Additive Manufacturing

What materials are used in Additive Manufacturing?

What materials can be used to create 3D-printed objects? Although thermoplastics drew the most attention in the early days of 3D printing, material options continue to grow. Additive manufacturing now uses materials like metals, ceramics, glass, composites, graphene-embedded plastics, paper, concrete, food, yarn and even bio-inks. The latter substance is used to create artificial organs and various soft tissues.

 

In September 2017, NASA announced the successful testing of an igniter made of multiple metal alloys. This bi-metallic capability could reduce rocket engine costs by one-third and manufacturing time by one-half.

 

Researchers at Lawrence Livermore National Laboratory used additive manufacturing to print flexible composite silicone objects that exhibit shape memory characteristics.

 

Additive manufacturing researchers continue to address challenges that define which materials can be used, including high melting points, layer thickness, print speed and production capacity. Larger machines with bigger build envelopes further expand the types of parts you can produce through additive manufacturing.

Metals

As recently as 2012, the use of metals was described as the "final frontier" in additive manufacturing. Today, it is a frontier that has been both reached and breached.

Metal powder and wire feedstock are both materials used in additive manufacturing, depending on the exact process used. Many metals are available to you in powdered form, including titanium, titanium alloys, steel, stainless steel, aluminum, copper alloys and various superalloys. Precious metals like gold, platinum, palladium and silver are also available in powdered form.

Wire feedstock options are even more wide-ranging. Steel and stainless steel alloys are materials available in wire form. Pure metals like titanium, tantalum, tungsten, niobium, molybdenum and aluminum are also available as wire feedstock.

Metals are either sintered or fully melted to create everything from specialized components to rapid prototypes to jewelry. With sintering, metal powder is partially melted to allow the particles to fuse to one another. Versatile direct metal laser sintering (DMLS) partially melts many different metals and alloys, yielding objects with a degree of porosity.

On the other hand, electron beam melting (EBM) uses powerful beams of electrons to fully melt various powdered metals, including titanium, steel and stainless steel. EBM is popular where porosity must be minimized, such as in high-stress, high-temperature aerospace applications.

These are some of the more popular metals used in additive manufacturing.

Titanium

When EBM is used, an electron beam gun deposits molten metal from titanium wire feedstock, creating parts for a variety of high-performance engineering applications, including jet engines and turbines.

Waste reduction is a key advantage with expensive titanium and other alloys. Lead times are often reduced, and limited production runs are far more feasible. Popular Mechanics reports that Boeing estimates it could save $3 million per 787 Dreamliner if the potential of 3D-printed titanium parts is fully achieved.

GE has built a functioning miniature 3D-printed jet engine with titanium components. A demonstrator engine tested by NASA sustained liquid hydrogen's minus 423 degrees F temperature, as well as the 6,000 degrees F temperature of the burning fuel.

 

Stainless Steel

EBM technology uses powdered stainless steel to produce dense, super-strong, waterproof parts for extreme environments like jet engines, rockets and even nuclear facilities. For example, in 2016, a feasibility study explored the viability of using low-carbon stainless steel in EBM machines to produce nuclear pressure vessels. The 316L steel was selected because it is weldable, corrosion-resistant and extremely strong.

 

High-Performance Alloys

Alloys like Inconel 625 and Inconel 718 are popular, because they are both rupture-resistant and corrosion-resistant. Such alloys resist thermal creep deformation, and they endure highly acidic environments. These materials are used in turbine engines, exhaust systems and fuel systems. Their resistance to corrosion also make them popular for use in various saltwater marine and naval applications. Cobalt chrome alloys are harder and more temperature-resistant than stainless steel and titanium, so they are also ideal for use in jet engines and turbines.

 

Aluminum

Aluminum is sintered in the DMLS process or melted in the SLM process. Fine detail down to 25 microns and wall thicknesses of as little as 50 microns are possible when aluminum is used. Parts typically have a textured, matte surface which distinguishes them from traditional milled aluminum parts. Due to its low weight, 3D-printed aluminum is used for automotive and racing parts.

 

Precious Metals

It is possible to sinter powdered gold, silver, platinum and palladium in DMLS machines. Extremely fine metal powder is partially melted to create jewelry. At the conclusion of the process, the object is removed from the remaining metal powder, akin to an archaeological dig.

Unique and beautiful pieces of jewelry feature interlocking or interwoven designs only possible with additive manufacturing. Forbes profiled a jeweler creating one-of-a-kind items with six-figure valuations, customized to customer preferences. To commemorate a Parisian honeymoon, one client requested and received a charm featuring a 3D-printed Eiffel Tower perched atop a pearl.

Polymers (Thermoplastics)

Various thermoplastic polymers have been used in 3D printing for decades. Filaments known by their acronyms (like ABS, PLA and PVA) are integral to the production of a wide variety of parts serving numerous industries.

