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Exploring the Manufacturability and Resistivity of Conductive Filament Used in Material Extrusion Additive Manufacturing Harry Gao and Nicholas A. Meisel Made By Design Laboratory School of Engineering Design, Technology, and Professional Programs, Penn State ABSTRACT Additive manufacturing (AM) has the unique ability to build multifunctional parts with embedded electronics without the need for post-print assembly. However, many existing forms of multifunctional AM are not easily accessible to hobby-level users. Most hobby-level desktop 3D printers are only used with non-conductive filaments. Recently however, conductive filaments have become increasingly available for material extrusion desktop printers. Ideally, the use of these filaments would allow circuitry to be printed simultaneously with the rest of the structure, enabling complex, inexpensive, multifunctional structures. However, the resistivity of conductive filament is significantly impacted by the geometry of the print and the printing parameters used in the build process. In this study, two types of commercially-available conductive filament were tested under a variety of parameters. It was found that print temperature, layer height, and orientation all significantly affect the resistivity in various ways. The knowledge from this research will allow users to design better multifunctional parts that have reduced resistivity. 1. INTRODUCTION Additive Manufacturing (AM, or 3D printing), is a process that forms complex three- dimensional parts by building layer by layer. Compared to traditional subtractive manufacturing processes, AM offers many unique advantages. With AM, complex geometries can be produced quickly with low tooling costs, reduced lead times, and rapid iteration [1]. The material extrusion process is one of the most popular and inexpensive form of AM. In this process, thermoplastic material is heated until it is past its melting point and then deposited onto a build platform. A fine nozzle is used to direct the deposition of material and a robotic structure controls the position of the nozzle to create the desired geometry [2]. Material extrusion is simple, easy to learn, and highly accessible, making it popular among both hobbyists and industrial manufacturers. The layer-wise nature of AM allows abundant flexibility in the design process, including access to the entire internal structure of a design as it is being manufactured. This makes it possible to embed foreign components within the internal structure and then continue to print over them. By building components directly into the structure, the final product can be manufactured without the need to assemble, fasten, or glue anything afterwards. The ability to embed components leads to multifunctionality, where fully functional products are created by embedding different foreign components (particularly electronics) within the print. Ideally, this would greatly shorten or even eliminate the time needed to assemble the product afterwards, speeding up production and reducing potential points of failure. However, many existing forms of printed electronics require expensive equipment and special inks, putting them out of reach for a large group of users. Recently however, carbon-based conductive filaments have been developed for use in desktop- scale material extrusion printers. The resistivity of these filaments have been measured by researchers under ideal circumstances [3], [4]. However, the material extrusion process can be 1612 Solid Freeform Fabrication 2017: Proceedings of the 28th Annual International Solid Freeform Fabrication Symposium – An Additive Manufacturing Conference Reviewed Paper

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  • Exploring the Manufacturability and Resistivity of Conductive Filament Used

    in Material Extrusion Additive Manufacturing Harry Gao and Nicholas A. Meisel

    Made By Design Laboratory

    School of Engineering Design, Technology, and Professional Programs, Penn State

    ABSTRACT

    Additive manufacturing (AM) has the unique ability to build multifunctional parts with

    embedded electronics without the need for post-print assembly. However, many existing forms of

    multifunctional AM are not easily accessible to hobby-level users. Most hobby-level desktop 3D

    printers are only used with non-conductive filaments. Recently however, conductive filaments

    have become increasingly available for material extrusion desktop printers. Ideally, the use of these

    filaments would allow circuitry to be printed simultaneously with the rest of the structure, enabling

    complex, inexpensive, multifunctional structures. However, the resistivity of conductive filament

    is significantly impacted by the geometry of the print and the printing parameters used in the build

    process. In this study, two types of commercially-available conductive filament were tested under

    a variety of parameters. It was found that print temperature, layer height, and orientation all

    significantly affect the resistivity in various ways. The knowledge from this research will allow

    users to design better multifunctional parts that have reduced resistivity.

    1. INTRODUCTION

    Additive Manufacturing (AM, or 3D printing), is a process that forms complex three-

    dimensional parts by building layer by layer. Compared to traditional subtractive manufacturing

    processes, AM offers many unique advantages. With AM, complex geometries can be produced

    quickly with low tooling costs, reduced lead times, and rapid iteration [1]. The material extrusion

    process is one of the most popular and inexpensive form of AM. In this process, thermoplastic

    material is heated until it is past its melting point and then deposited onto a build platform. A fine

    nozzle is used to direct the deposition of material and a robotic structure controls the position of

    the nozzle to create the desired geometry [2]. Material extrusion is simple, easy to learn, and highly

    accessible, making it popular among both hobbyists and industrial manufacturers.

    The layer-wise nature of AM allows abundant flexibility in the design process, including

    access to the entire internal structure of a design as it is being manufactured. This makes it possible

    to embed foreign components within the internal structure and then continue to print over them.

    By building components directly into the structure, the final product can be manufactured without

    the need to assemble, fasten, or glue anything afterwards. The ability to embed components leads

    to multifunctionality, where fully functional products are created by embedding different foreign

    components (particularly electronics) within the print. Ideally, this would greatly shorten or even

    eliminate the time needed to assemble the product afterwards, speeding up production and

    reducing potential points of failure. However, many existing forms of printed electronics require

    expensive equipment and special inks, putting them out of reach for a large group of users.

    Recently however, carbon-based conductive filaments have been developed for use in desktop-

    scale material extrusion printers. The resistivity of these filaments have been measured by

    researchers under ideal circumstances [3], [4]. However, the material extrusion process can be

    1612

    Solid Freeform Fabrication 2017: Proceedings of the 28th Annual InternationalSolid Freeform Fabrication Symposium – An Additive Manufacturing Conference

    Reviewed Paper

  • used with a wide range of parameters and geometries, which may impact resistivity beyond what

    has been measured. For example, resistivity is usually measured based on a solid, homogeneous

    block of material, which is not what actually would be used in a multifunctional part. Existing

    research has not looked at the effect of factors such as nozzle temperature, layer height, geometry,

    or orientation on the resistivity of these conductive filaments. In addition, the effect of encasing

    conductive filament with non-conductive filament (as in an embedded component) has not been

    studied. This is important since multifunctional parts commonly make use of embedded filaments,

    and it is necessary to ensure that embedding does not increase resistivity of conductive traces.

    In this research study, two different types of conductive filament, Protopasta conductive PLA

    and BlackMagic conductive graphene, are tested under different printing parameters and

    geometries to evaluate their resistivity and manufacturability. In addition, the effect of embedding

    (via a dual-extrusion process) on resistivity is evaluated. Taking what is learned from the

    experimentation, the end goal is to determine guidelines that can allow potential users to better

    design for additive manufacturing when using conductive filaments.

    2. EXISTING RESEARCH OF MULTIFUNCTIONAL ELECTRONICS IN AM

    Related research has been divided into three sections. Section 2.1 discusses the possibilities of

    multifunctional printing. Section 2.2 discusses direct write technology with conductive materials.

    Section 2.3 discusses recent studies into material extrusion conductive filaments.

    2.1 Multifunctional AM

    Since its introduction, AM has offered many advantages in the way components can be

    designed and made. The freedom of design for additive manufacturing (DfAM) and the availability

    of an ever-expanding library of materials has led to the growth of multifunctional AM. While

    standard AM uses just one material, the idea behind multifunctional printing is combining different

    types of materials - particularly electronics - so that functional components can be produced

    without the need to assemble any parts after the build process. Some recent work has explored the

    use of AM with conductive materials to see what can be done with current technology.

