Lindsey Bass, Nicholas Alexander Meisel and Christopher B. Williams
Understanding how material jetting process parameters affect material properties can inform design and print orientation when manufacturing end-use components. This study aims to…
Abstract
Purpose
Understanding how material jetting process parameters affect material properties can inform design and print orientation when manufacturing end-use components. This study aims to explore the robustness of material properties in material jetted components to variations in processing environment and build orientation.
Design/methodology/approach
The authors characterized the properties of six different material gradients produced from preset “digital material” mixes of polypropylene-like (VeroWhitePlus) and elastomer-like (TangoBlackPlus) materials. Tensile stress, modulus of elasticity and elongation at break were analyzed for each material printed at three different build orientations. In a separate ten-week study, the authors investigated the effects of aging in different lighting conditions on material properties.
Findings
Specimens fabricated with their longest dimension along the direction of the print head travel (X-axis) tended to have the largest tensile strength, but trends in elastic modulus and elongation at break varied between the rigid and flexible photopolymers. The aging study showed that the ultimate tensile stress of VeroWhitePlus parts increased and the elongation decreased over time. Material properties were not significantly altered by lighting conditions.
Research limitations/implications
Many tensile specimens failed at the neck region, especially for the more elastomeric parts. It is hypothesized that this is due to the material jetting process approximating curves with a pixelated droplet arrangement, instead of curved contour as seen in other additive manufacturing processes. A new tensile specimen design that performs more consistently with elastomer-like materials should be considered. The aging component of this study is focused solely on polypropylene-like (VeroWhitePlus) material; additional research into the effects of aging on multiple composite materials is needed.
Originality/value
The study provides the first known description of orientation effects on the mechanical behavior of photopolymers containing varied concentrations of elastomeric (TangoBlackPlus) material. The aging study presents the first findings on how time affects parts made via material jetting.
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Nicholas Alexander Meisel, David A. Dillard and Christopher B. Williams
Material jetting approximates composite material properties through deposition of base materials in a dithered pattern. This microscale, voxel-based patterning leads to macroscale…
Abstract
Purpose
Material jetting approximates composite material properties through deposition of base materials in a dithered pattern. This microscale, voxel-based patterning leads to macroscale property changes, which must be understood to appropriately design for this additive manufacturing (AM) process. This paper aims to identify impacts on these composites’ viscoelastic properties due to changes in base material composition and distribution caused by incomplete dithering in small features.
Design/methodology/approach
Dynamic mechanical analysis (DMA) is used to measure viscoelastic properties of two base PolyJet materials and seven “digital materials”. This establishes the material design space enabled by voxel-by-voxel control. Specimens of decreasing width are tested to explore effects of feature width on dithering’s ability to approximate macroscale material properties; observed changes are correlated to multi-material distribution via an analysis of ingoing layers.
Findings
DMA shows storage and loss moduli of preset composites trending toward the iso-strain boundary as composition changes. An added iso-stress boundary defines the property space achievable with voxel-by-voxel control. Digital materials exhibit statistically significant changes in material properties when specimen width is under 2 mm. A quantified change in same-material droplet groupings in each composite’s voxel pattern shows that dithering requires a certain geometric size to accurately approximate macroscale properties.
Originality/value
This paper offers the first quantification of viscoelastic properties for digital materials with respect to material composition and identification of the composite design space enabled through voxel-by-voxel control. Additionally, it identifies a significant shift in material properties with respect to feature width due to dithering pattern changes. This establishes critical design for AM guidelines for engineers designing with digital materials.
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Kazi Moshiur Rahman, Hadi Miyanaji and Christopher B. Williams
In binder jetting, the interaction between the liquid binder droplets and the powder particles defines the shape of the printed primitives. The purpose of this study is to explore…
Abstract
Purpose
In binder jetting, the interaction between the liquid binder droplets and the powder particles defines the shape of the printed primitives. The purpose of this study is to explore the interaction of the relative size of powder particles and binder droplets and the subsequent effects on macro-scale part properties.
