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ExOne Announces 15 New Materials Available for Binder Jetting Systems

Several companies—particularly Desktop Metal, GE Additive, and HP—have garnered a great deal of excitement for their new metal binder jetting technologies with the idea that they are revolutionizing metal additive manufacturing (AM) for mass production. One company that may have felt a bit out of the spotlight is ExOne, which has been making metal binder jetting systems for over 20 years.

ExOne reminded the AM sector that it is still the original manufacturer of metal binder jetting technology with the announcement that it has qualified 15 new metal, ceramic and composite materials for 3D printing. This brings the total materials that are printable on ExOne systems to 21: 10 single-alloy metals, six ceramics, and five composite materials. Additionally, the company has said that over 24 other powders are also qualified for use in research and development, such as aluminum and Inconel 718.

Some of ExOne’s qualified and R&D materials, including M2 Tool Steel, 316L, 304L, 17-74PH, copper, and Inconel 625. Image courtesy of ExOne.

Since 1996, ExOne has been developing metal binder jetting technology, which deposits a liquid binder onto a bed of metal powder. The resulting green parts are then placed into a debinding system before being transferred to a sintering furnace to create near-fully-dense metal parts. To further densify the components to near 99 percent, they are infiltrated with bronze.

With the announced qualification of 15 new materials, ExOne also revealed that it had established three material qualification levels, depending on customer applications: 1.) third party qualified, 2.) customer-qualified, and 3.) research and development materials. While there are over 40 materials currently in development (category 3), the 21 that fall into categories 1 and 2 are few enough to list here.

Tested and qualified by independent third party Tested and qualified by ExOne customers
Metals: 17-4PH, 304L, 316L, M2 tool steel Metals: cobalt chrome, copper, H13 tool steel, Inconel 625, titanium, tungsten heavy alloy
Metal Composites: 316 with bronze, 420 with bronze, and tungsten with bronze Ceramics: alumina, carbon, natural sand, synthetic sand, silicon carbide, and tungsten carbide-cobalt
Ceramic-metal composites: boron-carbide aluminum and silicon carbide with silicon

 

To see the complete list of R&D materials, you can visit the ExOne site. Some of the 26 materials that have passed the preliminary qualification phase include Inconel 718, tungsten with copper, and tungsten carbide. The company is also hoping to move aluminum out of the R&D category and into further qualification, due to the potential impact it could have on the automotive and aerospace industries.

“While our teams can binder jet aluminum in controlled R&D environments today, we believe that optimizing this material for high-speed 3D printing will eventually transform how car and airplane parts are made, making them smarter and lighter weight,” said Rick Lucas, Chief Technology Officer at ExOne. “Based on high demand from the marketplace, we have fast-tracked development of this material for use on our machines.”

The broad portfolio news may be the result of ExOne both receiving increased interest due to the hype generated by Desktop Metal, GE Additive, and HP, as well as the increased competition. Due to the firm’s established presence in bound metal printing, there should be no reason why companies looking to work with Desktop Metal or HP shouldn’t also look toward the originator of metal binder jetting.

After the 3D printing stock bubble of 2014, many of the listed AM manufacturers took serious financial hits. Like Stratasys and 3D Systems, ExOne saw changes in management as it struggled to redefine and reposition itself in the market. When Desktop Metal and HP announced the development of high-speed metal binder jetting, ExOne was upstaged in terms of the claimed speed and price of their machines.

The X1 160PRO from ExOne.

However, with the 2018 unveiling and 2019 commercial release of the X1 25Pro, ExOne was able to quickly revamp its image. This was soon followed by the announcement of the X1 160Pro. Using the same Triple ACT method for depositing, spreading and compacting powder as the X1 25Pro, the X1 160Pro has a massive build volume of 800 x 500 x 400 mm. When it hits the market later this year, it will be the largest metal binder jetting system on the market.

To further stand out from the newcomers, it is incumbent upon ExOne to demonstrate its advantages, such as a wide range of printable materials. While Desktop Metal and HP slowly introduce one metal at a time, the 3D printing stalwart was able to showcase 21 all at once.

ExOne will have to keep up the pace, however. GE Additive, too, has developed a metal binder jetting system with a scheduled release in 2021. Digital Metal, which previously only printed metal parts as a service, is now selling systems and working toward an automated production factory concept based around its metal binder jetting technology. A startup called Triditive is also developing an automated metal binder jetting system.

With all of this activity, it should be no surprise then that the bound metal printing market is expected to grow at twice the rate of the overall metal additive manufacturing market over the next ten years, according to SmarTech Analysis.

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3D Printing News Briefs: December 3, 2019

We’re starting today’s 3D Printing News Briefs out with a new case study, and then concluding with some business. CRP USA has been working with additive manufacturing in the motorsports sector. Moving on, Gardner Aerospace has acquired FDM Digital Solutions Ltd. Finally, the Head of Engineering at Formlabs is joining up with Digital Alloys.

