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Digital Ebook A Design World Resource
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3D printing• 3D-PRINTED REACTOR SPEEDS
CHEMICAL ANALYSIS ......................................................P2 Activated Research Company chose Proto Labs’ metal 3D printing process to produce functional parts for its award-winning reactor
• CONNECTING TO AN ANCIENT CIVILIZATION ............P6 The Metropolitan Museum of Art used 3D printing to create exhibition models
• 3D PRINTING TECHNOLOGIES FOR PROTOTYPING AND PRODUCTION ...............................P8 How to Leverage Additive Manufacturing to Build Better Products
• SELECTING THE RIGHT MATERIAL FOR 3D PRINTING .........................................P15
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3D-Printed Reactor Speeds Chemical AnalysisActivated Research Company chose Proto Labs’ metal 3D printing process to produce functional parts for its award-winning reactor
Fans of “CSI” know the drill: evidence goes into the crime lab’s gas chromatograph, the high-tech machine rapidly identifies whatever is in it and a dramatic arrest ensues — after a commercial break.
The gas chromatograph can indeed identify what may be hundreds of different molecules in a given sample. But what the TV show fails to explain, is that determining the amount of each compound with a gas chromatograph (GC), which separates molecules in a sample, and an accompanying flame ionization detector (FID), which detects those molecules, is both time-consuming and expensive.
Detectives may not need that detail. But knowing how much of a particular molecule is in a sample is critically important to analyzing potential new biofuels as well as pharmaceuticals, foods, fragrances, chemicals, and petroleum-based fuels and pesticides, according to Andrew Jones, partner and co-founder of Activated Research Company, a catalyst start-up in Eden Prairie, Minn.
“This is new technology that is revolutionizing and disrupting the way people think about analyzing samples. Unfortunately we don’t have quite the magic box that they portray on TV,” Jones says of the GC-FID technology. “It’s not that easy.”
Instead, what Activated Research Company offers is a small, stainless steel block — the Polyarc™ catalytic microreactor. The Polyarc™ reactor, integrated into a GC-FID system, quickly quantifies carboncontaining chemicals in a sample. Better yet, the Polyarc™ reactor does so, Jones says, without the slow, costly calibrations otherwise required to count molecules with GC-FID systems, widely used but largely unchanged for the past several decades.
“This device helps scientists do those analyses quicker, easier and cheaper than they could before,”
Jones says of the Polyarc™ reactor. “This is new technology that is revolutionizing and disrupting the way people think.”
The Polyarc™ reactor hit the market in early October 2015, some 15 months after Jones and former Proto Labs CEO Brad Cleveland founded Activated Research Company. As
This is new technology that is revolutionizing and disrupting
the way people think.
The complex Polyarc™ microreactor was 3D printed in stainless steel with direct
metal laser sintering technology.
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prototyping advanced, Cleveland’s familiarity with Proto Labs’ direct metal laser sintering (DMLS) process proved invaluable, Jones says, in turning an academic concept into a commercial, patent-pending product.
Prototyping a ConceptThe idea for what would become the Polyarc™ reactor originated with researchers at the Catalysis Center for Energy Innovation led by Paul Dauenhauer, a professor of chemical engineering and materials science at the University of Minnesota. Dauenhauer’s group published a paper proposing a “quantitative carbon detector” based on their research, which received funding from the U.S. Department of Energy’s Office of Basic Energy Sciences.
Dauenhauer and some of his students built a version of the detector using machined parts and off-the-shelf tubes and fittings. Activated Research Company began its prototyping with similar materials and had mixed results.
“Those were bulky, they were large and they didn’t lead to a finished product,” Jones says. “Not only was it not visually appealing, it had undesirable performance characteristics due to the machining process.”
For a commercial reactor, Jones envisioned a prototype that was both smaller and offered greater temperature control, ideas he discussed
with Cleveland. Jones and Cleveland had met through a mentorship program while Jones was earning his degree in chemical engineering and chemistry at the University of Minnesota. They stayed in touch as Jones completed a doctorate degree in chemical engineering at the University of California-Berkeley. The two teamed to launch Activated Research Company in 2014, with Jones leading technology development and Cleveland overseeing business strategy.
The design of the smaller reactor — a 2-inch by 1-inch block with a heater, a temperature measuring device, multiple channels and
3D-Printed Reactor Speeds Chemical Analysis continued:
An Inside Look at Industrial 3D PrintingOur industrial-grade 3D
printing service uses additive manufacturing
technologies to create parts ranging from highly complex
prototypes to functional, end-use parts. Both plastic
and metal materials are available through three
distinct 3D printing processes: stereolithography (SL), selective laser sintering (SLS) and direct metal laser
sintering (DMLS).
