In industrial laser cladding applications various new possibilities have opened up by introduction of laser sources with
powers over 10 kW. Higher laser power allows higher deposition rates, which enables new applications for example in
heavy engineering. However, to fully utilize the high power, beam area in focus needs to be increased significantly
compared to for example welding. For high brightness lasers, this often requires complicated processing optics as the
beam is usually Gaussian when defocused. In most surface treatment applications process would benefit from
homogenous intensity distribution instead of a Gaussian one. In this paper we present ideas for cladding applications
using a 12 kW disc laser coupled into a square-formed fiber with a 1000x1000 μm-core. The output of the fiber is
collimated by a newly developed collimator based on cylindrical lenses with an 1:3.3 aspect ratio of focal lengths. The
asymmetrically collimated beam is then condensed to a homogeneous rectangular spot on the work-piece using an f=500
mm focusing unit. With this setup we reach a spot size of 7.4x2.2 mm = 16.3 mm2, implying laser power densities up to
The asymmetric collimator is based on efficiently water-cooled cylindrical lenses with different focal lengths. Having
interchangeable fiber connector interfaces and Optoskand's standard exit interface, the collimator can easily be
implemented in optical heads. We present results on the optics performance including power transmission, image quality
and focal shifts at power levels up to 12 kW. Results of preliminary cladding tests using the asymmetrical optics and offaxis
tandem wire feeding will also be presented orally. Deposition rate and efficiency using high power levels will be
investigated. Analyses of cladding bead geometry and microstructure will be performed.
Solid solution strengthened cobalt based Stellite 21 hardfacing layers produced by off-axis and newly developed HPDL multi-feeder cladding techniques were compared. The properties studied include thickness of the heat-affected zone (HAZ), dilution, microstructure, microhardness and powder catchment efficiency. Both off-axis and multi-feeder cladding techniques were found to give pore and crack-free coating layers metallurgically bonded to the substrate. Energy dispersive spectroscopy (EDS) studies indicated that only a limited amount of dilution took place in all the coatings. Microhardness values (HV1) were observed to be in the range of 360 - 387 HV1 in as-laser-clad condition. Due to more stable cladding process and use of two side feeders, which produced more homogenous powder cloud along the laser beam axis and more accurately focused powder stream to the rectangular laser beam spot, multi-feeder cladding technique was more efficient in terms of powder catchment efficiency, which was at a level of 62 - 65 %. Both powder-feeding techniques produced relatively high heat input into the workpiece. Multi-feeder cladding technique produced smoother and less oxidised surface quality than off-axis technique, because shielding gas flow was implemented differently.
A series of exerpiments were performed to investigate the one-step laser cladding of Inconel 625 powder, injected off-axially onto Fe37 and 42CrMo4 substrates. The experiments were carried out using a 6 kW high power diode laser (HPDL) mounted to a 6 axis robot system. The rectangular shape of the delivering beam was focused to a spot size of 22 x 5 mm on the work piece. The coating samples were produced using different levels of powder feed rate (77 - 113 g/min), traveling speed (300 - 400 mm/min) and laser power (4.8 - 6 kW). Hot corrosion resistance of laser-clad Inconel 625 coatings were tested in Na2SO4 - V2O5 at 650°C for 1000 hours. Wet corrosion properties of the obtained coatings were tested in immersion tests in 3.5 wt.% NaCl solution. Diode laser power of 6 kW (808 and 940 nm) was high enough to produce 20 mm wide laser-clad tracks with a thickness of 2.5 mm in a single pass, when powder feed rate was more than 6 kg/h and traverse speed was 400 mm/min. Wet corrosion properties of laser-clad Inconel 625 coatings were found to be superior to sprayed and welded coatings. Hot corrosion resistance was even slightly better than corresponding wrought alloy. Finally, one-step HPDL cladding was demonstrated in coating of shaft for hydraulic cylinder with Inconel 625 powder. Due to high coating quality, high deposition rate and traverse speed HPDL devices are very promising for large area cladding applications.