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Author: MMH
Mentioned in Article: Nuala Gallagher, [email protected]; Louis Barnes,
[email protected]; John Hunter, [email protected]; John O’Hara,
[email protected]; Rick Morgan, [email protected]
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Hed: The Best 3D Printer Materials: Metals Edition
Dek: ENGINEERING.com explores the world of metals for metal 3D printing.
As powerful as plastics are for 3D printing, nothing says “critical parts” like metal additive manufacturing
(AM). As humans learned long ago, metals can provide strength like no other material can. As we’ve
continued our journey on this Spaceship Earth, humans have harnessed metals for ever greater
specialized applications, from radiation shielding on spacecraft to conductive components on printed
circuit boards (PCB).
ENGINEERING.com hopes to break down the wide variety of metals used in 3D printing as best we can,
but, before we can do that, what does metal 3D printing look like?
Powder Bed Fusion Processes
There are two broad categories of direct metal 3D printing, with some indirect forms and several
emerging technologies that may have a profound impact on the industry. Regardless of the form, the
metals themselves only change with regard to the delivery method necessary for a given process.
A diagram of the powder bed fusion process. (Image courtesy of Wikipedia.)
Selective laser melting (SLM) and direct metal laser sintering (DMLS) are terms used to describe powder
bed metal AM technologies in which an energy source is directed at a bed of metal powder. In the case
of SLM, the particles are fully melted together, whereas in DMLS, the particles are only sintered. While
both technologies feature a high powered laser, electron beam melting (EBM) is a specific form of SLM
invented by Arcam, in which powder is melted with an electron beam.
Parts made with powder bed fusion can have a high amount of geometric complexity, despite the fact
that metal support materials are required to make them. This means that internal cavities may be
difficult to produce because support structures within hollow parts need to be machined after printing.
Directed Energy Deposition
The other dominant form of metal 3D printing is directed energy deposition (DED), whereby a metal
wire or powder is fed directly to an energy source as it is deposited. With DED, more than one material
can be printed at a time and the use of a multi-axis system makes it possible to 3D print materials onto
an existing part (to add features or for repair purposes).
Various configurations of DED processes. (Image courtesy of Wikipedia.)
Some forms of DED may require specially refined powders, but others can use materials already on the
market for more traditional forms of manufacturing. For instance, Sciaky’s Electron Beam Additive
Manufacturing (EBAM) technology relies on metal wire made for the welding industry, fusing the
material with an electron beam at a rapid rate. “Our process uses welding wire as a feedstock,” stated
John O’Hara, Global Sales Manager for Sciaky. “The wire feedstock is typical welding wire, a supply chain
that has existed for decades.”
The reliance on welding wire opens the EBAM process to the wide range of materials already on the
market. “The most common alloys we work with, Titanium and Nickel alloys, exhibit excellent properties
relative to the wrought and forged properties. Unique to our process, refractory alloys such as any
versions of Molybdenum, Tantalum, Tungsten and Niobium, exhibit excellent properties and geometries
with our process,” O’Hara said.
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Though powder bed parts can be treated to reach densities of close to 100 percent, DED processes are
even closer to the properties of forged metals. As O’Hare explained, “Sciaky’s metal is typically going to
be nearly completely dense, and will have properties that will approach or meet the requirements of
forged or wrought metals. As with any AM process, the results will heavily depend on the material and
the post-deposition heat treatment. By completely dense, we mean what little porosity would be found
(nothing is perfect) would be considered micro porosity, and will occur at a very low frequency: in
general, will meet the inspection requirements of Forgings.”
The geometric complexity of DED parts is somewhat limited, with most processes producing a near-netshape part that is further machined to achieve the final product. That said, what DED lacks in geometric
complexity, it makes up for in speed and size. Of note, Sciaky makes the largest metal 3D printing
machines currently available.
Other Metal 3D Printing Processes
There are also binder jetting methods for 3D printing metal parts. Companies like ExOne manufacture
systems that deposit a binder material onto a bed of metal powder. Once printed, this “green” object is
placed in a furnace, where the binder is burned out and the part is combined with bronze to create the
final part.
Fabrisonic uses an interesting hybrid technique called Ultrasonic Additive Manufacturing to fuse metal
foils. The technique requires ultrasonic welding before a CNC tool cuts the part from the excess foil
material. This method makes it possible to combine different types of metals, and because no melting
occurs, electronic components can be incorporated into the part without fear of destroying them.