Design/methodology/approach
The effects of different particle size distribution (5–25 µm and 15–45 µm) of stainless steel 316 L powders and droplet sizes (10 and 30 pL) on part density, shrinkage, mechanical strength, pore morphology and distribution are investigated. Experimental samples were fabricated in two different layer thicknesses (50 and 100 µm).
Findings
While 15–45 µm samples demonstrated higher green density (53.10 ± 0.25%) than 5–25 µm samples (50.31 ± 1.06%), higher sintered densities were achieved in 5–25 µm samples (70.60 ± 6.18%) compared to 15–45 µm samples (65.23 ± 3.24%). Samples of 5–25 µm also demonstrated superior ultimate tensile strength (94.66 ± 25.92 MPa) compared to 15–45 µm samples (39.34 ± 7.33 MPa). Droplet size effects were found to be negligible on both green and sintered densities; however, specimens printed with 10-pL droplets had higher ultimate tensile strength (79.70 ± 42.31 MPa) compared to those made from 30-pL droplets (54.29 ± 23.35 MPa).
Originality/value
To the best of the authors’ knowledge, this paper details the first report of the combined effects of different particle size distribution with different binder droplet sizes on the part macro-scale properties. The results can inform appropriate process parameters to achieve desired final part properties.
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Mohammad I. Albakri, Logan D. Sturm, Christopher B. Williams and Pablo A. Tarazaga
This work proposes the utilization of electromechanical impedance measurements as a means of non-destructive evaluation (NDE) for additive manufacturing (AM). The effectiveness…
Abstract
Purpose
This work proposes the utilization of electromechanical impedance measurements as a means of non-destructive evaluation (NDE) for additive manufacturing (AM). The effectiveness and sensitivity of the technique for a variety of defect types commonly encountered in AM are investigated.
Design/methodology/approach
To evaluate the feasibility of impedance-based NDE for AM, the authors first designed and fabricated a suite of test specimens with build errors typical of AM processes, including dimensional inaccuracies, positional inaccuracies and internal porosity. Two polymer AM processes were investigated in this work: material jetting and extrusion. An impedance-based analysis was then conducted on all parts and utilized, in a supervised learning context, for identifying defective parts.
Findings
The newly proposed impedance-based NDE technique has been proven to be an effective solution for detecting several types of print defects. Specifically, it was shown that the technique is capable of detecting print defects resulting in mass change (as small as 1 per cent) and in feature displacement (as small as 1 mm) in both extruded nylon parts and jetted VeroWhitePlus parts. Internal porosity defects were also found to be detectable; however, the impact of this defect type on the measured impedance was not as profound as that of dimensional and positional inaccuracies.
Originality/value
Compared to currently available NDE techniques, the newly proposed impedance-based NDE is a functional-based technique with the advantages of being cost-effective, sensitive and suitable for inspecting AM parts of complex geometry and deeply embedded flaws. This technique has the potential to bridge the existing gaps in current NDE practices, hence paving the road for a wider adoption of AM to produce mission-critical parts.
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Kieran D. Beaumont, Joseph R. Kubalak and Christopher B. Williams
Material extrusion (MEX) additive manufacturing often requires support structures to enable manufacture of steep overhanging features. Multi-axis deposition (often enabled by a…
Abstract
Purpose
Material extrusion (MEX) additive manufacturing often requires support structures to enable manufacture of steep overhanging features. Multi-axis deposition (often enabled by a robotic arm) offers novel toolpath planning methods that can significantly reduce or eliminate supports. However, there is currently a lack of established design guidelines for the process.
Design/methodology/approach
This study investigates the relationship between achievable, support-free overhangs and the multi-axis build direction. Although altering build directions mid-print can increase the layer-to-layer overlap of an overhanging feature, the deposition paths on the overhanging surface may be less supported with respect to gravity. To interrogate these effects, a 6-degree-of-freedom robotic arm MEX platform printed test pieces with overhang angles (relative to the build direction) increasing from 0° to 75° at build directions varying from 0° (i.e., XY-planar) to 60° with respect to the global Z-axis.
