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How does PLA Color Influence Mechanical Properties in FDM 3D Printing?

All kinds of research has been conducted regarding the mechanical properties of 3D printing materials, such as how they are effected by things like infill density, build orientation, temperature, and porosity. Researchers Adi Pandžić and Damir Hodzic from the University of Sarajevo and Aleksa Milovanović with the University of Belgrade were curious how much the color of PLA would effect material tensile properties in FDM 3D printing, and published a paper on their work, titled “Influence of Material Colour on Mechanical Properties of PLA Material in FDM Technology.” Different colors need different extrusion temperatures in 3D printing. The additives that make your PLA a different color also have influence on how your part prints and what properties it has. This much was already known, but to which extent do the different color formulations influence your mechanical properties?

The abstract reads, “Topic of this article is to investigate whether colour of PLA material effect on material tensile properties and in what amount. It will be tested more than 10 different colours of PLA material, and for every colour it will be tested 3 specimens. Specimens are prepared according to ISO 527-2, and all printed with same 3D printing parameters and with 100% infill. Also, all used materials are of same company and for every colour specimen will be 3D printed from same filament spool. All this is done to avoid other parameters to effect on material properties. The results of this study will be useful for colour selection of the PLA material without compromising the material tensile properties of 3D printed product.”

Many parameters are taken into account when it comes to the quality of FDM printed products, including things like infill pattern, layer height, nozzle diameter, and material characteristics. Polylactic acid, or the popular PLA we all know and love, is a polymer with a melting point between 150°-160° C, and is still the reigning material on the desktop.

“By reviewing the literature it can be noticed that the greatest accent is given to the influence of parameters on mechanical properties of material. Another characteristic barely evaluated is the influence of different material pigmentations,” the researchers explained. “Today, there are many different colours of PLA material of the same manufacturer, and in most cases it is assumed to have the same mechanical properties regardless of colour. This is one of the reasons why we chose to examine whether and how much the colour of the PLA material influences the mechanical properties of the finished product.”

The team ordered 14 different colors of PLA from 3D Republika, with the same properties and characteristics, in order to investigate their potential influence on the mechanical properties of specimens made with the material. They used SOLIDWORKS to design samples according to ISO 527-2, and printed three different specimens for each color on an Ultimaker 2+, under the same conditions with 100% infill, and the “normal” profile from Cura 4.0.0 slicing software was used to prepare the G-code for the samples.

“Specimens are printed with “flat” printing orientation and 45˚ raster angle,” the researchers wrote. “Also brim around specimen is used for better adhesion with print bed and to reduce wrapping of material, after 3D printing it is removed from specimen.”

A Shimadzu AGS-X tensile machine was then used to perform tensile testing on the 42 3D printed PLA specimens. Properties like elastic modulus, strain, toughness, ultimate tensile strength (UTS), and yield strength were tested.

The team learned some interesting things, such as the fact that the red PLA had the highest elastic modulus, yield strength, and ultimate tensile strength, while pink had the lowest numbers for these. But, pink had the highest toughness and influence on strain, while blue had the lowest.

Once the testing was complete, the researchers determined the following:

• Color of PLA had an influence on elastic modulus, and varies up to 18% (from 2719MPa to 3217MPa) depending on color
• Color of PLA had an influence on yield strength, and varies up to 36% (from 30MPa to 41MPa) depending on color
• Color of PLA had an influence on ultimate tensile strength, and varies up to 31% (from 35MPa to 46MPa) depending on color
• Color of PLA had an influence on toughness, and varies over 300% (from 10J to 48J) depending on color
• Color of PLA had an influence on strain, and varies over 400% (from 7% to 108%) depending on color

“In future research, the influence of material colour on other mechanical properties (bending, hardness, pressure, etc.) should be examined, and also influence of colour on mechanical properties of other materials (ABS, PET, etc.),” they concluded.

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

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

3D printout with possible anisotropy vs. friction direction.

