New AM Machines, Materials Fill Niches

New AM Machines, Materials Fill Niches
SME Media March 2022
By Irene Wolff
https://www.sme.org/technologies/articles/2022/march/new-am-machines-materials-fill-niches/

Makers of new machines and materials for additive manufacturing are touting their products for the niches they fill—tool making and machine shop production, for example. They’re also talking about sustainability.

In fact, Desktop Metal subsidiary Forust has a new 3D printing process called Forust that essentially glues trees back together. The process uses binder jetting and two wood-industry byproducts, sawdust and lignin. Some of the sawdust left over from making paper, building homes and furniture is recovered. The rest of it is incinerated or landfilled, according to Forust’s website.

“When we saw this we said, ‘We can take this basically free raw material and if we can figure out how to glue it back together into a finished product we can rebuild trees’,” said Jonah Myerberg, CTO, Desktop Metal, Burlington, Mass. “We can take the wood from these processes and glue it together to form pieces of wood that would normally be cut from trees.”

AM with Forust is similar to 3D printing with sand, he said. Not only is it possible to print the sawdust with a natural-looking wood grain, when you drill a hole in a part the grain shows in the void.

It’s the spearhead of a bigger project for us, which is recycling materials,” Myerberg said. “How do we reuse materials instead of using fresh raw materials? That’s a huge mission of ours for the next 20 years.”

Also new from Desktop Metal is a metal binder jetting system engineered for machine shops, the Shop System.

New from other makers are resins to devise your own formulations of ceramics, a new material to use in a company’s ceramics printers, an industrial AM machine maker that’s offering its first desktop model, and a combination printer-CNC that creates its own toolpaths.

Tooling, and Nothing But

Mantle Inc., San Francisco, decided to include automated toolpath creation in its hybrid AM-CNC machine’s software. This was in light of the lack of skilled machinists and the time and money customers invest in creating step-by-step strategies for these machines to do their work.

“We think it’s something that is a really important part of the value that is delivered in our solution,” said Paul DiLaura, Mantle’s chief commercial officer.

Nilesh Dixit, head of software at Mantle, fwormerly led the team that created applications on Internet of Things software Predix at GE Digital.

Mantle’s software for its printer is doing double duty in that it has to create toolpaths not only for the metal-based, flowable paste that’s extruded from the print nozzle; it also has to figure out the right path for the milling that’s done inside the print box as a part is built.

The way it works is that one or more slices of a part are printed in layers of about 100 µm on the build plate, then are heated and dried, which removes almost all the liquid solvent from the paste. The metal particles in the paste subsequently pack together, “and they’re fairly dense at that point,” said DiLaura. “They’re firm enough that they hold the shape of what’s been printed, but it’s soft enough that it can be machined very easily.” At the end of the printing and machining processes, the part is put in a sintering furnace where it shrinks by 8 to10 percent (metal parts printed by other 3D processes can shrink more, by 17 to 25 percent, DiLaura said).

The process, which Mantle calls “TrueShape,” allows the user to cut conformal cooling channels and very deep features, he said.

“The milling is what allows us to achieve the precision that’s necessary for tooling,” which is the $45 billion market niche Mantle hopes to fill with its machine, DiLaura said.

“We have made the decision to focus exclusively, at the beginning, totally on tooling components,” DiLaura said. “These are principally inserts, cavities and cores for molds and dies. I would say the majority of what we work on are injection mold tools, cavities and cores. That’s what the majority of our customers are interested in, but we’ve also done work with die casting, metal forming, stamping—really anything where our tool steel material is going to be relevant.”

The startup also decided to make its machine easy to use by almost anybody in what DiLaura described as a “hands-off” operation.

“We had the owner of a tool maker into our office the other day and he saw this particular part we had printed and he said, ‘It would take me a year to train somebody how to make this,’ and he was kind of blown away by the fact that it doesn’t require really any training with our system,” DiLaura said.

Mantle offers two materials: P2X acts like P20 tool steel, but with improved corrosion and abrasion resistance; and H13, which acts like standard H13 tool steel and can be typically hardened to 50-52 Rockwell C.

