Everything you need to know about Metal Binder Jetting
Metal binder jetting is experiencing a renaissance. In the last ten years, many new companies have entered the binder jetting market, each with their own approach to this technology. These activities are partly driven by the many lucrative applications that this technology offers. For one, the high speed and precision of the metal binder jetting process may help it become a new method for mass production.
But what developments are driving the success of this technology?
Today we will look at how metal binder jetting has evolved and why it is coming onto the market as a new manufacturing technology.
The origins of metal binder jetting
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 the 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 metal binder jetting services and systems 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 revitalized with the vision of truly utilizing this technology for production in all industries.
How does the spraying of metal binders work?
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 layer of powder, whereby print heads selectively introduce droplets of binder into the powder bed. The printing plate lowers and another layer of powder is applied. The process is repeated until the part is complete. Unused powder (approx. 95%) is recycled and can be reused. When spraying with metal binders, the parts that have just been printed remain in a fragile green state and must then be reworked, e.g. sintered and infiltrated to strengthen the part. In addition to metals, the binder jetting can also be used with a range of other materials such as sand and ceramics.
Post-processing steps for the ejection of metal trusses
Conventional binder jetting technology uses a print head to apply a liquid binder to powder layers. However, in the additive manufacturing of metals using binder jetting technology, the parts require various post-processing steps as they are initially produced in a green state. This means that they have low mechanical properties and are very often weak and brittle. The post-processing phase aims to strengthen the parts and includes hardening, sintering, infiltration and other finishing processes.
1. curing
Curing increases the strength of the green parts so that they can be safely removed from the print bed. During the process, the parts are cured in an oven at approximately 200° C for a period of several hours, resulting in much higher mechanical properties.
2. sintering
Despite curing, the metal parts remain highly porous. The porosity of the parts is significantly reduced by sintering or infiltration processes. Typically, the sintering process takes place in a controlled atmosphere furnace where the part is heat treated for 24 to 36 hours at around 100°C and the binder is burned away. This helps to fuse the metal particles together and results in a strong metal component with a 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.
3. infiltration
To achieve a high density, the part must be infiltrated to fill the voids created by burning off the binder. This is usually done by applying molten bronze to infiltrate the remaining cavities in the part. These post-processing steps significantly improve the mechanical properties of the metal part. For example, a final density of 95% can be achieved by infiltrating stainless steel with bronze.
4th completion
Finally, the part can optionally be polished and plated with gold or nickel to achieve aesthetically pleasing surfaces.
What are the reasons for using metal binder jetting as a production technology?
Metal Binder Jetting offers a number of unique advantages that make it easier to use for production applications.
Firstly, spraying the binder does not melt the metal powder during the printing process, avoiding problems related to the build-up of residual stresses.
Secondly, no support structures are required for the metal binder jetting process, as printed parts are surrounded by loose, unused powder. Both advantages help to keep post-processing to a minimum.
In addition, 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) powders. These are significantly cheaper than metal powders developed specifically for 3D printing, which are typically produced in small batches using expensive production methods such as gas atomization. Switching to MIM powders therefore enables manufacturers to further reduce the operating costs for this technology. Not only does binder jetting use cheaper starting materials, but it can also print very accurate parts with mechanical properties comparable to those of conventionally produced metal components. Finally, the build speed of metal binder jetting is typically faster than other metal 3D printing processes. All these advantages together result in a very scalable and production-ready technology.
The latest developments in metal binder jetting
The 2010s mark a new era for metal binder jetting. From start-ups to established players, a number of companies are actively trying to push the boundaries of what is currently possible with this AM technology.
ExOne continues its innovations
ExOne is one of the oldest payers in this field. Throughout its history, ExOne has launched four metal binder systems, each representing an evolution of the previous one. For example, in 2018, the company introduced the Innovent +, which marks a new generation of machines at ExOne. While the system is slower than ExOne's previous M-Flex 3D printer, it has two new important features:
First, it is equipped with an ultrasonic coater designed to improve powder flowability and simplify material changes. ExOne says this new powder dispensing technology represents the most advanced powder dispensing technology on the market.
The recoater comes with four sieve configurations to ensure better material compatibility. This feature plays another important role: the machine can process standard MIM powders.
