Overview of Additive Manufacturing Technology

The additive manufacturing industry has quickly expanded over the past few decades, especially within the industrial sector. With impressive design ability and minimal tooling, manufacturing and engineering businesses have significantly benefited from the use of additive manufacturing. To help you learn more about this technology, we've provided a comprehensive introduction to additive manufacturing and the different types and techniques involved.

What Is Additive Manufacturing?

Additive manufacturing is a type of manufacturing technology that builds three-dimensional objects by building up materials, rather than cutting them away. Generally, the method involves adding layers of material such as plastic, metal and concrete. There are a variety of types of additive manufacturing, each using different techniques and materials to achieve the result. These methods all use a somewhat similar general process, consisting of the following steps.

1. 3D modeling: The first step in the additive manufacturing process is producing a digital model, usually through the use of computer-aided design, or CAD, software.
2. File conversion: After finalizing the CAD model, the designer must often convert it into a file type that is compatible with the equipment that will produce the part.
3. Manufacturing: The additive manufacturing equipment reads the data from the model and lays down materials to produce the object in question. Generally, these materials are liquid, powder or sheet products that can layer easily.
4. Removal: While some methods require little preparation and equipment to remove a finished part from additive manufacturing machinery, others have more complicated processes — it all depends on the method in question.
5. Post-processing: The post-processing required after removal depends entirely on the additive manufacturing method that produced the product. Some products are ready for immediate use, but generally, most products of additive manufacturing need some surface finishing technique.

What Types of Additive Manufacturing Are There?

While additive manufacturing often goes by the umbrella term "3D printing," especially in the media, there are a variety of additive manufacturing processes. Individual processes vary widely, offering unique methods, materials and benefits. In 2010, the American Society for Testing and Materials categorized seven primary additive manufacturing types and techniques:

Vat Photopolymerization

Photopolymerization is the process of creating a solid by exposing a photopolymer resin to light of a specific wavelength. Vat photopolymerization uses this technique to create a model within a vat of this photopolymer resin, hence the name. The two vat photopolymerization technologies in use are stereolithography, or SLA, and digital light processing, or DLP.

• SLA: SLA works by aiming a laser beam into a vat of photopolymer resin, solidifying the resin at points within the resin to build the model. The SLA machine uses a build platform to elevate the model, allowing the laser beam to add progressive layers underneath the emerging model. Once the model is complete, the part gets removed from the vat, rinsed in a chemical bath to remove excess resin, then cured in an ultraviolet oven. Because the finish the SLA method produces is extremely high-quality, it tends to be better for producing high-resolution parts.
• DLP: DLP is very similar to SLA, except that it uses a digital light projector screen to flash an image of an entire layer of the design all at once, solidifying the resin for each layer more quickly. The digital nature of this process projects the image as pixels, resulting in the layers forming in small rectangular bricks, or voxels. While this process can achieve faster print times than SLA because of its ability to complete entire layers with a single flash, the surface finishes of DLP-produced parts are lower-quality due to the presence of voxels. That makes DLP better for producing high volumes of intricate parts that don't require high resolution.
• Continuous DLP: Continuous DLP is a variation of DLP, with the only exception being that it uses the constant motion of the build platform to produce models more quickly.

Regardless of the specific process, vat photopolymerization is an excellent technology for creating parts with fine details and smooth surfaces, though these parts tend to be brittle, and the process tends to be more expensive compared to other techniques. Most commonly, vat photopolymerization technologies produce jewelry, injection molds and certain dental and medical products.

Powder Bed Fusion

Powder bed fusion, or PBF, technology produces parts by fusing particles of metal or plastic layer by layer, using various energy sources. Generally, these technologies put down progressive layers of powder for the fusion process, resulting in a powder-covered finished product. The most common powder bed fusion processes include selective laser sintering (SLS), selective laser melting (SLM), direct metal laser sintering (DMLS), electron beam melting (EBM) and multi-jet fusion (MJF).

• SLS: The SLS process produces solid plastic parts by using a laser to sinter designs into progressive layers of powdered plastic. The model gets built upon a moving platform, which drops down after completing each layer, allowing for a new coat of powder to be applied and sintered. Once complete, unsintered powder surrounds the model, which must get removed, cleaned and processed. Building these models doesn't require support structures, making it very easy to produce multiple models at once within the SLS machine in a process called "nesting."
• SLM: SLM is very similar to SLS, except that it produces metal parts. In the SLS process, a laser heats powdered metal until it melts, forming progressive layers of metal material as new layers of metal powder get added to the build platform. Additionally, SLM differs from SLS in that it requires support systems for models to prevent distortion during the build process. This method is common with single-component metals like copper, aluminum and steel, and produces parts with exceptional strength and surface quality.
• DMLS: DMLS is a popular additive manufacturing technology, and is similar to SLM in almost all regards. The primary difference between the two technologies is that the DMLS process only heats metal powder to near-melting temperatures, allowing particles to fuse together chemically. DMLS only works with alloy metals, and, like SLM, requires support structures to prevent warping during the build process.
• EBM: EBM is a similar process to SLM, using a high-energy beam instead of a laser to melt particles of metal powder together. The benefit of this high energy beam is that it exerts less stress on the material and uses less energy, resulting in less distortion and a quicker build time for each part. The primary downsides to EBM are the fact that models produced using this method tend to be of lower surface quality and strength than SLM-produced models, and the process requires completion within a vacuum with conductive materials like copper.
• MJF: MJF combines PBF processes with material jetting technology, using a carriage full of fusing agent followed by an IR energy source to sinter progressive layers of plastic powder. A detailing agent along the edges of the part prevents excess sintering.

