3D printing processes

Ultra-small features can be made with the 3D micro-fabrication technique used in multiphoton photopolymerisation. This approach uses a focused laser to trace the desired 3D object into a block of gel. Due to the nonlinear nature of photo excitation, the gel is cured to a solid only in the places where the laser was focused while the remaining gel is then washed away. Feature sizes of under 100 nm are easily produced, as well as complex structures with moving and interlocked parts.^[44]

Yet another approach uses a synthetic resin that is solidified using

In Mask-image-projection-based stereolithography, a 3D digital model is sliced by a set of horizontal planes. Each slice is converted into a two-dimensional mask image. The mask image is then projected onto a photocurable liquid resin surface and light is projected onto the resin to cure it in the shape of the layer.[46] The technique has been used to create objects composed of multiple materials that cure at different rates.^[46] In research systems, the light is projected from below, allowing the resin to be quickly spread into uniform thin layers, reducing production time from hours to minutes.^[46] Commercially available devices such as Objet Connex apply the resin via small nozzles.^[46]

Unlike stereolithography, the printing process is considered continuous by its founders and considerably faster than traditional DLP processes, enabling the production of parts in minutes instead of hours.^[47][48][49]

Recently, the use of stereolithographic 3D printing techniques has been developed further to allow for the additive manufacturing of ceramic materials. Successful 3D printing of ceramics using stereolithography is achieved through the

Computed axial lithography is a method for 3D printing based on reversing the principle of computed tomography (CT) to create prints in photo-curable resin. It was developed by a collaboration between the University of California, Berkeley with Lawrence Livermore National Laboratory.^[50][51][52] Unlike other methods of 3D printing it does not build models through depositing layers of material like fused deposition modelling and stereolithography, instead it creates objects using a series of 2D images projected onto a cylinder of resin.^[50][51][52] It is notable for its ability to build objects much more quickly than other methods using resins and the ability to embed objects within the prints.^[50]

Liquid additive manufacturing

Liquid additive manufacturing (LAM) is an additive manufacturing technique which deposits a liquid or highly viscous material (e.g. Liquid Silicone Rubber) onto a build surface to create an object, which is then vulcanised using heat to harden it.^[53][54][55] The process was originally created by Adrian Bowyer and was then built upon by German RepRap.^[53][56][57]

Lamination

In some printers, paper can be used as the build material, resulting in a lower cost to print. During the 1990s some companies marketed printers that cut cross-sections out of special adhesive coated paper using a carbon dioxide laser and then laminated them together.

In 2005 Mcor Technologies Ltd developed a different process using ordinary sheets of office paper, a tungsten carbide blade to cut the shape, and selective deposition of adhesive and pressure to bond the prototype.^[58]

There are also a number of companies selling printers that print laminated objects using thin plastic and metal sheets.

Ultrasonic Consolidation (UC) or Ultrasonic Additive Manufacturing (UAM) is a low temperature additive manufacturing or 3D printing technique for metals.

Directed Energy Deposition (DED)

Powder-fed directed-energy deposition

In powder-fed directed-energy deposition, a high-power laser is used to melt metal powder supplied to the focus of the laser beam. The laser beam typically travels through the center of the deposition head and is focused to a small spot by one or more lenses. The build occurs on an X-Y table which is driven by a tool path created from a digital model to fabricate an object layer by layer. The deposition head is moved up vertically as each layer is completed. Some systems even make use of 5-axis^[59][60] or 6-axis systems^[61] (i.e. articulated arms) capable of delivering material on the substrate (a printing bed, or a pre-existing part^[62]) with few to no spatial access restrictions. Metal powder is delivered and distributed around the circumference of the head or can be split by an internal manifold and delivered through nozzles arranged in various configurations around the deposition head. A hermetically sealed chamber filled with inert gas or a local inert shroud gas (sometimes both combined) are often used to shield the melt pool from atmospheric oxygen, to limit oxidation and better control the material properties. The powder fed directed energy process is similar to Selective Laser Sintering, but the metal powder is projected only where material is being added to the part at that moment. The laser beam is used to heat up and create a "melt pool" on the substrate, in which the new powder is injected quasi-simultaneously. The process supports a wide range of materials including titanium, stainless steel, aluminum, tungsten, and other specialty materials as well as composites and functionally graded material. The process can not only fully build new metal parts but can also add material to existing parts for example for coatings, repair, and hybrid manufacturing applications. LENS (Laser Engineered Net Shaping), is one example of the Powder Fed - Directed Energy Deposition process for 3D printing or restoring metal parts.^[63][64]