Emerging technologies from Markforged, Desktop Metal and Admatec also use an indirect form of metal
AM. In the case of Markforged and Desktop Metal, metal powder in a thermoplastic matrix is deposited
on a printbed similar to a fused deposition modeling (FDM) process. The part is then sintered in an oven,
which burns out the thermoplastic binder. In contrast, Admatec exposes a photopolymer loaded with
metal particles to UV light, hardening the object layer by layer. The green part is then sintered in an
oven.
Finally, XJet has invented an inkjet approach to metal 3D printing. Their method deposits metal
nanoparticle inks from a printhead within a heated chamber. Desktop Metal appears to have developed
a similar technology which will be released in 2018.
Making Metal Powders
In powder bed fusion processes, highly refined and often expensive metal powders are used. These
powders are usually produced through a gas or plasma atomization process, where induction heating or
plasma torches are used to melt metal. Molten metal is then poured into an atomization chamber and
high velocity gas is used to break up the metal stream into small droplets which fall through a vertical
chamber as they solidify.
In gas atomization, a metal feedstock is melted in a vacuum or inert gas. Gas is pushed into the melting chamber, which pushes
the material through a nozzle and high speed air causes the melting metal to break apart. Used most often for nickel, cobalt and
iron alloys and can be used for titanium and aluminum alloys. (Image courtesy of LPW Technology.)
LPW Technology is a UK-based firm that is focused entirely on the production and supply of metal
powders and control and monitoring technologies for AM. The firm uses a variety of processes to
produce a very wide range of materials for different AM technologies. John Hunter, General Manager of
LPW Inc., explained to ENGINEERING.com that gas atomization is used for over 90 percent of metal
powders for AM, but that plasma-based methods are used for higher purity metals such as titanium
based alloys or nickel-based superalloys.
In plasma atomization, wire feedstock is fed to a plasma torch, which atomizes the powder into highly spherical particles. LPW
uses a process known as plasma spheroidization to further refine powders for refractory metals like Tungsten and Tantalum.
(Image courtesy of LPW Technology.)
“Plasma will give you a better morphology, a more spherical particle than gas atomization. Gas
atomization also produces spherical particles, but not quite as perfect,” Hunter said. Both of these
processes differ from water atomization (utilized to produce the majority of metal powders outside of
AM) for metal injection molding, hot isostatic pressing and other applications. However, the particles
produced by water atomization are more irregular, making them difficult to use in 3D printing, partially
due to the smooth flow needed in AM.
Whereas Directed Energy Deposition (DED) processes that use powder work with coarser particles –
which can be in excess of 100 microns – and Electron Beam Melting (EBM) operates with metal powder
particles between 45 and 100 microns, other powder bed systems use powder particles between 10 and
45 microns in size.
Due to the various patents related to powder bed processes, manufacturers have often adopted
proprietary methods for spreading powder across the bed during printing, as well as refilling the build
platform. While one firm’s machines may use flat metal bars to spread powder and gravity to refill the
build area, others use a cylindrical roller and elastomeric material to spread the powder and a piston
feed to refill the chamber.
“When you’re talking about Particle Size Distribution (PSD), one of the things that LPW does is that we
sell to a number of machine OEMs. We know which powder characteristics work with various machines.
They’re all a little bit different,” Hunter continued. “Some are more forgiving about a powder that flows
less well than another.”
For that reason, when LPW sells material to a customer (whether it’s an end user or research lab), the
company will ask what type of machines are being used and will provide the range of acceptable particle
sizes for those machines.
Other factors to be considered when producing powder include the actual chemistry of the alloy itself,
as well as the density and porosity of the powder. Those last two variables are particularly important for
DED because the larger sizes of the particles leave more room for gas used in the manufacturing process
to create bubbles within the material. This can ultimately end up in the 3D-printed part, resulting in
porosity which can ultimately lead to cracks or changes in performance.
For that reason, LPW offers a variety of services and products in addition to the powders themselves.
This includes software and sensors for recording and monitoring powder quality, tools for verifying and
maintaining powders, labs for analyzing the material and interpreting a company’s powder-related data,
consultation services and powder lifecycle management.
An Alternative Form of Metal Powder Production
Outside of the more traditional processes for producing metal powder for AM, there is a method for
producing metal powder known as electrolysis, which is characterized by being more energy efficient
and generally more controllable in terms of the particle output.
Electrolytic powder manufacturing is an electrochemical process in which a metal oxide is introduced to
an electrified salt bath, usually made up of molten calcium chloride. As the current passes between the
metal oxide (acting as the cathode) and a carbon anode, oxygen is removed from the metal oxide. The
result is a purified powder form of the metal, which is then cleaned and dried for use.
