Step4: 3D Printing

If you’re new to the wonderful world of 3D printing, may we be the first to offer you a warm welcome. You’re going to find it fun, useful, and inspiring.

A challenge that many newcomers to 3D printing face is distinguishing between the several types of 3D printing processes. The uninitiated think of 3D printing as strings of plastic extruded from a hot nozzle and stacked up into a shape, but it’s so much more!

In fact, 3D printing, also called additive manufacturing, is an umbrella term covering several very distinct 3D printing processes using completely different machines and materials.

Just think of some of the things that are 3D printed today, from pencil holders to rocket engines, and you’ll realize that the technologies are worlds apart yet have key elements in common. For example, all 3D printing starts with a digital model since the technology is inherently digital. Parts or products start off as electronic files designed using computer-aided design (CAD) software or obtained from a digital part repository. Then the design file is put through special build preparation software that breaks it down into slices or layers to be 3D printed. This software, which is often unique to the type of 3D printing and even the brand of 3D printer, turns the model into slices and generates the path instructions for the 3D printer to follow.

Check out this video from RCwithAdam as he gives you a crash course into the world of 3D Printing

Did you know....

There are 7 main types and more than 20 subtypes of 3D printing

The types of additive manufacturing can be divided by what they produce or which type of material they use, but to apply structure to the technology worldwide, the International Standards Organization (ISO) divided them into seven general types:

The 7 Main 3D Types are:

MATERIAL EXTRUSION

Material extrusion 3D printing

As the printer moves the extrusion head along the specified coordinates on the XY plane, it proceeds to lay down the first layer. The extrusion head then raises to the next level height (the Z plane), and this process of printing cross-sections is repeated, building layer upon layer until the object is fully formed.

Depending on the object’s geometry, it is sometimes necessary to add support structures to hold up the model as it’s printed, for example, if a model has steep overhanging parts. These supports are removed after printing. Some support structure material can be dissolved in water or another solution.

3D bioprinting, or bio 3D printing, is an additive manufacturing process where organic or biological materials, such as living cells and nutrients, are combined to create natural tissue-like three-dimensional structures. In other words, bioprinting is a type of 3D printing that can potentially produce anything from bone tissue and blood vessels to living tissues. It’s used for various medical research and applications, including tissue engineering, drug testing and development, and in innovative regenerative medicine therapies.

The actual definition of 3D bioprinting is still evolving. In essence, 3D bioprinting works similarly to FDM 3D printing and is in the material extrusion family, although extrusion isn’t the only bioprinting method.

3D bioprinting uses materials discharged from a needle to create layers. These materials, known as bioinks, are mainly composed of living matter, such as cells within a carrier material – like collagen, gelatin, hyaluronan, silk, alginate, or nanocellulose – that act as a molecular scaffold for the structure to grow and nutrients to provide support.

Construction 3D printing is a rapidly growing area of material extrusion. The technology involves using extremely large-scale 3D printers, often measuring tens of meters high, to extrude building material, such as concrete, from a nozzle. These machines generally come either as gantry or robotic arm systems.

3D construction printing technology is used today for homes, architectural features, and construction projects from wells to walls. Proponents say it has the potential to significantly disrupt the entire construction industry because it reduces the need for labor and cuts down on construction waste.

There are dozens of 3D printed homes across the US and Europe, and research is underway to develop 3D construction technology that would use the materials found on the moon and Mars to build habitats for future expedition teams. Printing with local soil instead of concrete is also gaining attention as a more sustainable building method.

VAT POLYMERIZATION

VAT Polymerization

SLA holds the historical distinction of being the world’s first 3D printing technology. Stereolithography was invented by Chuck Hull in 1986, who filed a patent on the technology and founded the company 3D Systems to commercialize it. Today, the technology is available for hobbyists and professionals from a wide range of 3D printer makers.

An SLA printer uses mirrors, known as galvanometers or galvos, with one positioned on the X-axis and another on the Y-axis. These galvos rapidly aim a laser beam (or two) across a vat of resin, selectively curing and solidifying a cross-section of the object inside this building area, building it up layer by layer.

As each layer is cured in just the right places, it then moves up (almost imperceptively) to pull out the hardened resin layer and make space for another liquid layer that will then be cured by the laser.

