 3D printing is still a niche segment of the broader AM market, silicone material options are limited, which also creates accessibility issues, both in terms of availability and cost.
In its current state, silicone 3D printing also has limitations in terms of what types of parts it can create. Silicone 3D printing systems on the market have small build volumes and are thus not well-suited for the production of large-scale parts. This inevitably limits the prototyping and production applications for silicone 3D printing. Another consequence of being such a new technology, is that silicone 3D printing has few standards and documentation associated with it. Of course, this challenge is not as critical for prototyping applications and it will be addressed as the technology continues to advance and adoption increases.
Silicone additive manufacturing applications
Just as there are many applications for silicone materials, there are many opportunities for 3D printing silicone. Because 3D printing is well suited for one-off or small batch production, mass manufacturing of silicone products is still best left to traditional injection molding techniques. The big opportunity for 3D printing silicone applications therefore lies in the production of functional prototypes, custom parts, or small production batches, which would not be economically viable using injection molding.
Today, we see silicone 3D printing used in many industries, from medical to aerospace. Let’s take a closer look.
The medical and dental industries are among the most interested in silicone 3D printing capabilities. This is because silicone is a non-toxic, biocompatible material and 3D printing enables the production of patient-specific products. For example, silicone 3D printing can be used in the production of custom anatomical models (based on patient CT scans), which can improve pre-surgical preparation. Silicone is particularly interesting in these cases because of its transparent properties, allowing surgeons to visualize internal anatomical structures. In healthcare, silicone 3D printing also has potential to be used in the production of soft prosthetics, such as ears and noses, thanks to its flexible, soft texture. These properties are also useful in dentistry, where silicone 3D printing can create soft gum and gingiva models to complement dental models and devices made using hard materials on DLP or SLA platforms.
Silicone’s biocompatibility and flexible material properties are also advantageous in the consumer goods sector. For instance, 3D printing is used to produce customized products that come into contact with skin, such as earbud adapters for earphones, headphone pads, and more.
Last but not least, the technology offers unique advantages for robotic and industrial applications. For instance, the flexible yet durable material is ideal for soft robotic components. 3D printing enables engineers to design complex prototypes or end-use components, such as grippers or pneumatic actuators, for soft robots. Because of silicone’s electrical properties, the material is also well suited for prototyping or customizing electrical enclosures. Also in the industrial space, there is a growing interest in the use of silicone 3D printing for streamlining the prototyping of seals and gaskets used in the automotive and aerospace industries, among others.
Though silicone AM is still a nascent and specialized subsegment of the broader additive manufacturing industry, there is enormous potential for the technology. Silicone’s properties offer benefits for a wide range of applications, while 3D printing allows for rapid prototyping, customization, and increasingly complex designs. As more silicone 3D printing solutions and materials are developed, and the process is increasingly standardized, adoption and application opportunities will continue to grow.