How Does Thermal Aging Impact 3D Printed Carbon Fiber Parts?

Advances in developing composites for additive manufacturing have accelerated in the last few years, with increasing research and innovation in both, desktop and industrial AM using composites, using chopped or continuous fiber technology, with carbon fibers or nanotubes, or glass fibers most typically used for reinforcement.

3D printed composite materials and sandwich structures (lightweight core sandwiched by thin face sheets) have been the subject of increasing research at universities and national laboratories. But the focus has been more on studying compressive failure, load-carrying capacity, ductility, morphology, tensile or friction properties. This study, published in the Polymer Testing Journal, is a collaboration between researchers at Deakin University (Australia) and University of Siegen (Germany), and the focus was to investigate the impact to performance or properties in 3D printed composite (specifically cores) structures caused by accelerated thermal aging.

The authors chose to focus here due to a lack of investigative research in this area, and more pertinently, because such 3D printed materials/structures will be applied in various temperature conditions, and understanding how temperature impacts their mechanical properties and molecular structures would inform future applications and materials development. Indeed, composite material development and applications using AM are rapidly growing with the market for composites expected to reach $10 billion by 2028, as per SmarTech’s 2018 report, including part production, hardware and materials. Aerospace and medical industry applications are key drivers for composites at present, but that is expected to expand soon into other industries of automotive, construction, energy and consumer products.

FDM (using a FlashForge Creator Pro) was chosen to fabricate two types of composite structure, using ABS and ASA (acrylonitrile styrene acrylate) with carbon fiber face sheets. Two topological structures for the core were fabricated, one truss or triangle-like, and the other, honeycomb or hexagonal. To understand the effects of loading and thermal aging on the structures, compression, tensile and three point bending tests were used to study the mechanical behavior and failure of these components.

   Image Courtesy of Polymer Testing 91 (2020) Journal / Deakin University

The study also hinted toward how continuous fiber reinforcement may provide improved failure load properties over chopped fiber, since initial failure tended to occur at filament intersections within cell walls: “the honeycomb cells had better properties, as there is more continuous filaments between cell walls. The thermal aging also had a greater affect on these joins, as the relaxation and restructuring of the molecules increased the toughness of the join.”

To simulate thermal aging, specimens were ‘aged’ by subjecting them to changing temperatures in a climate test chamber. The max/min temperatures were 60 degrees and 22 degrees Celsius (below the glass temperature of polymers), with an automated, high precision and accuracy device, controlling the rate of temperature change at 1 degree Celsius/minute.

Image Courtesy of Polymer Testing 91 (2020) Journal / Deakin University

It was found that the honeycomb structure with ASA had the higher flexural strength, higher strain-to-load properties, and overall higher load carrying capacity (with ABS or ASA), and that thermal aging increased the maximum strength due to annealing (and molecular structure changes) in specimens with both patterns and materials. The annealing seemed to strengthen the bonds between layers and the print beads. The impacts due to thermal aging could also largely be attributed to aging time, with aging temperature having no significant effect. Thermally aged specimens also had better stiffness and failure load properties, with flexural stress being 15% higher than unaged specimens. In addition, the ASA core failed at a higher strain than the ABS core.

Interestingly, Deakin University is considered to be among the leading research and educational institutions in AM in the country, and worldwide. In 2017, Ian Gibson, Professor of Additive Manufacturing at the university, received the International Freeform and Additive Manufacturing Excellence (FAME) recognizing his lifetime achievements and contributions to 3D printing – which include coauthoring the influential ‘Additive Manufacturing Technologies’ that sold over 300,000 copies, establishing the Rapid Prototyping Journal and the Global Alliance of Rapid Prototyping Associations. Last month, the university launched a research and education program focused on MELD technology, an innovative open-air metal AM technology that can build parts, large or small, without melting any metal. In collaboration with US-based MELD Manufacturing Corporation, the university has placed a MELD machine at its Advanced Metal Manufacture Facility and plans to fund further research into materials, efficiency, and applications for MELD technology.

The post How Does Thermal Aging Impact 3D Printed Carbon Fiber Parts? appeared first on 3DPrint.com | The Voice of 3D Printing / Additive Manufacturing.

Michigan Tech Develops Open Source Smart Vision for 3D Printing Quality Control

Monitoring and quality control systems are becoming more widespread in additive manufacturing as a means of ensuring repeatability and aiming for first-time-right parts. A greater need for quality control are now trickling down to items that are more commonly made by the average consumer using FFF 3D printers, as detailed in “Open Source Computer Vision-based Layer-wise 3D Printing Analysis,” by Aliaksei L. Petsiuk and Joshua M. Pearce.

Dr. Joshua Pearce, an associate professor of materials science & engineering, and electrical & computer engineering at Michigan Technical University has performed extensive research into 3D printing, recyclability, and open-source platforms, along with protocrystallinity, photovoltaic technology, nanotechnology, and more.

As a proponent of 3D printing household items rather than purchasing them, Pearce foresees that the technology will infiltrate the mainstream and the average household much more deeply in the future. While there are many skeptics, this thinking is in line with many other tech visionaries who see great potential for 3D printing on all levels.

In a press release sent to 3DPrint.com, Pearce explains that quality control continues to be an issue at the household level—leading him to create a visual servoing platform for analysis in multi-stage image segmentation, preventing failure during AM, and tracking of errors both inside and out. In referring to previous research and development of quality control methods for “more mature areas of AM,” the authors realized that generally there is no “on-the-fly algorithm for compensating, correcting or eliminating manufacturing failures.

Analysis in Pearce’s program begins with side-view height validation, measuring both the external and internal structure. The approach is centered around repair-based actions, allowing users to enjoy all the benefits of 3D printing (speed, affordability, the ability to create and manufacture without a middleman, and more) without the headaches of wasted time and materials due to errors that could have been caught ahead of time. The overall goal is to “increase resiliency and quality” in FFF 3D printing.

