French Researchers Examine Heat Transfer & Adhesion in FFF 3D Printing

Researchers from Laboratoire de thermique et énergie de Nantes uncover some of the challenges in 3D printing versus thermoplastic injection, releasing the findings of their recent study in ‘Heat Transfer and Adhesion Study for the FFF Additive Manufacturing Process.’

Mechanical properties are often the topic of study today—from researching helpful additives to studying the influences of color, to issues with porosity, and far more—as users attempt to improve the functionality of parts. Adhesion between layers is a common problem, usually leading to further examination of technique and materials. In this study, the researchers focused on heat exchanges in an attempt to improve 3D printing.

Temperature remains one of the most important settings for users, leading to good quality and performance in printed parts—or in other unfortunate cases, major structural issues.

“To find precisely the limit of this optimal processing area,  the thermal history needs to be predicted accurately,” stated the researchers.

Polymer printability rules for FFF process.

With a better understanding of thermal factors, users may be able to avoid macro-porosities and adhesion problems. During FFF 3D printing, the following heat transfers occur:

  • Heat from the extruder
  • Convection cooling of filament
  • Exchanges between filaments
  • Heat from the support plates
  • Radiative losses
  • Heat from exothermal crystallization for semi-crystalline polymers

At least 6 different heat transfer phenomena are identified in the FFF process.

(a) Comparison of the heat transfer model existing in the literature of FFF process and (b) geometry for the 2D analytical model. Adapted from [7]

While controlling the 3D printing process with high temperatures, the researchers also reinforced PEKK materials with short carbon fibers. In the beginning of the experiment, however, the team used ABS due to ‘greater ease of implementation.’ An experimental bench was 3D printed on a CR-10 3D Printer from Creality3D for measurements of temperature, and then a simulation model was created via COMSOL Multiphysics® v5.4 for predicting temperature and healing.

Experimental bench showing the heated chamber for 3D printing of high temperature polymers and the infrared camera for temperature measurements.

Before printing, the authors customized the 3D printer in their lab, modifying the hardware so it would be able to attain the proper temperatures of up to 400°C.

“The extruder was changed, for a full-metal unit, with a water-cooling closed circuit system. A closed insulated chamber maintains the part in a 200°C atmosphere. It does not block the three translation moving system of the 3D printer  inside  the  chamber. Electronics and mechanical parts are kept   outside the chamber.  This heating chamber is mandatory for printing polymers like PEKK,” said the researchers.

Experimental set-up. A single filament wall was 3D printed. The pyrometer measures the temperature from the side in situ.

Geometry and boundary conditions used in the heat transfer model

The other specimen was a basic structure 3D printed with both ABS and PEKK, in the form of a 60×2.2×50 mm wall. For ABS, the researchers took qualitative measurements with a pyrometer, with quantitative measurements taken for both ABS and PEKK.

IR camera qualitative analysis for ABS.

“Because of the poor knowledge of the rheological properties,  the calculated degree of healing was found to be equal to 1 very quickly for ABS. However, this is the opposite for PEKK material, which reaches only a degree of healing of 0.45 after the cooling-down of the filament,” concluded the researchers.

“The  bench  was  designed to handle high temperature and future work will consist in studying deposition of PEKK more precisely,  and  also  for  carbon  fibers  reinforced  PEKK  with  different process parameters. The  short-term  perspectives  are  to  use  the  model  with  the  thermo-dependent  thermal properties, which were characterized in the  LTeN  laboratory  on  PEKK  polymer.”

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[Source / Images: ‘Heat Transfer and Adhesion Study for the FFF Additive Manufacturing Process’]

 

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3D Printing in Ophthalmology: Smartphone Slit-Lamp Adapter for Diagnostics

A trio of researchers from hospitals in Egypt and India recently published a paper, titled “Custom-made three-dimensional-printed adapter for smartphone slit-lamp photography,” about their work designing a custom 3D printed smartphone slit-lamp adapter for photography applications in ophthalmology. A slit-lamp consists of a high-intensity light source, used with a biomicroscope, that can be focused to shine light into the eye for examination of the anterior and posterior segments in order to diagnose many conditions, like macular degeneration, cataracts, corneal injuries, and a detached retina.

3D printed adapter fixed on eyepiece to refine the sizing.

Many people have smartphones these days, and they are being paired more often with 3D printing for diagnostic and imaging purposes, especially in the offices of eye doctors.

“Smartphone photography in ophthalmology has a wide variety of uses including examination with or without other examination tools such as slit lamp or condensing lenses,” the researchers wrote. “Smartphones can be used for fundus photography,[2],[3],[4] slit-lamp photography,[5] microscope-free anterior segment photography,[6] gonioscopy,[7] and more.[5]

3D printed adapters can help make these tasks more efficient, as they are a quick, low-cost option. Custom adapters are built for just one smartphone design and slit lamp, while universal adapters can be adjusted to fit many designs. There are pros and cons for each option, which is why these researchers chose to “combine the advantages of both approaches” for their 3D printed smartphone slit-lamp adapter.

Two copies of the blink 3D printed slit-lamp adapter (in gray and black ABS material) fixed to universal smartphone holders.

“It is built upon a commercially available part used in selfie sticks and tripods which is used to hold the phone,” they explained. “The rest of the adapter is designed and 3D printed to enable attaching the mobile with that holder to the selected eyepiece.”

Smartphone fixed on the Blink adapter and placed on slit-lamp eyepiece.

The goal was to make a design that complements different slit-lamps and automatically fits the microscope eyepiece that slides into the adapter; gravity, plus the weight of the smartphone, will keep it in place.  Then all of you have to do is place the phone’s camera against the eyepiece. The team named their creation Blink, for its “ease of use and quick adjustment like in a blink of an eye.”