New Desktop Joins Industrial, Dental Printers

While Mantle is offering its first machine, industrial and dental printer producer Nexa3D has introduced its first desktop model, XiP (pronounced “zip”).“We’re almost working this problem backward,” said Michael Currie, vice president and general manager of Nexa3D’s desktop business unit. “We have an industrial machine that we know can make lots of production parts … but how do you get to that end state? We have to design a part.”

Because Nexa3D didn’t want to force a new process and different materials on its customers who want to design a part on the desktop, the XiP’s lubricant sublayer photo-curing (LSPc) process is similar to that of the company’s industrial printers. Because of this, design and R&D teams can “keep moving at speed,” Currie said.

Nexa3D’s technology, XiP, falls into the category of vat polymerization, aka stereolithography. Inside the machine, a light source shines from below on a vat of liquid photopolymer resin. The light source is put through a lensing system to form a uniform plane of light that bathes an LCD screen, which acts as a mask for the light in the shape of a particular part layer. After curing the layer, it’s separated—or “peeled”—from the vat’s membrane surface and a new layer is added until the part is complete.

“LSPc is an advanced film technology that allows our parts to free themselves from the vat membrane very easily,” Currie said. “This puts less force on the part.”

The force used to remove film from a part can alter the workpiece, which can lead to subsequent print failure. Having a more advanced membrane technology like Nexa3D’s lets the user print more precisely with higher reliability because parts stay in place, which allows for faster printing, he explained.

“If you can peel away with less force you can return to the next layer that much faster,” Currie said.

Due to Nexa3D’s inverted building process, the amount of resin in a reservoir only has to be as thick as one layer, which could be a boon for conserving the liquid resin.

The process in the XiP’s build envelope happens at room temperature, where layers of 50, 100 or 200 µm are laid down.

In addition to making prototype iterations during the design phase, in an industrial setting the XiP is good for electronics enclosures, jigs, tools and fixtures. Dental offices and labs may like it for making teeth-whitening trays, mouth splints and models for surgical implant planning.

Get Resin, Add Powder, Print

Ceramic materials and 3D printer maker Tethon 3D, Omaha, Neb., received a patent in September 2021 for its Genesis line of resins. The Genesis line is used as a composite matrix to create ceramic products via stereolithographic, CLIP, LCD and DLP additive manufacturing methods.

The liquid matrix material doesn’t 3D print on its own but provides a starting point for photopolymer resin research development. It needs a solid powder added to build up enough thickness to print. Loaded Genesis resin cures at 365–405 µm.

Formulations incorporating alumina, zirconia, silica, silicon carbide and hydroxyapatite with the Genesis matrix are used in the aerospace, automotive, metal casting, dental, electronics and biomedical industries.

The Genesis matrix can be burned out of a finished part in a furnace with little or no binder leftover. The resins are available in standard, flexible and high-load formulations.

Tethon also sells a variety of powders that can be mixed with its resins—amounts can be adjusted to vary concentration. Another line of powders from Tethon are for use in binder jetting. The company’s material scientists can also formulate custom materials for either application.

“We found that people like to use their traditional powders,” said Tethon CEO Trent Allen.

The Genesis and other Tethon 3D resins are generally used at research institutions and corporate R&D labs, he said.

No CNC Needed for Ceramics

In August, XJet Ltd., Rehovot, Israel, made alumina available for its ceramic 3D printers. It also offers zirconia for ceramic printing and stainless steel for its metal 3D printers.

The company chose alumina (aluminum oxide) for its third material because it’s a widely used technical ceramic due to its extremely high mechanical strength, high hardness and very good electrical insulation properties. Alumina also has high wear resistance, high thermal conductivity and resistance to high temperatures. Both alumina and zirconia are technical ceramics with very good resistance to chemicals, making them non-corrosive. Their hardness means these materials are difficult to machine using traditional methods, especially after they’ve been sintered.

