Additive Manufacturing Utilizing Stock Ultraviolet Curable Silicone

Daniel A. Porter1, Adam L. Cohen1, Paul S. Krueger1, and David Son2

1 Dept. of Mechanical Engineering, Southern Methodist University Dallas, TX 75206 2 Dept. of Chemistry, Southern Methodist University Dallas, TX 75206

Abstract

Extrude and Cure Additive Manufacturing (ECAM) is a method that enables 3D printing (3DP) of common thermoset materials. Ultraviolet (UV)-curable silicone is an example of a thermoset material with a large number of industrial and medical applications. 3D printed silicone prototype parts are obtained using a custom high pressure ram, valve, and UV exposure system.

This paper will address issues with printing stock UV curable silicone such as electrostatic repulsion, in-nozzle curing, and extrudate slumping. One solution that addresses two issues is adding carbon black (CB) to the mixture to reduce electrostatic repulsion while also inhibiting UV cure depth, hence preventing material from curing in the nozzle. Evidence shows that too much carbon black can be detrimental to the structural stiffness of the resulting part.

Introduction

Additive manufacturing (AM) is a lucrative and active research area with significant growth potential due to its myriad of commercial applications [1]. Common AM process materials such as acrylonitrile butadiene styrene (ABS), polylactic acid (PLA), polyamide (nylon), and photosensitive polymers are better understood, with more research attention focusing on the expansion of the viable AM material repertoire. 3D printing silicone is the leading edge of research in academic and industrial environments.

Polyurethanes, epoxies, urea formaldehyde, polyimides [2], and silicone rubber are

thermoset materials that are difficult to 3D print via traditional additive manufacturing methods. Such techniques like material extrusion (ME) which include fused filament fabrication (FFF) are well researched for thermoplastics but are still being investigated for thermosets. Once crosslinking begins in the curing process for these materials, plastic reflow is impractical if not impossible. Introduced complexities may include unwanted cured material accumulation near the nozzle or part, system jams due to material curing in an improper place, mixing and system loading processes, and cleanup and maintenance after a print. Some benefits of using a ME setup for printing thermosets is the ability to utilize multiple materials (which is not compatible with stereolithography (SLA) and digital light processing (DLP)) not needing to encase the entire print bed to protect the curable material from initiators such as UV, and minimizing waste.

Although most materials that can be used in popular ME or FFF are of a rigid plastic nature,

recently, advanced elastomers have been investigated in the field of additive manufacturing. Materials such as thermal plastic elastomers (TPE) [3] and silicones [4] [5] are now of interest. Silicone as a printing material for additive manufacturing is one of the newest additions to the 3D

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

Reviewed Paper

printing field due to the numerous applications such as medical implants, component insulation, and prosthetics for their chemical, temperature, and moisture resistances along with mechanical flexibility, and weatherability [6] [7] [2].

San Draw Inc. (San Jose, CA) is able to print silicone in full color, adjustable hardness,

and with multi-material capability [8]. San Draw Medical (San Jose, CA) is currently printing silicone seals for fuel cells [9]. Sterne Elastomere (Cavaillon, France) is revealing a silicone 3D printer that prints 0.25 mm layers of UV cured silicone [10]. Keyence, a Japanese sensor and printer manufacturer, is also developing a silicone 3D printing [11]. Stamos + braun Prothesenwerk (Dresden, Germany) is making headway into the biomedical field by 3D printing silicone inserts and bone structures [12]. Wacker Chemie (Munich Germany) announced the world’s first industrial silicone 3D printer, the ACEO Imagine Series K [13], which utilizes drop on demand type printing for UV silicones. Fripp Design (Sheffield, U.K.) has the Picsima process which uses a needle to dispense a silicone component into a bath containing the other crosslinking component.

As of yet, UV curable silicones are not highly biocompatible, but the vast amount of non-

medical silicone applications makes investigating additive manufacturing in this area still highly viable. Some polymer materials that are at least somewhat biocompatible include medical grade polyurethanes [14], polypyrrole [15], poly-ε-caprolactone [16], and silicones [17]. Other recent advances in additive manufacturing include printing optically transparent glass [18], polyvinylidene fluoride (PVDF) [19], and ultra-soft thermoplastic elastomers (TPE) [20]; fiber encapsulation additive manufacturing [21], printing of drug delivery devices [22], stretchable embedded sensors [23], and capacitive force sensors [24].