    Aguilera et al. [5] designed and built a printed electric motor, taking advantage of the

    embedding capability of AM. Components such as the magnets, controllers, and wiring were

    embedded directly into the structure of the motor. The end result was a custom-built, fully

    functional motor that did not require any post-printing assembly. Similarly, MacDonald et al. [6]

    compared the use of AM (via direct write conductive inks and stereolithography) to traditional

    injection molding for the purposes of prototyping and manufacturing an electronic gaming die.

    The researchers found that the time to market could be significantly improved using AM compared

    to traditional manufacturing. They estimated that the additive method was at least 400% faster than

    the traditional method. By harnessing the capability to direct write and embed electronic circuitry

    into the products, they could be evaluated for fit, form, and function simultaneously. Klomp [4]

    explored the use and applications of the material extrusion method with conductive filaments. The

    researchers printed a capacitive touch wheel and a capacitive touch sphere using dual extrusion

    and conductive filament. By connecting the capacitive sensors to Arduinos, they were able to use

    them to control LED lights, music, and even video games. While these are only a few examples

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  • of how multifunctional AM has been utilized in product design, they nevertheless capture the

    possibility offered by multifunctional embedding or direct write.

    2.2 Direct Write

    Direct writing describes processes that can deposit thin layers of conductive materials at very

    high accuracy to support the creation of multifunctional structures. Hon [7] discusses many

    different methods of direct writing, including inkjet, laser, and mechanical systems. Direct writing

    is usually but not always related to electronic circuitry and conductive materials. As an additive

    process, direct writing offers many similar advantages such as reducing waste material, enabling

    greater design flexibility, and speeding up the manufacturing process [8]. There is significant

    overlap between technologies used for direct writing and for additive manufacturing. For example,

    extrusion-type direct write machines are very similar in basic function to a common material

    extrusion 3D printer. Inkjet and aerosol jet direct writing is similar to the polymer jetting method

    of additive manufacturing. However, compared to AM (especially material extrusion), most forms

    of direct writing are designed for specialized purposes and not easily accessible to an average user.

    There has also been significant research into the impact of design and processing on the

    conductivity of direct-write traces. For example, Perez [9] deposited silver conductive ink and

    embedded it into various geometries during the material jetting process, and the resistivity was

    observed. Encapsulating the conductive ink with non-conductive material was found to

    significantly increase the resistivity of traces compared to fully-exposed conductive ink. The

    researchers concluded that, due to the high resistivity of their sample traces, they would not be

    well suited for high power applications. However, they demonstrated that the method could be

    used for strain gauge and capacitive sensor applications.

    2.3 Conductive filament

    Currently, multifunctional printing and direct writing are out of reach of many hobby-level

    users, due to the need for expensive conductive inks and specialized equipment. In recent years,

    researchers and manufacturers have been working to develop carbon-composite filaments that

    would be capable of being used with common desktop-scale material extrusion printers. Since

    material extrusion is by far the most widely accessible form of AM, this would allow

    multifunctional printing to reach a much wider audience. Of course, the filament must not only be

    accessible but also sufficiently conductive. While matching the resistivity of direct write inks

    would be ideal, higher resistivity can still be useful for sensors and gauges, as stated by Perez [9].

    In general, conductive filaments are created by adding carbon to standard filament in order to

    improve its properties. By mixing small quantities of these materials into standard filament, the

    filament will takes on some of the properties of the carbon material, but can still be heated and

    extruded normally. Ibrahim et al. [3] performed an initial study on the resistivity of Protopasta

    conductive PLA under different lengths and volumes, and compared its resistivity to a conductive

    ABS filament. The researchers tested the resistivity of different lengths of the filament (before

    extrusion), as well as the resistivity of single strands of extruded filament. In both cases, the

    resistivity was found to be abnormally high within the first 10 mm of filament, quickly dropping

    down to a more consistent level around 20 mm. They found the resistivity of the extruded filament

    to be around 0.25 ohm-meters, which correlates with ProtoPlant's claims. Klomp [4] tested several

    1614

  • different conductive filaments, including Protopasta conductive PLA. They observed a resistivity

    of 0.46 ohm-m along the layers of a 3D-printed cube, and 0.84 ohm-m across the layers. Protopasta

    was found to be the best of the filaments they tested, being both the least resistive and the easiest

    to print. The numbers they observed are somewhat higher than Ibrahim and Protopasta’s claims.

    As this review of literature has shown, existing work has emphasized the mechanical properties

    and some potential applications of conductive filaments. However, the aspect of design for additive

    manufacturing with these new filaments has largely been ignored. This aspect is particularly

    important since it is unknown how the resistivity of these filaments can vary based on different

    conditions, including print parameters and part geometries. The goal of this research is to try to

    address this gap in knowledge. With a better understanding of the effects of different parameters,

    users will be able to design and print multifunctional parts with resistivity that better matches the

    designer’s intended application.

    3. EXPERIMENTAL APPROACH

    There are three primary objectives of this research study. The first is to investigate the effects

    of print parameters on the resistivity of conductive filaments, including nozzle temperature, layer

    height, extrusion speed, and travel speed. The second objective is to investigate the effects of print

    geometry on resistivity. This includes part orientation as well as single strands compared to printed

    blocks. The third objective is to investigate the effect of enclosing conductive material using a dual

    extrusion process. The work presented will determine which parameters and geometries will

    produce the lowest resistivity in the printed traces and will act as a guide for designers looking to

    maximize the effectiveness of these traces in low-cost printed electronics.

    3.1 Materials and equipment

    The printer used in this experiment is a Lulzbot TAZ5 fitted with a dual extrusion head. It was

    chosen for this experiment due to its versatility and compatibility with a dual extrusion head as

    well as custom filament materials [10]. The printer was controlled with Cura slicing software,

    which contains pre-made “quickprint” parameters for hundreds of unique filaments, one of which

    is Protopasta conductive PLA [11].

    An important difference between material extrusion and other forms of manufacturing is that

    parts made with material extrusion exhibit significant anisotropic properties affected by the

    orientation of the layers compared to the mechanical or electrical load [12]. As such, build

    orientation nomenclature is essential. According to ASTM standards [13], part orientation is

    named with the longest dimension first and the second-longest dimension second. X and Y are the

    two horizontal dimensions and Z is used for the vertical dimension. As shown in Figure 1, the XY

    orientation refers to a part lying flat on the build plate, the ZX orientation refers to a part standing

    vertically like a column, and the XZ orientation refers to a part lying horizontally on its edge. The

    authors use this standardized naming approach throughout the paper.

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  • Figure 1. Specimens on the build platform in various orientations: (a) XY, (b) ZX, and (c) XZ.

    The two conductive filaments described previously were tested: Protopasta conductive PLA

    and BlackMagic conductive graphene filament. Protoplant claims that its conductive PLA filament

    can achieve up to 0.3 ohm-m in-plane with the layers and 1.15 ohm-m perpendicular to the layers

    (in the ZX orientation) [14]. As previously discussed, Ibrahim et al. [3] were also able to observe

    a resistivity of approximately 0.25 ohm-m. The second conductive filament is Conductive

    Graphene Filament made by BlackMagic3D. The company claims that the filament has a volume

    resistivity as low as 0.006 ohm-m [15].

