The patent only mentioned printing with a “light curable liquid,” but after founding the company 3D Systems, Hull realized that this technique could be applied to other materials. This led to changing the definition to “any material capable of solidification or capable of altering its physical state,” thus creating the basis for what we now call additive manufacturing or 3D printing.
At first it was conceived as a rapid prototyping technology for industrial use, but it has advanced so much in terms of finish quality, the precision of printers and the variety of materials and technologies, that objects are already being produced to be used directly. Today, we can talk about 3D printing in many different areas: automobile and aerospace industries, medicine, construction, architecture, industrial design, and even the food industry, in which chocolate-based complex shapes and designs are no longer surprising. Furthermore, users can connect to a 3D printing service on the Internet from the comfort of their homes, order the manufacture of an object of their choice and receive it via postal mail, or buy their own desktop 3D printer, get the digital file they want to turn into a solid three-dimensional physical object and in just a few hours they will have what they were expecting.
In a not too distant future, the way purchases are made and even the distribution chain could change because some products would not need packaging or warehouses. Everything would be as simple as buying and downloading the file of a decorative vase from the Internet and manufacturing it, printing a key ring or making a part for a broken piece of equipment at home. This has triggered the Maker Movement, in which makers, as they are called, are engaged in providing the services of digital manufacturing from their homes and sending the products to their customers by mail.
These changes go hand in hand with available materials and different additive technologies. The most affordable and widespread because of its simplicity and type of use is Fused Deposition Modeling (FDM). In fused deposition, a continuous thermoplastic filament is melted on a platform by means of an extruder with a heated nozzle whose position is directed by the program in order to “draw” each layer. When a layer is completed, the support changes height to make room for the next layer and deposit again the semi melted material on the solidified layer until the object is built. Despite being considered to be the one with the least precision, it can build parts with wall and layer thicknesses of up to 0.1 mm.
Many different types of materials, which are sold in coils, are used in this process: PLA, ABS, nylon and PET, including experimental materials, such as filaments made of a mixture of resin and wood, bronze or coal dust.
One of the most humane applications of this technology is 3D printing of prosthetic for children. Orthodox prosthetics pose a challenge for growing children. They are very expensive and kids rapidly outgrow them. Now they can be manufactured in just hours, customized, with fun textures or colors, or with the kids’ favorite movie heroes.
Stereolithography (SLA) and Digital Light Processing (DLP) are very similar technologies. Both produce layers by solidifying the drawing made with photosensitive liquid, but they differ in the way they “draw” the layers. The former uses a laser and the latter, a digital projector screen towards the submerged platform. These 3D printers build very high definition parts with a smooth surface finish, which is why they are preferred for jewelry casting, sculptures with intricate features, prototypes and small parts. They are not recommended for printing large objects.
Another important technology is Selective Laser Sintering (SLS) that uses powdered materials, allowing a wider range of materials: plastics, glass, nylon, polystyrene, some ceramic materials, and metals such as steel, titanium, aluminum, iron, or nickel, cobalt or chromium alloys. It has a platform that is covered with this powder, the laser impacts on it drawing and fusing only the necessary material, which upon solidification creates the (sintered) layer. When the platform descends to give room for another layer (0.08 mm), the unsintered powder remains where it was and serves as support for pieces with complex geometries or protruding parts. Once the object is completed, the material can be removed and reutilized for other printings. This is SLS’s main advantage in terms of savings.
This technology has been used in Cuba for a number of years at the Neurosciences Center for the manufacture of hearing and dental implants. For dental prostheses, a dental impression is taken of the patient’s mouth and a plaster model is made. It is then placed on a 3D scanner to obtain the digital geometry, the part is designed virtually and the 3D printer turns it into a solid object, to be coated with the required aesthetic material.
There are many other processes that can generate volume by overlaying layers. In building, for example, they are already being applied to create larger-scale walls using cement mixtures directly as their material, being able to build a house in a single day.
These technologies, however, are not without limitations. They are not feasible for mass productions and the size of the final object depends on the size of each printer. Virtually anything can be manufactured—only a lack of ethics in their use could limit their benefits. ▪