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Kim, Pum

Publications and source records attributed to Kim, Pum.

At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

High-performance molded composites using additively manufactured preforms with controlled fiber and pore morphology

Here, large-scale multimaterial preforms produced by additive manufacturing (AM) underwent compression molding (CM) to produce high-performance thermoplastic composites reinforced with short carbon fibers. AM and CM techniques were integrated to control the fiber orientation (microstructure) and to reduce void content for the improved mechanical performance of the composite. The new integrated manufacturing technique is termed “additive manufacturing-compression molding” (AM-CM). For the present study, the most common materials were used for large-scale printing, i.e., acrylonitrile butadiene styrene (ABS), carbon fiber (CF)–filled ABS (CF/ABS) and glass fiber (GF)–filled ABS (GF/ABS). Three different manufacturing processes; (a) AM (b) extrusion compression molding (ECM), and (c) AM-CM were used to prepare four different panel configurations: (1) neat ABS, (2) CF/ABS, (3) overmold (CF/ABS over neat ABS), and (4) sandwich (neat ABS between two CF/ABS layers). The mechanical properties (tensile and flexural strength and modulus, and Izod impact energy) of samples prepared via all three manufacturing processes were compared. X-ray microcomputer tomography was employed to evaluate the fiber orientation distribution and the volumetric porosity content. The preform maintained high fiber alignment (≈ 82% of fibers within the range of 0–20° in the deposition direction), and the volumetric porosity was reduced by 50% from 3.79% to 1.91% after compression. The alignment of long pores along the deposition direction was also observed. The mechanical properties are discussed with correlation to the fiber alignment and void content in the samples. CF/ABS samples prepared by AM-CM showed significant improvement of 11.15%, 35.27%, 28.6%, and 74.3% in the tensile strength, tensile modulus, flexural strength, and flexural modulus, respectively, when compared with samples prepared by ECM. Unique aspects of this study are the demonstration of large-scale multimaterial AM and the use of multimaterials as preforms to make high-performance composites.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Thermal Analysis of Large Area Additive Manufacturing Resistance Heating Composites for Out of Oven/Autoclave Applications

Additive Manufacturing (AM) of carbon fiber (CF) reinforced composite has received growing attention because of the design flexibility, superior mechanical properties, improved thermal properties, and weight reduction. Autoclave tooling was proven to be a successful application for large scale AM technology. The capital cost, and cost associated with heating, and cycle time in a conventional autoclave process is relatively high. Thus, an innovative design of AM mold with an efficient heating scheme is essential. This study represents an innovative method of the resistive heating of composite molds which does not require a room size oven for heating during the curing processing. Therefore, it has the potential to reduce the operating cost drastically. For the design validation and feasibility study, we performed a numerical analysis of the wire embedded and AM mold parts. The goal of this study is to determine and optimize the thermal behavior of the printed mold with embedded wire technology. It is anticipated that the larger distance between the embedded wires along the printing direction (z-direction) increase the cold spot, on the other hand, a close distance of the wire can create the unwanted localize heating, thus melting. Constant thermal properties of the 20 wt.% short CF reinforced acrylonitrile butadiene styrene (ABS) was used for the simulation purpose. Thermal characterization was set to 100°C to avoid the thermal deformation or bulging on the part surface.

billah, Kazi↗
DOE OSTI2020

Thermal Analysis of Large Area Additive Manufacturing Resistance Heating Composites for Out of Oven/Autoclave Applications

Additive Manufacturing (AM) of carbon fiber (CF) reinforced composite has received growing attention because of the design flexibility, superior mechanical properties, improved thermal properties, and weight reduction. Autoclave tooling was proven to be a successful application for large scale AM technology. The capital cost, and cost associated with heating, and cycle time in a conventional autoclave process is relatively high. Thus, an innovative design of AM mold with an efficient heating scheme is essential. This study represents an innovative method of the resistive heating of composite molds which does not require a room size oven for heating during the curing processing. Therefore, it has the potential to reduce the operating cost drastically. For the design validation and feasibility study, we performed a numerical analysis of the wire embedded and AM mold parts. The goal of this study is to determine and optimize the thermal behavior of the printed mold with embedded wire technology. It is anticipated that the larger distance between the embedded wires along the printing direction (z-direction) increase the cold spot, on the other hand, a close distance of the wire can create the unwanted localize heating, thus melting. Constant thermal properties of the 20 wt.% short CF reinforced acrylonitrile butadiene styrene (ABS) was used for the simulation purpose. Thermal characterization was set to 100°C to avoid the thermal deformation or bulging on the part surface.