    3.2 Selection of independent variables

    Four independent variables were chosen to be analyzed in the initial set of experiments: Print

    temperature, layer height, extrusion speed, and travel speed. Once some consistent trends were

    established with the initial horizontal (XY) experiments, the vertical (ZX) experiments only looked

    at layer height as the independent variable. Finally, the independent variable for the dual extrusion

    experiments was how much of the conductive sample’s cross-sectional perimeter was enclosed.

    Five levels were chosen for each independent variable, summarized in Table 1 below. The

    levels were chosen based on recommended manufacturer settings and common 3D printer settings.

    In addition, manufacturability was used to determine the range of parameters. For example, test

    samples would not print reliably below 200ºC or above 240ºC. At temperatures below 200ºC, the

    filament was not hot enough to extrude, while at temperatures above 240ºC, the extruded filament

    would flow excessively and would not adhere to the intended structure.

    Table 1. Table of independent variables and parameters Temperature (C) Layer Height (mm) Extrusion Speed (mm/s) Travel Speed (mm/s)

    200 0.2 10 140

    210 0.3 30 160

    220 0.4 50 180

    230 0.5 70 200

    240 0.6 90 220

    3.2 Single Strand Samples

    The first part of the experimentation consisted of testing single strands of filament, for both

    Conductive PLA and graphene materials. The samples were printed with nominal dimensions of

    0.5 mm x 0.5 mm x 30 mm; however, due to the flexibility of extruded material before cooling

    and the use of different layer heights, the actual dimensions of the samples varied. For example,

    the strand printed at 0.2 mm layer height had a height of 0.2 mm and a width of 0.8 mm.

    1616

  • Meanwhile, a layer height of 0.5 mm would result in dimensions closer to 0.5 x 0.5 mm. Among

    samples with the same nominal dimensions, the physical dimensions varied by about ±0.05 mm.

    The cross-sectional width and height of the samples were measured using a Neiko digital caliper

    with an accuracy of 0.02 mm.

    Figure 2. A single strand sample being tested for resistivity

    The resistance of the samples were tested using a Hewlett-Packard 972A handheld multimeter.

    The accuracy for ohm measurements is 0.2%. The hook leads were pushed through a block of

    foam to maintain a constant 20 mm distance. The distance between the leads was confirmed via

    digital caliper. The resistivity was then determined by using the equation

    𝑅𝑒𝑠𝑖𝑠𝑡𝑖𝑣𝑖𝑡𝑦 (𝑜ℎ𝑚 ∗ 𝑚) = 𝑅𝑒𝑠𝑖𝑠𝑡𝑎𝑛𝑐𝑒 (𝑜ℎ𝑚) ∗ 𝑤𝑖𝑑𝑡ℎ (𝑚) ∗ ℎ𝑒𝑖𝑔ℎ𝑡 (𝑚)

    𝑙𝑒𝑛𝑔𝑡ℎ (𝑚)

    The conductivity could then be found by taking the inverse of the resistivity. To analyze trends

    across multiple changing variables, a Response Surface Methodology (RSM) was used. Minitab

    was used to generate a full response surface design, consisting of 31 runs, for the horizontal single-

    strand testing. For each run, three samples were printed using the parameters defined in the run.

    3.3 Horizontal Block Samples

    The second geometry was a thin, rectangular block, designed to test the layer-on-layer and

    road-to-road effects of printed filament. The dimensions of the block were 1.5 mm x 1.5 mm x 30

    mm. There was a difference of up to ±0.2 mm in the measured dimensions compared to the nominal

    dimensions. The samples were attached to the multimeter using alligator-type leads, shown in

    Figure 3. This method was used to measure the resistivity along the layers (in the XY orientation).

    The same response surface design used for the single strand testing was used again here. This

    included 31 different runs and 3 samples tested for each run.

    Figure 3. A horizontal block sample being tested for resistivity

    3.4 Vertical Block Samples

    The third geometry was similar to the second, but this time printed in the vertical (ZX)

    orientation so that the layers were stacked on top of each other. However, printing in the ZX

    1617

  • orientation is much more unstable since the base size is very small and tall samples tend to wobble

    when nearing the top of the print. Because of this, 2 x 2 mm dimensions were chosen for the

    vertical sample. Figure 4 shows an example of a 2 x 2 mm vertical sample. The samples were

    measured in the same fashion, but due to the different orientation, the resistivity across layers (ZX

    orientation) was now being measured.

    Figure 4. A 2 x 2 mm vertical sample with a layer height of 0.5 mm

    After a set of optimal build parameters had been determined from the horizontal testing, they

    could be used to narrow down the experimental variables for this geometry experimentation. Print

    temperature was held constant at 240℃, extrusion speed was held at 50 mm/s, and travel speed

    was held at 180 mm/s for the conductive PLA material. For the graphene filament, the print

    temperature was held constant at 230℃, extrusion speed was held at 30 mm/s, and travel speed

    was held at 180 mm/s. The only independent variable for the ZX oriented specimens was the layer

    height, which again ranged from 0.2 mm to 0.6 mm in 0.1 mm increments.

    3.4 Dual extrusion samples

    Finally, dual extrusion samples were tested in the horizontal (XY) and vertical (ZX)

    orientations. In the horizontal sample, the central non-conductive section was exactly 20 mm long

    and the ends of the conductive section were left exposed. This was done so that the alligator clips

    could be attached right against the central section, ensuring a constant distance for measurement.

    Figure 5. Horizontal and vertical dual extrusion samples.

    In the vertical orientation, the sample geometry had to be changed. In order to print the previous

    sample in the vertical orientation, the non-conductive sheath would have to be printed in the air.

    The geometry was too small to attach support material below the sheath. Printing would cause the

    sheath section to sag during the build process, making measurement inaccurate. Instead, a new

    sample and method of measurement was chosen. The sample and sheath were both printed to be

    1618

  • 20 mm tall. To measure the resistance, copper tape was attached to the top and bottom ends of the

    sample, which were then connected to the multimeter via alligator clips. For the dual extrusion

    testing, the only independent variable was whether or not the conductive sample was encased by

    a non-conductive sheath. The samples were printed using the same parameters discussed

    previously. All horizontal samples were printed at 0.2 mm layer height, and all vertical samples

    were printed at 0.6 mm layer height.

    4. RESULTS AND ANALYSIS

    As discussed in Section 3, response surface methodology (RSM) was used to analyze the

    results of the experiments. The RSM method fits a second-order polynomial to the model. In a

    RSM analysis of variance, the linear p-value determines the significance of a linear trend. The

    square p-value determines the significance of a parabolic trend. A parabolic trend suggests that the

    variable has a maxima or minima, unlike a simple linear relationship. The parabolic trend can be

    independent of the linear trend, so there does not need to be a significant linear p-value in order

    for the square p-value to be valid. In addition, the RSM analysis of variance also determines the

    relationship of interaction effects. A statistically significant two-way interaction effect can be

    confirmed as long as one of the individual main effects is also significant.

    4.1 Single Strand PLA Samples

    Assuming that a p-value of 0.05 or less denotes statistical significance, it can be seen in Table

    2 that there is a significant linear main effect for both nozzle temperature and extrusion speed with

    respect to the resistivity of the sample. There is also a significant parabolic main effect for

    temperature. This indicates that the relationship between temperature and resistivity can be

    described as a parabola. By looking at the following main effects plot in Figure 6, we can see the

    trends suggested by the data.

