Notice of Copyright. This manuscript has been authored by UT-Battelle, LLC under Contract No. DE-AC05-00OR22725 with the U.S. Department of Energy. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes. The Department of Energy will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan (http://energy.gov/downloads/doe-public-access-plan).

EFFECT OF INTER-LAYER COOLING TIME ON DISTORTION AND MECHANICAL PROPERTIES IN METAL ADDITIVE MANUFACTURING

Y.K. Bandari*, Y.S. Lee, P. Nandwana, B.S. Richardson, A.I. Adediran, L.J. Love

*Manufacturing Demonstration Facility, Oak Ridge National Laboratory, Knoxville, TN, 37932,USA

Abstract

Laser Metal Deposition with wire (LMD-w) is one of the novel Direct Energy Deposition (DED) processes that is gaining the attention of various industries, especially aerospace, due to the potential cost and lead time reductions for complex parts. However, subjects of development include optimization of process parameters (for example laser power, wire feed speed, robotic travel speed, inter-layer cooling time etc.) for large scale adaption of this process. These parameters influence residual stress which potentially results in distortion and subsequent mechanical properties. Inter-layer cooling time is one of the main influences on production volume and is typically used to help control the cooling conditions to mitigate part distortion. Therefore, this paper is aimed at investigating different inter-layer cooling times on distortion and resulting mechanical properties of the parts produced by LMD-w. Distortion of deposited Ti-6Al-4V walls was measured automatically using a laser scanner, which was attached to the robotic arm itself. Finally, suitable recommendations are discussed to optimize the inter-layer cooling time to produce parts with desired mechanical properties.

Keywords: Additive Layered Manufacturing, 3-D Printing, Direct Energy Deposition, Laser Metal Deposition with wire, Ti-6Al-4V, Laser Scanner, Distortion, Residual Stress

1. Introduction

Since their first introduction more than 30 years prior, additive manufacturing (AM) processes for metals have been produced and commercialized in the market under different names, for example, Direct Metal Deposition [1], Laser Engineered Net Shaping [2], Shaped Metal Deposition [3], Selective Laser Melting [4], and Electron Beam Freeform Fabrication [5]. In every one of these processes, a heat source is used to create a melt pool into which a wire or powderized feedstock is fed, or the heat source is applied to a powder bed to create beads after solidification. The beads are realized by relative movement of the melt pool and the substrate by using an industrial robotic arm or a gantry system [6]. A part is then manufactured by depositing beads adjacent to each other and layer upon layer. The most common technique to date has been to use a high-power laser as the heat source with metal powder as the feed stock. Other conventional welding techniques have likewise been introduced, for example, Tungsten Inert Gas (TIG) welding [7], Gas Metal Arc Welding (GMAW) [8], Plasma Transferred Arc (PTA) welding [9], [10], and Electron Beam (EB) welding [11].

The high-power laser-based technique remains the most common because of several advantages, for example, the relatively low heat input to the base material and good shape accuracy of the realized geometries. This Laser Metal Deposition (LMD) process has been dominated by

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Solid Freeform Fabrication 2018: Proceedings of the 29th Annual InternationalSolid Freeform Fabrication Symposium – An Additive Manufacturing Conference

powder-based technologies because of flexibility and robustness of the process. However, the powder-based technologies have been developed for building small and complex geometries, with very little focus on deposition rate. The deposition efficiency varies depending on the system set-up, and post treatment of the scattered powder is required. For large scale parts with moderate complexity, such as flanges or bosses, it is more rewarding to use wire-based processes, since these lead to higher deposition rates, better material quality and better surface finish [12]. While the utilization of powder requires specially planned and designed feeding nozzles, the wire-based processes require much simpler equipment and standard welding hardware.

Laser Metal Deposition with wire (LMD-w) is a novel process that fabricates components using a high-power laser source and adds material in the form of metal wire. The laser generates a melt pool on the substrate material into which the metal wire is fed and melted, forming a metallurgical bound with the substrate [13]. By moving the laser processing head and the wire feeder, i.e. the welding tool, relative to the substrate a weld bead is formed during solidification. The relative movement of the welding tool and the substrate is made using a 6-axis industrial robot arm. The formation of a weld bead is illustrated in Figure 1 along with images from the real process.

Figure 1 Left: Illustration of laser-wire interaction Right: Top and side view images of the real

process [13]

One main consideration for the resulting parts of the LMD-w process is the dimensional

precision compared to an initial input geometry. Each layer is formed by melting individual passes from the wire, which experiences rapid heating, melting, solidification, and cooling during the deposition process. While the part is manufactured, the deposited material experiences continuous heating and cooling cycles as more passes and layers are deposited. One of the consequences of the thermal gradients induced in the components by the layer-by-layer deposition of material in AM processes is the build-up of undesirable levels of residual stress and distortion [14].

