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Selective Separation Shaping (SSS) – Large-Scale Fabrication Potentials

Behrokh Khoshnevis, Xiang Gao, Brittany Barbara, Hadis Nouri

Epstein Department of Industrial & Systems Engineering, University of Southern California, Los

Angeles, CA 90089

Abstract

Selective Separating Shaping is a new additive manufacturing technique which is

capable of processing polymeric, metallic, ceramic and composites including cementitious

materials. In earlier experiments the capabilities of SSS in making metallic and ceramic

parts have been demonstrated. The focus of the research reported in this paper has been on

exploration of capabilities of SSS for creation of large-scale cementitious composite parts.

A prototype machine has been used to create specimens made of regular construction

cement (lime based), Sorel cement (magnesia based) and gypsum based composites. The

fabrication results, surface quality and flexural strength for these experiments are

presented.

Keyword: Selective Separation Shaping, Additive Manufacturing, cementitious,

composite

1. Introduction

Several AM technologies have emerged and extensive research has been carried

out to extend the capabilities of the processes, improve and develop new AM materials and

explore new application areas [1,2]. Current AM processes are predominantly suitable for

fabrication of meso-scale objects, primarily due to the fact that the available processes use

sub-millimeter layer heights which would render the fabrication of large parts impractical

[3-5]. Contour Crafting is the first large-scale AM process which was invented at

University of Southern California (USC) over two decades ago and its applications in

constructions of terrestrial as well as planetary structures have been pursued and

demonstrated [6-8]. Contour Crafting is an extrusion based AM process which started the

worldwide excitement and activities in 3D printing of buildings.

A significant class of AM processes are based on powder materials and so far all of

these processes have been limited to the processing of sub-millimeter powder layers [9].

Selective Separation Shaping (SSS) is a new versatile powder based AM process with

demonstrated capability for building meso-scale metallic and ceramic parts [10], and now

its capability to break the scale barrier in powder based processes is being demonstrated.

Based on our experiments, SSS is the first and only powder based AM process that

is capable of building with layers that may be multi-centimeter thick while producing very

smooth part surfaces at an unprecedented fabrication speed. Our focus in this study has

been on the fabrication of cementitious composite parts and results of experiments with

Portland cement, Sorel cement and gypsum are presented.

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

Reviewed Paper

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2. The SSS Process

In the meso-scale sintering-based SSS process, which has been recently reported in

the literature, a thin wall of high melting point separator powder material (S-powder) is

deposited within the base material powder (B-powder) to form a barrier on the boundary

of each layer. This barrier creates a separation between the part and surrounding material,

which allows for the separation of the part from the surrounding powder after sintering is

complete. Finally, the part is removed from the platform and inserted into sintering furnace.

After sintering the part is easily separated from the surrounding as the S-powder remains

in powder state because of its relatively higher sintering temperature.

In the extended SSS process for large-scale part fabrication the thickness of each

progressive powder layer is significantly higher than is in the case of meso-scale

fabrication. Thick layers are achieved by an S-powder insertion nozzle that is thin tube

with a longitudinal slot with height equal to the desired layer thickness. In the preliminary

experiments a 1.30mm diameter metallic nozzle tube with a 12 mm slut is used as shown

in Figure 1.

Figure 1. Deposition of thin wall of S-powder within a 12 mm thick layer

Unlike common additive manufacturing processes, a different slicing method is

required for SSS because the process only considers part surfaces and disregards the part

core. In SSS nozzle rotation is also programmed into the toolpath which traces the contours

of slices.

In the first process step a uniform layer of base powder is delivered onto the build

tank. The nozzle is then inserted into the base powder and the S-powder is deposited along

the layer contour. The nozzle is then raised and another layer of base powder is paved over

the previous layer. The process continues until all layers are processed. At this stage

sufficient amount of the bonding liquid (which could be water for hydraulically activated

cementitious base powders) is delivered to the top of the top layer. The liquid gradually

moves down by gravity and capillary action through the entire depth of the treated section

of the build tank and the part consolidation starts through chemical activation of bonding.

Depending on the base material choice, the initial weak consolidation may take within one

hour after which the part is strong enough to be removed from the build tank. Water (or a

binder liquid) is then added periodically to the part to achieve good part strength through a

more complete cement hydration process. Finally, the part is very easily separated from the

surrounding material as shown in Figure 2. A brush is used to clean the extra separator

material away from the obtained part.

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Figure 8. CAD model, top layer after separator powder deposition and separated part

3. Results

Experimental parts are built with Portland

cement, gypsum and Sorel cement using the beta

machine shown in Figure 3. Some of the fabrication

results are shown and discussed below.

