Multi-Material, Multi-Technology FDM System

A multi-material, multi-technology FDM system was developed and constructed to enable the production of novel thermoplastic parts. Two legacy FDM systems were modified and installed onto a single manufacturing system to allow the strategic, spatially controlled thermoplastic deposition of multiple materials during the same build. Additionally, a build process variation utilizing more than two extrusions tips was employed to deposit thermoplastic materials using variable layer thicknesses and road widths. The hardware and control software is discussed as well as the potential applications of multi-material polymeric parts. Benefits of multiple material FDM include: 1) achieving aesthetic requirements by using polymers of different colors, and 2) attaining desired properties (e.g., bulk tensile/compressive/flexural strength, weight, thermal conductivity) by strategically combining layers and regions within layers of polymers that display different properties. Parts produced using the build process variation exhibited internal road with 1200 ± 39µm road width and 497 ± 11µm layer height while the contours measured 269 ± 18µm road width and 133 ± 3µm layer thickness. Additionally, for a 50.8mm by 50.8mm square section (25.4mm tall), the build process variation required 4.0 hours to build while the original strategy required 6.2 hours constituting a 35% reduction in build time.Mechanical Engineerin

Measurement Systems Comparison on Various Feature Sizes of FDM Parts

12 identical FDM parts were produced in ABSM30, each having 16 features for replicated measurements. Half the features were positive (posts), half were negative (holes). Half of all features were rectangular, half were round. Two different CMMs with 1.5mm touch probes were compared, one CMM additionally used a laser, and manual measurements were taken with gauges and calipers. All features were measured using these 4 measurement systems. All measurements were compared against the theoretical feature size to generate a percent error value. The laser values were notably different than both probe values. The manual measurements were similar to one of the two CMM probes. Positive versus negative features were significantly different in 7 of 8 cases. Feature size and measurement error were inversely proportional. The largest features had the least amount of error in all cases while the features below 6mm had the most error and high variation.Mechanical Engineerin

Fused Deposition Modeling of Polymethylmethacrylate for Use in Patient-Specific Reconstructive Surgery

facial reconstruction and as bone cement and antibiotic-impregnated spacers in orthopaedics. The polymerization of PMMA in-situ causes tissue necrosis and other complications due to the long surgical times associated with mixing and shaping the PMMA. PMMA is a thermoplastic acrylic resin suitable for extrusion in FDM thus 3D anatomical models can be fabricated prior to surgery directly from medical imaging data. The building parameters required for successful FDM fabrication with medical-grade PMMA filament (1/16”Ø) were developed using an FDM 3000. It was found that a liquefier and envelope temperature of 235ºC and 55ºC, respectively, as well as increasing the model feed rate by 60%, were necessary to properly and consistently extrude the PMMA filament. Scaffolds with different porosities and fabrication conditions (tip wipe frequency and layer orientation) were produced, and their compressive mechanical properties were examined. Results show that both the tip wipe frequency (1 wipe every layer or 1 wipe every 10 layers) and layer orientation (transverse or axial with respect to the applied compressive load) used to fabricate the scaffolds, as well as the porosity of the scaffold had an effect on the mechanical properties. The samples fabricated with the high tip frequency had a larger compressive strength and modulus (Compressive strength: 16 ± 0.97 vs. 13 ± 0.71 MPa, Modulus: 370 ± 14 vs. 313 ± 29 MPa, for samples fabricated in the transverse orientation with 1 tip wipe per layer or 1 tip wipe per 10 layers, respectively). Also, the samples fabricated in the transverse orientation had a larger compressive strength and modulus than the ones fabricated in the axial orientation (Compressive strength: 16±0.97 vs. 13±0.83 MPa, Modulus: 370±14 vs. 281±22 MPa, for samples fabricated with 1 tip wipe per layer, in the transverse and axial orientation, respectively). Overall, the compressive strain for the samples fabricated with the four different conditions ranged from 8 – 12%. In regards to the porosity of the samples, in general, the stiffness, yield strength and yield strain decreased when the porosity increased (Compressive strength: 12±0.71 – 7±0.95 MPa, Modulus: 248±10 – 165±16 MPa, Strain: 7±1.5 – 5±1% for samples with a porosity ranging from 55 – 70%). The successful FDM fabrication of patient-specific, 3D PMMA implants with varying densities, including the model of a structure to repair a cranial defect and the model of a femur, was demonstrated. This work shows that customized structures with varying porosities to achieve tailored properties can be designed and directly fabricated using FDM and PMMA.Mechanical Engineerin

