3D printing turns digital 3D models into solid objects by building them in layers. After initially being developed in the 1980s, manufacturers and designers have increasingly accessed the technology for rapid prototyping (RP). As is the case with other technologies that were born to serve niche markets, 3D printing has begun to evolve into a much more widely utilized manufacturing technology – one that has the potential to radically transform many design, production, and logistics processes and even reach the consumer market.

How It Works
3D printing usually starts with a computer-aided design (CAD) model or a digital scan. The design is then ‘sliced’ by dividing the object into thin cross sections. Material is then expelled from the printer head in thin layers, usually no more than 1mm thick. Successive layers are printed out one on top of the other, gradually building up in the shape of the desired object.

Although the 3D printing industry is evolving at a rapid pace, at the moment, there are essentially four categories of 3D printers:

  • printers that extrude a semi-liquid material
  • printers that solidify a curable resin
  • printers that bind or fuse the granules of a powder
  • printers that stick together cut sheets of material

Even among these four categories, however, several different processes are used to print a completed 3D item.

Material extrusion
Today, material extrusion is the most common 3D printing process. It uses a nozzle to extrude a semi-liquid material to create successive object layers. Usually, the ‘build material’ is a thermoplastic delivered to the print head as a solid, thin strand or ‘filament’ that is then heated into a molten state.
This type of 3D printer is the first to reach the consumer market and can often be purchased for a few hundred dollars. Chances are, if you have a 3D printer in your home or office at some point over the next ten years, it will be a material extrusion printer. At the other end of the spectrum, high-end industrial machines, costing hundreds of thousands of dollars, can produce final objects comparable to injection molded parts. There is even one large enough to fabricate the chassis and body of a full-sized car.

Vat photopolymerization
Vat photopolymerization uses a light source such as a laser to build up consecutive layers within a container of liquid photopolymer. Stereolithographic printers (SLAs) position a perforated platform just below the surface of the liquid photopolymer. An ultraviolet laser beam then traces the design’s first layer on the liquid’s surface, causing a very thin layer to solidify. The perforated platform is lowered very slightly, and the process repeats until a complete object has been printed.
Currently, vat photopolymerization 3D printers are expensive to run due to the cost of their photopolymer resins, but they offer very high resolutions and deliver excellent surface quality.

Material jetting
Material jetting uses a print head to spray liquid layers that are then solidified, usually through exposure to UV light. This method results in very high-resolution 3D prints (objects). Material jetting is becoming popular because it can produce multicolored output by spraying several different materials from its multi-nozzle print head.

Currently under development is a new material jetting technology called “Nanoparticle Jetting (NPJ),” which injects and suspends metal nanoparticles into a liquid base, allowing inkjet-style technology to print highly detailed metal parts in 3D.

Binder jetting
Binder jetting uses a print head to spray binding materials, such as glue, onto consecutive layers of powder. Binder jetting 3D printers can add colored inks to the critical materials to produce full-color output.

Binder jetting allows designers to produce negatives, molds, and finished objects. When a binder is sprayed onto the sand, the resulting hollow object is used as a sand-cast mold or pattern into which molten metal is poured. Once the metal has cooled solid, the sand is then broken away.

Powder bed fusion
Powder bed fusion uses a heat source to fuse successive layers of powdered plastic or metal materials. This method is expensive and complex to master and, therefore, not in heavy use. However, When utilized, it can produce very high-quality industrial parts.

Directed energy deposition
Directed energy deposition uses a targeted heat source to fuse powdered metal build material as it is being deposited. Unlike powder bed fusion, the powdered build material is deposited from a nozzle through a high-power laser or electron beam that fuses it into solid metal. This method can also fuse metal objects together, such as broken or damaged items.

Sheet lamination
Sheet lamination bonds together cut paper, plastic, or metal sheets using pressure and heat. The stacked item is then cut into the desired shape with a laser or cutting blade and sprayed with color inks to create incredibly detailed models.

Is a 3D printer in your future?
Perhaps, but probably not right away. Although the market for personal 3D printing is growing annually, their consumer “usefulness” – measured by the types of objects that can currently be fabricated on a home or office 3D printer – is pretty limited. Relative to the other technologies you have in front of you right now, 3D printers are in a very, very early stage of development. Devices allowing mainstream consumers to fabricate a wide range of products are unlikely to arrive on the market for another decade or more.

BONUS: What is 4D printing?
As the name implies, 4D printing is 3D printing with the addition of an additional dimension – time. When time and/or an additional stimulus are applied to a 3D-printed object, that object transforms pre-programmed. The trigger could be any number of things – pressure, heat, water, electrical charge, etc. 4D printing, therefore, has more to do with the printing material than the act of 3D printing itself.

The concept of 4D printing introduces a unique concept that scientists and technologists are currently exploring – can we use a 3D printer to create objects that can (re)create themselves?

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