Product Code: ICA13_2001

Laser Cladding Using Scanning Optics - Effect of the Powder Feeding Angle and Gas Flow on Process Stability
Authors:
Joonas Pekkarinen, Lappeenranta University of Technology; Turku Finland
Antti Salminen, Lappeenranta University of Technology; Lappeenranta Finland
Veli Kujanpaaa, Vtt Technical Research Centre of Finland; Lappeenranta Finland
Jarmo Ilonen, Lappeenranta University of Technology, Machine Vision and Pattern Recognition Laboratory (MVPR); Lappeenranta Finland
Lasse Lensu, Lappeenranta University of Technology, Machine Vision and Pattern Recognition Laboratory (MVPR); Lappeenranta Finland
Heikki Kalviainen, Lappeenranta University of Technology, Machine Vision and Pattern Recognition Laboratory (MVPR); Lappeenranta Finland
Presented at ICALEO 2013

Powder feeding is one of the most important single factors defining qualitative outcome of cladding process. If the powder feeding or the powder cloud suffers from some form of interference it is seen directly in the quality of clad bead, e.g. as an increase in the dilution or as too low a clad bead height. Laser cladding with scanning optics has in turn created a lot of flexibility for the process enabling the adjustment of the width of the clad bead by adjusting the scanning amplitude of the optics. However, the behavior of powder cloud under the scanned laser beam has not been studied thoroughly. Even though scanned beam delivers lasers energy to relatively large are it still has high local power intensity which can disturb the powder feeding. This study focusses on how the powder feeding angle and flow rate of the powder carrying gas effect on powder cloud behavior under the scanned laser beam in laser cladding process.
In this study the powder feeding angles from 40 to 70 degrees are tested with different powder feeding gas flows of 3 and 6 l/min and different laser scanning frequencies, 80 to 150 Hz. Used additive material was 316L and as a substrate material mild steel. Test were performed using 5 kW of laser power and cladding speed of 5 mm/s. Powder cloud behavior is monitored simultaneously in situ with high speed camera and spectrometer. The results show that the stability of the powder cloud is highly dependent on the tested parameters. On a steep powder feeding angle (70º) the powder cloud is strongly vaporized emitting bright visible light. However, when 60º or 40º degree powder feeding angles are used powder clouds behavior is more stable, i.e. there is less or no vaporization noticed, and the emitted light is fainter. Also a straight correlation between the vaporization of powder cloud and the increase of dilution is noticed. When the powder particles are vaporized inside powder cloud, it causes disturbance in powder feeding to the melt pool and thus increases the dilution.