The more you know about available materials, the easier it will be to get the final build results you seek.

By Leslie Langnau, Managing Editor

The key to a thriving 3D printing / additive manufacturing (3DP/AM) industry will be materials. For many users, however, the variety of available materials is insufficient or the selection that is available is not open for use on other brands of AM machines. And users continue to question the high costs of some materials.

The challenges of creating AM materials

The story has been that there are specific challenges in developing the kinds of materials users are looking for. The question naturally arises–what are those challenges?

Some vendors are turning this question around and asking users if they really need the same material they would use in a traditional manufacturing process?

Said Tom Pasterik, manager of business and process development at ExOne, “Engineers have been constrained for decades and they are still getting comfortable with the freedom they now have with AM, including with materials. For example, we printed a part for the oil and gas industry out of 420 stainless steel infiltrated with bronze. This part lasts for 600 hours versus the 200 hours of a part made out of traditionally machined material. The challenge with materials that we see is more about learning to think outside of the box.”

Noted Fred Fisher, Director of Materials and Applications Product Management, Stratasys Ltd., “It’s more about closing the gap of knowledge with the idiosyncrasies between AM and traditional manufacturing, improving the knowledge about the uniqueness of the materials so that engineers can make informed decisions about their designs and when to use AM in their application space.”

Added Steve Hanna, vice president, Global Materials Sales and Marketing, 3D Systems, “There are many materials for AM that an engineer would never consider as part of their ordinary “tool-box.” Would an engineer with a traditional background choose DuraForm® HST? No way. But this is the way forward for even mission-critical parts where weight is a factor but strength remains an issue.”

The other part of the answer is chemistry

Noted Fisher, “Several AM processes alter the properties of materials. This is one of the more exciting discoveries to come out in the last three to five years of development. With fused deposition materials, we are kind of cracking the semi-crystalline side of the thermoplastic family. In some cases, the material is uniquely better than the materials used in traditional manufacturing processes. For example, additively building parts that previously were welded together removes one of the weak points of the object.

“In addition, we can develop material properties that emulate or come closer to meeting injection-molding properties. But this development is definitely more true of the metals side.”

Said Andy Snow, Regional Director of EOS North America, “Laser sintering with metals is achieving some unique results, such as annealing, because of how long a material is sitting in the AM process. Titanium, for example, in laser sintering can result in a part with cycle times and fatigue testing that is superior to something forged.”

The other issue with materials is the need for good documentation about material properties. The process to develop such information is labor intensive and usually done mainly for those materials with volume usage.

“From a metal perspective,” said Snow, “the biggest challenge is developing build parameters that will yield excellent mechanical properties and fully dense parts with accurate geometries.”

“For polymers,” noted Donnie Vanneli, president of Advanced Laser Materials LLC, (a part of EOS North America Inc.), “we never get a fully dense part because we don’t have enough pressure, and so we are always trying to mimic a set of properties engineers desire. We may not use the same material to get to those properties, whereas on the metals side, you more often get like for like. On plastics, it’s more sensitive as to how the material melts and re-solidifies, and so it’s more challenging to find materials that engineers are accustomed to calling out, like Nylon 6 or Nylon 6,6 or polypropylene.”

“We have an application partnership where we try to teach users how to design parts to accommodate the materials advantages,” continued Vanneli, “Like thin walls. In aerospace, engineers are building thin wall ducting. You can’t get the same thinness in injection molding because the plastic won’t flow properly. But we teach how to design for laser sintering to get around some of those design challenges.”

Knowledge is power here; the more you understand about the particular AM equipment and material, the better you can take advantage of both.

But you might ask why aren’t 3DP/AM companies doing more material research into new materials? Mostly, it’s done on a custom basis because the labor and testing involved to develop a material for general market use is extensive, and requires considerable financial resources.

Can 3DP material be reused?

Another popular question from users concerns the amount of material consumed in a build. Can some of this material be re-used for another build, which can help reduce cost per part?

It’s easier to use left over metal material. On the FDM side, technically, some materials can be re-used, but there are issues of predictability and cleanliness. Exposure to temperature in a build alters a plastic’s properties, reducing material predictability. The accidental introduction of impurities will affect the build materials properties as well.