CRP USA AM in Motorsports Case Study

3D printed oil pan in Windform SP, University of Victoria’s Formula SAE race car 2019 version

The University of Victoria (UVic) Formula Motorsport team has been using 3D printed oil pans on their SAE competition cars for the last four years that were created with CRP USA‘s laser sintering process, and Windform TOP-LINE composite materials. As a CRP case study details, carbon-composite Windform XT 2.0 was used to print the oil pans for the race vehicles in 2016, 2017, and 2018, and while they performed “amazingly” the first two years, the engine overheated during a test of last year’s car, which caused the temperature of the oil to rise above what the pan could handle.

For this year’s vehicle, the team decided to use the carbon-filled Windform SP composite material to 3D print the oil pan, as it has a higher melting point. They also made the mating flange thicker to lessen the chances of failure, and both of these changes led to a better, more robust oil pan. At next week’s Performance Racing Industry (PRI) Trade Show in Indianapolis, CRP USA will be showing off some of the other 3D printed solutions it’s helped create for the motorsports industry at booth 1041 in the Green Hall.

Gardner Aerospace Acquires FDM Digital Solutions

Graeme Bond (FDM) & Dominic Cartwright (Gardner Aerospace)

Global manufacturer Gardner Aerospace announced its acquisition of FDM Digital Solutions Limited, one of the UK’s top polymer additive layer manufacturers. FDM was formed in 2012, and its business model of original design solutions, manufacturing capability, and customer collaboration is successful in the aerospace, automotive, medical, and motorsports industries. The company will now become part of the new Gardner Technology Centre business unit, which is focused on R&D and advanced technology.

“Gardner Aerospace is breaking new ground in terms of technology. The acquisition of FDM and the creation of our new Technology Centre business unit provides us with the perfect opportunity to expand our technical knowledge, R&D capability and product offering, and aligns us with our customers’ growing expectations on innovative solutions, continuous improvement and cost competitiveness,” stated Gardner Aerospace CEO Dominic Cartwright.

“The role of 3D printing within manufacturing is constantly expanding and this newly acquired additive layer manufacturing capability complements Gardner’s long-standing capabilities as a producer of metallic detailed parts and sub-assemblies.”

Formlabs’ Head of Engineering Joins Digital Alloys

Carl Calabria

Carl Calabria, an AM industry veteran and the Head of Engineering at Formlabs, is leaving the company to join Digital Alloys, Inc. as its CTO. The Burlington, Massachusetts-based 3D printing company introduced its unique Joule printing last year, which it claims is the fastest way to make the hardest metal parts, as the wire-feed process doesn’t require any metal powder. By adding Calabria to its team, where he will be responsible for the company’s research and engineering, Digital Alloys can accelerate the release of its high-speed metal AM process.

“Leaving Formlabs was a difficult decision, but I was drawn to the size of Digital Alloys’ market, the team, and the opportunity to use Joule Printing to deliver metal printing solutions that have the speed, cost and quality needed for volume manufacturing of larger parts,” said Calabria. “The remarkable technology is producing titanium and tool steel parts faster, and at lower cost than conventional manufacturing processes.”

Watch this video to see Digital Alloys’ Joule printing process in action:

 

What do you think? Discuss these stories and other 3D printing topics at 3DPrintBoard.com or share your thoughts in the comments below. 

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Testing Low-Density Polyethylene Glass Composites in FDM 3D Printing

Wear resistance in 3D printed materials is critical for many users, with few research studies so far delving into such details for ABS or PC-ABS blends. Much of the concern is centered around anisotropic mechanical properties too, all in relation to ‘friction direction,’ with their findings outlined in ‘Preliminary Characterization of Novel LDPE-Based Wear-Resistant Composite Suitable for FDM 3D Printing.’

3D printout with possible anisotropy vs. friction direction.

The particle size distribution of the obtained glass powder (left) and the powder with low-density polyethylene (LDPE) granules (right).

Low-density polyethylene (LDPE) is a polymer used in many different types of packaging, and the authors point out that it is responsible for a substantial amount of waste—which optimally, should be recycled in FDM 3D printing. And while this is certainly not a novel idea, with the exercise of recycling plastic that has been discarded and grinding it into pellet or powder form for re-use being completely feasible, it is not a habit that has become widespread with users yet.

In exploring LDPE, the authors point out that it not only has inferior strength and stiffness but is also responsible for adhesion issues and high shrinkage—all qualities pointing to the need for a composite material with the potential for adding ceramic or metal.

“As mentioned before, adding ceramic or metal powders to LDPE can improve its storage modulus, reduce shrinkage, and increase its mechanical properties. Currently, LDPE composites with a mold flow index (MFI) of 10 g/10 min were successfully printed, so it is possible to manufacture an LDPE composite filament for FDM printing made from waste materials,” stated the researchers.

