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The complete guide to binder-based metal 3D printing


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Metal binder jetting technology, now also generally known by the acronym MBJ, is, at the same time, the first and, together with other binder-based technologies – commonly known by the acronym BMP, which stands for bound metal printing – the newest opportunity for binder-based metal AM processes.

Invented at MIT in 1993, the technology uses an inkjet printhead to apply binder to a bed of metal powder and form green parts which are similar to parts produced by metal injection molding (MIM). These parts then undergo a series of post-process (which differ for each specific technology), including sintering, to deliver final parts.

Segment pioneer ExOne (now part of the Desktop Metal group) introduced its first metal binder jetting nearly two decades ago, after licensing the original patent from MIT in 1996. However, only recently has the company introduced new systems tailored for higher productivity. ExOne did so as a response to several other large players announcing plans to enter the market for metal binder jetting. In particular, working with metal binder jetting technology inventor Eli Sachs, Desktop Metal was founded in 2015 by serial entrepreneur Ric Fulop and introduced the concept of a high-productivity metal binder jetting system. Fulop’s intuition was that by optimizing and automating the post-processing phase (including eliminating the need for metallic supports during the build phase), metal binder jetting workflows could deliver significantly higher productivity and thus lower per part cost than the more established metal powder bed fusion technologies.

After extensive development, these machines have now entered full-scale commercialization. The relationship between the two companies came full circle when Desktop Metal conducted a successful IPO via a SPAC merger in 2020 and used the funds to acquire ExOne in 2021.

The growing competition in this segment, as the technology evolves to target larger batch production than metal PBF processes, brought these two fierce competitors together, within a scenario that is seeing many things happening at the same time. Desktop Metal and ExOne joined forces to compete against two large industrial groups that have already become leaders in different areas of production 3D printing: GE (GE Additive) and HP (HP 3D Printing).

The metal binder jetting process

The metal binder jetting process involves selective deposition of binder droplets and ex- tensive post-processing. First, inkjet-style printheads selectively deposit droplets of binder material onto a bed of metal powder until an entire layer has been created; the printing plate then lowers, a new layer of powder is applied, and another layer of binder is deposited. When every layer of the binder has been deposited, the part (in its brittle green state) is left to cure for several hours. To further increase its strength and reduce its porosity, the part must be put through a process of sintering or infiltration. Sintering involves heating the part for up to 36 hours in a furnace at around 100°C. This burns away the binder material and causes the metal particles to fuse together. Infiltration introduces a molten metal with a low melting temperature, which seeps through the part and fills the voids left by the burnt-out binder material. There are advantages and disadvantages to each method. Infiltration pro- duces slightly less dense parts than sintering, but sintering can cause unwanted and unpredictable part shrinkage.

The complete guide to metal binder jetting (MBJ) and to other binder-based metal 3D printing (bound metal/BMP) technologies.
A binder jetting printhead from ExOne jetting binder.

Metal binder jetting, or MBJ, is seen by multiple stakeholders as the most viable solution for introducing high-throughput, cost-effective, large batch and serial additive manufacturing to segments such as mass-market automotive and consumer products, as well as a viable solution for large batch production of parts for industrial machinery.

Because the metals are not melted during the process, binder jetting eliminates some issues related to in-process residual stresses and prints green parts at a very high speed. No supports are required, as overhangs are supported by loose powders in the bed, which results in shorter post-processing and more complex geometrical possibilities.

New and established firms are now investing heavily in building up production capabilities, driving metal material companies to develop more powder materials. One expected key benefit of newer binder jetting technologies is the ability to rapidly adapt powders used in MIM processes to the binder jetting process, further lowering material costs. However, several obstacles remain, including the fact that one of the most relevant materials for binder jetting adoption, aluminum, is not well suited for MIM processes.

The complete guide to metal binder jetting (MBJ) and to other binder-based metal 3D printing (bound metal/BMP) technologies.
Metal binder jetting parts from HP.

In addition to process-related challenges, the need to sinter parts in a furnace after fabrication presents some inherent challenges. These include the cost of sintering systems, the long times required for furnace sintering and the need to account for significant part shrinkage through advanced software capabilities, which presents more challenges for AM than other manufacturing processes due to the complexity of certain AM parts.

MBJ BENEFITS

  • Higher productivity (up to tenfold compared to PBF)
  • Several large operators entering the market with significant investments
  • Does not require supports
  • Potentially lower CapEx (compared to PBF)
  • Produces net shape parts
  • Very high resolution

MBJ CHALLENGES

  • Still unproven for large-scale production
  • Requires lengthy sintering in a furnace as a post-process step
  • Some MBJ processes require lengthy debonding
  • Significant part shrinkage to account for
  • Still mostly unproven for fully dense parts without additional infiltration steps
  • Still limited selection of available materials (compared to PBF)
  • Some processes require finer powders than PBF
  • Challenging to produce large parts

MBJ trends Vs. other metal AM technologies

In its latest Metal AM Market Report, 3dpbm Research forecasted overall metal AM hardware revenues to grow at 33.7% CAGR over the next 10-year period, from just under $1 billion in yearly global sales in 2020 to just over $18 billion in yearly global sales by 2030. While they represent a marginal segment today, metal binder jetting (and other binder-based metal technologies are expected to grow at the highest rates.

