The Metal 3D Printing Technology Report: Chapter 1: Core Metal 3D Printing Technologies

Understand the Future of Metal 3D Printing

The Metal 3D Printing Technology Report is your essential guide to the latest advances, applications, and real-world insights into additive manufacturing with metal. Packed with detailed case studies,  practical information, and interviews with industry leaders, this report reveals how metal 3D printing is transforming industries and pushing the boundaries of manufacturing.

Read the intro to the report here and an excerpt from Chapter 1 below. 

Core Metal 3D Printing Technologies

The metal additive manufacturing market is not a homogenous one: several different types of processes that build components using different types of metal feedstock. In this chapter, we examine the dominant methods of metal 3D printing—metal laser powder bed fusion (LPBF), directed energy deposition (DED), metal extrusion, and binder jetting—as well as other still-emerging or more niche processes.  

Metal Laser Powder Bed Fusion (LPBF)

Metal LPBF was the first form of metal AM and today remains the predominant metal AM technology used, representing a significant majority of the metal AM market share. Similar to polymer-based PBF (i.e. selective laser sintering), this AM approach consists of using a laser (or multiple lasers) to selectively sinter a fine layer of powder material. In this case, the powder feedstock is made from metal (produced using water atomization, gas atomization, or plasma atomization). In the LPBF process, a layer of metal powder is spread over the build platform using a recoater system. When one layer has been melted, the build platform lowers incrementally and the recoater adds a subsequent layer of powder and the process continues until the part is complete. It is also essential that the 3D printing build chamber be entirely enclosed and an inert atmosphere is maintained. This is achieved using gases such as argon and nitrogen, which protect the metal powders from oxygen and the effects of high-temperature oxidation. 

Leading providers of metal LPBF

The metal LPBF market is shaped by a select number of companies that manufacture industrial-grade systems. They include:

Metal powder bed fusion materials

In metal powder bed fusion, the quality of materials is crucial. Metal powder properties like particle size, shape, and flowability can dramatically influence the final properties and overall quality of a 3D print. For that reason, powders specifically manufactured for additive manufacturing are typically required for this technology group. AM powders are higher quality than more readily available metal injection molding (MIM) powders and are thus more expensive. High-quality metal LPBF powders are characterized by uniform particle size (in the range of 15-45μm), spherical shape (which allows for more dense packing), and smooth surfaces (for good flowability). 

It’s worth pointing out that new materials are continually being developed for metal LPBF technologies and validated for specific systems and applications. The current range of compatible metal materials (specific alloys vary depending on the process and system in question) include:

• Aluminum alloys 

• Cobalt chromium alloys

• Copper alloys

• Nickel alloys 

• Stainless steels 

• Tool steels 

• Case hardening steels

• Titanium alloys 

Advantages and limitations of metal powder bed fusion

There are several advantages to using metal powder bed fusion technologies, as well as certain limitations, some of which are inherent in the technology and others that are being addressed through hardware advances and process optimization. In this subsection, we’ll look at both, starting with the advantages.

Advantages of metal PBF

One of the primary benefits of metal PBF, particularly when compared to traditional metal production techniques, is design freedom. The additive nature of the process, in combination with the use of a powder bed for support, enables users to design and realize incredibly complex geometries, including organic shapes, internal channels, and lattices. 

Design complexity is complemented by very high-resolution capabilities. This specification varies depending on the laser type and beam diameter, as well as the minimum layer height. In the case of the Nikon SLM Solutions’ SLM280 Production Series, the system can print with a minimum layer height of 30 µm and a minimum feature size of 150 µm. Metal LPBF solutions are therefore suitable for producing highly detailed products as well as parts that require tight tolerances.

Another important advantage of metal LPBF when compared to other metal additive processes is that the technology does not require significant post-processing. This is due to the nature of LPBF, which uses lasers to sinter pure metal powders within the printer to create dense metal components. Other processes, such as extrusion-based metal 3D printing, typically require binders or additives in the metal feedstocks, which adds debinding and sintering post-processing steps.

Limitations of metal LPBF

Many of the limitations surrounding LPBF are related to accessibility. While it is the most well-established metal 3D printing approach, it remains one of the most expensive. This high cost is driven by a few different factors. For one, the cost of the raw materials is still very elevated due to the high quality of metal powders that are required. The hardware for LPBF is also costly—with systems costing hundreds of thousands of dollars, even up to a million—due to the price of lasers, inert gases like argon, as well as powder management equipment.