After they chose their target slit-lamp microscope, the researchers used Vernier calipers to measure the eyepiece, and used the dimensions to create a CAD model of the adapter in Tinkercad. They refined the model using SketchUp, and prepared it for printing with Repetier software. The adapter was then 3D printed out of ABS material on a Rostock MAX v2 3D printer from SeeMeCNC.

Measurements of slit-lamp eyepiece being taken with digital Vernier calipers.

The 3D printed adapter was then fixed to the universal smartphone holder, and finally the fitting was “tested and refined to account for manufacturing tolerances.” Once the smartphone was placed in the holder, the device was attached to the slit-lamp’s eyepiece for easy imaging.

“The blink 3D-printed smartphone slit-lamp adapter was successfully designed, modeled, 3D-printed, and tested,” the researchers wrote. “Each type of slit-lamp eyepiece required a small modification in the 3D design based on measurements. Good-quality images could be captured in diffuse, slit, retro, and cobalt-blue illumination.”

The time it took to remove and modify the device was only seconds, which makes the 3D printed adapter very useful in slit-lamp photography.


“More units can be easily made by printing the same CAD file and fixing it to the universal smartphone holding bracket,” the researchers noted.


Additionally, the team confirmed that they could image the fundus – the part of the eyeball opposite the pupil – using a 90D lens.


“Our article describes the process of designing and building a smartphone slit-lamp adapter to solve the problem of slit-lamp photography,” the researchers concluded. “The cost of 3D printing a small part such as the adapter described here is small and can be done at a 3D printing shop which is available in all major cities in India, Egypt, and many other countries. Most of the work involved is in designing the CAD model according to measurements and physical constraints.

“Development of this type of innovation from idea to virtual design to hardware does not need much time or money – only an innovative mind and the drive to learn these new techniques.”

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Analyzing Parameters of Pure and Reinforced 3D Printed PLA and ABS Samples

If you want high-quality 3D printed parts, then you need to choose the right print parameters. Research on this topic is ongoing, and the latest comes from the University of Manchester. Chamil Abeykoon, Pimpisut Sri-Amphorn, and Anura Fernando, with the Northwest Composite Centre in the Aerospace Research Institute, published “Optimization of fused deposition modeling parameters for improved PLA and ABS 3D printed structures,” about their work studying various properties and processing conditions of 3D printed specimens made with different materials.

There are multiple variables involved in 3D printing, and changing just one parameter could cause “consequential changes in several other parameters” at the same time. Additionally, the most commonly used FDM printing materials are thermoplastic polymers with low melting points – not ideal for “some high performance applications.”

“Therefore, attempts have been made to improve the properties of printing filaments by adding particles such as short-fibres, nanoparticles and other suitable additives [18]. Thanks to these extensive researches and developments in the area of FDM, fibre-reinforced filaments are becoming popular and are currently available for practical applications,” they explained.

In order to optimize parameters and settings for these new reinforced materials, the team says we need more 3D printing research and development. In their study, they investigated the process using seven infill patterns, five print speeds, and four set nozzle temperatures, and observed and analyzed the mechanical, thermal, and morphological properties.

They used five commercially available materials, with 1.75 mm diameters:

  • Polylactic acid (PLA)
  • Acrylonitrile butadiene styrene (ABS)
  • Carbon fiber-reinforced PLA (CFR-PLA)
  • Carbon fiber-reinforced ABS (CFR-ABS)
  • Carbon nanotube-reinforced ABS (CNT-ABS)

The samples were designed with SOLIDWORKS and printed on a MakerBot Replicator 2, MakerBot Replicator 2X, and MakerBot Replicator Z18.

3D CAD images of test specimens: (a) Tensile, (b) Bending, and (c) Compression.

The team studied seven infill patterns – catfill, diamond, hexagonal, Hilbert, linear, moroccocanstar, and sharkfill –  and infill densities of 25%, 30%, 40%, 50%, 70%, 90%, and 100%. Two shell layers were used for all samples, and the print bed temperature was between 23-70° for CFR-PLA, and 110°C for the three types of ABS material, to help reduce shrinkage and warping.

“At each test condition of all the types of tests (mechanical, rheological and thermal), 3 test specimens were prepared and tested, and then the average value was taken for the data analysis to improve the accuracy and reliability of the experimental data,” the team wrote.

Appearance of the printed compression test specimens: (a) PLA, (b) ABS, (c) CFR-PLA, (d) CFR-ABS, and (e) CNT-ABS.

First, the 3D printed samples underwent mechanical testing to determine tensile modulus, flexural modulus, and compression properties. Using differential scanning calorimetry (DSC), the researchers measured melting and crystallization behaviors in a liquid nitrogen atmosphere, and found “the volume fractions of the reinforcement and matrix of the composite filaments” with the help of thermal gravimetric analysis (TGA).

Appearance of printed tensile test specimens: (a) PLA, (b) ABS, (c) enlarged view of PLA, and (d) enlarged view of ABS.

Using a thermal imaging camera, they detected how much heat was released as the figure above was printed with 100% infill density, 20 mm/s infill speed, and 215°C set nozzle temperature. Finally, they used scanning electron microscopy (SEM) to observe and perform morphological testing on the surfaces of the 3D printed specimens that were broken during mechanical testing.

Infill density affects the strength of 3D printed parts. By increasing infill density, you then increase the tensile modulus and decrease porosity, which increases the “strength of the mechanical bonding between layers.”

Relationship between tensile modulus and infill density for PLA.

“For pure PLA, parts with 100% infill density obtained the highest Young’s modulus of 1538.05 MPa,” the researchers note.

But, structure gaps can occur more frequently with low infill densities, which reduces part strength. In the figure below, you can see “the changes in porosity of the structure with the infill density.”

