Influence of standoff distance and laser defocusing distance on direct laser metal deposition of a nickel-based superalloy

Abstract

The direct laser metal deposition (DLMD) is an additive manufacturing technology, based on laser cladding, which focuses mainly on 3D manufacturing applications. DLMD allows the production of thin-walled components by overlaying single-track depositions. Several issues can affect the deposition process and compromise the flatness of the surface on which subsequent tracks will be deposited. This work focused on deposition troubles simulated by means of a designed variation of the standoff distance and the laser defocusing distance. The effects of these two important process parameters on the deposition process were investigated. The experimental tests were performed by depositing a nickel-based superalloy powder on AISI 304 stainless steel plates through a coaxial nozzle. The work was carried out using an ytterbium fiber laser source and a deposition head equipped with an advanced and innovative motorized optics system. This allows the decoupled variation of the laser defocusing distance and consequently the laser spot size on the substrate surface with respect to the standoff distance. Results showed an influence of standoff distance and laser defocusing distance on the geometrical characteristics of the clad, such as clad width, clad height, penetration depth, and dilution. An experimental setup consisting of a light coaxial to the powder flow and a laterally positioned camera was designed to investigate the spatial powder distribution. Moreover, an analytical model for the powder distribution and clad width were proposed and validated. The analysis of variance (ANOVA) with a general linear model was also employed to describe the results.

In process monitoring of geometrical characteristics in laser metal deposition: A comparative study

“…It was also noted that the standoff distance (SOD) tends to decrease with the increase of the layer number. Slight reductions in standoff distance usually leads to a variation in the laser power density and powder flow distribution, deviating from the optimal conditions [4]. As a result, the amount of caught powder and the layer height decreases [20].…”

“…The monitoring of the LMD process is carried out in different fields: monitoring of the thermal field for the high temperatures developed by the laser during the process [3], monitoring of the powder flow [4] and monitoring of geometrical parameters of the produced component [5]. Among the several outputs that need to be monitored and controlled to ensure the quality of the process/component, standoff distance and layer height are very important.…”

Advancements in 3D Printing: Directed Energy Deposition Techniques, Defect Analysis, and Quality Monitoring

“…Such laser-powder interactions, in conjunction with the inert gas, generate a molten pool or liquid metal with a HAZ beneath, showing varying penetration depths. This phenomenon, known as dilution, represents the minimum level of metallurgical bonding between layers, typically ranging from 10% to 30% [84,85]. Dilution can be simply described by the melt pool Height-over-Depth (H/D) ratio [86,87].…”

Nozzle Designs in Powder-Based Direct Laser Deposition: A Review

“…The geometry of the nozzle determines some characteristics of the gas-powder stream, such as the vertical axis point, molten pool vertical separation (also known as standoff distance) [39,40] and main and secondary flow gas velocity. The internal geometry of these nozzles is typically a circular and converging-diverging one [39].…”