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Standard methods for additive manufacturing, also known as 3D printing, have major drawbacks with regards to process speed and mechanical strength of the finished product.
Standard commercial technology uses a layer-by-layer approach to fabricate. As you might imagine, the mechanical speed of a printer arm and the curing rate of the material limits the process.
Mechanical parts made from additive manufacturing can be of inconsistent quality, with variable durability and mechanical qualities based on the print direction and the mechanical layer-by-layer approach.
Continuous Liquid Interface Production (CLIP) is a technology developed by the California-based start-up Carbon that addresses these major drawbacks through a fabrication process that “grows” objects out of a pool of resin, rather than mechanically putting down layer after layer.
CLIP is based on a photochemical system involving the interface of liquid resin and a light source that triggers a photochemical reaction, curing the resin into a solid state. The Carbon system relies on a tuneable light sequence that meticulously manages the light-resin interaction.
CLIP also uses an oxygen-permeable window in the base of the resin vat, just above the light source, to create a hair-thin polymerization-free zone. Dubbed the "dead zone", this oxygenated region prevents resin from curing and adhering to the projection window. It also allows resin to flow into areas where the light source can cure it.
Cross-sectional images of the object are played in sequence from the light source underneath the resin pool, creating a physical object that rises from the dead zone. The result is a 3D printing process that can happen swiftly without interruption or the creation of highly discreet layers.
After the printing process, excess resin is cleaned from the object and build plate, while supports are removed. At this point, most materials require a secondary, thermal cure in an oven for 4 to 13 hours. A secondary chemical reaction caused by this curing increases durability.
This system is a bit comparable to digital light processing (DLP). However, the Carbon approach is up to 100 times faster and is also capable of creating higher-resolution items with stronger mechanical qualities.
In April 2016, Carbon unveiled its first commercial CLIP-based printer called the M1. The M1 has a build envelope measuring 144 x 81 x 330 mm, which is an ideal size for prototyping and low-volume production.
The M1 uses analytic software and sensors to perform diagnostics and optimize performance to improve the overall process over time. Internet connectivity allows the machine to perform seamless software updates.
The company also released seven different resins with the M1. Three Rigid Polyurethane (RPU) resins were designed to be extremely stiff, making them very versatile and well-suited for use in electronics, automotive parts and other applications that require robust mechanical qualities. The other resins, such as the Flexible Polyurethane (FPU) and Prototyping Resin (PR), were engineered for specific mechanical purposes.
Beyond CLIP?
In January 2019, researchers at the University of Michigan announced the development of a system capable of 3D printing an entire object with a single flash of light, rather than the layer-by-layer approach used in CLIP. The Michigan team achieve this by using a dual light source instead of an oxygen membrane.
The Michigan system features two different-colored lights with correspondingly varied wavelengths: ultraviolet and blue light. Lights can be adjusted to begin or halt curing as needed using a resin mixture made up of photo-initiators and photo-inhibitors.
By adjusting the strength of the light, the novel technique is also able to perform topographical patterning with a single exposure.
As opposed to CLIP oxygen membrane, the combination of lights permits a much thicker "dead zone", where polymerization doesn’t happen. This, in turn, allows for more viscous and structurally robust materials to be used in the fabrication process.
References and Further Reading
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