3D printed specimens with infill densities: (a) 25% (b) 50% and (c) 100%.

“Of the tested infill speeds from 70 to 110 mm/s; 90 mm/s infill speed gave the highest Young’s modulus for pure PLA,” they wrote.

Print speeds over 90 mm/s could cause polymer filament to melt, and result in poor adhesion and lower strength. To avoid this, the print speed must be compatible with the set nozzle temperature, and an appropriate combination of speed and set nozzle temperature “can reduce the shrinkage of the parts being printed.”

Relationship between tensile modulus and infill speed for PLA.

3D printed PLA samples were tested with the different infill patterns at 50% infill density, 90 mm/s speed, and 215°C set nozzle temperature.

3D printed samples with infill patterns: (a) Linear, (b) Hexagonal, (c) Moroccanstar, (d) Catfill, (e) Sharkfill, (f) Diamond, and (g) Hilbert.

“Among these seven patterns, the linear pattern gave the highest tensile modulus of 990.5 MPa. This can be justified as the linear pattern should have the best layer arrangement (in terms of the bonding between the layers) with the lowest porous structure,” the team explained.

They found that the print temperature has “a significant effect on the tensile modulus.” 215°C provided the best tensile performance, as lower temperatures might cause poor melting, and thus weak bonding. The set nozzle temperature and print speed correlate, and “should be chosen carefully based on the material being used and the part geometry being printed.”

To study the effect on tensile properties, they were printed with the following parameters: 90 mm/s infill speed, linear pattern, 10% infill density, and 215°C set nozzle temperature for PLA, and 230°C for ABS. The researchers found that the tensile modulus of pure PLA (1538.05 MPa) was far higher than for pure ABS.

“In this study, CFR-PLA gave the largest tensile modulus of 2637.29 MPa while pure ABS (919.52 MPs) was the weakest in tensile strength,” they wrote.

Tensile modulus of the five printing materials.

Reinforcing ABS and PLA with fiber causes higher tensile modulus, though pure PLA was stronger than the CNT-ABS.

Even at 90° of bending, the PLA and ABS samples only had a small crack in the middle, and did not break.

3D printed specimen in bending test.

At 1253.62 MPa, the CFR-PLA had the highest bending modulus, while pure PLA was the lowest at 550.16 MPa.

During compression tests, none of the materials were crushed or broken, and pure ABS was found to be the toughest.

“As evident, pure PLA gave the highest compressive strength while the compressive modulus of CFR-PLA (1290.24 MPa) is slightly higher than that of pure PLA (1260.71 MPa) (higher gradient of the liner region). CFR-ABS and CNT-ABS follow the same trend but CNT-ABS is slightly tougher than CFR-ABS,” the team explained. “Pure ABS shows the lowest compressive strength and modulus (478.2 MPa) but shows the most ductile behavior of the five materials.”

Compressive stress-strain curves of test materials.

Finite element analysis (FEA) by ANSYS was used to visualize stress distribution for the tensile, bending, and compression testing of PLA.

Equivalent stress distribution for tensile test.

“The stress distribution shows that a uniform stress is created in the gauge length of the test piece,” they explained.

“Higher compressive loading will cause the material to have internal crack initiations thereby allowing the PLA to buckle excessively.”

The team concluded through DSC analysis that “the strength of the 3D printed samples is dependent upon the set printing parameters and the printing materials more than the crystallisation.” While the infill speeds differ, the glass transition temperature (Tg) of the samples were similar.

“In this study, cooling of 3D printed parts occurred naturally by releasing heat to the surroundings while printing without any control on the cooling rate,” they stated.

DSC curves of PLA parts printed at different set nozzle temperatures.

As expected, the set nozzle temperature did not significantly effect the Tg, and material crystallization at different temperatures didn’t really affect part strength. But, the tensile modulus did change with the temperature.

TGA was used to analyze the weight loss variation of the composite materials against increased print temperature.

TGA diagrams of short fiber-reinforced composite filaments.

“Degradation temperatures (Td) of these materials can be determined from the mid-point of the descending part of each curve, which is approximately 331.85 °C for PLA. This value showed some sort of agreement to the value reported in commercial PLA data sheets – 353 °C,” they wrote.

Pure PLA typically has a higher Young’s modulus than pure ABS, so it can help to add “a higher volume fraction of reinforcement into the ABS matrix.” Brittle CFR-PLA and CFR-ABS filaments could have their flexibility affected if more carbon fiber is added, which can cause filament feed issues.

Thermal image during 3D printing.

An infrared thermal camera was used to observe 3D printing. The yellow area is the brightest, and hottest: this is where the polymer was extruded from the nozzle. The color changes to orange where the material starts to solidify, and the “red, pink, purple, and blue areas are at lower temperatures, respectively.” The red circle marks the temperature at the printer wall – less than the sample actually being printed.

“SEM images showed that the strength of the printed samples was dependent upon the arrangement of their layers,” the team noted.

Normal and SEM images of fracture surfaces of PLA samples: (a) 25% and (b) 100% infill density.

Observing the fracture surfaces of broken PLA samples with SEM showed that “the air gaps of 25% infill density sample is larger than that of 100% infill density.”

Looking at infill speed with SEM, the team noted that “the best orderliness” comes from 90 mm/s infill speed.

Incompatibility between the material matrix and the reinforcement can cause porosity in the 3D printed samples, but the latter can “contribute in increasing the mechanical properties by bearing the load.” You can see below that the pure PLA has a more regular layer alignment when compared to pure ABS.

SEM images of 3D printed parts at 19X magnification: (a) PLA, (b) ABS, (c) CFR-PLA, (d) CFR-ABS, and (e) CNT-ABS.

