Investigation into the crystalline structure and sub-Tpm

exotherm of selective laser sintered Polyamide 6

Peng Chen, Shifeng Wen, Chunze Yan *, Jie Liu*, Yusheng Shi

State key Laboratory of Materials Processing and Die & Mould Technology, School of

Materials Science and Engineering, Huazhong University of Science and Technology,

Wuhan 430074, China.

Abstract

Selective Laser Sintering (SLS) has achieved a wide acceptance for direct manufacture

of complex functional components. However, the performance of SLS part still needs

to be improved, in which the crystalline structure plays an important role. Every

crystalline form has specific properties, and the whole material behaviors have great

relationships with the various species and crystalline structure. Therefore, this paper

investigates crystalline structure of laser sintered Polyamide 6 (PA6) and quantifies the

different HT-α and LT-α phases using thermal analysis. The results show that the

sintered parts are uniformly characterized by a relatively stronger (2 0 0) and a weaker

(0 0 2) diffraction peak. This crystalline structure variation is basically consistent for

all SLS parts and independent of laser power. In addition, the sub-Tpm crystallization

transition concerning α phase was found for SLS PA6 part, which is derived from the

release of strain energy absorbed during SLS processing.

Key words: Additive Manufacturing (AM), Selective Laser Sintering (SLS),

Polyamide 6 (PA6), Crystalline Structure

*Corresponding author. Tel: +86(0)2787558155. E-mail address: c_yan@hust.edu.cn

(C. Yan), hustliuj@mail.hust.edu.cn (J. Liu).

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

Reviewed Paper

1.Introduction

Polyamides (PA) have much better thermo-mechanical properties than polyolefins

which make them more suitable for applications requiring creep and fatigue resistance

in the automotive industry. Using of high-performance PA6 (also known as

polycaprolactam and nylon 6) materials in place of conventional metal materials has

been growing in the manufacturing of structural parts, such as manufacturing of parts

in the engine compartments, bearings and gears [1-5]. Currently, there appears a

demand of integrated manufacturing that combines complex structures and good

mechanical properties, such as automobile cylinder head. In this case, the traditional

tooling method will be no longer fit and Additive Manufacturing (AM) will be a smarter

choice.

Selective Laser Sintering (SLS), one of the most promising polymeric AM

technologies, can fabricate complex 3D structures via selectively fusing successive

layers of powdered material. The principal advantage of SLS is the ability to

manufacture parts with great complexity of geometry accompanied with good tensile

strength and elastic modulus comparable to their injection moulded counterparts [6].

However, the laser sintered parts with good mechanical properties are mainly limited

to long-chain polyamides, such as PA12 and PA11 [6, 7]. The performance of SLS PA6

part still needs to be improved, in which the crystalline structure plays an important

role [8-10].

PA6 has two common crystalline forms: the α and γ forms [11]. It is generally

believed that the α form (monoclinic crystal) is more thermodynamically stable and has

a higher Young’s modulus compared to the γ form (hexagonal/pseudohexagonal crystal)

[12]. These two crystalline forms usually coexist in materials with different

compositions depending largely on processing conditions. As for SLS, the laser sintered

PA6 material exhibited a combination of two different α crystal forms (HT-α and LT-α

forms) [13]. Both crystal forms are matched to distinct regions within the material’s

observable microstructure. The presence of unmolten particle cores (LT-α) makes the

laser sintered material a composite-like structure and may have important influence on

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mechanical properties. Therefore, the aim of this paper is to investigate the crystalline

structure and composition of laser sintered PA6 and make the connection with

mechanical properties.

2.Experiment

2.1 Material and SLS process

The material used for investigation is virgin PA6 powder obtained from Solvay

S.A. Group. Laser sintering process of the powder was carried out on a self-developed

machine HK-P320 with a CO2 laser (wavelength 10.6 μm, laser beam diameter 0.4

mm) [14]. In order to investigate the influence of laser power on crystalline structure

and composition, different levels of laser power were selected, while other parameters,

i.e. laser scan spacing (s), layer thickness (h) and powder bed temperature (Tb) were set

as constant values. All the processing parameters are listed as shown in Table. 1.

Table. 1 SLS processing parameters for PA6 powder

Materials Bed temp.

