| Abstract Scope |
Laser blown powder (LBP) DED models need developed to ensure high quality deposits for a range of deposit size features. The LBP deposition head consists of a laser focusing head and a powder delivery nozzle. The nozzle is a very important consideration as it controls the powder delivery characteristics such as powder spot size, waist, minimum and maximum flow rate and consistency. The laser focusing head characteristics are also critical to appropriately pair the optical configuration with the powder delivery nozzle. There is a need to transfer procedures between different LBP deposition heads, so different systems can be used to make similar features and parts. This project evaluated two commercial nozzles; one nozzle used a coaxial feed and the other used a three-port design. A weight per unit time method was used to characterize the powder feed rate with each nozzle using nickel super alloy powder feedstock. High speed video (HSV) analysis procedures were developed to further characterize the powder flow for each LBP nozzle. Powder spot size, waist and focal position was measured for each nozzle over its deposition powder flow rate capability. The laser beam characterization was completed with power measurements and Primes focus monitor to find laser spot size, beam quality and power delivery. A range of single bead per layer deposition tests were then used to develop relationships between laser spot size and power to powder flow and spot size characteristics on surface quality and powder capture. The relationship between powder and laser spot sizes were very important to control surface fairness and powder capture efficiency. These factors effect efficiency and are necessary for process monitoring, control, and DED modeling efforts to ensure quality over a full range of features. Using these relationships, procedures were developed to maximize powder capture and surface finish quality on both minimum wall and block test features. Methods for characterizing LBP powder delivery and feed rate systems should be standardized to support LBP DED process calibration, deposition performance, and transference of procedures between machines. |