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separate reaction chambers — created challenges in prototyping with machined parts.
“Our application requires tiny channels and the ability to connect those channels in different geometries,” Jones explains. “Small channels are difficult but then being able to have small channels that turn and move around and connect in different geometries, I don’t know any way to do that with traditional machining.”
Cleveland suggested using Proto Labs’ DMLS service, an industrial metal 3D printing process that Jones knew little about, to make prototype parts for the Polyarc™ microreactor. Jones’ experience using an in-house desktop 3D printer to produce the intricate geometries that the interior channels of the reactor would require persuaded him to give DMLS a try.
3D-Printed Reactor Speeds Chemical Analysis continued:
DMLS Replaces MachiningThe early results from DMLS prototyping convinced Jones to choose that process over machined parts for the Polyarc™ reactor.
“The reason we chose 3D printing as opposed to machining is that we could never get the attention to detail, the small geometries of the internal channels in there with traditional machining techniques,” Jones says. “We really had to go to 3D printing to get those small geometries and those connectivities to make it such a small package and allow us to do the chemistry that we want to do. 3D printing also allowed us to control the flow dynamics so that we’re having the right sort of mixing that we need.”
Activated Research Company went through more than 20 DMLS iterations of the Polyarc™ reactor to arrive at its final design. One potential concern dispelled along the way, Jones says, was that Polyarc™ reactor parts made with the DMLS process would have greater potential to leak than forged metal parts.
“I was a little worried that the 3D printing might lead to porosity that could let gases leak out,” Jones says. “We are thoroughly testing each part ... to make sure this new technology of 3D printing will work for a high-temperature, gastight application. Because there’s no precedent for this that I know about for chemical reactors.”
The laser sintered parts from Proto Labs typically arrived in less than a week and “not for a huge, exorbitant cost,” Jones says. Proto Labs’ DMLS parts do cost more than machined ones but the turnaround on getting those made typically is longer.
“We’re obviously using it and that’s testament enough that it works,” Jones says of the DMLS process. “We’ve been happy with the performance.”
In addition to accommodating the reactor’s internal geometries, the DMLS process enabled Activated Research Company to customize its exterior.
“Because you’re printing, you can print any external design that you want,” Jones says.
“So we have ‘patents pending’ on here, we have our logo, the name of the product, something that you’d normally have to stamp on. It just prints it right on.”
Scaling Up To ProductionActivated Research Company’s use of DMLS parts has gone beyond prototyping to full production of end-use parts for the Polyarc™ reactor. The company is choosing the performance of DMLS over the economies of scale machining could offer, Jones
We’re obviously using it and that’s testament enough that it works.
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explains: “We are able to justify that because we are making a high-value product.”Proto Labs’ online parts quoting system has been useful in prototyping and production, especially its reorder feature, Jones says.
“I used the quoting system when I was
rapidly prototyping and making changes, and that was quick and able to keep up with our demand for parts,” Jones explains. “Then when I needed to go into production, I could just repeat the latest prototype and go right into production with it. We’re happy with the ability to do one-off parts when we need them but also to scale up.”
Jones is considering new reactor designs that would use laser sintering to produce parts in metals such as titanium and aluminum or alloys, at what he says would be little additional cost. Activated Research Company is working on new products as well and using Proto Labs for some prototyping for those.
“We move fast and so does Proto Labs,” Jones says. “It’s a good match.”
The Polyarc™ reactor appears to be a match for what some potential clients are looking for as well. In October, the Polyarc™ reactor won the new product showcase at the Gulf Coast Conference, which spotlights chemical analysis technology in the petrochemical, refining and environmental fields. It took the conference’s 2015 Best New Product Award honors, recognized alongside new analytical instruments from industry giants such as Thermo Fisher Scientific and Agilent Technologies.
“People are very interested and we are very excited about all the demand that is coming,” Jones says, with Activated Research Company seeing the petroleum industry as a big potential market for the Polyarc™ reactor.
3D-Printed Reactor Speeds Chemical Analysis continued:
A 3D CAD model of the Polyarc™ reactor illustrates some of the challenging text and through holes that DMLS builds with ease.