Regardless of the technique, PBF technologies offer numerous benefits. PBF technology tends to provide a great deal of design freedom, especially processes like SLS that do not need support systems. Additionally, PBF-made parts are typically strong and offer a variety of finishing options, depending on the needs of the application. There are limitations to PBF, however, including surface roughness, internal porosity and distortion of the final product. Additionally, this process cannot produce fully enclosed hollow parts, since doing so would trap excess powder inside the model.

Material Jetting

Material jetting is conceptually similar to a 2D ink jetting process. The process involves jetting three-dimensional material onto a build platform in progressive layers. These materials are often photopolymers, metals or waxes that harden when exposed to UV light or elevated temperatures. In fact, material jetting processes allow the use of multiple materials in the same print. Material jetting primarily uses the following technologies.

• Material jetting: Material jetting works by dispensing a photopolymer in successive layers from hundreds of small nozzles in a printhead. This technique allows for quick, line-based deposition that tends to be faster than other point-based manufacturing methods. Once deposited, the material gets cured using UV light before moving on to the next layer. Simultaneously, the printhead can build a structural support system from another dissolvable material, allowing for quick removal during post-processing.
• Nanoparticle jetting: The nanoparticle jetting process deposits extremely thin layers of liquid full of metal nanoparticles onto a build plate. Once deposited, the material gets heated to high temperatures, causing the liquid to evaporate and leave the metal behind.
• Drop-on-demand (DOD): DOD material jetting printers have two print jets: one with the build material and the other with a dissolvable support material. These materials get deposited simultaneously on a build platform, after which point a fly-cutter skims the build area to ensure the surface of the build is perfectly flat before proceeding. Generally, DOD technology is best for producing waxy patterns for mold and cast-making applications.

Material jetting is highly beneficial for its ability to print multiple elements in a single print. It allows printing products in various colors or with easily removable support systems. Additionally, the process results in highly detailed models with excellent surface finishes. The only drawbacks to this technique are the relatively high costs and the brittleness of certain materials, like UV-activated photopolymers.

Direct Energy Deposition

Directed energy deposition, or DED, is a complex printing process that creates parts by melting metal powder or wire material as it gets deposited onto a build platform. This additive manufacturing process usually uses one of two technologies.

• Laser-engineered net shape (LENS): LENS processes use a laser to melt powder into solid layers on the build platform. The laser and powder both get ejected from the deposition head of the printer, with the laser creating a melt pool on the build area that the powder hits and melts into. This process works best when adding material to an existing part.
• Electron beam additive manufacture (EBAM): EBAM uses an electron beam to weld metal powder or wire into metal parts. Like LENS, EBAM works by creating a melt pool, but this process tends to be more energy-efficient and can operate in a vacuum.

DED is exclusively a metal additive manufacturing technology that produces high-quality parts. It is an excellent method for adding material to existing parts for repair operations or build-outs, but because it requires extensive support structures, it isn't ideal for producing parts from scratch.

Material Extrusion

Material extrusion technologies push build materials onto a platform through a nozzle, which draws designs layer by layer. Material extrusion primarily relies on a process called fuse deposition modeling, or FDM, where a material gets drawn through a nozzle, heated and deposited in progressive layers. This process initially developed in the late 1980s, and a company called Stratasys, one of the world's leading additive manufacturing companies, commercialized and patented it.FDM, alternatively called fused filament fabrication, is the most widely used form of additive manufacturing. The process works by heating filaments of thermoplastic material and depositing it through a nozzle. The FDM printer moves this nozzle around in the horizontal plane, drawing the model in progressive layers as the build platform moves vertically to make room. While thermoplastic polymers are most common in this process, ABS, PLA, polycarbonate, polyamide, polystyrene, lignin, rubber and other materials are also effective materials.

Material extrusion is extremely quick and cost-effective compared to other additive manufacturing techniques, making it an ideal method for producing prototypes. While the final product may not have the best surface quality, dimensional accuracy or strength, FDM is suitable for testing and short-run manufacturing purposes.

