Despite the largest variety of 3D-printed plastic materials and the largest share of the 3D printing market, metal materials still have unparalleled advantages in “critical component” applications. Humans have long realized that metals can achieve strengths that no other material can. As human activity on Earth continues to develop, we are using metal materials for more specialized fields, from radiation defense devices in spacecraft to conductive components in PCB boards.
We want to be able to use as many metal materials as possible for 3D printing processes, but how advanced is metal 3D printing today?
Powder bed molten metal 3D printing process
There are two broad categories of direct metal 3D printing processes, as well as some indirect processes or emerging processes that may have a profound impact on the industry. Regardless of the form of the process, the state of the metal 3D printing material is only adjusted according to the transport form of the specific process.
Selective Laser Melting (SLM) and Direct Metal Laser Sintering (DMLS) are typical examples of powder bed fused metal 3D printing processes that use a high-energy heat source that acts directly on a powder bed. The powder in the SLM process is completely melted, while the powder in the DMLS process is only burned into a whole. Although both processes feature high-energy lasers, Arcam’s Electron Beam Melting (EBM) process is a special case of the SLM process, which uses electron beams to melt metal powders.
Parts machined by the powder bed molten metal 3D printing process can be geometrically very complex, although support structures are required during processing. This means that machining the internal hollow structure can be very difficult because the internal support needs to be removed after the printing is complete.
Direct energy deposition process
Another major metal 3D printing process is Direct Energy Deposition (DED), where a wire or powder is sent to an energy source to melt. For the direct energy deposition process, multiple materials can be printed at once, and the multi-axis system makes it possible to add materials to existing parts (adding features or product restoration).
Some DED processes require special powders, while others can use powders available on the market for other traditional processes. For example, Sciaky’s EBAM process (Electron Beam Additive Manufacturing) uses wires from the welding industry to rapidly melt metal materials using a beam of electrons. “Our process uses welding wire as a raw material,” says John O ‘Hara, global sales manager at Sciaky. “Our wire is a typical welding wire that has been in the supply chain for decades.”
The use of welding wires means that the EBAM process can be applied to a large number of materials on the market. “Our most commonly used materials, including titanium alloys and nickel-based alloys, show very excellent forging properties. The unique advantage of our process is that any refractory metal such as molybdenum, tantalum, tungsten, niobium, etc., exhibits excellent properties and geometric forming capabilities.” “O ‘Hara said.
Although the density of the powder bed process parts can be close to 100% after treatment, the performance of DED process products is closer to that of forged parts. As O ‘Hare said, “Sciaky’s metal parts are nearly fully dense and their performance will meet or exceed the needs of the forging industry.” For any 3D printing process, the results are heavily dependent on the material and post-deposition heat treatment. The full density here means that the holes we can find (no product is perfect) are very small occur very infrequently, and usually meet the inspection requirements of forgings.”
The complex geometric modeling capability of the DED process is limited to some extent, and most of the processing is near-net molding, requiring further machining to obtain the final product. In other words, the DED process has some shortcomings in geometric modeling, but it is better in processing speed and size. Sciaky is said to have built the largest metal 3D printing device in existence.
Other metal 3D printing processes
There are also binder spray processing methods for metal parts. Devices like ExOne deposit binder materials on a bed of metal powder. Once printed, the prototype needs to be sintered in the furnace, the binder is removed, and the pores in the part can penetrate the copper to get the final product.
Fabrisonic uses a blend of Additive and subtractive materials known as Ultrasonic 3D printing (UAM) to melt metal foils. This process involves ultrasonic welding before CNC cutting removes excess foil. This method makes it possible to combine different types of metals, and since no melting process occurs, electronics can be packaged inside the parts without fear of damaging them.
Technologies emerging from Markforged, Desktop Metal, Admatec, and others also take indirect forms of molding. For Markforged and Desktop Metal, they add metal powders to a thermoplastic matrix for deposition printing in a form similar to the FDM process. The printed prototype is sintered in the furnace to remove the thermoplastic binder. Instead, Admatec mixes the metal powder with a photosensitive polymer, which is then illuminated with an ultraviolet lamp to cure layer by layer, and the prototype also needs to be sintered in a furnace.
XJet has developed an inkjet metal 3D printing technology. Their technology uses a print head to spray metal nanoparticle inks and deposit accumulations in a heated molding chamber. Desktop Metal seems to be working on a similar technology, which will be released in 2018.
Preparation of metal powder
For powder bed melting processes, high-quality, expensive metal powders are usually used. These powders are usually prepared by aerosol or plasma atomization processes, where the metal is melted by induction heating or plasma torches, respectively. The molten metal liquid is injected into the atomizing chamber, broken into small droplets by high-speed airflow, and gradually solidified during the falling process.