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

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

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

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

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

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

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

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

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

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

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

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

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

 

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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Study Shows Anisotropic Properties of 3D Printed Nickel Super Alloy K418 (713C)

3D printing materials don’t just suddenly appear and get put to use without further thought – there is a great deal of study that goes into them, particularly metal materials. Their behaviors and properties must be known in order to make sure they perform. Especially now that our technology is being used in high-value applications such as aero-engines and medcine research about material properties and performance is growing in both volume and importance. In a new study entitled “Anisotropy of nickel-based superalloy K418 fabricated by selective laser melting,” a group of researchers used 3D printed samples to study the anisotropic mechanical behavior of one particular material – K418, a nickel-based superalloy.

K418 was developed in the 1960s and has been used on a widespread basis in aerospace engines, hot end turbocharger impellers, turbine blades the automotive industry, and more. It has excellent mechanical properties, excellent ductility and fatigue strength, good oxidation resistance at high temperatures, making it a stable and reliable material. It is difficult to machine by conventional methods at room temperature, however, due to excessive tool wearing, high cutting temperature, and other issues. Components made from K418 are often complex, with inner chambers, thin walls, and overhangs, making them difficult to fabricate through one single method such as machining. This alloy is also known as 713C Alloy, 713C,or Inconel 713C Alloy and many derivatives thereof. Inconel is actually a superalloy that was developed in the 60″s but became a catch-all name for the many superalloys developed around the same time frame. Inconel 713LC was a proprietary alloy made by the INCO (INCO was a global Canadian mining company that was the world’s largest producer of nickel, bought by Vale in 2006) and this term plus all of the derivatives are used interchangeably. 713C or as it is also known K418 has been used extensively in rocket engines, turbo stages and in the space and defense industries since the 60’s. SpaceX, NASA, Rocketdyne and others are all using this material to 3D print rocket engines.

Selective laser melting (SLM, also called powder bed fusion, DMLS, Direct Metal Laser Sintering, PBF) has shown itself to be more effective than conventional techniques like machining at manufacturing complex metal components. Thanks to its high temperature and rapid cooling, it also offers better mechanical properties than casting.

In this study, the researchers looked at the anisotropic properties of the K418 alloy. Anisotropy is defined as a difference in physical or mechanical properties when measured along different axes – in other words, a material’s properties could be different along the vertical axis than along the horizontal axis. In FDM (material extrusion) printed parts for example parts are weaker in between layers than laterally.

The researchers used a self-developed SLM 3D printer to produce several cylinders from the K418 material. The samples were manufactured both horizontally and vertically, or transverse and longitudinal. Microstructural anisotropy analysis was performed on both the horizontal and vertical samples.

“The microstructural anisotropy analysis was performed by optical microscopy (OM) and scanning electron microscopy (SEM),” the researchers explain. “Electron backscatter diffraction (EBSD) analysis was used to identify their crystallographic preferred orientation (texture) and to correlate the anisotropy of the mechanical strength with the texture of the material. The results showed that the transverse specimens had slightly higher yield strength, but much significantly higher ductility than that of the transverse specimens with the elongated columnar grains along the building direction.”

SEM micrographs of (a and b) the horizontal samples and (b and c) the vertical samples.

The extremely high thermal gradient and rapid cooling rate during the SLM process led to strong non-equilibrium solidification of the molten pool and the formation of ultrafine grain structure, which resulted in anisotropic microstructures and mechanical properties in different directions.

“The presence of textures renders the SLM processed K418 samples anisotropic in their mechanical properties, indicating that the transverse specimens display a ductile-brittle hybrid fracture mode with a slightly higher yield strength, while the vertical specimens show a ductile fracture mode with a significant increase in ductility,” the researchers continue.

The fact that SLM-produced K418 has anisotropic properties is an interesting finding. The finding may mean that engineers will feel more comfortable using and designing K418 parts using 3D printing. Metal 3D printing is an extremely effective method for producing components from this material, particularly complex structures. Given the performance envelope of this material and its space applications, this is sure to be an article that many will take an interest in. For some more reading on Inconel this article discusses cooling rates and their effects on Inconel 718 and in this article, we look at how Inconel 718 is being used by Launcher.

Authors of the paper include Zhen Chen, Shenggui Chen, Zhengying Wei, Lijuan Zhang, Pei Wei, Bingheng Lu, Shuzhe Zhang, and Yu Xiang.

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