Improving Tensile Mechanical Properties of FDM-Manufactured Specimens via Modifying Build Parameters

In this paper, the focus was on improving tensile mechanical properties of FDMmanufactured parts by adjusting FDM processing parameters and analyzing stress concentration features between adjacent roads of material. FDM processing parameters are specified by the user via Insight – the file preparation software for most FDM machines. Even though Insight gives the impression that adjacent roads are to be deposited and connected throughout, an optical imaging observation of the deposited material revealed that adjacent roads are not consistently connected forming voids that reduce mechanical performance. Therefore, this work reports the tensile mechanical properties of specimens built using three sets of parameters: standard/default parameters, an Insight revision method, and a visual feedback method. When compared to the default build parameters, the experimentally determined, visual feedback approach produced specimens, in some cases, exhibiting as high as 19% improvement in ultimate tensile strength.Mechanical Engineerin

Sterilization of FDM-Manufactured Parts

Fused Deposition Modeling (FDM) can be used to produce an array of medical devices; however, for such devices to be practical, they must be manufactured using sterilizable materials. Nine FDM materials were tested using four methods of sterilization: autoclave, ethylene oxide, hydrogen peroxide, and gamma radiation. Sterility testing was performed by incubating the samples in Tryptic Soy Broth for 14 days. The majority of the materials were sterilizable by all four methods while deformations were caused by autoclaving. Results from this research will allow medical staff to sterilize an FDM-manufactured device using a suitable method.Mechanical Engineerin

In-situ Electrical Resistance Measurements for Soldering Studies in Hybrid AM

This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof: The views and opinions of-authors expressed herein do not necessarily state or reflect those of the-United States Government or any agency thereof.Mechanical Engineerin

Using Additive Manufacturing to Print a CubeSat Propulsion System

Small satellites, such as CubeSats, are increasingly being called upon to perform missions traditionally ascribed to larger satellite systems. However, the market of components and hardware for small satellites, particularly CubeSats, still falls short of providing the necessary capabilities required by ever increasing mission demands. One way to overcome this shortfall is to develop the ability to customize every build. By utilizing fabrication methods such as additive manufacturing, mission specific capabilities can be built into a system, or into the structure, that commercial off-the-shelf components may not be able to provide. A partnership between the University of Texas at El Paso, COSMIAC at the University of New Mexico, Northrop Grumman, and the NASA Glenn Research Center is looking into using additive manufacturing techniques to build a complete CubeSat, under the Small Spacecraft Technology Program. The W. M. Keck Center at the University of Texas at El Paso has previously demonstrated the ability to embed electronics and wires into the addtively manufactured structures. Using this technique, features such as antennas and propulsion systems can be included into the CubeSat structural body. Of interest to this paper, the team is investigating the ability to take a commercial micro pulsed plasma thruster and embed it into the printing process. Tests demonstrating the dielectric strength of the printed material and proof-of-concept demonstration of the printed thruster will be shown

Development of a Fused Deposition Modeling System for Low Melting Temperature Metal Alloys

This research focused on extending the applications of fused deposition modeling (FDM) by extrusion and deposition of low melting temperature metal alloys to create threedimensional metal structures and single-layer contacts which may prove useful for electronic interconnects. Six commercially available low melting temperature solder alloys (Bi36Pb32Sn31Ag1, Bi58Sn42, Sn63Pb37, Sn50Pb50, Sn60Bi40, Sn96.5Ag3.5) were tested for the creation of a fused deposition modeling for metals (FDMm) system with special attention given to Sn-Bi solders. An existing FDM 3000 was used and two alloys were successfully extruded through the system's extrusion head. Deposition was achieved through specific modifications to system toolpath commands and a comparison of solders with eutectic and non-eutectic compositions is discussed. The modifications demonstrate the ability to extrude simple single-layer solder lines with varying thicknesses, including sharp 90 deg angles and smooth curved lines and showing the possibility of using this system for printed circuit board applications in which various connections need to be processed. Deposition parameters altered for extrusion and the deposition results of low melting temperature metal alloys are introduced