Most SLA printers use a solid-state laser to cure parts. One disadvantage of this version of vat polymerization is that a point laser can take longer to trace the cross-section of an object when compared to our next method (DLP), which flashes a light to harden an entire layer at once. Lasers, however, can produce stronger light which is required by some engineering-grade resins.

Just like it sounds, this version of SLA in the vat polymerization family, prints parts on the micro-scale, or resolutions between 2 microns (µm) and 50 microns. For reference, the average width of a human hair is 75 microns. It’s one of the so-called “Micro 3D Printing” technologies. µSLA involves exposing photosensitive material (liquid resin) to an ultraviolet laser. The difference is the specialized resins, the sophistication of the lasers, and the addition of lenses, which generate almost unbelievably small points of light.

Another micro 3D printing technology, TPP (also known as 2PP) can be categorized under SLA because it also involves a laser and photosensitive resin. It can print parts even smaller than µSLA, down to 0.1 microns.

TPP uses a pulsed femtosecond laser focused into a tight spot in a vat of special resin. This spot is then used to cure individual 3D pixels, also known as voxels, in the resin. By sequentially curing these nano- to micrometer-small voxels layer by layer, in a predefined path, you can create 3D objects. These can be several millimeters large while maintaining the nanometer resolution.

TPP is currently used in research, medical applications, and manufacturing for tiny parts, such as micro-sized electrodes and optical sensors.

DLP 3D printing uses a digital light projector (instead of a laser) to flash a single image of each layer all at once (or multiple flashes for larger parts) on a layer or resin.

DLP is (more often than SLA) used to produce larger parts or larger volumes of parts in a single batch since each layer flash takes exactly the same amount of time regardless of how many parts are in the build, which makes it generally faster than the laser method in SLA.

Because the projector is a digital screen, the image of each layer is composed of square pixels, resulting in a layer formed from small rectangular blocks called voxels. Light is projected onto the resin using light-emitting diode (LED) screens or a UV light source (lamp) that is directed to the build surface by a digital micromirror device (DMD).

Qualifying as a distinct type of vat polymerization in its own right, we’ll add PµSL here as a subcategory of DLP. It’s another Micro 3D Printing technology.

PµSL uses ultraviolet light from a projector to cure layers of specially formulated resin at the micro-scale (2-micron resolution and down to a 5-micron layer height). This additive manufacturing technique is growing due to its low cost, accuracy, speed, and also the range of materials that it can use, which include polymers, biomaterials, and ceramics. It has shown potential in applications ranging from microfluidics and tissue engineering to micro-optics and biomedical microdevices.

Another remote cousin of DLP, this method of 3D printing with light and resin creates tiny metal parts for applications including surgical tools and micromechanical parts. In LMM, metal powder is homogeneously dispersed in a light-sensitive resin and then selectively polymerized by exposure with blue light via a projector. After printing, the “green” parts have their polymer component removed, leaving fully metal “brown” parts that are finished in a sintering process in a furnace. Feedstocks include stainless steel, titanium, tungsten, brass, copper, silver, and gold.

Liquid crystal display (LCD), also called masked stereolithography (MSLA), is very similar to DLP above, except, instead of a digital micromirror device (DMD) it uses an LCD screen, which has a noticeable impact on the 3D printer’s price.

Like DLP, the LCD photomask is digitally displayed and composed of square pixels. The pixel size of the LCD photomask defines the granularity of a print. Thus, the XY accuracy is fixed and does not depend on how well you can zoom or scale the lens, as is the case with DLP.

Another difference between DLP-based printers and LCD technology is that the latter uses an array of hundreds of individual emitters rather than a single-point emitter light source like a laser diode or DLP bulb.

POWDER BED FUSION

Powder Bed Fusion

Selective laser sintering (SLS) creates objects out of plastic powder by using a laser. First, a bin of polymer powder is heated to a temperature just below the polymer’s melting point. Next, a recoating blade or wiper deposits a very thin layer of the powdered material – typically 0.1 mm thick – onto a build platform. A laser (CO2 or fiber) then begins to scan the surface according to the pattern laid out in the digital model. The laser selectively sinters the powder and solidifies a cross-section of the object.