Binder Jetting

The binder jetting process involves depositing a liquid binding agent onto a bed of powder material, causing the powder layer to bind in progressive layers. The print head with the binding agent moves horizontally, while the build platform moves down with each layer to make room for the next. Once complete, the new parts are post-processed to improve their mechanical properties. Binder jetting is unique for its ability to print with ceramics and metals, and for the fact that it does not use heat during the build process.

• Ceramic binder jetting: Binder jetting can use ceramic-based materials like glass or gypsum to create ceramic products, which get cured with heat and strengthened with cyanoacrylate adhesive. This method typically creates aesthetic builds like architectural models and packages, since the final parts tend to be very brittle. However, ceramics made with binder jetting can also develop sand casting molds.
• Metal binder jetting: Metal binder jetting uses metal as the powder component, most commonly stainless steel. Once complete, the build can undergo a hot isostatic pressing technique to improve density. This approach can create highly functional components more cost-effectively than SLM and DMLS techniques, but parts made with metal binder jetting tend to have poorer mechanical properties.

Regardless of the material, binder jetting can produce large, high-quality parts very quickly and cost-effectively when compared to other additive manufacturing techniques.

Sheet Lamination

Sheet lamination processes are both additive and subtractive, using full sheets of material to produce each layer of a build, and cutting away excess material with a laser or knife. Sheet lamination processes include ultrasonic additive manufacturing, or UAM, and laminated object manufacturing, or LOM.

• LOM: Lamination is one of the earliest additive manufacturing techniques, making use of paper and adhesive to create models. The LOM process uses inexpensive A4 paper cut using a cross-hatching method that both supports the build and allows for easy removal once the build is complete. This method is very affordable to set up and complete compared to other methods, but almost exclusively produces visual and aesthetic models, rather than structural or functional parts.
• UAM: The UAM process builds models by binding sheets or ribbons of metal together with ultrasonic welding. UAM can use metals like aluminum, copper, stainless steel and titanium in entire sheets or in metallic ribbons, though any excess material needs to be machined off after the build is complete. This process is particularly advantageous for electronics, since it is low-heat and low-energy and allows for the use of multiple materials and the creation of complex internal geometries.

While these processes are mostly for aesthetic purposes, rather than functional ones, sheet lamination technologies are beneficial for their easy post-processing and low cost.

Applications of Additive Manufacturing Techniques

Additive manufacturing technology has advanced quickly within the past few decades, expanding the number of additive manufacturing applications across multiple industries. Here are just a few examples.

• Automotive: The automotive industry uses additive manufacturing on a massive scale, from racing vehicles to commercial automobiles. Typically, additive manufacturing produces both high- and low-volume parts like prototypes, fixtures, molds and custom parts. Analysts project the market for additive manufacturing in the automotive industry to continue expanding, which is impressive, considering the automotive industry already accounted for 16.1 percent of all additive manufacturing processes in 2015.
• Aerospace: The aerospace industry was one of the early adopters of additive manufacturing, and is one of the sectors leading the continued development of additive manufacturing techniques. As of 2015, the aerospace and defense industries contributed 16 percent of the global revenue from additive manufacturing. Typically used for low-production custom parts and prototypes, additive manufacturing has achieved much in the aerospace industry.
• Medical: Additive manufacturing has had an enormous impact on the medical industry, introducing new possibilities that were previously unimaginable. Thirteen percent of all additive manufacturing revenue came from the medical industry as of 2015, and it's easy to see why. 3D printers now make surgery easier by producing patient-specific surgical guides and models, and doctors of all fields can produce several types of implants within their offices. Researchers are even exploring the technology for its potential to print human organs.

• Architecture and construction: Additive manufacturing is common in the architectural and construction industry, particularly for creating architectural models. These detailed models are essential for architects promoting their designs or planning projects, and additive manufacturing technologies allow people to make them quickly and cheaply. Construction businesses are also looking into additive manufacturing techniques on a much bigger scale, with some companies prototyping large-scale 3D printers that can print concrete buildings. If perfected, this technique could affordable houses more quickly than a human crew ever could.
• Consumer goods: Additive manufacturing has increasingly been indispensable in the production of consumer products, as the technology has become more accessible. Though it is primarily helping produce prototypes and custom parts, many are predicting consumers themselves will eventually own 3D printers on a massive scale, printing products from online models.

While this only skims the surface of what is possible with additive manufacturing, it's clear to see from just these few examples how additive manufacturing is making an impact on modern manufacturing techniques.

Learn More

Additive manufacturing is a powerful technology you can use to make products precisely to your specifications. But how are you going to ensure your product is ready for mass production? If you need product testing, inspection or certification, turn to NTS. NTS provides testing and certification services for product developers and manufacturers, serving as one of the largest commercial test laboratory networks in the U.S.Talk to one of our experts or request a quote for our services today.