Types of 3D printing Technologies
The term 3D printing covers a host of processes and technologies that offer a full spectrum of capabilities for the production of parts and products in different materials. Essentially, what all of the processes and technologies have in common is the manner in which production is carried out a layer by layer in an additive process, which is in contrast to traditional methods of production involving subtractive methods or moulding/casting processes.
FDM Technology (Fused Deposition Modeling )
Monikers: Fused Filament Fabrication (FFF), filament extrusion, fused filament deposition, material deposition, FDM
How it Works: FDM extrudes heated thermoplastic through a nozzle layer by layer to form parts. FDM uses multiple nozzles for final part and support material. After each layer is extruded, the build platform moves down making room for the following layer. FDM can deposit thicker or thinner layers which in turn can speed up a build (thicker layers) or decrease hand finishing time (thinner layers) due to the smoother surface. FDM requires support material to build angles, overhangs and holes that can’t be built on thin air.
Materials: FDM materials can be opaque to semi-transparent in multiple colors including blue, red, yellow, white, black, and tan. FDM thermoplastics include FAR-rated and biocompatible thermoplastics, and many thermoplastics common to injection molding such as ABS and ASA.
Applications: FDM is commonly used to build aircraft interior components and ducting, and medical, consumer, industrial, and transportation prototypes and products.
Why it’s Significant: FDM uses the same materials aerospace, medical and industrial sectors have relied on from injection molding with the ability to build complex geometries and the lower material consumption associated with 3D printing. Because FDM builds layer by layer, features and multiple components can be combined into one design, minimizing assembly. Undercuts, interior features, attachment fittings are seamlessly incorporated into one part. FDM has become invaluable to sectors requiring lightweight, strong and affordable plastic parts – without the need for hard tooling or machining.
Monikers: Material jetting, photocuring, inkjet printing
How it Works: Think of PolyJet like your home 2-D paper printer. Your 2-D color printer lays out minuscule droplets of color onto your paper, forming words and images. In a similar fashion, PolyJet uses fine print head nozzles to deposit droplets of photocurable material in layers as fine as 16 microns to form detailed 3-D parts. Material is simultaneously cured as it is deposited via UV light.
PolyJet parts require support structures to build overhanging features and holes. Without support structures, the material can escape its intended form resulting in inaccurate walls, features and other details. PolyJet support material is a separate composition formulated to release from the part when blasted with water. Other material jetting technologies like PolyJet use wax supports which require an oven to melt off and remove.
Materials: PolyJet relies on photopolymer resins. Photopolymers or photocurable materials come in many different kinds of compositions, from flexible to rigid, transparent to opaque. PolyJet is one of two 3D printing technologies to print color directly into a part and it is the only technology capable of printing multiple materials simultaneously, offering gradations from stiff to flexible in one part.
Applications: Because PolyJet uses UV energy to cure liquid resins, parts can warp and change color with prolonged exposure to heat and light which means PolyJet parts are not used for stressful applications involving rugged use. Ideal PolyJet applications include: Master patterns for cold or low temperature molds; show models; detailed prototypes, and form, fit and feel models.
Why it’s Significant: PolyJet 3D printing is the fastest 3D printing technology commercially available. Parts within a 5” cube can print within as little as 2 hours. Outside of a 5” cube, PolyJet becomes slower (remember, the nozzle is moving back and forth across the platform depositing a thin layer of material, therefore, the farther the nozzle travels, the slower the process becomes). PolyJet prints in the thinnest layers of any 3D print process and that means less visible layer lines for smooth, detailed parts. Its speed, resolution and affordability make it ideal for quick-turn applications, from master patterns to show models to early design prototypes.
SLA Technology (Stereolithography)
Monikers: Vat photopolymerization, photocuring, SLA, SL
How it Works: Stereolithography relies on a precise UV laser to cure liquid plastic layer by layer. Its build platform sits atop a bath of liquid plastic. The build platform is coated with a thin layer of liquid plastic. A UV laser hits dynamic mirrors which direct the UV energy downwards across the build platform, curing the liquid plastic in precise patterns one cross-section at a time. After each layer is cured, the build platform retracts into the bath of liquid while a recoater blade evenly distributes the plastic across each new layer.
As with PolyJet, Stereolithography also requires build supports. Stereolithography support material is the same material as the final part. Unlike PolyJet, Stereolithography parts do not fully cure during build. During printing, the resin within the chamber can become trapped within the part or pool in certain part features. If leftover resin is not removed, it reabsorbs into the part causing bloating and design distortion. Therefore, after a build is complete, excess resin is drained and supports are removed. The part then enters a UV oven to complete curing.
Materials: Stereolithography uses photocurable plastics to form rigid, opaque and transparent parts in white, grey and clear. Stereolithography materials, which can warp or change color with prolonged exposure to light and heat, aren’t ideal for stressful applications.
Applications: Stereolithography is perhaps best known for its ability to build mostly hollow parts with a thicker outer shell and a honeycomb interior. The most common application for hollow Stereolithography parts is investment casting patterns. Additional common applications for Stereolithography include: large entertainment models, prototypes, and master patterns for cold or low temperature molds.
Why it’s Significant: While Stereolithography is a staple in prototyping and modeling for clear, large and lightweight patterns and parts, it’s most significant contribution to production applications might be its ability to print mostly hollow, lightweight investment casting patterns. Stereolithography is an alternative to conventional investment cast patterns. Traditional lost wax patterns for investment casting can take weeks to build and, should an error or design modification arise, the tool must be scraped and re-built. In contrast, Stereolithography does not require tooling and is built all in one piece eliminating the need for multi-part assembly work. Investment cast pattern designs can go directly from designer to printer to foundry without the significant investment of time and money associated with lost wax tooling.
SLS Technology (Laser Sintering)
Monikers: Powder bed fusion, Selective Laser Sintering, LS, SLS
How it Works: Laser Sintering requires an enclosed build chamber to heat and fuse parts layer by layer. Laser Sintering begins by heating its internal build chamber to just below the melting point of the powdered plastic. A CO2 laser hits the powder in determined design patterns, thus bringing specific areas to full melting point to form parts one layer at a time. Laser Sintering is the only 3D printing process that is completely free from added support structures. The unsintered powder within the chamber is dense enough to support the part as it builds.
Materials: Laser Sintering utilizes Nylon 11 and 12, raw and filled, to deliver FAR-rated and biocompatible plastics. A filled nylon used with Laser Sintering is a composite of one or two more materials, including glass, carbon or aluminum. Filled nylons can increase rigidity, strength, heat deflection or as-built surface finish.
Applications: Laser Sintering is one of the most widely used 3D printing plastic technologies for aerospace ducting and similar rugged, high temperature uses. It is also used in the automotive, medical, consumer, art, and architecture sectors for thousands of products.
Why it’s Significant: Laser sintering was one of the earliest 3D printing processes to be adopted into end-use part production. It was one of the first 3D printing technologies to take to the skies through aerospace ducting production. Laser Sintering doesn’t require labor to remove support structures; powder is simply shaken out of interior areas. Therefore Laser Sintering is able to produce truly zero-cost complexities. It is used to consolidate tricky ducting applications because it can build interior, no-access features seamlessly while using high-temperature, chemical-resistant materials. It uses lightweight material with exception strength to deliver fuel tanks, ailerons, control surfaces, and many other critical UAV features.