CFR-ABS is more porous than CFR-PLA, and both are rougher than the materials in their pure forms.

“Meantime, CNT-ABS shows a better arrangement of individual layers than the other two carbon fibre reinforced materials and also than the pure ABS as well,” they explained.

The last SEM images compare the size of the carbon fiber and carbon nanotube reinforcements. The fracture surface of the CNT-ABS shows some small holes, “due to the embedded carbon nanotubes in the matrix.”

“Compared to the matrix-reinforcement compatibility, both materials show some sort of incompatibility by having cracks and voids between the fibre and matrix,” they wrote.

“On the other hand, although the overall strength of CNT-ABS is improved by CNT particles, the flexibility of this material was decreased compared to the pure ABS as CNT-ABS being more brittle.”

SEM images of fracture surfaces at 1.00 KX magnification: (a) CFR-PLA and (b) CNT-ABS.

They found that the optimal settings to improve the performance of the five 3D printing materials were 100% infill density, 90 mm/s infill speed, 215 °C of set nozzle temperature, and linear infill. Of the five materials, CFR-PLA had the strongest tension, bending, and compression, with the highest modulus.

Overall, it is obvious that the set printing parameters can significantly influence the mechanical properties of 3D printed parts. It can be claimed that the printing speed and set nozzle temperature should be matched to ensure proper melting of filaments and also to control the material solidification process,” the researchers concluded.

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Researchers Create Low-Cost 3D Printed Polarimeter for Use in Chemistry Classrooms

The adoption of 3D printing in the classroom has opened up new horizons for creating teaching tools. Science teachers, in particular, can make personalized models of nanostructures, and educational tools like colorimeters. But there haven’t been any 3D printable designs for polarimeters, which measures the angle of rotation of polarized light once it’s passed through an optically active solution or substance. Paweł Bernard from Jagiellonian University and James D. Mendez from Indiana University – Purdue University Columbus published a paper about their creation of a low-cost 3D printed polarimeter.

“3D printing and simple electronics were used to create a polarimeter suitable for a variety of chemistry courses,” they wrote. “This device allows instructors to demonstrate optical activity but is also easy to use and low cost enough to be widely available for student use, as well. The instrument uses an LED light source and detector housed in a 3D-printed base. By rotating the top piece, users can visually detect changes in brightness or measure this directly with a multimeter.”

A polarimeter consists of a sample chamber, monochromatic light, and a polarizing filter before, and a rotatable one behind, the sample. This second filter can be adjusted to the angle of the rotated light, after it’s passed through a sample, in order to “minimize or maximize the transmitted light.”

Basic polarimeter schematic and working theory.

High school and college teachers normally demonstrate the optical activity of substances using overhead projection, as most regular polarimeters are too expensive for use in a school laboratory setting. One researcher created a no-cost polarimeter using sunglasses and a mobile phone, which was good for demonstration purposes, but not for student experiments. Another inexpensive polarimeter was made using a shoebox, but it wasn’t durable enough.

“Therefore, the use of 3D printing technology is a perfect solution,” the researchers stated. “The body of a polarimeter can be printed in a reasonable time; the price of the plastic and electronics is low, and the actual assembly of the elements is relatively simple.”

3D printed polarimeter schematic.

A basic polarimeter can use either a test tube or 3D printed cuvette, and light detection can be merely eyeballed, or precisely measured with a low IR radiation sensitivity photodiode. Both are compatible with low-voltage, inexpensive LEDs; the RBG diode at the bottom can be plugged into a 4.5 or 5 V battery, or a standard 9 V battery can be used with a simple circuit.

9 V power supply circuit schematic.

“In the construction, two layers of polarizing filters (polarizing film) are used. It is a low-cost, commercially available material, used for the construction of 3D glasses among other things,” Bernard and Mendez explain. “Our experience shows that it is easier to identify the lowest (rather than highest) intensity of the light passing through the sample; therefore, we advise arranging two layers of polarizing film rotated by 90°. In such a setup at neutral position (0° angle) without a sample, or with a sample of optically nonactive substance, it is dark, showing the lowest light intensity. 

“The construction of the device using a test tube as a sample container is simpler but also more problematic in use. The bottom of a test tube scatters the light. Usually, the center of the light spot is darker, but there is an unpolarized light ring around it.”

A test tube does not ensure a complete blackout at the minimum light point, so a 3D printed container with a flat bottom is useful. The researchers 3D printed the elements out of ABS and PLA filaments, which were black to ensure stable light readings. PVA supports and a dual extruder printer were used to 3D print the rotary cup and main body.

(a) Operating 3D printed cuvette polarimeter with photodiode detector at zero position (minimum signal); (b) operating 3D printed test tube polarimeter (maximum signal); (c) operating 3D printed test tube polarimeter (min signal); (d) operating the 3D printed cuvette polarimeter (max signal); (e) operating 3D printed cuvette polarimeter (min signal).

The researchers tested 50 high school chemistry students in Poland and 15 organic chemistry university students in the US on taking measurements with the 3D printed polarimeter. Working in groups of 2-3, they ran measurements with pure liquids first, and then aqueous solutions. It’s quick and easy to use – the students can change samples and adjust a cap rotation in less than a minute, though they must be told which way to rotate the tool for different substances as “the device gives the same readings in both directions (90° = −270°).”

“It is also advised to adjust the concentration of the sample solution and path length so that the readings are in the range of the provided rotation scale (from −180° to +180°). Using measured rotation and simple mathematical relations, students can calculate a substance’s specific rotation,” the researchers said.

The students used (R)-limonene, fructose, and sucrose, and ran initial measurements both visually and with the 3D printed polarimeter, which allowed them to take measurements with three colors thanks to its RBG diode. They made 4 to 6 measurements for a sample and after dilation for the aqueous solutions.