billah, Kazi↗
DOE OSTI2020

Thermal Analysis of Large Area Additive Manufacturing Resistance Heating Composites for Out of Oven/Autoclave Applications

Additive Manufacturing (AM) of carbon fiber (CF) reinforced composite has received growing attention because of the design flexibility, superior mechanical properties, improved thermal properties, and weight reduction. Autoclave tooling was proven to be a successful application for large scale AM technology. The capital cost, and cost associated with heating, and cycle time in a conventional autoclave process is relatively high. Thus, an innovative design of AM mold with an efficient heating scheme is essential. This study represents an innovative method of the resistive heating of composite molds which does not require a room size oven for heating during the curing processing. Therefore, it has the potential to reduce the operating cost drastically. For the design validation and feasibility study, we performed a numerical analysis of the wire embedded and AM mold parts. The goal of this study is to determine and optimize the thermal behavior of the printed mold with embedded wire technology. It is anticipated that the larger distance between the embedded wires along the printing direction (z-direction) increase the cold spot, on the other hand, a close distance of the wire can create the unwanted localize heating, thus melting. Constant thermal properties of the 20 wt.% short CF reinforced acrylonitrile butadiene styrene (ABS) was used for the simulation purpose. Thermal characterization was set to 100°C to avoid the thermal deformation or bulging on the part surface.

billah, Kazi↗
DOE OSTI2020

HYBRID MANUFACTURING TECHNIQUE USING LARGE-SCALE ADDITIVE MANUFACTURING AND COMPRESSION MOLDING FOR HIGH PERFORMANCE COMPOSITES

Additive Manufacturing (AM) or 3-D printing has moved from small-scale prototypes to large-scale functional structures. With the introduction of large-scale 3D printers into the market a new industry has been born. For the first time, we are presenting the idea of preparing large-scale 3-D printed β-stage preforms to be used in traditional compression molding (CM) manufacturing technique to prepare final functional structures. Short carbon fiber (CF) reinforced material acrylonitrile butadiene Styrene i.e. ABS with 20% CF is used in present work. It is shown that highly aligned 3D printed short carbon fiber composite maintains its orientation after compression molding. A sandwich panel is prepared to show the capability to prepare complicated parts by integrating AM and CM. Interphase of the prepared dissimilar material is also studied using SEM. Samples prepared using AM-CM integration showed 11% and 79 % improvement in tensile strength and tensile modulus respectively compared to the traditional extrusion compression molding (ECM) process.

Kumar, Vipin↗
DOE OSTI2020

CHARACTERIZATION ON ANISOTROPIC THERMAL CONDUCTIVITY FOR BIG AREA ADDITIVE MANUFACTURING WITH POLYMERS

Additive manufacturing with polymers has been used mainly for prototyping. A recent development of Big Area Additive Manufacturing (BAAM) at Oak Ridge National Laboratory has opened its applications in the mold and die industry. A numerical simulation and prediction for a mold heating performance requires accurate anisotropic thermal properties of the printed material, which are challenging to obtain, and often requires the use of multiple techniques. The transient plane source (TPS) technique has been widely used due to its ability to measure the thermal properties of an extensive range of materials (solids, liquids, powder). Despite the capability to characterize thermal conductivity k of isotropic and anisotropic materials, the measurements of latter materials are limited to the cases, where the samples have the same thermal conductivity k along x- and y-axis that form the radial plane. In this work, the method for a characterization of k in all three dimensions is developed, and the application of TPS is extended to the determination of thermal properties along the x-, y-, and z-axis individually. The materials are represented by additively manufactured polymers including polylactic acid (PLA) and styrene maleic anhydride (SMA). The developed method consists of (1) a determination of the heat capacity of the polymers by means of TPS in combination with the developed in this work data analysis procedure, (2) a machining three types of cylindrical samples from the same material, with the height corresponding either to x-, y-, or z-direction of printing, and (3) a determination of axial thermal conductivity employing anisotropic model and using previously determined heat capacity

