What is additive manufacturing?
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How does additive manufacturing work?
The term “additive manufacturing” references technologies that grow three-dimensional objects one superfine layer at a time. Each successive layer bonds to the preceding layer of melted or partially melted material. Objects are digitally defined by computer-aided-design (CAD) software that is used to create .stl files that essentially "slice" the object into ultra-thin layers. This information guides the path of a nozzle or print head as it precisely deposits material upon the preceding layer. Or, a laser or electron beam selectively melts or partially melts in a bed of powdered material. As materials cool or are cured, they fuse together to form a three-dimensional object.
GE Additive specializes in developing Powder Bed Fusion (PBF) machines for the additive manufacturing of metal parts. The three processes GE offers with in the PBF category, recognized by the American Society for Testing and Materials (ASTM), include: Direct Metal Laser Melting (DMLM), Electron Beam Melting (EBM), Binder Jetting.
In all of GE Additive’s machines the process involve the spreading of the metal powder layer by layer and uses either a laser or electron beam to melt and fuse powder together to create a part. The process repeats until the entire part is created. Loose or unfused powder is removed during post processing and is recycled for the next build.
A variety of additive manufacturing processes:
Powder bed fusion
Powder Bed Fusion (PBF) technology is used in a variety of AM processes, including direct metal laser sintering (DMLS), selective laser sintering (SLS), selective heat sintering (SHS), electron beam melting (EBM) and direct metal laser melting (DMLM). These systems use lasers, electron beams or thermal print heads to melt or partially melt ultra-fine layers of material in a three-dimensional space. As the process concludes, excess powder is blasted away from the object.
Binder Jetting is an additive manufacturing process in which an industrial printhead selectively deposits a liquid binding agent onto a thin layer of powder particles — either metal, sand, ceramics or composites — to build high-value and one-of-a-kind parts and tooling. The process is repeated layer by layer, using a map from a digital design file, until the object is complete.
Direct energy deposition
The process of directed energy deposition (DED) is similar to material extrusion, although it can be used with a wider variety of materials, including polymers, ceramics and metals. An electron beam gun or laser mounted on a four- or five-axis arm melts either wire or filament feedstock or powder.
Material extrusion is one of the most well-known additive manufacturing processes. Spooled polymers are extruded, or drawn through a heated nozzle mounted on a movable arm. The nozzle moves horizontally while the bed moves vertically, allowing the melted material to be built layer after layer. Proper adhesion between layers occurs through precise temperature control or the use of chemical bonding agents.
With material jetting, a print head moves back and forth, much like the head on a 2D inkjet printer. However, it typically moves on x-, y- and z-axes to create 3D objects. Layers harden as they cool or are cured by ultraviolet light.
Laminated object manufacturing (LOM) and ultrasonic additive manufacturing (UAM) are two sheet lamination methods. LOM uses alternate layers of paper and adhesive, while UAM employs thin metal sheets conjoined through ultrasonic welding. LOM excels at creating objects ideal for visual or aesthetic modeling. UAM is a relatively low-temperature, low-energy process used with various metals, including titanium, stainless steel and aluminum.
With vat photopolymerization, an object is created in a vat of a liquid resin photopolymer. A process called photopolymerization cures each microfine resin layer using ultraviolet (UV) light precisely directed by mirrors.
Industries and applications
AM excels at producing parts with weight-saving, complex geometric designs.
In August 2013, NASA successfully tested a SLM-printed rocket injector during a hot fire test that generated 20,000 pounds of thrust. In 2015, the FAA cleared the first 3D-printed part for use in a commercial jet engine. During the 2017 Paris Air Show, FAA-certified, Boeing 787 structural parts fabricated from titanium wire were displayed, according to Aviation Week.
In the auto industry, AM's rapid prototyping potential garners serious interest as production parts are appearing. For example, aluminum alloys are used to produce exhaust pipes and pump parts.
CNN reported the McLaren racing team is using 3D-printed parts in its Formula 1 race cars. A rear wing replacement took about 10 days to produce instead of five weeks. The team has already produced more than 50 different parts using AM.
Medical and orthopedic applications for AM are expanding, particularly as the safety and efficacy of AM-built medical devices are established.
Medical device manufacturing company Stryker are funding a research project in Australia that will use additive manufacturing technology to create custom, on-demand 3D printed surgical implants for patients suffering from bone cancer.
As the potential for AM's design flexibility is realized, once impossible design concepts are now being successfully re-imagined. Additive manufacturing unleashes the creative potential of designers who can now operate free of the constraints under which they once labored.
Additive manufacturing technologies
Sintering is the process of creating a solid mass using heat without liquefying it. Sintering is similar to traditional 2D photocopying, where toner is selectively melted to form an image on paper.
direct metal laser sintering
Within DMLS, a laser sinters each layer of metal powder so that the metal particles adhere to one another. DMLS machines produce high-resolution objects with desirable surface features and required mechanical properties. With SLS, a laser sinters thermoplastic powders to cause particles to adhere to one another.
DMLM & EBM
By contrast, materials are fully melted in the DMLM and EBM processes. With DMLM, a laser completely melts each layer of metal powder while EBM uses high-power electron beams to melt the metal powder. Both technologies are ideal for manufacturing dense, non-porous objects.
Stereolithography (SLA) uses photopolymerization to print ceramic objects. The process employs a UV laser selectively fired into a vat of photopolymer resin. The UV-curable resins produce torque-resistant parts that can withstand extreme temperatures.
Additive manufacturing materials:
Thermoplastic polymers remain the most popular class of additive manufacturing materials. Acrylonitrile butadiene styrene (ABS), polylactic acid (PLA) and polycarbonate (PC) each offer distinct advantages in different applications. Water-soluble polyvinyl alcohol (PVA) is typically used to create temporary support structures, which are later dissolved away.
Many different metals and metal alloys are used in additive manufacturing, from precious metals like gold and silver to strategic metals like stainless steel and titanium.
A variety of ceramics have also been used in additive manufacturing, including zirconia, alumina and tricalcium phosphate. Also, alternate layers of powdered glass and adhesive are baked together to create entirely new classes of glass products.
Biochemical healthcare applications include the use of hardened material from silicon, calcium phosphate and zinc to support bone structures as new bone growth occurs. Researchers are also exploring the use of bio-inks fabricated from stem cells to form everything from blood vessels to bladders and beyond.
The technology enables engineers to design parts that incorporate complexity that is not possible using other methods. Intricate features, such as conformal cooling passages, can be incorporated directly into a design. Parts that previously required assembly and welding or brazing of multiple pieces can now be grown as a single part, which makes for greater strength and durability. Designers are no longer restricted to the limitations of traditional machines and can create parts with greater design freedom.
Additive manufacturing is ideal for getting prototypes made quickly. Parts are manufactured directly from a 3D CAD file, which eliminates the cost and lengthy process of having fixtures or dies created. Plus, changes can be made mid-stream with virtually no interruption in the process.
By incorporating organic structures into designs, designers can eliminate substantial weight while maintaining the part’s strength and integrity. An illustration of this advantage can be seen in a GrabCAD® Bracket Challenge conducted by GE. An existing bracket was redesigned for additive manufacturing, with the winning entry maintaining strength of the original while reducing the weight by 84%.