    Table 2. Analysis of Variance for the Single-Strand Conductive PLA samples. Variable p-value

    Temperature

  • 230ºC. This correlates with Protoplant's recommended print temperature. The layer height and

    travel speed plots are not statistically significant. For extrusion speed, the analysis of variance says

    that the linear trend is significant, but the parabolic trend is not. In other words, resistivity generally

    increases with greater extrusion speed, but there is probably not a significant local minimum as

    suggested by the plot.

    It makes intuitive sense for higher temperature to result in lower resistivity. Zhang et al. [16]

    suggested that the extrusion process affects resistivity by orienting the conductive particles. A

    higher printing temperature increases the filament viscosity [17], which may allow the particles to

    flow more freely and better distribute themselves within the filament instead of getting

    agglomerating. An extrusion speed that is too high may lead to inaccurate deposition [17], which

    could cause the conductive particles to be further apart than desired. Conversely, an extrusion

    speed that is too low may cause clogging and inconsistent deposition. In this case, the layer height

    is not significant because only one layer was printed; its largest effect was changing the dimensions

    of the single layer. Also, travel speed is not significant since only a single strand was printed, so

    there are no actual travel movements.

    The measured resistivity of the single-strand filament ranges from 0.045 ohm-m in the best-

    case scenario (print temperature at 230°C) to 0.055 ohm-m at a print temperature of 200°C. In

    comparison, Ibrahim [3] observed a value of 0.25 ohm-m for single-strand extruded filament, with

    print temperature in the range of 210ºC to 230ºC. The observed resistivity was around 80% lower

    than Ibrahim’s data. This may be due to the use of a different method of measurement.

    4.2 Single Strand Graphene Samples

    For the graphene samples, only temperature was found to have a statistically significant effect.

    Again, temperature had a parabolic relationship with a minimum resistivity at 230ºC. The overall

    resistivity was only a small amount lower than the Conductive PLA, with a range of about 0.01

    ohm-m to 0.05 ohm-m.

    Table 3. Analysis of Variance for the Single-Strand Graphene samples. Variable p-value

    Temperature

  • This measured resistivity is approximately 2-8 times larger than the resistivity claimed by

    BlackMagic for their filament. This could be due to a number of factors. First, BlackMagic did not

    specify whether their value was measured based on a printed sample or if it was based on a pure

    block of graphene. Second, when measuring very low resistances, the magnitude of any possible

    errors are magnified. While the actual resistances that were being measured should be well within

    the capability of the multimeter, any sort of error caused by an imperfect connection to the sample

    or an incorrect caliper measurement could have a significant impact on the result. For instance, the

    measurement error of the calipers is ±0.02 mm, which is up to 5% of a single dimensional

    measurement. When combined with the 3 dimensions, and the fact that an error in length may also

    affect the measured resistance, the effect of caliper error could be 15-20%.

    4.3 Horizontal (XY) Block PLA Samples

    The analysis of variance for the PLA horizontal block samples shows that both temperature

    and layer height were statistically significant based on a linear relationship. However, the parabolic

    relationships were not significant. This suggests that higher temperature (240ºC) and lower layer

    height (0.2 mm) tend to reduce resistivity in the horizontal (XY) orientation. The effect of

    extrusion speed was found to be not significant in the linear but significant in the parabolic. This

    suggests that there is an ideal extrusion speed at approximately 50 mm/s, and going too far below

    or above this speed will cause resistivity to increase. The effect of travel speed was again not found

    to be significant.

    Table 4. Analysis of Variance for the Horizontal Block Conductive PLA samples. Variable p-value

    Temperature

  • freely. The effect of lower layer height is also as expected. Lower layer height means that the

    dimensions of the block are filled more completely and there are fewer gaps between printed roads.

    This should result in less contact resistance as the current flows in the direction of the layers.

    The observed resistivity for each of the block samples is much higher than the single-strand

    samples, which makes sense since contact resistance now plays a much greater role in overall

    resistivity. Based on the contour plot, it appears that an ideal sample printed at 240ºC with 0.2 mm

    layer height and 50 mm/s extrusion speed should have a resistivity of close to 0.1 ohm-m. In

    comparison, the manufacturer claims a resistivity of 0.25 ohm-m for printed parts in the XY

    orientation [14], and Klomp observed a resistivity of 0.46 ohm-m in the XY orientation [4]. The

    resistivity observed this study is about 60-80% lower. One potential explanation for this

    discrepancy is the difference in sample geometry. The standard sample geometry for volume

    resistivity testing is a 10 mm cube, and this is what was used by both the manufacturer and Klomp.

    However, Ibrahim [3] found that the resistivity of single-strand conductive PLA was abnormally

    high in the first 10 mm, dropping down to a consistent value after 20 mm. Further research should

    be done to see if this may have an effect on printed samples as well.

    4.4 Horizontal (XY) Block Graphene Samples

    For the graphene samples, only temperature and layer height were found to be significant, and

    this time temperature had a parabolic relationship. The temperature has a minimum at about 230ºC,

    which correlates well with BlackMagic's recommended print temperature of 220°C. This time the

    extrusion speed was found to have very little significance at all.

    Table 5. Analysis of Variance for the Horizontal Block Graphene samples. Variable p-value

    Temperature 0.018

    Layer Height 0.012

    Temperature*Temperature 0.040

    Figure 9. Main Effects Plot for Graphene Horizontal Block samples

    From Figure 9, the overall resistivity ranges from just under 0.06 ohm-m to 0.085 ohm-m,

    which is two orders of magnitude higher than the manufacturer’s claimed resistivity. While this

    seems significant, as noted before, the manufacturer’s claimed resistivity may not have been

    measured based on a printed part. BlackMagic readily admits that "the resistivity will change

    depending on your print" so a higher resistivity than the ideal is to be expected [15]. In this case,

    1622

  • it is likely that the contact resistances between the printed layers and strands are preventing the

    current from flowing as quickly as it could in a homogeneous block of material.

    4.5 Vertical (ZX) Block PLA Samples

    After several rounds of testing, the effect of print temperature was found to relatively

    consistent, with a temperature of 230-240ºC being the best for most samples. The effect of

    extrusion speed was also relatively consistent, with an optimal extrusion speed at 50 mm/s for

    PLA. The ideal numbers also generally match up well with the parameters recommended by the

    manufacturers. Travel speed has been found to be insignificant in all cases so far. Due to these

    findings, for the vertical (ZX) block samples, experimentation focused on the most important

    variable, layer height. Each layer height was tested three times, and the results were averaged. A

    one-way ANOVA was performed to determine the statistical significance of the effect of layer

    height on ZX block specimens; the calculated p-value was less than 0.001.

    Figure 10. Plot of resistivity vs. layer height for the vertical conductive PLA samples.

    The resistivity results of the vertical samples were contrary to the original hypothesis. Instead

    of lower layer heights causing lower resistivity, Figure 10 shows that higher layer heights result in

    lower resistivity. Of course, this is for the vertical orientation only - in the horizontal, lower layer

    heights still produce less resistivity. This result is surprising at first, but makes sense on closer

    examination. In the horizontal orientation, the current was flowing along the layers - as if flowing

    through a wire. However, in the vertical orientation, the current is flowing across the layers. A low

    layer height means a much larger number of interfaces that the current must cross, and each one

    has contact resistances. A higher layer height means much fewer interfaces, and therefore less

    resistance. See Figure 11 for a visualization. In the space of one 0.6 mm layer, there could be three

    0.2 mm layers. In the 0.2 mm sample, the current would have to cross three different layers, while

    in the 0.6 mm sample, the current can flow unimpeded across a homogeneous single layer.

