A Review of the Anomalies in Directed Energy Deposition (DED) Processes & Potential Solutions - Part Quality & Defects

Perspective Chapter: Direct Energy Deposition of Cu-Fe System Functionally Graded Materials – Miscibility Aspects, Cracking Sources, and Methods of Assisted Manufacturing

“…The common process of the DED of FGM could be divided into several stages briefly described below. a. Preheating of the substrate (optional; decreases the temperature difference between substrate and material, reduces stresses and strains in the resulted part, prevents warping and the separation from the substrate [31]); b. Laser heating of the substrate along with heating and melting of the first particles of powder, which falls on the substrate and particularly absorbs the energy from the laser beam; c. While the laser head moves in the X-Y coordinate plane, the new powder particles become heated and melted; simultaneously previous areas rapidly cool down and solidify; d. When the first layer of the part is finished, the laser turns off, and the powder stream stops (it may take a small time delay between the shutdown of the laser and the moment when the last powder particles are thrown away from the powder nozzle by the feeding gas; thus, these particles can anyway sinter with the substrate or previous layer and cause satellite defects such as balledup protrusion [31]. These defects could be eliminated by machining, or prevented by the proper scan path planning, appropriate terminations, and suitable powder delivery [31][32][33]); e. Cooling time between layers: a process is paused for several seconds to let the previous layer(Às) cool down.…”

“…a. Preheating of the substrate (optional; decreases the temperature difference between substrate and material, reduces stresses and strains in the resulted part, prevents warping and the separation from the substrate [31]); b. Laser heating of the substrate along with heating and melting of the first particles of powder, which falls on the substrate and particularly absorbs the energy from the laser beam; c. While the laser head moves in the X-Y coordinate plane, the new powder particles become heated and melted; simultaneously previous areas rapidly cool down and solidify; d. When the first layer of the part is finished, the laser turns off, and the powder stream stops (it may take a small time delay between the shutdown of the laser and the moment when the last powder particles are thrown away from the powder nozzle by the feeding gas; thus, these particles can anyway sinter with the substrate or previous layer and cause satellite defects such as balledup protrusion [31]. These defects could be eliminated by machining, or prevented by the proper scan path planning, appropriate terminations, and suitable powder delivery [31][32][33]); e. Cooling time between layers: a process is paused for several seconds to let the previous layer(Às) cool down. On the one hand, it prevents overheating and re-melting of the previous layer(Às) (especially if they were fabricated from another material characterized by higher heat conductivity, higher laser radiation absorption, and lower melting point) and provides a more appropriate thermal history (therefore, in some cases, the cooling time could be artificially increased to provide more intense cooling), but on the other hand, it could increase the further undesired thermal strains and stresses due to growth of the temperature gradient, and cause cracking.…”

“…The same was shown by parts, deposited in a vertical direction without ultrasonic assistance (Figure 5, right picture). The increase in a surface roughness of the first part could be caused by a spatter due to significant vibration, or by the difference in the cooling rate of the lowest and the highest layers [31]. This difference comes from the fact that layers, larger affected by ultrasonic vibration, undergo more intense stirring provided by cavitation and acoustic flow effects [67] in a melt pool.…”

“…Machining (including milling, turning, vibratory grinding, abrasive, chemical and electrical polishing, ultrasonic nanocrystal surface modification) of the DEDfabricated parts is a common process, which improves their surfaces' overall quality [87]. These techniques provide a decrease of the roughness of the laser deposited part surface and eliminate the satellite defects (such as protrusions), various edge defects (such as unsuitable levels of edges and their shape), and the morphological defects (such as waviness, blobs, and zits) [31]. Particularly for the Cu-based system, a magnetically driven abrasive polishing was implemented by I. Karakurt et al [88] to improve the quality of electron beam melting-fabricated copper samples.…”

Opportunities for the Application of 3D Printing in the Critical Infrastructure System

“…• DED-Directed Energy Deposition: the targeted melting of supplied material. A process in which concentrated energy melts a material in layers during deposition (concentrated heat energy emitted as a laser beam, electron beam or plasma arc) [24,[53][54][55][56]; • SL-Sheet Lamination: cross-section lamination. A process in which successive sections of a model are cut out from sheets of material glued to each other in succession [57][58][59][60].…”