When the entire cross-section is scanned, the build platform moves down one layer thickness in height. The recoating blade deposits a fresh layer of powder on top of the recently scanned layer, and the laser will sinter the next cross-section of the object onto the previously solidified cross-sections.

These steps are repeated until all objects are manufactured. The powder that hasn’t been sintered remains in place to support the objects, which reduces or eliminates the need for support structures. After removing the part from the powder bed and cleaning, there are no other required post-processing steps. The part can be polished, coated, or colored.

There are dozens of differentiating factors among SLS 3D printers, including not only their size but the power and number of lasers, the spot size of the laser, the time and manner in which the bed is heated, and how the powder is distributed, to name just a few.

The most common material in SLS 3D printing is nylon (PA6, PA12), but parts can also be printed to be flexible using TPU and other materials.

μSLS could fall under SLS or under laser powder bed fusion (LPBF) described below. It uses a laser to sinter powdered materials, like SLS, but that material is typically metal not plastic, so it’s more like LPBF.

In any case, as the μ indicates, it’s another micro 3D printing technology that creates parts on a micro-scale (sub-5 μm) resolution.

In μSLS, a layer of metal nanoparticle ink is coated onto a substrate and then dried to produce a uniform nanoparticle layer. Next, laser light that has been patterned using a digital micromirror array is used to heat and sinter the nanoparticles into the desired patterns. This set of steps is then repeated to build up each layer of the 3D part in the μSLS system.

Of all the 3D printing technologies, this one has the most aliases. Officially called laser powder bed fusion (LPBF), this metal 3D printing method is also widely known as direct metal laser sintering (DMLS) and selective laser melting (SLM).

In the early years of this technology development, machine manufacturers created their own names for the same process that are kept to this day. Make no mistake; these three terms refer to the same process, even if some mechanical details vary.

As a subtype of powder bed fusion, LPBF involves a bed of metal powder and a high-powered laser or several (up to 12). LPBF 3D printers use lasers to selectively fuse metal powder together layer-by-layer on a molecular basis until the model is complete. LPBF is a highly precise and accurate method of 3D printing and is commonly used for creating complex metal parts for aerospace, medical and industrial applications.

Like SLS, LPBF 3D printers start with a digital model divided into slices. The printer loads powder into the build chamber, and a recoater blade (like a windshield wiper) or roller spreads it into a thin layer across the build plate. The laser traces the layer onto the powder. The build platform then moves down, and another layer of powder is applied and fused to the first, until the entire object is built. The build chamber is closed, sealed, and in many cases, filled with inert gas, such as nitrogen or argon blends, which ensures that the metal doesn’t oxidize during meting and helps remove debris from the melting process.

The packed powder on the printing bed provides some support to the model during the printing process, but supports are also used. The unused metal powder can be reused for the next print.

After printing, parts are removed from the powder bed, cleaned, and often given a secondary heat treatment to remove stresses. The leftover powder is reclaimed and reused.

Differentiating factors among LPBF 3D printers include the type, strength, and number of lasers. A small, compact LPBF printer might have a single 30-watt laser, whereas an industrial version may have 12 1,000-watt lasers.

LPBF machines use common engineering alloys, such as stainless steels, nickel superalloys, and titanium alloys. There are dozens of metals available for the LPBF process.

EBM, also called electron beam powder bed fusion (EB PBF), is a 3D printing method for metals similar to LPBF but uses an electron beam instead of a fiber laser. This technology is used to manufacture parts, such as titanium orthopedic implants, turbine blades for jet engines, and copper coils.

EBM is chosen over its laser-based metal 3D printing cousin for several reasons. First, the electron beam generates more power and heat, which is required for certain metals and applications. Next, instead of an inert gas environment, EBM takes place in a vacuum chamber to prevent beam scattering. The build chamber temperature can reach up to 1,000 °C and in some cases, even higher. Because the electron beam uses electromagnetic beam control, it moves at higher speeds than a laser and can even be split up to expose several areas simultaneously.

One of EBM’s advantages over LPBF is its ability to process conductive materials and reflective metals, such as copper. Another feature of EBM is the ability to nest or stack separate parts on top of each other in the build chamber since they do not necessarily have to be attached to the build plate, which greatly increases volume output.