Said Vanneli, “It depends on the polymer. You can go from a 2/1 ratio of needing 2 kg of material for every 1 kg you use to build a part, or a 1.1 kg of material for every 1 kg used to build a part for a loss of about 10%. Research is exploring how to make these materials more reusable, because it can reduce waste. But the research is also exploring how to improve the consistency of reusable material, because polymer materials age inside the powder bed from heat exposure. If a material is under high temperature for a long time, it builds up the molecular weight, so it doesn’t flow as well under a laser. If the aging can be reduced, then the quality of the powder is more consistent from one build to the next, which results in better part quality.”

Added Hanna, “Selective laser sintering (SLS) and Direct Metal Printing (DMP) have about a 65% recycle rate on material. This means that the unused powder gets sifted, any melted items removed, and then it is reinstalled for the next print. Stereolithography has essentially no wasted resin in the process; just a small amount of the support material is lost. But currently parts cannot easily be recycled into fresh build material. In some cases, though, they can be recycled for other purposes.”

Snow said that in metals, material waste from powder metals is about 5 to 10% due to the support structures needed for some part geometry. Any metal powder that remains unsintered can be reused without a problem. Metals can be melted and re-solidified.

One issue about recycling or reusing some of the powder material is the cost involved in reclamation and cleaning. Presently, volumes are not high enough to justify the development of better processes.

Why are materials specific to a machine or brand?

Two short answers here: it depends on the AM process as to whether you can use a “non-genuine” brand as some processes handle it fine, and it depends on how that material will affect machine operation and reliability.

Noted Fisher, manufacturers tailor the system and the material to each other; focusing on mechanical properties, esthetics, dimensional stability, yield, as well as system reliability. Some systems can make use of other materials not specified for use with the systems, but there will be tradeoffs, particularly in reliability and output quality.

AM manufacturers believe that professional users of this equipment want tools that they can depend and rely on. When equipment does not function properly, engineers tend not to use it. To address this issue, they tailor the materials to the equipment to increase operational time and efficiency.

Said Snow, “Metal materials for our process need a certain part size distribution and shape that allows the material to flow evenly across the build platform. But we have several customers that use third party suppliers. And our customers have the freedom to develop their own materials. A rule of thumb with our micro laser welding process is that any material that is ‘weldable’ is a candidate for our laser sintering processes.”

Added Pasterik, “Our machines use spherical powders with specific mesh tolerances and in sizes of 30 and 60 µm. We can change that. We have worked with irregular powders. We just adjust the machines. But our machines can print a range of materials as long as they are in our mesh and/or micron sizes.”

For plastics, Vanneli said, “The issues concern controlling particle size, shape, distribution, molecular weight, melting points, how the material wants to resolidify in the machine, how responsive it is to the laser, what sort of volatility it may have, out-gassing issues, and how the material will change molecularly under high temperatures over a period of time. Each of these factors is hard to control, and each one can mean the material will not run. The third party plastics side is very hard. There’s a limited subset of materials that exhibit the melting and re-crystallization behavior, the proper viscosity to work in the machine in addition to being clean of any volatiles and residual monomers that might react.

“The laser sintering process is very hard on plastics. Most plastics are designed to be injection molded, which is a process that happens in fractions of a second. With laser sintering you are staying at close to the plastic’s melting point for hours, or maybe days. So plastics don’t like this, and it is a stability issue. As long as users are using a material engineered for this process, it will be fine. But other plastics are not geared for this exposure and could show problems.”

While you want to be sure you are using a material geared for your AM process, you can also work with the AM manufacturer to develop a custom material. Most are working with universities and others on materials and are available to work with you to develop something specific to your application needs.

The most common bit of advice on working with 3DP/AM materials from manufacturers is to stop designing a part for the process, as is required with traditional manufacturing processes. Instead, design the part to solve the problem. Vendors and service bureaus are available to ensure the part is built.

Here’s a look at recent material introductions.