In this work Extrude and Cure Additive Manufacturing (ECAM) is performed at the

Laboratory for Additive Manufacturing, Robotics, and Automation (LAMRA) to cure materials that are extruded and cured layer by layer or in situ. High pressures and friction inside the system create some difficulties for the given ME approach. Some of the greatest challenges are electrostatic repulsion, an effect that causes two masses to push apart due to significant charge of the same sign, and nozzle jamming. Carbon black is added to the UV curable silicone mix to reduce the repulsion effect and the amount of nozzle jams while curing in situ. The mechanical properties of 3D printed dog bones with different concentrations of carbon black are quantified and discussed in these proceedings.

Experimental Methods Machine Setup

The custom ECAM machine built at LAMRA labs is shown Figure 1. A high-torque geared stepper motor drives a linear sled which in turn operates a high pressure hydraulic cylinder, Figure 1a). Material is loaded into the cylinder by pulling vacuum and in the case of high viscosity, assisted with a pressurized device. A manual valve at the end of the cylinder allows the material to be pushed through a Teflon high pressure hose, then high pressure metal tubing, and subsequently into a high pressure stainless steel pneumatically actuated valve shown in Figure 1b). From the pneumatic valve, material is deposited and positioned by the X and Y linear stages. The

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constructed 3D printer with UV shielding is shown in Figure 1c). For silicones with additives, a filter is placed between the hydraulic cylinder and the metal plumbing on the Z stage.

Figure 1. 3D printer utilized in this research. a) High pressure ram rendering, b) rendering of

3D printer, and c) constructed printer with valve controller and UV exposure system.

A custom UV wand holder is 3D printed in ABS and a render of the setup is shown in Figure 2. This custom holder ensured repeatability of prints by keeping the angle and distance of UV exposure wands fixed. The UV source is a Dymax Bluewave 200 (40 W/cm2 total intensity) which has four wands optically coupled to the source. Four wands covered the immediate part being printed and ensured a cured layer for moderate part size despite extrusion direction. Brass nozzles with short throat lengths are used to ensure the pressure drop in the system is minimized.

Figure 2. Custom UV wand holder and high pressure pnuematic valve setup with shield ring.

Initial Observations

Initial prints revealed problems such as significant slumping of certain materials, nozzle material accumulation (Figure 3b)), in nozzle curing (Figure 3a)), and electrostatic repulsion. Slumping was only a problem if the UV curable silicone was not cured immediately after extrusion. One way to get around the slumping problem was to print low aspect ratio beads. However this technique simultaneously increased cured material accumulation on the nozzle and interfered with the print process by rubbing against the part, reducing print quality and reliability. It became apparent that curing in situ was a preferred method when using low viscosity, non-shear-thinning materials. The material, if optically translucent, may act as a light guide and gradually cure material in the nozzle thus clogging the system.

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Figure 3. a) Rendering of a typical silicone nozzle clog in which the material cures in the

dispense orifice and b) an image of nozzle material accumulation.

Electrostatic repulsion is observed in this system configuration with silicones from Momentive Performance Materials (Waterford, NY). The effect seems greater in higher viscosity materials like UV Silopren 2030 when compared to UV Electro 225-1 which has viscosities of ~450 Pa-s and ~70 Pa-s respectively at 10 s-1 according to Momentive’s technical data sheet. After a few minutes of material extrusion, the silicone upstream of the nozzle starts to locally accumulate electrostatic charge. Combined with the charging that occurs during UV curing, the resulting effect is a significant repulsion force acting on the extruded silicone. This can be observed by the extrudate deviating from its intended deposition path, degrading part geometry and potentially mechanical quality to suffer. Illustrating this effect is Figure 4d) and f). The silicone used in Figure 4 is UV Silopren 2030 and is shown as a free stream in Figure 4a). Observe the lack of an electrostatic repulsion effect to a black nitrile glove in Figure 4b), an uncured blob of silicone in Figure 4c), and an aged 3D printed silicone part in Figure 4e). Contrast this to a freshly 3D printed silicone part in Figure 4d) and cured silicone blob in Figure 4f). Diversion of the viscous fluid indicates electrostatic repulsion effects.