Trofimov, Artem↗
DOE OSTI2020

Additive manufacturing of two-phase lightweight, stiff and high damping carbon fiber reinforced polymer microlattices

Carbon fiber reinforced polymer (CFRP) composite is known for its high stiffness-to-weight ratio and hence is of great interest in several engineering fields such as aerospace, automotive, defense, etc. However, such a composite is not suitable for energy dissipation as failure occurs with very little or no plastic deformation. Herein, we present an extendable multi-material projection microstereolithography process capable of producing carbon-fiber-reinforced cellular materials that achieve simultaneously high specific stiffness and damping coefficient. Inspired by the upper bounds of stiffness-loss coefficient in a two-phase composite, we designed and additively manufactured CFRP microlattices with soft phases architected into selected stiff-phase struts. Our results, confirmed by experimental and analytical calculations, revealed that the damping performance can be significantly enhanced by the addition of only a small fraction of the soft phase. The presented design and additive manufacturing strategy allow for optimizing mutually exclusive properties. As a result, these CFRP microlattices achieved high specific stiffness comparable to commercial CFRP, technical ceramics, and composites, while being dissipative like elastomers.

36 MATERIALS SCIENCE↗
DOE OSTI2019

CREATING TOOLPATHS WITHOUT STARTS AND STOPS FOR EXTRUSION-BASED SYSTEMS

Toolpath generation for extrusion-based additive manufacturing systems, called slicing, involves operations on polygonal contours that are derived from an STL file. Slicing generates multiple paths per layer (both closed-loop and open-loop) that are designed to optimally fill the space outlined by the polygon(s). In the course of printing a layer, the extruder must start and stop, the tip must be wiped, and the extruder must travel between paths without printing. Any amount of time the printer spends moving without printing is considered wasted time because the part isn’t being constructed. In addition, the start/stop point, known as the seam, is often a blemish on the surface of the part that contributes to weaker material properties. Therefore, a single path for creating multi-bead walled structures is desirable because it would save machine time and create parts with better surface finish. This paper will cover one method of modifying the CAD file and slicing engine to allow for parts to be printed without starting and stopping the extruder.

Roschli, Alex↗
DOE OSTI2019

Analysis on Part Distortion and Residual Stress in Big Area Additive Manufacturing with Carbon Fiber-Reinforced Thermoplastic using Dehomogenization Technique

Part distortion and bottom surface warpage often occur in extrusion-based additive manufacturing. The undesirable deformations during the printing process are due to residual stresses caused by material shrinkage. Analysis on residual stress and deformation requires accurate thermo-mechanical material properties. Polymer composites reinforced with short fibers have intrinsic inhomogeneities with nonuniform fiber orientation. Therefore, homogenized macro properties may not accurately represent the progressive damage behavior or distortion. In this study, fiber orientations in Acrylonitrile Butadiene Styrene (ABS) reinforced with 20%wt carbon fiber are calculated using a de-homogenization technique. Thermal expansion coefficients in multiple directions are obtained from Thermo-Mechanical Analysis (TMA) tests. Temperature dependent stiffness is measured, and temperature dependent strength is estimated. Thermal conductivities in multiple directions and thermal capacity are measured. The calibrated thermo-mechanical properties of the composite with de-homogenized technique are used to analyze the residual stress and distortion of a 4 ft-wide wall printed in the Big Area Additive Manufacturing (BAAM) system. For experimental measurement on the wall printing, Infra-Red (IR) camera captures the temperature field, and Linear Variable Differential Transformer (LVDT) is installed to measure the warpage at the bottom surface. The experimental data are compared to the numerical analysis results. The temperature profile and the distortion profile from experiment are close to the simulation results. Damages due to residual stress and distortion are analyzed.