    0.1

    0.15

    0.2

    0.25

    0.3

    0.35

    0.4

    0.45

    0.5

    0.55

    0.2 0.3 0.4 0.5 0.6

    Re

    sist

    ivit

    y (o

    hm

    *m)

    Layer Height ( mm)

    1623

  • As the data shows, the 0.4 mm layer height has almost the same resistivity as the 0.6 mm layer

    height in the vertical orientation. However, it has much lower resistivity in the horizontal

    orientation. Therefore, if a component needs to be printed using conductive filament in both

    horizontal and vertical orientations, then 0.4 mm layer height would be a well-balanced

    compromise choice. Protoplant originally claimed a resistance of 1.15 ohm-m when measuring

    resistivity across the layers [14], and Klomp observed a resistance of 0.84 ohm-m [4]. These results

    show resistivity that is around 60-80% lower. The resistivity would depend on the layer height that

    Protoplant and Klomp used when testing, which is unknown. If they used 0.2 mm or lower, then

    the results differ by the same margin as the horizontal samples.

    4.6 Vertical (ZX) Block Graphene Samples

    For the graphene samples, a similar decreasing trend can be seen in Figure 12, with a p-value

    of 0.3745. However, since the overall resistivity of the graphene samples is much lower (while the

    standard deviation was similar), the results cannot be considered statistically significant. Based on

    the behavior of the conductive PLA, it seems likely that graphene should also exhibit less

    resistivity with higher layer height. However, more accurate testing must be done in order to

    confirm this.

    Figure 12. Plot of resistivity vs. layer height for the vertical graphene samples.

    4.7 Dual Extrusion Samples

    The dual extrusion experiments were conducted to see if enclosing the conductive filament

    with regular non-conductive filament would affect its resistivity. In an actual multifunctional part,

    most conductive filament would be enclosed, so this is an important factor in overall resistivity.

    Based on the calculated p-values for each pair of samples, the effect of dual extrusion was not

    found to have a statistically significant effect on resistivity in all cases.

    0.1

    0.12

    0.14

    0.16

    0.18

    0.2

    0.2 0.3 0.4 0.5 0.6

    Re

    sist

    ivit

    y (o

    hm

    *m)

    Layer Height ( mm)

    Figure 11. A schematic comparing interfaces for 0.2 mm layer height with 0.6 mm layer height.

    1624

  • Table 6. Dual extrusion results (XY = horizontal, ZX = vertical, SE = single extrusion, DE =

    dual extrusion) Resistivity 1 Resistivity 2 Resistivity 3 Average (ohm-m) Std Dev p-value

    PLA XY SE 0.101 0.122 0.115 0.113 0.0107

    PLA XY DE 0.106 0.135 0.124 0.122 0.0146 0.647

    Graphene XY SE 0.0587 0.0622 0.0683 0.0631 0.00486

    Graphene XY DE 0.0572 0.0733 0.0637 0.0647 0.00810 0.950

    PLA ZX SE 0.212 0.194 0.204 0.203 0.00902

    PLA ZX DE 0.186 0.234 0.215 0.212 0.0242 0.606

    Graphene ZX SE 0.134 0.146 0.102 0.127 0.0227

    Graphene ZX DE 0.167 0.128 0.175 0.157 0.0251 0.208

    5. CONCLUSIONS AND FUTURE WORK

    The goal of this research study was to analyze the effect of print parameters such as

    temperature, layer height, extrusion speed, and travel speed on the resistivity of conductive

    filaments. The second major goal was to analyze the effects of on resistivity. The third major goal

    was to determine whether dual extrusion would affect resistivity. Two different types of

    commercially-available conductive filament were selected, tested, and compared. Various samples

    were printed under a range of different parameters and geometries, and their resistivities were

    analyzed using response surface methodology. Based on these tests, the authors conclude that:

    Generally, higher print temperature correlates to lower resistivity, up to certain limits. Conductive PLA does best at around 240°C, and graphene does best at around 230°C.

    Excessively high nozzle temperatures cause unreliable extrusion.

    Smaller layer height reduces resistivity when measuring along the filament (horizontal orientation). When measuring across the filament (vertical orientation), smaller layer

    height increases resistivity. A good balance can be struck at 0.4 mm layer height if

    conductivity in both orientations is required.

    The best extrusion speed for conductive PLA is around 50 mm/s. Extrusion speed does not appear to have a significant effect on the resistivity for graphene.

    Travel speed does not appear to have a significant effect on resistivity at all. Enclosing a conductive trace within standard non-conductive filament does not appear to

    impact its resistivity.

    To expand the breadth of this research, future work should focus on studying applications of

    this technology. The knowledge of print parameters and the effects of different geometries can be

    applied to the design of printed electronics, such as capacitive sensors and strain gages. Future

    work could study how to best use conductive material extrusion printing to produce low-cost,

    customizable electronic components. In addition, future work could look into the chemical

    composition of conductive filaments to gain a more concrete understanding of why the resistivity

    changes under different conditions, which may lead to more useful and versatile conductive

    filaments in the future. Another potential area of research would be studying a wider range of

    conductive filaments. In addition to conductive PLA and graphene, there are a range of other

    commercially available conductive filaments, including filaments that are loaded with silver or

    copper particles.

    1625

  • 6. REFERENCES

    [1] P. Isanaka and F. Liou, “The Applications of Additive Manufacturing Technologies in

    Cyber Enabled Manufacturing Systems,” Proc. Annu. Int. Solid Free. Fabr. Symp. - An

    Addit. Manuf. Conf., pp. 341–353, 2012.

    [2] D. Espalin et al., “Rapid Prototyping Journal A review of melt extrusion additive

    manufacturing processes: I. Process design and modeling,” Rapid Prototyp. J. Rapid

    Prototyp. J. Rapid Prototyp. J. Iss Rapid Prototyp. J., vol. 20, no. 3, pp. 192–204, 2014.

    [3] M. Ibrahim, Y. Mogan, S. N. Shafiqah Jamry, and R. Periyasamy, “Resistivity study on

    conductive composite filament for freeform fabrication of functionality embedded

    products,” ARPN J. Eng. Appl. Sci., vol. 11, no. 10, pp. 6525–6530, 2016.

    [4] S. Klomp, “Printing Conductive and Non-Conductive Materials Simultaneously on Low-

    End 3D Printers,” University of Ghent, 2015.

    [5] E. Aguilera et al., “3D Printing of Electro Mechanical Systems,” Proc. 24th Solid Free.

    Fabr. Symp., pp. 950–961, 2013.

    [6] E. MacDonald et al., “3D printing for the rapid prototyping of structural electronics,”

    IEEE Access, vol. 2, pp. 234–242, 2014.

    [7] K. K. B. Hon, L. Li, and I. M. Hutchings, “Direct writing technology-Advances and

    developments,” CIRP Ann. - Manuf. Technol., vol. 57, no. 2, pp. 601–620, 2008.

    [8] K. H. Church, C. Fore, T. Feeley, C. M. S. Technetronics, N. Richmond, and H. Road,

    “Commercial Applications and Review for Direct Write Technologies,” Mater. Res. Soc.