The electrolysis process employed by Metalysis to create metal powders for AM. (Image courtesy of Metalysis.)
A leading manufacturer in the AM realm that uses electrolysis is the UK company Metalysis. Dion
Vaughan, CEO of Metalysis, explained to ENGINEERING.com that the company’s process offers a number
of benefits when compared to other forms of powder production.
“With processes like plasma atomization, you get a normal distribution of particle sizes,” Vaughan said.
“Essentially, if you are trying to produce powders for AM, the range of particle sizes may be a very
narrow slice of what you actually convert and what you’re actually producing. If you’re producing 100
tons of material per year, the particle range for a given AM system, such as SLM, may be just 10 tons, for
instance.”
With electrolysis, it’s possible to control the process in such a way that almost all of the output can be
used for a specific AM system. Therefore, if a company is producing powder for an SLM machine from
SLM Solutions, the process can be tuned to manufacture particles only in that necessary range, and the
same would be true for an EOS machine or a DED system.
Because electrolysis operates at temperatures between 800°C and 1000°C, the energy required is much
less than what would be needed to melt the same amount using heat. “If you compare our process to
conventional titanium powder production, plasma atomization, you’re using roughly 50 percent less
energy, we estimate,” Vaughan said.
This energy reduction has environmental consequences, but also factors into a reduced cost for the
customer. Additionally, electrolysis can be used to produce powder from a much broader specrum of
metals, regardless of the high melting temperature.
Metalysis is now on its fifth generation of the technology, which began as an R&D development, and is
about to undergo feasibility studies to expand its fully-fledged powder production capabilities. Vaughan
stated that the Generation 5 powder production system will expand on the Generation 4 system
Metalysis is scheduled to complete this year. Generation 4 will be capable of producing 20 tons of light
powder and 60 tons of heavier metals, and Generation 5 will provide manufacturing options for
hundreds to thousands of tonnes per annum of high value metal and alloy powders. The technology will
be available through a unique licensing model which is flexible depending on the need of the customer.
Titanium
Though Metalysis’ process is capable of producing a variety of metal powders, the company’s primary
focus is on titanium. “In general terms, titanium is a wonder metal,” Vaughan asserted. “It is light, but
strong and very corrosion resistant.”
The primary forms of titanium available for 3D printing are titanium alloys 6Al-4V (known as grade 5 or
Ti64) and 6Al-4V ELI, referred to as grade 23 or Ti64ELI. Grade 5 titanium is the most widely used form of
titanium on the planet due to its utility. The material can be welded, heat treated for increased strength,
can withstand temperatures of up to 600° F, has a high strength-to-weight ratio and offers high
corrosion resistance. For these reasons, grade 5 titanium is often found in high performance industries
like aerospace, medical, marine and chemicals.
A custom titanium 3D-printed cranio-maxillofacial implant made using EBM technology. (Image courtesy of Arcam.)
Grade 23 is a higher purity and biocompatible form of this alloy that can be shaped into coils and wires
while maintaining a high strength-to-weight ratio, corrosion resistance and toughness. The material is
often found in biomedical applications, including surgical devices and implants.
Aluminum
The two most common forms of Aluminum alloys available for 3D printing are AlSi12 and AlSi10Mg.
Though both are made up of a combination of aluminum and some silicon, AlSI10Mg also includes
magnesium. Both are casting alloys that are particularly useful for creating parts with thin walls and
complex geometries.
The world’s first aluminum 3D-printed guitar made by Olaf Diegel and printed on an EOS M400. (Image courtesy of ODD
Guitars.)
These materials feature impressive strength and hardness and can be used for high loads. Their light
weight and temperature resistance make them ideal for applications such as motorsports or the interior
parts of aircraft. They can also be easily post-processed via machining, welding, shot-peening and
polishing.
Steel
There are a variety of steel materials that fall into the three broad categories of stainless steels, tool
steels and maraging steels. Maraging steels are created through an extended heat treatment process
that enable high strength and toughness, without losing malleability. This means that they can be
machined easily after printing and further hardening. As a result, maraging steel may be used for series
production parts and tooling.
This 3D-printed steel bike frame was made using a unique technology developed by MX3D to weld freeform metal structures in
the air. (Image courtesy of MX3D.)
Stainless steels are known for their high abrasion, wear and corrosion resistance. Therefore, these
materials are often used in applications such as cutlery and surgical instruments, and in the construction
of acid or corrosion resistant parts.