LPW Technology is a British company specializing in the production and supply of metal powder, 3D printing control, and monitoring technology. For different 3D printing processes, the company uses a variety of processes to produce different types of metal powders. John Hunter, general manager of LPW, believes that more than 90% of the metal 3D printing powder is produced by the gas atomization process, and the plasma method is used to process higher purity powders, such as titanium and nickel-based alloys.
The sphericity of powder prepared by plasma atomization is higher. Aerosolization can also produce spherical particles, but it’s not as ideal, “Hunter said. Both processes differ from the water atomization process used to prepare powder for injection molding, hot isostatic pressing, and other applications, which are used to produce most metal powders except for 3D printing. However, powders prepared by the water atomization process are more irregular, making them difficult to apply to the 3D printing industry, in part because of the fluidity requirements of 3D printing.
The DED process uses a coarser powder whose particle size may exceed 100 microns, the EBM process powder particle size is 45-100 microns, and other powder bed process powder particle size is 10-45 microns.
Due to the large number of patents related to the powder bed process, manufacturers often use proprietary methods to lay powder and fill the processing platform during the printing process. A company may use metal strips to lay powder and rely on gravity to fill the machining area. Another may use cylindrical rollers and elastic materials to lay powder, and piston feed to fill the molding chamber.
“For powder Size Distribution (PSD), LPW also takes into account when selling powder to different equipment manufacturers. We know which powder characteristics are suitable for different devices. They’re always a little different, “Hunter added. “Some devices are less sensitive to low powder mobility.”
For that reason, when LPW sells materials to users, whether end users or research LABS, it asks them what type of equipment they use to provide powders in an acceptable particle range depending on the machine.
There are other factors to consider when making powder, including the chemical composition, density, and porosity of the alloy itself. The last two factors are particularly important for the DED process because the coarse powder will have more room to hold the gas when it is prepared, resulting in the presence of air bubbles inside the powder. This will increase the porosity inside the 3D printed parts, eventually leading to cracks, and affecting the mechanical properties of the product.
For this reason, LPW offers a wide range of services and products in addition to powders. This includes software and sensors to record and monitor powder quality, tools to detect and preserve powder, laboratories to analyze materials and interpret powder-related data, consulting services, and powder lifecycle management.
An alternative method for metal powder production
In addition to the more traditional 3D printing metal powder production process, there is also a method of electrolytic preparation of metal powder, which is typically more energy-saving and more controllable powder output.
Electrolytic pulverization is an electrochemical process that introduces metal oxides into a salt pond, usually consisting of molten calcium chloride. As the current passes through the metal oxide (as the cathode) and the graphite anode, the oxygen element of the metal oxide is removed. The result is a pure metal powder that can be cleaned and dried for application.
The British company Metalysis, which uses electrolysis to produce metal 3D printing powder, is a well-known 3D printing manufacturer. Dion Vaughan, CEO of Metalysis, says its process has several advantages over other powder preparation technologies.
“For a pulverization process like plasma atomization, you get a powder with a normal particle size distribution,” Vaughan said. “If you’re making a 3D printed powder, the particle size range you need is a very narrow part of the powder you’re producing. “If you can produce 100 tons of powder a year, but for a specific 3D printing process (such as SLM), you can only use 10 tons of powder.”
The electrolytic powder process can control this process well, and almost all powders can be prepared for a specific 3D printing system. So, if a company is producing powder for SLM Solutions’ SLM devices, you can adjust the process parameters to produce only the desired particle size range, which is also true for EOS devices or DED systems.
Since the electrolysis process operates at 800-1000 ° C, it requires much less energy than melting metals of the same mass. “If you compare our process to traditional titanium powder preparation processes, such as plasma atomization, we estimate that you only need about 50 percent of the energy consumption,” Vaughan said.
The reduction of energy consumption is more beneficial to the environment and can reduce the purchase cost of customers. In addition, electrolysis can be used to prepare a wide range of metal powders, regardless of their melting point.
Metalysis has now progressed to its fifth-generation technology, which began in development, and is preparing to conduct feasibility studies to expand its fully-fledged pulverization capabilities. Vaughan said the fifth-generation pulverization system will be expanded based on the fourth generation, which Metalysis plans to complete this year. The fourth generation system can produce 20 tons of light metal powder and 60 tons of heavy metal powder annually, while the fifth generation can produce several hundred to several thousand tons of high-value metal and alloy powder annually. This technology is available through a unique licensing model, which can be flexibly adapted to the needs of users.
Although the Metalysis process can produce many types of metal powders, its primary focus is on the preparation of titanium powders. “In a nutshell, titanium is a pretty amazing metal,” Vaughan said. “It’s light, but it has high strength and good corrosion resistance.”