LDPE as a friction material offers potential, and especially when wear resistance is a critical issue; for example, the soles of shoes also require hardness, plasticity, elasticity, and more. LDPE can also be used as a near-surface filler or in creating products like sliding pads (commonly used with furniture).

The team created a composite, recycling even further with glass waste—obtained from shredded car windshields—refining both technological and wear-resistance properties and testing their results.

Composites exhibited suitable layer adhesion, devoid of cracks or voids. The research team employed a mathematical model for feed rate and printing speed—discovering in this study that the higher modulus allowed for more rapid printing, but also offered greater potential in defects due to the speed. Higher crystallinity was also found, but only slightly and ‘close to the error limit.’ The addition of the recycled glass was a suitable ‘reinforcement’ according to the researchers, who found that it did strengthen wear resistance further.

“An evident effect of the friction direction vs. the printed path direction on the wear appeared, which was probably related to differences in the removal of friction products from the friction area for different print-path layouts against the friction direction,” concluded the researchers.

“The LDPE composite with auto-screen glass particles is a promising material and should be studied further.”

Composites have become not only an interesting area of focus for 3D printing users but also a useful one as researchers and developers strengthen materials with wire composites, reinforced carbon fiber, and PLA. What do you think of this news? Let us know your thoughts! Join the discussion of this and other 3D printing topics at 3DPrintBoard.com.

Composite filament microstructure: (a) LDPE15, (b) LDPE30

Composite filament microstructure: (a) LDPE15, (b) LDPE30

[Source / Images: ‘Preliminary Characterization of Novel LDPE-Based Wear-Resistant Composite Suitable for FDM 3D Printing’]

 

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Improving Mechanical Properties of 3D Printing with Continuous Carbon Fiber Shape Memory Composites

Researchers Yongsan An and Woon-Ryeol Yu explore improved 3D printing through the study of alternative materials. In the recently published ‘Three-dimensional printing of continuous carbon fiber-reinforced shape memory polymer composites,’ the authors discuss challenges with mechanical properties that plague many industrial users.

In this study, they experiment with continuous carbon fiber reinforced shape memory polymer composites (SMPC), in FDM 3D printing—using both thermoplastics and thermosets.

Mechanical properties of continuous fiber-reinforced polymer composites, short fiber reinforced polymer composites, and polymer matrix fabricated by FDM.

Parameters were tested, and samples were printed, as the researchers learned more about the benefits and limits of smart materials like SMPs—able to change with their environment and then morph back to their normal shape. This type of material borders on the 4D and allows users much greater flexibility in use—across a wide variety of applications. With the addition of carbon composites, the research team hoped to improve fabrication processes.

The team created a customized FDM 3D printer for the study, to fabricate continuous fiber-reinforced SMPC parts. For materials, two different types were chosen for evaluation: PLA and a polyurethane-type of SMP filaments (as the thermoplastic matrices) and an SMP epoxy as the thermoset matrix. The team then added the continuous carbon fibers for reinforcement to the filament.

Schematic diagram of the 3D printing system of continuous carbon fiber-reinforced polymer composites for (a) thermoplastics and (b) thermosets.

They experimented with differences in temperature and print speed in printing out samples to be tested. Mechanical and shape memory properties were then assessed by the team.

3D printing of CF and PLA composites. (a) only PLA, (b) 1.5 mm-diameter nozzle, and (c) 2 mm- diameter nozzle.

“The storage modulus (G’), loss modulus (G’’), and the viscosity of the PLA were decreased around its melting point. The storage modulus was decreased at a larger rate than the loss modulus, resulting in more liquid-like properties of PLA. Therefore, the PLA could be easily extruded from the nozzle of which temperature was 180℃,” the researchers wrote.

“The PLA filament without CF was smoothly extruded from a nozzle whether its diameter was larger than the fusion area or not. However, for a nozzle with 1.5 mm diameter, the PLA matrix was extruded like wrapping the CF helically. It was due to a fact that the PLA was extruded more than the CF because the CF was not stretched during extrusion. In addition, harsh temperature and different extrusion speed caused CF to fail during 3D printing. On the other hand, for a nozzle with 2 mm diameter, the PLA and CF were extruded straightly because their extrusion speeds were synchronized.”

There were numerous challenges—such as the CF not coated completely with PLA. The researchers created an improved printhead for better optimization in terms of supplying speed of PLA and CF and the structure and fusion time of the materials. They also added calendar rolls and a proper tension device.

“The printed SMPC showed good mechanical properties compared to those of conventionally 3D printed polymer in the fiber direction,” stated the researchers.

Strength and stability in mechanical properties are a constant challenge in 3D printing—but there are constant improvements as researchers are determined to perfect the materials and processes of progressive fabrication techniques from testing carbon lattices, to titanium, to examining issues in biocompatibility.

What do you think of this news? Let us know your thoughts! Join the discussion of this and other 3D printing topics at 3DPrintBoard.com.