(℃)

Laser power

(W)

Scan velocity

(mm/s)

Scan spacing

(mm)

Layer thickness

(mm)

PA6 195 20, 25, 30 4000 0.3 0.12

2.2 Characterization

Thermal analysis experiments of powder and laser sintered samples were

conducted on a Diamond DSC (PerkinElmer Instruments, USA) under nitrogen

protecting atmosphere and the heating rate was set as 10 °C/min. The determination of

special points such as onset and end point of melting, and the calculation of melting

enthalpy were performed using TA Universal Analysis 2000 software. The degree of

crystallinity 𝑋𝑋𝐶𝐶 can be calculated using the formula below:

𝑋𝑋𝐶𝐶 =∆𝐻𝐻𝑚𝑚∆𝐻𝐻𝑚𝑚0

× 100% (1)

where the ∆𝐻𝐻𝑚𝑚 is the melt enthalpy of sample and the ∆𝐻𝐻𝑚𝑚0 is the melt enthalpy of

the perfect crystal. The melt enthalpy for 100% crystalline PA6 material was taken as

230 J/g [11]. The polymorphism and crystalline characteristics were analyzed on a

X’Pert3 powder X-ray diffractometer (PANalytical B.V., Netherlands) with a PIXcel

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detector, using Cu Kα radiation at scan speed 3°/min. X’pert-HighScore Plus 3.0.5

software was utilized for experimental data handling and analysis. Tensile samples were

prepared according to the standard ASTM D638-03 Type Ⅴ. The tensile tests were

performed on E1000 (Instron-Division of ITW Limited) instrument at the tensile speed

of 1 mm/min. Four samples were used for the calculation of average data.

3.Results and discussion

3.1 Thermal Analysis and Quantification of HT-α and LT-α Phases

Figure. 1 Schematic diagram of HT-α and LT-α crystalline forms. DSC heating curve

of sample laser sintered at 20W, 4000 mm/s.

Figure. 2 Distinct microstructure of tensile failure section corresponding to different

crystal forms.

Just as Figure. 1 shows, the laser sintered PA6 sample usually has two different α

crystalline forms (HT-α and LT-α), which correspond to the high-temperature melting

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peak Tpm1 and the low-temperature melting peak Tpm2. The LT-α form is related to the

melted-recrystallized region, while the HT-α is the unmelted particle spherulites that is

essentially the laser-affected powder material [13]. What is unfamiliar is that the laser

sintered PA6 has a sub-Tpm1 crystallization exotherm concerning α phase. This sub-Tpm1

exothermic peak locates at DSC heating curve between HT-α and LT-α endotherms,

which is derived from the release of strain energy absorbed during SLS processing and

cannot be found in PA12 [13, 15, 16].

Both crystal forms are matched to distinct regions within the material’s observable

microstructure as shown in Figure. 2. This makes the laser sintered PA6 behave as a

micro-composite material. Therefore, the content of unmelted particle spherulites

(reinforcement phase) and their interface connected with melted-recrystallized region

become the main factors influencing mechanical properties. In order to figure out their

influence on mechanical properties, we quantificationally calculate the enthalpies of

HT-α, LT-α and sub-Tpm1 exotherm of samples sintered at different laser power using

DSC. The DSC curves of all samples are shown in Figure. 3 and the calculation results

are shown in Table. 2. It can be seen that with the increase of laser power, the relative

content of ∆𝐻𝐻𝑚𝑚𝐿𝐿𝐿𝐿 is increasing and the value of ∆𝐻𝐻𝑚𝑚𝐻𝐻𝐿𝐿 is becoming smaller. This

suggests that the relative quantity of unmelted particle spherulites is reducing, and thus

the interface with melted-recrystallized region becomes less. Their effect on mechanical

properties will be discussed in the section 3.3.

Figure. 3 DSC curves of sintered PA6 at different laser power.

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Table. 2 Quantitative data of thermal properties of HT-α and LT-α phases

Laser

power

Melting enthalpy (J/g) Crystallinity (%) Sub-Tpm1

exotherm

(J/g) ∆𝐻𝐻𝑚𝑚𝐿𝐿𝐿𝐿 ∆𝐻𝐻𝑚𝑚𝐻𝐻𝐿𝐿 𝑋𝑋𝑐𝑐𝐿𝐿𝐿𝐿 𝑋𝑋𝑐𝑐𝐻𝐻𝐿𝐿 𝑋𝑋𝑐𝑐𝛼𝛼

20W 29.88

(59.81%)

20.08

(40.19%) 12.99 8.73 21.72 5.75

25W 39.66

(80.97%)

9.39

(19.03%) 17.24 4.08 21.32 1.69

30W 37.05

(88.09%)

5.01

(11.91%) 16.11 2.18 18.29 1.72

* The relative content of HT-α (LT-α) in α is inside the parentheses.

3.2 Analysis of Crystalline Structure

Figure. 4 Crystalline structure of PA6 powder and laser sintered sample at 20W.

