3D Printing Techniques

Technology keeps advancing, but not everyone advances with it. It can be easy to stop paying attention to latest inventions, but every novel creation opens up new possibilities, so it’s crucial that the general public keeps in touch with cutting-edge technology. 3d printing, in particular, is a fast-paced field which continues to become more affordable and diverse. Many may not realize that 3d printing is a broad name given to numerous different methods of manufacturing unique objects for both large industries and individual consumers. Each technique offers different benefits and therefore every type is worth mentioning.

The first type of 3D printer is perhaps the most well known, and is the type used at Rocky Hill. Fused Deposition Modeling (FDM) printers are one of the easiest to comprehend. This type of printer, like all others, creates the object layer by layer, which the object has been split into through the computer software. The width of a layer varies and is adjustable on some 3d printers, ranging from 25 – 100 um (1 um or 1 micron = 0.001mm). The greater the width, the less time the will take to print but less the detail it will have. FDM printers have an extruder  which thin filament (made of plastic, metal, etc.) feeds into and is heated to its melting point or above. PLA filament, for example, can be heated to 401 degrees fahrenheit and adjusted from that temperature. Once the filament is a liquid, it comes out of the bottom of the extruder onto a build table and is placed on the coordinates of the layer (x,y). The liquid cools within seconds, creating a solid structure, and the the build table moves down (along the z axis) the width of a layer. The next layer is then printed and this process is repeated until the entire object is created. It is important to note that in this style of printing if a layer is not supported by the layer below it, computer software (if enabled) will generate a support which can be removed afterwards. While these supports allow for “floating” objects, they do not always detach completely and remnants can lower the quality of the print. FDM printers are chosen because they are compact and affordable, used for commercial prototyping and general consumer use. Material Jetting (MJ) printers use the same method as FDM printers, but the difference is that MJ printers use wax and have greater detail. The object itself prints in a wax with a high melting point, and the supports for it print in a wax with a lower melting point. Once the print is complete, the supports can be melted away in a heated bath while the object remains solid. Material jetting printers are most often used by jewelers making experimental wax castes because it is more affordable and time efficient than manually creating a wax caste.

Stereolithography (SLA) and digital light processing (DLP) printers are similar two similar printing techniques. A pool of liquid plastic resin is placed above a laser or projector and a build table is submerged in the pool one layer width from the bottom in both techniques. The resin is a sensitive polymer which solidifies when exposed to UV light, which is the lightsource beneath the resin in the case of SLA and DLP printers. The light hits the resin in the shape of the layer and causes it to solidify on the build table. The build table then raises the width of a layer and the process repeats until the object is created. The difference between SLA and DLP printers is that SLA printers use a laser whereas DLP printers rely on a projector. While projecting an entire layer is faster than a laser going to individual coordinates one at a time, the projector is digital and therefore pixelated, whereas a laser is able to create curved edges. SLA  printers offer greater detail but DLP printers take a fraction of the time, so the choice is left to the preference of the consumer. Both printers are used more often commercially than by individual consumers because of their greater cost and precise detail than FDM printers.

Selective laser sintering (SLS) selective laser melting (SLM) printers are near-identical techniques, and SLM printing is often considered a subcategory of SLS printing. In both cases a photon-emitting laser traces each layer of an object on a bed of metallic (steel, aluminum, titanium, etc.) powder and causes the particles to fuse together. After the layer is complete the table lowers the width of a layer and a roller places a new layer of metal powder on top of the old one. Once the object is complete it must be dug from the powder. The difference between two is that SLS printers only sinter metal particles (combines them into a porous mass) whereas SLM printers melt the particles so the object becomes a homogenous mass. While SLM printers are stronger because there are no air pockets in the material, they rely on metals melting points and can only work for a single metal, so if the material is an alloy an SLS printer should be used. Similar to these printers is the electron beam melting (EBM) printer, which uses a stream of electrons rather than a laser and requires a vacuum in order to function. All three types of printers are expensive because of their price (high powered lasers and electron beams have an exorbitant price) and because the metal powder which the objects are created from. The printers are mostly used commercially such as in the aerospace industry though consumers can order prints done in this technique from professional 3d printing companies such as Sculpteo.

Similar to to SLS printers, binder jetting (BJ) printers have a bed of a granular solid, though in addition to metal powder they can also use materials including sand and ceramics. BJ printers excrete a liquid bonding agent which binds together the particles and each layer. While they do allow for color prints (changing the color of the binder) and are cost-effective, the objects created are not durable. An advancement in this technique are multi-jet fusion (MJF) printers which first lays down a fusing agent to create a solid layer and then a detailing agent which refines the layer’s shape. Infrared light is then shone upon the layer to\ catalyze the fusing agent and solidify the layer. The benefits of printing with MJF printers are that the objects are strong, conductive, and chemical resistant.

Perhaps the most unique type of 3D printer is the laminated object manufacturing  (LOM) printer. The printer creates objects by rolling a sheet of paper, plastic, or metal across a build table. The paper and plastic sheets are coated in an adhesive, so that when they are heated and pressed by a roller they fuse together. A computer-controlled laser or knife then cuts the shape of the layer from the sheet, the build table lowers, and excess material is removed. This process is repeated until the object is created, and paper prints can be sealed afterword with paint to prevent water damage. LOM printers are expensive, are not particularly accurate and cannot create hollow objects, their materials are affordable, they’re fast, and they’re great for prototyping and cast-making.

3D tissue and organ printing is a rapidly advancing field, and organ printers are more complex than most. One type of bioprinter, Novogen MMX, uses the the FDM technique except with dual extruders, one places cells and the other places hydrogel, which keeps the cells in place (a structural support). Another type, inkjet printers, print directly on top of a wound and create a skin graft. The most intricate is the six axis printer, which prints from multiple directions at once (not just ground up) so that each piece can be created separately and more quickly. The valves of a heart, for example, are printed once the interior of the heart is completed. Bioprinting offers great opportunities, such as healing wounds faster and ending the shortage of organs, but there are obstacles. For example, even though a subjects own cells may be used to create the organ or tissue, they may be rejected by the body and not function properly.

3d printers are an amazing technological tool that can aid fields such as aerospace, art, and medicine, and breakthroughs occur every year. Ignoring or dismissing them as insignificant is not an option because of their rapid integration into industry and education, and if communities such as the Rocky Hill chose to fully realize their potential then students can be well-prepared for their future.

Works Cited

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Cortlandt Meyerson

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