scholarly journals In-Line Height Measurement Technique for Directed Energy Deposition Processes

2021 ◽  
Vol 5 (3) ◽  
pp. 85
Author(s):  
Herman Borovkov ◽  
Aitor Garcia de la Yedra ◽  
Xabier Zurutuza ◽  
Xabier Angulo ◽  
Pedro Alvarez ◽  
...  
Keyword(s):  
Energy Deposition ◽  
Contact Angles ◽  
Weld Bead ◽  
Inspection System ◽  
Layer By Layer ◽  
Height Measurement ◽  
Bead Width ◽  
Metal Solidification ◽  
Directed Energy Deposition ◽  
Directed Energy

Directed energy deposition (DED) is a family of additive manufacturing technologies. With these processes, metal parts are built layer by layer, introducing dynamics that propagate in time and layer-domains, which implies additional complexity and consequently, the resulting part quality is hard to predict. Control of the deposit layer thickness and height is a critical issue since it impacts on geometrical accuracy, process stability, and the overall quality of the product. Therefore, online feedback height control for DED processes with proper sensor strategies is required. This work presents a novel vision-based triangulation technique through an off-axis located CCD camera synchronized with a 640 nm wavelength pulsed illumination laser. Image processing and machine vision techniques allow in-line height measurement right after metal solidification. The linearity and the precision of the proposed setup are validated through off-and in-process trials in the laser metal deposition (LMD) process. Besides, the performance of the developed in-line inspection system has also been tested for the Arc based DED process and compared against experimental weld bead characterization data. In this last case, the system additionally allowed for the measurement of weld bead width and contact angles, which are critical in first runs of multilayer buildups.

scholarly journals Model-Based Feedforward Control of Part Height in Directed Energy Deposition

Materials ◽  
2021 ◽  
Vol 14 (2) ◽  
pp. 337
Author(s):  
Qian Wang ◽  
Jianyi Li ◽  
Abdalla R. Nassar ◽  
Edward W. Reutzel ◽  
Wesley F. Mitchell
Keyword(s):  
Laser Power ◽  
Energy Deposition ◽  
Inverse Dynamics ◽  
Feedforward Control ◽  
Layer By Layer ◽  
Model Based ◽  
Melt Pool ◽  
Directed Energy Deposition ◽  
Proposed Model ◽  
Directed Energy

Control of the geometric accuracy of a metal deposit is critical in the repair and fabrication of complex components through Directed Energy Deposition (DED). This paper developed and experimentally evaluated a model-based feedforward control of laser power with the objective of achieving the targeted part height in DED. Specifically, based on the dynamic model of melt-pool geometry derived from our prior work, a nonlinear inverse-dynamics controller was derived in a hatch-by-hatch, layer-by-layer manner to modulate the laser power such that the melt-pool height was regulated during the simulated build process. Then, the laser power trajectory from the simulated closed-loop control under the nonlinear inverse-dynamics controller was implemented as a feedforward control in an Optomec Laser-Engineered Net Shape (LENS) MR-7 system. This paper considered the deposition of L-shaped structures of Ti-6AL-4V as a case study to illustrate the proposed model-based controller. Experimental validation showed that by applying the proposed model-based feed-forward control for laser power, the resulting build had 24–42% reduction in the average build height error with respect to the target build height compared to applying a constant laser power through the entire build or applying a hatch-dependent laser power strategy, for which the laser power values were obtained from experimental trial and error.