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2. Literature Review

The development of residual stress and distortion in AM processes has several similarities with multi-pass welding. Several researchers have explored techniques to reduce distortion in similar multi-pass welding processes including the investigations by Michaleris and DeBiccari [15] who demonstrated that decreasing heat input would result in a decrease in workpiece distortion and Masubuchi [16] who confirmed that constraining the workpiece can limit distortion. Futhermore, Deo and Michaleris [17] examined the impact of heating the weld region immediately prior to welding and found that the technique can be utilized to achieve zero net distortion. In AM research Klingbeil et al. [18] and Cornin et al. [19] each found that bulk substrate preheating can be used to decrease distortion in deposited workpieces.

In AM processes, the influence of change in path planning and inter-layer cooling time between passes on residual stress and distortion have also been studied. For instance, the selection of different deposition paths has been shown by Nickel et al. [20] to notably affect distortion in AISI 1117 C-Mn steel, and has also been studied by Mercelis and Kruth (2001) to influence residual stress in AISI 316 austenitic stainless steel. With respect to changing inter-layer cooling time between passes, Jendrzejewski et al. (2007) reported that shorter delays reduce the measured residual stress in deposited Cobased stellite SF6 alloy, and Klingbeil et al. [18] concluded delays to reduce distortion in AISI 308 austenitic stainless steel. Fessler et al. [21] reported that allowing deposition to cool between passes decreases distortion of nickel-base INVAR alloys and austenitic stainless steels. Costa et al. [22] and Torries et al. [23] studied the effect of introducing inter-layer cooling time between deposited layers on the resulting thermal history and microstructure of laser deposited AISI 420 steel and Ti-6AL-4V respectively. The study concluded that low inter-layer cooling times result in higher temperature levels and notably altered microstructure when compared with longer inter-layer cooling times.

Whereas these studies have concentrated on post-process measurements of accumulated distortion, others have used in-situ measurements to monitor the temporal accumulation of distortion. Lundbäck [24] estimated in-situ distortion on single wall builds utilizing an optical measurement system to validate their model of the GTAW process. Plati et al. [25] utilized a linear variable differential transformer to measure the deflection of the free end of a cantilevered substrate during powder-based cladding. Grum et al. [26] recorded in-process strain using resistance measuring rosettes to measure strain accumulation during laser cladding. Ocelik et al. [27] utilized digital image correlation to measure distortion of single and multi-bead Nanosteel, Eutroloy 16012, and MicroMelt 23 powder laser depositions on C45 steel and 301 stainless steel substrates. The in-situ measurements taken in these works offer more prominent understanding into distortion accumulation than conventional post-process distortion measurements, but do not compare the impact of changing materials or inter-layer cooling time. The in-situ distortion measurements have primarily been conducted for model validation. Also, some of the other researchers Ding et al. [28], [29], [30], Montevecchi et al. [31], Simunovic et al. [32] have developed thermo-mechanical models to predict residual stress and the resultant distortion in the large parts. However, the relationship between inter-layer cooling time and heat input was not discussed and then interlayer cooling time is one of the parameters which affects the overall production rate.

Much of this previous work on the accumulation of distortion during the deposition has focused on welding and laser cladding processes. AM, on the other hand, involves the deposition of

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multiple layers and potentially large volumes of material to produce discrete shapes and components. In cases where AM processes have been investigated, the impact of changes in the inter-layer cooling time between multiple passes on the accumulation of distortion and the impact on the mechanical properties of the realized components has not been investigated. In the work reported here, in-situ measurements of distortion during the deposition of Ti-6Al-4V are made to investigate the effect of inter-layer cooling time on the mechanical properties.

3. Experimental Procedure

This section describes the base materials, consumables, deposition conditions, power supplies, set-up and techniques deployed during the investigation. The experiments were performed using Ti-6Al-4V plates and delivered according to the specifications AMS 4911; a 1.6 mm diameter Ti-6Al-4V solid wire consumable was used and delivered according to the specifications AMS 4954. The compositions in wt.% for substrate and electrode wire are shown in the Table 1.

Table 1 Chemical composition of substrate and wire

Element Substrate (wt.%) Wire (wt.%) Carbon 0.01 0.02

Iron 0.16 0.18 Aluminum 6.35 6.03 Titanium Remainder Remainder Vanadium 4.13 4.08

Hydrogen (ppm) 25 25 Nitrogen 0.01 0.01 Oxygen 0.19 0.18

3.1 Preparation of substrate

The titanium substrates were cut from a large titanium plate with a thickness of 6.4 mm. The dimensions of the substrate used for the investigation was 500 mm x 155 mm. The substrate’s surface was first wiped using an acetone dampened clean paper cloth. Then a finishing disk Cibo SAG/5/115 was mounted on a hand-held grinder with a low rotational speed and the surface was ground to eliminate oxide layers and impurities. Finally, degreasing was repeated using the acetone dampened clean paper cloth. The substrate was clamped onto a steel block with ceramic washers in between them to avoid heat transfer through conduction. The steel block was then placed onto an aluminum table. A schematic diagram of the arrangement is shown in Figure 2.

3.2 Equipment set-up

All the investigations were conducted with a 6-axis KUKA ‘KR90 2900 extra HA’ robot. Two fiber delivered diode lasers each with the power of 10.7 kW and wavelengths of 940 – 980 nm and 1020 – 1060 nm were used, and they were combined using a laser head combiner to form a laser with 20 kW power. The laser light was conveyed to the optics to eventually form a 7.69 mm diameter out of focus laser spot on the work piece. Abicor Binzel was used as the wire feeder.