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Connecting to an Ancient CivilizationThe Metropolitan Museum of Art used 3D printing to create exhibition models
For the Metropolitan Museum of Art’s exhibition, “Ancient Egypt Transformed: The Middle Kingdom,” on view at the New York museum through Jan. 24, 2016, exhibit planners decided to reconstruct the pyramid complex of King Senwosret III in both a virtual and physical model.
The physical 1:150-scaled model of the site is based on a 3D virtual model that was produced first, and modeled after 3D-printed prototype parts that were created by Proto Labs. For perspective, the main pyramid of the original complex was more than 206-ft. high. In the scaled model, it is 1.5 feet.
This scale model of the pyramid site is displayed in the exhibition’s galleries alongside the show’s 230 objects. These works of art range in size from monumental stone sculptures to delicate jewelry, assembled from more than 30 international collections, with about a third from the Met itself.
The model is intended to help bring this important Middle Kingdom era to life for visitors to the exhibition, says Ronald Street, the museum’s senior manager of 3D imaging, molding and prototypes, who has been with the Met for more than three decades.
The result of the physical model? “Remarkable,” Street says in a recent museum blog post. “The overall image of the finished model in its two forms — virtual and physical — can be considered a true-to-life reconstruction of the builders’ original vision,” as it was in ancient Egypt, around 1870 B.C.
A Creative ChallengeSo, how did Street and his museum colleagues get to that “remarkable” result?
More than 20 years ago, the Metropolitan Museum began excavating and studying the site of King Senwosret III in Egypt, located in what is now modern Dahshur, the site of several pyramids, about 25 miles south of Cairo.
It should be noted that other excavations and archaeological studies by the museum’s archaeologists have occurred for decades at other Egyptian sites. The Met’s Department of Egyptian Art began in 1906.
In 2014, the museum began planning and developing the concept for an exhibition based on the archaeological evidence from the King Senwosret site, and the idea for the models emerged.
The scale model of the pyramid site is displayed in the Metropolitan Museum
of Art's galleries as a part of the exhibition “Ancient Egypt Transformed:
The Middle Kingdom.”
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Connecting to an Ancient Civilization continued:
A 3D CAD model was the first step. Computer modeling was developed and refined over the course of a year, according to Street, resulting in the creation of a NURBS-based wire-frame virtual model of the archaeological site in a 1:1 scale. This 3D virtual model provides the opportunity for visualizing the entire, full-scale pyramid complex as it was nearly 4,000 years ago.
A Traditional (and Digital) SolutionTranslating the CAD model into a physical, 1:150-scaled model was the next step.
This stage would eventually be accomplished through the use of traditional sculpting, modelmaking, mold-making, casting, carpentry and faux painting. But, before those traditional methods were deployed, and concurrently with those traditional techniques, Street also used more modern and digital methods of fabrication, specifically 3D printing. This additive manufacturing process served as Street’s prototyping phase that helped replicate the unique parts of the model.
As Street observes, the creation of the physical model was an intriguing blend that required him to move “from traditional artist to digital artist, adding modern computer and fabrication techniques on top of traditional techniques.”
This process fits well for Street, who began his art career as a ceramicist and studio glass blower, and is also known internationally as one of the first museum practitioners to adopt and
incorporate into his work digital techniques such as 3D scanning.
He chose Proto Labs’ industrial 3D printing services for several prototype iterations. These prototypes would help bridge the 3D virtual models into the final physical models, which, essentially, are molded-cast epoxy models based on the 3D prototypes. The prototypes themselves, using the additive manufacturing process of stereolithography (SL), were made of an ABS-like thermoplastic.
Street says that as he worked through those several iterations in the prototyping phase, he was especially pleased with Proto Labs’ speed — getting parts back in days rather than weeks or longer — and the prototype parts’ level of detail.
“It enabled us to get our parts back quickly. It would have been far more difficult to build the piece by hand than it was to model it in the computer and extract the parts I needed.”
The level of detail of the prototype parts was especially beneficial, Street says. “The detail of the 3D-printed part — it would have been very difficult to achieve that type of exacting geometry without the use of 3D printing.”
Proto Labs’ stereolithography (SL) process is especially suited for these types of projects that call for small parts with complex geometries and precise patterns.
A Model OutcomeThe virtual and physical models, Street says, provide an important aid “in interpreting and
visualizing the evidence which has been known from traditional means of reporting it in 2D drawings and excavation reports.”
Ultimately, the benefit for visitors of viewing the model within “Ancient Egypt Transformed: The Middle Kingdom,” is significant, Street says. “The model especially brings to life the beauty and complexity of this pyramid complex for visitors.”