Figure. 4 illuminates the crystalline structure difference caused by SLS. It can be

seen that the XRD curve of powder is mainly featured by two α peaks corresponding to

the diffraction of (2 0 0) and (0 0 2) planes respectively. The (2 0 0) plane contains

chains only linked by van der Waals forces, whereas the (0 0 2) refers to the hydrogen-

bonded sheets [11]. Both two diffraction peaks have similar intensities. However, after

SLS processing, these two peaks are depressed more or less. From the XRD curve of

laser sintered part, it is easy to find out that the hydrogen-bonded (0 0 2) plane is more

influenced and weaker than (2 0 0). This suggests that the diffraction intensity of

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hydrogen-bonded planes (0 0 2) is more sensitive to laser than that of (2 0 0) revealing

the more pronounced influence of laser on the H-bonds as compared to van der Waals

interactions. In order to make it clear that if there are the same phenomena for all

sintered samples, the XRD data of samples sintered at different laser power were

collected (Figure. 5).

Figure. 5 Crystalline structure of laser sintered sample at 20W, 25W, 30W

respectively.

Unexpectedly, all the XRD curves exhibit similar peaks with a stronger (2 0 0) and

a weaker (0 0 2). This further proves that the diffraction intensity of hydrogen-bonded

planes (0 0 2) is more sensitive to laser than that of (2 0 0). In addition, what should be

noted is that diffraction angle of (0 0 2) is decreasing with the increase of laser power.

According to the Bragg equation, it can be concluded that the interplanar spacing of (0

0 2) is increasing. This may be attributed to the chain growth of melt-state

polycondensation which happens during the laser sintering process [14]. What’s more,

after SLS processing, the inconspicuous γ peak of the powder experiences the melt-

recrystallization process and can be hardly found in the laser sintered part. This means

that the crystallization of laser sintered melt is similar to that of normal melt-

crystallization and tends to form α phase.

3.3 Mechanical Properties and Connection with Phase Composition and

Crystallinity

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Figure. 6 Tensile strength (a) and elongation at break (b) of laser sintered sample at

20W, 25W, 30W respectively.

Figure. 6 shows the results of tensile tests, and the data are shown in Table. 3. It

can be seen that the 20W sintered part has the highest tensile strength (TS) and

elongation at break (EB). Interestingly, it is worth to note that the 20W sintered part

also has the maximum value of ∆𝐻𝐻𝑚𝑚𝐻𝐻𝐿𝐿 and Sub-Tpm1 crystallization enthalpy, suggesting

a high content of unmelted particle spherulites (reinforcement phase) and abundant

interface connected with melted-recrystallized region. What more, the crystallinity of

α phase (𝑋𝑋𝑐𝑐𝛼𝛼) of 20W sintered part is also the largest. This means that there may be

some connection between mechanical properties and phase composition. In order to

figure out the relationships between the phase composition, crystallinity of α phase and

mechanical properties, the Figure. 7 is plotted.

Table. 3 Data of PA6 tensile tests at different laser power.

Mechanical properties

PA6 sintered at different laser power

20W 25W 30W

TS (MPa) 45.84±0.88 44.45±0.19 33.88±0.78

EB (%) 81.02±8.11 44.16±2.55 36.54±4.67

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Figure. 7 The relationships between (a) relative content of HT-α and elongation at

break, (b) relative content of HT-α and tensile strength, (c) crystallinity of α phase and

elongation at break, (d) crystallinity of α phase and tensile strength.

It can be seen from Figure.7 that in general, the relative content of HT-α, the

crystallinity of α phase and the Sub-Tpm1 exotherm have the similar decreasing trend as

tensile strength and elongation at break in the 20~30W. This suggests that in this laser

power range, the higher content of HT-α, crystallinity of α phase and Sub-Tpm1

exotherm are more beneficial to the tensile strength and elongation at break.

Furthermore, it is easy to find that the Figure.7a, 7d, 7e have the basically identical

trends, which are different from those of Figure.7b, 7c, 7f. Therefore, we can further

1578

conclude that in comparison with the crystallinity, the elongation at break has stronger

correlation with content of HT-α (unmelted particle spherulites) and Sub-Tpm1 exotherm

(interface connected with melted-recrystallized region). On the contrary, the tensile

strength has a stronger correlation with crystallinity rather than the content of HT-α and

Sub-Tpm1 exotherm.

In section 3.2 (Figure.4), we can easily identify that the powder has a more perfect

crystalline structure and higher crystallinity of α than the sintered part due to its sharper

α peaks and greater integral area. The more perfect crystalline structure usually has a

better mechanical property. As is concluded above, the higher crystallinity of α phase

is more beneficial to the tensile strength, and the higher content of HT-αand Sub-Tpm1

exotherm is more beneficial to the elongation at break. Therefore, we can conclude that

sintered parts obtained by complete melting of powder do not definitely have the best

the tensile properties due to the lower crystallinity and less reinforcement phase. In fact,

an appropriate amount of unmelted powder would be more beneficial to mechanical

properties.

