Additive Manufacturing Materials for Production
Ian Wright posted on May 15, 2018 |
Are open-source materials the key to enabling 3D printing for production applications?
(Image courtesy of TRUMPF.)
(Image courtesy of TRUMPF.)
Just as a craftsman is only as good as his tools, a 3D printer is only as good as its feedstock. We’re all familiar with the hype surrounding additive manufacturing, but there’s a lot standing in the way of moving this technology from rapid prototyping to volume production.

Material constraints are undoubtedly one of the biggest barriers to turning 3D printing into a production process, but we’ve come a long way since the days of proprietary filaments. Metal additive manufacturing has exploded in recent years, and the trend toward an open-platform approach to 3D printing polymers is encouraging major players like DuPont to develop new material options for the additive market.

What are your material options these days when it comes to additive manufacturing?

Read on to find out.

State of the Additive Manufacturing Industry

It almost goes without saying that the growth in the additive manufacturing market over the last decade has been tremendous. Moreover, current projections suggest that the 3D printing market will continue to outpace those of more traditional manufacturing technologies, such as injection molding and CNC machining. The outlook for metal additive manufacturing in particular is even more optimistic, which might explain why companies that have previously focused on polymer-based additive manufacturing have started to invest in metal—such as Stratasys’ spin-out Vulcan Laboratories.

The monumental changes that have taken place the additive manufacturing industry are easiest to appreciate when you consider just how far the industry has come in such a short time. “Compared to 2008, where there was only a handful of 3D printing companies, the whole idea of desktop 3D printing didn’t really exist yet and metal 3D printing was small time—a few companies developing platforms and selling a couple of units a year for research—the whole industry is in a significantly different place than it was ten years ago,” said John Kawola, President of Ultimaker North America.

Gordon Styles, President and founder of Star Rapid, noted the changes in additive materials in particular: "Ten years ago, I would have never imagined that you could print with a material having high strength, chemical resistance and heat deflection," he said. "Until recently, when out of nowhere Markforged, a startup company, began doing just that. Instead of a larger corporation initiating this technology, Markforged first began creating parts with Onyx, and even filament with Kevlar, Carbon fiber and HSHT fiberglass."

As Kawola and Styles illustrate, the contrast between 2008 and 2018 is a stark one for the 3D printing industry. In ten years, we’ve gone from a few companies to hundreds; we’ve seen an explosion of options for desktop 3D printing as well as a sharp decline in price; and we’ve gone from 3D printing with metals and other materials being largely theoretical to additive parts being certified for aerospace applications.

Spools of filament shrink-wrapped to guard against moisture. (Image courtesy of Maurizio Pesce.) 
For comparison, although Motorola’s RAZR V3 was the most popular phone at the time, we already had the first iPhone in 2008, along with Facebook, Twitter and most of the other online mainstays of today. In terms of manufacturing technology, 2008 was the year that the open communication standard MTConnect—which is currently on Version 1.4.0 as of this writing—premiered at IMTS. Other highlights from IMTS 2008 included multi-functional machine tools (e.g., combining grinding and hard turning) and non-metal (i.e., plastic and composite) machining. All of these technologies have progressed over the last decade, but none of them have seen the explosive growth that additive manufacturing has seen, and continues to see today.

Materials in the Additive Industry

According to the Wohlers Report for 2017, the additive manufacturing materials market grew 17 percent in 2016. That’s a slower pace than the polymer-based additive manufacturing market as a whole, which has demonstrated a compound annual growth rate (CAGR) of 29 percent between 2010 and 2017. This diversion isn’t really surprising: the materials market is fairly well established, and it’s much easier to build a new 3D printer than it is to develop a new printable material.

That being said, material diversity is still a problem in additive manufacturing, though not nearly as much of one as it was a decade ago. “If you go back to 2008, basically all the companies on the plastics side were using proprietary materials—3D Systems, Stratasys, I worked for a company at that time called Z Corporation—we all had our own materials,” Kawola explained. “From a vendor point of view, it was beautiful: customers can only buy from you, gross margins are high and there’s no sales cost. But if you stepped back and looked at all of the materials scientists working in the industry at that time, there were maybe dozens, certainly not hundreds.”

