It is yet another technological advancement made possible by the transition from analog to digital processes. In recent decades, communications, imaging, architecture and engineering have all undergone their own digital revolutions. Now, AM can bring digital flexibility and efficiency to manufacturing operations.
Additive manufacturing uses data computer-aided-design (CAD) software or 3D object scanners to direct hardware to deposit material, layer upon layer, in precise geometric shapes. As its name implies, additive manufacturing adds material to create an object. By contrast, when you create an object by traditional means, it is often necessary to remove material through milling, machining, carving, shaping or other means.
Although the terms “3D printing” and “rapid prototyping” are casually used to discuss additive manufacturing, each process is actually a subset of additive manufacturing.
While additive manufacturing seems new to many, it has actually been around for several decades. In the right applications, additive manufacturing delivers a perfect trifecta of improved performance, complex geometries and simplified fabrication. As a result, opportunities abound for those who actively embrace additive manufacturing.
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. It is possible to use different substances for layering material, including metal powder, thermoplastics, ceramics, composites, glass and even edibles like chocolate.
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.
The journey from .stl file to 3D object is revolutionizing manufacturing. Gone are the intermediary steps, like the creation of molds or dies, that cost time and money.
There are a variety of different additive manufacturing processes:
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.
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.
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.
The binder jetting process is similar to material jetting, except that the print head lays down alternate layers of powdered material and a liquid binder.
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.
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.
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.
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.
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.
It is possible to use many different materials to create 3D-printed objects. AM technology fabricates jet engine parts from advanced metal alloys, and it also creates chocolate treats and other food items.
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.
Additive manufacturing is already used to produce an impressive array of products — everything from food creations to jet engine parts.
AM excels at producing parts with weight-saving, complex geometric designs. Therefore, it is often the perfect solution for creating ight, strong aerospace parts.
In August 2013, NASA successfully tested an 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. CFM’s LEAP engine features 19 3D-printed fuel nozzles. At the 2017 Paris Air Show, FAA-certified, Boeing 787 structural parts fabricated from titanium wire were displayed, according to Aviation Week.
CNN reported that 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 additive manufacturing. 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, and polymers are used to produce bumpers.
At the New York University School of Medicine, a clinical study of 300 patients will evaluate the efficacy of patient-specific, multi-colored kidney cancer models using additive manufacturing. The study will examine whether such models effectively assist surgeons with pre-operative assessments and guidance during operations.
Global 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.
In general, healthcare applications for additive manufacturing are expanding, particularly as the safety and efficacy of AM-built medical devices is established. The fabrication of one-of-a-kind synthetic organs also shows promise.
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.