3D printing parameters allowing failure correction

“The developed framework analyzes both global (deformation of overall dimensions) and local (deformation of filling) deviations of print modes, it restores the level of scale and displacement of the deformed layer and introduces a potential opportunity of repairing internal defects in printed layers,” explain Petsiuk and Pearce in their paper.

Parameters such as the following can be controlled:

  • Temperature
  • Feed rate
  • Extruder speed
  • Height of layers
  • Line thickness

While in most cases it may be impossible to compensate for mechanical or design errors, a suitable algorithm can cut down on the number of print failures significantly. In this study, the authors used a Michigan Tech Open Sustainability Technology (MOST) Delta RepRap FFF-based 3D printer for testing on a fixed surface improving synchronization between the printer and camera, based on a 1/2.9 inch Sony IMX322 CMOS Image Sensor and capturing 1280×720 pixel frames at a frequency of 30 Hz.

Visual Servoing Platform: working area (left), printer assembly (right): a – camera; b – 3-D printer frame; c – visual marker plate on top of the printing bed; d – extruder; e – movable lighting frame; f – printed part.

Projective transformation of the G-Code and STL model applied to the source image frame: a – camera position relative to the STL model; b– G-Code trajectories projected on the source image frame. This and the following slides illustrate the printing analysis for a low polygonal fox model [63].

The algorithm monitors for printing errors with the one camera situated at an angle, watching layers being printed—along with viewing the model from the side:

“Thus, one source frame can be divided into a virtual top view from above and a pseudo-view from the side.”

3D printing control algorithm

Currently, the study serves as a tool for optimizing efficiency in production via savings of time and material but should not be considered as a “full failure correction algorithm.”

Example of failure correction

Interested in finding out more about how to use this open-source analysis program? Click here.

[Source / Images: “Open Source Computer Vision-based Layer-wise 3D Printing Analysis”]

The post Michigan Tech Develops Open Source Smart Vision for 3D Printing Quality Control appeared first on 3DPrint.com | The Voice of 3D Printing / Additive Manufacturing.

Colorful Structures Made with Just One 3D Printing Ink

With the use of nonequilibrium self-assembly with direct-write 3D printing, researchers have created photonic crystals (PCs) with tunable structure color. Inspired by nature, University of Illinois at Urbana-Champaign (U of I) scientists have demonstrated how to produce multiple colors from a single ink.

Releasing the details of their study in the recently published “Tunable structural color of bottlebrush block copolymers through direct-write 3D printing from solution,” the team was able to recreate similar properties to those seen in chameleons, butterflies, and opals, using PCs.

These nanoscale structures are able to reflect light in such a way as to generate a variety of colors due to the way the light rays interfere with one another. With well-ordered PCs thousands of times smaller than a human hair, the resulting structural coloration produces vivid colors. The U of I researchers modified a desktop 3D printer to reproduce this same effect.

“It is challenging to reproduce these vibrant colors in the polymers used to produce items like environmentally friendly paints and highly selective optical filters,” said study leader Ying Diao, a chemical and biomolecular engineering professor at U of I. “Precise control of polymer synthesis and processing is needed to form the incredibly thin, ordered layers that produce the structural color as we see in nature.”

The key to the process was the 3D printing of bottlebrush-shaped block copolymers, tuning the thickness of the print layers to modify the color reflected by the PCs in the process. Ahead of the build, the ink is dissolved in a solution that bonds the branched, chemically separate polymer chains within. Once printed, the solution dries and the distinct segments separate, resulting in nanoscopic layers that demonstrate a variety of physical properties based on how quickly the object is built.

To showcase the possibilities, chameleon patterns were fabricated as continuous prints.

“The incorporation of color into 3D printing has significant pedagogical and cosmetic advantages but has so far been demonstrated only for single colors through dyed filament stock or the use of complex and time-consuming multi-nozzle, multi-material methods for multicolored prints,” explain the researchers. “By depositing BBCP from the solution phase with a volatile solvent, we force molecular assembly (microphase segregation) to compete with evaporation and demonstrate on-the-fly tuning of nanoscale morphology and structural color for vibrant, multicolored prints from a single stock ink.”

(A) Seed anionic ring opening polymerization of hexamethylcyclotrisiloxane to produce PDMS macromonomers. (B) 8-diazabicyclo[5.4.0]undec-7-ene (DBU) catalyzed ring opening polymerization of lactide to produce PLA macromonomers. (C) Sequential graft-through ring-opening metathesis polymerization (ROMP) of PDMS and PLA macromonomers. (D) Molecular weight versus time plot for the synthesis of PDMS-b-PLA bottlebrush. PDMS macromonomers are polymerized first (t < 30 min), and then PLA macromonomers are added and polymerized (t > 30 min). (E) Image of dried, as-synthesized bottlebrush stock material. (F) Microscope camera image of a drop-cast film taken at normal incidence under a ring light. Photograph courtesy of Bijal Patel, University of Illinois.

Although there are some challenges in using ‘consumer 3D printers’ for such research, the research team chose ‘to deposit from the solution phase.’ This allowed also for added dimension in the BCP phase diagram. Solvents encouraged molecular mobility, as well as assisting in control of the assembly process.

“Having control over the speed and temperature of ink deposition allows us to control the speed of assembly and the internal layer thickness at the nanoscale, which a normal 3D printer cannot do,” said Bijal Patel, lead author of the study. “That dictates how light will reflect off of them and, therefore, the color we see.”

Programmatic variation of optical properties via modulation of printing speed and temperature. Optical microscopy images of printed meanderline patterns on bare silicon are shown in the figure. At each temperature (pair of rows), images at low magnification (inset A) and high magnification (inset B) are shown. (D) Chameleon patterns printed as continuous prints under constant printing conditions (pressure, printing speed, and bed temperature). (E) Complex pattern printed in three layers at three bed temperatures. Print speed was tweaked on the fly to tune line thickness, color, and intensity throughout the print, leading to intended variation seen in the green/blue 25°C lines.

“This work highlights what is achievable as researchers begin to move past focusing on 3D printing as just a way to put down a bulk material in interesting shapes,” Patel said. “Here, we are directly changing the physical properties of the material at the point of printing and unlocking new behavior.”