A CAD model of the pyramid was initially created as an .STL file (top), then built in SL out of a white ABS-like thermoplastic material (bottom).
The detail of the 3D-printed part — it would have been very difficult to achieve that type of exacting geometry without the use of 3D printing.
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3D Printing Technologies for Prototyping and ProductionHow to Leverage Additive Manufacturing to Build Better Products
Architects don’t build without modeling. They create “blueprints,” produce renderings, and build 3D models. But while these planning tools may resemble the actual building in shape, there is no resemblance in size or materials. As a result, except in the case of manufactured or modular buildings, the finished product will be the first time that real building materials have come together in exactly that configuration. That is one of the reason that architecture tends to be conservative in its rate of change. Without real-world testing, big change is risky.
Product development is different. Today’s products are designed to be manufactured in thousands or hundreds of thousands, and both parts and assembled products can be built and tested throughout the development process. That, in part, explains today’s high rate of product innovation. But it also puts a lot of pressure on the prototyping process. New products have to meet or exceed buyer expectations in a very competitive market. In many cases, their value proposition is their innovation, the fact that they are different from anything that has existed before. And they have
to be developed and rolled out quickly to beat competitors to market. Smart prototyping can support all of those goals; the challenge is choosing the right prototyping processes at each point in development. Additive manufacturing, or 3D printing as it’s regularly called, is a process that uses digital CAD models to build physical, often layered, real-life objects. The appropriateness of the technology depends on the application of the part. A concept model of a brain, for example, has inherent medical value to a doctor during surgical planning, but it would never go into production because
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3D Printing Technologies for Prototyping and Production continued:
only one or two printed pieces are needed in a plastic-like material. Other times, additive manufacturing might be used to create fully functional end-use parts in small quantities of engineering-grade metals.
Additive manufacturing, or 3D printing as it’s regularly called, is a process that uses digital CAD models to build physical, often layered, real-life objects. The appropriateness of the technology depends on the application of the part. A concept model of a brain, for example, has inherent medical value to a doctor during surgical planning, but it would never go into production because only one or two printed pieces are needed in a plastic-like material. Other times, additive manufacturing might be used to create fully functional end-use parts in small quantities of engineering-grade metals.
However, if manufacturing will eventually entail a process like injection molding, 3D printing will have more limited use
in development. In the later stages of development of a cast or molded part, for example, it will be important to test parts that are identical (or nearly so) to final production parts. This will involve injection molding plastic or metal prototypes in a repeatable fashion. Thus, the method of prototype manufacturing can shift during the development process depending on application, material requirements, manufacturability and other factors.
Early-stage prototypes are typically produced in very small numbers and don’t necessarily have to hold true to all the functional characteristics of production parts. Since material selection and internal structure of the part are not as critical at this stage, prototypes can be produced using a variety of additive technologies that are both fast and affordable.
Uses of parts produced by additive processes include:• Production parts• Functional models• Visual aids• Fit and assembly testing• Tooling patterns and components• Jigs and fixtures• Concept models• Patterns for casting
The Right Tool for the JobDifferent prototyping methods serve different purposes. Take, for example, a designer or engineer who is developing a handheld device containing moving parts. The
High-speed stereolithography equipment can rapidly produce parts with excellent surface finishes that mimic plastics like ABS, polycarbonate and polypropylene.
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3D Printing Technologies for Prototyping and Production continued:
development process might begin with a series of 3D CAD models. These allow quick creation and virtual assembly of the components. When ready for first physical prototypes, the designer might produce additive prototypes from the CAD models, choosing SL prototypes for the shell components for that method’s superior surface finish and SLS prototypes for the internal components for that method’s good material properties. As development proceeds, there might be several iterations using those processes as the shell and internal part designs evolve.
When it comes time for functional testing — seeing how the internal parts perform under load and how the case withstands being dropped — the designer might initially send out the 3D CAD models to have one or several prototypes of each component machined from appropriate materials. These prototypes would have the physical characteristics of production parts and, particularly in the case of the shell, duplicate the cosmetic appearance. For larger-scale testing, the same CAD models could be used to produce rapid injection-molded parts for physical and market evaluation. If testing indicated that the product was ready for the market, those same molds could be used to produce parts for market while steel tooling was being milled for high-volume production.
