scholarly journals Causes and Measures of Fume in Directed Energy Deposition: A Review

2020 ◽  
Vol 58 (6) ◽  
pp. 383-396
Author(s):  
Kang-Hyung Kim ◽  
Chan-Hyun Jung ◽  
Dae-Yong Jeong ◽  
Soong-Keun Hyun
Keyword(s):  
Laser Processing ◽  
Energy Deposition ◽  
Laser Flash ◽  
Travel Speed ◽  
Trial And Error ◽  
Directed Energy Deposition ◽  
Directed Energy ◽  
Harmful Effects ◽  
Gas Supply ◽  
Metal Additive

Pores and cracks are known as the main defects in metal additive manufacturing (MAM), including directed energy deposition(DED). A gaseous fume is often produced by laser flash (instantaneous high temperature) during laser processing, which may cause various defects such as porosity, lack of fusion, inhomogeneity, low flowability and composition change, either. However the cause and harmful effects of fume generation in DED are known little. In laser processing, especially laser welding, many studies have been conducted on the prevention of fume because it generates defects that hinder uniform reactions between the laser beam and the materials. Generally, the fume occurs with easily vaporizing low melting point components or sensitive oxidizing elements. Unsuitable conditions are also known to have an effect, including laser power, travel speed, powder feed rate and shielding gas supply. Practically, there are many more fume generating factors in the DED process, and the lack of understanding requires a lot of trial and error. In this article the laser-related and weld metallurgy literatures were reviewed, focusing on the prevention of fume in powder DED. The causes of the fume, were explained to result from the stages of cavitation bubbles generated by the laser induced plasma and the nanoparticles released. Additionally, the effects of alloying components and environmental conditions for fume generation in the DED process were investigated, and suggestions are proposed to prevent fume.

Predicting Part-Level Thermal History in Metal Additive Manufacturing Using Graph Theory: Experimental Validation With Directed Energy Deposition of Titanium Alloy Parts

2019 ◽  
Author(s):  
Reza Yavari ◽  
Jordan Severson ◽  
Aniruddha Gaikwad ◽  
Kevin Cole ◽  
Prahalad Rao
Keyword(s):  
Heat Flux ◽  
Titanium Alloy ◽  
Additive Manufacturing ◽  
Energy Deposition ◽  
Process Conditions ◽  
Theoretic Approach ◽  
Temperature Trends ◽  
Directed Energy Deposition ◽  
Directed Energy ◽  
Metal Additive

Abstract The objective of this paper is to experimentally validate the graph-based approach that was advanced in our previous work for predicting the heat flux in metal additive manufactured parts. We realize this objective in the specific context of the directed energy deposition (DED) additive manufacturing process. Accordingly, titanium alloy (Ti6Al4V) test parts (cubes) measuring 12.7 mm × 12.7 mm × 12.7 mm were deposited using an Optomec hybrid DED system at the University of Nebraska-Lincoln (UNL). A total of six test parts were manufactured under varying process settings of laser power, material flow rate, layer thickness, scan velocity, and dwell time between layers. During the build, the temperature profiles for these test parts were acquired using a single thermocouple affixed to the substrate (also Ti6Al4V). The graph-based approach was tailored to mimic the experimental DED process conditions. The results indicate that the temperature trends predicted from the graph theoretic approach closely match the experimental data; the mean absolute percentage error between the experimental and predicted temperature trends were in the range of 6% ∼ 15%. This work thus lays the foundation for predicting distortion and the microstructure evolved in metal additive manufactured parts as a function of the heat flux. In our forthcoming research we will focus on validating the model in the context of the laser powder bed fusion process.

Elastic Properties of IN718 Fabricated via Laser Directed Energy Deposition (DED)

2021 ◽  
Author(s):  
M. M. Rahman ◽  
G. Huanes-Alvan ◽  
H. Sahasrabudhe ◽  
S. K. Chakrapani
Keyword(s):  
Elastic Properties ◽  
Elastic Constants ◽  
Laser Processing ◽  
High Performance ◽  
Energy Deposition ◽  
Boundary Segregation ◽  
Secondary Phases ◽  
Directed Energy Deposition ◽  
Wide Range ◽  
Directed Energy

Abstract Additive manufacturing of nickel based super alloys such as IN718 is highly desirable since they have a wide range of applications in high performance structures. Compared to conventional methods, laser processing allows for near net shaping of complex geometries. However, laser processing can result in very complex microstructures including meta-stable phases, grain boundary segregation of precipitates, dendritic grains and cellular microstructure. Describing elastic properties of such structures can be quite challenging due to these features. This article explores the use of resonant ultrasound spectroscopy (RUS) to characterize the elastic properties of IN718 samples fabricated using Laser Directed Energy Deposition (DED). For initial estimates of the elastic constants, ultrasonic wave (longitudinal and shear) velocities measured at 5MHz and 2.25 MHz respectively. The initial assumption was that the eventual structure will be orthotropic and the 9 elastic constants were determined using a combination of RUS and propagating wave experiments. A finite element approach was adopted to model this system and to minimize the values of elastic constants. The results seem to suggest that the secondary phases such as Laves will influence the eventual anisotropy of the bulk structure.

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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