What’s New and What’s Possible in Additive Manufacturing for Plastics, Metal and More

By Liz Stevens, writer, Plastics Business

3D printing has come a long way from its origins in the 1980s when researchers, inventors and entrepreneurs in labs and garages imagined ground-breaking methods and built the first machines. At first a novelty and then embraced primarily by hobbyists, additive manufacturing has matured and become a workhorse in a growing variety of industries.

As noted in his SME.org article, “It’s Time to Revisit Additive Manufacturing,”1 Christopher Williams, PhD, L.S. Randolph Professor in the Department of Mechanical Engineering at Virginia Polytechnic Institute and State University, recalled a dramatic resurgence of interest in the discipline about 10 years ago when desktop-scale 3D printing emerged and additive manufacturing with metals began to gain traction. “The newfound excitement for a 30-year-old technology created a spark that attracted a tremendous diversity of technical expertise to the field that we had not seen prior,” Williams wrote. “Originally born from the minds of mechanical and industrial engineers primarily focusing on how best to physically create 3D-CAD models, AM conferences became suddenly filled with metallurgists and polymer scientists eager to explore fundamental process-structure-property relationships, computer and data scientists willing to donate their expertise to provide a pathway toward in-situ process monitoring, and experts in multiphysics and multiscale simulation looking to enable prediction of a part’s response to changing process parameters.”

That mindset of innovation and invention continues today in research institutes and in corporate laboratories. At the industrial level, additive manufacturing now reliably, repeatedly delivers prototypes, one-off items, custom and customizable products, just-in-time replacement components, and low- to medium-run production loads. 3D is suitable for creating metal mold inserts and for producing an ever-growing field of plastic parts and products. Rubber production via 3D printing is an emerging discipline, and one to watch. In Germany, for example, innovatiQ GmbH & Co builds extrusion printers for liquid additive manufacturing (LAM) that use liquid silicone rubber. And Adaptive 3D, a Plano, Texas company, has created a family of photopolymer resins for use with DLP (vat polymerization) printers that are strain-tolerant, flexible and tough.

This article features a broad overview of the state of additive manufacturing materials and 3D printers in the 2020s. Granular input has been included from two printer/material/software companies – Carbon and Mantle – which offer vat polymerization and extrusion hardware, respectively, for plastics, metal and elastomeric materials.

Machines and Materials

Speed, quality and quantity of today’s additive manufacturing printers have increased dramatically across the board. “Some AM processes have seen a hundred-fold increase in printing speed,” wrote Williams. “We now talk about print sizes in terms of feet and meters thanks to new large-scale metal, polymer and concrete printing technologies. Dedicated latticing, topology optimization and generative ‘design for AM’ software has enabled the realization of higher-performance, lighter-weight and cheaper parts.”

“Over the past decade,” he continued, “we have witnessed a dramatic increase in the catalog of materials that are able to be processed by AM. Better understanding of the processes have not only led to the translation of established materials as AM feedstocks, but also to wholly new alloys and polymers…”

The materials that can be used for 3D printing now range from the commonplace (plastics, metal and elastomers) to the newly common (ceramics or concrete) to the exotic (chocolate and biogel). Three types are especially relevant for the plastic, rubber and mold-making sectors: plastics, metals and elastomeric materials.

Carbon, Inc., Redwood City, California, is an industry pacesetter that offers a comprehensive suite of hardware, software, materials and training. Founded in 2013, Carbon’s Digital Light Synthesis™ (DLS) technology is the basis for its vat polymerization printers. Carbon’s proprietary materials include rigid, semi-rigid and elastomer resins and also offers third-party materials. Jason Rolland, SVP of Materials at Carbon, offered additional input for this article.

Mantle, San Francisco, California, has just exited development-oriented mode and now is poised to become a partner to the manufacturing industry, with hardware, software and materials designed for producing a variety of metal inserts for tools and dies. Founded in 2015, Mantle offers an extrusion printer with built-in 3-axis part finishing technology, a sintering furnace and metal materials that include P20 and H13 tool steels. Mantle’s chief commercial officer, Paul DiLaura, offered additional input for this article.

