Everything You Need to Know About Metal Binder Jetting

Metal Binder Jetting is experiencing a renaissance. Over the past ten years, many new companies have entered the Binder Jetting market, each with its own approach to this technology. These activities are driven in part by the many lucrative application fields that this technology offers. On one hand, the high speed and precision of the metal binder jetting process can help it develop into a new process for mass production.

Today we will look at how Metal Binder Jetting has evolved and why it is coming to market as a new manufacturing technology.

The origins of this AM technology date back to 1993, when the Massachusetts Institute of Technology (MIT) developed an inkjet-based process for creating three-dimensional objects from metal powders. Interestingly, the term "3D printing" was originally coined by MIT in reference to metal binder jetting technology.

The manufacturing company Extrude Hone Corporation received an exclusive license for MIT technology in 1996. Since then, the company has developed and marketed Metal Binder Jetting systems. The first 3D printer, ProMetal RTS-300, was delivered to Motorola in 1999. ExOne, which was spun off from Extrude Hone Corporation in 2005, was the only company offering services and systems for Metal Binder Jetting until the early 2010s. At that time, the early MIT patents for the technology began to expire, allowing new companies to enter the market. Since then, the technology has been revived with the vision of truly utilizing this technology for production across all industries.

In Metal Binder Jetting, a liquid binder is selectively applied to bond powder particles layer by layer. The process begins with the distribution of a thin powder layer, whereby print heads introduce binder droplets in a controlled manner into the powder bed. The build platform lowers and another powder layer is applied. The process is repeated until the part is complete. Unused powder (approximately 95%) is recycled and can be reused. When spraying with metal binders, the freshly printed parts remain in a fragile green state and must subsequently be post-processed, for example sintered and infiltrated to strengthen the part. In addition to metals, Binder Jetting can also be used with a variety of other materials such as sand and ceramics.

Conventional binder jet technology uses a print head to apply a liquid binder to powder layers. However, in additive manufacturing of metals using Binder Jetting technology, parts require various post-processing steps since they are initially produced in the green state. This means they have low mechanical properties and are often weak and brittle. The post-processing phase aims to strengthen the parts and includes curing, sintering, infiltrating, and other finishing processes.

Curing increases the strength of the green parts so that they can be safely removed from the build platform. During the process, the parts are cured in an oven at approximately 200° C for a period of several hours, which results in significantly higher mechanical properties.

Despite curing, the metal parts remain highly porous. The porosity of the parts is significantly reduced through sintering or infiltration processes. Typically, the sintering process takes place in an oven with controlled atmosphere, where the part is heat-treated for 24 to 36 hours at approximately 100°C and the binder is burned away. This helps the metal particles fuse together and results in a strong metal component with low porosity. However, sintering can lead to inhomogeneous shrinkage of the part and is difficult to predict - this must therefore be taken into account in the design phase.

To achieve high density, the part must be infiltrated to fill the voids created by the burnout of the binder. This is normally done by applying molten bronze to infiltrate the remaining voids in the part. These post-processing steps significantly improve the mechanical properties of the metal part. For example, bronze infiltration of stainless steel can achieve a final density of 95%.

Finally, the part can optionally be polished and plated with gold or nickel to achieve aesthetically appealing surfaces.

Metal Binder Jetting offers a range of unique advantages that facilitate its application for production applications.

First, the spraying of the binder does not melt the metal powder during the printing process, which avoids problems associated with the buildup of residual stresses. Second, no support structures are required for the metal binder jetting process, since printed parts are surrounded by loose, unused powder. Both advantages help keep post-processing to a minimum. Furthermore, Binder Jetting machines are more cost-effective than 3D printers based on SLM or DED processes. One reason for this is that they do not use expensive lasers or electron beams. Newer machines can also use metal injection molding (MIM) powder. These are significantly cheaper than metal powders specially developed for 3D printing, which are typically produced in small quantities using expensive production methods such as gas atomization. The switch to MIM powder therefore enables manufacturers to further reduce the operating costs of this technology. With Binder Jetting, not only are cheaper raw materials used, but very precise parts can also be printed with mechanical properties comparable to those of conventionally manufactured metal components. Finally, the build speed of Metal Binder Jetting is typically higher than that of other metal 3D printing processes. All of these advantages combined result in a very scalable and production-capable technology.

The 2010s mark a new era for metal binder jetting. From start-ups to established players, a number of companies are actively trying to expand the boundaries of what is currently possible with this AM technology.

ExOne is one of the oldest players in this field. Throughout its history, ExOne has brought four metal-binder systems to market, each of which represents a further development of the previous one. For example, the company introduced the Innovent + in 2018, which marks a new generation of machines at ExOne. While the system is slower than ExOne's previous M-Flex 3D printer, it features two important new functions: First, it is equipped with an ultrasonic coater that was developed to improve powder flowability and simplify material changeover. ExOne states that this new powder-dispensing technology represents the most advanced powder metering technology on the market. The recoater is supplied with four sieve configurations to ensure better material compatibility. This feature plays another important role: the machine can process standard MIM powder. Other 3D metal powder printers, particularly those using a laser or electron beam, require specially formulated powders to operate consistently. However, such powders are often much more expensive than materials for traditional metal processing technologies. By supporting MIM powders through the Innovent +, ExOne can bring cost savings and greater material flexibility to users of its machines. The company continues to innovate and has scaled the technology behind the Innovent + to the X1 25PRO 3D printer at the production level. The machine was introduced in June 2019 and can print up to 10 different materials on its large build volume of 400 x 250 x 250 mm. With this system, the company aims to enable the manufacturing of industrial metal components with high resolution, tight tolerances, and improved surfaces.