(A) Diffuse reflection spectra obtained using the integrating sphere geometry, vertically shifted for clarity. Y axis represents reflectivity (% versus spectralon standard). (B) Lorentzian peak fits describing peak position and FWHM as a function of printing speed. Error bars denote SE of the fit.

Full analysis details and code are provided in section S14. Images beside plot correspond to the numbered ticks. All data shown in (A) to (C) were obtained at a substrate temperature of 50°C and applied pressure of 30 kPa. (A) Meniscus height profile versus time for samples 3D printed at various printing speed. Images below are snapshots of transmission-mode video taken for sample printed at 60 mm/min. Inset contains plots of drying time (x intercept) versus printing speed. (B) Intensity plotted against elapsed time for 3D-printed samples. Images below are snapshots from the reflection-mode video corresponding to labeled tick marks for sample (60 mm/min) within plot. (C) Assembly time (peak intensity) plotted against drying time, showing close matching between the two. Dashed line indicates a slope of one. (D) 2D SAXS pattern for solution (100 mg/ml) of BBCP in THF. (E) 1D azimuthally averaged profiles for backbone DP of 400 (top two curves) and 200 (lower curve). Inset depicts fitting of the low-q peak to a lamellar structure factor. (F) Cartoon of bottlebrush conformation in micellar and lamellar assemblies.

While the color spectrum that the team was able to produce was limited, the researchers believe that they can improve on the technique through understanding how layers are created. They are also exploring ways to make the technology more suitable for industrial purposes, due to the fact that large-scale 3D printing is not possible with the existing methodology.

“This work highlights what is achievable as researchers begin to move past focusing on 3D printing as just a way to put down a bulk material in interesting shapes,” Patel said. “Here, we are directly changing the physical properties of the material at the point of printing and unlocking new behavior.”

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: ‘Tunable structural color of bottlebrush block copolymers through direct-write 3D printing from solution’; EurekAlert]

 

The post Colorful Structures Made with Just One 3D Printing Ink appeared first on 3DPrint.com | The Voice of 3D Printing / Additive Manufacturing.

3D-Printed Fuel Cells May Be Catalyst for Change in Energy Sector

Consumption of energy around the world and never-ending demand leads researchers to continue searching for clean, sustainable alternatives. In the quest to slow global warming, we must begin to prevent emissions, too. The list of options is actually quite long for avoiding extended pollution and making sweeping change, but the challenges lie in global awareness and the ability to act.

In recent years, 3D printing has been used far beyond its original intentions for rapid prototyping as researchers continue to harness the technology in a wide range of projects and innovations impacting the energy industry, from energy harvesting wearables to storing wind energy, and a variety of techniques for making 3D-printed batteries.

Now, expert market research shows that 3D-printed fuel cells—very similar to batteries but they convert fuel rather than storing it—are being developed for greater optimization and ruggedness in structures too. Fuel cells and electrolyzers may act as the catalyst for substantial change in the shift to zero emissions. While fuel cells can transform hydrogen into electricity, electrolyzers can change water into hydrogen, when accompanied by electricity.

These new systems offer enormous potential for energy change as they are capable of serving as ‘massive storage’ for electricity, and they can also decarbonize intense areas of energy usage. With 3D printing, industrial users are able to take advantage of savings on the bottom line, the ability to fabricate more complex geometries, and also the possibility to create products never before possible with conventional techniques.

While previously solid oxide fuel and electrolysis cells (SOFCs and SOECs) have been considered efficient for use, development and manufacturing is also cost-prohibitive, and it is difficult to produce complex geometries that may be desired. It looks like this is about to change, however, according to a recent press release from IDTechEx. The market researcher firm indicated that approval has been received for a novel SOFC system this year via a rapid assessment meant to fast-track development and subsequent use. Recent industry news from the same source also informs us that South Korea is accelerating its investments in hydrogen fuel cells for alternative energy.

Solid oxide electrolysis cells (SOES) are gaining ground as new sources of energy too. Also acting as streamlined converters of energy, they are known to offer better yields in production, and use less electricity. As of this year, a SOFC was fabricated via SLA 3D printing, marking a groundbreaking move not within digital fabrication, but also the energy industry.

V–j curves of the planar and corrugated cells measured in fuel cell (a) and co-electrolysis modes (b) at 900 °C. Corresponding Nyquist plots from EIS measurements are represented for the fuel cell at 0.7 V (c) and co-electrolysis cell at 1.3 V (d) [‘Image from ‘3D printing the next generation of enhanced solid oxide fuel and electrolysis cells’]

Researchers from Spain have also released their findings regarding the potential for revolution in the energy sector, in “3D printing the next generation of enhanced solid oxide fuel and electrolysis cells.” As complex shapes continue to be explored, it is expected that further progress will emerge in manufacturing via 3D printing, resulting in devices that can be easily customized.

“Among others, electroceramic-based energy devices like solid oxide fuel and electrolysis cells are promising candidates to benefit from using 3D printing to develop innovative concepts that overcome shape limitations of currently existing manufacturing techniques,” state the authors.

Values of area-specific resistance (total, electrolyte and electrode contributions) obtained from equivalent circuit fitting of the EIS spectra for both planar and corrugated cells measured in fuel cell and co-electrolysis mode at 900 °C. [‘Image from ‘3D printing the next generation of enhanced solid oxide fuel and electrolysis cells’]

Other researchers are 3D printing batteries, like Jennifer Lewis of Harvard. These structures are actually micro-sized, only as big as a piece of sand. Able to transfer electricity to small devices, some of which may have been ‘lingering’ for long periods of time as there was no type of storage available.

“Not only did we demonstrate for the first time that we can 3D-print a battery, we demonstrated it in the most rigorous way,” said Jennifer Lewis, Ph.D., senior author of the recent study.

It’s also worth highlighting the work of Keracel, which claims to have developed a method for 3D printing solid state batteries using a binder jetting technique. The company has partnered with Musashi Seimitsu Industry, a Japanese automotive supplier.