Electron beams generally produce larger layer thicknesses and less detailed surface features than lasers. EBM printed parts may not need to be stress relieved with a post-print heat process, due to the high temperature in the build chamber.

MATERIAL JETTING

Material Jetting

Material jetting (M-Jet) for polymers is a 3D printing process where a layer of photosensitive resin is selectively deposited onto a build plate and cured with ultraviolet (UV) light. After one layer has been deposited and cured, the build platform is lowered down one layer thickness, and the process is repeated to build up a 3D object.

M-Jet combines the outstanding detail of resin 3D printing with speeds better than filament 3D printing (FDM) to create parts and prototypes in true-to-life color and texture.

You may hear it M-Jet referred to by manufacturer-specific names such as PolyJet by Stratasys or MultiJet Printing (MJP) by 3D Systems, but it’s not just branding. All material jetting 3D printing technology is not exactly the same. There are variances between printer makers and proprietary materials.

M-Jet machines deposit build material from rows of print heads in a line-wise fashion. This method enables the printers to fabricate multiple objects in a single line without impacting build speed. So long as models are correctly arranged on the build platform, and the space within each build line is optimized, M-Jet can produce parts faster than many other types of resin 3D printers.

Objects made with M-Jet require support, which is printed simultaneously during the build from a dissolvable material that is removed during the post-processing stage. M-Jet is one of the only types of 3D printing technology to offer objects made from multi-material printing and full color.

There are no hobbyist versions of material jetting machines. These are for professionals found at automakers, industrial design firms, art studios, hospitals, and all types of product manufacturers looking to create accurate prototypes to test concepts and get products to market faster.

Unlike vat polymerization technologies, M-Jet doesn’t require post-curing since the UV light in the printer fully cures each layer.

Aerosol Jet is a unique technology developed by a company called Optomec that’s used primarily for 3D printing electronics. Components such as resistors, capacitors, antennas, sensors, and thin film transistors have all been printed with Aerosol Jet technology.

It can be crudely likened to spray paint, but it distinguishes itself from an industrial coating process in that it can be used to print full 3D objects.

Electronic inks are placed into an atomizer, which creates a dense mist of material-laden droplets between 1 to 5 microns in diameter. The aerosol mist is then delivered to the deposition head, where it is focused by a sheath gas, which results in a high-velocity particle spray.

This technology is sometimes categorized with directed energy deposition because of the energy method, but since the material, in this case, is in droplets, we’ve included it in material jetting.

German company Arburg created a technology called Plastic Freeforming (APF) that’s a cross between extrusion and material jetting technologies. It uses commercially available plastic granulates that are melted as in the injection molding process and moved to the discharge unit. A high-frequency nozzle closure generates rapid opening and closing movements of up to 200 tiny droplets of plastic per second with a diameter between 0.2 and 0.4 mm. The droplets are bonded with the hardened material as they cool down. In general, there is no post-processing required. If support material was used, it has to be removed.

One of the few proprietary technologies that defy easy categorization, NanoParticle Jetting (NPJ), developed by a company called XJet uses an array of printheads with thousands of inkjet nozzles that simultaneously jet millions of ultrafine drops of materials onto a build tray in ultrathin layers while simultaneously jetting a support material.

Metal or ceramic particles are suspended in the liquid. The process occurs under high heat, which evaporates the liquid upon jetting, leaving mostly just the metal or ceramic material. The resulting 3D part has only a small amount of bonding agent remaining that’s removed in a sintering post-process.

BINDER JETTING

Binder Jetting

Binder Jetting can also be used to fabricate solid metal objects with complex geometries well beyond the capabilities of conventional manufacturing techniques.

Metal binder jetting is a very appealing technology for volume metal part production and to achieve lightweighting. Because binder jetting can print parts with complex pattern infills instead of being solid, the resulting parts are dramatically lighter while being as strong. Binder jetting’s porosity feature can also be used to achieve lighter end parts for medical applications, such as implants.

Overall, the material properties of metal binder jet parts are equivalent to metal parts produced with metal injection molding, which is one of the most widely used manufacturing methods for the mass production of metal parts. Plus, binder jet parts exhibit higher surface smoothness, especially in internal channels.