Tool steels are used to produce tools and molds for manufacturing due to their hardness, abrasion and
deformation resistance, and the ability to maintain a cutting edge, unlike maraging steels. Tool steels
can then stand up to the wear and tear required to form other materials. Once 3D-printed, unique
cooling channels can be integrated into tool steel parts, optimizing the injection molding process.
Cobalt
A variety of cobalt-chrome alloys are available for 3D printing and often employed for their high
strength, hardness, and resistance to corrosion and high temperatures. Cobalt is usually combined with
materials like chromium and tungsten to create heavy duty cutting tools or dies, as well as with
magnetic and stainless steels for jet and gas turbine components.
A bridge framework 3D-printed in CE-certified cobalt chrome with Renishaw’s LaserPFM dentistry 3D printing. (Image courtesy
of Renishaw.)
Nickel
Nickel-based superalloys Inconel 625, 718 and HX (all made from nickel and chromium) are the most
predominant nickel alloys in 3D printing. These materials are heat, oxidization and corrosion resistant
and exhibit high strengths in very elevated temperatures up to 1200 °C. Parts made from nickel alloys
are very weldable and can be post-processed with heat treatment for further strength. Altogether, these
materials are used in the aerospace and motorsport industries in cases where high temperatures and
oxidation are a significant risk, such as combustion chambers and fans.
3D-printed nickel alloy borescope boss for the Airbus A320neo jetliner. (Image courtesy of MTU Aero Engines.)
Though Inconel 625 has higher corrosion resistance and long-term stability under high temperatures
when compared to 718, the latter is about twice as strong and much more conductive. Inconel HX may
be the most weldable of the three varieties.
A representative from powder manufacturer Additive Metal Alloys (AMA) told ENGINEERING.com at the
AMUG event in Chicago this year that while AMA manufactures a variety of materials, nickel alloys are a
big focus for the company. Located near the GE Aviation plant in Cincinnati, Ohio, AMA sees aerospace
as a big market for nickel-alloys due to their strength, resistance, and hardness when heat treated.
“Titanium, is not as heat resistant, but it’s very lightweight and strong, giving it a very high strength-toweight ratio,” the representative explained. “Nickel-alloys are heavier, but because of the heat
resistance the material, it can operate inside of an engine.”
Copper
Copper is not widely available in 3D printing, but a couple of companies do manufacture copper alloy
powder for powder bed fusion processes. Additionally, DED systems may use copper materials already
available to the welding industry. The material can be used for jewelry and the arts because of the
greater aesthetic and hardness values when compared to silver alloys. Copper is also being used in
aerospace.
The first full-scale copper engine part, 3D printed by NASA engineers, is a combustion chamber liner meant to operate at
extreme temperatures and pressures. (Image courtesy of NASA.)
NASA’s Materials and Processing Laboratory at Marshall Space Flight Center and Aerojet Rocketdyne
have used copper alloys in powder bed fusion systems to 3D print rocket engine components with
unique cooling channels. The high conductivity of the material makes it possible to quickly heat rocket
fuel.
Precious Metals
Precious metals available for 3D printing include silver, gold and platinum. These materials are often
ductile, shiny and less reactive. In many cases, they may also be highly conductive. Along with Concept
Laser, Cooksongold is one of the few to offer 3D printing with gold (yellow, rose and white) and
platinum. The main applications for these materials are for jewelry and artistic objects.
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Silver nanoparticle inks have been utilized by several companies like Voxel8 and Nano Dimension to
print conductive traces on parts. Nano Dimension, in particular, is working to develop nickel-based and
copper-based inks, which have higher conductivity. Silver inks make it possible to 3D print circuits, either
for PCB prototyping or to integrate electronics directly into a 3D-printed object.
Refractory Metals
Refractory metals are a small class of metals (niobium, molybdenum, tantalum, tungsten, and rhenium)
known for their extremely high heat and wear resistance. They all maintain melting points above 2000
°C, are chemically inert, have high densities and are very hard.
Tantalum has a high corrosion resistance and is very conductive, which makes it useful for electronics.
According to Los Alamos National Laboratory, 60 percent of the material’s use is for vacuum furnace
parts and electrolytic capacitors. It has been theorized that Tantalum could be used to increase the
radioactivity of nuclear fallout, a terrifying process known as “salting”.
In its pure form, Tungsten has the highest melting point of any element at 6,192 °F (3,422 °C). Highly
dense, the material is also difficult to work with, but its rigid composition makes it desirable for wear
resistance in knives, drills, mills and saws. Tungsten is also very resistant to oxygen, acids and alkalis and
can be used for radiation shielding.