Another limitation of LPBF is related to safety. Because the process uses fine metal powders as feedstock, operators must wear suitable PPE when removing parts from the print bed and handling equipment or components to avoid inhaling the harmful particles as well as any fumes generated in the sintering process. Similarly, environments where LPBF is being used must be properly equipped with ventilation and fume extraction, as well as meet local standards for fire safety, as metal powders—particularly reactive ones—come with a risk of fire and explosion.

For this reason, LPBF technologies require highly skilled operators, which presents another challenge, since the metal AM industry is still faced with a knowledge and skills shortage. This is a particular limitation for smaller enterprises, who may not have the resources to a) bring the technology in-house and b) have the skills needed to implement it. Working with specialized AM services can help bridge this gap.

Directed Energy Deposition (DED)

Directed Energy Deposition (DED) is a category of metal additive manufacturing processes that is characterized by the use of an energy source (such as an electron beam, laser, or electric arc) that melts a metal feedstock (wire or powder) onto a substrate. The DED family includes technologies like Electron Beam Additive Manufacturing (EBAM), Laser Metal Deposition (LMD), Wire Arc Additive Manufacturing (WAAM) and is known for its rapid build rates and suitability for maintenance and repair operations.

While the various types of DED technologies have different processes, there are two main types of process: powder-fed DED and wire-fed DED. In both cases, the metal feedstock is fed through a deposition head that is mounted onto a robotic arm. As the material is deposited onto the print plate or substrate, the energy source simultaneously melts the material, building up metal layers gradually.

The energy source also influences how the process works. For example, electron beam DED systems are capable of high deposition rates (in the range of 18 kg of material per hour) but tend to consume high amounts of energy and must be operated in a vacuum environment. Laser-based DED systems, for their part, require less energy and require an inert gas atmosphere. Laser-based DED technologies are capable of achieving higher degrees of detail and precision, however their deposition rates are lower than EBAM methods (0.5 to 1 kg of material per hour). Notably, some EBAM DED systems are actually hybrid, integrating a machining component to improve the dimensional accuracy and surface finish of metal parts.

Directed Energy Deposition materials

DED processes are known for their ability to process a wide range of metals and metal alloys, including reactive and refractory metals, which are challenging to process using other metal AM processes such as LBPF. 

Wire-based DED processes are compatible with most weldable metal wire feedstocks, including:

• Titanium alloys

• Nickel alloys

• Stainless steel

• Aluminum alloys

• Tantalum

• Tungsten

• Niobium

• Cobalt-Chromium Alloys

• Tool steels

In terms of powders, there is also a broad range of metals that are compatible with DED processes, including: 

• Titanium alloys

• Nickel alloys

• Aluminum alloys

• Stainless steel

• Maraging steel

Advantages and limitations of DED

Directed Energy Deposition processes have a number of benefits, but their strengths differ from other metal additive manufacturing processes, which make them more suitable for certain types of applications. In this subchapter, we will go over DED’s main advantages as well as its limitations. 

Advantages of DED

The main advantages of DED technologies are that they have a rapid build rate and can build large-scale metal parts. For example, DED processes have been shown to be 10 times faster than LPBF. due to higher deposition rates. 

DED additive manufacturing is also more affordable than LPBF. In one study conducted by Optomec, DED was found to be five times cheaper than LPBF when printing a mid-sized metal part with a simple geometry. Part of the lower cost is driven by the cost of raw materials: since DED can use welding materials, the cost is generally lower than that of AM-specific powders. 

Since DED is typically controlled by a multi-axis robotic arm, it does not share the same size constraints as other metal AM processes, making it suitable for large-scale manufacturing. For instance, MX3D’s WAAM technology was used to build a 12-meter-long bridge from stainless steel. It is also capable of printing directly onto existing components, making it uniquely suited for repair applications.

Limitations of DED

While DED is known for faster deposition rates, this build speed does come with certain caveats, including less precision and dimensional accuracy. In fact, many DED processes print a near-net-shape part which must then undergo finishing processes, like machining, to achieve the correct tolerances and surface resolution. Many DED components also require some degree of heat treatment to ensure optimal density and material properties, which can add time and costs to the production process.

Residual stresses in metal DED components can also be an issue. These residual stresses, as well as changes in microstructure, are caused by the high heat and the rapid cooling rates in the DED process. If residual stresses do occur, it can lead to other problems like distortion, cracking, and delamination from the substrate. However, these risks can be minimized through process optimization and thermal treatments.