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: IDTechEx / Images: ‘3D printing the next generation of enhanced solid oxide fuel and electrolysis cells’]

The post 3D-Printed Fuel Cells May Be Catalyst for Change in Energy Sector appeared first on 3DPrint.com | The Voice of 3D Printing / Additive Manufacturing.

Comparing 3D-Printed and Traditional Guide Plates for Placing Orthodontic Brackets

The most important part of orthodontic treatment is the correct positioning and bonding of the brackets. Direct bonding is less accurate and often takes longer due to saliva and inaccessible tooth positions, while indirect bonding is quicker and less likely to cause bracket positioning errors, but is costlier. A team of researchers from Beijing published a paper, “Comparison of three-dimensional printing guides and double-layer guide plates in accurate bracket placement,” where they designed different types of transfer trays, using 3D printing and traditional impressions, and evaluated their “clinical efficacy.”

“With the increasing applications of indirect bonding, various designs of transfer trays and novel technologies are implemented in the treatment procedure. In the laboratory stage, the patients’ occlusal interrelationship can be duplicated either by impression or digital scanning,” the researchers wrote. “The former is a traditional method to generate double-layer guide plates; though with a lower cost, this method typically takes longer laboratory time and is susceptible to human errors. The latter is incorporated with cutting-edge 3D printing technology that provides various advantages, such as precise 3D images, convenience in file storage, and accuracy in image analysis and outcome prediction [5].”

The study model. (a) Maxillary model with marking points. (b) Mandibular model with marking points.

In the laboratory stage of indirect bonding, brackets are bonded to the patient’s orthodontic model, and then a customized transfer tray is used to place them on the actual surface of the tooth in the clinical stage. To make the models for this study, the team collected 140 teeth with normal crown morphology and no evident defects or restorations, sterilized them, and arranged them into “five pairs of full dentition” before labeling the marking points “on the buccal/labial surface of the crown.”

Digital design and 3D printing guides. (a) Distinguishing teeth and gingiva on the digital models. (b) Establishing the occlusal plane. (c) Adjusting the bracket positioning. (d) Simulation of bracket positioning. (e-f) Guide plate for indirect bonding on digital models. (g) 3D printing guide – whole denture type, and (h) single tooth type.

Next, they created 3D printable indirect bonding guide plates, beginning by generating digital models with the 3Shape TRIOS Standard intraoral scanner. The occlusal plane, axis, and center of individual crowns were established, and the marginal gingiva labeled, using 3Shape software, and guide plates for the whole denture type and single tooth type for 3D printed on a ProJet 3510 DP.

“The brackets were positioned in the 3D printing guides (the whole denture type or the single tooth type), and 3 M Unitek Transbond™ XT light-curable adhesives were applied to the base of the brackets,” the team explained about the indirect bonding procedure. “The 3D printing guides were then placed on the study models, and each border of the brackets was light-cured for 5 s.”

3D printing guides and indirect bonding procedure. 3D printing guide of the (a) maxillary and (b) mandibular dentitions. 3D printing guides placed on the (c) maxillary and (d) mandibular study models. Completion of bracket positioning on the (e) maxillary and (f) mandibular study models.

In making the traditional trays, the researchers used silicone-based materials to get impressions of the working models with intact marking points, and created plaster casts from the silicone molds.

“A thin layer of separation agents was applied to the cast tooth surfaces; then, the brackets were positioned and adhered on the crowns using 3 M Transbond™ XT light-curable adhesives and light-cured for 5 min,” they wrote. “Double-layer guide plates were manufactured by Erkoform-3D Thermoformer with a 1 mm inner layer (soft film) and 0.6 mm or 0.8 mm outer layer (hard film). Lastly, we trimmed the excess materials of the inner layer to 2 mm above the crowns and the outer layer until covering 2/3 of the brackets.”

The impression of (a) maxillary and (b) mandibular dentitions, and the plaster casts of (c) maxillary and (d) mandibular dentitions.

Bracket positioning on the (a-c) maxillary and (d-f) mandibular dentitions. Double-layer guide plate of the (g) maxillary and (h) mandibular dentitions.

For this indirect bonding procedure, the bracket were placed in the double-layer guide plates, with one solution applied to the surfaces of the teeth and another to the bracket base. Then, the guide plates were put on the study models, and after two minutes of fixation, the researchers removed the outer hard layer first, and then the inner soft layer.

Double-layer guide plates placed on the (a-c) maxillary and (d-f) mandibular study models. Completion of bracket positioning on the (g-i) maxillary and (j-l) mandibular study models.

Next, Materialise Mimics software was used to measure the distance between the marking points and bracket positions in the digital models of both the whole denture and single tooth designs for the 3D printed guide group, while electronic calipers measured the distance in the study models.

Electronic caliper.

Marking points on the plaster cast and study model.

SPSS software was used to analyze the distance.

“The accuracy of indirect bonding between 3D printing guide and double-layer guide plate was compared using the paired t-test. P < 0.05 indicated statistical significance,” they explained.

The data, reflected in the tables below, showed that there was no statistical difference in the accuracy of bracket positioning between the two types (p = 0.078), and that the 0.6 mm type in the double-layer guide group had much better results (p = 0.036) than the 0.8 mm one.

“We then further compared the accuracy of indirect bonding between 3D printing guides (whole denture type) and double-layer guide plates (0.6 mm), the results were comparable between two groups (P = 0.069),” they wrote. “However, indirect bonding using double-layer guide plates (0.6 mm) cost less chair-side time than the 3D printing guides group.”

Table 1: Comparison of different designs in 3D printing guide group.

Table 2: Comparison of different designs in double-layer guide plate group.

Table 3: Comparison of bracket positioning accuracy between 3D printing guide and double-layer guide plate.

However, while the data showed no statistical significance, the researchers noted that “the overall discrepancy before and after bracket transfer was lower in the 3D printing guides group.”

“This finding might be due to our in vitro study models with only mild malocclusion,” they explained. “Further in vivo studies in more severe clinical cases, such as malocclusion with torsion/tilting/overlapping, will be essential to investigate the efficacy and generalizability of 3D printing guides and double-layer guide plates.”