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All the investigations were performed in a closed argon environment with less than 250 ppm O2 content. The equipment set up is shown in Figure 3.

A laser line scanner was added to the system to measure the height of deposited layers, and it enabled the implementation of layer height control. It scans from the left end of the plate to the right end of the plate and records data for every 0.5 mm of travel. The laser scanner then generates layer height maps; subsequently, the correction data for the subsequent layer is generated from the control algorithm generated in-house, to maintain a set layer height for all the layers. The control algorithm was developed using LabVIEWTM software and was executed in a computer. LabVIEWTM software was also used to interface with the robot, laser and wire feed systems as well as collecting and logging data.

(a) Top view

(b) Side view

Figure 2 Arrangement (a) Top view (b) Side view

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3.3 Design of Experiments

The weld parameters used for deposition are listed below in Table 2. The dimensions of the walls were 200 x 20 x 11 mm3. Continuous weld beads 200 mm long were deposited one layer at a time in the same deposition direction. With the weld parameters listed below, the single bead width and single bead height ranged between 9-12 mm and 0.8-1.2 mm respectively. Thus, two beads were deposited next to each other with an overlap that resulted in a flat deposited layer of width 21 mm.

Figure 3 LMD-w cell

Table 2 Deposition and weld bead parameters

Parameter Value Laser power 11.5 kW Robot travel speed 12 – 14 mm/s Deposition rate 2.0 +/- 1.0 kg/hr Single bead width 9-12 mm Single bead height 0.8-1.2 mm

Before depositing a new layer, the previously deposited layer was scanned using the laser

line scanner, and the height data was recorded. To maintain a constant layer height, the control algorithm created new weld parameters which were then used to deposit the subsequent layer automatically. In total six walls were deposited. Three of them were clamped all-round the substrate, and three were clamped only at the center. Interlayer cooling time is the wait time between the end of depositing a layer and start of height scan for that layer. Each wall was deposited using a different interlayer cooling time. In total ten layers were deposited for each wall. The six walls are denoted as Wall 1, Wall 2 and so on until Wall 6 and are described below.

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Wall 1 was built with clamps all-round the substrate with no inter-layer cooling time. Wall 2 was built with clamps all-round the substrate with an inter-layer cooling of 30 min after depositing every five layers. Wall 3 was built with a center clamp with no inter-layer cooling time. Wall 4 was built with clamps all-round the substrate with an inter-layer cooling time of 30 min after depositing every two layers. Wall 5 was built with center clamp with an inter-layer cooling time of 30 min after depositing every two layers. Wall 6 was built with center clamp with an inter-layer cooling time of 30 min after depositing every five layers. These are described in the form of a table below (Table 3). Table 3 Description of walls deposited

Sample Clamped/unclamped Inter-layer cooling time of 30 min after every ‘n’

layers of deposition (n) Wall 1 Clamped 10 Wall 2 Clamped 5 Wall 3 Unclamped 10 Wall 4 Clamped 2 Wall 5 Unclamped 2 Wal 6 Unclamped 5

4. Results and discussion

Below are the graphs that show a correlation between the layer number and vertical deformation for each wall. Figure 4 and Figure 5 show the vertical deformations of the plate at the left end and right end of the plate respectively with respect to the layer number.

Figure 4 Deformation of left end of the plate with an increase in layer number

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Figure 5 Deformation of right end of the plate with an increase in layer number

The vertical deformation on layer zero indicates the deformation of the plate without any

deposited material. Likewise, the vertical deformation on layer 10 indicates the deformation of the plate after 10 layers of deposition and 30 min of cooling time.

As shown in Figure 4 and Figure 5, the walls built using only center clamps experienced more vertical deformation on the right end of the plate than on the left end of the plate; the vertical deformation also increased as more layers were deposited. This is due to the preheating effect. The robot moves from the left end to the right end of the plate depositing beads from left to the right. Therefore, the heat also transfers from left to right and downwards through conduction mode primarily. There is more heat accumulation on the right end compared to the left end, which is also seen from the thermocouple readings, that were attached on the both ends of the plate. Subsequently, there is more residual stresses and thus, more deformation. Therefore, the deformation at the right end of the plate is more than the deformation at the left end of the plate.

It is also seen that deformation increases with both an increase in layers and the introduction of inter-layer cooling time; the, deformation decreases after depositing the subsequent layer. From Figure 6, it is seen in the case of Wall 5, which was built using only center clamps and with an inter-layer cooling time after every two layers. The deformation before the third layer of deposition was 4.5 mm, and then it decreased to 3.5 mm just before fourth layer of deposition. A similar trend was seen for Wall 3 and Wall 6, too. This trend is due to the shrinkage of the deposited metal, which causes the plate edges to lift resulting in vertical deformation. Then when a subsequent layer is deposited after the inter-layer cooling time, the deposited metal adds heat to the previously deposited layers, which then expand and lower the edges of the plate [14].