Another limitation of DED is the high cost of hardware. While the process itself can be economical (thanks in part to lower material costs compared to LPBF), the initial investment in the technology hardware can be prohibitive. Moreover, the DED process, while highly automated, must be operated by skilled machinists or technicians.

Current applications and use cases

The leading application area for DED technologies has been in the repair and maintenance of metal structures and products. Thanks to the technology’s ability to print directly onto a substrate, a number of end users in aerospace, defense, automotive, maritime, energy and industrial manufacturing have found DED to be a suitable solution to accelerate MRO, extend the lifespan of legacy systems, and overcome inventory and supply chain weaknesses. DED is also used in the production of functional prototypes to speed up product development cycles and to produce near-net shape end-use parts with complex geometries in cases where small volumes are required.

Metal Extrusion

Metal extrusion, also referred to as Bound Powder Extrusion (BPE) or Bound Metal Deposition (BMD), is a relatively new metal additive manufacturing technology, which is gaining in popularity due to its accessibility. Metal extrusion functions similarly to polymer deposition processes like Fused Filament Fabrication (FFF) in that it uses a heated nozzle to extrude melted filament (or filament-like feedstocks) onto a build plate, building up a part vertically layer by layer. Instead of thermoplastic filaments, however, metal extrusion technologies use a filament feedstock made of metal powder particles bound in a wax and polymer matrix. The part made from this filament is technically a green part, which must undergo at least two post-processing steps: debinding, in which the polymer matrix is removed using either heat or solvents; and sintering, where the metal powder particles are fused into a final dense metal part. These essential post-processing steps do result in a certain degree of shrinkage, since the wax and polymer binder is removed and the metal particles are consolidated. This feature of metal extrusion can be taken into account in the design and pre-printing stages.  

Metal extrusion materials

As metal extrusion is still emerging as a production method, the materials compatible with the few commercial technologies are limited. Today, it is possible to 3D print using bound materials filled with the following metal powder particles (this compatibility depends on the 3D printing system in question):

• 17-4PH Stainless Steel

• 316L Stainless Steel

• Copper

• Nickel alloy Inconel 625

• H13 Tool Steel

• A2 Tool Steel

• D2 Tool Steel

• 4140 Low-Alloy Steel

• Ti64 Titanium

Advantages and limitations of metal extrusion

As a relatively new metal additive manufacturing process, metal extrusion stands out in the market for its unique advantages, but also has certain limitations that influence how the technology is used.

Advantages of metal extrusion

Metal extrusion offers a number of advantages related to cost, safety, and accessibility. In terms of cost, both the printing hardware and materials are significantly cheaper than LPBF processes and loose powder materials, respectively. 

The technology is also far safer than other metal AM technologies. Since it does not use hazardous loose powders as feedstock or require a gas atmosphere to function, metal extrusion can be used safely in an office environment and does not require extensive training to use. 

Another advantage inherent to metal additive manufacturing more generally is design freedom. More specific to metal extrusion, however, is the ability to print metal parts with an infill, which can reduce part weight and minimize material consumption while still maintaining necessary levels of strength and resistance. 

Metal extrusion also has the advantage of being able to manufacture parts using difficult-to-machine metals like tool steels. This capability means that manufacturers can prototype tools or other industrial parts using the same metals as the final production.

Limitations of metal extrusion

Metal extrusion technologies do come with some limitations, which will continue to influence how the technology is used. The main limitation today is scalability: metal extrusion processes are ideally suited to prototyping, tooling, or small-batch production, but the speed of production does not allow for economical series production. 

Metal extrusion technologies require at minimum two-step post-processing—debinding and sintering—which requires equipment and time. Moreover, parts made using metal extrusion technologies can require machining or additional post-processing if tight tolerances are required.

Part shrinkage is another limitation of the technology, which occurs in the sintering process. As the metal particles fuse together without the binder, shrinkage rates in the range of 17% to 22% occur (depending on the material). Adjustments must be made in slicing software to account for this.

Current applications and use cases

Presently, metal extrusion systems are largely intended for prototyping and tooling applications, rather than scalable production applications in industries like automotive, electronics, energy, and manufacturing. In particular, having a metal extrusion 3D printer on-site can enable manufacturers to print custom tools or metal replacement parts on demand (and at a lower cost per part) to keep operations running smoothly.