The most common 3D-printed titanium powders are titanium alloys Ti6Al4V (also known as Grade 5 or Ti64) and Ti6Al4V ELI (also known as Grade 23 or Ti64ELI). Due to its versatility, Grade 5 titanium powder is the most widely used titanium-based powder at present. This material can be welded, can be strengthened by heat treatment, can withstand temperatures up to more than 300 degrees Celsius, and has a high specific strength and corrosion resistance. For these reasons, Grade 5 titanium powder is often used in high-performance industries such as aerospace, medical, Marine, and chemical industries.
Grade 23 titanium powder has higher purity and biocompatibility, it can be made into coils and wires, and still maintain high specific strength, corrosion resistance, and toughness. This material is commonly used in the biomedical field, including surgical instruments and implants.
The two most common 3D-printed aluminum alloy powders are AlSi12 and AlSi10Mg. Although both are composed of aluminum and some silicon, AlSI10Mg also contains the element Mg. Both are cast alloys that are very useful for making thin-walled and geometrically complex parts.
These metals are characterized by high strength and hardness and can be used in heavy-load environments. Their low density and heat resistance make them ideal for building components like motorcycles or spacecraft interiors. They are also easy for post-processing, including machining, welding, shot peening, and polishing.
There are many types of steel, which can be divided into three categories: stainless steel, tool steel, and maraging steel. Martensitic aged steel obtained high strength and hardness by extended heat treatment process but did not lose ductility. This means that it is easy to machine once the print is complete, allowing for further hardening. Therefore, maraging steel can be used in mass parts and molds.
Stainless steel is known for its high wear resistance, durability, and corrosion resistance. Therefore, this metal is often used in the field of tools, and surgical instruments, and is also suitable for parts processing with acid and corrosion resistance requirements.
Unlike martensitic steel, tool steel has high hardness, wear resistance, and deformation resistance to maintain sharp edges, and tool steel is commonly used to make tools and produce molds. The high wear resistance of tool steel can meet the needs of forming other materials. Once machined with 3D printing, unique cooling channels can be added to the inside of the part to optimize the injection molding process.
Many kinds of cobalt-chromium-molybdenum alloys can be 3D printed, and they often exhibit high strength, high hardness, corrosion resistance, and high-temperature properties. Cobalt is often combined with elements such as chromium and tungsten to make heavy-duty cutting tools or dies, and is also used with magnetic stainless steel in jet or gas turbine parts.
Inconel 718, Inconel 625, and HX (all composed of nickel and chromium elements) are the most commonly used nickel-based alloys for 3D printing. These materials are resistant to high temperatures, oxidation, and corrosion, and still show high strength at up to 1200 ° C. The welding performance of the chipping alloy parts is excellent, and the strength can be further improved by post-heat treatment. These materials are used in the aviation and racing industries, especially in environments where there is a significant risk of high temperature and oxidation, such as combustion chambers and fans.
At high temperatures, although Inconel 625 is more corrosion-resistant and stable than 718, the latter is twice as strong and conductive as the former. Of the three materials, Hastelloy may have the best weldability.
A representative of powder manufacturer AMA (Additive Metal Alloys) has said that although AMA makes many types of powders, nickel-based alloys are a big focus for AMA. Located near GE Aviation’s Ohio facility, AMA targets aviation as a big market for nickel-based alloys.
“Titanium is not as resistant to heat, but it has a low density and a high strength, that is a very high specific strength,” the representative explained. “Nickel-based alloys are relatively dense, but because of their excellent heat resistance, nickel-based alloys are suitable for working inside engines.”
The application of copper in the 3D printing industry is not common, but there are still some companies developing copper alloy powders for the powder bed melting process. In addition, the DED process may have used copper in the welding industry. Compared to silver, copper has a higher aesthetic value and hardness, and this material can be used in jewelry and crafts. Copper is also used in aviation.
NASA’s Materials and Processes Laboratory at Marshall Space Flight Center and Rockdyne have applied copper alloys to powder bed melting systems and 3D printed rocket engine parts with special cooling channels.
Precious metals that can be 3D printed include silver, gold, and platinum. These materials are usually soft, high gloss, and have low chemical activity. In many cases, they also conduct very well. In addition to Concept Laser, Cooksongold is one of the few companies offering 3D printing in gold (yellow, pink, white) and platinum. These materials are mainly used in jewelry and crafts.
Several companies are already using silver nanoparticle inks to print circuits on parts, such as Voxel8 and Nano Dimension. Nano Dimension focuses on developing nickel-based and copper-based inks, which have better electrical conductivity. Silver ink makes it possible to 3D print circuits, either to prototype PCBS or to integrate electronics directly into 3D printed objects.
There are fewer types of refractory metals, including niobium, molybdenum, tantalum, tungsten, and rhenium, which are known for their extremely high heat resistance. Their melting point is more than 2000℃, the chemical reaction is not active, high density, and high hardness.
