Process of direct annular laser beam metal wire deposition

Za izdelavo kovinskih komponent z uporabo dodajalnih tehnologij se zaradi svojih prednosti pogosto uporablja tudi proces direktnega laserskega nanašanja žice (DLNŽ). V okviru doktorskega dela smo preučili vpliv procesnih parametrov na stabilnost procesa DLNŽ z uporabo anularnega laserskega žarka (ALŽ). Uporaba ALŽ omogoča dovod žice v talilni bazen v osi laserskega žarka ter simetrično in sočasno osvetljevanje konca žice in obdelovanca v različnih deležih. Slednje smo opisali z novim procesnim parametrom, deležem osvetljenosti obdelovanca (DOO). Za karakterizacijo stabilnosti procesa smo podrobno eksperimentalno analizirali začetno in stacionarno fazo procesa ter okarakterizirali izdelane nanose. Pokazali smo, da je za uspešno izvedbo začetne faze potrebna natančna časovna sinhronizacija moči laserskega žarka in hitrosti podajanja žice ter obdelovanca. Najbolj robustno izvedbo začetne faze in prehod v stacionarno fazo dosežemo z začetno lego konca žice na obdelovancu. Pri tem sta pri izbranih hitrostih podajanja žice in obdelovanca začetna moč in moč laserskega žarka v stacionarni fazi procesa, ki zagotavljata stabilno izvedbo procesa, nelinearno odvisna od DOO. Izbor neustreznih parametrov rezultira bodisi v tvorjenju viseče kapljice ali v trku žice s površino obdelovanca. DOO vpliva tudi na obliko in geometrijo nanosov, in sicer višji DOO povzroči manjše dilucijsko razmerje, kar je v linearni korelaciji z izmerjenimi temperaturami talilnega bazena in obdelovanca. Fenomenološka obravnava procesa je pokazala, da so kompleksni vplivi procesnih parametrov na stabilnost procesa, obliko in geometrijske lastnosti nanosov poleg procesnega DOO posledica številnih fizikalnih pojavov, vključujoč odboje laserskega žarka, prevoda toplote in Marangonijevega toka v talilnem bazenu.The process of direct laser wire deposition (DLWD) is often used for metal additive manufacturing due to its advantages. In this doctoral thesis, we examined the influence of process parameters on the stability of the annular laser beam (ALB) direct wire deposition process. Usage of the ALB enables coaxial wire feeding and symmetrical and simultaneous irradiation of the wire-end and the workpiece surface in different proportions, which is evaluated with a new process parameter, the workpiece irradiation proportion (WIP). To characterize the DLWD process, the initial and stationary phases of the process were studied and clad geometry was analyzed. It was shown that the precise synchronization of mutually-dependent laser beam power and wire and workpiece feeding velocity is required for process initialization. The most robust initial phase and stable transition into the stationary phase of the process was achieved with the initial wire-end position on the workpiece surface. At the selected wire and workpiece feeding velocities, initial and stationary laser beam power are nonlinearly dependent on the WIP. Improper process parameters result in either pending droplet formation or collision between the wire-end and the workpiece surface. The WIP also affects clad geometry, where higher WIP results in a lower dilution ratio which is linearly correlated with the workpiece and melt pool temperatures. Phenomenological characterization of the process showed that complex effects of process parameters on process stability and clad geometry are in addition to effective WIPE related to numerous physical phenomena, including laser beam reflection, heat transfer, and Marangoni flow in the melt pool