Discuss this and other 3D printing topics at 3DPrintBoard.com or share your thoughts below.

The post Comparing 3D-Printed and Traditional Guide Plates for Placing Orthodontic Brackets appeared first on 3DPrint.com | The Voice of 3D Printing / Additive Manufacturing.

Dental Students Compare Conventional and 3D Printed Surgical Training Models

There are few things I hate more than going to the dentist. That’s why I’m always glad to hear stories of dental students using 3D printed training models to learn on – if they have to work in my mouth, then I want them to know what they’re doing. A group of researchers from University Hospital Münster in Germany published a paper on this topic, relaying the results of their work using real patient data to create 3D printed surgical training models for root tip resection. Then, they compared them against a commercial typodont model, which is a common simulation model used at university dental clinics with replaceable gingiva masks and teeth that often “show idealized eugnathic situations, which are rarely encountered in everyday practice.”

“Furthermore, the ready-made standard models do not usually depict special pathological or anatomic situations,” they wrote.

A root tip resection, or apicoectomy, removes inflammation around the tip of the tooth’s root. The researchers explained that the typodont model at their university features teeth “in direct contact with the hard plastic that simulates the jawbone,” and simulates the inflammation (apical granuloma) with wax, though it’s missing a sensitive periodontal ligament.

“The teeth used are idealized stereotypes. Anatomical variations, such as extremely long or even curved roots, cannot be simulated with these industrially produced models. Therefore, we have developed a method to create more realistic, individualized training models,” the researchers explain.

The model they created is of a real patient’s upper jaw with three anterior root apices, periodontal ligament, and the apical granuloma, along with a gingival mask.

“We also present an evaluation of the model by dental students and compare it with their evaluation of the conventional typodont model,” the team wrote. “Our intention was to evaluate whether dental students accept the 3D-printed surgical training model just as well as the popular typodont model.”

L-R: Modified plaster cast, modified plaster cast with wax layer.

They used CAD/CAM technology to design the training model, which allowed them to add the simulated inflamed tissue, and took a conventional impression of the area in question in order to make a plaster cast. The gingiva was modeled with a 1 mm thick layer of wax, and an industrial 3D scanner was used to attain the shape of the modified cast with and without the wax gingival mask.

L-R: Scanned surface of the plaster cast without wax layer and meshes of the three teeth aligned to the upper jaw.

The cone beam computed tomography (CBCT) data of another patient was used to create 3D models/meshes of teeth 11, 12, and 21 in Materialise Mimics, and the 3D reconstruction was modified using Rhinoceros 5. To make a model of the periodontal ligament, which the typodont model doesn’t include, they deleted the upper parts of the teeth mesh and thickened the rest by 0.25 mm in Geomagic Wrap.

L-R: Meshes of the roots (rear faces of mesh in blue-green), extruded root surfaces representing periodontal ligament.

They constructed a 6 mm sphere around the root apex of tooth 11 to simulate an apical granuloma.

“The material used to represent the periodontal ligament and the apical granuloma is softer than the material used for the other parts of the model. This allows a more realistic representation than in the typodont model,” they explained.

Meshes of the granuloma on tooth 11 and the periodontal ligament on teeth 11, 12 and 21, 3D printed in soft support material (red).

The 3D printed model also includes a silicone gingival mask so students can practice the surgical incision. A 3D printed matrix technique was used to fabricate the mask directly onto the model, and the model was 3D printed out of liquid photopolymer on an Objet Eden 260V PolyJet 3D printer. The undercut areas and the cavities in the model that simulated apical granuloma and periodontal ligament were filled with a soft support material. It took roughly six hours to 3D print 12 models in a single build.

Silicone gingival mask.

“Dental students, about one year before their final examinations, acted as test persons and evaluated the simulation models on a visual analogue scale (VAS) with four questions (Q1–Q4),” the researchers wrote.

35 students evaluated the typodont model, while 33 students used the 3D printed simulation model. Participants watched a video of the root tip resection exercise, and then completed the procedure once. They were given a questionnaire about the simulation model and the difficulty of the exercise, rated on a visual analogue scale (VAS). There was also an optional free-text section if a participant wanted to express their opinion in their own words.

Surgical incision guidance on the 3D printed model in the phantom.

Osteotomy of the root tip.

Presentation of the root tip. Note: torn gingiva mask.

Resected root tip with demarcation to the bone.

Suture exercise on the gingiva mask.

54.5% of the Group 2 participants said in the free-text section that the gingiva mask in the 3D printed model tore during the procedure, while 20% in Group 1 said that it detached from the typodont model.

Questionnaire results; white dots denote the mean values.

“Shapiro–Wilk normality tests revealed that, with the exception of Q4, normality cannot be assumed,” they explained. “Wilcoxon rank sum tests were therefore carried out to identify differences in the assessments of the two model types. The alternative hypothesis for each test was “The rating for the typodont model is higher than that for the 3D printed”. As the p-values presented in Table 1 reveal, the alternative hypothesis has to be rejected in all cases.”

Table 1.

The researchers determined that their 3D printed training models were “not inferior to the industrially manufactured typodont models,” and that the approach is very flexible – the models can be easily redesigned and adapted for different learning scenarios, and it’s much faster to fix them when necessary. While the 3D printers weren’t cheap, the material costs for a 3D printed single-use model were only about €10, compared to €300 for the multi-use hypodont model.

“A shortcoming of our study is that the exercises were performed by students without surgical experience. As a result, there is a lack of professional evaluation of the models in terms of how well they reflect the reality. Thus, we were not able to check an important quality aspect of the models,” the researchers noted.

“Future studies with experienced surgeons could provide more information about the realism of the 3D-printed models.”

Other issues include the missing color difference between anatomical structures or cortical and cancellous bone structures, and the gingiva mask needs improvement, either through alternative technologies or materials.

“Individual 3D-printed surgical training models based on real patient data offer a realistic alternative to industrially manufactured typodont models. However, there is still room for improvement with respect to the gingiva mask for learning surgical incision and flap formation,” they concluded.

