Antti Salminen

Inert gas cutting of thick-section stainless steel and medium-section aluminum using a high power fiber laser

Inert gas assisted laser cutting of 10 mm stainless steel plate and 4 mm aluminum sheet was performed with a 5 kW fiber laser. The effects of laser power, cutting speed, focal point position, and assist gas pressure on the cutting performance and cut quality were investigated. Clean cut surfaces without or with minimal dross were achieved with some combinations of process parameters and attempts were made to define parameter windows in terms of cutting speed and laser power for good quality cutting. The maximum cutting speeds for acceptable cut quality were determined at different power levels. The range at which complete through cutting could be achieved (so-called parameter window) was limited upwards by insufficient power intensity to obtain through cutting at high cutting speeds and downwards by heat conduction at slow cutting speeds. The effects of focal point position and assist gas pressure on the striation pattern (cut surface roughness) were also examined. Low surface roughness was achieved with the focal point position inside the workpiece showing the need for a wider kerf for better melt ejection in thick-section metal cutting. There was also a reduction in surface roughness with increase in assist gas pressure, but there was no significant reduction in surface roughness above the gas pressure of 16 bar, which could be due to the gas flow dynamics inside the narrow cut kerf at high assist-gas pressures.

The effect of the relative location of laser beam with arc in different hybrid welding processes

Hybrid welding requires that several parameters are properly adjusted in order to reach high weld quality. One of the main setup parameters of hybrid welding is the order of the different power sources. The selection partly depends on the results desired for welding whether it is gap bridging, penetration depth, welding speed, melting efficiency, process stability, control of weld width, porosity reduction or weld appearance. In this paper we have studied how the placement of the different sources in laser hybrid welding influences the overall weld quality. The paper is based on an analysis of the results of various studies carried out by different research groups. The process is analyzed with regard to process parameters, the type and thickness of the base material, power and beam quality together with the optical parameters of the laser system applied.Hybrid welding requires that several parameters are properly adjusted in order to reach high weld quality. One of the main setup parameters of hybrid welding is the order of the different power sources. The selection partly depends on the results desired for welding whether it is gap bridging, penetration depth, welding speed, melting efficiency, process stability, control of weld width, porosity reduction or weld appearance. In this paper we have studied how the placement of the different sources in laser hybrid welding influences the overall weld quality. The paper is based on an analysis of the results of various studies carried out by different research groups. The process is analyzed with regard to process parameters, the type and thickness of the base material, power and beam quality together with the optical parameters of the laser system applied.

Visual measurement and tracking in laser hybrid welding

This paper presents a novel system for the automatic analysis of a hybrid welding process. High-speed imaging and laser illumination are used to measure the regularity of electric arc frequency and flight directions of filler metal droplets. A fuzzy c-means clustering method is used to detect arcs and segment the video sequences. The droplets are localized by combining principal component analysis and a support vector machine classifier. The flight of a droplet is tracked using Kalman filtering. Experiments indicate that the system is able to track the flights of droplets and to determine the regularity of the arc frequency with a high accuracy if the imaging conditions are stable.

Cutting of Stainless Steel With Fiber and Disk Laser

Laser cutting is a major application of laser materials processing. The cutting is usually performed with CO2-laser due to its good beam quality and its relatively low costs of ownership. Ever since entering the market the high power solid state lasers have been expected to achieve a dominating role also in cutting applications. This has not happened mainly due to the fact that beam quality has not been sufficient. The introduction of new generation of solid state lasers has raised the interest of use of them in cutting application. This study was concentrated on use of fiber and disk lasers, the new laser types with a high beam quality, in cutting of austenitic stainless steel. The performance of these new lasers at power level of 4 kW was compared with CO2-laser in respect of cutting speed, kerf width, kerf edge roughness and perpendicularity (squarness) in order to validate the potential of both of the new lasers against traditional CO2-laser. The results showed that the new lasers offer a great potential in improving the productivity of cutting phase with an acceptable edge quality. This is emphasized in thin sheets of 1.3 and 2.3 mm thickness. In that case the width of the cut kerf is considerably narrow especially when using a fiber laser. In case of thicker sections (4.3 and 6.2 mm) the focal length was increased in order to reach an acceptable cut quality still providing a competitive cutting speed in comparison to a CO2-laser. The fiber laser was the fastest cutting laser in case of each thickness. The results were very promising and it can be stated that these new laser types have a great potential in cutting and will probably gain a considerable market share not only in 3D cutting applications but also in ordinary flat sheet cutting.Laser cutting is a major application of laser materials processing. The cutting is usually performed with CO2-laser due to its good beam quality and its relatively low costs of ownership. Ever since entering the market the high power solid state lasers have been expected to achieve a dominating role also in cutting applications. This has not happened mainly due to the fact that beam quality has not been sufficient. The introduction of new generation of solid state lasers has raised the interest of use of them in cutting application. This study was concentrated on use of fiber and disk lasers, the new laser types with a high beam quality, in cutting of austenitic stainless steel. The performance of these new lasers at power level of 4 kW was compared with CO2-laser in respect of cutting speed, kerf width, kerf edge roughness and perpendicularity (squarness) in order to validate the potential of both of the new lasers against traditional CO2-laser. The results showed that the new lasers offer a great potent...