[Source / Images: Three-dimensional printing of continuous carbon fiber-reinforced shape memory polymer composites]

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Oak Ridge National Laboratory Investigates New Lignin-Nylon Composite 3D Printing Material

Lignin is an organic polymer that is present in the cell walls of many plants, giving them rigidity such as in wood and bark. It’s also a byproduct of biorefinery processes, and, thanks to work by researchers at Oak Ridge National Laboratory (ORNL), it could make up a new kind of 3D printing material. The research is documented in a paper entitled “A path for lignin valorization via additive manufacturing of high-performance sustainable composites with enhanced 3D printability.“

“Finding new uses for lignin can improve the economics of the entire biorefining process,” said ORNL project lead Amit Naskar.

The researchers combined a melt-stable hardwood lignin with conventional plastic – a low-melting nylon – and carbon fiber to create a composite with excellent mechanical properties and strength between layers, as well as extrudability. One of the issues of lignin is that it chars easily and can only be heated to a certain temperature before it becomes too viscous to be extruded. When the researchers combined it with nylon, however, they found that its room temperature stiffness increased while its melt viscosity decreased. The composite had tensile strength similar to nylon alone and lower viscosity than ABS or polystyrene.

The researchers conducted neutron scattering at the High Flux Isotope Reactor and used advanced microscopy at the Center for Nanophase Materials Science to investigate the composite’s nuclear structure. They discovered that the combination of lignin and nylon “appeared to have almost a lubrication or plasticizing effect on the composite,” according to Naskar.

“Structural characteristics of lignin are critical to enhance 3D printability of the materials,” said ORNL’s Ngoc Nguyen.

The researchers were also able to mix a higher percentage of lignin – 40 to 50 percent by weight – and then add 4 to 16 percent carbon fiber. The result was a new composite that heats up more easily, flows faster, and results in a stronger 3D printed product.

“ORNL’s world-class capabilities in materials characterization and synthesis are essential to the challenge of transforming byproducts like lignin into coproducts, generating potential new revenue streams for industry and creating novel renewable composites for advanced manufacturing,” said Moe Khaleel, Associate Laboratory Director for Energy and Environmental Sciences.

The lignin-nylon composite is patent-pending, and the researchers will continue to work with it to refine it and find other ways to process it. ORNL has been working with lignin for several years, and has done a lot of work with other novel 3D printing materials as well. As the researchers point out, petroleum-based thermoplastics still dominate the 3D printing materials market; the market for wood- and plant-based 3D printing materials is still limited because of their inherent difficulties in melt processing.

“Our study opens a new avenue of using isolated lignin as a feedstock for formulating 3D-printing materials having superior mechanical and printing characteristics,” they conclude. “Our findings have the potential to create additional revenue streams for biomass processing industries via the added value of lignin. In addition, it may accelerate installation of pilot biomass fractionation units in rural areas before feeding the whole biomass to a biorefinery and boost local polymer compounding industries that manufacture or compound materials for 3D printing and injection molding.”

Authors of the paper include Ngoc A. Nguyen, Sietske H. Barnes, Christopher C. Bowland, Kelly M. Meek, Kenneth C. Littrell, Jong K. Keum and Amit K. Naskar.

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[Source/Images: ORNL]

 

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Wageningen University: Adding Some Sparkle to 3D Printed Objects with Gold Nanoparticles

Nanotechnology may seem novel and advanced, but it has actually been used for thousands of years. Metallic nanoparticles are present in glass and pottery from hundreds and thousands of years ago, giving the items a shiny, glittering look. In a paper entitled “Plastic embedded gold nanoparticles as 3D printing dichroic nanocomposite material,” a group of researchers discusses how they fabricated a 3D printable nanocomposite composed of dichroic gold nanoparticles and a 3D printable polymer.

“Dichroic AuNP (gold nanoparticles) were prepared using a modified Turkevich method, thus reducing gold ions to gold nanoparticles using citrate as both reducing and capping agent,” the researchers explain. “In the classical Turkevich method, a boiling chloroauric acid solution is reacted with citrate using a molar ratio citrate to gold of 10, producing AuNP of around 10 nm. When this ratio is changed, the size of the obtained nanoparticles changes as well. We discovered that a citrate/gold ratio between 0.6 and 0.8 produced dichroic nanoparticles that showed a brownish reflection and a purple transmission.”

The nanoparticle solution was studied by transmission electron microscope (TEM).

“The presented synthesis is easy and fast, as it takes only few minutes to obtain the dichroic solution after the addition of the citrate,” the researchers continue. “During the synthesis, the solution changed color multiple times: the yellow solution of the gold ions become blue one minute after the addition of the citrate solution. Two minutes later, the solution showed an intense black color, before becoming dichroic after another two minutes of boiling. The color changed during the synthesis hint that the dichroic nanoparticle formation is not just seeded growth, but a more complex mechanism.”