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In case of walls built with clamps all-round the substrate, the deformation was found to be nearly zero, both at the left and right ends of the plates irrespective of inter-layer cooling times.

After depositing 10 layers with inter-layer cooling time and allowing them to cool down, all the Ti-6Al-4V plates were un-clamped. Then, the distortion at the right end of the plate was measured. Figure 6 shows the distorted plates after un-clamping. The vertical deformation at the right end of the plate for each wall is measured using a ruler and is presented in Table 3.

Wall 1 Wall 2

Wall 3 Wall 4

Wall 5 Wall 6

Figure 6 Ti-6Al-4V Walls after unclamping

Table 4 Vertical deformation of un-clamped deposited walls

Sample ID Vertical deformation (mm) Wall 1 6 Wall 2 7 Wall 3 8 Wall 4 7 Wall 5 12 Wall 6 9

All six deposited walls were used to extract samples for room temperature tensile testing

in accordance with the ASTM E-08 13a standard. One half of the wall was tested in an as-deposited condition, while the other half was subjected to the heat treatment recommended by the AMS 4999 standard, which involved annealing the samples at 538 oC +/- 14 for 4 hours +/- 0.25. Table 4 compares the monotonic tensile properties of as-deposited samples across different processing conditions, while Table 5 compares the tensile properties of their heat-treated counterparts.

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Table 5 Tensile properties of as-deposited samples

Sample ID Temp. UTS (ksi)

0.2 YS (ksi)

Elong (%)

Reduction in Area (%)

Modulus (Msi)

Wall 1 Room 144.2 127.0 8.0 13 16.4 Wall 2 Room 145.5 128.8 11 19 16.8 Wall 3 Room 143.9 128.0 11 22 14.5 Wall 4 Room 146.1 129.5 11 23 15.5 Wall 5 Room 145.6 129.2 13 24 15.9 Wall 5 Room 144.1 127.0 13 21 16.5

Table 6 Tensile properties of heat treated samples

Sample ID Temp. UTS (ksi)

0.3 YS (ksi)

Elong (%)

Reduction in Area (%)

Modulus (Msi)

Heat Treated Wall 1 Room 136.5 123.6 13 18 15.5 Heat Treated Wall 2 Room 139.8 126.8 15 32 15.6 Heat Treated Wall 3 Room 138.2 124.7 15 24 15.6 Heat Treated Wall 4 Room 139.7 126.6 11 13 15.9 Heat Treated Wall 5 Room 140.9 128.0 15 29 16.1 Heat Treated Wall 5 Room 139.9 127.6 15 30 16.0

In the as-deposited condition, the samples have similar Yield Strength (YS) and ultimate

tensile strength (UTS) irrespective of the processing condition involved. However, there is some scatter in the elongation to failure. The similarity of YS may arise from near similar microstructures in the as-deposited condition, whereas the scatter in elongation may result from the presence of porosity in the as-deposited samples. Upon heat treatment, there is a noticeable drop in the YS and UTS values in all cases, and yet again the properties are within scatter. There is an increase in elongation on the heat-treated samples in general. The reduction in strength along with the increase in elongation is indicative of microstructural coarsening that is to be expected at the annealing temperatures. To better understand the impact of varying cooling times and clamping states during deposition of these samples, the microstructures from two extreme cases (Wall 1 and Wall 4) were evaluated via scanning electron microscopy. The micrographs are presented in Figure 7.

Microscopic examination shows the presence of basketweave in both the processing conditions. However, the similarity in microstructures is intriguing. These similarities in microstructures may have been caused by the start plate, or heat sink, being much larger than the part itself. Thus, Wall 1 maintained a high enough cooling rate over 10 layers to result in a basketweave microstructure. However, in the case of Wall 4, the cooling rate was as fast as that of Wall 1 during the deposition of the first two layers. In such a case, the deposited bead may already have cooled down to the background substrate temperature, which acts as a heat sink. On deposition of the subsequent two layers after a 30 minutes wait, if the prior layers are already at the background temperature, then the cooling rate will be similar as the build progresses. Thus, in the limited 10-layer build, the effect of the larger heat sink dominates over any potential impact the inter-layer cooling time can have. However, for taller, it is very likely that a continuous build

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may have a coarser microstructure compared to one that has substantial inter-layer cooling time because of the thermal buildup resulting from the poor thermal conductivity of titanium.

Figure 7 Microstructures of Wall 1 and Wall 4 in as-deposited conditions

5. Conclusions and Future Work

1) Cooling time between deposited layers influences the distortion of the plate, and

unclamped samples showed more distortion than the clamped samples. 2) Longer inter-layer cooling time will cause larger distortion. 3) Since the built walls were not high, all the heat was transferred to the large heat sink or

start plate thus, similar microstructure and mechanical properties are seen. 4) Wall 1 showed minimal distortion. Thus, for building large scale parts that are 10 layers or

less, it is recommended not to use any inter-layer cooling time. This way total production time can be reduced.

5) Cooling time influences distortion but not mechanical properties for large scale parts that are not high.

6) There is a need to correlate amount of distortion to microstructure and mechanical properties for large scale components.