Metal extrusion applications include:

• Functional prototypes

• Casting prototypes

• Custom or low-volume end-use parts

• Brazing and soldering fixtures

• Production line tools

• Injector mold with built-in cooling channels

• Extrusion dies

Metal Binder Jetting

Metal binder jetting is an emerging but highly valuable segment in the broader metal AM market, with many leading systems being commercialized in recent years. One of the main draws of metal binder jetting is that it offers a scalable, cost-effective, and energy-efficient way of creating metal parts. The process shares some similarities with LPBF, in that it applies fine layers of metal powder over the print bed. However, instead of using a laser to sinter the metal powder, binder jetting selectively deposits a binding agent onto the powder bed, before another powder layer is applied and the binder deposition repeats. Binder jet systems can print quickly since they use a series of inkjets to deposit the binder across the entire build surface simultaneously.

When the printing process is complete, unbound powder can be removed (and in many cases recycled and reused), and green parts are cleaned. In many cases, green parts require a curing step before sintering, which hardens the binder in the parts so they can be moved into the sintering furnace more easily for full densification. In the sintering process, the binder is burned away and the metal powder particles are fused together, resulting in a dense final part. Infiltration is another commonly used process to finish metal binder jet components. This consists of injecting a molten metal, such as bronze, to fill any porosity left by the binder as it is removed to improve density and minimize shrinkage. 

Leading providers of metal binder jetting

Today, there are only a handful of providers of metal binder jetting solutions. Below are the key players in this segment:

Metal binder jetting materials

Metal binder jetting consumes metal powder feedstock, but the current selection of available materials is far more limited than other powder-based metal AM processes, such as LPBF. This is despite the fact that metal injection molding (MIM) powders can be used on certain binder jetting systems—these materials are more widely available and cheaper than AM-specific powders. Today the main types of qualified metal powders for metal binder jetting are stainless steel grades, however other metals are also being developed and printed. Metal binder jetting materials available at the time of writing include:

• Stainless steel

• Tool steels

• Nickel alloys

• Aluminum alloys

• Titanium alloys

• Copper

• Low-alloy steels

• Metal composites

Advantages and limitations of metal binder jetting

As metal binder jetting becomes increasingly viable for production applications, manufacturers seek to benefit from several things, but should also be aware of certain limitations with the technology.

Advantages of metal binder jetting

Speed and scale are among the main advantages of metal binder jet 3D printing. Compared to other metal AM processes that rely on point or line printing, binder jetting is able to print a full cross-section of powder simultaneously using arrays of thousands of inkjet heads. By some accounts, the technology can be up to 100 times faster than LPBF. Large build envelopes are also conducive to printing multiple components in a single build, which facilitates production scales and unlocks lower costs per part. 

The nature of the process also means that binder jetting itself consumes less energy and is less costly than metal additive manufacturing technologies that require an intense energy source, such as a laser or electron beam.  

In terms of quality, while shrinkage does have to be taken into account, binder jetting generally produces net-shaped parts with good resolutions and low surface roughness, meaning minimal post-processing is required after sintering.

Another advantage of binder jetting is that it can print complex geometries without the need for support. This is because the powder bed functions as a support for the parts. While powder removal is therefore a critical step, manufacturers do not need to worry about removing supports with this process.

Limitations of metal binder jetting

There are limitations to be aware of when using metal binder jetting. For one, it necessitates curing and sintering post-processes, which not only adds time to production cycles, but also requires additional equipment.

Binder jet parts also succumb to shrinkage between their green and final states. With sintering especially, shrinkage rates can be as high as 25%. Infiltration can minimize shrinkage rates, but not eliminate the phenomenon entirely. The shrinkage caused by the densification process also means that binder jetting is not particularly well suited to the production of large parts, since cracks, stresses, and deformation are more likely to occur.

Current applications and use cases for metal binder jetting

Metal binder jetting is suitable for the production of numerous small components in a single build, since parts can be stacked or nested. The technology is also largely intended for series production, since the best cost per part can be achieved if the usage of the 3D printer’s build space is maximized. Mass customization is another suitable application area for metal binder jetting, since unique or customized geometries can be strategically nested in a single build.

Other Metal AM Technologies

While LPBF, DED, Metal Extrusion, and Metal Binder Jetting are the main metal additive manufacturing processes today, there are also technologies that exist that are either still emerging or will remain niche. These technologies include processes like cold spray additive manufacturing (CSAM), electron beam melting (EBM), and ultrasonic additive manufacturing (UAM). 

Read more about these technologies by downloading the full report.