Once the gold nanoparticle solution was prepared, the nanoparticles were embedded in a 3D printable material that could be used with a standard off-the-shelf FDM 3D printer. The researchers used polyvinyl alcohol (PVA) as the carrier, as it is one of the most commonly used 3D printing materials, it is water soluble and can thus be mixed with the nanoparticles without need of changing solvent, and because it can be used as a capping agent for nanoparticles.

The researchers compared TEM results of the original dichroic solution to the AuNP-PVA dissolved in water, and found that the nanoparticles were still of the same size and shape as the original ones, showing that the embedding in PVA does not influence the stability of the nanoparticles. Finally, they extruded the material to create a filament for FDM 3D printing. The small percentage of gold did not affect the printability of the PVA. The researchers then 3D printed a replica of the fourth-century Lycurgus cup and coated it in PDMS so it could hold water.

“In conclusion, we showed how to synthesize and embed dichroic nanoparticles in 3D printable material,” the researchers conclude. “The AuNP-PVA nanocomposite is mechanically similar to the bare plastic and its dichroic optical properties are similar to the one shown by the AuNP solution. The 3D printed objects can be coated to achieve water impermeability and stability at room temperature for long time. We can envision this methodology to be used not only by artists, but also for studying optical properties of nanoparticles or, for example in 3D fabrication of optical filters.”

Authors of the paper include Lars Kool, Anton Bunschoten, Aldrik H. Velders and Vittorio Saggiomo.

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Researchers Prepare Silicon Carbide-Polymer Composite Materials for SLS 3D Printing

Silicon carbide, or SiC, has a lot of potential for use in industrial applications, like aeronautic and aerospace engineering, the automotive industry, and the machinery industry, due to its excellent physical and chemical properties. But, because of the high production costs that come with mold manufacturing, machining, and high temperature and pressure sintering processes, this industrial use is rather limited.

SEM images of SiC/PVB composite powders with the PVB binder contents in the range of 2 to 7 wt. %. (a–f) are 2 wt. %, 3 wt. %, 4 wt. %, 5 wt. %, 6 wt. % and 7 wt. %, respectively.

Selective laser sintering (SLS) 3D printing could be used to help lower these costs, and a collaborative team of Chinese researchers from the Southern University of Science and Technology, Southeast University, and the Harbin Institute of Technology recently published a paper, titled “Development of SiC/PVB Composite Powders for Selective Laser Sintering Additive Manufacturing of SiC,” that explains how they prepared SiC-polymer composites with good dispersity and flowability, using a ball milling method, for SLS 3D printing. By combining multiple materials into a composite material, completed components can benefit from the respective strengths of each material.

The abstract reads, “Subsphaeroidal SiC/polymer composite granules with good flowability for additive manufacturing/3D printing of SiC were prepared by ball milling with surface modification using polyvinyl butyral (PVB). PVB adheres to the particle surface of SiC to form a crosslinked network structure and keeps them combined with each other into light aggregates. The effects of PVB on the shape, size, phase composition, distribution and flowability of the polymer-ceramic composite powder were investigated in detail. Results show that the composite powder material has good laser absorptivity at wavelengths of lower than 500 nm.”

There are two approaches to manufacturing ceramic parts using SLS technology: direct and indirect. For this study, the researchers created their composite powder materials, using polyvinyl butyral (PVB) as a binder in order to investigate its effect on the powders’ surface modification, for indirect SLS processing.

“For indirect SLS processing, the polymers are used for a sacrificial binder phase,” the researchers explained. “There are three steps for indirect SLS: (a) The first step is to select a suitable ceramic and polymer phase to prepare ceramic/polymer composite powders as the starting materials of indirect SLS; (b) the second step is to use a laser to melt the organic phase in the ceramic/polymer composite powder, and then the ceramic particles will be bonded by the binder and the green parts are prepared; (c) the final step for indirect SLS is to remove the binder and sinter the green part to increase its density and strength.”

SEM images of SiC/PVB composite powders with different weight contents of the PVB binder. (a,b) for 0 wt. %; (c,d) for 0.5 wt. %; (e,f) for 1 wt. %.

As many commercial ceramic powders have irregular morphology and poor flowability, they’re not great for use in 3D printing. So the most important step of indirect SLS processing is the actual production of the polymer-ceramic composite powder agglomerates.

The team combined PVB, polyvinylpyrrolidone (PVP), and commercial SiC powder with anhydrous alcohol, and then ball milled the mixture at 120 rpm for 12 hours. The resulting powders were sieved through a 120 mesh screen, before a Concept Laser M2 was used to complete the composite’s preliminary spreading and forming tests.

The composite powder’s laser absorptivity was studied, and scanning electron microscopy (SEM) was used to examine the granulated particles’ morphology and microstructure, while X-ray diffraction identified the phase composition of the composite powders, laser diffraction measured the size of the agglomerates, and the materials’ UV-Vis analysis was also tested.