“Alumina parts that are manufactured on XJet systems with XJet technology are virtually identical to alumina parts that would have been created with ceramic injection molding, for example, and thus can be machined the same way,” said Dror Danai, chief business officer at XJet. “However, there is no real need to machine such a part—the part can be designed to the end requirement. With XJet systems it is all about the details, which means that you can accurately manufacture complex geometries, fine details, intrinsic structures, smooth surfaces, inner channels etc., so once the part has been printed and sintered it is ready, and there is simply no need to further machine it.”

Alumina is ideal for electrical insulators, nozzles and valves, machining and cutting tools, impellers and more. It’s used in the medical devices, consumer electronics and aerospace industries.

“We are manufacturing some parts of our own additive manufacturing system—the XJet Carmel 1400C,” said Danai. “One of these parts is a guide/housing for electrical wiring, and the alumina provides the electrical insulation necessary for that part.”

CNCs and This Printer are Besties

Desktop Metal has made a 3D printing system called the Shop System that’s engineered for machine shops doing mid-scale production.

“When we talk about mid-scale production it’s really the next step above prototyping,” said CTO Myerberg. “And it means essentially making a production run of parts of any size or scale.”

The company’s website promotes the “affordable material costs” of Desktop Metal’s proprietary metal powders used in the Shop System and its other binder jetting printers.

Laser-based processes require two important things to be true about the powder they use, Myerberg explained.

First, the powder has to be uniform: the metal in the powder has to be spherical and the spheres have to be identical in size. That’s necessary for the printer to properly and consistently use its laser energy to melt the powder to the same depth every time while forming a part.

However, producing the powder creates spheres of different sizes in a randomized fashion. On a graph, mapping the sizes would create a bell curve. The powder needed for laser printing needs to be a very specific size, so powder producers take only a very narrow portion of the powder batch and the rest of the material is used for something else.

“So that prime cut, just like you get a prime cut of beef, is very expensive,” Myerberg said.

Second is its chemistry. When the laser melts the powder to make a part it has to be so clean it doesn’t trap any chemical that would be unwanted in the final part.

“The particles need to be the same size within a narrow distribution and they need to be perfectly clean, which makes them very expensive to produce,” said Myerberg.

Binder jetting is different. It takes particles of any size. In fact, the varied sizes of the metal particles enhance the process because they can be packed more tightly together than identically sized spheres. Also, it doesn’t matter what type of surface contaminants might be on the powder because the printed part is going into a furnace for sintering and the high temperature allows them to be burned off completely. The sintering process also eliminates any porosity in the metal.

The CTO also explained the process for fine-tuning Desktop Metal’s machines.

“We give the user all types of controls to tune in their process … because everyone’s part is different,” he said.

For example, the user can tune out part bleeding. As the spherical droplet of binder penetrates into the surface of the powder bed it spreads out and can bleed out on the edges. For parts with very fine features, one edge can bleed into a neighboring edge, which is an undesirable result. If that happens, the user can create a little more space around the edges. In thick sections, he can decrease the amount of binder glue that’s sprayed down.

“This process must be geometrically agnostic,” Myerberg said. “Anyone should be able to put in any image or any part into the printer and get it out. We can’t test every part that anyone wants, we can just give guidelines and rules and knobs to turn. So we say, ‘Hey, if you want really fine features we can give you bleed control so those features don’t bleed into each other [but are] kept separate.’ And bleed control is just one of many knobs we give users to turn.”

A separate depowdering station from Desktop Metal is for excavating parts from the powder reservoir and keeping the metal material clean. Once the binder jetted parts are excavated, they can be treated like any other metal part.

“After you sinter the part, if you cross-section it and look at the grain structure you’ll never even know it was a powder part to start with,” Myerberg said. “It looks just like a cast part. The metals and the grain structures and the chemistry that we are producing with binder jetting are just like any other metal of that chemistry. They can be heat treated and their properties can be changed just like traditionally produced parts.

“You can do polishing, machining, sand or bead blasting and finishing on binder jetted parts. These are all great post-processing methods that have been developed over the past hundred years and they’re all applicable to binder jetted parts. This is the beauty of putting a binder jetting process inside a machine shop right next to cutting tools. Binder jetting does not produce the accuracy or the surface finish you can get out of a CNC machine. Flat surfaces, cylindrical bores and threads need to be cut to get the precision needed.”