Discuss this and other 3D printing topics at 3DPrintBoard.com or share your thoughts below.

The post Dental Students Compare Conventional and 3D Printed Surgical Training Models appeared first on 3DPrint.com | The Voice of 3D Printing / Additive Manufacturing.

Researchers Evaluate Feasibility of Closing Multiple Atrial Septal Defects Guided by 3D Printed Model

We’ve often seen physicians use 3D printed heart models to help during surgeries, but a group of researchers from China published a paper on using them to help with an alternative to surgery for repairing secundum atrial septal defect (ASD), a rare congenital defect characterized by a hole in the wall between the atria. Their goal was to evaluate how feasible it was to use a single device to close several ASDs guided by the 3D printed heart model and transthoracic echocardiography (TTE).

Due to interference between devices and threat of repeat intervention, it’s difficult to use multiple devices simultaneously, or in staged device closure, in percutaneous transcatheter closure of an ASD. But using an over-sized device, can tear the atrial septum. So the best plan is to use single device closure for patients with multiple ASDs, as it preserves the anatomical structure.

“However, this strategy is technically challenging because of inability to determine the target defect for catheter passage and occluder selection, warranting careful interventional planning with comprehensive anatomical information for successful device closure,” the team wrote.

That’s where the 3D printed heart model comes in. The researchers used the single-device strategy, assisted by 3D printing, to perform multiple ASDs closure, and compared their results of “3D printing-based and transthoracic echocardiography (TTE)-guided percutaneous transcatheter closure with those of traditional fluoroscopy-guided closure.”

Simple working flowchart in patients with multiple ASDs, from image acquisition to 3D printed solid and hollow model.

62 patients diagnosed by TTE with two or more ASDs with a 5mm or more diameter, were enrolled in their non-randomized study for analysis. 30 had cardiac computed tomography angiography (CTA) ahead of surgery in order to get data to create their 3D printed heart models. The CTA images were reconstructed and saved in DICOM format, before being imported to Materialise Mimics software. Cardiac masks were generated for 3D models, and 3-matic software was used to hollow them. The STL files were 3D printed, in hollow fashion, at 1:1 scale on a ProJet MJP 2500 Plus 3D printer out of silicone.

3D printed model of a patient with multiple ASDs. (a) and (b) show the model from left and right atrial sides, respectively. The arrows depict the position of the ASDs. (c) and (d) illustrate the status after occluder deployment in the model.

The surgeons performed in vitro simulated occlusion with the 3D printed models as a pre-op evaluation. Then, while the other 32 patients underwent ASD closure with fluoroscopic guidance, this group had TTE-guided closure procedures.

“The apical four-chamber view and parasternal short-axis view were used for guidance, and the multipurpose catheter was passed through the targeted defect, which was determined using the 3D printing model and intraoperative TTE,” the researchers explained.

“Then, a single septal occluder was inserted for ASD closure under TTE guidance. An ASD occluder or PFO occluder was selected based on the in vitro simulated occlusion in a 3D printing model.”

After implantation, the device position was evaluated through subcostal, apical four-chamber, and parasternal short-axis views, and they also performed Color Doppler assessment to detect any issues, like coronary sinus return or residual shunting. Once they determined that the occluder had been implanted correctly, “it was released by rotating the cable counterclockwise under TTE guidance,” and a reassessment was then performed in echo views, below.

Percutaneous closure of multiple ASDs under TTE guidance. (a) Multiple ASDs image displayed in subcostal view. (b) The left disc was released (parasternal short-axis view). (c) The ASDs were closed (four-chamber view).

“In the conventional group, multiple ASDs occlusion was performed under fluoroscopic guidance using the single occlusion device,” they wrote. “Based on TTE measurements, the single device was selected, equal to or up to 4 mm larger than the main defect [10]. According to experience [102021], the device was usually implanted into the largest defect. The occluder was replaced if echography found more than two residual shunts, the residual shunt was >5 mm in diameter, or the device compressed the mitral valve.”

Immediately post-op, and 6 months after the device closure, all 62 patients were evaluated via TTE and electrocardiogram, with the researchers noting the presence of any arrhythmia, residual shunt, or valve dysfunction. A Brand-Altman analysis was used to evaluate the agreement “between device size of 3D printed model and traditional estimation,” and the data was analyzed with SPSS software.

Bland–Altman plot analysis. Bland–Altman plot of empirical estimation versus 3D printed model estimation of occluder size.

They found that 26 patients in the 3D printing/TTE group, and 27 patients in the conventional group, achieved successful transcatheter closure with a single device. The prevalence of residual shunts was lower in the first group immediately and 6 months post-op, and there were no complications in either group during the procedure or the two follow-ups.

“Gender, age [18.8 ± 15.9 (3–51) years in the 3D printing and TTE group; 14.0 ± 11.6 (3–50) years in the conventional group], mean maximum distance between defects, prevalence of 3 atrial defects and large defect distance (defined as distance ≥7 mm), and occluder size used were similarly distributed between groups,” the team wrote. “However, the 3D printing and TTE group had lower frequency of occluder replacement (3.8% vs 59.3%, ), prevalence of mild residual shunts (defined as <5 mm) immediately (19.2% vs 44.4%, ) and at 6 months (7.7% vs 29.6%, ) after the procedure, and cost (32960.8 ± 2018.7 CNY vs 41019.9 ± 13758.2 CNY, ).”

They did note that the occluder on the 3D printed model was “consistently larger than in the empirical estimation but similar to final clinical selection,” which indicates a higher level of accuracy. Even in patients with a large defect distance, the results of the study suggest that “interventional therapy with a single occluder for multiple ASDs is feasible,” especially as technical difficulties and complex anatomy make successful single device closure tricky to achieve. It’s important to remember that the accuracy of the 3D printed anatomic model is paramount in attaining single device closure in patients with multiple ASDs.

“Occluders’ sizes preestimated by the 3D printed model were similar to the size actually used for patients and larger than the size from conventional empirical estimation. These results indicate that preevaluation using the 3D printed model can avoid unnecessary interventions, the possibility of enlarging ASD by changing occluders and the financial waste of replacing occluders,” they explained.

