Joonas Pekkarinen

Laser cladding with scanning optics: Effect of power adjustment

Laser cladding with fiber laser using scanning optics is a relatively new way of laser cladding. Modern oscillating scanners enable laser power adjustment according to scanning direction. This is a versatile tool for making process more stable as well as modifying the shape of clad bead. Laser cladding was made using 5 kW IPG fiber laser with ILV-oscillating scanner, using 316L powder as clad material and S355 mild steel plate as substrate material. These tests showed that power adjustment is necessary for cladding process stability when sinusoidal scanning is used. Power adjustment can be used also for adjusting the geometry of clad bead and for constructing simple geometries. The oscillating scanner enables flexibility for controlling the geometry of clad bead and process stability compared to the conventional laser cladding with static optics.

Laser cladding with scanning optics: Effect of scanning frequency and laser beam power density on cladding process

Scanning optics is an effective way to manipulate a laser beam for laser cladding. The numerical adjustment of the scanner gives a great deal of flexibility to the cladding process. However, the effect of the scanned beam on the cladding process itself has not been studied very thoroughly so far. This study concentrates on explaining how the scanning frequency and power density of the laser beam affect the stability of the cladding process. The results showed that both of these factors significantly influence the process stability and the outcome of the cladding process. If the local specific energy input was over 2.46 J/mm2, the process was noticed to be unstable. This limit was cross when scanning frequency was under 40 Hz. Power densitys limit value for stable process was found to be 191 kW/cm2 and higher power densities than this was found to produce unstable process. If the cladding process was found to be unstable, dilution increased significantly and process started to resemble more laser alloying.

Laser welding parameters effects on austenitic stainless steels welds microstructure

This study is focused to determine empirically, which microstructural changes occur in austenitic stainless steels when heat input is controlled by welding parameters. Test welds were done bead-on-plate without shielding gas using 5 kW fiber laser. In this study austenitic stainless steels used were 1.4372 (AISI 201), 1.4404 (AISI 316L) and 1.4547 (high-alloyed 6% Mo). Two of these steels, 1.4372 and 1.4404, solidify usually as primary ferritic mode and 1.4547 solidifies as primary austenitic mode. As generally known, the microstructural properties austenitic stainless steels welds are dependent on solidification mode.In this study it was noticed that the welding speed affects austenitic stainless steels welds microstructure. In 1.4372 and 1.4404 steels solidification mode was changed to wards primary austenitic solidification mode when welding speed was increased caused by increase in weld solidification growth rate and cooling rate. For 1.4547 steel changes in microstructure were mostly concerned on micro segregation of molybdenum. It was noticed that micro segregation of molybdenum decreased when welding speed increased caused by finer microstructure.In practice, chances in solidification mode effect on filled wire selection. When high welding speeds are used filled wire is desirable choose so that weld solidifies as primary ferritic mode. In that way chance of hot crack formation decreases significantly. Decrease of micro segregation at high welding speeds is beneficial because then it is possible to use lower alloyed filled wire than usually and still get sufficient molybdenum concentration through the whole weld.This study is focused to determine empirically, which microstructural changes occur in austenitic stainless steels when heat input is controlled by welding parameters. Test welds were done bead-on-plate without shielding gas using 5 kW fiber laser. In this study austenitic stainless steels used were 1.4372 (AISI 201), 1.4404 (AISI 316L) and 1.4547 (high-alloyed 6% Mo). Two of these steels, 1.4372 and 1.4404, solidify usually as primary ferritic mode and 1.4547 solidifies as primary austenitic mode. As generally known, the microstructural properties austenitic stainless steels welds are dependent on solidification mode.In this study it was noticed that the welding speed affects austenitic stainless steels welds microstructure. In 1.4372 and 1.4404 steels solidification mode was changed to wards primary austenitic solidification mode when welding speed was increased caused by increase in weld solidification growth rate and cooling rate. For 1.4547 steel changes in microstructure were mostly concerned on mic...