The researchers successfully prepared subsphaeroidal SiC/polymer composite granules, complete with good flowability, for SLS 3D printing, and added PVB binder to include surface modification. They investigated the effects of PVB on the distributions, flowability, shapes, and sizes of polymer-ceramic composite powder agglomerates, and determined some important information.

The typical spreading (a) and forming (b) tests of SiC/PVB composite powders with 3 wt. % binder addition using the 3D printing machine.

First, the added PVB has an optimal value (~3 wt. %), and the SiC granules modified with this material showed good spreading performance and flowability. In addition, when the wavelength is below 500 nm, the composite powder had good laser absorptivity, which suggests that using SLS 3D printing to fabricate the material could work with systems of a corresponding wavelength.

“Results show that the addition of the polymer binder improves the size distribution characteristic and flowability of the granulated particles within a certain range,” the researchers concluded. “However, when the PVB content increases to a higher value (e.g., more than 7 wt. %), greater addition of PVB will not have much influence on the apparent density, tap density, Carr index or Hausner ratio.”

Co-authors of the paper are Peng Zhou, Huilin Qi, Zhenye Zhu, Huang Qin, Hui Li, Chenglin Chu, and Ming Yan.

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Strengths of Three Materials Combine to Form Composite 3D Printed Components

In a paper entitled “On the 3D printing of recycled ABS, PLA and HIPS thermoplastics for structural applications,” a group of researchers discusses multi-material 3D printing for structural applications. The materials they use are recycled ABS, PLA and HIPS to create composite parts. The point was to combine the materials so that the final component benefited from the respective strengths of each material.

“ABS is amorphous in nature and having high impact resistance,” the researchers state. “Low thermal conductivity, heat resistance and toughness, bio-degradability and bio-compatibilities are the key advantages of PLA, whereas HIPS is a low strength structural polymer which have better machinability and fabrication characteristics with low cost.”

The researchers 3D printed the sample components, which had four layers of each material. Testing was then performed on the components, including MFI characterization, differential scanning calorimetric (DSC) analysis, tensile testing, Lee’s disc thermal conductivity measurement, flexural testing and pull out testing. ABS, PLA and HIPS were found, through DSC testing, to be compatible with each other, all of them having similar ranges of integral heat value.

“As the practical application requires the requirement for maximum strength with minimum elongation, HIPS was having most desired elongation and PLA was having most desired tensile strength values,” the researchers continue. “After 3D printing of multi-material component, it was observed that tensile strength and elongation values of all multi-material printed components were observed intermediate to the HIPS and ABS which shows the usefulness of present study.”

Several conclusions were made from the study, as stated by the researchers:

  • In tensile testing, the Young’s modulus of multi-material component (325 MPa) was observed higher at experiment number 3, than single thermoplastic (Young’s modulus of PLA 47.9 MPa, ABS of 175 MPa and for HIPS 112.5 MPa).

  • Pull out testing revealed the fact that elongation and strength properties of 3D printing can be controlled through multi-material printing at predicted input processing setting. It was noted that break elongation of multi-material components was observed smaller as compared to ABS and PLA. At the same time, break load and break strength has been observed greater than HIPS in case of pull out tests.

  • 3D printing of multi-material components at predicted settings resulted in the observation that flexural strength was attained higher than HIPS (2.01 MPa) material as 2.96 MPa but lower than PLA (9.07 MPA) and ABS (7.04 MPa).

  • It was noted that PLA was having thermal conductivity of 0.2225 W/m.K, ABS of 0.1722W/m.K and HIPS of 0.3232W/m.K. For structural applications, it requires the thermal conductivity to be desired minimum. Multi-material printing of these materials resulted in thermal conductivity of 0.2732W/m.K (dt/dT = 0.814 K/s) which was lesser than HIPS material shows the utility of multi-material 3D printing.

Overall, the three materials were compatible with each other, and their strengths worked together to create composite components that were superior to single-material components. With the growing sophistication of 3D printers, and the greater accessibility of printers with multimaterial capabilities, it is becoming easier to 3D print composite components like these for functional applications that benefit from the best characteristics of ABS, PLA and HIPS.

Authors of the paper include Ranvijay Kumar, Rupinder Singh and Ilenia Farina.

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Michigan Tech Researchers Recycle Wood Furniture Waste into Composite 3D Printing Material

A) PLA during mechanical mixing with wood-waste powder, B) PLA and wood-waste powder-based WPC after mixing and cooling to room temperature, C) chipped WPC, and D) homogeneous WPC material after first pass through recyclebot.

From artwork, instruments, and boats to gear shift knobs, cell phone accessories, and even 3D printers, wood has been used often as a 3D printing material. It’s a valuable renewable resource that stores carbon and is easily recycled, so why wouldn’t we think to use it in 3D printing projects?

