A Study on the In-Situ Melt Pool Size Estimation Method for Directed-Energy Additive Manufacturing Based on Modal Parameters

Abstract This article highlights work at Oak Ridge National Laboratory’s Manufacturing Demonstration Facility to develop closed-loop, feedback control for laser-wire based Directed Energy Deposition, a form of metal Big Area Additive Manufacturing (m-BAAM), a process being developed in partnership with GKN Aerospace specifically for the production of Ti-6Al-4V pre-forms for aerospace components. A large-scale structural demonstrator component is presented as a case-study in which not just control, but the entire 3D printing workflow for m-BAAM is discussed in detail, including design principles for large-format metal AM, toolpath generation, parameter development, process control, and system operation, as well as post-print net-shape geometric analysis and finish machining. In terms of control, a multi-sensor approach has been utilized to measure both layer height and melt pool size, and multiple modes of closed-loop control have been developed to manipulate process parameters (laser power, print speed, deposition rate) to control these variables. Layer height control and melt pool size control have yielded excellent local (intralayer) and global (component-level) geometry control, and the impact of melt pool size control in particular on thermal gradients and material properties is the subject of continuing research. Further, these modes of control have allowed the process to advance to higher deposition rates (exceeding 7.5 lb/hr), larger parts (1-meter scale), shorter build times, and higher overall efficiency. The control modes are examined individually, highlighting their development, demonstration, and lessons learned, and it is shown how they operate concurrently to enable the printing of a large-scale, near net shape Ti-6Al-4V component.

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On Process Temperature in Powder-Bed Electron Beam Additive Manufacturing: Model Development and Validation

Journal of Manufacturing Science and Engineering ◽

10.1115/1.4028484 ◽

2014 ◽

Vol 136 (6) ◽

Cited By ~ 71

Author(s):

Bo Cheng ◽

Steven Price ◽

James Lydon ◽

Kenneth Cooper ◽

Kevin Chou

Keyword(s):

Thermal Conductivity ◽

Electron Beam ◽

Additive Manufacturing ◽

Thermal Characteristics ◽

Pool Size ◽

Process Temperature ◽

Thermal Imager ◽

Powder Bed ◽

Melt Pool ◽

Melt Pool Size

Powder-bed beam-based metal additive manufacturing (AM) such as electron beam additive manufacturing (EBAM) has a potential to offer innovative solutions to many challenges and difficulties faced in the manufacturing industry. However, the complex process physics of EBAM has not been fully understood, nor has process metrology such as temperatures been thoroughly studied, hindering part quality consistency, efficient process development and process optimizations, etc., for effective EBAM usage. In this study, numerical and experimental approaches were combined to research the process temperatures and other thermal characteristics in EBAM using Ti–6Al–4V powder. The objective of this study was to develop a comprehensive thermal model, using a finite element (FE) method, to predict temperature distributions and history in the EBAM process. On the other hand, a near infrared (NIR) thermal imager, with a spectral range of 0.78 μm–1.08 μm, was employed to acquire build surface temperatures in EBAM, with subsequent data processing for temperature profile and melt pool size analysis. The major results are summarized as follows. The thermal conductivity of Ti–6Al–4V powder is porosity dependent and is one of critical factors for temperature predictions. The measured thermal conductivity of preheated powder (of 50% porosity) is 2.44 W/m K versus 10.17 W/m K for solid Ti–6Al–4V at 750 °C. For temperature measurements in EBAM by NIR thermography, a method was developed to compensate temperature profiles due to transmission loss and unknown emissivity of liquid Ti–6Al–4V. At a beam speed of about 680 mm/s, a beam current of about 7.0 mA and a diameter of 0.55 mm, the peak process temperature is on the order around 2700 °C, and the melt pools have dimensions of about 2.94 mm, 1.09 mm, and 0.12 mm, in length, width, and depth, respectively. In general, the simulations are in reasonable agreement with the experimental results with an average error of 32% for the melt pool sizes. From the simulations, the powder porosity is found critical to the thermal characteristics in EBAM. Increasing the powder porosity will elevate the peak process temperature and increase the melt pool size.