Analysis of laser cladding process parameter influence on the clad bead geometry

In the present study, fiber laser has been used in laser cladding with an off-axis powder injection. The aim of this study is to analyze the effects of the laser cladding process parameters on the clad layer geometry. The parameters studied were laser power, cladding speed, and powder feeding rate. This study was conducted by using single-pass clad layers. The powder material used was stainless steel AISI 316L and the substrate material used was structural steel S355. The relationship between the laser cladding process parameters and the clad layer geometry was established by using statistical analysis.Analysis of the cladding results concluded that the laser power and cladding speed are the main parameters that control the clad layer width. The majority of the variations were in the clad height, but the clad bead side angle was also dependent on the powder feed rate and cladding speed. This study successfully established the relationship between the laser cladding process parameters and the clad geometry.

Laser cladding using scanning optics - Effect of the powder feeding angle and gas flow on process stability

Powder feeding is one of the single most important factors which defines the qualitative outcome of the cladding process. If the powder feeding or a powder cloud suffers from any form of interference, it will directly affect the quality of the clad bead. This study thus focuses on the effect of the powder feeding angle and the flow rate of the powder carrying gas on powder cloud behavior under the scanned laser beam during the laser cladding process. In this study, powder feeding angles from 40 to 70 degrees were tested with powder feeding gas flow rates of 3 and 6 l/min and with laser scanning frequencies ranging from 80 to 150 Hz. Additive material used was 316L, and the substrate material was low alloyed steel. Powder cloud behavior was simultaneously monitored in situ with a high-speed camera and spectrometer. The results showed that the stability of the powder cloud was highly dependent on the tested parameters. Also, a direct correlation between the vaporization of the powder cloud and the increase of dilution was noticed.Powder feeding is one of the single most important factors which defines the qualitative outcome of the cladding process. If the powder feeding or a powder cloud suffers from any form of interference, it will directly affect the quality of the clad bead. This study thus focuses on the effect of the powder feeding angle and the flow rate of the powder carrying gas on powder cloud behavior under the scanned laser beam during the laser cladding process. In this study, powder feeding angles from 40 to 70 degrees were tested with powder feeding gas flow rates of 3 and 6 l/min and with laser scanning frequencies ranging from 80 to 150 Hz. Additive material used was 316L, and the substrate material was low alloyed steel. Powder cloud behavior was simultaneously monitored in situ with a high-speed camera and spectrometer. The results showed that the stability of the powder cloud was highly dependent on the tested parameters. Also, a direct correlation between the vaporization of the powder cloud and the increase ...

Embedded processing methods for online visual analysis of laser welding

Online monitoring and closed-loop control of laser welding offer great possibilities for achieving better weld quality. Earlier work on visual laser welding monitoring has mainly focused on aluminum and fairly thin steel used, for example, in car production. We extend this work by focusing on the automated analysis of the phenomena present in the laser welding of thick steel, where all of the phenomena related to the weld quality are still not well understood or controlled. This paper presents the implementation, test results and analysis for weld monitoring methods implemented on a compact smart camera system. The applied embedded sensor–processor platform allows for high-speed implementation of image capture and dynamic range compression, real-time seam tracking and spatter feature extraction. The paper describes experimental results from implemented real-time algorithms for seam tracking and spatter extraction and additional off-line analysis of methods for spatter tracking and seam widening detection, which are also feasible for future online hardware implementation. The results suggest that it is possible to integrate a compact laser welding analysis system, which achieves analysis rates that are sufficient for real-time process control.

Powder cloud behavior in laser cladding using scanning optics

Powder feeding is one of the single most important parameters that defines a qualitative outcome of the cladding process. This study focuses on how powder feeding angle and powder carrying gas flow rate affect the powder cloud behavior in laser cladding with scanning optics. Focus of this study is to provide the knowledge on how scanned laser beam affects the powder cloud and what kind of phenomena can occur during cladding process. In this study, powder feeding angles from 40° to 70° were tested with powder feeding gas flow rates of 3 and 6 l/min and with laser scanning frequencies ranging from 80 to 150 Hz. Powder material used was 316L, and the substrate material was low alloyed steel. The results showed that the stability of the powder cloud was highly dependent on the tested parameters. At a steep powder feeding angle, the powder cloud under laser radiation was strongly vaporized, emitting bright visible light. However, at gently sloping powder feeding angle, the powder cloud behavior was more stable...