Metal binder jetting parts require secondary processes after printing to achieve their good mechanical properties. Right off the printer, parts basically consist of metal particles bound together with a polymer adhesive. These so-called “green parts” are fragile and not useable as is.

After printing and removing the parts from the bed of metal powder (a process called depowdering) they’re heat-treated in a furnace (a process called sintering). Both the printing parameters and the sintering parameters are tuned for the specific part geometry, material, and desired density. Bronze or another metal is sometimes used to infiltrate the voids in a binder jetted part, resulting in zero porosity.

Plastic Binder Jetting is a very similar process to metal binder jetting since it involves a powder and a liquid binding agent, but the applications are vastly different.

Once printed, plastic parts are removed from their powder bed, cleaned, and can often be used without any further processing, but these parts lack the strength and durability found in 3D printing processes, such as SLS where the polymer powder is essentially melted together. Plastic binder jetting parts can be infilled with another material to boost strength.

Binder jetting with polymers is prized for its ability to produce multi-color parts used in medical modeling and product prototypes.

Sand binder jetting is arguably not a distinct technology from plastic binder jetting but the printers and applications are different enough to earn a separate entry here. In fact, producing large sand-casting molds, models, and cores is one of the most common uses for binder jetting technology.

The low cost and speed of the process make it an excellent solution for foundries. Elaborate pattern designs that would be very difficult or impossible to produce using traditional techniques can be printed in a matter of hours.

The future of industrial development continues to place high demands on foundries and suppliers. Sand 3D printing is at the beginning of its potential.

Sand binder jetting 3D printers product parts from sandstone or gypsum. After printing, the cores and molds are removed from the build area and cleaned to remove any loose sand. The molds are typically immediately ready for casting. After casting, the mold is broken apart, and the final metal component is removed.

Another one of the unique and brand-specific 3D printing processes that doesn’t fit easily into any existing category and isn’t actually binder jetting is Multi Jet Fusion from HP—yes, the same company that makes 2D printers.

MJF is a polymer 3D printing technology involving a bed of powder material and a liquid fusing material, and a detailing material. The reason it’s not considered binder jetting is the addition of heat in the process, which creates parts with far higher strength and durability, and the fact that the liquid isn’t exactly a binder. The process gets its name from the multiple inkjet heads that carry out the printing process.

In the Multi Jet Fusion printing process, the printer lays down a layer of material powder, usually nylon, on the printing bed. Following this, an inkjet head runs across the powder and deposits both a fusing and a detailing agent onto it. An infrared heating unit then moves across the print. Wherever a fusing agent was added, the underlying layer melts together, while the areas with the detailing agent remain as a powder. The powdery parts shed off, which produces the desired geometry. This also eliminates the need for modeling supports, as the lower layers support those printed above them.

To finish the printing process, the entire powder bed – and the printed parts in it – are moved to a separate processing station. Here, the majority of the loose unfused powder is vacuumed up, allowing it to be reused instead of producing excess waste.

Multi Jet Fusion is a versatile technology that has found use in several industries from automotive to healthcare to consumer products.

DIRECTED ENERGY DEPOSITION

Directed Energy Deposition

Laser Directed Energy Deposition (L-DED), also called laser metal deposition (LMD) or Laser Engineered Net Shaping (LENS), is a 3D printing technology using a metal powder or wire fed through one or more nozzles and fused via a powerful laser on a build platform or on a metal part. An object is built up layer by layer as the nozzle and laser move or as the part moves on a multiple-axis turntable.

The build rates are faster than powder bed fusion but result in lower surface quality and significantly lower accuracy, often requiring extensive post-machining.

Laser DED printers often have sealed chambers filled with argon to avoid oxidation. They also can operate with just a localized argon or nitrogen flood when processing less reactive metals.

Metals commonly used in this process include stainless steels, titanium, and nickel alloys.

This printing method is often used to repair high-end aerospace and automotive components, such as jet engine blades, but it is also used to produce entire components.

Electron beam DED, also called wire electron beam energy deposition, is a 3D printing process very similar to DED with a laser. It is carried out in a vacuum chamber, which produces very clean, high-quality metal. As a metal wire is fed through one or more nozzles, it is fused by an electron beam. Layers are built up individually, with the electron beam creating a tiny melt pool and the weld wire fed into the melt pool by a wire feeder.