Making the Un-manufacturable ManufacturableBuilding a part in thousands of thin layers affords those designing CAD models for 3D printing the opportunity to create highly complex geometries that are often impossible to mold — internal channels and holes that are unreachable by end mills, or entire assemblies printed as a single piece. But what happens when additive prototypes are ready to graduate to injection molding? Moving from stainless steel prototypes built by direct metal laser sintering (DMLS) into low-volume metal injection molding (MIM) works as a good product development example. Whereas the importance of molding-specific design considerations like draft, radii and uniform wall thickness are minimal in 3D printing, once a shift is made into MIM, these elements become much more critical. At Proto Labs, automated software identifies
moldability issues and recommends solutions in an interactive quote. That might mean a bit of design retooling, but it can quickly turn a printed prototype into a production-ready part.
Economies of ScaleAdditive processes all share the common impracticality of mass production into the thousands and tens of thousands. Is a new
Selective laser sintering fuses layers of fine powder to form parts in various grades of nylon thermoplastics.
Precision metal sintering machines build production-quality parts in metals like stainless steel, cobalt chrome, aluminum and others.
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3D Printing Technologies for Prototyping and Production continued:
frontier of additive scalability an area that additive could soon explore? According to Terry Wohlers, from independent consulting firm Wohlers Associates, Inc., medical and aerospace industries are beginning to embrace increased printed part production as well as companies in dental and jewelry fields. For a seismic shift to occur, it will likely take more than that. Currently, additive plastic materials are typically 50 to 100 times more expensive than traditional manufacturing, according to Wohlers, not 50 to 100 percent more. So presently, low quantities are suitable for additive manufacturing. When equipment throughput increases and equipment and material decrease, the potential for larger production volumes will increase. Until then, processes like injection molding — that involve an
initial tooling investment, but lower per-part price as quantities increase — remain a logical next step after prototyping.
Choosing ProcessesThere isn’t necessarily a preferred additive prototyping process. The challenge is finding the best prototyping methods for your project and for each phase of your project. Variables among prototyping methods include speed, cost, appearance, supported materials and a variety of physical characteristics. In some cases, all you need is something you can hold in your hand; in others, fit with other components is required.
Binder jetting is one of the simplest and most basic additive prototyping processes. An inkjet print head moves across a bed of powder, selectively depositing a liquid binding material, and the process is repeated until the complete part has been formed. After completion, the unbound powder is removed leaving the finished object.
Pros Cons • Fast • Rough surface• Inexpensive • Low strength• Easily colored • Unsuitable for functional testing• Easily duplicates complex geometries • No information on manufacturability
BJET Binder Jetting
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FDM Fused Deposition Modeling
Fused deposition modeling (FDM) melts and re-solidifies thermoplastic resin (ABS, polycarbonate or ABS/polycarbonate blend) in layers to form a finished prototype. Because it uses real thermoplastic resins, it is stronger than binder jetting and may be of limited use for functional testing.
Pros Cons • Moderately priced • Rippled surface• Moderate strength • Limited suitability for functional testing• Partial match to physical characteristics • Slower production than binder jetting; of ABS or PC parts can take days to produce large parts• Easily duplicates complex geometries • Poor strength on the z axis • No information on manufacturability
SL Stereolithography
Stereolithography (SL) uses a computer controlled laser to build parts in a pool of UV-curable resin. As each layer is drawn by the laser, the part is lowered in the pool of liquid resin allowing the next layer of liquid to be solidified. Quality of the finished part depends largely on the quality of the equipment and process used.
Pros Cons • Moderately priced • Lower strength• Excellent surface finish • Cured resin can become brittle over time• Easily duplicates complex geometries • Limited use for functional testing• One of the best surface finishes for an • No information on manufacturability additive process
SLS Selective Laser Sintering
Selective laser sintering (SLS) employs a computer controlled CO2 laser to fuse layers of powdered material such as nylon from the bottom up. Strength is better than that of SL but lower than that produced by subtractive processes like injection molding or CNC machining. It also has some use as a production method.
Pros Cons • Moderately priced • Limited resin choice• Supports a range of materials • Rough surface finish• Very good accuracy of size and form • No information on manufacturability• More durable than SL parts• Suitable for some functional testing• Easily duplicates complex geometries
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PJET PolyJet
PolyJet (PJET) uses a print head to spray layers of photopolymer resin that are cured, one after another, using ultraviolet light. The layers are very thin allowing superior resolution. The material is supported by gel matrix that is removed after completion of the part.