3.1 Portland Cement

The first material tested is Portland cement

because of its wide application in Huge Construction

Industry. The solidification process of hydraulic

cement is complex as it involves many physical and

chemical processes. Extensive effort has been

devoted to finding the proper parameters for our

cement curing process as in SSS curing starts right

after water is added without any mixing.

Figure 3. Selective Separation

Shaping prototype

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Figure 4. Single-layer (above) and double-layer (below) Portland cement parts made by SSS

The part shown in Figure 4 has been built in 20 minutes. The thickness of the petal

shape is 22 mm. The single layer outer surface is fairly good.

3.2 Gypsum

The result of building parts with gypsum (Plaster of Paris in this case) is shown

Figure 5.

Figure 11. Gypsum parts made by SSS

The gypsum petal shape is 10 mm high and is made within 13 minutes. After 2

hours allowed for solidification the part is easily separated from its surrounding. The

surface of some gypsum parts experience some cracks, if rapid evaporation of water

content takes place.

3.3 Sorel Cement

Sorel cement, also called magnesia cement, is a widely applied cement type as it

possesses properties like faster solidification and hardening speed and larger early strength.

Fabrication of Sorel cement parts with SSS have been attempted and the result is shown in

Figure 6.

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Figure 6. Sorel cement parts made by SSS

Sorel cement utilized here has a combination of different size aggregates. The

existence of large size particles affect the formation of separation wall, and hence

negatively impact the part surface quality. Also Sorel cement is more sensitive to the

proportion of water in its volume, and has a water absorption rate that is significantly less

than that of Portland. Water should be added to Sorel cement powder with a well-controlled

flow rate, otherwise gas bubbles may be generated which badly deform the part surface

structure resulting in porous surfaces of the final part.

4. Surface Quality

The surface quality of Portland cement parts built by SSS has been studied in more

detail. SSS part surface quality may be better than what can be achieved with other cement

based 3D printing processes. In SSS part surfaces are of two kinds: surfaces which are

created by the insertion of the separation powder and creation of the part boundary, and

bottom and op surfaces which are not created by separation powder insertion.

4.1 Surface’s quality interacted with separation powder

4.1.1 Impact of separation powder choice

Proper choice of S-powder can impact part surface quality considerably. A smooth

and compact separation wall made of the right choice of S-powder can create smooth part

surfaces. For the experiments conducted in this study soda lime is selected as separation

powder because of the following favorable properties:

Firstly, with low water penetration rate, this material entraps most of the water in

the base powder preventing it from easily escaping across part boundary.

Secondly, with 40 to 60 micron particle size and high stiffness, soda lime can easily

generate strong capillary bridge between particles when exposed to liquid, which leads to

a stronger separation wall structure post water addition. Moreover, fine separation powder

size prevents the diffusion of cement slurry through the part boundary. Such diffusion can

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badly affect part surface quality as base powder segments outside the layer boundary may

also be fused to the part.

Thirdly a separation wall made with soda lime retains most of the delivered water

(or any fluid used as bonding agent) within the volume of the part thereby preventing rapid

evaporation which causes cracking and allowing for a more complete curing process which

results in stronger parts.

A cement part surface without any post-processing is shown in Figure 7. It can be

seen that the part surface is very smooth and, as measurements have shown, geometric

dimensions of the part shown have been within a few microns of target dimensions.

Figure 7. A 24mm tall Portland cement part built with SSS

4.1.2 Separation powder deposition

Even though soda lime have these good properties, insufficient separation powder

deposition will limit its function. If powder deposition is not sufficient, a stiff separation

wall cannot be generated or can only be generated with low quality, then soda lime’s

characteristics to keep products’ shape and dimensions cannot take effect. In figure 8, two

pictures are shown for comparison between surface with and without sufficient separation

powder deposition.

Figure 8. Cross section of layer without and with sufficient soda lime as s powder( without on the

left and with soda lime on the right)

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From the picture above, we can easily see that surfaces’ quality with sufficient

separation powder are much better than surfaces with insufficient separation powder.

To ensure sufficient deposition, it is critical to keep deposition powder flow stable

and prevent separation powder clogging inside powder container, which is a common

challenge in hopper powder flow situation [12].

Figure 9. Arch generation inside powder container [9]

It is known that, under function of gravity, arch will be generated during powder’s

deposition in a hopper shape, which will block powder from further depositing. There are

two methods to break the arch: Add air flow through bottom of hopper to blow up the arch;

Add vibration to break the arch. In SSS, a combination solution is introduced as an

economical and efficient solution to ensure a stable and sufficient powder flow.