Keeping materials proprietary is a good way to maintain a monopoly, but it’s also a disincentive to develop new materials. If your customer has no choice but to buy their materials from you, then it doesn’t matter if your competitor has comparable materials with better properties because the barrier to accessing them—buying yet another 3D printer—is simply too high.

Segmenting the market in this way also discourages material suppliers from innovating. If you’re DuPont, it’s much more cost-effective to develop 3D-printable Nylon materials that can run on many different machines, as opposed to having to create a custom formula for each brand.

Fortunately, the additive manufacturing materials market has opened up considerably in recent years, as Styles explained: "With the exception of Stratasys and 3D Systems, we now see most printer manufacturers open to the development and sourcing of raw materials by their customers and/or third parties. This may be largely due to the rising number of lower cost competitors in the space and the fact that new material development and validation is expensive and can have a very niche application area. This is especially true in the case of metal alloys."

"That’s why the 3D printing industry—including companies like Ultimaker and HP—has embraced an open-platform approach to materials in more recent years," said Kawola. "This has opened the door for the big materials companies of the world—DuPont, Dow, Owens Corning, Mitsubishi, DSM, it goes on and on. I think that’s made a big difference for pushing 3D printing more toward manufacturing, because now you have the best people in the world on polymer materials who are taking a lot of the same materials that are used in injection molding and adapting them for 3D printing.”

That being said, material certification can still be an issue when using additive manufacturing in production. 

"Validation of additive manufacturing materials and proving that they are on par, if not better than traditional methods and sources is a major roadblock for additive manufacturing in production applications," Styles said. "These activities are expensive and take time. In a production environment, you need to prove that you can achieve the same quality and quantity across your multiple suppliers, as well as the spread and number of suppliers across regions needs to increase." 

"High and consistent quality requirements for the raw materials are difficult to achieve across a broad supply base, not to mention differences in the manufacturing techniques employed and raw material sources from the raw material suppliers used are all factors to consider," he added.

The options for additive materials are certainly opening up as major material suppliers get in on the action, but what additive materials are actually available for production applications today?

Types of Additive Materials

Although there’s a host of other additive materials out there—including sand, glass, ceramics and even chocolate—this article will focus on the two material categories that matter most for production applications: polymers (i.e., thermoplastics) and metals.

Metal 3D Printing Materials

The metal additive manufacturing market has been growing at an even faster rate than the additive manufacturing market as a whole, and materials may be a big part of the reason why. Unlike polymer-based 3D printers, which essentially required the development a whole new materials industry, metal 3D printers use wire or (more commonly) metal powders, feedstocks from industries that already existed.

Size comparison of metal powder. (Image courtesy of Renishaw.)
Granted, if you want to produce a metal additive part that’s up to snuff, you should use a powder that’s been specifically designed for additive applications so that—for example—grain size is roughly homogenous. Still, the material continuity between metal coatings and metal 3D printing no doubt helped the latter industry get off and running much faster than it would have otherwise. More importantly, this means that you can make metal additive parts out of the very same material from which they would normally be machined.

Additionally, the additive manufacturing process itself introduces new options for materials that were impossible using more conventional methods. For example, some metal 3D printing methods enable layering of different metals—such as aluminum, tantalum and nickel—together in a single part. On the other hand, the 3D printing process also introduces new potential issues and sources of error, including porosity, residual stress and warpage.

As a general rule, if a metal welds or casts well, then it should also be amenable to additive manufacturing. As noted above, there is already a wide range of metals and alloys that can be 3D printed, either from powder or wire. These include:

  • Aluminum
  • Cobalt
  • Copper
  • Inconel
  • Nickel
  • Precious Metals (Gold, Silver, Platinum)
  • Stainless Steel
  • Tantalum
  • Titanium
  • Tool Steel
  • Tungsten

Let’s look at three of the metals on this list in more detail.