Pros • Moderately priced • Easily duplicates complex geometries
Cons • Limited resin choice • Poor strength• Not suitable for functional testing• No information on manufacturability• Costly materials
DLP Digital Light Processing
Digital light processing (DLP)-based additive manufacturing digitally slices a solid into layers, which a Texas Instruments DLP chip projects, one after another, onto the surface of a liquid photopolymer bath. The projected light hardens a layer of liquid polymer resting on a movable build plate. The build plate moves down in small increments as new images are projected onto the liquid, hardening each subsequent layer to produce the finished object. The remaining liquid polymer is then drained from the vat, leaving the solid model. The process can be useful for producing low volumes of small, highly detailed parts but is less suitable for larger parts, especially those requiring smooth finishes.
Pros • Relatively fast • Competitively priced • Resolution can be high • Can produced complex shapes
Cons• Limited resin choicex• May not be suitable for functional testing• No information on manufacturability• Can produce rough finish particularly on supported surfaces
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DMLS Direct Metal Laser Sintering
Direct metal laser sintering (DMLS) is the leading additive method for making metal prototypes. It is similar to selective laser sintering of plastic resin, but is suitable for use with metals including aluminum, stainless steel, titanium, cobalt chrome and Inconel. It offers good accuracy and detail, and excellent mechanical properties. DMLS can be used for very small parts and features, and because it is an additive process, it can reproduce geometries that might be impossible to machine such as enclosed spaces. Layers can be as thin as 20 microns, and tolerances on small features can be as small as ±0.002 inches. Secondary operations on parts produced by DMLS can include machined drilling, slotting, milling and reaming, and finishing procedures including anodizing, electro-polishing, hand polishing, and powder coating or painting.
Pros Cons • Capable of working with nearly any alloy • Relatively slow• Mechanical properties equal to • Expensive conventionally formed parts • Requires expertise to make quality parts• Can make geometries that are • Usually requires expensive post-processing impossible to machine or cast
Outsourced PrototypingWhile a few of the processes described can be carried out in-house, the majority of this kind of prototyping is outsourced. Outsourcing allows the developer to choose the best methods for any particular need. That can entail using multiple prototyping methods over the course of a single project. In selecting a vendor, consider the needs and goals of your project:
• Can the manufacturer provide suitable prototyping methods for your specific needs?
• Can it help you select the best method at each stage of the process?• Does it offer any kind of design assistance?• If you need a series of prototypes, can the manufacturer provide
continuity?• How experienced is the manufacturer in the processes you will use?• Can it produce the maximum quality available for each prototyping
method?• If necessary, can it provide secondary operations for your prototypes?• If material is critical, what materials can the manufacturer offer in
the selected method, and if a particular method cannot utilize your preferred material, can it offer other methods?
• What turnaround times does it offer?• What is the manufacturer’s reputation for meeting deadlines?
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Selecting the Right Material for 3D Printing
Materials must be suited to the application in order to have successful results. The properties of any material become increasingly important as a product progresses from concept and functional prototyping to production.
However, material properties can only be evaluated when the manufacturing process is considered. It is the combination of the material and the process that dictates the characteristics. For example, an alloy processed by die casting has different properties when it is metal injection molded. Likewise, a thermoplastic will have different properties if it is injection molded or CNC machined.
Additive manufacturing (AM), or 3D printing, is unique. It is different from all other manufacturing processes, so the material properties and characteristics of parts that it produces are different, even when using a nearly identical alloy or thermoplastic. In terms of material properties, it is not a matter of being better or worse; it is simply important to recognize that the results will be different.
Recognizing that there is a difference, the following information will aid in the characterization, and ultimately the selection, of materials from three widely used industrial 3D printing processes: direct metal laser sintering (DMLS), selective laser sintering (SLS) and stereolithography (SL).
Material AdvancementsThe materials used in 3D printing have been improving, as would be expected. These advancements have allowed the technology to move beyond models and prototypes to functional parts for testing, shop floor use and production.
And while the output of 3D printing is different from that of other manufacturing processes, it can offer a suitable alternative when seeking a direct replacement. Yet, its advantages increase when users experiment with the possibilities that it offers.
However, experimentation is a bit challenging because of 3D printing’s differences that extend beyond, but
are related to, material properties. For example, additive materials lack the rich set of performance data that characterize a material over a range of conditions. Instead, 3D printing users are presented with a single data sheet that contains a limited set of values. Those values are also likely to present a best case scenario based on testing of virgin material (unrecycled powders), for example.