4.Conclusion

Mechanical properties have great relationships with the crystalline structure and

composition. In this paper, we investigate the crystalline structure of laser sintered PA6

using XRD, and quantitatively analyze the phase composition through DSC. The

relationships between mechanical properties and phase composition and crystallinity

are also discussed. The main conclusions are:

The XRD curves of laser sintered parts exhibit similar peaks with a stronger (2 0

0) and a weaker (0 0 2) because the diffraction intensity of hydrogen-bonded (0 0

2) plane is more sensitive to laser than that of (2 0 0).

In comparison with the crystallinity, the elongation at break has stronger

correlation with content of HT-α and Sub-Tpm1 exotherm. On the contrary, the

tensile strength has a stronger correlation with crystallinity rather than the content

of HT-α and Sub-Tpm1 exotherm.

The sintered PA6 parts obtained by complete melting of powder do not

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definitely have the best the tensile properties due to the lower crystallinity and

less reinforcement phase. An appropriate amount of unmelted powder would

be more beneficial to mechanical properties.

Reference [1] C.M. Sonsino, E. Moosbrugger, Fatigue design of highly loaded short-glass-fibre reinforced

polyamide parts in engine compartments, International Journal of Fatigue 30(7) (2008) 1279-1288. [2] A. Benaarbia, A. Chrysochoos, G. Robert, Thermomechanical behavior of PA6.6 composites

subjected to low cycle fatigue, Composites Part B-engineering 76 (2015) 52-64. [3] L. Chang, Z. Zhang, H. Zhang, A.K. Schlarb, On the sliding wear of nanoparticle filled

polyamide 66 composites, Composites Science and Technology 66(16) (2006) 3188-3198. [4] A. Bernasconi, P. Davoli, A. Basile, A. Filippi, Effect of fibre orientation on the fatigue

behaviour of a short glass fibre reinforced polyamide-6, International Journal of Fatigue 29(2) (2007) 199-208.

[5] S. Mortazavian, A. Fatemi, Fatigue behavior and modeling of short fiber reinforced polymer composites: A literature review, International Journal of Fatigue 70(Supplement C) (2015) 297-321.

[6] R.D. Goodridge, C.J. Tuck, R.J.M. Hague, Laser sintering of polyamides and other polymers, Progress in Materials Science 57(2) (2012) 229-267.

[7] S. Berretta, K.E. Evans, O. Ghita, Processability of PEEK, a new polymer for High Temperature Laser Sintering (HT-LS), European Polymer Journal 68(Supplement C) (2015) 243-266.

[8] S. Das, S.J. Hollister, C.L. Flanagan, A. Adewunmi, K. Bark, C. Chen, K. Ramaswamy, D. Rose, E. Widjaja, Freeform fabrication of Nylon‐6 tissue engineering scaffolds, Rapid Prototyping Journal 9(1) (2003) 43-49.

[9] G.V. Salmoria, J.L. Leite, L.F. Vieira, A.T.N. Pires, C.R.M. Roesler, Mechanical properties of PA6/PA12 blend specimens prepared by selective laser sintering, Polymer Testing 31(3) (2012) 411-416.

[10] S. Rhee, J.L. White, Crystal structure, morphology, orientation, and mechanical properties of biaxially oriented polyamide 6 films, Polymer 43(22) (2002) 5903-5914.

[11] J. Pepin, V. Miri, J.-M. Lefebvre, New Insights into the Brill Transition in Polyamide 11 and Polyamide 6, Macromolecules 49(2) (2016) 564-573.

[12] L.S. Loo, K.K. Gleason, Insights into Structure and Mechanical Behavior of α and γ Crystal Forms of Nylon-6 at Low Strain by Infrared Studies, Macromolecules 36(16) (2003) 6114-6126.

[13] P. Chen, H. Wu, W. Zhu, L. Yang, Z. Li, C. Yan, S. Wen, Y. Shi, Investigation into the processability, recyclability and crystalline structure of selective laser sintered Polyamide 6 in comparison with Polyamide 12, Polymer Testing.

[14] P. Chen, M. Tang, W. Zhu, L. Yang, S. Wen, C. Yan, Z. Ji, H. Nan, Y. Shi, Systematical mechanism of Polyamide-12 aging and its micro-structural evolution during laser sintering, Polymer Testing 67 (2018) 370-379.

[15] S. Dadbakhsh, L. Verbelen, O. Verkinderen, D. Strobbe, P. Van Puyvelde, J.-P. Kruth, Effect of PA12 powder reuse on coalescence behaviour and microstructure of SLS parts, European Polymer Journal (2017).

[16] N. Hopkinson, C.E. Majewski, H. Zarringhalam, Quantifying the degree of particle melt in

1580

Selective Laser Sintering®, CIRP Annals - Manufacturing Technology 58(1) (2009) 197-200.

1581

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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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