A trio of researchers from Michigan Technological University recently published a paper, titled “Wood Furniture Waste-Based Recycled 3-D Printing Filament,” that looks to see how viable a solution it is to use wood furniture waste, upcycled into a wood polymer composite (WPC) material, as a 3D printing feedstock for building furniture.

The abstract reads,  “The Michigan furniture industry produces >150 tons/day of wood-based waste, which can be upcycled into a wood polymer composite (WPC). This study investigates the viability of using furniture waste as a feedstock for 3-D printer filament to produce furniture components. The process involves: grinding/milling board scraps made of both LDF/MDF/LDF and melamine/particleboard/paper impregnated with phenolic resins; pre-mixing wood-based powder with the biopolymer poly lactic acid (PLA), extruding twice through open-source recyclebots to fabricate homogeneous 3-D printable WPC filament, and printing with open source FFF-based 3-D printers. The results indicate there is a significant opportunity for waste-based composite WPCs to be used as 3-D printing filament.”

While a lot of wood is wasted by burning it, it may be better to upcycle it into WPCs, which contain a wood component in particle form inside a polymer matrix. These materials can help lower costs and environmental impact, as well as offer a greater performance.

A) 0.15 mm layer height drawer knob being 3D printed with a screw hole for attachment. B) Completed drawer knob fully attached on left of wood block with example pre-printed hole on right of block, 30wt% wood furniture waste.

“There is a wide range of modification techniques for wood either involving active modifications such as thermal or chemical treatments, or passive modification, which changes the physical properties but not the biochemical structure,” the researchers wrote. “However, WPCs still have limitations due to production methods, such as producing waste material or orientation reliant fabrication, which may be alleviated with alternative manufacturing techniques such as additive manufacturing.”

While lots of PLA composite manufacturers are already in the market to make virgin, wood-based 3D printing filaments, the Michigan Tech study investigated using wood furniture waste as a 3D printing feedstock for WPC filament, which could then be used to make new furniture components.

“The process uses grinding and milling of two furniture waste materials – boards scraps made of both LDF/MDF/LDF (where LDF is light density fill and MDF is medium density fill) and melamine/particleboard/paper impregnated with phenolic resins. A pre-mixing process is used for the resultant wood-based powder with PLA pellets,” the researchers wrote. “This material is extruded twice through an open source recyclebot to fabricate homogeneous 3-D printable filament in volume fractions of wood:PLA from 10:100 to 40:100. The filament is tested in an open source FFF-based industrial 3-D printer. The results are presented and discussed to analyze the opportunity for waste based composite filament production.”

Surface contours of a personalized drawer handle with the Herman Miller emblem. A coloration change from the outside to the center is shown due to induced temperature changes during printing to provide a tree ring.

The team received wood-based waste material, in both sawdust and bulk form, from several furniture manufacturing companies, and completed some important steps to turn the wood waste into WPCs for 3D printing filament:

  1. Size reduction from macro- and meso-scale to micro-scale
  2. Mix fine wood-based filler material with matrix polymer
  3. Extrude feed material into filament of homogeneous thickness and density

Then, the material was loaded into a delta RepRap 3D printer, as well as an open source Re:3D Gigabot 3D printer, to make a high-resolution drawer knob that was “attached to a printed wood block using a wood screw threaded through a pre-printed hole.”

“The wood screw was easily twisted through both objects with a Phillips screwdriver and the resulting connection withstood normal forces expected in everyday use. Additionally due to the flexibility of 3-D printing orientations a unique or personalized surfaces may be printed onto objects,” the researchers wrote.

“This is shown through the particular geometries or print directions which may be modified directly by altering gcode, or more conveniently by changing parameters in slicer programs. This enables mass-scale personalization of not only furniture components with wood, but any 3D printed part using recycled waste-based plastic composites.”

Once an optimized 3D printing profile was obtained, the recycled wood furniture waste-based WPC filament was able to produce parts without too many errors. However, there was a greater frequency of filament blockages and nozzle clogging with this material, when compared to pure PLA.

Five desk cable feedthrough parts 3D printed consecutively, 30wt% wood furniture-based waste.

“This study has demonstrated a technically viable methodology of upcycling furniture wood waste into usable 3-D printable parts for the furniture industry,” the researchers concluded. “By mixing PLA pellets and recycled wood waste material filament was produced with a diameter size of 1.65±0.10 mm and used to print a small variety of test parts. This method while developed in the lab may be scaled up to meet industry needs as the process steps are uncomplicated. Small batches of 40wt% wood were created, but showed reduced repeatability, while batches of 30wt% wood showed the most promise with ease of use.”

The researchers wrote that further work on creating waste-based WPC filament should include quantifying the material’s mechanical properties after the first cycle, and then comparing it to other materials, such as pure PLA and modified wood fiber powder. Additionally, industrial equipment and grouped 3D printing nozzles should be evaluated in terms of scaling up the process.