Global Tungsten & Powders (GTP) is one of the few companies that produces tungsten, tungsten carbide
and molybdenum powders, marketing only powders that have been successfully printed. Rick Morgan,
R&D Manager of W and WC Powders at GTP, explained the process the company uses to make its
tungsten materials: “GTP is vertically integrated and has the ability to take tungsten ore and chemically
refine it to APT, oxidize and reduce it to W metal powder, take the W metal powder and carburize it to
WC, spray dry it with cobalt, and then spheroidize it for use in Additive Manufacturing,” Morgan said.
ExOne offers a bonded tungsten material for its binder jetting process. The company markets the
material as a replacement for lead, which is more toxic, in medical devices and aerospace parts. GTP’s
tungsten carbide cobalt material was successfully binderjet printed by ExOne, and the company has
developed a debinding/sintering schedule to achieve acceptable density.
The Future of Metals
SmarTech Markets Publishing has estimated that the market of metal powders for AM would grow to
$930 million by 2023, and recently suggested that this growth would be driven in large part by the
aerospace industry. Davide Sher, Senior Analyst for the European division of SmarTech and founder of
3D Printing Business Media, was able to provide some insights by relying on the company’s recent
report on metal powders, including which materials will be the most popular.
“For the foreseeable future the most used metal AM powders are going to be Steel, Titanium, Nickel
Alloys (Inconel) and Cobalt Chrome,” Sher said. “Titanium is the most used in aerospace because cost is
not an issue and the slightly improved performances compare to other less costly metals justify the
expense. Inconel—also costly—is also used primarily in aerospace and defense manufacturing. Titanium
is also very much used in medical applications (implants) - once again costs are justified by
performance.”
Dion Vaughan, CEO of Metalysis, also believes that titanium use will increase and that his company’s
process will aid in a greater adoption of AM technology: “Historically, titanium production has been
challenged by the fact that conventional processing routes were very energy inefficient and expensive,
even today with advanced plasma processing,” Vaughan said. Electrolysis, however, is more efficient
and less expensive, which should result in a greater use of metal AM and further drive down the cost of
the powder.
Vaughan envisions the possibility of powder production co-located with the manufacturing process,
which would enable greater efficiency. This would also be important for the emerging trend of
distributed manufacturing, where part production is closer to the point of end use.
Davide Sher has stated that due to its primary use in the large AM segment of dentistry, cobalt chrome
will be even more important for part production. Steel, the first metal powder for 3D printing, is usually
the most common choice. Aluminum is much lower in cost, which makes it feasible for producing parts
for the automotive industry, resulting in higher volumes of parts. Precious metals (particularly platinum)
may have interesting applications, but their use will be limited, according to Sher.
“[T]he recent expansion of powder fed (DED, high deposition rate technologies) are going to drive up
demand significantly,” Sher mentioned. “Now these technologies are no longer used just for part repair
but also for large part production. Also the size and speed of powder bed fusion technologies is going up
very quickly, almost doubling every two years.”
According to Sher, metal may not be king in industrial 3D printing, as high performance plastics like PEEK
and PEKK, as well as carbon fiber reinforced materials can be used to replace metals for a lower cost.
“[These] may take away some of the market for metal AM in aerospace and medical applications
especially,” concluded Sher.
GE’s formation of GE Additive, after acquiring Arcam and Concept Laser, certainly speaks to the growth
estimated by SmarTech. The purchase of Arcam gave the corporate behemoth simultaneous access to a
3D printer manufacturer as well as a titanium powder maker.
John Hunter, of LPW, used this example to suggest that more vertical integration would be coming. He
added that powder manufacturers, including LPW, had been adding capacity for powder production. His
branch in the United States is moving to a larger facility where it will focus on conditioning the materials.
LPW is also increasing its activities related to recycling materials, a trend that Hunter said is increasing in
popularity.
This growth, he pointed out, is being driven by the use of AM for production, as opposed to the
prototyping it was initially used for. “The powder market is growing so quickly as more and more of
these machines are installed,” Hunter said. “Instead of just making prototypes and then testing them for
a couple of months, a lot of these prototypes are now in production. So, these machines are running
daily or weekly building parts. They’re using a lot more powder now than they were just a year ago.”
Hunter did stress that his optimistic comments about the future of AM and the power market are only
his personal opinions and observations.
In other words, as metal 3D printing is incorporated into the manufacturing supply chain as a means of
producing end parts, more metal powder is going to be consumed, resulting in a larger amount of power
being produced. As metal AM continues to evolve, expect the powder industry to continue to grow and
expand in tandem.