Initial transient phase and stability of annular laser beam direct wire deposition

Abstract

In this paper the stability of the annular laser beam (ALB) direct wire-deposition process, which enables process symmetry and a well-defined ALB workpiece irradiation proportion (WIP) and related energy input onto the workpiece and the wire surface is considered. Various initial process phase strategies with respect to different initial wire-end positions and WIPs were analysed based on the process visualization and outcome, and the melt pool temperature. It was shown that in addition to a precise synchronization of the mutually time-dependent ALB power, wire and workpiece feeding velocity, the fastest and the most robust transition into a stable stationary process could be achieved with the initial position of the wire-end on the workpiece surface. Additionally, the WIP was shown to have a strong and nonlinear influence on the process stability.

Directed Energy Deposition (DED) Process: State of the Art

“…The WLAM process is one of the MAM processes to produce metallic parts without porosity using a laser, such as diode, disc, Nd:YAG, CO 2 , and fiber lasers, as a thermal energy source and an metallic wire [4,24,61,67,73,153,[185][186][187][188][189][190][191][192][193][194][195][196][197][198][199][200][201][202]. The WLAM process fundamentally uses the concept of laser cladding and welding, as shown in Table 1 [4,24,66,67].…”

“…In addition, the lateral feeding of the wire causes anisotropic deposition problems, limited mobility of the deposition head and reduced flexibility of the deposition geometry [61,153]. In order to overcome disadvantages of the lateral feeding type WLAM process, several co-axial feeding type WLAM processes with vertical feeding of the wire have been introduced [61,[199][200][201][202][203]. The wire is vertically fed to the laser focus for the case of the co-axial wire feeder.…”

“…11c [61]. Kotar et al [202] devised an experimental set-up to investigate the initial transient phase and the stability of the annular laser beam direct wire deposition (ALB-DWD) process. Fu et al [199] developed a WLAM process using an axisymmetric multi-laser source and vertical wire feeding.…”

“…In addition, they reported that power decay strategies or close-loop temperature control is needed to maintain a stable molten pool size through the prevention of heat accumulation during multi-layer deposition [61]. Kotar et al [202] developed process-stability windows to predict an appropriate combination of initial laser power and workpiece irradiation proportion (WIP) of each wire feed rate for the deposition of SS 316 wire on a SS 304 substrate using the ALB-DWD process. Deposition rate and area can be estimated by the ratio of the wire feed rate to the travel speed when the diameter of the wire is fixed [24,186,194].…”

“…Recently, combinations of different monitoring devices were used for in-process monitoring of the DED process, as shown in Table 12 [78,94,160,178,202,[266][267][268][269][270]. Combinations of a visible camera and a pyrometer were used to control the temperature of the molten pool and the deposition height of part for the DMD process and to investigate the effects of the temperature distribution on the microstructure formation of the WAAM process [78,178].…”