Co-authors of the paper are Adam M. Pringle, Mark Rudnicki, and Joshua Pearce.

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Comparing FDM 3D Printed Parts with Carbon Nanotubes, Continuous Carbon Fiber and Short Carbon Fiber

Fused deposition modeling, or FDM, 3D printing has several advantages – thermoplastics can be used, which are easy to handle and are strong and durable enough to be used for producing both prototypes and practical parts. Additionally, FDM 3D printers use a simple mechanism to melt and extrude resin that doesn’t need expensive parts, like lasers, which makes the machines less expensive. But, the technology does not always provide enough strength for mechanical parts.

That’s why additional materials with good mechanical properties, such as carbon nanotubes (CNT) and fiber reinforced composites, are often added to improve strength; depending on the length, carbon fiber can also be divided up into both short and continuous fiber. A group of researchers from Doshisha University and Kyoraku Co., Ltd., both in Japan, recently published a study, titled “Comparison of strength of 3D printing objects using short fiber and continuous long fiber,” that compared the usefulness and strength of objects 3D printed with short carbon fiber, continuous carbon fiber, and multi-wall carbon nanotube (MWCNT).

The abstract reads, “In this research, composite materials were used to improve the strength of FDM 3D printed objects. The nanocomposites made from polylactic acid as matrix and multi-wall carbon nanotube as filler, short carbon fiber reinforced composite and continuous carbon fiber reinforced composite were prepared, and tensile test was carried out. As a result, the continuous fiber reinforced material exhibited tensile strength of about 7 times and elastic modulus about 5 times that of the other two materials. The strength was greatly improved by using the continuous fiber. The fracture surface after the test was observed using a scanning electron microscope. The result of observation shows that adhesion between the laminated layers and the relationship between the fiber and the matrix are bad, and improving these are necessary to increase strength. Comparing those materials, it is possible to improve the strength in some degree by using short fiber while maintaining ease of printing. On the other hand, by using continuous fiber it can be achieved significant strength improvement while printing was complicated.”

The fracture surface of PLA/MWCNT

To make their PLA/MWCNT nanocomposite, the researchers used polylactic material as a matrix, with MWCNT as a filler, and formed the material into a 1.75 mm filament. They used commercial ONYX, carbon fiber, and NYLON materials from Markforged to 3D print tensile test pieces from continuous carbon fiber reinforced thermoplastic (continuous CFRTP) and short carbon fiber reinforced thermoplastic (short CFRTP).

“The specimen shape is different due to the limitation by the performance of the 3D printer,” the researchers wrote in the paper. “For PLA/MWCNT, smaller one was chosen to avoid warp and print quickly. The PLA/MWCNT has three outer walls and fills inside alternately at 45 degrees and -45 degrees.”

For the continuous CFRTP, carbon fibers oriented in the load direction were 3D printed in the center, while the outside was covered with either neat resin or short fiber reinforced composite; this last was used to 3D print the short CFRTP in the same manner as the PLA composite had been fabricate.

The researchers completed a tensile test on the pieces, and used a scanning electron microscope to observe images of the specimen’s fracture surface. They also looked at their stress and strain.

“In PLA/MWCNT, the stress increased almost linearly until fracture,” the paper explained. “The breaking strain was about 1 ~ 2%, and no stress reduction was occurred. Compared with neat PLA, the elastic modulus was not greatly improved but the tensile strength was improved and increased by 48% when 1wt% of MWCNT is added. In that case, the tensile strength was 53 MPa and the Young’s modulus was 3 GPa. Until 1 wt%, the tensile strength was improved as more CNT is added, but strength was decreased when 3wt% was added. It is because the aggregation of MWCNT. The aggregations are considered to act as internal defects of the material.”

Aggregates and voids

When more MWCNT was added, the number of aggregates increased. The researchers found that the relationship between the fiber and the matrix, along with adhesion between the laminated layers, was not good – when these are improved, the strength will increase. Significant strength improvements can be achieved by using continuous fiber, but the 3D printing process is complicated, and it’s necessary to use modified equipment, such as a special nozzle. But short fiber is easier to print, and still offers some degree of improved strength.

“The short CFRTP and PLA/MWCNT are inferior in mechanical properties compared to the continuous. But they can be printed with conventional 3D printers without special modifying,” the researchers explained. “Especially the nanocomposites demonstrate its effect by adding a small amount. The mass concentration of fiber was 35.7 wt% for continuous CFRTP and 14.3 wt% for short CFRTP, but MWCNT was 3wt% or less. Generally, the smaller the amount of reinforcement, the more easy to print. In fact the PLA/MWCNT nanocomposite can be printed with commercially available 3D printer without special modified in this study. Continuous fiber and short fiber material should each have merits and demerits and should be used properly.”

The broken specimen (continuous CFRTP)

Co-authors of the paper are T. Isobe, T. Tanaka, T. Nomura, and R. Yuasa.

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