7) There is also a need to focus on the deposition pulling away from the start plate due to the residual stress build up.

6. Acknowledgements

The research was sponsored by the US Department of Energy, Office of Energy Efficiency and

Renewable Energy, Advanced Manufacturing Office under contract DE-AC05- 15 00OR22725 with UT-Battelle, LLC. This work is also supported in part by Cooperative Research and Development Agreement with GKN Aerospace, under contract No. NFE-15- 05725.

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WelcomeTitle PagePrefaceOrganizing CommitteePapers to JournalsTable of ContentsBroader ImpactsUsing Additive Manufacturing as a Pathway to Change the Qualification ParadigmTechnology Integration into Existing CompaniesLattice Design Optimization: Crowdsourcing Ideas in the ClassroomEducation of Additive Manufacturing – An Attempt to Inspire ResearchPrinting Orientation and How Implicit It IsMethod for a Software-Based Design Check of Additively Manufactured ComponentsThe Recycling of E-Waste ABS Plastics by Melt Extrusion and 3D Printing Using Solar Powered Devices as a Transformative Tool for Humanitarian Aid

Binder JettingEvaluating the Surface Finish of A356-T6 Cast Parts from Additively Manufactured Sand MoldsEconomies of Complexity of 3D Printed Sand Molds for CastingMitigating Distortion During Sintering of Binder Jet Printed CeramicsBinder Jetting of High Temperature and Thermally Conductive (Aluminum Nitride) CeramicBinder Jetting Additive Manufacturing of Water-Atomized Iron

Data Analytics in AMEffects of Thermal Camera Resolution on Feature Extraction in Selective Laser MeltingArtificial Intelligence-Enhanced Multi-Material Form Measurement for Additive MaterialsMachine Learning for Modeling of Printing Speed in Continuous Projection StereolithographyCurvature-Based Segmentation of Powder Bed Point Clouds for In-Process MonitoringNondestructive Micro-CT Inspection of Additive Parts: How to Beat the BottlenecksNon-Destructive Characterization of Additively Manufactured Components Using X-Ray Micro-Computed TomographyPrecision Enhancement of 3D Printing via In Situ MetrologyLayer-Wise Profile Monitoring of Laser-Based Additive ManufacturingCorrelative Beam Path and Pore Defect Space Analysis for Modulated Powder Bed Laser Fusion Process

Hybrid AMCharacterization of High-Deposition Polymer Extrusion in Hybrid ManufacturingMechanical Properties Evaluation of Ti-6Al-4V Thin-Wall Structure Produced by a Hybrid Manufacturing ProcessDevelopment of Pre-Repair Machining Strategies for Laser-Aided Metallic Component RemanufacturingViscosity Control of Pseudoplastic Polymer Mixtures for Applications in Additive ManufacturingCuring Behavior of Thermosets for the Use in a Combined Selective Laser Sintering Process of PolymersEffect of Porosity on Electrical Insulation and Heat Dissipation of Fused Deposition Modeling Parts Containing Embedded WireA New Digitally Driven Process for the Fabrication of Integrated Flex-Rigid ElectronicsHybrid Manufacturing with FDM Technology for Enabling Power Electronics Component FabricationDigitally-Driven Micro Surface Patterning by Hybrid ManufacturingPotentials and Challenges of Multi-Material Processing by Laser-Based Powder Bed FusionA Digitally Driven Hybrid Manufacturing Process for the Flexible Production of Engineering Ceramic ComponentsStereolithography-Based Manufacturing of Molds for Directionally Solidified CastingsExamination of the Connection between Selective Laser-Melted Components Made of 316L Steel Powder on Conventionally Fabricated Base BodiesCharacterization and Analysis of Geometric Features for the Wire-Arc Additive Process

ApplicationsGeometry/Surface FinishEffect of Inter-Layer Cooling Time on Distortion and Mechanical Properties in Metal Additive ManufacturingEffect of Shield Gas on Surface Finish of Laser Powder Bed Produced PartsMaterial Characterization for Lightweight Thin Wall Structures Using Laser Powder Bed Fusion Additive ManufacturingMetal Additive Manufacturing in the Oil and Gas IndustryDevelopment of a Customized CPAP Mask Using Reverse Engineering and Additive Manufacturing

Specific PartsMultimaterial Aerosol Jet Printing of Passive Circuit ElementsAdditive Manufacturing of Liners for Shaped ChargesAn Aerospace Integrated Component Application Based on Selective Laser Melting: Design, Fabrication and Fe SimulationAdditive Manufacturing of Metal Bandpass Filters for Future Radar ReceiversFast Prediction of Thermal History in Large-Scale Parts Fabricated via a Laser Metal Deposition ProcessDesign Guidelines for a Software-Supported Adaptation of Additively Manufactured Components with Regard to a Robust Production

Large Scale PartsIncreasing Interlaminar Strength in Large Scale Additive ManufacturingUsing Post-Tensioning in Large Scale Additive Parts for Load Bearing StructuresPrecast Concrete Molds Fabricated with Big Area Additive Manufacturing3D Printed Fastener-Free Connections for Non-Structural and Structural Applications – An Exploratory InvestigationCorrelations of Interlayer Time with Distortion of Large Ti-6Al-4V Components in Laser Metal Deposition with WireModel Development for Residual Stress Consideration in Design for Laser Metal 3D Printing of Maraging Steel 300Topology Optimisation of Additively Manufactured Lattice Beams for Three-Point Bending Test