Another company that has made a name for itself in the development of metal binder jetting is Digital Metal, a subsidiary of a leading metal powder manufacturer in the Höganäs Group. Digital Metal was founded in 2012 and has been offering its metal binder jetting technology as a service since 2013.

In 2017, Digital Metal introduced the 3D printer DM P2500 to the market, which is intended for series production of small, complex parts. The machine distributes a layer of metal powder with a thickness of 0.042 mm. A binder is then ejected according to the part geometry. It is reported that this process is precise and repeatable, making it possible to produce very small yet incredibly detailed parts with a resolution of 35 micrometers.

The subsequent sintering process results in an average surface roughness of Ra 6.0 micrometers, which is sufficient for many end-use parts and features such as internal channels. Digital Metal states that its 3D metal printers have already produced over 300,000 components across various industries, including aerospace, luxury goods, dental tools, and industrial equipment. To further develop its technology, Digital Metal launched a fully automated production concept last year. According to this concept, a robot handles the majority of process steps, such as loading the printer with build boxes and removing them for post-processing. The goal is to avoid all manual work in order to enable continuous production in high volumes.

With the introduction of this no-hands production line, Digital Metal has made a huge leap forward with its Metal Binder Jetting technology.

After HP introduced Multi Jet Fusion technology for polymer parts in 2016, HP presented the next expansion of its additive manufacturing offering in 2018: the Metal Jetting 3D printing system. The new 3D metal printer is powered by Binder Jetting technology. However, the unique advantage that HP has associated with this technology lies in its innovative printhead and ink technology. Although Binder Jetting technology is inherently fast, HP has applied its knowledge of printhead technology to make it even faster. The Metal Jet system is equipped with 6 printheads, each with 5,280 nozzles. The presence of these multiple nozzle arrays increases the productivity and reliability of the printer. Furthermore, thanks to its expertise in ink technology, HP has developed an innovative binder to make the sintering process faster and more cost-effective. "In metal injection molding, typically more than 10% of the component weight must be burned out in the form of binder. In our case, we have less than 1%, a significant order of magnitude less, which makes sintering faster, more cost-effective and easier," says Tim Weber, HP's Global Head of Metals. Together, these advances result in a metal 3D printer that is intended to achieve cost-effectiveness and efficiency comparable to conventional manufacturing technologies. HP is not yet selling the machine. Instead, the company has launched a parts manufacturing service to make the 3D printer commercially available in 2020. Given the claims HP has made regarding Metal Jetting, this technology could be the key to substantially unlocking a sustainable value proposition for metal 3D printing - series production of additively manufactured components.

The Process Behind 3DEO's Intelligent Layering® Technology

Many companies strive to make 3D metal printing competitive with other manufacturing techniques. One such company is 3DEO, which was founded in 2016 with the goal of enabling mass production through Metal Binder Jetting. To achieve this, the company completely reinvented the process. Instead of inkjet for selective binder deposition, 3DEO machines use a proprietary spray system to apply the binder evenly across the entire layer.

The result is a hard, thin layer of metal powder, which is then processed with micro-shaft mills. The CNC operation cuts the part geometry for each layer. This technology, referred to as Intelligent Layering, is the first combination of Binder Jetting and CNC milling in a hybrid system. With such a combination, 3DEO can produce very precise small metal parts with a density of over 99.5% after sintering.

The Intelligent Layering technology from 3DEO is currently only offered through the company's production service. By limiting the technology to its own production service, 3DEO ensures high quality of printed parts while keeping the platform very flexible.

Currently, 3DEO is processing some of the largest orders in the metal 3D printing industry and recently received an order for 28,000 parts.

Although the company does not plan to sell its machines, the growing production volume serves to confirm the technical capabilities of Binder Jetting, namely to deliver production parts that are comparable to conventionally manufactured components.

The Boston-based start-up Desktop Metal was founded in 2015 with the goal of fulfilling the promise of 3D printing for production. To achieve this, the company developed an extremely fast production system.

The technology behind the metal 3D printer is called Single Pass Jetting (SPJ) by the company, a faster version of the typical BJ process.

The system is equipped with two full-width print heads and an advanced powder distribution system with which powder and binder are effectively distributed over the build platform in a single fast pass.

With a build volume of 750 x 330 x 250 mm, this bidirectional system enables high-resolution printing at up to 12,000 cm3/h, which corresponds to over 60 kg of metal parts per hour. This speed is orders of magnitude higher than other metal 3D printers on the market, making it ideal for manufacturing complex metal parts in high volumes.

Furthermore, the production system is the first binder jetting system equipped with an industrial inert environment that offers gas recycling and solvent recovery for safe printing of reactive metals. This opens up the possibility of printing a broader range of metals, such as aluminum.

Desktop Metal has maximized the advantages of Metal Binder Jetting with its production system by adding a substantial speed improvement.

Desktop Metal has only recently offered its production system for purchase, so it will take some time before its claims regarding production speed prove themselves. In this case, the production system would be the fastest Binder Jetting 3D printer currently available on the market.

Metal binder jetting is becoming one of the most important key technologies among metal 3D printing technologies. This is enabled by the unique capability of the technology to achieve high printing speeds and manufacture highly precise components. Another key development for the success of metal binder jetting is the compatibility with already known and relatively inexpensive MIM powders. A number of companies have recognized the breakthrough potential of metal binder jetting and are working intensively to capitalize on the opportunities presented. In the future, these companies will continue to develop Metal Binder Jetting. Ultimately, this will help the technology gain a valuable share of the overall manufacturing market.