L-PBF technologies are, and will remain, the primary revenue area for metal AM hardware, growing from $640 million in global sales recorded in 2020 to an expected $8.9 billion in 2030, with an expected CAGR of 30%. L-DED technologies will experience a more rapid growth trend with a CAGR of 34.7%, however, among the most relevant high-growth revenue opportunities we will find all binder-based processes—both bound metal (a segment closely related to metal binder jetting) and metal binder jetting itself. Binder jetting is expected to grow at 55% CAGR.

This very high rate is down to binder jetting being only marginally commercially explored as of 2020, whilst very significant investments are being poured into these technologies by major stakeholders. Binder jetting is seen as a key technology to enable large throughput AM production in segments such as automotive and consumer products. Bound metal is currently more established than binder jetting, hence the lower CAGR of 45.8%; however, its overall potential as the most affordable metal AM process is also still largely unexplored.

The complete guide to metal binder jetting (MBJ) and to other binder-based metal 3D printing (bound metal/BMP) technologies.
10-year forecast of metal AM hardware revenues CAGR by technology. Source: 3dpbm Research – Metal AM Market Opportunities and Trends 2020-2030.

Metal binder jetting is here

Starting in 2017-2018, GE Additive and HP 3D printing revealed they were entering the market for metal binder jetting with the goal of offering high-productivity systems within a few years. The pandemic slowed down their effort but the time has now arrived for full market commercialization of their first metal binder jetting systems. In the meantime, other companies also entered this market segment offering credible production solutions: these include Markforged (the US company acquired another MBJ pioneer, Digital Metal, in 2022) and Ricoh (by developing its own solution in-house).

HP 3D Printing vs GE Additive

As we examined more in-depth in the dedicated feature story of our latest Metal AM Focus eBook, HP 3D Printing was the first large industrial player to commit to developing a production-capable MBJ technology. What is today known as MetalJet was first announced at the IMTS 2018 exhibit, along with a timeline for the technology’s development in collaboration with key alpha and beta partners. The market-ready machine, the Metal Jet S100 was finally presented at IMTS 2022 and is on show for European customers for the first time at Formnext 2022. HP is entering the metal 3D printing production segment leveraging the overall successful experience in the polymer AM segment with MultiJet Fusion technology, which dramatically accelerated and reduced costs for the production of polymer AM parts.

The complete guide to metal binder jetting (MBJ) and to other binder-based metal 3D printing (bound metal/BMP) technologies.
The complete metal binder jetting solution from HP.

The company is leveraging this experience, together with its leadership in the overall global inkjet printhead market, to open the doors for a digital reinvention of the global metals manufacturing sector, with a strong focus on end-to-end supply chain solutions in both software and hardware. HP has identified stainless steel as the primary material for high-throughput applications and will build its offering around these materials similar to the way its polymer AM production strategy was centered on nylon 12.

The next largest contender to MBJ market dominance, GE Additive, is entering this segment from the experience that the company built in metal AM production via metal PBF processes. In 2016, General Electric acquired German laser metal PBF hardware manufacturer Concept Laser and Swedish electron beam metal PBF hardware manufacturer Arcam (and Arcam-owned metal powder manufacturer AP&C). Both companies formed the foundation of the GE Additive division and their technologies have been progressively developed to accelerate productivity and cater to the needs of serial manufacturers. At the same time, GE Additive began developing its metal binder jetting technology in-house under codename H1 (later H2) in 2018. What started as a purely experimental project rapidly picked up momentum and has led to GE Additive releasing the Binder Jet Line and Series 3 printers, which are on display for the first time at Formnext 2022.

A large metal binder jetting part from GE Additive

The Binder Jet Line Series 3 has been developed to additively manufacture complex, small, and large parts, up to the weight of 25kg, in stainless steel, with no known limitations on maximum wall thickness. Based on input from customers and partners during the technology development phase, GE Additive is focused on enabling the eventual deployment of 40, 50, and 100+ machine installations that will drive repeatable process quality, while minimizing operator contact with equipment and materials.

Markforged/Digital Metals and Ricoh

The remaining contenders include Markforged/Digital Metal and Ricoh. While the investments and efforts behind these projects are not nearly as significant as those made by the previously mentioned companies, they both present unique opportunities.