    Symp. Proc., vol. 624, pp. 3–8, 2000.

    [9] K. B. Perez, “Hybridization of PolyJet and Direct Write for the Direct Manufacture of

    Functional Electronics in Additively Manufactured Components,” Virginia Tech, 2013.

    [10] “Lulzbot TAZ 5 specifications.” .

    [11] “TAZ Cura Profiles.” .

    [12] A. Bellini and S. Güçeri, “Mechanical characterization of parts fabricated using fused

    deposition modeling,” Rapid Prototyp. J., vol. 9, no. 4, pp. 252–264, 2003.

    [13] ASTM Norma, “Standard Test Method for Tensile Properties of Plastics,” Annu. B. ASTM

    Stand., pp. 1–15, 2004.

    [14] “Electrically Conductive PLA Printer Filament,” 2015. .

    [15] “Conductive Graphene Filament,” 2016. .

    [16] D. Zhang et al., “Fabrication of highly conductive graphene flexible circuits by 3D

    printing,” Synth. Met., vol. 217, pp. 79–86, 2016.

    [17] A. H. Peng and Z. M. Wang, “Researches into Influence of Process Parameters on FDM

    Parts Precision,” Appl. Mech. Mater., vol. 34–35, pp. 338–343, 2010.

    1626

    WelcomeTitle PagePrefaceOrganizing CommitteePapers to JournalsTable of ContentsMaterialsScanning Strategies in Electron Beam Melting to Influence Microstructure DevelopmentRelating Processing of Selective Laser Melted Structures to Their Material and Modal PropertiesThermal Property Measurement Methods and Analysis for Additive Manufacturing Solids and PowdersPrediction of Fatigue Lives in Additively Manufactured Alloys Based on the Crack-Growth ConceptFatigue Behavior of Additive Manufactured Parts in Different Process Chains – An Experimental StudyEffect of Process Parameter Variation on Microstructure and Mechanical Properties of Additively Manufactured Ti-6Al-4VOptimal Process Parameters for In Situ Alloyed Ti15Mo Structures by Laser Powder Bed FusionEfficient Fabrication of Ti6Al4V Alloy by Means of Multi-Laser Beam Selective Laser MeltingEffect of Heat Treatment and Hot Isostatic Pressing on the Morphology and Size of Pores in Additive Manufactured Ti-6Al-4V PartsEffect of Build Orientation on Fatigue Performance of Ti-6Al-4V Parts Fabricated via Laser-Based Powder Bed FusionEffect of Specimen Surface Area Size on Fatigue Strength of Additively Manufactured Ti-6Al-4V PartsSmall-Scale Mechanical Properties of Additively Manufactured Ti-6Al-4VDesign and Fabrication of Functionally Graded Material from Ti to Γ-Tial by Laser Metal DepositionTailoring Commercially Pure Titanium Using Mo₂C during Selective Laser MeltingCharacterization of MAR-M247 Deposits Fabricated through Scanning Laser Epitaxy (SLE)Mechanical Assessment of a LPBF Nickel Superalloy Using the Small Punch Test MethodEffects of Processing Parameters on the Mechanical Properties of CMSX-4® Additively Fabricated through Scanning Laser Epitaxy (SLE)Effect of Heat Treatment on the Microstructures of CMSX-4® Processed through Scanning Laser Epitaxy (SLE)On the Use of X-Ray Computed Tomography for Monitoring the Failure of an Inconel 718 Two-Bar Specimen Manufactured by Laser Powder Bed FusionLaser Powder Bed Fusion Fabrication and Characterization of Crack-Free Aluminum Alloy 6061 Using In-Process Powder Bed Induction HeatingPorosity Development and Cracking Behavior of Al-Zn-Mg-Cu Alloys Fabricated by Selective Laser MeltingEffect of Optimizing Particle Size in Laser Metal Deposition with Blown Pre-Mixed PowdersAluminum Matrix Syntactic Foam Fabricated with Additive ManufacturingBinderless Jetting: Additive Manufacturing of Metal Parts via Jetting NanoparticlesCharacterization of Heat-Affected Powder Generated during the Selective Laser Melting of 304L Stainless Steel PowderEffects of Area Fraction and Part Spacing on Degradation of 304L Stainless Steel Powder in Selective Laser MeltingInfluence of Gage Length on Miniature Tensile Characterization of Powder Bed Fabricated 304L Stainless SteelStudy of Selective Laser Melting for Bonding of 304L Stainless Steel to Grey Cast IronMechanical Performance of Selective Laser Melted 17-4 PH Stainless Steel under Compressive LoadingMicrostructure and Mechanical Properties Comparison of 316L Parts Produced by Different Additive Manufacturing ProcessesA Parametric Study on Grain Structure in Selective Laser Melting Process for Stainless Steel 316L316L Powder Reuse for Metal Additive ManufacturingCompeting Influence of Porosity and Microstructure on the Fatigue Property of Laser Powder Bed Fusion Stainless Steel 316LStudying Chromium and Nickel Equivalency to Identify Viable Additive Manufacturing Stainless Steel ChemistriesInvestigation of the Mechanical Properties on Hybrid Deposition and Micro-Rolling of Bainite SteelProcess – Property Relationships in Additive Manufacturing of Nylon-Fiberglass Composites Using Taguchi Design of ExperimentsDigital Light Processing (DLP): Anisotropic Tensile ConsiderationsDetermining the Complex Young’s Modulus of Polymer Materials Fabricated with MicrostereolithographyEffect of Process Parameters and Shot Peening on Mechanical Behavior of ABS Parts Manufactured by Fused Filament Fabrication (FFF)Expanding Material Property Space Maps with Functionally Graded Materials for Large Scale Additive ManufacturingConsidering Machine- and Process-Specific Influences to Create Custom-Built Specimens for the Fused Deposition Modeling ProcessRheological Evaluation of High Temperature Polymers to Identify Successful Extrusion ParametersA Viscoelastic Model for Evaluating Extrusion-Based Print ConditionsTowards a Robust Production of FFF End-User Parts with Improved Tensile PropertiesInvestigating Material Degradation through the Recycling of PLA in Additively Manufactured PartsEcoprinting: Investigating the Use of 100% Recycled Acrylonitrile Butadiene Styrene (ABS) for Additive ManufacturingMicrowave Measurements of Nylon-12 Powder Ageing for Additive ManufacturingImprovement of Recycle Rate in Laser Sintering by Low Temperature ProcessDevelopment of an Experimental Laser Sintering Machine to Process New Materials like Nylon 6Optimization of Adhesively Joined Laser-Sintered PartsInvestigating the Impact of Functionally Graded Materials on Fatigue Life of Material Jetted SpecimensFabrication and Characterization of Graphite/Nylon 12 Composite via Binder Jetting Additive Manufacturing ProcessFabricating Zirconia Parts with Organic Support Material by the Ceramic On-Demand Extrusion ProcessThe Application of Composite Through-Thickness Assessment to Additively Manufactured StructuresTensile Mechanical Properties of Polypropylene Composites Fabricated by Material ExtrusionPneumatic System Design for Direct Write 3D PrintingCeramic Additive Manufacturing: A Review of Current Status and ChallengesRecapitulation on Laser Melting of Ceramics and Glass-CeramicsA Trade-Off Analysis of Recoating Methods for Vat Photopolymerization of CeramicsAdditive Manufacturing of High-Entropy Alloys – A ReviewMicrostructure and Mechanical Behavior of AlCoCuFeNi High-Entropy Alloy Fabricated by Selective Laser MeltingSelective Laser Melting of AlCu5MnCdVA: Formability, Microstructure and Mechanical PropertiesMicrostructure and Crack Distribution of Fe-Based Amorphous Alloys Manufactured by Selective Laser MeltingConstruction of Metallic Glass Structures by Laser-Foil-Printing TechnologyBuilding Zr-Based Metallic Glass Part on Ti-6Al-4V Substrate by Laser-Foil-Printing Additive ManufacturingOptimising Thermoplastic Polyurethane for Desktop Laser Sintering

