Above: Binder jetting has the ability to print large parts and is often more cost-effective than other additive manufacturing methods.

December 2018 - It’s funny how you look for one thing and find another. We looked for a new angle on stainless steel and discovered a company that uses binder jetting and metal injection molding technology to build a different kind of additive manufacturing (AM) machine. Their sideline happens to be qualifying metal powders (including stainless steels) for its own printers and for the products customers want to apply to both that material and that technology.

ExOne Corp., formerly Extrude Hone, became the exclusive licensee in 1996 of a three-dimensional printing process developed at the Massachusetts Institute of Technology for metal parts and tooling. The company won research contracts from the Office of Naval Research, the National Science Foundation and the National Institute of Standards and Technology to develop and commercialize the process, materials and equipment for defense and commercial industrial applications.

ExOne machines today can print in such materials as silica sand, ceramics, stainless steel, tool steels, nickel-based alloys and bronze, and the company is in varying stages of qualifying additional industrial materials.

ExOne is leveraging its staff’s experience in developing material that meets standards, specifically the Metal Powder Industries Federation (MPIF) Standard 35.

How it works

ExOne uses binder jetting technology to print complex parts in industrial-grade materials. With binder jetting, a liquid binding agent is selectively deposited to join powder particles. Layers of material are then bonded to form an object. The printhead strategically drops binder into the powder. The “build box” for the part lowers and another layer of powder is then spread and binder is added. Over time, the part develops through the layering of powder and binder.

Metal parts must be cured then are typically sintered, and sometimes infiltrated with another material, depending on the application. Hot isostatic pressing may be employed to achieve full densities in solid metals.

Andrew Klein, director of research and development at ExOne, says the company has grown by more than 20 percent each year since 2010. The timing was fortuitous: “We went public just as metal 3D printing was starting to get a lot of publicity,” he says.

Technological expertise is everything. “We have machine engineering and materials R&D. On machine engineering, much of that team has been with the company since the original printers were developed. They have been through many iterations—developing recoating technology and printheads, building machines that can print uniform, consistent parts throughout the build.”

On the material side, says Klein, “That is where we have PhD material scientists, powder metallurgy experts and various other engineers. A lot of experience is combined there. When you look at our technology, there is a strong corollary between the binder jet process and metal injection molding. With respect to metal injection molding, ExOne is leveraging the staff’s experience in developing material that meets standards,” specifically the Metal Powder Industries Federation (MPIF) Standard 35.

Applications for ExOne-printed materials include oil and gas components, molds, fixtures, tools, pumps, automotive parts, all kinds of prototypes and even Naval submarine castings.

Choosing stainless

ExOne began experimenting with the two most common alloys in the metal injection molding (MIM) world, grades 316L and 17-4PH. “To leverage and help with low volumes or prototyping of parts that people would make with MIM, [these grades] were  obvious materials to start with,” Klein says. “From there, we are expanding into [stainless steel grade] 304L and are working to develop Inconel 718,” a nickel-based superalloy, in addition to M2 and H11 tool steels, which are used for molding applications. Another key material ripe for AM development is tungsten-carbide-cobalt (WC-Co), he says.

“We don’t develop the powders,” he explains. “We buy them from major suppliers and we print and sinter to get them to high density. We sell the printers, but we also have a production service center to sell parts. So if someone wants a part, we deliver them a sintered 17-4PH part.”

To be clear, the primary business line is manufacturing 3D printers. But it has delved into refining material and installing a production center so customers can learn, at ExOne, how to make their products on ExOne printers. Says Klein, “we don’t limit the use of materials or how they are used in our printers.”

Applications

ExOne builds three different AM machines for printing metal parts. The smallest printer has a work envelope of 160mm by 65mm by 65mm (6.29 inches by 2.56 inches by 2.56 inches). “Our largest metal printer is 800mm by 500mm by 400mm (31.5 inches by 19.68 inches by 15.75 inches),” Klein says. “Every day, customers are giving us larger and more complex parts for which we are developing sintering techniques.

“When we discuss applications, one of the big ones is oil and gas, such as wire line guides, and downhole drilling parts, such as bit heads, staters and rotors. In the auto industry, we are seeing the printers used for restoration parts, for prototyping and for aftermarket customized parts.

“Most of our applications, when we print parts, are under a non-disclosure agreement so we cannot share them. However, many of our customers have really interesting designs and think of cool ways to leverage our technologies.”

Designed for the laboratory environment, the Innovent Research & Education 3D Printer is ExOne’s most compact and budget friendly printer, with no sacrifice in quality.

As for competition, Klein says a few other companies manufacture binder jet printers, some of which have come out in the last year or so, “but as far as we know, there is only one other that is currently delivering metal binder jet printers.”

Another common application for ExOne printers are firearms. “A lot of that is making aftermarket components, customized parts.” And then there is general prototyping beyond automotive, “like tooling that has long lead times and is very expensive.”

So it isn’t required to reinvent the wheel, Klein says ExOne typically employs powders that are used in standard powder metallurgy processes. “We are able to leverage the MIM supply chain and get lower cost. Then we develop print parameters, and use typical MIM sintering furnaces and profiles to get our final parts. We are leveraging MIM and PM for powders. Our sweet spot is to develop these together so they print in the most uniform and consistent manner. Then once we get those final part properties, we go to an outside lab and get the material data and place that on our material data sheets and show that we meet or exceed standard 35.”

Transition

Klein says the company is seeing “great potential” for binder jet printing. “Customers are starting to see the value of binder jetting and are printing significant quantities of parts. That is a nice transition from small batches to production quantities. So whether they are buying thousands of our [parts] or more of our machines,” that signifies wider adoption and growth.

The company prints metal parts out of its production service center based in the headquarters in North Huntingdon, Pennsylvania.

“Everything we are printing is a near net shape of the final part. We are printing the files that customers give us,” Klein says.

Customers are also encouraged to come to ExOne production service centers to work with the engineers and “figure out the technology.” Frequently, as the customer builds up enough trust in the process and the viability of the business, “they then buy a machine and print the parts in house. We find that when people get the part and see the resolution and finish, they get excited. You can’t describe it. You see the quality and smoothness and that is what gets them to want to print more.”

Over the last few years, says Klein, ExOne has released three high-density single-alloy materials qualified for its proprietary process. Before that, ExOne was solely printing metal matrix composites. “The matrix [material] sustained us for awhile—it was well adopted and very affordable, but customers were pushing us to qualify the high-density single alloys on our printers. Each time we qualify a new material,” he says, “we are opening up new market segments.”

Klein is excited about the future. “We are constantly coming up with more. We will be able to use the widest range of powders. We continue to develop new binders, so we are revolutionizing the binder jet technology. We are trying to get more material on the market for our printers.” MM