Kim, Pum↗
DOE OSTI2019

Simulation Assisted Design for an Additively Manufactured Autoclave Tool Accounting for an Anisotropic Expansion

Carbon fiber reinforced polymer composites have been used in Big Area Additive Manufacturing (BAAM) to decrease the distortion during the printing process and increase functional stiffness. These materials are also important for additively manufactured autoclave tooling which expands when exposed to the high temperatures of the operational cycle, causing the dimensions of the mold to differ from the targeted design. Since the reinforcing fibers generally align during the extrusion process, the thermal expansion of the composite along the deposition direction is restrained by fibers, whereas the thermal expansion perpendicular to the bead is largely unconstrained. This leads to an anisotropic expansion of the material that is dependent upon the local deposition path, which may be tortuous and complex. To obtain an accurate final part geometry during the autoclave process, a computational prediction of the thermal expansion of a tool is required to account for the complex extrusion deposition directions. A multi-step approach is presented that accounts for (1) anisotropic thermal expansion of the extruded bead, (2) the complex deposition directions, and (3) internal geometry determined by slicing software. The thermal expansion coefficient in the deposition direction and perpendicular to the deposition direction were measured at multiple locations in the test specimen. A revised model geometry was generated to achieve the target dimensions when accounting for thermal expansion.

Hassen, Ahmed↗
DOE OSTI2019

Maximizing the Performance of a 3D Printed Heat Sink by Accounting for Anisotropic Thermal Conductivity During Filament Deposition

Newly developed high thermal conductivity polymer composite 3D printing filaments are used to characterize the thermal properties as a function of print orientation. The thermal conductivity of a printed part is anisotropic and varies by 2-6 times depending on the print direction - demonstrating higher conductivity in the deposition direction (in-plane) than in the two directions perpendicular to the deposition direction (cross-plane and through-plane). Therefore, deposition path planning greatly affects the overall heat dissipation rate and the performance of the heat sink. Traditionally, 3D printing slicers generate deposition paths based solely on geometric constraints. This work investigates a new approach of deposition path planning assisted by computational predictions of the heat sink thermal performance. The proposed approach uses a thermal simulation of a 3D-printed part, accounting for the anisotropic thermal properties, and the orientation of the local material properties are assigned based on the deposition path in multiple print orientations. The performances predicted via the simulations are compared, and the optimal deposition path is determined. For the highest thermal conductivity 3D printing filament (~ 12 W/m- K in-plane), a heat sink printed with the print direction parallel to the fins z-axis had ~20% improved performance in comparison to a heat sink with print direction perpendicular to the fins z-axis. Moreover, a plastic 3D printed heat sink was able to perform within 7% of an extruded Aluminum heat sink with similar geometry under natural convection. The computational predictions show the same trend as experimental measurements using 3D printed heat sinks.

Smith, Matthew↗
DOE OSTI2019

Z-Pinning approach for 3D printing mechanically isotropic materials

Conventional 3D printing approaches are restricted to building up material in a layer-by-layer format, which is more appropriately considered “2.5-D” printing. The layered structure inherently results in significant mechanical anisotropy in printed parts, causing the tensile strength in the build direction (z-axis) to be only a fraction of the in-plane strength – a decrease of 50–75% is common. In this study, a novel “z-pinning” approach is described that allows continuous material to be deposited across multiple layers within the volume of the part. Here, the z-pinning process is demonstrated using a Fused Filament Fabrication (FFF) printer for polylactic acid (PLA) and carbon fiber reinforced PLA. For both materials, z-pinning increased the tensile strength and toughness in the z-direction by more than a factor of 3.5. Direct comparisons to tensile strength in the x-axis showed a significant decrease in mechanical anisotropy as the volume of the pin was increased relative to the void in the rectilinear grid structure. In fact, the PLA sample with the largest pin volume demonstrated mechanically isotropic properties within the statistical uncertainty of the tests. Tensile test results were also analyzed relative to the functional area resisting deformation for each sample.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Structural Health Monitoring of 3D Printed Structures

3D printed parts are used in industry for both tooling application and smaller parts in assembled structures. Articles made through polymer based additive manufacturing are anisotropic and may have defects throughout the part. For instance, the layer to layer interactions are weaker than the in-plane printing which can cause delamination of the layers. Identifying when and where the cracks form can be very difficult if the cracks are inside the structure This paper introduces an innovative patent-pending method to monitor polymer-based 3D printed structures for internal failures by printing a highly sensitive conductive material into the part itself. When a section of the conductive material inside the part is damaged or split, the resistance across the conductive pathway increases which will indicate that the article has been damaged. We present several small printed circuits and observations that show as a crack is introduced to the structure, the resistance measured increases which alerts users that a crack has formed/propagated.