    ModelingReal-Time Process Measurement and Feedback Control for Exposure Controlled Projection LithographyOptimization of Build Orientation for Minimum Thermal Distortion in DMLS Metallic Additive ManufacturingUsing Skeletons for Void Filling in Large-Scale Additive ManufacturingImplicit Slicing Method for Additive Manufacturing ProcessesTime-Optimal Scan Path Planning Based on Analysis of Sliced GeometryA Slicer and Simulator for Cooperative 3D PrintingStudy on STL-Based Slicing Process for 3D PrintingORNL Slicer 2: A Novel Approach for Additive Manufacturing Tool Path PlanningComputer Integration for Geometry Generation for Product Optimization with Additive ManufacturingMulti-Level Uncertainty Quantification in Additive ManufacturingComputed Axial Lithography for Rapid Volumetric 3D Additive ManufacturingEfficient Sampling for Design Optimization of an SLS ProductReview of AM Simulation Validation TechniquesGeneration of Deposition Paths and Quadrilateral Meshes in Additive ManufacturingAnalytical and Experimental Characterization of Anisotropic Mechanical Behaviour of Infill Building Strategies for Fused Deposition Modelling ObjectsFlexural Behavior of FDM Parts: Experimental, Analytical and Numerical StudySimulation of Spot Melting Scan Strategy to Predict Columnar to Equiaxed Transition in Metal Additive ManufacturingModelling Nanoparticle Sintering in a Microscale Selective Laser Sintering Process3-Dimensional Cellular Automata Simulation of Grain Structure in Metal Additive Manufacturing ProcessesNumerical Simulation of Solidification in Additive Manufacturing of Ti Alloy by Multi-Phase Field MethodThe Effect of Process Parameters and Mechanical Properties Oof Direct Energy Deposited Stainless Steel 316Thermal Modeling of 304L Stainless Steel Selective Laser MeltingThe Effect of Polymer Melt Rheology on Predicted Die Swell and Fiber Orientation in Fused Filament Fabrication Nozzle FlowSimulation of Planar Deposition Polymer Melt Flow and Fiber Orientaiton in Fused Filament FabricationNumerical Investigation of Stiffness Properties of FDM Parts as a Function of Raster OrientationA Two-Dimensional Simulation of Grain Structure Growth within Substrate and Fusion Zone during Direct Metal DepositionNumerical Simulation of Temperature Fields in Powder Bed Fusion Process by Using Hybrid Heat Source ModelThermal Simulation and Experiment Validation of Cooldown Phase of Selective Laser Sintering (SLS)Numerical Modeling of High Resolution Electrohydrodynamic Jet Printing Using OpenFOAMMesoscopic Multilayer Simulation of Selective Laser Melting ProcessA Study into the Effects of Gas Flow Inlet Design of the Renishaw AM250 Laser Powder Bed Fusion Machine Using Computational ModellingDevelopment of Simulation Tools for Selective Laser Melting Additive ManufacturingMachine Learning Enabled Powder Spreading Process Map for Metal Additive Manufacturing (AM)

    Process DevelopmentMelt Pool Dimension Measurement in Selective Laser Melting Using Thermal ImagingIn-Process Condition Monitoring in Laser Powder Bed Fusion (LPBF)Performance Characterization of Process Monitoring Sensors on the NIST Additive Manufacturing Metrology TestbedMicroheater Array Powder Sintering: A Novel Additive Manufacturing ProcessFabrication and Control of a Microheater Array for Microheater Array Powder SinteringInitial Investigation of Selective Laser Sintering Laser Power vs. Part Porosity Using In-Situ Optical Coherence TomographyThe Effect of Powder on Cooling Rate and Melt Pool Length Measurements Using In Situ Thermographic TecniquesMonitoring of Single-Track Degradation in the Process of Selective Laser MeltingMachine Learning for Defect Detection for PBFAM Using High Resolution Layerwise Imaging Coupled with Post-Build CT ScansSelection and Installation of High Resolution Imaging to Monitor the PBFAM Process, and Synchronization to Post-Build 3D Computed TomographyMultisystem Modeling and Optimization of Solar Sintering SystemContinuous Laser Scan Strategy for Faster Build Speeds in Laser Powder Bed Fusion SystemInfluence of the Ratio between the Translation and Contra-Rotating Coating Mechanism on Different Laser Sintering Materials and Their Packing DensityThermal History Correlation with Mechanical Properties for Polymer Selective Laser Sintering (SLS)Post Processing Treatments on Laser Sintered Nylon 12Development of an Experimental Test Setup for In Situ Strain Evaluation during Selective Laser MeltingIn Situ Melt Pool Monitoring and the Correlation to Part Density of Inconel® 718 for Quality Assurance in Selective Laser MeltingInfluence of Process Time and Geometry on Part Quality of Low Temperature Laser SinteringIncreasing Process Speed in the Laser Melting Process of Ti6Al4V and the Reduction of Pores during Hot Isostatic PressingA Method for Metal AM Support Structure Design to Facilitate RemovalExpert Survey to Understand and Optimize Part Orientation in Direct Metal Laser SinteringFabrication of 3D Multi-Material Parts Using Laser-Based Powder Bed FusionMelt Pool Image Process Acceleration Using General Purpose Computing on Graphics Processing UnitsBlown Powder Laser Cladding with Novel Processing Parameters for Isotropic Material PropertiesThe Effect of Arc-Based Direct Metal Energy Deposition on PBF Maraging SteelFiber-Fed Laser-Heated Process for Printing Transparent GlassReducing Mechanical Anisotropy in Extrusion-Based Printed PartsExploring the Manufacturability and Resistivity of Conductive Filament Used in Material Extrusion Additive ManufacturingActive - Z Printing: A New Approach to Increasing 3D Printed Part StrengthA Mobile 3D Printer for Cooperative 3D PrintingA Floor Power Module for Cooperative 3D PrintingChanging Print Resolution on BAAM via Selectable NozzlesPredicting Sharkskin Instability in Extrusion Additive Manufacturing of Reinforced ThermoplasticsDesign of a Desktop Wire-Feed Prototyping MachineProcess Modeling and In-Situ Monitoring of Photopolymerization for Exposure Controlled Projection Lithography (ECPL)Effect of Constrained Surface Texturing on Separation Force in Projection StereolithographyModeling of Low One-Photon Polymerization for 3D Printing of UV-Curable SiliconesEffect of Process Parameters and Shot Peening on the Tensile Strength and Deflection of Polymer Parts Made Using Mask Image Projection Stereolithography (MIP-SLA)Additive Manufacturing Utilizing Stock Ultraviolet Curable SiliconeTemperature and Humidity Variation Effect on Process Behavior in Electrohydrodynamic Jet Printing of a Class of Optical AdhesivesReactive Inkjet Printing Approach towards 3D Silcione Elastomeric Structures FabricationMagnetohydrodynamic Drop-On-Demand Liquid Metal 3D PrintingSelective Separation Shaping of Polymeric PartsSelective Separation Shaping (SSS) – Large-Scale Fabrication PotentialsMechanical Properties of 304L Metal Parts Made by Laser-Foil-Printing ProcessInvestigation of Build Strategies for a Hybrid Manufacturing Process Progress on Ti-6Al-4VDirect Additive Subtractive Hybrid Manufacturing (DASH) – An Out of Envelope MethodMetallic Components Repair Strategies Using the Hybrid Manufacturing ProcessRapid Prototyping of EPS Pattern for Complicated Casting5-Axis Slicing Methods for Additive Manufacturing ProcessA Hybrid Method for Additive Manufacturing of Silicone StructuresAnalysis of Hybrid Manufacturing Systems Based on Additive Manufacturing TechnologyFabrication and Characterization of Ti6Al4V by Selective Electron Beam and Laser Hybrid MeltingDevelopment of a Hybrid Manufacturing Process for Precision Metal PartsDefects Classification of Laser Metal Deposition Using Acoustic Emission SensorAn Online Surface Defects Detection System for AWAM Based on Deep LearningDevelopment of Automatic Smoothing Station Based on Solvent Vapour Attack for Low Cost 3D PrintersCasting - Forging - Milling Composite Additive Manufacturing ThechnologyDesign and Development of a Multi-Tool Additive Manufacturing SystemChallenges in Making Complex Metal Large-Scale Parts for Additive Manufacturing: A Case Study Based on the Additive Manufacturing ExcavatorVisual Sensing and Image Processing for Error Detection in Laser Metal Wire Deposition