Potential AM applications using thermoplastics are expanding as researchers discover ways to strengthen objects along the z axis. Typically, fused filament fabrication demonstrates better strength along the x and y axes than the z axis. Now, research into thermal welding techniques provides a way to provide the all-important "z strength" vital in products like load-bearing prosthetics.

These are some of the more popular thermoplastics used for 3D printing.

Acrylonitrile Butadiene Styrene (ABS)

Acrylonitrile butadiene styrene (ABS) is a strong, durable material with excellent dimensional accuracy. To a create a 3D-printed object using ABS, the filament must be heated to a relatively high 230-250 degrees C. The higher melting point of ABS makes for objects that are relatively warp and crack-resistant. This makes ABS a good choice for producing certain casings and other end-use parts. ABS is also used in rapid tooling and for creating concept models.

 

Polylactide (PLA)

Polylactide, or polylactic acid (PLA), filaments comprise one of the most popular categories of thermoplastic materials. Since PLA is made from cornstarch or sugar cane, it is biodegradable and therefore eco-friendly. Due to its sugar content, PLA filament gives off a slightly sweet odor when heated. It is also non-toxic and warp-resistant, although typically not quite as strong as ABS. Hard objects printed using PLA are easy to sand and drill. The polymer is used in diverse applications, including rapid prototyping, candy wrappers and biodegradable sutures.

 

Nylon

Nylon is strong, flexible and durable. It also demonstrates excellent material memory. Objects printed from nylon filament demonstrate good adhesion between layers. Since nylon is moisture-sensitive, it is often necessary to print in a vacuum or at high temperatures. Designers and engineers perform tests using functional prototypes printed from nylon. Low-run, smooth-finish nylon parts are used in everything from consumer electronics to adventure sports.

 

Polycarbonate (PC)

Polycarbonate (PC) plastics are light and dense, and they possess excellent tensile strength. PC plastics are as much as 10 times more impact-resistant than certain acrylics. Polycarbonates are relative newcomers to additive manufacturing, in part because it is necessary to maintain high nozzle temperatures of 260-300 degrees C. Although PC is naturally transparent, is possible to color PC materials as desired.

Carbon-reinforced PC plastics are strong and heat-resistant enough to use in manufacturing intake manifolds and other parts subject to high temperatures.

 

Polyvinyl Alcohol (PVA)

Polyvinyl alcohol (PVA) is a water-soluble compound used to print support structures in internal cavities and beneath overhangs. Therefore, PVA enables the creation of complex objects in dual extrusion printers when PLA is the primary material. Once the primary object is fully printed, the PVA is simply dissolved away, often by warm water.

Ceramics and Glass

Ceramic and glass are increasingly used in additive manufacturing as researchers solve the challenges of working with materials at very high temperatures. The prospect of creating geometrically complex ceramic and glass parts attracts those in disciplines as disparate as aerospace and art.

Ceramics

Additive manufacturing using silicon-carbide (SiC) ceramics offers short-run, cost-effective production, in part because the time-consuming process of creating molds is eliminated. Geometrically complex ceramic parts deliver better performance with less weight, properties very attractive to jet engine and rocket engine manufacturers.

Commercially viable production is already underway using various AM processes, including binder jetting, material extrusion and stereolithography. For example, finely detailed porcelain objects are created via stereolithography from an extruded aqueous ceramic paste consisting of a photopolymer mixed with ceramic powder. Curing, firing and glazing complete the process.

The process yields ceramic parts with injection-mold quality, but with more intricate designs, including delicate cavities and undercuts. The tool-free production method eliminates unmolding and other inefficiencies that can reduce your costs.

In general, ceramic 3D printing is quickly progressing from the short-run production of specialized components to the mass production of customized products. Ultimately, the use of additive manufacturing to produce high-performance ceramics may radically alter the manufacturing landscape. A NASA researcher at Ohio's Glenn Research Center says, "3D printing of ceramics has the potential to be game changing."

 

Glass

In selective laser sintering (SLS), glass powder is partially melted by lasers to create 3D objects useful in architectural and product design. There may also be applications for 3D-printed glass in the field of optoelectronics. Due to its thermal stability and high transmissivity, fused quartz is also being considered for optical, communication, electronic and hermetic sealing applications.

3D-printed optically transparent glass requires high-temperature processing of glass powder into a fully annealed product. To successfully create glass objects using additive manufacturing, it is necessary to precisely control viscosity, feed rate, layer thickness, flow rate and adhesion.

Research continues into the feasibility of efficiently producing optically transparent glass using a material extrusion process. For example, MIT developed a process for using extruded materials to produce optically transparent glass. To produce objects, material is extruded through a ceramic nozzle operating at 1,900 degrees F. The resulting stream of molten glass looks like honey.

If the production of optically transparent glass using additive manufacturing is perfected, completely new applications may appear. For example, researchers envision the possibility of fiber optics built right into printed glass building facades.