“The results were a starting point for a discussion on optical rotatory dispersion phenomena. Calculating the specific rotation of the substances was homework, verified by the teacher during subsequent classes,” the researchers stated.

Measured rotation for aqueous solutions of sucrose in the concentration range of 0.05–0.35 g·mL, a series for red, green, blue light measured with a 3D printed polarimeter, and accompanied by results from commercial polarimeter with a sodium lamp 589 nm.

In another project, instructors prepared kits with all of the materials needed to assemble the polarimeter, including breadboards and the 3D printed body. 16 chemistry majors in Poland and four US undergrad students constructed the device, working in pairs, and none had previous experience using breadboards or building measuring devices. But they followed detailed instructions, with some help from teachers, and succeeded in building operational polarimeters in less than one hour.

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Safety Suggestions for 3D Printing Medical Parts at Home: FDM Polymers

This does not constitute medical advice or indeed is meant to convey any particular indication that it would be safe to print medical parts at home. In a moment bereft of optimal choices however people are printing medical and ancillary medical things at home using desktop FDM systems. In order to make this safer, we’ve penned a number of articles encouraging you to do no harm, some safety suggestions on your print room setup and how to keep it clean and the relevant safety guidelines available including if you’ll print what category of items you’ll print. GMP plus the right materials and certifications is the only way to safely make a medical product or a quasi-medical product. If you print irresponsibly or cough on a face shield that you give to a hospital you may, in fact, kill someone who would have lived without you face shield. Please be careful.

Cleaning

1, Parts should be cleaned with soap and water. This is a guide on cleaning for COVID.

Disinfectant 

2. Subsequently, you can disinfect them. This is a list of EPA approved disinfectants. You should make sure that you yourself are clean and wearing gloves before doing this step. A newly washed apron, gloves, mask, and a face shield should be worn before disinfecting. All surfaces should be cleaned and disinfected before doing this step. Do not eat, drink, let people or pets in the room before this step.

Sterilization

3. Sterilization is a required step. There are a number of different processes that can all kill the living things that will inhabit your parts. Here is a quick guide, here are the CDC guidelines on sterilization and this is a practical guide.

Autoclaving

Autoclaving is the most common form of sterilization for a lot of polymer 3D printed parts. This gives you a good overview. Essentially your parts are sterilized under pressurized steam at around 121C. Immediately you’ll know that PLA won’t fare well under these conditions. These parts will often delaminate and fail.

In fact, most FDM materials do not fare well when autoclaved as their heat deflection temperatures are too low. Materials such as PPSU/PSU/PPSF are good candidates for autoclaving and can be exposed to repeated cycles. Their print temperatures range in the 380C range and 100C bed temperature however and this is beyond the reach of many desktop machines. The material is also around $380 per 500g or $216 per 500g, depending on approvals and the vendor. You could also consider materials such as PEEK or PEKK which also are expensive and high performance. PEI also withstands repeated cycles. PEEK is very difficult to print, PEKK and PEI are generally easier. To process these materials well you will have to have a highly modded printer or a high-temperature printer with a nozzle print temp of 400C, bed temp 100C and chamber temperature of 100C.

ABS is generally not a good candidate for autoclaving and ABS parts often fail in the autoclave. All other materials not mentioned here are also not good. This is a guide specifying which polymers are good candidates for the autoclave.

Should you wish to go the low-cost route then Polypropelene is also an alternative. Some polycarbonates could work but parts may warp and strength is reduced. Stratasys’ PC-ISO material is a good candidate for autoclaving. Polyamide filaments (but only really PA6) can, in a limited way, be autoclaved and are more accessible. POM (Acetal) is a risk in terms of fumes but with sufficient industrial ventilation could be managed. I personally wouldn’t print POM at home even with an enclosed system, filters and good ventilation.

WARNING: Please never 3D print PVC filament, it is too high risk to use, even in an industrial setting with HVAC and high safety standards. Fumes are highly toxic and dioxins may remain on your printer or on parts. There is no safe way to 3D print PVC. 3D printed PVC parts may have highly toxic dioxin residue on or in them. Here are articles on dioxins and PVC and thermal decomposition and in fires. During the 3D printing of PVC: hydrogen chloride may be released, cancer causing PAH’s may be released, as may toxic and carcinogenic dioxins.

Never use CF or GF or carbon nanotube or carbon black filaments for this application and try for the natural color if possible. Please note that even natural color filaments do often contain undisclosed not MSDS listed processing additives but generally no colorants. Please purchase filaments with the relevant approvals.

Other Options 

Typically the users will have their very own processes and adhere to them. There are some other options as well. Prusa has done a great job on identifying them for their face shield designs. They’ve found that for their shields autoclaving specifically will deform them. With some different materials this may not be the case. I’d always go with a part that can work in an autoclave. This is a readily available sterilization technology.

Also, the nice thing about an autoclave is that it is a very well understood, widely practiced, reliable technology. For the other methods above the processes could be less controllable. So design parts that work in materials that work in an autoclave, If this is impossible then I’d move to other sterilization methods.

What is encouraging for parts made in the home for the home or for you sterilizing a mask before you give it to your brother for example, is that a 5 minute bath in IPA seems to do the trick. Bleach could also be a solution. This means that with care, there are methods by which you could do a rudimentary sterilization at home. Now rudimentary sterilization is a bit like saying you’re half pregnant. Especially with cleaning, disinfecting and sterilizing we want to be incredibly careful.