The Markforged/Digital Metal deal is almost identical in nature and strategy to the Desktop Metal/ExOne merger. Markforged is a direct competitor to Desktop Metal in the bound metal 3D printing segment (the two companies also went through a lengthy patent court case), however, Markforged can leverage an already successful composite 3D printing solutions business. Just like Desktop Metal, Markforged went public through a SPAC merger finalized in 2022 and raised significant funds. Some of these were immediately used to acquire metal binder jetting pioneer Digital Metal from Swedish company Hoganas.

Digital Metal’s DMP PRO

While the two companies have not yet begun the integration process, Digital Metal MBJ technology is relevant as the company has been using it to produce large numbers of very small, highly complex parts for well over a decade. As such, Digital Metal developed a production solution, the DMP/PRO which can produce up to 1,000 cm3 of parts per hour at 1600 dpi, with a build volume of 250 × 217 × 70 mm. Hoganas understood it would not have the resources needed to emerge in a highly competitive MBJ market and the deal with Markforged – an increasingly solid and strong company both in terms of product offering and marketing capabilities – could prove an ideal match.

Ricoh is farther behind in the metal MBF segment but the company’s world-leading expertise in the inkjet printhead market can be a formidable asset, as it has been in HP’s own venture. The Japanese company is currently keeping its additive manufacturing development under relatively tight wraps, with much of it taking place at its Customer Experience Center in Telford, UK. The CEC is looking to develop 3D printers and a total solution for production workflow to manufacture aluminum parts using MBJ 3D. The company chose aluminum as it is one of the most challenging materials to sinter however it would be an ideal material for many MBJ applications due to its low cost, lightweight and high versatility. In fact aluminum is a key element in both Desktop Metal’s and ExOne’s strategy, however, it has not yet yielded results in terms of commercial applications.

These are the very first aluminum parts produced with Ricoh’s new metal binder jet system, now in development.

One last company to keep in mind in this segment is US-based 3DEO. The reason why we do not consider them a contender in the MBJ market is that they use a proprietary MBJ technology for internal part production. Focusing primarily on large batches of very small parts (similarly to Digital Metals), 3DEO has produced the largest number of MBJ 3D printed parts out of any company to date, according to data published in 3dpbm’s Metal AM Opportunities and Trends 2020-2030 market report. At this time, it does not appear that the company intends to make its technology available to external customers, however, its service capabilities provide a clear indication of the potential that MBJ can have for the AM industry and all metal manufacturing.

Bound Metal Printing

Bound metal printing includes processes that are similar to those already used for 3D printing other materials such as polymer and ceramics. The most widely adopted bound metal printing process uses bound metal filaments or proprietary sticks of bound metal materials for material extrusion. Often priced below $50,000 (and in some cases much lower), these systems have been built for increased affordability in metal prototyping and small batch production. Because they do not use fine, atomized powders, they are well suited for use in an office, studio or shop environment.

The extrusion-based BMP process consists of heating and extruding bound metal rods onto a build plate—not unlike FFF technology, where plastic filaments are melted and deposited layer by layer to build up an object. The bound metal rods used in the process are composed of metal powder contained within a wax and polymer binder. Once every layer has been printed, the BMP part undergoes a debinding and sintering process, during which the binder is removed and the metal particles are sintered, resulting in a dense metal component.

The Studio System BMP solution from Desktop Metal.

Photopolymerization-based BMP, such as Lithography‐based Metal Manufacturing (LMM) technology offered by Incus GmbH, uses a different material base to produce metal components. Specifically, it relies on a slurry made from a photoreactive metal-filled feedstock, which is solidified layer by layer using a high-performance projector. This results in a green part which then undergoes debinding and sintering to create a dense, metal component. Because the process does not require a protective gas atmosphere, it is easier and safer to implement than many other metal AM processes.

Recently a new process called ColdMetalFusion (which we will heretofore refer to by the acronym CMF) emerged, introduced by the startup Headmade Materials. The process leverages the existing base of SLS (polymer laser PBF) 3D printers introducing specific metallic powder coated by a polymeric binder which can be processed via SLS to form green parts. This is not an entirely new approach to SLS (we’ve seen it in ceramics in the past) however Headmade Materials was able to fine-tune the process for high-throughput production, at a time when many SLS 3D printer manufacturers are looking for new opportunities to use their technology to compete with low-cost systems and high-speed thermal PBF systems, thus generating enthusiasm across the entire segment.

Key BMP evolutionary trends

BMP technologies were first introduced by Markforged and Desktop Metal—the two companies also faced each other in court over patent infringement issues and eventually settled—to make metal 3D printing more affordable and easier to implement. The technologies use filaments (or sticks in the case of Desktop Metal) made of metal powder bound in a thermoplastic material and process them via a relatively standard thermal material extrusion process. Because no loose powders are involved, bound metal processes are suitable even for use in an office environment.