Additive Manufacturing with Titanium

Titanium is one of the most popular materials for 3D printing in production, particularly for aerospace and medical applications. It combines the lightness of aluminum with the strength of steel, in addition to being biocompatible. However, these advantages are offset by titanium’s relatively high cost. For this reason, the potential for waste reduction makes additive manufacturing an attractive option for titanium parts.

Powdered titanium is pyrophoric and reacts explosively with water at temperatures in excess of 700C. For this reason, titanium powder has to be 3D printed in a vacuum or argon gas chamber. It’s also possible to 3D print titanium using electron beam melting (EBM) with a wire feedstock, which eliminates the risk of explosive reaction.

The two most common titanium alloys used in additive manufacturing are 6Al-4V and 6Al-4V ELI.

3D Printing with Aluminum

Aluminum is a lightweight and versatile metal that can be used to 3D print aerospace components as well as parts for auto racing. Though not as strong as steel, aluminum is much lighter and more resistant to corrosion. It’s also more expensive, though not as expensive as titanium.

The biggest advantage aluminum offers for 3D printing is the ability to produce parts with fine detail and thin walls—as thin as 50 microns. Aluminum parts made with additive manufacturing tend to have a textured, matte surface, as opposed to the milled surface that’s typical of machined aluminum parts.

The most common aluminum alloy used for 3D printing is AlSi10Mg.

Additive Manufacturing with Stainless Steel

Compared to aluminum, titanium, and most of the other metals on our list, stainless steel is by far the most affordable option. It can be used to 3D print water-proof parts with high strength and density for use in extreme environments, such as jet engines and rockets. There have also been several  studies indicating the viability of using 316L stainless steel to produce nuclear pressure vessels made via additive manufacturing.

Although 316L is ordinarily non-heat treatable, a report from Renishaw suggests that the AM process yields higher strength alloys compared to wrought material, with some users achieving a tensile strength greater than 600 MPa. Stainless steel parts can be 3D printed using direct metal deposition or binder jetting, and they can also be plated with other metals to change their appearance or surface properties

The most common stainless steels used in additive manufacturing are 17-4PH, 15-5-PH, ASM 316L and 304L.

Thermoplastic 3D Printing Materials

The materials market for thermoplastic- or polymer-based additive manufacturing has had several decades to establish itself, and with the recent trend toward an open-platform approach to 3D printing materials, it’s only going to get more robust. Kawola put it this way:

“OEMs are buying their materials for injection molding by the trainload from the big plastics companies of the world,” he said. “If those companies are also developing filaments or powders for 3D printing, then there’s continuity between using those materials in the prototyping stage to potentially using them on a 3D printer for production, and then using them for traditional manufacturing processes, like injection molding. That whole idea is fairly new, and it’s only been happening in the last few years.”

Maintaining a continuity of materials between 3D printing and injection molding has several advantages. For one, there’s the peace of mind that comes from using the same material throughout your entire manufacturing process, from prototyping to production. There are also more tangible benefits, such as not needing additional material certifications and increasing the rate of adoption.

"If you compare using injection molding to make a part and using a 3D printer to make the same part, the processes are different, but if they’re using essentially the same material, companies have a much better shot at adopting additive technologies for end-use production,” Kawola said.

Styles noted the recent introduction of one popular material in particular: "Just this year we saw the introduction of PEEK, which is a colorless organic thermoplastic polymer, for a variety of manufacturing systems," he said. "PEEK is quite popular in the automotive, medical, aerospace and chemical process industries due to its impact resistance (hardness), strength, durability, melting temperature of over 300 degrees Celsius and FDA approval for contact with food."