Metal wire processes

Laser-based wire-feed systems, such as

It is also possible to use conventional

In selective powder deposition, build and support powders are selectively deposited into a crucible, such that the build powder takes the shape of the desired object and support powder fills the rest of the volume in the crucible. Then an infill material is applied, such that it comes in contact with the build powder. Then the crucible is fired up in a kiln at the temperature above the melting point of the infill, but below the melting points of the powders. When the infill melts, it soaks the build powder. But it doesn't soak the support powder, because the support powder is chosen to be such that it is not wettable by the infill. If at the firing temperature, the atoms of the infill material and the build powder are mutually defusable, such as in case of copper powder and zinc infill, then the resulting material will be a uniform mixture of those atoms, in this case, bronze. But if the atoms are not mutually defusable, such as in case of tungsten and copper at 1100°C, then the resulting material will be a composite. To prevent shape distortion, the firing temperature must be below the solidus temperature of the resulting alloy.[68]

Printers

Industry use

As of October 2012, additive manufacturing systems were on the market that ranged from $2,000 to $500,000 in price and were employed in industries including aerospace, architecture, automotive, defense, and medical replacements, among many others. As of 2018, 3-D printers have dropped in cost to as little $100 and low-cost higher quality desktop printers are approximately $2500. These types of devices are used widely in industry for prototyping, jig making, fixturing, fixing small custom components, and even additive manufacturing of actual products.^[69]

In addition, higher end 3-D printers have now become relatively common for production and

Military and defense are also incorporating the use of 3D printers. The Royal Netherlands Air Force is using desktop 3D printers at their Woensdrecht Air Force Base to make fixtures and alignment tools.[73] In the United States, the Hill Air Force base is using 3D printed parts in repair of fighter jets.^[74]

Higher education has proven to be a major buyer of desktop and professional 3D printers.^[75] Significant desktop 3D printer purchases by both K-12 and universities helped sustain a desktop 3D printer market that had problems in 2015–2016.^[76] As higher education is the home to research, 3D printing is being used to fabricate equipment to further research and hold down costs. For example, chemists can 3D print flow reactor systems that would otherwise be too costly to purchase.^[77] The UCL School of Pharmacy in the UK created a modular flow reactor system for chemical synthesis that can easily be 3D printed in laboratories around the world at low cost.^[78] Libraries around the world have also become locations to house smaller 3D printers for educational and community access.^[79]

Consumer use

Several projects and companies are making efforts to develop affordable 3D printers for home desktop use. Much of this work has been driven by and targeted at

As the costs of 3D printers have come down, they are becoming more appealing financially to use for self-manufacturing of personal products.[95] In addition, 3D printing products at home may reduce the environmental impacts of manufacturing by reducing material use and distribution impacts.^[96]

In addition, several

Some companies^[specify] are also offering software for 3D printing, as a support for hardware manufactured by other companies.^[100]

Large 3D printers

Large 3D printers have been developed for industrial, education, and demonstrative uses. A large delta-style 3D printer was built in 2014 by SeeMeCNC. The printer is capable of making an object with diameter of up to 4 feet (1.2 m) and up to 10 feet (3.0 m) in height. It also uses plastic pellets as the raw material instead of the typical plastic filaments used in other 3D printers.^[101]

Another type of large printer is Big Area Additive Manufacturing (BAAM). The goal is to develop printers that can produce a large object in high speed. A BAAM machine of Cincinnati Incorporated can produce an object at the speeds 200-500 times faster than typical 3D printers available in 2014. Another BAAM machine is being developed by Lockheed Martin with an aim to print long objects of up to 100 feet (30 m) to be used in aerospace industries.^[102]

See also Construction 3D printing

Microscale and nanoscale 3D printing

Microelectronic device fabrication methods can be employed to perform the 3D printing of nanoscale-size objects. Such printed objects are typically grown on a solid substrate, e.g. silicon wafer, to which they adhere after printing as they are too small and fragile to be manipulated post-construction.

In one technique, 3D nanostructures can be printed by physically moving a dynamic stencil mask during the material deposition process, somewhat analogous to the extrusion method of traditional 3D printers. Programmable-height nanostructures with resolutions as small as 10 nm have been produced in this fashion, by metallic physical vapor deposition Mechanicalpiezo-actuator controlled stencil mask having a milled nanopore in a silicon nitride membrane.^[103]

Another method enhances the photopolymerization process on a much smaller scale, using finely-focused lasers controlled by adjustable mirrors. This method has produced objects with feature resolutions of 100 nm.^[104] Micron wide, millimetre long copper wires have also been printed using lasers.^[105]

See also

• List of 3D printing software

References