Residual StressMorphable Components Topology Optimization for Additive ManufacturingNext-Generation Fibre-Reinforced Lightweight Structures for Additive Manufacturing

Topology OptimizationTopology Optimized Heat Transfer Using the Example of an Electronic HousingMicrostructural and Mechanical Characterization of Ti6Al4V Cellular Struts Fabricated by Electron Beam Powder Bed Fusion Additive ManufacturingEffect of Wall Thickness and Build Quality on the Compressive Properties of 304L Thin-Walled Structure Fabricated by SLMMechanical Behavior of Additively Manufactured 17-4 Ph Stainless Steel Schoen Gyroid Lattice Structure

Lattices and CellularAn Investigation of the Fatigue Strength of Multiple Cellular Structures Fabricated by Electron Beam Powder Bed Fusion Additive Manufacturing ProcessOn the Mechanical Behavior of Additively Manufactured Asymmetric HoneycombsFabrication of Support-Less Engineered Lattice Structures via Jetting of Molten Aluminum DropletsFinite Element Modeling of Metal Lattice Using Commercial Fea PlatformsA CAD-Based Workflow and Mechanical Characterization for Additive Manufacturing of Tailored Lattice StructuresA Comparison of Modeling Methods for Predicting the Elastic-Plastic Response of Additively Manufactured Honeycomb StructuresNumerical and Experimental Study of the Effect of Artificial Porosity in a Lattice Structure Manufactured by Laser Based Powder Bed FusionSize and Topology Effects on Fracture Behavior of Cellular StructuresRheological, In Situ Printability and Cell Viability Analysis of Hydrogels for Muscle Tissue RegenerationDevelopment of a Thermoplastic Biocomposite for 3D PrintingDesign Rules for Additively Manufactured Wrist Splints Created Using Design of Experiment Methods

Biomedical ApplicationsDesign and Additive Manufacturing of a Patient Specific Polymer Thumb Splint ConceptMandibular Repositioning Appliance following Resection Crossing the Midline- A3D Printed GuideA Sustainable Additive Approach for the Achievement of Tunable PorosityEffects of Electric Field on Selective Laser Sintering of Yttria-Stabilized Zirconia Ceramic PowderFabrication of Ceramic Parts Using a Digital Light Projection System and Tape CastingSlurry-Based Laser Sintering of Alumina CeramicsMaterial Properties of Ceramic Slurries for Applications in Additive Manufacturing Using Stereolithography

MaterialsCeramicsAdditive Manufacturing of Alumina Components by Extrusion of In-Situ UV-Cured PastesMechanical Challenges of 3D Printing Ceramics Using Digital Light ProcessingEffect of Laser Additive Manufacturing on Microstructure Evolution of Inoculated Zr₄₅ꓸ₁Cu₄₅ꓸ₅Al5Co₂ Bulk Metallic Glass Matrix CompositesFiber-Fed Printing of Free-Form Free-Standing Glass StructuresAdditive Manufacturing of Energetic MaterialsMethods of Depositing Anti-Reflective Coatings for Additively Manufactured OpticsA Review on the Additive Manufacturing of Fiber Reinforced Polymer Matrix Composites

Non-Traditional Non-MetalsDesign and Robotic Fabrication of 3D Printed Moulds for CompositesMechanical Property Correlation and Laser Parameter Development for the Selective Laser Sintering of Carbon Fiber Reinforced Polyetheretherketone4D Printing Method Based on the Composites with Embedded Continuous FibersFabricating Functionally Graded Materials by Ceramic On-Demand Extrusion with Dynamic Mixing

CompositesThe Effect of Shear-Induced Fiber Alignment on Viscosity for 3D Printing of Reinforced PolymersProcessing Short Fiber Reinforced Polymers in the Fused Deposition Modeling ProcessImpact Testing of 3D Printed Kevlar-Reinforced Onyx MaterialDeposition Controlled Magnetic Alignment in Iron-PLA CompositesEffects of In-Situ Compaction and UV-Curing on the Performance of Glass Fiber-Reinforced Polymer Composite Cured Layer by LayerGeneral Rules for Pre-Process Planning in Powder Bed Fusion System – A ReviewDevelopment of an Engineering Diagram for Additively Manufactured Austenitic Stainless Steel AlloysFatigue Life Prediction of Additively Manufactured Metallic Materials Using a Fracture Mechanics ApproachCharacterizing Interfacial Bonds in Hybrid Metal Am Structures

Direct WriteThe Mechanical Behavior of AISI H13 Hot-Work Tool Steel Processed by Selective Laser Melting under Tensile Stress