The Plastics

In “A review on polymeric materials in additive manufacturing,”2 authors J.M. Jafferson and Debdutta Chatterjee report on an extensive review of the polymers used in 3D printing. They characterize these polymers as thermoplastics, elastomers, thermosets, bio-polymers, polymers with integrated fillers, and polymers blended with biological materials. The authors further categorize the polymers used in additive manufacturing by dividing them into two large groups – amorphous and semi-crystalline – and by describing the relative “grade” of the polymers as general purpose, engineering grade or ultra performance. Their categorization looks like this:

Jason Rolland explained that Carbon’s materials are dual-cure resins; first cured with UV light and then thermally cured. “The reactive components are kept separated and blended just prior to going into the printer,” Rolland said. “Now we have something that has both UV-curable chemistry and thermally-curable chemistry. During printing, the UV-curable chemistry in the built part is activated to define the shape of the part; this forms an initial UV network or matrix that entraps the thermally-cured chemistry in the part.” After cleaning to remove residual resin, the part goes into an oven for a baking step. “During that baking step,” he said, “we activate the thermally-curable chemistry. The dual curing facilitates superior characteristics and unique properties.”

Carbon describes its plastics offerings as “materials [that] uniquely combine excellent mechanical characteristics, high resolution and exceptional surface quality into isotropic parts ready for real-world products.” Carbon’s plastics materials include rigid polyurethane (RPU), epoxy (EPX), medical polyurethane (MPU), cyanate esters (CE), flexible polyurethane (FPU), urethane methacrylate (UMA) and dental production plastic (DPR).

One of Carbon’s most recent rigid material introductions is EPX 86FR, a dual-cure material that is epoxy-based. “The highlight of this material is flame retardancy,” said Rolland, “which is a requirement in some industries and especially for items like electrical housings, automotive components and aerospace components.” Rolland explained that UL 94 V-0 is the highest rating in flame retardancy, meaning that the material is self-extinguishing. It can be burned with a blowtorch but as soon as the blowtorch is removed, the material completely extinguishes. “EPX 86FR has a UL 94 V-0 rating for flame resistance,” said Rolland, “but also has very high mechanical performance and thermal properties. It has high impact strength and high stiffness; it’s just a terrific all-around material.”

The Metals

According to the Printed Electronics World article, “Metal 3D Printing Technology Landscape – The Trends and the Whitespace,”3 additive manufacturing with metal now can be accomplished for a component as small as a fingertip or as large as a double-decker bus in materials ranging from stainless steels, aluminum and nickel to cobalt-chrome and titanium alloys, as well as precious metals like platinum, silver and gold.

A comprehensive report by IDTechEx, cited in the aforementioned Printed Electronics World article, explains that the metal 3D specialty includes 14 separate 3D printing technologies and includes material forms such as powder, wire, paste, filament, pellets and resin. Some of these materials are very expensive, but many emerging technologies utilize less expensive metal feedstocks such as paste, pellets and wire.

Paul DiLaura explained the background on Mantle’s own metal materials. “Metal paste is a foundational element of our technology,” said DiLaura. “One of the company’s co-founders, Steve Connor, is a chemist by background with experience in making metals in a paste format. Then he turned his attention to the question of whether it was possible to 3D print a metal paste,” DiLaura said, “and that led to the creation of the initial aspects of our technology, which is 3D printing metal paste.” Connor then teamed up with Mantle co-founder and CEO Ted Sorom, who has a background in tooling and product development. “Sorom thought this technology could be really applicable for tooling,” said DiLaura, “but that it would require a tool steel. The focus then switched to developing tool steel materials.”

Mantle’s Flowable Metal Paste materials include H13 tool steel and P2X, a material that behaves like P20 tool steel. One of the things that sets Mantle’s materials apart is the company’s mix of different particle shapes and sizes within the paste. “By using particles of different shapes and sizes,” DiLaura explained, “we are able to pack the particles together more densely. That is important because with particles that are packed closely together, when components are put in the sintering furnace for the final operation, they don’t shrink very much.” While other processes that rely on sintering may have shrink rates of 17%, 20% or 25%, Mantle’s shrink rate is 8% to 9%. This low shrink rate allows Mantle’s technology to produce parts that are more accurate and precise.