Another complication is that 3D printing produces anisotropic properties where the values differ for the X, Y and Z axes. The degree of anisotropism varies with each additive technology — direct metal laser sintering is the closest to isotropic, for example — but it should always be a consideration.
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However, the material suppliers rarely publish material specifications that document the change in properties from one axis to another, as the data behind these specifications can vary greatly by material, process and even type of machine.
By designing for the 3D printing process and adjusting the build orientation, anisotropism or inadequate material properties can be overcome. To do this, leverage the experiences from past projects or that of a qualified service organization to fill in the data gaps that exist because of the limited material properties data. When performance is critical, also consider independent lab testing of additive materials.
While success is dependent on material properties, they are not the only considerations. Each additive material and build process will also dictate characteristics such as maximum part size, dimensional accuracy, feature resolution, surface finish, production time and part cost. So it is advised to select a suitable material and then evaluate its ability to meet expectations and requirements related to time, cost and quality.
Material SelectionGenerally, one or two material properties distinguish an additive material from all others. For example, if seeking the average tensile strength of polyamide (PA) 11, a stereolithography photopolymer maybe be a better option than a selective laser sintering PA. Conversely, if the heat deflection temperature (HDT) of an ABS is needed, the best option would be a sintered nylon.
Recognizing that a few properties will separate one material from the others, the recommended approach for selecting a material for 3D printing is to first define what mechanical or thermal properties are critical. Then review the material options to find a fit. With the options narrowed, review other remaining properties to determine if the material will be acceptable for the project.
Since 3D printing is unique, a goal of finding a perfect match to a cast, molded or machined material is ill-advised. Instead, investigate the material options to find the material that satisfies the most critical requirements.
Direct Metal Laser SinteringDMLS uses pure metal powders to produce parts with properties that are generally accepted to be equal or better than those of wrought materials. Because there is rapid melting and solidification in a small, constantly moving spot, DMLS may yield differences in grain size and grain boundaries that impact mechanical performance. Research is ongoing to characterize the grain structures, which can change with the laser parameters, post-build heat treatment and hot isostatic pressing. However, the results are not widely available. Ultimately, this difference will become an advantage when grain structure can be manipulated to offer varying mechanical properties in a part.
Of the three additive manufacturing processes discussed here, DMLS produces parts with material properties that approach an isotropic state. However, there will be some property variance when measured along different axes. For a visual comparison of DMLS material properties, see Chart 1 for tensile strength, Chart 2 for elongation and Chart 3 for hardness.
Stainless steel is a commonly used DMLS material, and it is available in two grades at Proto Labs: 17-4 PH and 316L. Select 17-4 for its significantly higher tensile strength (190 ksi vs. 70 ksi), yield strength and hardness (47 HRC vs. 26 HRC), but recognize that it has far less elongation at break (EB) than 316L (8% vs. 30%), which means that it will be less malleable. Both 17-4 and 316L offer corrosion resistance, but 316L is better at resisting acids. 316L is also more temperature resistant than 17-4. Note that 17-4 may be heat treated to modify mechanical properties, while 316L is only offered in the stress-relieved state.
DMLS aluminum (Al) is comparable to a 3000 series alloy that is used in casting and die casting processes. Its composition is AlSi10Mg. Al has an excellent strength-toweight ratio, good temperature and corrosion resistance, and good fatigue, creep and rupture strength.
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Compared to die-cast 3000 series aluminum, the Al properties for tensile strength (36 ksi to 43 ksi) and yield strength (30 ksi to 32 ksi) far exceed the average values. However, elongation at break is significantly lower (1% vs. 11%) when compared to the average for 3000 series aluminums.
DMLS titanium (Ti-64 ELI) is most commonly used for aerospace and defense applications due to its strengthto- weight ratio, temperature resistance and acid/corrosion resistance. It is also used in medical applications. Versus Ti grade 23 annealed, the mechanical properties are nearly identical with a tensile strength of 130 ksi, elongation at break of 10% and hardness of 36 HRC.
Cobalt chrome (CoCr) is one of two DMLS superalloys that tend to be used for specialty applications in aerospace and medical. CoCr has an exceptional EB (20%), and it is creep and corrosion resistant. Versus ASTM F-75 CoCr (dependent on heat treating), DMLS CoCr offers moderate material properties (DMLS vs. F-75): tensile strength of 130 ksi vs. 95-140 ksi, EBof 20% vs. 8-20%, yield strength of 75 ksi vs. 65-81 ksi, and hardness of 25 HRC vs. 25-35 HRC. Of all DMLS metals, CoCr has the best biocompatibility — which requires additional biocompatibility processing outside of Proto Labs — making it ideal for medical applications such as dental implants.