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3D Printing for COVID-19: ID Badge/Door Opener from 3D LifePrints UK

A number of small companies are attempting to support the supply shortages being faced by hospitals in the face of the COVID-19 outbreak and provide new devices that can reduce the potential risk of contamination for medical professionals. Meanwhile, some large manufacturers that might be deployed for a massive World War Two-style production effort are not stepping up or being government mandated to provide production capacity. In fact, they are even laying off staff in the midst of a health crisis that has also become an economic crisis. (See our comments about GE worker protests in a previous article for an example.)

One such small firm lending a hand to the supply shortages is 3D LifePrints UK, an additive medical device manufacture specialist that makes such items as implants for craniofacial surgery, surgical guides and pre-surgical models for National Health Service trusts, medical device companies, research institutions and others in the U.K., Europe and around the world. 

3D LifePrints has been asked by a number of medical institutions to investigate and provide prototype designs for personal protection equipment (PPE) such as Facial mask connectors, mounts for ICU devices that are being moved into other venues, and a simple 3D printable device called the “Distancer.” This last item makes it possible for healthcare professionals to open a door or swipe an ID card without the need to touch potentially contaminated surfaces. 

“A doctor goes through a door up to 150 times a day in a hospital. The phrase we hear all the time is ‘the doors are like lava.’ The surface retention of COVID-19 is quite high on stainless steel and plastic,” founder and CTO Paul Fotheringham said.

Fotheringham explained that, in addition to the regular protocol for which hospital employees use their IDs, presenting proper identification in healthcare facilities is necessary to prevent the theft of supplies by hospital staff. 

To ensure the maintenance of proper protocol and prevent the spread of the virus, 3D LifePrints UK and the Alder Hey NHS Foundation Trust designed a 3D printed device that can hang off a keychain or lanyard and allow for the slide insert of a user’s electronic ID card. The Distancer features a handle so that the user does not have to touch the actual card, a hook that allows users to open a door, and a flat end for pushing doors closed. 

The company is 3D printing the items from materials that will not deteriorate during the cleaning process, which is essential for items that have exposure to COVID-19: nylon PA 12, ABS or anti-microbial PLA that includes an embedded nano-copper additive. It is available in two designs, either flat-packed with living hinges and one-click assembly, which could be mass produced with injection molding, or a 3D printed version.  

The 3D printed Distancer from 3D LifePrints UK. The file is available for download on the company website. Image courtesy of 3D LifePrints UK.

3D LifePrints is in the process of producing and delivering 4,000 Distancers to NHS hospitals at the moment, while it designs and evaluates other items. The firm is also working with the NHS to develop a specialty connector that can join an off-the-shelf scuba mask to an anesthesia filter that results in a respirator-style device for clinicians (not patients). This is in contrast to the CPAP-type device being developed in Italy using masks from Decathlon. The device is currently being evaluated with the NHS, but it is promising due to the fact that the scuba mask is form fitting and sealed against the face with rubber in a way that is required for the safety of clinicians.  

Fotheringham stressed that 3D LifePrints didn’t simply begin making supplies for the U.K.’s medical facilities out of the blue, but is acting on specific requests from the NHS and British hospitals and is working with medical partners to ensure the safety of the devices, while it is his firm’s job to design, iterate and produce the parts to the needs and specifications of the medical professionals. 

Typically, these devices would require significant clinical testing and approval from the proper regulatory bodies, but due to the emergency nature of the current public health crisis, devices that have not yet received certification are being fast-tracked for approval. 

Other considerations being taken into account are the specific production technologies and materials used to produce parts. More common and less expensive material extrusion printers, for instance, are known to make items that are more porous and have rougher surface finish than those made with selective laser sintering and other polymer powder bed fusion technologies. This reduces the chance for bacteria developing in hidden crevices and makes the parts easier to clean. 

As for materials, the company is focusing on the ability of plastics to withstand the use of chemical disinfectants to minimize the degradation of the part over time. In this case, PLA (the most common polymer used in desktop machines and made from corn starch), is not ideal. However, polypropylene, from which 3D LifePrints intends to injection mold its Distancer, is more durable and can sustain repeated cleanings. 

Fotheringham urged 3D printing enthusiasts and experts to use caution and proper time management when volunteering to combat the COVID-19 supply crisis. He suggested that these devices should be made in conjunction with medical professionals to ensure proper protocol is followed. One way would be to use official channels such as the FDA in the U.S., who we have reached out to in order to learn more about the safety of 3D printed medical devices made in response to the public health crisis. We will cover this topic in greater depth in a follow-up article.

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New ABS/HDPE FFF Blend Gets Stronger with Time

Plastic pellets for injection molding exist in a much wider variety than 3D printing filaments, thus offering the potential for a much greater range of applications.  At the same time pellets are, at the moment, significantly less expensive than filament. There are a small number of pellet-extrusion 3D printers on the market, but the fact that there are not more is somewhat surprising. One team of researchers from Massey University in Auckland, New Zealand is performing its own work to change things.

Previously, the group—led by Khalid Mahmood Arif, Senior Lecturer in Mechatronics and Robotics from the school’s Center for Additive Manufacturing—developed a micropellet extruder for 3D printing. The researchers went further than creating the technology and even characterized for strength, surface quality and consistency of the parts that it made.

The group’s upgraded extruder design.

The team is continuing its work by developing and characterizing new materials for the 3D printing system. Most recently, Arif, et al. published an article in Materials and Manufacturing Processes discussing a new combination of ABS/HDPE for use in their micropellet extrusion 3D printer, resulting in a printed material that actually grew stronger as it aged, beating out some of the stronger polymers in desktop and industrial FFF 3D printing.

In the paper, titled “Preparation and characterization of thermally stable ABS/HDPE blend for fused filament fabrication”, the authors describe the advantages and drawbacks of both ABS and HDPE. As many of our readers may know, ABS is nearly ubiquitous in desktop 3D printing, for its tensile strength, ability to deform without breaking, ability to repel water and other features that make it suitable for a wide variety of applications. HDPE, on the other hand, is a very difficult material to print and is rarely used.