The researchers ultimately determined that it’s feasible to use a 3D printed model to help achieve successful device closure for patients with multiple ASDs with a defect distance of ≥7 mm. The model can also help screen patients who may not be well-suited for the closure route, and should instead seek direct surgical repair.

“The combination of the 3D printing technology and ultrasound-guided interventional procedure provides a new approach for individualized therapeutic strategy of structural heart disease and in particular a reliable therapeutic method for multiple ASDs, especially for challenging cases with large defect distance,” they concluded.

Discuss this research and other 3D printing topics at 3DPrintBoard.com or share your thoughts below.

The post Researchers Evaluate Feasibility of Closing Multiple Atrial Septal Defects Guided by 3D Printed Model appeared first on 3DPrint.com | The Voice of 3D Printing / Additive Manufacturing.

3D Printed Plastic Geoboards Teach Visually Impaired Students about Geometry

Geometry is the branch of mathematics that relates to angles, geometric shapes, lines and line segments, and rays, and you use geometry concepts to measure lengths and areas of 2D shapes and calculate the volume and surface area of 3D shapes. I was never any good at geometry (or any mathematics, to be honest), so I can’t imagine how hard it must be to learn when you are visually impaired. Three researchers from Thailand wrote a paper, “The Designation of Geometry Teaching Tools for Visually-Impaired Students Using Plastic Geoboards Created by 3D Printing,” about making 3D printed teaching tools for visually impaired students – a concept we’ve seen before.

Visually impaired students must interpret 2D shapes through a sense of touch.

“There are several teaching tools available on the market that can serve this purpose effectively; however, the imported products are too expensive,” the researchers explained.

Traditional wooden geoboards.

A geoboard is a great way to teach visually impaired students geometry, as it helps them better understand geometric reasoning, terminology, and theorems. It’s a physical board with rivets half driven in, and rubber bands are wrapped around the nails to teach plane geometry concepts and polygons.

“According to the difficulty of wooden geoboard making and carrying, we propose to replace the existing model with the unlimited design of light and colorful geoboards,” the team wrote.

Using 3D printing to make lightweight geoboards out of plastic costs less money, and they can be customized to fit user requirements. The researchers created colorful geoboards to teach visually impaired elementary students in Bangkok about angles, circle components, line segments, shape areas, and 3D geometric shapes, like prisms and cubes. They also made additional teaching tools, like arrowheads, protractors, and 3D object models, for lessons about 2D and 3D shapes and geometry.

The SketchUp model and 3D printing of geoboards.

SketchUp was used to create the colorful 20 x 20 cm geoboards, which were printed out of PLA on a Flashforge Creator Pro over 18 hours. Two patterns were made – a 10 x 10 grid on the x-axis and y-axis with a square edge, and a 4-quadrant graph with a circular edge and 24 circumference scales. Braille scales are included so the students can identify 0-10 on the x and y axes, and the top right corner of the boards have two columns of three dots to show that they’re upright.

“Z-axis pillars with different heights, identified by braille, were also created for 3D geometry teaching,” the team explained.

“There were 24 points identified by the letters A to Y on the circumference with a 15-degree angle difference for teaching about circles and tangents. The central point was identified by the letter O and the circle diameter was 13 cm. Raised grid lines 1.5 mm in height were also generated for exploring direction by blind touch.”

Plastic geoboards with square and circle edges, learning accessories, and segments of 3D objects for spheres, cones, cylinders, pyramids, and cubes.

15 visually impaired fourth graders and three experienced teachers participated. The experimental group and the control group each completed 15 one-hour periods of different learning activities. After a pre-test, the control group continued with traditional geoboards, while the experimental group switched to the 3D printed ones.  You can see teaching and assessment contents with related exercises for the experimental group in a portion of Table 1 below.

“The coordinate points of 2D geometry were explored by blind touch on braille scales and raised grid lines, while z-axis pillars were used for 3D geometry by connecting rubber bands to the plane,” the researchers explained.

The students in the experimental group used the 3D printed geoboards to learn about 2D geometry. For example, they stretched rubber bands across rivets on the square board, connecting two points to draw a straight line and “an angle of 2 lines from 3 points on the coordinate plane.” To learn about straight and parallel lines, rays, and right, acute, and obtuse angles, arrowheads could be attached to the ends of the lines.

Teaching about straight lines, parallel lines, rays, and angles.

They used the circular geoboard for learning angle measurements and circle components, like radius and diameter, and 2D geometric shapes, like squares and triangles.

Teaching about angles, circle components, squares and triangles.

The geoboards were also used to teach 3D geometry with plastic pillars on the z-axis. Once the students had the basic concept down, pillars on this axis “with different heights of 4, 5 and 6 units can be used to teach 3D geometric shapes and volumes.” Multiple pillars were used to create prism, and pyramids with differently-shaped bases.

Teaching to create 3D geometric shapes for pyramids and prisms, similar to 3D object models.

“The raised grid lines with braille numbering are handy for identifying shape locations, measuring distance, and calculating areas or perimeters; and scales can be applied for measuring the diameter or radius of a circle on a cylinder, cone, or sphere and multiplying the area by the height to find the volume,” they wrote.

At the end, both student groups took another test, and independent two-sample t-tests were used to analyze and compare the differences in the mean scores of the pre-test and post-tests between the groups. You can see the mean scores (x) and standard deviations (SD) for the tests below.

The participants also completed a questionnaire, using a 5-point Likert scale, about how satisfied they were with the 3D printed geoboards. They evaluated the quality of the teaching tools and the benefits of the learning activities, and answered open-ended questions regarding areas for improvement and their personal opinions.

“The response showed that the new geoboards as a teaching tool were considered to be much more satisfactory than the traditional tool because the mean scores were very high (>4.8) in all areas,” the researchers noted.

All the participants agreed that the 3D printed geoboards made class more enjoyable for the visually-impaired students, and that they “enhanced the mental imagery and understanding of geometry.”