Considering that hopper applied in SSS is in small size, vibration generating

method is applied in the first stage. After experiments, vibration piezo with amplitude 5

microns and 3000 frequency is applied. Under this vibrating condition, arch generation can

be avoided during manufacturing.

In second stage, proper air flow is chosen and applied on upper surface, other than

from bottom, of separation powder in container. Experiments’ result shows that this

method is capable to increase low deposition rate caused by powder particle’s viscosity.

To obtain stable and adequate separation powder deposition, a miniature pump with proper

air pressure is installed on separation powder container to provide air flow onto separation

powder.

4.2 Quality of bottom and top surfaces

In the current SSS process, bottom and top surface are not covered with deposition

powder but interact with the bottom machine platform plate, or with water sprayed from

above the top surface, which make surface quality control rather harder.

Since water spray is impossible to be sprayed on manufacturing area exactly even

and with negligible impact, it will cause uneven water distribution on powder’s surface and

then surface displacement.

To make water distribution even and reduce the impact of spray pressure on surface

deformation, coarse sand with size ranging from 200 microns to 400 microns is used to

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cover bottom and upper surfaces. On upper surface, water drop will reach to coarse sand

before penetrate into cement. Water can spread easily inside coarse sand, which help even

water distribution in manufacturing area. In addition, sand will reduce direct impact of

water spray to powder base’s surface. Same sand are paved under bottom layer to prevent

extra water accumulate in lower layers.

A spray system, shown in Figure 10, is also developed to generate water mist for

water spraying, which is believed to be helpful to reduce water’s impact. With the spray

system, small water drop will be generated and spread onto powder bed, which will ensure

a relatively water distribution and small impact onto base powder. All those methods are

beneficial to products’ surface quality. The excellent product’s quality is shown in Figure

7.

Figure 10. A spray system with four nozzles to spread water

5. Strength Analysis

In this section several parameters influencing cement products’ final strength are

discussed, and a proper process to reach high strength economically and sufficiently is

introduced. Portland cement is the choice of material to be studied for achieving good

strength, because cement is the most common and economical material in industry to build

mega-scale and large products. Flexural test is used to determine relative strength of the

specimens. This test is preferred to compressive and tensile strength test because of its

simplicity.

Water/cement ratio, the ratio between water and cement’s weight, is the most

important parameter for cement’s final strength. Water/cement ratio impacts cement’s

saturation level, porosity level and microstructure [13], which collectively determine

product’s mechanical behavior. For conventional concrete water cement ratio is usually

0.35 to 0.5. In SSS process, a specific water cement ratio is expected, because no stirring

process is included in the SSS process, which may lead to insufficient water cement mixing

and cement curing. Additives, like Silica fume and superplasticizer, are also considered as

potentially helpful components to be added to concrete strength [14].

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Maintenance during curing process is another element to affect good cement

products’ strength. Hydration temperature and moisture are the two most important factors

in maintenance situation during curing process. An environment with proper temperature

and moisture will keep cement’s hydration speed within controlled level and hence reduces

crack generation [15].

To analyze different parameters’ effects, 7 sets of experiments have been conducted

and samples’ flexural strength are measured after 14 days’ curing according to standard

ASTM C348 - 14. The strength measurement device used is shown in Figure 11. During

the measurement process, 20 by 20 by 80 mm samples are firstly fabricated by SSS

machine, and force will be applied on the center of parts by a NK-500 analog force gauge

after parts are fixed on a testing bed, which is shown in Figure 11.

Table 1 shows the parameter values for 7 different settings, where every experiment

with the same setting is repeated three times and flexural strength is calculated as average

of the results. Set 1 to 3 experiments are conducted to test samples with different water

cement ratios. The material used in set 4 is a mixture of cement and sand in order to

understand the effect of sand on the specimen’s strength. In set 5, silica fume is added to

cement where silica fume’s weight is 5% of the whole mass. In set 6, a plasticizer admixture

is mixed with water in percentage of 14%, and water is added into cement with water ratio

of 0.4 by mass. Set 7 is a sample built with mold, where cement is stirred with water and

paste is injected into a mold. In set 1 to 7, samples are submerged in pure water under 25

℃ after primary curing, which is usually within 24 hours. In set 8, samples are not

submerged into water to serve as a basis for comparison.