Effect of External Magnetic Field on the Microstructure of 316L Stainless Steel Fabricated by Directed Energy Deposition

2019 ◽  
Author(s):  
Jin Wang ◽  
Yachao Wang ◽  
Jing Shi ◽  
Yutai Su
Keyword(s):  
Magnetic Field ◽  
Stainless Steel ◽  
External Magnetic Field ◽  
Energy Deposition ◽  
316L Stainless Steel ◽  
High Energy ◽  
Layer By Layer ◽  
Horizontal Magnetic Field ◽  
Directed Energy Deposition ◽  
Directed Energy

Abstract Directed energy deposition (DED) is a major additive manufacturing (AM) process, which employs high energy beams as the heat source to melt and deposit metal powder in a layer-by-layer fashion such that complex components can be manufactured. In this study, a magnetic-field-assisted DED method is applied to control the microstructure and element distribution in the deposited materials. For this purpose, to control the microstructure of DED-built 316L stainless steel, a horizontal magnetic field is introduced during the DED process at different levels of magnetic field intensities (i.e., 0T, 1.0T and 1.8T). Scanning electron microscopy (SEM) and energy dispersive X-Ray spectroscopy (EDS) are used to characterize the microstructure of components obtained with different magnetic field strengths. The results show that the microstructure of deposited materials is significantly affected by the external magnetic field. Also, the result of interdendritic microsegregation pattern presents a transformation from continuous morphology to discrete morphology because of the applied magnetic field. Along with the increasing horizontal magnetic field intensity, nickel and chromium content are changed significantly in austenite and ferrite.

scholarly journals Working Distance-Based Feedforward Control of the Weld Bead Height in Directed Energy Deposition

2020 ◽  
Vol 53 (2) ◽  
pp. 11806-11811
Author(s):  
Johann Stoppok ◽  
David Dillkötter ◽  
Magnus Thiele ◽  
Cemal Esen ◽  
Sebastian Leonow ◽  
...  
Keyword(s):  
Energy Deposition ◽  
Feedforward Control ◽  
Weld Bead ◽  
Directed Energy Deposition ◽  
Directed Energy ◽  
Bead Height ◽  
Working Distance

scholarly journals Correction to: Characterization and Optimization of Process Parameters for Directed Energy Deposition Powder-Fed Laser System

2021 ◽  
Author(s):  
Daniel Andres Rojas Perilla ◽  
Johan Grass Nuñez ◽  
German Alberto Barragan De Los Rios ◽  
Fabio Edson Mariani ◽  
Reginaldo Teixeira Coelho
Keyword(s):  
Process Parameters ◽  
Energy Deposition ◽  
Laser System ◽  
Directed Energy Deposition ◽  
Optimization Of Process Parameters ◽  
Directed Energy

scholarly journals Hot-Wire Laser-Directed Energy Deposition: Process Characteristics and Benefits of Resistive Pre-Heating of the Feedstock Wire

Metals ◽  
2021 ◽  
Vol 11 (4) ◽  
pp. 634
Author(s):  
Agnieszka Kisielewicz ◽  
Karthikeyan Thalavai Pandian ◽  
Daniel Sthen ◽  
Petter Hagqvist ◽  
Maria Asuncion Valiente Bermejo ◽  
...  
Keyword(s):  
Heat Input ◽  
Energy Deposition ◽  
Fine Tuning ◽  
Hot Wire ◽  
Process Stability ◽  
Electrical Signals ◽  
Melt Pool ◽  
Directed Energy Deposition ◽  
Directed Energy ◽  
The Stability

This study investigates the influence of resistive pre-heating of the feedstock wire (here called hot-wire) on the stability of laser-directed energy deposition of Duplex stainless steel. Data acquired online during depositions as well as metallographic investigations revealed the process characteristic and its stability window. The online data, such as electrical signals in the pre-heating circuit and images captured from side-view of the process interaction zone gave insight on the metal transfer between the molten wire and the melt pool. The results show that the characteristics of the process, like laser-wire and wire-melt pool interaction, vary depending on the level of the wire pre-heating. In addition, application of two independent energy sources, laser beam and electrical power, allows fine-tuning of the heat input and increases penetration depth, with little influence on the height and width of the beads. This allows for better process stability as well as elimination of lack of fusion defects. Electrical signals measured in the hot-wire circuit indicate the process stability such that the resistive pre-heating can be used for in-process monitoring. The conclusion is that the resistive pre-heating gives additional means for controlling the stability and the heat input of the laser-directed energy deposition.

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