“The prototype testing showed that the experimental group had a higher mean score on the post-test than did the control group, indicating that the learning achievement of the visually-impaired students who learn with the new geoboards is significantly higher than that of the students who learn with the regular tools. The participants’ satisfaction with the geoboards in terms of learning about geometry was evaluated highly on the part of the teachers and the students because the tangible teaching tools were considered more effective for understanding geometry with good visual imagery than when using the traditional tools,” the team concluded.

Discuss this and other 3D printing topics at 3DPrintBoard.com or share your thoughts below.

The post 3D Printed Plastic Geoboards Teach Visually Impaired Students about Geometry appeared first on 3DPrint.com | The Voice of 3D Printing / Additive Manufacturing.

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.

Discuss this and other 3D printing topics at 3DPrintBoard.com or share your thoughts below. 

The post Analyzing Parameters of Pure and Reinforced 3D Printed PLA and ABS Samples appeared first on 3DPrint.com | The Voice of 3D Printing / Additive Manufacturing.

Using Robotic GMAW Additive Manufacturing to Make Metal Components for Industrial Applications

Gas metal arc welding (GMAW) additive manufacturing is a more affordable metal technology, with a high deposition rate for potentially fabricating medium and large components. Van Thao Le, with Le Quy Don Technical University in Vietnam, has published a paper, titled “A preliminary study on gas metal arc welding-based additive manufacturing of metal parts,” that centers around investigating the mechanical properties and internal quality of components 3D printed using a GMAW robot.

GMAW-based technology is better for manufacturing metal parts with large dimensions than gas tungsten arc welding (GTAW) and plasma arc welding (PAW) methods because of its higher deposition rate. It’s important to achieve high internal quality of GMAW-printed parts, which is why it’s necessary to gain a better understanding of their microstructures – particularly when the component will be used in a load-bearing condition. This technology is consistently used in Vietnam because of its lower cost, so manufacturers should know all they can about the method in order to attain good results.

“Therefore, the objective of this study is to investigate the internal quality of thin-walled parts manufactured by the GMAW-based AM process. The results obtained in this study allow us to demonstrate the feasibility of using the GMAW robot for manufacturing or repairing/remanufacturing of metal components according to the AM principle,” the author wrote.

Figure 1. (a) Schema of the GMAW-based AM system, (b) built thin-walled sample, (c) positions for cutting the specimens, & (d) five zones for observing microstructures and measuring the hardness on a cut surface of the specimen.

An industrial GMAW robot built a thin-walled component using the wire arc additive manufacturing (WAAM) process, out of mild steel copper-coated welding wire on a low-carbon steel substrate plate. The 6-axis robot used a welding torch to deposit layers from the substrate, and you can see the welding process parameters in the table below.

“The distance between the GMAW torch and the workpiece was 12 mm. The deposition was conducted at room temperature and without preheating the substrate,” Le explained. “Once the deposition of a welding layer was finished, the welding torch is retracted to the beginning point for the deposition of the next layer with a dwell time of 60 seconds. The dwell time used between two successive layers aims at cooling down the workpiece and transferring accumulated heat to the environment.”

A wire-cut electrical discharge machining (EDM) machine was used to cut two groups of tensile specimens from the thin-walled sample, so that the author could measure the built material’s hardness, using a digital microhardness tester, get a closer look at its microstructures with an optical microscope, and test the tensile properties.

Figure 2 . Dimensions of the tensile specimen.

“Before cutting these specimens, two side surfaces of the built thin wall were machined to obtain an effective width of the built thin-walled materials,” Le wrote.

Figure 3. Microstructures of built materials observed in five zones: (a) upper zone, (b) middle zone, (c) lower zone, (d) heat-affected zone (HAZ), and (e) substrate zone.

The specimen’s microstructure was observed in five different zones. The upper zone, which features three types of ferrite grains and a high variation of thermal and high-cooling rates, has “lamellar structures with primary austenite dendrites” that distribute perpendicular to the substrate. The middle zone has two types of grains, and mostly features “the granular structure of ferrites with small regions of pearlites at grain boundaries.” The microstructures found in the lower zone, which has a slower cooling rate than the upper, are made of “equiaxed grains of ferrite, in which thin lamellae are distributed and coexisting with thin strips of pearlite.” These grains are finer than the ones in the middle zone, because the value of thermal shock is higher here.

In the heat-affected zone (HAZ), the microstructures transfrom from austenite to martensite, while the substrate zone features ferrite/perlite banded microstructures – the total opposite of the middle zone’s “homogenous distribution of phases.”

The above table shows the hardness (HV) measurement in the five zones. The upper zone had the highest HV, while the middle had the lowest, and the HAZ’s value was slightly lower than the substrate zone.

Specimens were tested on a tensile machine, and Le also figured the engineering strain-stress curves.

Figure 4 . Tensile tests with two specimens TSv1 and TSh1: (a) Installation of the specimen on the tensile test machine, (b) the broken specimens after the tensile tests, and (d) the engineering stress-strain curves.

“The hardness (ranged between 164±3.46 HV to 192±3.81 HV), yield strength (YS offset of 0.2% ranged from 340±2 to 349.67±1.53 ), and ultimate tensile strength (UTS ranged from 429±1 to 477±2 ) of the GMAW-based AM-built components were comparable to those of wrought mild steel,” he explained.

“There is also a significant difference in terms of YS and UTS between the vertical and horizontal specimens due to non-uniform microstructures of built materials. Moreover, the mechanical properties of the thin-walled component built by the GMAW-based AM process are comparable with those of parts manufactured by traditional processes such as forging and machining.”

This study found that the metal components built by GMAW-based robotic AM have “adequate and good mechanical properties for real applications.” Le concluded that it is feasible to use a GMAW robot to 3D print parts that can be used in industrial applications.

Discuss this research and other 3D printing topics at 3DPrintBoard.com or share your thoughts in the Facebook comments below.

The post Using Robotic GMAW Additive Manufacturing to Make Metal Components for Industrial Applications appeared first on 3DPrint.com | The Voice of 3D Printing / Additive Manufacturing.