Inconel 718 (IN718) is a nickel chromium superalloy used in high service temperature applications, such as aircraft engine components. DMLS IN718 parts have an impressive operating temperature range of -423°F to 1,300°F coupled with excellent corrosion resistance, and good fatigue, creep and rupture strength.
DMLS IN718 has higher tensile strength (180 ksi vs. 160 ksi) and comparable yield strength (133 ksi vs. 160 ksi) than conventionally processed IN718. However, its EB is half that of conventionally processed IN718 (12% vs. 25%).
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Selective Laser SinteringSLS uses thermoplastic powders, predominantly polyamide (PA), to make functional parts that have greater toughness and higher impact strength than parts produced through SL, as well as high HDTs (351°F to 370°F). The tradeoffs are that SLS lacks the surface finish and fine feature details available with SL.
Generally, SLS PAs, when compared to the average values of their injection-molded counterparts, have similar HDT values but lower values for the mechanical properties. The exception is the fiber-filled DuraForm HST composite, which exceeds a mineral-filled PA 12 in all areas except tensile strength. In a few instances, SLS PAs report properties that document the degree of anisotropism. For a visual comparison of SLSmaterial properties, see Chart 4 for heat deflection, Chart 5 for elongation at break and Chart 6 for tensile strength.
DuraForm HST Composite is a fiber-filled PA that is similar to a 25% mineral-filled PA 12. The fiber content in HST significantly increases strength, stiffness and HDT. Compared to other SLS and
SL options (excluding ceramic-filled materials), HST has the highest tensile strength, flexural modulus and impact strength, and it maintains an elevated HDT. This makes HST a great choice for functional applications where temperatures exceeding 300°F may be present. The material is somewhat brittle, however, with an EB of 4.5%. Also consider that like injection-molded fiber-filled materials, there is a significant delta in the Z-axis values.
PA 850 Black delivers ductility and flexibility with a tensile modulus of 214 kpsi and EB of 51%, all without sacrificing tensile strength (6.9 ksi) and temperature resistance (HDT of 370°F). These characteristics make PA 850 a popular general-purpose material and the best solution for making living hinges for limited trials.
When compared to the averages for injection-molded PA 11, PA 850 has a higher HDT (370°F vs. 284°F) with similar tensile strength and stiffness. However, its EB, while the highest of all AM plastics, is 60% less than that for a molded PA 11.
Another factor that distinguishes PA 850 is its uniform, deep-black color. Black has high contrast, which makes features pop, and
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it hides dirt, grease and grime. Black is also desirable for optical applications due to low reflectivity.
ALM PA 650 is a balanced, economical, go-to material for general-purpose applications. PA 650 is stiffer than PA 850 (tensile modulus of 247 ksi vs. 214 ksi) and has a similar tensile strength (7.0 ksi vs. 6.9 ksi). While its EB is half that of PA 850, at 24% it’s still one of the top performers in terms of ductility. PA 650 is loosely comparable to the average properties for an injectionmolded PA 12. It has similar stiffness but roughly half the tensile strength and EB. However, its HDT is significantly higher: 351°F vs. 280°F.
PA 615-GS is a polyamide powder loaded with glass spheres that make it stiff and dimensionally stable. However, the glass filler makes PA 615-GS brittle, significantly decreasing impact and tensile strengths. The glass spheres also make PA 615-GS parts much heavier than those made with any other AM material.
PA 615-GS mimics the average value of glass-filled injection molded nylons. When compared to 33% glassfilled nylon, the HDT is lower at 350°F vs. 490°F with a much lower tensile strength (80%) and EB (50%).
StereolithographySL uses photopolymers, thermoset resins cured with ultraviolet (UV) light. It offers the broadest material selection with a large range of tensile strengths, tensile and flexural moduli, and EBs. Note that the impact strengths and HDTs are generally much lower than those of common injection-molded plastics. The range of materials also offers options for color and opacity. Combined with good surface finish and high feature resolution, SL can produce parts that mimic injection molding in terms of performance and appearance.
The photopolymers are hygroscopic and UV sensitive, which may alter the dimensions and performance of the part over time. Exposure to moisture and UV light will alter the appearance, size and mechanical properties. For a visual comparison of SL material properties, see Chart 7 for heat deflection Chart 8 for elongation at break and Chart 9 for tensile strength (ONLINE).
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