Other metal 3D powder printers, especially those that use a laser or electron beam, require specially formulated powders to work 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 expanded the technology behind the Innovent + into the production-level X1 25PRO 3D printer. The machine was launched 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 production of industrial metal components with high resolution, tight tolerances and improved surfaces.
Digital Metal: Automation of metal binder jetting
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 launched the DM P2500 3D printer, which is designed for the series production of small, complex parts. The machine spreads 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 accurate and repeatable, allowing very small but incredibly detailed parts to be produced with a resolution of 35 microns.
The subsequent sintering process results in an average surface roughness of Ra 6.0 microns, 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 in 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 takes over the majority of the process steps, e.g. loading the printer with build boxes and removing them for post-processing. The aim is to avoid all manual work in order to enable continuous production in large quantities.
With the introduction of this no-hand production line, Digital Metal has taken a giant leap forward with its Metal Binder Jetting technology.
HP Metal Jet: Making 3D printing a cost-effective production option
After introducing Multi Jet Fusion technology for polymer parts in 2016, HP unveiled the next addition to its additive offering in 2018: the Metal Jetting 3D printing system.
The new metal 3D printer is powered by binder jetting technology. However, the unique advantage HP has associated with this technology lies in the innovative print head and ink technology.
Although binder jetting technology is inherently fast, HP has applied its knowledge of print head 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 rows of nozzles increases the printer's productivity and reliability. In addition, thanks to its expertise in ink technology, HP has developed an innovative binder to make the sintering process faster and more cost-effective.
"Metal injection molding usually requires more than 10% of the part weight to 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, cheaper and easier," says Tim Weber, HP's Global Head of Metals.
Together, these advances result in a metal 3D printer that should achieve economics and efficiencies comparable to conventional production 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 about metal jetting, this technology could be the key to unlocking a sustainable value proposition for metal 3D printing at scale - volume production of additively manufactured parts.
3DEO: Combination of binder jetting and milling
The process behind 3DEO's Intelligent Layering® technology
Many companies are striving to make 3D metal printing competitive with other manufacturing techniques. One such company is 3DEO, which was founded in 2016 with the aim of enabling mass production through metal binder jetting. To achieve this, the company has completely reinvented the process. Instead of using inkjet to selectively deposit the binder, 3DEO machines use a proprietary spraying system to apply the binder evenly over the entire layer.
The result is a hard, thin layer of metal powder, which is then machined with micro end mills. The CNC operation cuts out the part shape for each layer. This technology, known 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.
3DEO's Intelligent Layering technology is currently only offered through the company's production service. By limiting the technology to its own production service, 3DEO ensures a high quality of printed parts while the platform remains very flexible.
3DEO is currently working on some of the largest orders in the metal 3D printing industry and recently received an order for 28,000 parts.
Although the company has no plans to sell its machines, the growing production volume serves to confirm the technical capabilities of Binder Jetting to deliver production parts that are comparable to conventionally manufactured components.
Desktop Metal: Printing metal parts at a remarkable speed
Boston-based start-up Desktop Metal was founded in 2015 with the aim of fulfilling the promise of 3D printing for production. To achieve this, the company has developed an extremely fast production system.
The company calls the technology behind the metal 3D printer Single Pass Jetting (SPJ), a faster version of the typical binder jetting process.
The system is equipped with two full-width printheads and an advanced powder distribution system that effectively distributes powder and binder across the build area in a single rapid 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 equates to over 60 kg of metal parts per hour. This speed is orders of magnitude faster than other metal 3D printers on the market, making it ideal for high volume production of complex metal parts.
In addition, the production system is the first binder system equipped with an industrial inert environment that offers gas recycling and solvent recovery for the safe printing of reactive metals. This opens up the possibility of printing a wider range of metals, such as aluminum.
Desktop Metal's production system has maximized the benefits of metal binder jetting by adding a significant speed improvement.
Desktop Metal has only recently made its production system available for purchase, so it will take some time for its production speed claims to be proven. In this case, the production system will be the fastest binder jetting 3D printer currently available on the market.
Looking into the crystal ball
Metal binder jetting is becoming one of the most important key technologies among metal 3D printing technologies. This is made possible by the technology's unique ability to achieve high printing speeds and produce high-precision components.
Another key development for the success of metal binder jetting is its compatibility with already well-known and relatively cheap MIM powders.
A number of companies have recognized the breakthrough potential of metal binder jetting and are working hard to take advantage of the opportunities it offers. 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.