ABS good qualities degrade as ABS is exposed to temperatures over 40°C. In an attempt to preserve these desirable mechanical properties, the researchers decided to blend the plastic with high-density polyethylene (HDPE), which demonstrates good thermal stability when blended with other polymers. Required in the mix was a polyethylene graft maleic anhydride (PE-g-MAH).

The team made a variety of combinations of the materials, settling on one after others proved unprintable. Arif, et al. also had to modify its micropellet extruder by adding a liquid cooling system, which prevents uncontrolled heating inside of the extruder, resulting in a uniform extrusion temperature. In order to ensure the printability of the final mixture, they had to apply some tape to the printbed.

Once the proper blend was achieved, tensile, compression and flexure samples were printed according to ASTMD and ISO standards. They also tested printability under various temperature regiments, with extrusion temperatures ranging from 185°C to 205°C and bed temperatures ranging from 25°C to 75°C. In addition to physical tests, the authors performed visual and machine analysis of the printed material that included fourier transform infrared spectroscopy, differential scanning calorimetry, thermogravimetric analysis and scanning electron microscopy (SEM).

The results of the study were actually quite striking. According to the authors, the ABS/HPDE blend not only demonstrated good thermal stability, but it actually got stronger with time. Moreover, the authors claim that, based on research regarding other durable 3D printing materials and processes on the market, the flexural strength of their blend might be the strongest. In particular, they said that an aged blend of ABS and HDPE had a greater flexural strength than ABSPlus from Stratasys and polyamide 6 with carbon fiber reinforcement from Markforged.

“As compared with literature, the ultimate compressive strength of 162 MPa achieved for 6 days aged samples is one of the highest in FFF to date, to the best of our knowledge,” the authors wrote.

The authors concluded with these three takeaways:

  1. “The blend has one of the highest mechanical proper- ties among the existing FFF blend materials. The tensile strength is the second highest, flexural strength and compressive strength is the highest among existing literature on blends for FFF.
  2. The aging has significantly increased the mechanical strength (tensile, flexure, and compressive) instead of degradation. This shows the thermal stability at high temperatures.
  3. Thermal aging has improved the cold crystallization as observed in DSC. This heterogeneous crystallization has improved the diffusion among beads during 3D printing that leads to improved properties.”

The research team did not discuss the feasibility of such an ABS/HPDE blend in filament form, nor any plans for commercialization.

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Reinforcing Concrete Fabric Formwork with 3D Printed Plastics

In the recently published ‘Tailored flexibility: reinforcing concrete fabric formwork with 3D printed plastics,’ authors Jon Engholt and Dave Pigram create a construction system integrating robotics and new techniques. The study focused on concrete because of its flexibility, while pointing out that this material is still somewhat limited—thus explaining why flat forms are still so often used routinely while curved structures are avoided. Flexible materials offer great potential for improving the structure of buildings, however.

3D printing, accompanied by robotics capable of plastic extrusion, can outweigh some of the previous challenges often connected to fabric framework. This also includes benefits like added options for forms and surface qualities, with plastic working to reinforce material and performing as a design medium too. Concrete is usually cast in molds, and curves are typically considered hard to achieve, leaving users to turn to materials like timber; however, wood and milled foam generally result in significant amounts of waste.

a. Wall by Kenzo Unno (Copyright: Kenzo Unno) b. Facade by Miguel Fisac
(Copyright: Miguel Fisac Foundation) c. P_wall by Matsys Design (Copyright: Andrew Kudless).

“Fabric formwork addresses some of these issues as a sustainable alternative to traditional formwork, utilised as both a means to reduce material use in formwork and a means to realise more complex and structurally efficient forms,” state Engholt and Pigram, also pointing out that there have been strides made with CNC 3D knitting, although the techniques are still somewhat limited.

For this research, they performed numerous tests, including matching extrusion and fabric material, tuning the print technique, and then dealing with the composition of concrete. They also detoured to compare 3D plastic printing to that of fabric frameworks and ‘the logic of tensile shuttering.’ The set up for this experiment consisted of a large-scale plastic extruder mounted on a KUKA 7-axis robotic arm, using ABS. The authors tested numerous fabrics:

“The textural quality and resolution of the fabric presented one variable that suggests perfect conditions for mechanical adhesion of extrusion material by partly penetrating the fabric,” explained the researchers. “The coarse resolution of both tulle fabric and geotextile weaves suggested a sufficiently uneven surface for adhesion.

“However, due to the material composition of these fabrics (tulle made of polyester and geotextile of polypropylene), the chemical bonding properties appeared to be the primary means of adhesion, preventing the extrusion material to bond with the surfaces.”

During the cooling process, the researchers discovered that ABS shrank while cooling, causing warping, and transformation in fit. The problem continued further as printing went on, with the plastic becoming ‘irregularly warped.’ As they experimented with PLA, the researchers found that they were able to get shrinkage under control, but then experienced decreased tensile strength and even brittleness.

“These issues with material strength and shuttering flexibility suggest further studies into printing media with different mechanical properties,” stated the researchers.

Initial casting evaluated shuttering of fabric and plastic extrusion, along with the weight of the concrete. The authors stated that the toolpath generation approach was abandoned; however, they did note that the discrete part toolpath generation permitted structural considerations to become part of the process.

a. Printed shuttering in rigid frame b. Shuttering before demoulding c. Concrete cast.