Electron beams are chosen for DED when working with high-performance metals and reactive metals, such as alloys of copper, titanium, cobalt, and nickel.

Metal wire-fed DED using electron beams is faster than powder fed. The process is carried out in a vacuum chamber.

DED machines are practically not limited in terms of print size. 3D printer manufacturer Sciaky, for example, has an EB DED machine that can produce parts nearly six meters long at a rate of 3 to 9 kilos of material per hour. In fact, electron beam DED is touted as one of the fastest ways to build metal parts, although not the most precise, which makes it ideal for building up large structures, such as airframes, or replacement parts, such as turbine blades that are then machined.

Wire Directed Energy Deposition, also known as Wire Arc Additive Manufacturing (WAAM), is 3D printing that uses energy in the form of plasma or wire arc to melt metal in wire form where it’s deposited layer on top of layer by a robotic arm onto a surface, such as a multi-axis turntable, to form a shape.

This method is chosen over similar technologies involving lasers or electron beams because it doesn’t require a sealed chamber and it can use the same metals (sometimes the exact same material) as traditional welding.

Electric direct energy deposition is considered the most cost-effective option among the DED technologies because it can use existing arc-welding robots and power supplies, so the barrier to entry is relatively low.

Unlike welding, this technology uses complex software to control a menu of variables in the process, including the thermal management and toolpath of the robotic arm.

There are no support structures to remove, and finished parts are typically CNC machined to tight tolerances if necessary or surface polished. Often, printed parts receive a heat treatment to relieve any residual stresses.

Cold spray is a DED 3D printing technology that sprays metal powders at supersonic speeds to bond them without melting them, which produces almost no thermal stress that can produce hot-cracking or other common problems that can affect melt-based technologies.

Since the early 2000s, it’s been used as a coating process, but more recently, several companies have adapted cold spray for additive manufacturing because it can layer metal in exact geometries up to several centimeters at about 50 to 100 times higher speed than typical metal 3D printers, and there’s no need for inert gases or vacuum chambers.

Like all DED processes, cold spray doesn’t produce prints of great surface quality or detail, but that’s not always required and parts can be used right off of the print bed.

Molten Direct Energy Deposition is a 3D printing process that uses heat to melt (or near melt) metal, usually aluminum, then deposit it on a build plate layer by layer to form a 3D object.

This technology differs from metal extrusion 3D printing in that the extrusion versions use a metal feedstock with a bit of polymer inside to make the metal extrudable. The polymer is then removed in the heat treatment stage. Molten DED, on the other hand, uses a pure metal.

One could also liken molten or liquid DED to material jetting, but instead of an array of nozzles depositing droplets, the liquid metal is generally streamed from a nozzle.

Variations on this technology are in development, but molten metal 3D printers are rare; Grob offers the GMP300 and Xerox recently ceased production of its ElemX liquid metal printer.

The potential benefit of using heat to melt and then deposit metals is the ability to use less energy than other DED processes and potentially use recycled metal directly as feedstock instead of wire or highly processed metal powders.

SHEET LAMINATION

Sheet Lamination

Laminating is a 3D printing technology where sheets of material are layered on top of each other and bonded together using glue then a knife (or laser, or CNC router) is used to cut the layered object into the correct shape.

The technology is less common today because the cost of other 3D printing technology has fallen while the size, speed, and ease-of-use of 3D printers in other technology categories has dramatically increased.

VLM is a patented 3D printing process from BCN3D that laminates thin layers of high-viscosity photosensitive resins onto a transparent transfer film. The mechanical system allows the resin to be laminated from both sides of the film, making it possible to combine different resins to get multi-material parts and easy-to-remove support structures.

This technology, not yet launched commercially, could just as well reside under one of the resin 3D printing technologies.

Startup Impossible Objects patented this technology that fuses mats of carbon, glass, or Kevlar with a thermoplastic to create parts.

EnvisionTEC, now called ETEC and owned by Desktop Metal, developed this technology in 2016 that uses thermoplastics as a base material and woven fiber composites. It’s uncertain if Desktop Metal still supports this method.