Figure 4. Repulsion effects for a) free stream of UV Silopren 2030 next to b) a nitrile glove, c) an uncured blob of silicone, d) a recent 3D printed silicone part, e) an aged 3D printed silicone

part, and f) a bulk UV cured blob of silicone.

Reducing the repulsion effect would require eliminating or neutralizing the surface charge of the part, the tribocharged silicone emerging from the nozzle, or both. Adding electrically conductive fillers can ameliorate this problem. Options for electrically conductive fillers include antimony-tin doped oxide [25], aluminum, silver, copper, silicon-carbide [26], ZnO [27], carbon black (CB) powder [28], carbon nanotubes [29], among others. The carbon black option is inexpensive and simple but also increases the opaqueness of the silicone, thus impeding the curing

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depth. Impeding the curing depth can be detrimental to part mechanical properties but could also alleviate some problematic observation like silicone curing in the nozzle.

CB in silicone has been explored before with research being done to understand the benefits

and effects [30] [28] [31] [32]. Electrical conductivity percolation thresholds for carbon black in a medium vary significantly, but some typical values are 10-25 percent by volume when in a styrene butadiene rubber (SBR) [33]. The objective is to not make the silicone as conductive as a bulk material, but rather to reduce the localized tribocharging which appears to cause the electrostatic repulsion. With this in mind, UV Electro 225-1 is mixed with small amounts of Vulcan XC605 carbon black from Cabot (Boston, MA). All samples tested and printed were mixed with a FlackTek SpeedmixerTM DAC 150.1 FVZ-K (Landrum, SC) to ensure thorough dispersion of the CB. The samples were mixed at 2500 RPM for 150 seconds, then the composite was scraped off the inner sides of the container and mixed again. Even with the Speedmixer, there are conglomerates of CB that exist which clog the nozzle and require in line system filtering. Quantifying Slumping of Silicone Understanding how much a material slumps is important to 3D printing. It is vital to know just how the height of a bead changes as a function of time. To obtain this information ten traces of UV Electro 225-1 and UV Silopren are printed 100 mm long at 20 mm/s. A dwell time of about 30 seconds is held in-between each trace giving a total dwell time range of about 300 seconds. Immediately after the ten traces are printed a UV flood exposure is done at max intensity so that all of the silicone lines are cured as fast as possible. Traces of 0.25, 0.20, and 0.10 mm height are printed and have an equivalent flow rate that would allow for a 0.5 mm wide trace assuming a pill shaped cross section.

The glass substrate with the printed silicone lines is taken to a microscope, Olympus (Shinjuku, Tokyo, Japan) BX60, where a marking compound is drawn across a section of each trace to improve measurability. Height measurements are performed by focusing on the glass substrate and then on top of the marked trace while a Fowler (Newton, MA) Digital Indicator to measure the displacement. Extrudate widths are measured using a digital microscope camera from Dino Lite (New Taipei City, Taiwan) AM-7023B. These experiments are repeated three times for each type of silicone and trace height and then averaged. Figure 5 shows the glass plate with three sets of slumping experiments right after UV exposure.

Figure 5. Three sets of cured UV Electro 225-1 traces with a light marking compound applied.

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Mechanical Property Testing

Dog bone structures adhering to ASTM standard D638 T1 are 3D printed in UV Electro 225-1 with different loadings of CB. For comparison, bulk cast molds of the same dog bone are done for the same material. Print specifications for the samples are shown in Table 1. There are five prepared samples for each dog bone lot.

Table 1. Printing parameters for dog bone samples.

Parameter Value Notes

Feed rate (mm/s) 15 X, Y total vector velocity Layer height (mm) 0.25 Extrudate width (mm) 0.50 Trace to trace spacing Infill % 100 Infill pattern type Rectilinear Alternates by 90 degrees each layer Infill angle (deg) 45 Outer perimeters 3 UV wand distance (mm) ~15 From wand to plane surface UV wand angle (deg) 30 Measured from vertical

The samples are covered in talc powder and marked so that the gauge length marks (50mm)

may easily be observed with a HD camera. Each sample is loaded into a tensile testing apparatus and strained at 500 mm/min until an end displacement of 100 mm is achieved. Pictures are captured intermittently from above while force data is recorded. The tensile testing apparatus with a bulk 0.00 and 3D printed 0.15wt% loaded is shown in Figure 6a) and Figure 6b). A single sample from the bulk and 0.00, 0.15, 0.50, and 1.00 wt% CB 3D printed dog bones is shown in Figure 6c) through g).