“The limited strength of the plastic thus introduced two resolutions of support: An overall distribution of clamps and a finer-resolution mesh of printed material – both of which had a finite limit in scale to prevent collapse. Printing bespoke ‘pinch-mould’ details to block out the shuttering and locally create openings through the casts mainly relied on the rigidity of the two clamped sides rather than adhesion and tensile strength – and thus proved efficient.”

a. Printed shuttering b. Fabric shuttering with cast c. Concrete cast.

Because the plastic was so limited, the researchers found two new ‘resolutions of support’ in the distribution of clamps—plus, finer resolution mesh of printed material. Overall, they discovered ‘a vast space of possibilities’ with a small number of variables.

“The process thus affords a high complexity in material manifestation through a low complexity in formal operations and design. Since the flexibility of the tailored shuttering allows it to adapt and attach to non-flat geometries, the process suggests a combination with bespoke bent rebar reinforcement that might offer enough rigidity to avoid any additional formwork components,” concluded the authors.

3D printing encompasses numerous elements, beginning with hardware; however, the study of materials and resulting form is critical—and as the choices continue to expand, users can experiment widely, from the use of different thermoplastics to metal composites, and other alternative materials. 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.

Small selection of combinations of tile designs and pixel distributions

Intersections: a. Horizontal overlap b. Vertical overlap c. Crossing d. Clamp
opening.

[Source / Images: ‘Tailored Flexibility: Reinforcing concrete fabric formwork with 3D printed plastics’]

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Basalt Fiber-Reinforced ABS: Researchers Develop Thermoplastic Composite for Use in Space

In the recently published ‘Development and Mechanical Properties of Basalt Fiber-Reinforced Acrylonitrile Butadiene Styrene for In-Space Manufacturing Applications,’ we learn more about materials necessary for building in space; for example, a habitat on Mars would most likely be built out of a combination of materials from Earth as well as what is naturally found there, cutting expenses exponentially.

As technology progresses, we realize that space travel and colonizing will mean extreme measures in sustainability. As the reality of a NASA mission to Mars looms, there are years of preparation ahead, along with enormous research and development efforts required to figure out logistics and countless details. Materials science will figure in predominantly though as it is critical to areas like aircraft maintenance and more, but also colonization.

The researchers list the most important features for space material:

  • Strength
  • Stiffness
  • Impact resistance
  • Ability to shield from radiation

For the near future, the research team decided to develop and test a thermoplastic composite, mixing both acrylonitrile butadiene styrene (ABS) and basalt for testing at the Additive Manufacturing Facility at the International Space Station. During this study, one of the main considerations was the expense for transporting materials, leading to a strong focus on how much local material would be available and could be used.

“The most reasonable alternative is to use as much locally available material as possible along with any recyclable waste from cargo missions, such as packaging materials,” stated the researchers. “This is different than traditional composite material design, in which there is an optimization between the amount of reinforcing fibrous material that strengthens the material and cost of the fibrous materials.”

(Left) Dreytek 3 mm basalt fibers, (Right) Basalt fibers and ABS pellets premixed for compounding.

3D printing in space has gone from a concept to a reality as astronauts have been fabricating test items, tools, and more at the ISS. Test samples sent back to Earth have been reviewed and evaluated as successful, with a 3D printer now installed at the ISS permanently.

In examining the materials found on Mars, the researchers remind us that this smaller planet has a surface not unlike the crust found on Earth. Fine particles and basalt cover a volcanic rock layer around 6 to 30 miles thick. Basalt fibers can be made in a similar fashion to the manufacturing of glass fibers and then used for reinforcement. Previous research has shown basalt mixed with PLA quite successfully, but these projects were not centered around space travel and colonization.

The composite developed for this study was used with FFF 3D printing, in the form of a FlashForge Creator Pro 3D printer and 1.75mm filament. Five ratios were fabricated, and four were 3D printed in the end. Basalt can be easily mined and made into fibers, and while there were several choices of material to mix it with, the research team chose ABS because of low extrusion temperature and previous testing in microgravity experiments. It can be recycled too, and even used as packaging for other cargo.

The filament manufacturing extrusion process (a) Single-screw extruder (b) Extrudate puller (c) Spooler (d) Spooled ABS-basalt filament.

Composite pellets were created for each fiber ratio, with accompanying 1.75mm filament. And while the 60 percent fiber ratio was assessed as too stiff for spooling and not suitable for small 3D printers, the researchers did not see that as an issue if large-scale printers were to be in use in space, fed by pellets. X-rays showed an even mix of the composite during both extrusion and deposition. They also proved that the material could be used for the fabrication of small tools.

“Further testing needs to be done on this material to learn about its fatigue strength (SN curve). Repeating similar testing to this paper but adding additional fiber content ratios between 25% and 40% would also be beneficial to future designers,” concluded the researchers.

“Fiber ratios above 40 percent should also be tested on large scale 3D printers equipped with a pellet extruder. Finally, studies should be conducted related to the recyclability of ABS packaging materials then used as an ABS-Basalt construction material for 3D printing.”

While 3D printing at the International Space Station is fascinating in its own right, the idea of colonizing the moon or Mars is doubly so; however, there is much ground to cover, from what type of materials and construction to use, to how long people will be able to sustain themselves. 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.

Fiber distribution of the final 3D printed component.

[Source / Images: ‘Development and Mechanical Properties of Basalt Fiber-Reinforced Acrylonitrile Butadiene Styrene for In-Space Manufacturing Applications’]

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Romanian researchers develop 3D printed Geneva drives for advanced mechanisms

Researchers from Politehnica of Bucharest University, Romania, have explored the behaviors of 3D printed gear mechanisms otherwise known as geneva systems. According to the study, published in IOP Conference Series: Materials Science and Engineering, such systems are of great practical importance in applications including weaving looms, precision measurement instruments, automated packaging and printing machinery. Thus, various FFF/FDM materials have […]