Findings
Characterization of printed surface quality revealed no statistically significant difference in the fidelity of the overhanging surface as the build direction was changed. These results suggest that the overhang threshold observed in traditional XY-planar printing (typically 45°) remain consistent regardless of build direction (e.g. a build direction of 60° successfully printed a relative overhang of 45°), indicating that deposition quality was not negatively impacted by gravitational forces.
Originality/value
This study provides insight into how tool orientation can be optimized to maximize part accuracy and minimize support material requirements; after quickly screening for the XY-planar overhang threshold, designers can freely select multi-axis build directions throughout part geometries, provided the overhanging surfaces are below that relative threshold.
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Joseph R. Kubalak, Alfred L. Wicks and Christopher B. Williams
Material extrusion (ME) suffers from anisotropic mechanical properties that stem from the three degree of freedom (DoF) toolpaths used for deposition. The formation of each layer…
Abstract
Purpose
Material extrusion (ME) suffers from anisotropic mechanical properties that stem from the three degree of freedom (DoF) toolpaths used for deposition. The formation of each layer is restricted to the XY-plane, which produces poorly bonded layer interfaces along the build direction. Multi-axis ME affords the opportunity to change the layering and deposition directions locally throughout a part, which could improve a part’s overall mechanical performance. The purpose of this paper is to evaluate the effects of changing the layering and deposition directions on the tensile mechanical properties of parts printed via multi-axis ME.
Design/methodology/approach
A multi-axis toolpath generation algorithm is presented and implemented on a 6-DoF robotic arm ME system to fabricate tensile specimens at different global orientations. Specifically, acrylonitrile butadiene styrene (ABS) tensile specimens are printed at various inclination angles using the multi-axis technique; the resulting tensile strengths of the multi-axis specimens are compared to similarly oriented specimens printed using a traditional 3-DoF method.
Findings
The multi-axis specimens had similar performances regardless of orientation and were equivalent to the 3-DoF specimens printed in the XYZ orientation (i.e. flat on the bed with roads aligned to the loading condition). This similarity is attributed to those sets of specimens having the same degree of road alignment.
Practical implications
Parts with out-of-plane loads currently require design compromises (e.g. additional material in critical areas). Multi-axis deposition strategies could enable local changes in layering and deposition directions to more optimally orient roads in critical areas of the part.
Originality/value
Though multi-axis ME systems have been demonstrated in literature, no prior work has been done to determine the effects of the deposition angle on the resulting mechanical properties. This work demonstrates that identical mechanical properties can be obtained irrespective of the build direction through multi-axis deposition. For ABS, the yield tensile strength of vertically oriented tensile bars was improved by 153 per cent using multi-axis deposition as compared to geometrically similar samples fabricated via 3-DoF deposition.
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Jacob P. Moore and Christopher B. Williams
– This paper aims to seek to fill a gap in the literature by characterizing the fatigue life and microstructure of a printed elastomer material, the TangoBlackPlus material.
Abstract
Purpose
This paper aims to seek to fill a gap in the literature by characterizing the fatigue life and microstructure of a printed elastomer material, the TangoBlackPlus material.
Design/methodology/approach
Because the TangoBlackPlus material is marketed as “rubber-like”, the printed elastomer specimens were tested according to the ASTM D4482-11 “Test Method for Rubber Property Extension Cycling Fatigue”. The microstructure of the printed material and multi-material interface was examined by slicing specimens and examining them under an optical microscope.
Findings
Findings are developed to show the relationship between elongation and expected fatigue life. Findings also indicate that the smoother, non-support encased “glossy” surface finish option for PolyJet parts improve the fatigue life of components and that there are a number of microscopic voids in the TangoBlackPlus material that seem to be concentrated at layer and print head boundaries.