In the case of Mantle’s combination of metal paste materials and a dual-function machine that does additive printing as well as subtractive machining, users can print a component, dry it in the printer to a semi-hard state and then machine it to refine the shape, accuracy and finish, before finalizing and hardening the component in a sintering oven. “There are other additive manufacturing technologies that have dual-function machines,” said DiLaura, “but we are the only ones that machine the material when it is in a relatively soft state, which allows us to machine more quickly without introducing stresses into the part.”

The Elastomers

Until recently, additive manufacturing using rubber and rubber-like material lagged behind plastics and metals. In their article “Basic Research for Additive Manufacturing of Rubber”4 – an article focused on additive extrusion processing with elastomers – the authors offer a short, informative explanation for the lag. “Although there are numerous additive processes as well as usable materials [for 3D printing in general], there is still no technical solution for the additive manufacturing of elastomers made of vulcanizable rubber.” The complex material composition of vulcanizable rubbers accounts for the challenges in using elastomers in most additive manufacturing processes, but Carbon has developed a successful elastomer technology. In other areas, progress has been made using TPE (thermoplastic elastomer) materials with fused deposition modeling (FDM), and a new technique called “drop on demand” is being explored.

Elastomers were Carbon’s original calling card in additive manufacturing. “We saw a huge business opportunity in the market for 3D printed elastomers,” Rolland said, “and, with our dual-cure process, we are able to make high-performance polyurethane elastomers, which are especially useful in the footwear industry. That helped us land our partnership with adidas (the Herzogenaurach, Bavaria, Germany multinational corporation that designs and manufactures shoes, clothing and accessories), after which we developed a category of elastomers that are useful for a variety of applications.”

This category of materials includes elastomeric polyurethane and silicone urethane. The company’s newest elastomer material, EPU 44, is a 40% bio-based resin. “Our first-generation material was EPU 41, which allowed us to get into the market space and make footwear that held up very well,” said Rolland. “But we wanted to see how we could further improve it.” Carbon used its elastomer chemistry expertise to create EPU 44, a material with greater stiffness and improved green strength that enabled adidas to design running shoe midsoles with lattices that lighten the weight of the shoe and deliver advanced performance functionality. “At the same time,” said Rolland, “we were looking at areas where we could improve the sustainability of our materials.”

For increased sustainability, Carbon turned to a new polyurethane building block, Susterra®, which is derived from corn sugar. “With plant-based raw materials, you are using CO2 and sunlight to grow a plant, the plant makes sugar, and you can derive building blocks from the sugar.” EPU 44 therefore has a lower carbon footprint for its base materials and, in addition, has a lower viscosity than some of the alternate materials that Carbon had been using. As Rolland points out, “In vat-based 3D printing, viscosity translates directly into faster print time, and that translates directly into lower cost.”

Mantle – TrueShape™ Technology and Flowable Metal Paste

DiLaura explained the unique nature of Mantle’s extrusion printing approach to additive manufacturing. “Since we had differentiated technology with our tool steel metal paste, we felt that we could add value in the toolmaking sector,” said DiLaura. “A challenge was that the requirements for accuracy and surface finish are extreme; making an injection mold component requires a very high degree of precision.”

Mantle’s technology is geared toward creating metal inserts for molds. “We are focused on the detailed area where the plastic meets the metal, often called the inserts or the cavities and cores,” DiLaura said. “There are other components in a mold that can be made very well conventionally, with a CNC machine. We are not trying to compete with that. We are providing a better way to make the complex parts that require a lot of machining operations, a lot of EDM operations. We can make those components more efficiently.”

Achieving high dimensional accuracy and surface finish quality called for Mantle to create a hybrid system. “We knew that extruding the paste alone would not be sufficient for accuracy and surface finish,” DiLaura explained, “and so we incorporated 3-axis traditional machining. By combining the additive aspect of depositing the paste with the subtractive aspect of machining, our technology can create parts that are very precise in terms of accuracy, surface finish and the fine features.”