Broad IssuesAdditive Manufacturing of Metal Functionally Graded Materials: A ReviewUnderstanding Adopting Selective Laser Melting of Metallic MaterialsThe Effect of Processing Parameter on Zirconium Modified Al-Cu-Mg Alloys Fabricated by Selective Laser MeltingSelective Laser Melting of Al6061 Alloy: Processing, Microstructure, and Mechanical PropertiesSmall-Scale Characterization of Additively Manufactured Aluminum Alloys through Depth-Sensing IndentationEffects of Process Parameters and Heat Treatment on the Microstructure and Mechanical Properties of Selective Laser Melted Inconel 718Effects of Design Parameters on Thermal History and Mechanical Behavior of Additively Manufactured 17-4 PH Stainless Steel

AluminumThe Effects of Powder Recycling on the Mechanical Properties of Additively Manufactured 17-4 PH Stainless SteelMechanical Properties of 17-4 Ph Stainless Steel Additively Manufactured Under Ar and N₂ Shielding GasRecyclability of 304L Stainless Steel in the Selective Laser Melting ProcessThe Influence of Build Parameters on the Compressive Properties of Selective Laser Melted 304L Stainless Steel

NickelCharacterization of Impact Toughness of 304L Stainless Steel Fabricated through Laser Powder Bed Fusion Process

17-4PH Stainless SteelIncorporation of Automated Ball Indentation Methodology for Studying Powder Bed Fabricated 304L Stainless SteelEffect of Powder Degradation on the Fatigue Behavior of Additively Manufactured As-Built Ti-6Al-4VVolume Effects on the Fatigue Behavior of Additively Manufactured Ti-6Al-4V Parts

304 Stainless SteelEffects of Layer Orientation on the Multiaxial Fatigue Behavior of Additively Manufactured Ti-6Al-4VAmbient-Temperature Indentation Creep of an Additively Manufactured Ti-6Al-4V AlloyIndividual and Coupled Contributions of Laser Power and Scanning Speed towards Process-Induced Porosity in Selective Laser MeltingA Comparison of Stress Corrosion Cracking Susceptibility in Additively-Manufactured and Wrought Materials forAerospace and Biomedical Applications

316L Stainless SteelEffect of Energy Density on the Consolidation Mechanism and Microstructural Evolution of Laser Cladded Functionally-Graded Composite Ti-Al System

TitaniumMechanical Properties of Zr-Based Bulk Metallic Glass Parts Fabricated by Laser-Foil-Printing Additive ManufacturingExperimental Characterization of Direct Metal Deposited Cobalt-Based Alloy on Tool Steel for Component RepairPEEK High Performance Fused Deposition Modeling Manufacturing with Laser In-Situ Heat TreatmentA Comparative Investigation of Sintering Methods for Polymer 3D Printing Using Selective Separation Shaping (SSS)Not Just Nylon... Improving the Range of Materials for High Speed SinteringMaterial Property Changes in Custom-Designed Digital Composite Structures Due to Voxel SizeQuantifying the Effect of Embedded Component Orientation on Flexural Properties in Additively Manufactured Structures

Non-Traditional MetalsInfluences of Printing Parameters on Semi-Crystalline Microstructure of Fused Filament Fabrication Polyvinylidene Fluoride (PVDF) ComponentsEffects of Build Parameters on the Mechanical and Di-Electrical Properties of AM Parts

Novel PolymersLaser Sintering of PA12/PA4,6 Polymer CompositesUnderstanding Hatch-Dependent Part Properties in SLSInvestigation into the Crystalline Structure and Sub-Tₚₘ Exotherm of Selective Laser Sintered Polyamide 6The Influence of Contour Scanning Parameters and Strategy on Selective Laser Sintering PA613 Build Part PropertiesProcessing of High Performance Fluoropolymers by Laser Sintering

Polymers for Material ExtrusionReinforcement Learning for Generating Toolpaths in Additive ManufacturingControl System Framework for Using G-Code-Based 3D Printing Paths on a Multi-Degree of Freedom Robotic ArmAnalysis of Build Direction in Deposition-Based Additive Manufacturing of Overhang Structures

Polymers for Powder Bed FusionTopology-Aware Routing of Electric Wires in FDM-Printed ObjectsUsing Autoencoded Voxel Patterns to Predict Part Mass, Required Support Material, and Build TimeContinuous Property Gradation for Multi-Material 3D-Printed ObjectsConvection Heat Transfer Coefficients for Laser Powder Bed FusionLocal Thermal Conductivity Mapping of Selective Laser Melted 316L Stainless Steel

ModelingFinite Element Modeling of the Selective Laser Melting Process for Ti-6Al-4VModelling the Melt Pool of the Laser Sintered Ti6Al4V Layers with Goldak’S Double-Ellipsoidal Heat SourceA Novel Microstructure Simulation Model for Direct Energy Deposition ProcessInfluence of Grain Size and Shape on Mechanical Properties of Metal Am MaterialsExperimental Calibration of Nanoparticle Sintering SimulationSolidification Simulation of Direct Energy Deposition Process by Multi-Phase Field Method Coupled with Thermal Analysis