The list of 3D-printable polymer materials is even longer than the one for metals, but here are some of the most popular:

  • Acetal
  • Acrylic
  • Acrylonitrile Butadiene Styrene (ABS)
  • Acrylonitrile Styrene Acrylate (ASA)
  • High Impact Polystyrene (HIPS)
  • Nylon
  • Polycarbonate (PC)
  • Polyether Ether Ketone (PEEK)
  • Polyethylene Terephthalate (PET)
  • Polyethylene Trimethylene Terephthalate  (PETT)
  • Polyethylene Yerephthalate Glycol-Modified (PETG)
  • Polylactic Acid (PLA)
  • Polypropylene (PP)
  • Polyvinyl Alcohol (PVA)
  • Thermoplastic Elastomer (TPE)

As with metals, let’s look at three on this list in more detail.

Additive Manufacturing with Acrylonitrile Butadiene Styrene (ABS)

ABS is by far the most popular material in production applications of 3D printing. Although PLA is more popular overall, ABS is almost always a better choice for manufacturing, due to it’s strength, durability and low cost. ABS needs to be heated to a relatively high range of 230-250C to be printable on a 3D printer, and as such, also generally requires a heated print bed to ensure proper cooling and prevent warping.

ABS parts can be additively manufactured using fused deposition modelling (FDM), binder jetting, stereolithography (SLA) or polyjetting. The major drawback to ABS is the fact that it’s toxic, as are the fumes it emits when it reaches its melting point. 3D-printed ABS parts are most often found as casings in end-use products or in rapid tooling applications.

3D Printing with Nylon

Nylon—generically known as polyamide—is a synthetic polymer that offers more strength than ABS at an increased cost. It’s also flexible and demonstrates excellent material memory. Layer adhesion for 3D-printed parts made with nylon is also above average.

Nylon’s moisture sensitivity requires that it be additively manufactured either in a vacuum or at high temperatures, and it should also be stored in air-tight containers. Some nylon parts can be prone to shrinkage, making it less accurate than ABS.

The most popular types of Nylon for additive manufacturing are Taulman 618, Taulman 645 and Bridge Nylon.

Additive Manufacturing with Polycarbonate (PC)

Polycarbonate plastics—also known under the trade name Lexan—are both light and dense, with excellent tensile strength. It’s transparency enables PC to be used in a variety of applications, including sunglasses. Carbon-reinforced PC can be used to create intake manifolds and other parts subject to high temperatures.

PC is soluble in dichloromethane and melts at temperatures of 260-300C, which is quite high for 3D printing. Though it’s naturally transparent, PC can be colored if necessary. Like ABS, it requires a heated print bed to ensure adhesion and reduce the chance of warping.

Materials for 3D Printing

These M781 components were 3D-printed during a six-month collaborative effort that involved RDECOM, ManTech and America Makes, the national accelerator for additive manufacturing and 3D printing. They cost tens of thousands of dollars less than identical components created with standard production methods. (U.S. Army photo by Sunny Burns, ARDEC)
These M781 components were 3D-printed during a six-month collaborative effort that involved RDECOM, ManTech and America Makes, the national accelerator for additive manufacturing and 3D printing. They cost tens of thousands of dollars less than identical components created with standard production methods. (U.S. Army photo by Sunny Burns, ARDEC)
For all the progress that’s been made over the last 30 years, 3D printing is still more niche technology than mainstream in manufacturing. Kawola explained additive manufacturing’s place in the sector as a whole today by considering two extremes on the spectrum of production:

“On the one side you have, for example, 3D printing Legos, which are being made for something like half a cent each,” he said. “You’re never going to beat that with 3D printing, at least in my lifetime. At the other extreme, you have 3D printing in dental markets, where everything’s printed in volumes of one. So, the biggest opportunity for 3D printing in production is coming up from that low end, where you’re printing in volumes of 100 or 1,000.”

When it comes to materials, Styles noted a particular issue that needs to be addressed. "More people need to be aware of the cost of the raw materials and production for additive manufacturing," he said. "Many people don’t realize how expensive additive manufacturing can be. A better understanding of costs can help people make an informed decision about whether to 3D print or opt for traditional technologies such as plastic injection molding or CNC machining."

To learn more about your material options in additive manufacturing, check out our 55-page eBook on 3D printing materials, including photopolymers, metals, carbon fiber and more.

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