Figure 11. Left: flexural strength measure device, right: a broken part after measure

Table 1. Parameter settings for strength measure

Sample

Number

W/C

Ratio

Cement

Agent

Percent

cement Stirring

Days

Submer

ged

Additive

Force

Applied

(N)

Flexural

Strength

(MPa)

1 0.35 Portland 100 No 14 N/A 191.25 7.32

2 0.4 Portland 100 No 14 N/A 217.5 8.32

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3 0.45 Portland 100 No 14 N/A 125 4.78

4 0.4 Portland 60 No 14 N/A 42.5 8.09

5 0.4 Portland 100 No 14

Silica

Fume 228.48 8.74

6 0.4 Portland 100 No 14 Plasticizer 195.54 7.48

7 0.4 Portland 100 Yes 14 N/A 250.13 9.57

8 0.4 Portland 100 No 1 N/A 114.76 4.39

Table 2. Mean Flexural Strength Index

According to Table 1 and Table 2, 0.4 is the best water/cement ratio for the SSS

process, and addition of silica fume and super plasticizer do not significantly increase

sample’s final strength. As shown in the data for set 4, the mixture with sand is a good

choice if cost reduction has a high priority, because mixtures with sand do not reduce the

specimen’s strength. Though compared with set 4, set 7 has higher flexural strength, SSS

is still considered a proper manufacturing process for cement, because samples built with

SSS are 15% weaker than typical industrial concrete building methods. Filling this gap is

a potential for further research. As shown in set 8, samples without maintenance process

during curing are much weaker than samples curing under maintenance environment,

which leads to the conclusion that our submersion maintenance process is critical to

samples’ strength.

6. Conclusion

A new additive manufacturing technique for large-scale construction is introduced,

and its process is explained in detail. A prototype machine is developed to demonstrate the

7.328.32

4.78

8.098.74

7.48

9.57

4.39

0

2

4

6

8

10

12

1 2 3 4 5 6 7 8

Flexural Strength (MPa)

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feasibility and potential of the technology. Surface quality and flexural strength of Portland

cement based specimens produced by the prototype machine are also evaluated. Results of

the experiments demonstrate that the Selective Separation Shaping technology has great

potential in large-scale fabrication of parts out of a variety of cementitious materials.

Further investigation needs to be carried out on properties of the base materials and the

choice of curing agent in order to further improve part strength and obtain the desired

surface quality. Application of SSS can further expand to rapid fabrication of urban

structures, hardscaping, public art, building facades and pavement engineering using inter-

locking tiles built in-place. SSS is also a very appealing construction technology for

building structures on other planets using in-situ material. The technology has won the

Grand Prize in the 2016 NASA international competition on In-situ Challenge [16]. SSS is

considered to be a high-potential candidate process for construction of planetary landing

pads and roads among other infrastructure elements.

Acknowledgement

SSS has been conceived and developed in the course of a Phase-II NASA

Innovative Advanced Concepts (NIAC) project in relation to the part of the project that

concerned landing pad construction.

Reference:

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scaffolds for engineering replacement tissues and organs." Biomaterials 24.13 (2003): 2363-2378.

[2] Chia, N., and Benjamin M. Wu. "Recent advances in 3D printing of biomaterials." Journal of

biological engineering 9.1 (2015): 1.

[3] http://www.stratasys.com/3d-printers/production-series/fortus-900mc

[4] http://www.exone.com/Systems/Production-Printers/S-Max

[5] http://www.voxeljet.de/en/systems/vx4000/

[6] Khoshnevis, B. “Automated construction by contour crafting - Related robotics and

information technologies.” Autom. Constr., vol. 13, pp. 5–19, 2004.

[7] Khoshnevis, B. and M. Thangavelu, X. Yuan, and J. Zhang, “Advances in Contour Crafting

Technology for Extraterrestrial Settlement Infrastructure Buildup.” in AIAA SPACE 2013

[8] Khoshnevis, B, X. Yuan, B. Zahiri, and B. Xia, “Construction by Contour Crafting using

Sulfur Concrete with Planetary Applications.” Conference and Exposition, 2013.

[9] Nouri, H., and B. Khoshnevis. "Study On Inhibition Mechanism of Polymer Parts in Selective

Inhibition Sintering Process.” Solid Free Form Fabrication Symposium, Austin, Texas 2015

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[10] Zhang, J. and B. Khoshnevis, B. “Selective Separation Sintering (SSS) – A new Additive

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[11] John S. Nadeau and Jacqueline M. Hay “Effects of Different Curing Conditions on Slow

Crack Growth in Cement Paste.” Cement and Concrete Research. Vol. 4, pp. 953- 965, 1974

[12] Rumpf, H., 1975. Particle Technology. Chapman and Hall, London

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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 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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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