Tantalum has high corrosion resistance and very good conductivity, which is very meaningful in the electronics industry. According to Los Alamos National Laboratory research, 60% of this material is used in vacuum furnace parts and electrolytic capacitors. In theory, tantalum can increase the radioactivity of nuclear particles.
The melting point of pure tungsten is higher than any other element, up to 3422 ° C. This metal has a high density and is difficult to process, but its stability is suitable for wear-resistant products such as knives, drills, grinds, saws, etc. Tungsten oxidation resistance, acid, and alkali resistance are also very good and can be used for radiation shielding.
Global Tungsten & Powders (GTP) is one of the few companies producing tungsten, tungsten carbide, and molybdenum powders, selling only successfully printed powders. Rick Morgan, Research and Development Manager at GTP, explains his company’s pulverization process: “GTP is vertically integrated, it can mine tungsten ore, chemically extract it, prepare tungsten powder and tungsten carbide powder, dry it with cobalt spray, and modularly process it for 3D printing.” “Morgan said.
ExOne supplies bonded tungsten powder for its binder injection process. The company introduced the material to replace lead in manufacturing medical devices and aerospace parts because lead is more toxic. GTP’s tungsten carbide cobalt material has been successfully applied by ExOne, which has developed a degreasing/sintering solution to ensure density.
The future of metal 3D printing
SmarTech Markets Publishing expects the market for 3D printed metal powders to reach $930 million by 2023, noting that its growth is driven by the demand for large-size parts in the aerospace sector. Based on the company’s recent research report on metal powders, Davide Sher, senior analyst at SmarTech and founder of 3D Printing Business Media, offered some insights, including which materials will be widely used.
“In the foreseeable future, the most common metal 3D printing materials are steel, titanium alloy, nickel alloy, cobalt-chrome-molybdenum alloy,” Sher said, “Titanium alloy is the most used in the aviation sector, because cost is no longer an issue, and the performance gains achieved through lightweight will make up for it.” Nickel-based alloys are also mainly used in the aerospace and defense sectors. Titanium alloys will also be used in the medical field (implants), which will also cover the cost through performance improvements.”
Dion Vaughan, CEO of Metalysis, agrees that demand for titanium alloys will increase and that the company’s process will drive the adoption of 3D printing technology: “Historically, the production of titanium alloys has been limited by traditional methods, which are inefficient and expensive, even to the current advanced plasma atomization processes,” Vaughan said. “However, electroelectrochemical methods are more efficient and less costly, which will drive the popularity of metal 3D printing and further reduce powder costs.”
Vaughan envisions the possibility of co-location of powder production and manufacturing processes, which he says will improve overall efficiency. This is important for the emerging trend of distributed manufacturing, where parts are manufactured closer to the end user.
Davide Sher said that because it is mainly used in the large dental industry, cobalt-chrome-molybdenum alloy is more important for product production. Steel, the first metal 3D-printed powder, is usually the most common choice. Aluminum alloy will be lower in cost, it is suitable for the processing of parts in the automotive industry, and there will be larger 3D printed parts in the future. Precious metals, particularly platinum, have interesting applications, but Sher sees them as more limited.
“The recent rapid development of DED will significantly drive demand for powders,” Sher said. “These technologies are no longer limited to parts repair but are also being used to print large parts. The size and speed of the powder bed melting process is also increasing rapidly, doubling every two years.”
She believes that metal materials are not necessarily the first in industrial 3D printing, and high-performance plastics such as PEEK, PEKK, and carbon fiber reinforced materials may replace metal because of their lower cost. “Especially in the aerospace and medical sectors, these materials will capture a portion of the metal 3D printing market,” Sher concluded.
Following the acquisition of Arcam and Concept Laser, GE formed GE Additive, which supports SmarTech’s forecast for 3D printing growth. The acquisition of Arcam gives the enterprise giant access to both a 3D printer maker and a powder manufacturer.
John Hunter of LPW uses this as an example of how vertical integration is coming. He believes powder manufacturers, including LPW, must increase their powder production capacity. His branch in the United States will move to a larger plant to accommodate powder production. LPW is also increasing its activities related to material recycling, a trend Hunter believes will become more popular.
He noted that the growth in powder usage is driven by 3D-printed end products, which are distinct from the earliest prototyping applications. “The powder market is growing so fast as more and more machines are being installed,” Hunter said. “Instead of machining prototypes and using printouts for months of testing, a lot of printouts are now being used in the final product. So these devices are printing parts all day, all week. They’re using a lot more powder now than they were a year ago.” Hunter expressed his optimism about the future of 3D printing, and his comments on the powder market are merely his personal opinions and observations.
In other words, as metal 3D printing is integrated into the manufacturing supply chain to process end parts, more metal powder will be consumed, resulting in greater powder production volumes. As metal 3D printing continues to evolve, the powder industry can be expected to grow and evolve in tandem.