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Ultrasonic Frequency Effects on the Melt Pool Formation, Porosity, and Thermal-Dependent Property of Inconel 718 Fabricated by Ultrasonic Vibration-Assisted Directed Energy Deposition

Journal of Manufacturing Science and Engineering ◽

10.1115/1.4048515 ◽

2020 ◽

Vol 143 (5) ◽

Author(s):

Fuda Ning ◽

Dayue Jiang ◽

Zhichao Liu ◽

Hui Wang ◽

Weilong Cong

Keyword(s):

Ultrasonic Vibration ◽

Inconel 718 ◽

Energy Deposition ◽

Pool Size ◽

Peak Temperature ◽

Ultrasonic Frequency ◽

Melt Pool ◽

Directed Energy ◽

Pool Formation ◽

Melt Pool Size

Abstract Ultrasonic vibration-assisted (UV-A) directed energy deposition (DED) has become a promising technology to improve the as-built quality and mechanical performance of metal parts. Ultrasonic frequency, a critical parameter of the ultrasonic vibration, can remarkably affect the ultrasonic vibration behaviors in assisting DED processes. However, leveraging varied ultrasonic frequencies in UV-A DED attracts little attention, and the effects of ultrasonic frequency have been thus overlooked. Linking ultrasonic frequency and part performance emphasizes the need for an understanding of the underlying thermodynamics in the melt pool due to the key role of thermal history in the DED process. In this work, we fabricated Inconel 718 (IN718) parts using the UV-A DED process under different levels of ultrasonic vibration frequency (including 0, 25 kHz, 33 kHz, and 41 kHz). For the first time, melt pool size, temperature distribution, and peak temperature within the melt pool, as well as the peak temperature fluctuation within a layer deposition, were studied. Porosity and thermal-dependent properties including grain size and microhardness were also investigated. The results indicated that the increase in ultrasonic frequency led to an increase in both melt pool size and peak temperature. Moreover, the lowest porosity was obtained at an ultrasonic frequency of 25 kHz, while grain refinement and microhardness enhancement were achieved at the highest frequency of 41 kHz. This investigation provides great insights into the link among ultrasonic frequency, melt pool formation, temperature field, porosity, and thermal-dependent properties in the UV-A DED-built IN718 parts.

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From mine to part: directed energy deposition of iron ore

Rapid Prototyping Journal ◽

10.1108/rpj-10-2020-0243 ◽

2021 ◽

Vol 27 (11) ◽

pp. 37-42

Author(s):

Himani Naesstroem ◽

Frank Brueckner ◽

Alexander F.H. Kaplan

Keyword(s):

Additive Manufacturing ◽

Laser Beam ◽

High Speed ◽

Iron Ore ◽

Energy Deposition ◽

Content Type ◽

Melt Pool ◽

Directed Energy Deposition ◽

Directed Energy ◽

Melt Pool Size

Purpose This paper aims to gain an understanding of the behaviour of iron ore when melted by a laser beam in a continuous manner. This fundamental knowledge is essential to further develop additive manufacturing routes such as production of low cost parts and in-situ reduction of the ore during processing. Design/methodology/approach Blown powder directed energy deposition was used as the processing method. The process was observed through high-speed imaging, and computed tomography was used to analyse the specimens. Findings The experimental trials give preliminary results showing potential for the processability of iron ore for additive manufacturing. A large and stable melt pool is formed in spite of the inhomogeneous material used. Single and multilayer tracks could be deposited. Although smooth and even on the surface, the single layer tracks displayed porosity. In case of multilayered tracks, delamination from the substrate material and deformation can be seen. High-speed videos of the process reveal various process phenomena such as melting of ore powder during feeding, cloud formation, melt pool size, melt flow and spatter formation. Originality/value Very little literature is available that studies the possible use of ore in additive manufacturing. Although the process studied here is not industrially useable as is, it is a step towards processing cheap unprocessed material with a laser beam.

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In situ X-ray quantification of melt pool behaviour during directed energy deposition additive manufacturing of stainless steel

Materials Letters ◽

10.1016/j.matlet.2020.129205 ◽

2021 ◽

Vol 286 ◽

pp. 129205

Author(s):

Yunhui Chen ◽

Samuel J. Clark ◽

Yuze Huang ◽

Lorna Sinclair ◽

Chu Lun Alex Leung ◽

...

Keyword(s):

Stainless Steel ◽

Additive Manufacturing ◽

Energy Deposition ◽

X Ray ◽

Melt Pool ◽

Directed Energy Deposition ◽

Directed Energy

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Beyond the Toolpath: Site-Specific Melt Pool Size Control Enables Printing of Extra-Toolpath Geometry in Laser-Wire Directed Energy Deposition

10.20944/preprints201909.0305.v1 ◽

2019 ◽

Author(s):

Brian T. Gibson ◽

Brad S. Richardson ◽

Taylor W. Sundermann ◽

Lonnie J. Love

Keyword(s):