Smith, Tyler↗
DOE OSTI2018

Z-Pinning Approach for Reducing Mechanical Anisotropy of 3D Printed Parts

The mechanical strength of extrusion-based printed parts is often greatly reduced (25-50%) in the build direction (z-direction) compared to the in-plane strength due to poor bonding between successively deposited layers. This effect can be magnified (75-90% difference) when depositing fiber-reinforced materials or larger print areas with long layer times. Therefore, a patent-pending approach has been developed that deposits material into intentionally aligned voids in the zdirection, allowing continuous material to span multiple layers. The “z-pinning” approach can be applied to several concepts for improving the interlaminar strength of extrusion-based 3D printed parts as well as techniques for applying the technology across a broad spectrum of deposition platforms and material systems. Initial experimental results demonstrate a significant improvement (>3x) in mechanical strength and (>8x) toughness for fiber reinforced components.

Duty, Chad↗
DOE OSTI2018

Graded Infill Structure of Wind Turbine Blade Accounting for Internal Stress in Big Area Additive Manufacturing

In additively manufactured (AM) components, infill structure significantly affects the mechanical performance of the final printed part. However, mechanical stress induced by operation loads has been so far neglected for infill patterning. Most slicers currently available in the market provide infill patterns that are uniform in shape and size regardless of the operational loading. We develop a design approach for infill patterns that accounts for the induced stress. This approach differs from topology optimization as it focuses on the porous infill, which allows the external shape of the printed part to remain intact. The proposed approach uses a computational stress analysis to control the distribution of the local density of the infill pattern. We have applied the approach to a wind turbine blade core with infill densities optimized based on the structural loads. The blade core is fabricated in our big area additive manufacturing (BAAM) system. To ensure less warpage and better inter-layer bonding, fast layer deposition is critical in BAAM system. We have optimized the tool path sequences to minimize the deposition time via the solution to the Chinese Postman Problem (CPP). For the application of wind turbine infill, the deposition from the CPP method is twice faster than the deposition from conventional slicing.

Kim, Pum↗
DOE OSTI2018

Large-scale additive manufacturing with reactive polymers

The focus on large-scale polymer Additive Manufacturing (AM) has previously been on thermoplastic materials. However, Magnum Venus Products (MVP) along with researchers at Oak Ridge National Laboratory’s (ORNL) Manufacturing Demonstration Facility (MDF) are introducing a unique AM system capable of depositing reactive polymers in a large format. The system’s footprint is 4.88 m (16ft) x 2.44 m (8ft). The benefits of printing with reactive polymers rather than thermoplastic polymers include reduced dependence on temperature control of the process, chemical reactions across the bead-to-bead interfaces, and increased toolpath flexibility that is currently unattainable with existing large-scale systems. This flexible AM system can be used with a variety of polymers, and pre-processin and post-processing operations will be performed outside of the printer on a removable print bed. Examples of printed structures and machine capabilities leading to improved productivity of AM equipment are presented herein.

Lindahl, John↗
DOE OSTI2018

Parametric Analysis on Vertical Pins for Strengthening Extrusion-Based Printed Parts

For extrusion-based additive manufacturing, the mechanical performance in vertical direction (z-direction) is significantly lower than that in the printed layer plane (xy-direction). This paper presents a vertical extrusion approach across several layers to improve the mechanical properties of a 3D printed part. This approach is patent pending, and it involves depositing pins in the z-direction into predefined holes. It requires the vertical pins to mechanically engage with the surrounding structure of the holes. To maximize the mechanical performance of the printed structures with pins, we then analyzed the penetration quality of the pins with a wide range of hole depths, hole sizes, and pin volumes and obtained the relationship between the hole width and the hole depth for the full penetration of pins.

Kim, Pum↗