Figure 6. Dog bones with 0.00 wt% and 0.15 wt% CB marked and loaded into the tensile tester.

Bulk dog bone with c) 0.00 wt% and 3D printed UV Electro 225-1 dog bones with d) 0.00, e) 0.15, f) 0.50, and g) 1.00 wt% CB loading.

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Hardness of all samples is measured using a Rex DD-4 Type M durometer (Rex Durometers, Buffalo Grove, IL) and with LabVIEW (National Instruments, Austin, TX) data logging software. Measurements are taken on three different positions on the samples and then averaged. Hardness is a good indicator of how well cured each sample is.

Results and Discussion

Carbon Black Effect on Repulsion Different amounts of CB are added to Silopren 2030 and bulk cured under a UV wand for

around 3 minutes. The larger the wt% of CB, the thinner the layer of cured silicone in the bulk solid due to the CB attenuating the curing depth of the UV. Repulsion effects for the different wt% loadings in UV Silopren 2030 are shown in Figure 7a) through e). Figure 7f) shows that a freshly printed part in UV Electro 225-1 next to a stream of the same material having the same CB loading has negligible repulsion effects.

Figure 7. Effects of a) 0.01 wt%, b) 0.16 wt%, c) 0.31 wt%, d) 1.25 wt%, and e) 2.50 wt% bulk cured CB loaded UV Silopren 2030 on the repulsion effect given a 0.00 wt% CB free stream of

the same material. A 0.15 wt% CB free stream of UV Electro 225-1 f) flows next to a freshly 3D printed silicon part fabricated with the same silicone.

In addition to the reduction of the electrostatic repulsion, all prints with carbon black loading of 0.15 wt% or higher showed a significant decrease in the occurrence of nozzle jams that were caused by silicone curing in the dispense orifice. In fact there was only one jam which occurred when 3D printer was left idle for about 30 minutes while the UV exposure system was active. Nozzle material accumulation was lessened with the same amount of carbon black but eventually still occurs with the given setup. Slumping of Silicone Results for slumping of UV Electro 225-1 and UV Silopren 2030 are shown in Figure 8. From Figure 8a) and b). The slopes of width versus dwell time are greater for the less viscus silicone UV Electro 225-1. Also the heights in Figure 8c) and d) show the same general trend that UV Electro drops faster than UV Silopren 2030. Images of UV Electro 225-1 after 30 seconds of dwell time, Figure 9 a), show widening by 20 percent. 300 seconds of dwell time for UV Silopren 2030 start to show significant widening, Figure 9 b).

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Figure 8. Slumping result widths for a) UV Electro 225-1 and b) UV Silopren 2030. Slumping

result heights for c) UV Electro 225-1 and d) UV Silopren 2030. The results of the slumping test show the importance of needing to cure in situ for materials like UV Electro 225-1. These experiments were performed on glass substrates so the results of slumping may be slightly different for a substrate of tacky silicone of the same type. This would reveal the effect of wettability on slumping.

Figure 9. Images of a) UV Electro 225-1 trace after 30 seconds of dwell time b) vs UV Silopren

2030 after 300 seconds.

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Stiffness of Dog Bone Samples Initial dog bone tensile testing revealed that the bulk, 0.00, and 0.15 wt% CB dog bone samples have almost equivalent stiffness responses. The stiffness results are averaged for all five samples in each category for simplicity. The higher 0.50 and 1.00 wt% CB samples had much lower stiffness values as shown in Figure 10a). Secant modulus results for the stress versus strain curves are shown in Figure 10b). A drop in stiffness for higher loaded CB dog bones was expected because UV curing starts to become significantly attenuated enough that the bottom part of the 3D printed traces are not fully cured by the time the entire layer is finished.

Figure 10. Tensile test results for all as cast and as printed dog bone samples.