Research limitations/implications
This paper provides a glimpse into the fatigue properties and microstructure of printed elastomeric parts, a previously unstudied area. This work is limited in that it only looks at specimens created in a single orientation, on a single machine, with a single material. More work is needed to understand the general fatigue properties of printed elastomers and the factors that influence fatigue life in these materials.
Practical implications
The authors provide several design guidelines based on the findings and previous work that can be used to increase the fatigue life of printed elastomer components.
Originality/value
As additive manufacturing (AM) technology moves from a prototyping tool to a tool used to create end use products, it is important to examine the expected lifespan of AM components. This work adds to the understanding of the expected product lifecycle of printed elastomer components that will likely be expected to withstand large repeated loading conditions.
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Nicholas A. Meisel, Christopher B. Williams, Kimberly P. Ellis and Don Taylor
Additive manufacturing (AM) can reduce the process supply chain and encourage manufacturing innovation in remote or austere environments by producing an array of replacement/spare…
Abstract
Purpose
Additive manufacturing (AM) can reduce the process supply chain and encourage manufacturing innovation in remote or austere environments by producing an array of replacement/spare parts from a single raw material source. The wide variety of AM technologies, materials, and potential use cases necessitates decision support that addresses the diverse considerations of deployable manufacturing. The paper aims to discuss these issues.
Design/methodology/approach
Semi-structured interviews with potential users are conducted in order to establish a general deployable AM framework. This framework then forms the basis for a decision support tool to help users determine appropriate machines and materials for their desired deployable context.
Findings
User constraints are separated into process, machine, part, material, environmental, and logistical categories to form a deployable AM framework. These inform a “tiered funnel” selection tool, where each stage requires increased user knowledge of AM and the deployable context. The tool can help users narrow a database of candidate machines and materials to those appropriate for their deployable context.
Research limitations/implications
Future work will focus on expanding the environments covered by the decision support tool and expanding the user needs pool to incorporate private sector users and users less familiar with AM processes.
Practical implications
The framework in this paper can influence the growth of existing deployable manufacturing endeavors (e.g. Rapid Equipping Force Expeditionary Lab – Mobile, Army’s Mobile Parts Hospital, etc.) and considerations for future deployable AM systems.
Originality/value
This work represents novel research to develop both a framework for deployable AM and a user-driven decision support tool to select a process and material for the deployable context.
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Nicholas A. Meisel and Christopher B. Williams
The purpose of this study/paper is to present the design and implementation of a novel vending machine concept based on desktop-scale extrusion additive manufacturing (AM). Due to…
Abstract
Purpose
The purpose of this study/paper is to present the design and implementation of a novel vending machine concept based on desktop-scale extrusion additive manufacturing (AM). Due to cost, access to AM technologies at academic institutions tends to be limited to upper-level courses to support project-based coursework. However, with the decreasing cost of desktop-scale AM technology, there is potential to improve student access to such technologies and provide more opportunities for AM education.
Design/methodology/approach
The authors present the design and implementation of an AM “vending machine” that is powered by desktop-scale extrusion-based AM systems. This system intends to provide students broad, unrestricted access to entry-level AM tools and promote informal learning opportunities.
Findings
Student users of the AM vending machine are found to be primarily engineering majors at various levels in their studies. Manufactured parts are evenly split between functional and decorative parts, though 75 per cent of students are creating their own designs rather than simply printing found design files.
Research limitations/implications
Future work will focus on improving the system’s ease-of-maintenance, lowering the barrier to entry with a simpler user interface and establishing a method for better recording part and user information.
Practical implications
The interface of the AM vending machine lowers the barrier of entry into engaging with AM and places this emerging technology in a familiar and “safe” context. It provides students at various levels and disciplines the opportunity to fabricate parts for classroom and personal projects.
Social implications
A “vending machine” system may have far-reaching implications for public access and use of AM. Such broad access has the potential to further educate and impassion the public about the potential of AM.
Originality/value
This work represents the creation and assessment of the world’s first AM vending machine.