Physical ModelingThermal Modeling Power BedsEstablishing Property-Performance Relationships through Efficient Thermal Simulation of the Laser-Powder Bed Fusion ProcessAn Investigation into Metallic Powder Thermal Conductivity in Laser Powder-Bed Fusion Additive ManufacturingSimulation of the Thermal Behavior and Analysis of Solidification Process during Selective Laser Melting of AluminaLow Cost Numerical Modeling of Material Jetting-Based Additive ManufacturingScrew Swirling Effects on Fiber Orientation Distribution in Large-Scale Polymer Composite Additive Manufacturing

Multi/Micro-Scale ModelingNumerical Prediction of the Porosity of Parts Fabricated with Fused Deposition ModelingNumerical Modeling of the Material Deposition and Contouring Precision in Fused Deposition ModelingEffect of Environmental Variables on Ti-64 Am Simulation Results

Advanced Thermal ModelingNon-Equilibrium Phase Field Model Using Thermodynamics Data Estimated by Machine Learning for Additive Manufacturing SolidificationMulti-Physics Modeling of Single Track Scanning in Selective Laser Melting: Powder Compaction EffectTowards an Open-Source, Preprocessing Framework for Simulating Material Deposition for a Directed Energy Deposition ProcessQuantifying Uncertainty in Laser Powder Bed Fusion Additive Manufacturing Models and Simulations

Modeling Part PerformanceOptimization of Inert Gas Flow inside Laser Powder-Bed Fusion Chamber with Computational Fluid DynamicsAn Improved Vat Photopolymerization Cure Model Demonstrates Photobleaching EffectsNonlinear and Linearized Gray Box Models of Direct-Write Printing DynamicsInsights into Powder Flow Characterization Methods for Directed Energy Distribution Additive Manufacturing SystemsEffect of Spray-Based Printing Parameters on Cementitious Material Distribution

Modeling InnovationsAligning Material Extrusion Direction with Mechanical Stress via 5-Axis Tool PathsFieldable Platform for Large-Scale Deposition of Concrete StructuresMicroextrusion Based 3D Printing–A Review

ImprovementsTheory and Methodology for High-Performance Material-Extrusion Additive Manufacturing under the Guidance of Force-FlowKnowledge-Based Material Production in the Additive Manufacturing Lifecycle of Fused Deposition ModelingAcoustic Emission Technique for Online Detection of Fusion Defects for Single Tracks during Metal Laser Powder Bed FusionDevelopment of an Acoustic Process Monitoring System for the Selective Laser Melting (SLM)

Process DevelopmentDepositionLow Cost, High Speed Stereovision for Spatter Tracking in Laser Powder Bed FusionMultiple Collaborative Printing Heads in FDM: The Issues in Process PlanningAdditive Manufacturing with Modular Support StructuresPick and Place Robotic Actuator for Big Area Additive Manufacturing

Extrusion3D Printed ElectronicsFiber Traction Printing--A Novel Additive Manufacturing Process of Continuous Fiber Reinforced Metal Matrix CompositeImmiscible-Interface Assisted Direct Metal Drawing

ImagingIn-Situ Optical Emission Spectroscopy during SLM of 304L Stainless SteelTool-Path Generation for Hybrid Additive ManufacturingStructural Health Monitoring of 3D Printed StructuresMechanical Properties of Additively Manufactured Polymer Samples Using a Piezo Controlled Injection Molding Unit and Fused Filament Fabrication Compared with a Conventional Injection Molding ProcessUse of SWIR Imaging to Monitor Layer-To-Layer Part Quality During SLM of 304L Stainless Steel

Novel MethodsDMP Monitoring as a Process Optimization Tool for Direct Metal Printing (DMP) of Ti-6Al-4VEffects of Identical Parts on a Common Build Plate on the Modal Analysis of SLM Created MetalOn the Influence of Thermal Lensing During Selective Laser MeltingDevelopment of Novel High Temperature Laser Powder Bed Fusion System for the Processing of Crack-Susceptible AlloysTowards High Build Rates: Combining Different Layer Thicknesses within One Part in Selective Laser MeltingLaser Heated Electron Beam Gun Optimization to Improve Additive ManufacturingTwo-Dimensional Characterization of Window Contamination in Selective Laser SinteringLaser Metal Additive Manufacturing on Graphite

Non-Metal Powder Bed FusionPredictive Iterative Learning Control with Data-Driven Model for Optimal Laser Power in Selective Laser SinteringRealtime Control-Oriented Modeling and Disturbance Parameterization for Smart and Reliable Powder Bed Fusion Additive ManufacturingMicrowave Assisted Selective Laser Melting of Technical CeramicsResearch on Relationship between Depth of Fusion and Process Parameters in Low-Temperature Laser Sintering ProcessFrequency Response Inspection of Additively Manufactured Parts for Defect IdentificationNanoparticle Bed Deposition by Slot Die Coating for Microscale Selective Laser Sintering Applications

Spinning/Pinning/StereolithographyFabrication of Aligned Nanofibers along Z-Axis – A Novel 3D Electrospinning TechniqueZ-Pinning Approach for Reducing Mechanical Anisotropy of 3D Printed PartsStructurally Intelligent 3D Layer Generation for Active-Z PrintingmicroCLIP Ceramic High-Resolution Fabrication and Dimensional Accuracy Requirements

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