High Feed Rate Wire Heating and Embedding for Large Area Additive Manufacturing of Parts Containing Embedded Electronic Functionality

The introduction of large area thermoplastic extrusion additive manufacturing (AM) for direct fabrication of large end-use parts (such as prototype vehicle components) or tooling for indirect fabrication of large carbon fiber parts has seen much attention. While challenges related to interlayer bonding, thermomechanical simulations, and development of new materials are being addressed by other research efforts, the work described here is focused on the development of a wire heating and embedding technology for use with large area thermoplastic extrusion AM. The automated inclusion of wires within large thermoplastic 3D printed parts promises to augment a part’s structural function by, for example, introducing electronic functionality that can aid in instrumenting parts with embedded sensors for health monitoring or embedding heating elements to increase the temperatures of carbon fiber layup tooling. Considering the requirements of relatively high wire feed rates (on the order of 5,000 mm/min), the use of relatively large copper wire diameters (~1 mm), and desired temperature increases of at least 250°C, thermal analytical models were identified in this work and used to compare two wire heating methods: resistance heating (also known as Joule or I2R heating) method and arc heating method. Of the considered methods, the use of a discharge arc (similar to what is used in tungsten inert gas welding) was found to induce a higher temperature increase with smaller required currents. This is mainly due to resistance heating being well suited for materials with high resistivity. When considering copper, whose resistivity is low, the resistance heating method is not suitable, especially for large wire diameters. As such, an experimental benchtop stand was designed and constructed to drive wire across a discharge electrical arc, akin to arcs produced by the tungsten inert gas welding process, so that temperature measurements were allowed during wire driving and heating using the direct current electrode negative configuration. The use of infrared thermography allowed for making temperature measurements on stationary and driven bare copper wire. When making observations on stationary wire, arc blowing and arc narrowing were observed. When making observations on drive copper wire, two primary temperature regions were identified: a region of temperature ramp and a region of relatively constant temperature. In the region of temperature increase, the rate of temperature increase was the same regardless of the arc current used. However, it was noted that the time required to reach the relatively constant temperature during the ramp increased with increasing arc current. In the constant temperature region, the wire temperature was a function of the supplied electrical arc current. Wire temperatures were in the range of 200°C to 300°C and, as previously mentioned, the temperature was a function of the electrical arc current with good fit to a linear trend. After being driven and exposed to different arc currents, the processed wires were measured and it was determined that the diameters of arc-exposed wires had a statistical significant difference when compared to the diameters of non-exposed wires. A decrease in wire diameter, when compared to vendor supplied dimension, was noted in the range of 5–6%, where 1% error was noted in the as-received wire diameter. Even though a change in diameter was noted because of the arc exposure, the volume and weight resistivity was the same for all wires, regardless of arc current or exposure. As an alternative to copper material where heating elements are desired, nickel chromium was also evaluated for use with the arc heating method. Through testing and temperature observations, it was determined that the arc heating method was applicable for nickel chromium. For experiments performed using 10 A arc current, 1.6 mm wire diameter, and 4,792 mm/min wire feed rate, the nickel chromium average temperature was recorded as 140°C. For the same experimental setup, copper’s average temperature was recorded as 201°C versus. The difference in temperature was driven by the materials difference in volumetric heat capacity (3.61 J˙°C-1˙mm-3 for nickel chromium and 3.39 J˙°C-1˙mm-3 for copper), where average temperature increase had an inverse relationship with volumetric heat capacity. Future applications of the proposed technology (i.e., large area material extrusion AM with integrated wire embedding capabilities) can include the 3D printing of form-in-place gasket tooling for aircraft production. Through information provided by Lockheed Martin, it was determined that lead time for the conventional manufacturing of such tooling is approximately 8 weeks..