Energy Deposition ◽

Closed Loop ◽

Size Control ◽

Pool Size ◽

Bead Geometry ◽

Site Specific ◽

Melt Pool ◽

Directed Energy Deposition ◽

Directed Energy ◽

Melt Pool Size

A variety of techniques have been utilized in metal additive manufacturing (AM) for melt pool size management, including modeling and feed-forward approaches. In a few cases, closed-loop control has been demonstrated. In this research, closed-loop melt pool size control for large-scale, laser-wire based Directed Energy Deposition is demonstrated with a novel modification: site-specific changes to the controller set-point were commanded at trigger points, the locations of which were generated by the projection of a secondary geometry onto the primary 3D-printed component geometry. The present work shows that, through this technique, it is possible to print a specific geometry that occurs beyond the actual toolpath of the print head. This is denoted as an extra-toolpath geometry and is fundamentally different from other methods of generating component features in metal AM. A proof-of-principle experiment is presented in which a complex oak leaf geometry was embossed on an otherwise ordinary double-bead wall made from Ti-6Al-4V. The process is introduced and characterized primarily from a controls perspective with reports on the performance of the control system, the melt pool size response, and the resulting geometry. The implications of this capability, which extend beyond localized control of bead geometry to the potential mitigations of defects and functional grading of component properties, are discussed.

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Measuring the melt pool size in a wire arc additive manufacturing process using a high dynamic range two-colored pyrometric camera

Welding in the World ◽

10.1007/s40194-020-00892-5 ◽

2020 ◽

Vol 64 (8) ◽

pp. 1349-1356

Author(s):

C. Halisch ◽

T. Radel ◽

D. Tyralla ◽

T. Seefeld

Keyword(s):

Additive Manufacturing ◽

Manufacturing Process ◽

Dynamic Range ◽

High Dynamic Range ◽

Pool Size ◽

Melt Pool ◽

High Dynamic ◽

Melt Pool Size ◽

Wire Arc Additive Manufacturing

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3D Build Melt Pool Predictive Modeling for Powder Bed Fusion Additive Manufacturing

Volume 9: 40th Computers and Information in Engineering Conference (CIE) ◽

10.1115/detc2020-22662 ◽

2020 ◽

Author(s):

Zhuo Yang ◽

Yan Lu ◽

Ho Yeung ◽

Sundar Kirshnamurty

Keyword(s):

Neural Network ◽

Additive Manufacturing ◽

Pool Size ◽

Powder Bed Fusion ◽

Neural Network Approach ◽

Validation Data ◽

Powder Bed ◽

Melt Pool ◽

Scan Pattern ◽

Melt Pool Size

Abstract Melt pool size is a critical intermediate measure that reflects the outcome of a laser powder bed fusion process setting. Reliable melt pool predictions prior to builds can help users to evaluate potential part defects such as lack of fusion and over melting. This paper develops a layer-wise Neighboring-Effect Modeling (L-NBEM) method to predict melt pool size for 3D builds. The proposed method employs a feedforward neural network model with ten layer-wise and track-wise input variables. An experimental build using a spiral concentrating scan pattern with varying laser power was conducted on the Additive Manufacturing Metrology Testbed at the National Institute of Standards and Technology. Training and validation data were collected from 21 completed layers of the build, with 6,192,495 digital commands and 118,928 in-situ melt pool coaxial images. The L-NBEM model using the neural network approach demonstrates a better performance of average predictive error (12.12%) by leave-one-out cross-validation method, which is lower than the benchmark NBEM model (15.23%), and the traditional power-velocity model (19.41%).

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Beyond the Toolpath: Site-Specific Melt Pool Size Control Enables Printing of Extra-Toolpath Geometry in Laser Wire-Based Directed Energy Deposition

Applied Sciences ◽

10.3390/app9204355 ◽

2019 ◽

Vol 9 (20) ◽

pp. 4355

Author(s):

Brian T. Gibson ◽

Bradley S. Richardson ◽

Tayler W. Sundermann ◽

Lonnie J. Love

Keyword(s):

Energy Deposition ◽

Closed Loop ◽

Size Control ◽

Pool Size ◽

Bead Geometry ◽

Site Specific ◽

Melt Pool ◽

Directed Energy Deposition ◽

Directed Energy ◽

Melt Pool Size

A variety of techniques have been utilized in metal additive manufacturing (AM) for melt pool size management, including modeling and feed-forward approaches. In a few cases, closed-loop control has been demonstrated. In this research, closed-loop melt pool size control for large-scale, laser wire-based directed energy deposition is demonstrated with a novel modification, i.e., site-specific changes to the controller setpoint were commanded at trigger points, the locations of which were generated by the projection of a secondary geometry onto the primary three-dimensional (3D) printed component geometry. The present work shows that, through this technique, it is possible to print a specific geometry that occurs beyond the actual toolpath of the print head. This is denoted as extra-toolpath geometry and is fundamentally different from other methods of generating component features in metal AM. A proof-of-principle experiment is presented in which a complex oak leaf geometry was embossed on an otherwise ordinary double-bead wall made from Ti-6Al-4V. The process is introduced and characterized primarily from a controls perspective with reports on the performance of the control system, the melt pool size response, and the resulting geometry. The implications of this capability, which extend beyond localized control of bead geometry to the potential mitigations of defects and functional grading of component properties, are discussed.

Download Full-text