UV Electro 225-1 was found to be fully cured after baking in an oven at 121°C for 10 minutes. Three of the dog bone samples were put into an oven and baked for the same settings to see if stiffness and hardness improvments could be made. The average stiffness response for the three dog bones in the post-oven cured experiment are shown in Figure 11. It is evident from Figure 11 that post-oven curing the bulk and 3D printed samples will fully cure the silicone. An enhancement in stiffness over simple UV curing is also observed with post-oven processing at the prescribed time and temperature.

Figure 11. Post-oven cure tensile test results for cast and printed dog bone samples.

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Quantifications for dog bone tensile testing is shown in Table 2 along with the standard deviation for 100% strain measurements. For UV Electro 225-1, a CB wt% of 0.15 gave the best benefit in terms of alleviating nozzle clogging and electro static repulsion while still maintaining a comparable stiffness to the bulk and 0.00wt% CB 3D printed samples.

Table 2. Tensile test results for all dog bone samples showing modulus at 100% strain. Percent

difference is with reference to the initial tensile testing results.

Modulus 100% (MPa), initial

Modulus 100% (MPa), post-oven cure

Average Std. Dev. Average

Std. Dev. % Diff

Bulk Cast 0.310 0.004 0.340 0.008 9.59 3D Printed, 0.00 wt% CB 0.312 0.007 0.336 0.004 7.45 3D Printed, 0.15 wt% CB 0.306 0.008 0.331 0.007 8.36 3D Printed, 0.50 wt% CB 0.235 0.017 0.332 0.008 41.61 3D Printed, 1.00 wt% CB 0.197 0.007 0.327 0.007 65.82

Hardness of Dog Bone Samples

Durometer results for the dog bone samples also reveal that 0.50 and 1.00 wt% CB samples are under cured compared to the others. Once post-oven cured, the samples increased in Durometer like the results of the stiffness tests. Momentive reports that the durometer for a fully cured UV Electro 225-1 sample is about Shore 25 A which correlates to about ~26-27 Shore M (assuming sample thickness is not small) indicating the bulk cast, 3D printed 0.00, and 0.15 wt% carbon black samples are most likely fully cured via UV exposure.

Table 3. Durometer results for all dog bone samples. Percent difference is with respect to initial

durometer measurements. Hardness, M

initial Hardness, M

post-oven cured

Average Std. Dev. Average Std. Dev. % Diff

Bulk Cast 26.8 1.05 26.7 0.59 -0.48 3D Printed, 0.00 wt% CB 26.1 1.30 26.0 0.20 -0.29 3D Printed, 0.15 wt% CB 26.1 0.31 26.5 0.17 1.55 3D Printed, 0.50 wt% CB 24.6 1.03 26.9 0.54 9.25 3D Printed, 1.00 wt% CB 22.6 1.03 27.4 0.27 21.26

Conclusions and Future Work UV curable silicone dog bone samples are 3D printed with a high pressure ECAM system. Slumping of silicones is investigated and is found to be significant for the low viscosity and non-shear-thinning UV Electro 225-1 thus leading to the need of in situ curing. Problems with in situ curing using stock silicone materials are in nozzle curing, nozzle material accumulation, and electrostatic repulsion. Carbon black is selected as an inexpensive additive and was found to

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significantly stop system jams due to silicone curing in the nozzle and reduce the amount of nozzle material accumulation. Material property tests revealed that bulk cast, 0.00 and 0.15 wt% CB 3DP dog bones responded approximately the same to applied force. The 0.50 and 1.00 wt% CB loaded 3DP dog bones showed lower stiffnesses indicating that they were not fully UV cured. This could be detrimental to printing silicone parts that have high aspect ratios as the entire part could accumulate a large Z height error due to weight. A post-oven cure on three of the samples from each lot increased all of the dog bone stiffnesses to levels comparable to bulk cured material. Thus a small amount of carbon black in UV silicones can allow for continuous high intensity in situ UV curing to minimize slumping effects while retaining mechanical stiffness and harnesses. One downside is that the color of the silicone is tinted. Work to eliminate nozzle material accumulation currently entails using UV opaque materials with smooth surfaces and nonstick properties. The printing process must be optimized because silicone may still cure around the nozzle in a ring shape which could mechanically lock itself in place. Inexpensive additives that reduce slumping and inhibit UV curing depth while retaining translucent optical properties are also being investigated.

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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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