    ApplicationsEmbedding of Liquids into Water Soluble Materials via Additive Manufacturing for Timed ReleasePrediction of the Elastic Response of TPMS Cellular Lattice Structures Using Finite Element MethodMultiscale Analysis of Cellular Solids Fabricated by EBMAn Investigation of Anisotropy of 3D Periodic Cellular Structure DesignsModeling of Crack Propagation in 2D Brittle Finite Lattice Structures Assisted by Additive ManufacturingEstimating Strength of Lattice Structure Using Material Extrusion Based on Deposition Modeling and Fracture MechanicsControlling Thermal Expansion with Lattice Structures Using Laser Powder Bed FusionDetermination of a Shape and Size Independent Material Modulus for Honeycomb Structures in Additive ManufacturingAdditively Manufactured Conformal Negative Stiffness HoneycombsA Framework for the Design of Biomimetic Cellular Materials for Additive ManufacturingA Post-Processing Procedure for Level Set Based Topology OptimizationMulti-Material Structural Topology Optimization under Uncertainty via a Stochastic Reduced Order Model ApproachTopology Optimization for 3D Material Distribution and Orientation in Additive ManufacturingTopological Optimization and Methodology for Fabricating Additively Manufactured Lightweight Metallic MirrorsTopology Optimization of an Additively Manufactured BeamQuantifying Accuracy of Metal Additive Processes through a Standardized Test ArtifactIntegrating Interactive Design and Simulation for Mass Customized 3D-Printed Objects – A Cup Holder ExampleHigh-Resolution Electrohydrodynamic Jet Printing of Molten Polycaprolactone3D Bioprinting of Scaffold Structure Using Micro-Extrusion TechnologyFracture Mechanism Analysis of Schoen Gyroid Cellular Structures Manufactured by Selective Laser MeltingAn Investigation of Build Orientation on Shrinkage in Sintered Bioceramic Parts Fabricated by Vat PhotopolymerizationHypervelocity Impact of Additively Manufactured A356/316L Interpenetrating Phase CompositesUnderstanding and Engineering of Natural Surfaces with Additive ManufacturingAdditive Fabrication of Polymer-Ceramic Composite for Bone Tissue EngineeringBinder Jet Additive Manufacturing of Stainless Steel - Tricalcium Phosphate Biocomposite for Bone Scaffold and Implant ApplicationsSelective Laser Melting of Novel Titanium-Tantalum Alloy as Orthopedic BiomaterialDevelopment of Virtual Surgical Planning Models and a Patient Specific Surgical Resection Guide for Treatment of a Distal Radius Osteosarcoma Using Medical 3D Modelling and Additive Manufacturing ProcessesDesign Optimisation of a Thermoplastic SplintReverse Engineering a Transhumeral Prosthetic Design for Additive ManufacturingBig Area Additive Manufacturing Application in Wind Turbine MoldsDesign, Fabrication, and Qualification of a 3D Printed Metal Quadruped Body: Combination Hydraulic Manifold, Structure and Mechanical InterfaceSmart Parts Fabrication Using Powder Bed Fusion Additive Manufacturing TechnologiesDesign for Protection: Systematic Approach to Prevent Product Piracy during Product Development Using AMThe Use of Electropolishing Surface Treatment on IN718 Parts Fabricated by Laser Powder Bed Fusion ProcessTowards Defect Detection in Metal SLM Parts Using Modal Analysis “Fingerprinting”Electrochemical Enhancement of the Surface Morphology and the Fatigue Performance of Ti-6Al-4V Parts Manufactured by Laser Beam MeltingFabrication of Metallic Multi-Material Components Using Laser Metal DepositionA Modified Inherent Strain Method for Fast Prediction of Residual Deformation in Additive Manufacturing of Metal Parts 2539Effects of Scanning Strategy on Residual Stress Formation in Additively Manufactured Ti-6Al-4V PartsHow Significant Is the Cost Impact of Part Consolidation within AM Adoption?Method for the Evaluation of Economic Efficiency of Additive and Conventional ManufacturingIntegrating AM into Existing Companies - Selection of Existing Parts for Increase of AcceptanceRamp-Up-Management in Additive Manufacturing – Technology Integration in Existing Business ProcessesRational Decision-Making for the Beneficial Application of Additive ManufacturingApproaching Rectangular Extrudate in 3D Printing for Building and Construction by Experimental Iteration of Nozzle DesignAreal Surface Characterization of Laser Sintered Parts for Various Process ParametersDesign and Process Considerations for Effective Additive Manufacturing of Heat ExchangersDesign and Additive Manufacturing of a Composite Crossflow Heat ExchangerFabrication and Quality Assessment of Thin Fins Built Using Metal Powder Bed Fusion Additive ManufacturingA Mobile Robot Gripper for Cooperative 3D PrintingTechnological Challenges for Automotive Series Production in Laser Beam MeltingQualification Challenges with Additive Manufacturing in Space ApplicationsMaterial Selection on Laser Sintered Stab Resistance Body ArmorInvestigation of Optical Coherence Tomography Imaging in Nylon 12 PowderPowder Bed Fusion Metrology for Additive Manufacturing Design GuidanceGeometrical Accuracy of Holes and Cylinders Manufactured with Fused Deposition ModelingNew Filament Deposition Technique for High Strength, Ductile 3D Printed PartsApplied Solvent-Based Slurry Stereolithography Process to Fabricate High-Performance Ceramic Earrings with Exquisite DetailsDesign and Preliminary Evaluation of a Deployable Mobile Makerspace for Informal Additive Manufacturing EducationComparative Costs of Additive Manufacturing vs. Machining: The Case Study of the Production of Forming Dies for Tube Bending

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