The build volume of Mantle’s printer is 8″ x 8″ x 6″. “We currently can print multiple parts that fit within this build volume,” said DiLaura. “The largest single part we have qualified is 6″ x 6″ x 4″. We will continue to develop our capabilities to print larger parts, but the maximum part size for this generation of printer will be 8″ x 8″ x 6″.” Mantle’s sintering furnace can accommodate two build plates at a time. With an eye toward the future, Mantle is in development on its next Flowable Metal Paste material, a stainless steel.

Carbon – Digital Light Synthesis (DLS™) Process, Design Engine
and a Line of 3D Printers

Carbon offers a line of DLP 3D printers – the M1, M2, M3, M3 Max and L1 – all of which use the company’s Digital Light Synthesis™ printing process and Continuous Liquid Interface Production™. The printers offer a variety of build volumes, resolutions and print speeds. Carbon’s hardware and software is available on a subscription basis.

Carbon’s Design Engine, a software system used for creating lattice designs for use in both plastics and elastomer parts, is available with a subscription and also has launched in 2022 as a standalone software package. “With Design Engine,” explained Rolland, “one inputs a CAD file of a solid part and adds specs on the required mechanical properties. The engine uses a series of algorithms to generate a lattice that meets the requirements.” Lattice structures are useful for elastomer part design and for polymeric parts, providing avenues for creating lightweight but very strong structures, and for introducing specialized material performance capabilities.

The Takeaway

Christopher Williams summed up the state of 3D printing in his previously noted SME.org article. “The processes, materials and industrial applications of AM have seen a massive evolution over the past decade,” he wrote. “All these advances are thanks to the influx of interdisciplinary expertise.” Williams expressed faith, though, that a new generation of experts, who grew up surrounded by technologies like 3D printing, will lead the world in another round of growth and advancement in materials, processes, hardware and software for additive manufacturing. And perhaps, with increased adaptation in manufacturing facilities and the ingenuity of engineers and operations personnel, another evolution is coming in the plastics, rubber and mold building industries.

References

  1. Williams, Christopher. “It’s Time to Revisit Additive Manufacturing,” SME.org, April 6, 2022. https://www.sme.org/technologies/articles/2022/april/its-time-to-revisit-additive-manufacturing/
  2. Jafferson, J.M., Chatterjee, Debdutta. “A review on polymeric materials in additive manufacturing,” Materials Today: Proceedings, March 2021. DOI: 10.1016/j.matpr.2021.02.485.
  3. Dadhania, Sona. “Metal 3D Printing Technology Landscape – The Trends and the Whitespace,” Printed Electronics World, June 2, 2022. https://www.printedelectronicsworld.com/articles/26806/metal-3d-printing-technology-landscape-the-trends-and-the-whitespace
  4. Drossel, Welf-Guntram, Ihlemann, Jörn, Landgraf, Ralf, Oelsch, Erik and Schmidt, Marek. “Basic Research for Additive Manufacturing of Rubber,” Polymers 2020, 12, 2266. DOI: 10.3390/polym12102266.
  5. “3D Printing Technology Guide: The Types of 3D Printing Technology in 2022,” All3DP.com. https://all3dp.com/1/types-of-3d-printers-3d-printing-technology/

For more information on Carbon’s technology and materials, visit www.carbon3d.com. For more information on Mantle’s technology and materials, visit www.mantle3d.com.


The Seven Major 3D Printing Types

Following is a breakdown chart of today’s seven major additive manufacturing printing processes, as characterized in the comprehensive and informative All3D.com article, “3D Printing Technology Guide: The Types of 3D Printing Technology in 2022”.5 Almost all of these methods support multiple technologies. Vat polymerization printing, for example, can be used with stereolithography, digital light processing, masked stereolithography and other technologies. The direct energy deposition process, for another example, can accommodate electron beam additive manufacturing, laser engineered net shaping, cold spray and other technologies.