The green parts require sintering in a furnace, but this process can also be carried out in a non-factory setting. Green parts can be printed relatively quickly and supports removed easily, enabling more geometric freedom, but the process remains slow and limited to prototyping, tooling or very small batch productions. This workflow can, in theory, be scaled by adding more 3D printers; however, high-quality sintering at an industrial level remains challenging both in terms of the process and in terms of designing intentionally oversized green parts that accurately account for shrinkage during the sintering process.

The Metal X solution from Markforged.

As other companies and third-party material manufacturers such as BASF have begun to develop and market bound metal filament materials for use with generic thermoplastic filament extrusion systems, this segment of metal AM is becoming larger and more accessible. Consequently, the cost of 3D printing certain types of metal parts has been brought to an unprecedented low. This trend towards expansion will continue, but BMP should not be seen as directly competing with high-end industrial metal PBF. As per the vision of manufacturers such as Desktop Metal, bound metal is a prototyping technology that is complementary to production metal binder jetting and can be seen as complementary to industrial PBF processes as well. The presence of a much larger number of low-cost 3D printers that can process bound metal filament materials is going to have a significant effect on the shape of the market. This will be further discussed in section 2.7 of this chapter.

The rapid evolution of ColdMetalFusion technology is one of the most interesting trends to emerge recently. Because this technology (and material system) leverages the existing (very large) base of SLS systems, while also offering significant advantages in terms of speed, geometry and green part strength, it has gathered significant momentum. Several stakeholders (SLS hardware companies, post-processing companies, gas companies, furnace companies) have joined in the ColdMetal Fusion Alliance, in order to accelerate development, adoption and growth at a time when adopters are increasingly looking at ways to implement metal AM for serial production.

Parts 3D printed by ColdMetalFusion.

Another relevant development in bound metal printing processes is the use of bound metal slurries, made up of metal powder and a photopolymerizable binder, for use in stereolithographic processes. This approach is still in an earlier evolutionary phase and actively marketed by only two companies that specialize in advanced ceramics stereolithography: Incus (a spinoff of Lithoz) and Admatec. Because the systems and the materials implemented in this process are more costly, the primary objective of metal stereolithographic processes at this time is to provide a higher definition and smooth surface finish on small parts that cannot be achieved via other metal AM processes.

BMP benefits

  • More affordable systems (lowest CapEx for metal AM hardware)
  • Not metal powder-based; can operate in an office environment
  • Some systems can use generic bound metal filaments
  • Easy to remove supports from green parts

BMP challenges

  • Slow material extrusion or stereolithographic processes unsuited for production
  • Require de-binding and sintering in a furnace
  • Some systems use proprietary materials
  • Some geometric limitation inherent to the extrusion and stereolithography processes

Key vendors and systems

Desktop Metal has created an entirely new market segment by introducing a commercial desktop system based on Bound Metal Deposition (BMD) technology, a type of bound metal printing that uses material extrusion. In this effort, it has been joined by a number of other contenders, including Markforged, Xerion, Ultimaker, Makerbot (experimental), BCN3D and Triditive, among others who have proposed viable solutions using bound metal printing approaches with filaments (BASF notably introduced a 316 steel specifically for these processes). At the same time, stereolithography-focused firms, such as Incus and Admatec, have introduced bound metal 3D printing systems that use photopolymerizable slurries.

The Tritone DOMINANT system.

Also notable is Tritone. This Israeli startup developed its DOMINANT metal AM system based on its unique MoldJet process. The system includes six trays and six stations: each tray moves from station to station resulting in the production of near-net shape (NNS) metal parts. First, the tray goes through for mold printing using a polymer material and four inkjet printheads. A paste consisting of a water-based binder and MIM powder is deposited into the mold cavity. A blade then passes over the metal paste to remove excess material and compress it. In the next station, the build tray undergoes a drying and hardening process before moving on to a detect and control (DAC) quality check for every printed layer. From there, the tray is moved to a low-temperature oven station to remove the polymer mold before sintering.

Vendor

Desktop Metal

Markforged

Xerion

Tritone

Triditive

Incus

Admatec

System

Studio System

Metal X

Fusion Factory

DOMINANT

AMCELL

HammerLab 35

Admaflex 300

Size (mm)

300 x 200 x 200

300 x 220 x 180

245 x 230 x 200

400 x 240 x 120

220 (Ø) x 330

89,6 x 56 x 120

260 x 220 x 500

Est. Price Range

$$

$$

$$$$

$$$$

$$–$$$

$$

$$$$

Highlights

Leading BMP

Leading BMP

Integrated furnace

Production

Production cell

Stereolithography

Stereolithography

 



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