Development of a multi-material, multi-technology FDM system for process improvement experimentation

Over the last three decades, developments within the area of Additive Manufacturing (AM) have resulted in novel technologies capable of producing highly customized, complex part geometries in a fraction of the lead time required by traditional manufacturing methods (e.g., injection molding, metal casting). In particular, fused deposition modeling (FDM), a material extrusion AM process, can produce parts using production-grade thermoplastics like acrylonitrile butadiene styrene, polycarbonate, and polyetherimide. Additionally, non-commercial materials (e.g., polycaprolactone, ceramic loaded polymers, carbon nanotube loaded polymers) have been processed using FDM in part to demonstrate the potential diversity in material selection. Recently, a myriad of personal 3D Printers using material extrusion processes have received much attention because they resemble the initial steps towards transforming AM technologies into a home consumer item. These steps were also taken during the 1980s by inkjet printing technologies when they were first entering the home consumer market. However, before inkjet printers became a home consumer item, challenges related to the controlled flow of inks and the clogging of print heads needed to be resolved. Synonymously, FDM technologies need to resolve issues related to part accuracy, surface roughness, build time, and mechanical properties before they can be fully adopted by industry and home consumers. A multi-material, multi-technology (MMMT) FDM system was developed to enable experimental methods related to the FDM attributes in need of improvement. The MMMT FDM system consists of two legacy FDM systems, a pneumatic slide, and an overall control system. The FDM systems were modified so that they mimic a gantry system enabling a work piece to be transported between each FDM system. A build platform was attached to the pneumatic slide to enable the transportation of the workpiece. A software program named FDMotion was developed to control each FDM system and the pneumatic slide via a graphic user interface as well as provide in-process instructions to the user. The functional MMMT FDM system was used to explore build process variations, the effect of ultraviolet ozone surface treatments at every layer on mechanical properties, and the development of a novel heat treatment for multi-material parts produced via FDM. Additionally, the system was employed to demonstrate the fabrication of multi-colored parts as well as multi-material parts made from discrete similar and dissimilar thermoplastics. The build process variation consisted of depositing fine contours to promote dimensional accuracy and reduce surface roughness while depositing larger internal fill rasters to decrease build time. The internal roads were four times thicker and five times wider than the outer roads. A 55% improvement in surface roughness was measured on a plane that was inclined 10° from vertical and a 35% reduction in build time was observed when fabricating a simple square prism (50.8mm by 50.8mm and 25.4mm tall). Additionally, a student\u27s t-test confirmed that the tensile properties of tensile specimens were not significantly altered by the build process variation. Multi-material fabrication was demonstrated with the MMMT FDM system by depositing different materials (similar and dissimilar) into different layers and different regions within a layer. This fabrication method was performed to construct simple geometries requiring little to no support material as well as complex geometries that required support material for a majority of the layers. An interlayer bond improvement strategy was explored in which an ultraviolet ozone (UV/O3) surface treatment was implemented before the deposition of a new layer. The UV/O3 treatment was intended to increase surface energy and reduce the local glass transition temperature, which in turn was expected to increase interlayer bonding. A design of experiments (DOE) and analysis of variance (ANOVA) was conducted using six UV/O3 exposure times to determine their effect on surface energy and mechanical properties (ultimate tensile stress (UTS), strain at UTS, and modulus of elasticity). While the surface energy increased by 26% when exposing ABS P400 for 1 minute, the mechanical properties remained unchanged. The UV/O3 surface treatment, however, can be used to increase the surface energy and wettability of FDM-fabricated parts for adhesive bonding processes requiring clean and chemically active surfaces. To improve the tensile properties of FDM-fabricated specimens, a novel multi-material fabrication method and heat treatment were developed; the result being an increase of 25% in ultimate tensile strength with minor dimensional changes. A shell-and-core configuration was used wherein the shell material (PC) exhibited a higher glass transition temperature (Tg) than that of the core (ABS). The specimens were heat-treated at a temperature above the Tg of the core material but below the Tg of the shell material. This heat treatment removed the interstices between roads of the core material while limiting dimensional changes of the shell material. (Abstract shortened by UMI.