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Design and Prototyping of a Continuous Coaxial Nozzle for Uniforml Metal Powder Deposition at Various Angles

Nasiri Khansari, Mohammad Taghi | 2023

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 55987 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Movahhedy, Mohammad Reza
  7. Abstract:
  8. Direct metal deposition (DMD) process is an additive manufacturing technology that is rapidly gaining laser importance due to its various capabilities in applications such as coating, repairing high-value damaged parts, rapid prototyping and even production in small quantities. Among the equipment needed for this process, nozzle is perhaps the most important component because its performance affect the efficiency of powders trapped in the molten pool, and is crucial to the quality of the deposited layer. The existing nozzle designs can be categorized in two groups; lateral and coaxial nozzles; and the coaxial ones are divided into continuous and discontinuous types. Coaxial nozzles have recently gained popularity, especially due to their application in repairing of two and three-dimensional surfaces of damaged parts. However, when a continuous coaxial nozzle is tilted from the vertical axis for coating inclined surfaces, the gravity affects the uniform distribution of the powder at the nozzle outlet. This limits the application of the nozzle at non-zero inclination angles in multiaxial coatings. The main objective of the present thesis is to present a new design for continuous coaxial nozzles that are less sensitive to gravity, and thus, can improve the performance of the nozzle at inclined angles. The new design is based on changing of the input mechanism of existing continuous coaxial nozzles and leading the powder flow through several grooves. The powder stream is divided into eight parts before entering the nozzle, and then, the divided powder flow enters into eight inlet channels with circular cross sections. Finally, each part of the stream enters into a groove embedded in the internal cone. The performance of the new design was evaluated by numerical simulation of powder flow in Fluent software. In the simulation, the powder-gas flow is modeled as two continuous and discrete phases. From the simulation, the design and operational parameters of the nozzle, including the dimensions of the powder inlet and outlet sections and the velocity of the carrier gas, were extracted. It is observed that using the new design, the deviation of the powder focal point from the nozzle axis at inclined angles is reduced. The simulation results show that for the inclination angles of 0, 20, 30 and 45 degrees, 90%, 89%, 87% and 86% of the powder pass through a circle of 2.5mm diameter, respectively. This demonstrates that the tilting of the nozzle has little effect on the amount of powder passing through a circular area around the nozzle axis in the focal plane. After simulating and extracting the improved parameters, the primary model was modified and the nozzle was fabricated for experimental tests. Experimental results show that the deviation of the powder focal point in the presented nozzle is negligible and probably does not have a significant effect on the quality of the process because the focal point remains in the effective area of the laser spot. In addition, the agreement between the simulation and experimental results provides the ability to predict the nozzle behavior for further optimization. Finally, according to the results obtained from the simulation and experimental tests, it can be concluded that the proposed nozzle still maintains its efficiency at non-zero inclination angles, and the negative effects of gravity on the performance of the nozzle are minimized. This matter can extend the use of continuous coaxial nozzles in the multiaxial cladding at a wide range of inclination angles
  9. Keywords:
  10. Direct Metal Deposition ; Coaxial Nozzle ; Nozzle Design ; Gravity Effect ; Improved Powder Efficiency ; Powder-Gas Flow ; Additive Manufacturing

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