A new additive manufacturing technique could make 3D printing even more attractive for applications in the manufacturing industry and others. The technique uses light to convert a liquid into a solid in a short time. This makes it possible to print an entire object in just a few minutes, something that quickly takes hours with many other printers.
The printer has been developed by the University of California Berkeley (UC Berkeley). The 3D printer is called the 'replicator', which is a reference to a device from Star Trek that can be used to create objects.
'FDM has many drawbacks'
With the replicator, researchers aim to address limitations of existing 3D printers. Many existing 3D printers - including variants that already use light - use fused deposition modelling (FDM), a technique in which a new layer is printed each time to build up an object layer by layer. This approach offers several limitations and drawbacks, according to the researchers:
With FDM, it is relatively difficult to print flexible objects as flexible materials deform during the printing process.
To print certain shapes such as arcs, supporting structures are needed, which have to be removed after the printing process.
As objects are printed layer by layer, a 'staircase effect' is created on the sides of an object.
Viscose liquid
The replicator offers an answer to these limitations and drawbacks. The printer uses a viscous liquid. If this liquid - which is also described as a resin - is exposed to a certain amount of light, a reaction occurs that causes the material to harden. By accurately projecting patterns of light onto a rotating cylinder of the viscose liquid, this liquid can be cured into a desired shape in a single pass. These patterns of light the researchers compare to films.
The printing process requires easily available components. "Basically, you take a standard video projector, which I literally brought from home, and plug it into a laptop to project a series of computerised images, while a motor spins a cylinder containing 3D printing resin," explains Hayden Taylor, a university lecturer in mechanical engineering at UC Berkeley. "Of course, there are all sorts of subtleties here, such as how you build the resin and especially how you generate the images that are projected. However, the barrier to creating a very simple version of this tool is not great."
Printing material around an existing object
The researchers claim that the replicator can printer objects that are smoother, more flexible and complex than is possible with traditional 3D printing techniques. Among other things, the replicator makes it possible to print a new layer of material around an existing object. As an example, the researchers cite the handle of a screwdriver, which is printed around the metal part.
The technique behind the replicator could have a major impact on the deployment of 3D printers, researchers expect. "I think this is a route to being able to customise objects on a large scale, whether that means prosthetics or running shoes," Taylor said. "The fact that you can take a metal component or something from another manufacturing process and add customised geometry to it could completely change the way products are designed."
The team has now printed a series of objects with the replicator. These objects range from a small sculpture to a custom-made model of a jaw. Using the 3D printer, objects up to about 10 centimetres in diameter can currently be printed.
Inspired by CT scanners
The technique behind the replicator is inspired by healthcare CT scanners, which allow doctors to look inside the human body. A CT scanner sends X-rays or other electromagnetic beams into the human body at different angles. By analysing the resulting patterns, it is possible to visualise organs and tissues. "In fact, we are reversing this principle," Taylor said. "We are trying to create an object rather than measure an object. However, much of the underlying theory required for this can be translated from the theory behind computed tomography (CT)."
The resin used consists of liquid polymers mixed with light-sensitive molecules and dissolved oxygen. Exposing this resin to light activates these light molecules. This creates a process that dissolves the oxygen in the resin. Only where the oxygen is completely dissolved do the polymers form the compounds that convert the liquid resin into a solid. Resin that is not used in this process can be 100% reused. As a result, hardly any material is lost when printing objects, according to the researchers.
Object need not be transparent
The researchers stress that although light must be able to penetrate the resin for it to cure, the final object does not have to be transparent. This is possible thanks to the use of a special paint that allows light waves needed to cure the resin to pass through, but absorbs other light waves.
Author: Wouter Hoeffnagel
Source: UC Berkeley
Photo by: Hayden Taylor of UC Berkeley