3D Systems:

• VisiJet M5-X is a strong, rigid material with hybrid ABS/polypropylene-like properties that comes in a bright white color for high definition applications for the Projet 5000. Printing resolution is comparable to injection molding. Applications include packaging products, such as bottles, household plastics, piping, valves and other parts that need stiffness.

• VisiJet M5 Black is a strong, flexible polypropylene-like material that prints high definition parts with intricate feature details. The material’s flexibility allows for easy snap-fit assemblies while the midnight black color fits electronics, plastic automotive components and chic black appliances.

• For the Projet 4500 3D printer, VisiJet C4 Spectrum materials are suitable for strong semi-rigid parts, which is impressive coming from a layer-by-layer, powder printer process. Plus, these materials are available in Pantone-like color, with a “superior surface finish.” Because of the powder bed printing method, no support material is needed.

 
DSM:

Royal DSM, the global Life Sciences and Materials Sciences company, recently introduced Somos PerFORM. This composite material suits parts that need thermal stability, accuracy and that can be turned around quickly, such as those developed for the aerospace and automotive industries. It allows tooling to be designed with the strength to achieve more parts per mold than traditional stereolithography materials used in the injection molding industry. It is available for 355 nm and 365 nm photopolymer-based machines for 3D printing.

 
EOS:
The most recent product introductions from EOS are Titanium Ti64ELI and StainlessSteel 316L.

Parts built in EOS Titanium Ti64 have a chemical composition and mechanical properties corresponding to ASTM F136. Parts made from it have high-detail resolution. This alloy can be processed on an EOSINT M 280 system and is corrosion resistant. Due to its biocompatibility and high grade of purity it is suitable for the additive manufacturing of medical implants.

EOS StainlessSteel 316L is for the EOSINT M 280 metal laser-sintering system. The material shows good corrosion resistance and high ductility; its chemical composition corresponds to ASTM F138 (“Standard Specification for Wrought 18Cr-14Ni-2.5Mo Stainless Steel Bar and Wire for Surgical Implants UNS S31673”). In medical applications, this alloy is suitable for surgical instruments, endoscopic surgery, orthopedics and implants.

 
ExOne:
ExOne offers several metals and metal alloys, including: 316 Stainless Steel Infiltrated with Bronze, 420 Stainless Steel Infiltrated with Bronze (Annealed & Non-Annealed), Bronze, Iron Infiltrated with Bronze, and Bonded Tungsten.

Additional material systems are in development, and partnership opportunities are available for specific materials. The 3D printing process in metal includes printing, curing, depowdering, sintering, infiltrating, and annealing.

 
Stratasys Ltd:

The Objet500 Connex3 Color Multi-material 3D Printer uses triple-jetting technology that combines droplets of three base materials to produce parts with nearly unlimited combinations of rigid, flexible, and transparent color materials as well as color digital materials—all in a single print run. The three-color materials are VeroCyan, VeroMagenta and VeroYellow, and are combined to produce hundreds of vivid colors.

New rubber-like Tango colors also became available with the introduction of the Objet500, ranging from opaque to transparent colors in various shore values to address markets such as automotive, consumer and sporting goods and fashion.

VeroGlaze (MED620) dental material is for use with the Objet EdenV and OrthoDesk 3D Printers. It is for dental models and delivers precise A2 teeth color shade, producing natural looking dental models with fine details and resolution. These materials combine accurate detail visualization with high dimensional stability, printing ultrafine 16-µm layers.

The most recently introduced material is Endur, a simulated polypropylene material for use with all Objet EdenV, Objet Connex, Objet500 Connex3, and Objet 30Pro 3D Printers. Durable and flexible, Endur offers high impact resistance and elongation at break, resulting in tough parts. The material has a heat-deflection temperature up to 129°F / 54°C (HDT @ 0.45MPa per ASTM D-648-06) with good dimensional stability for its material class. It is suitable for flexible living hinges, moving parts, assembled parts, and snap-fit parts such as those used for lids and packaging case applications. It is available in bright white and shows good surface finish for a smooth look and feel.
3D Systems
www.3Dsystems.com
DSM
www.dsm.com
EOS
www.eos.info
ExOne
www.exone.com
Stratasys Ltd
www.stratasys.com