Effect of welding parameters and the heat input on weld bead profile of laser welded T-joint in structural steel

The high power fiber laser has become one of the most efficient energy sources for deep penetration welding processes used in heavy manufacturing and marine industries. Combinations of cost-efficient, easily automatable process together with fairly mobile and flexible welding equipment have raised high expectations for improved quality and economic feasibility. In this study, the fillet welding of a low alloyed structural steel was studied using a 10 kW fiber laser. Plates of 8 mm thick AH36 were welded as a T-joint configuration in flat (1F) and horizontal (2F) positions using either an autogenous laser welding or a hybrid laser arc welding process. The effect of heat input on the weld bead geometry was investigated using one variable at a time approach. The impact of single process parameter such as laser power of 4.5–6 kW, welding speed of 0.5–2.5 m/min, beam inclination angle of 6°–15°, focal point position of −2 to +2 mm, and welding positions of 1F and 2F were studied. All welds were visually evaluated for weld imperfections described in EN ISO 13919-1 standard. Penetration depth, geometries of the fusion and heat affected zones, and hardness profiles were measured. Produced joints have a high depth to width ratio and a small heat affected zone; full penetration welds with acceptable weld quality on both sides of the joint were produced. The parameter configurations for optimizing the welding processes are proposed.

Evaluation of Different Monitoring Methods of Laser Additive Manufacturing of Stainless Steel

Different monitoring methods for the laser additive manufacturing process were studied in this study. Possibilities and downfalls of three different methods were compared to each other to define their applicability in future on-line and adaptive monitoring use in LAM processes. The material used on all the LAM process tests was EOS StainlessSteel PH1 in fine powder form. In this study, e.g. parameters like scanning speed, layer thickness and hatch space were tested. Based on the results of this study, the pyrometer seems to be more easily adaptable to continuous monitoring than the spectrometer or systems based on active illumination imaging system. It seems that the pyrometer is a promising method for quality control. The ability to control quality through on-line measurements can be further utilized in future e.g. for on-line quality control and dynamic process control, i.e. the ability to change and correct parameters on the fly.

Fiber Laser Welding of Direct-Quenched Ultrahigh Strength Steels: Evaluation of Hardness, Tensile Strength, and Toughness Properties at Subzero Temperatures

The recently developed direct-quenched ultrahigh strength steels (UHSS) possess an appropriate combination of high tensile strength and toughness properties at subzero temperatures down to −80 °C, while simultaneously having low carbon contents, which is beneficial for weldability. In this study, butt joints of Optim 960 QC direct-quenched UHSS with a thickness of 8 mm were welded with a 10 kW fiber laser to evaluate the characteristics of the joints within the range of low to high heat inputs possible for this welding process. The mechanical properties of the joints were studied by subjecting the specimens to a number of destructive tests, namely, hardness and tensile testing, as well as impact toughness testing at temperatures of −40 °C and −60 °C. It was found that high quality butt joints with superior tensile strength and good impact toughness properties at −40 °C could be obtained. However, having a high level of all these properties in the joint narrows the process parameters’ window, and the heat input needs to be strictly controlled.

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.

Monitoring of temperature profiles and surface morphologies during laser sintering of alumina ceramics

Abstract Additive manufacturing of alumina by laser is a delicate process and small changes of processing parameters might cause less controlled and understood consequences. The real-time monitoring of temperature profiles, spectrum profiles and surface morphologies were evaluated in off-axial set-up for controlling the laser sintering of alumina ceramics. The real-time spectrometer and pyrometer were used for rapid monitoring of the thermal stability during the laser sintering process. An active illumination imaging system successfully recorded the high temperature melt pool and surrounding area simultaneously. The captured images also showed how the defects form and progress during the laser sintering process. All of these real-time monitoring methods have shown a great potential for on-line quality control during laser sintering of ceramics.

Quality aspects in remote laser cutting

The new single-mode fibre lasers have made it possible to work with long working distances and high power densities in new ways. This enables a process called remote laser cutting, which is still quite new a process in the field of laser cutting but is now already proven to be a successful process for cutting various materials and forms. Process parameters of remote laser cutting differ from those of traditional laser cutting because of differences in basic process principles. Process parameters and performance also vary significantly between different materials and equipment. Parameters have to be optimized for each system in order to achieve the best cut quality. This study focuses on defining the possible quality of the remote laser-cut edge and its comparison to that of conventional CO2 laser cutting with equivalent materials. In this study, various metals were cut with the remote laser cutting process. The quality of the cut kerfs was measured by kerf surface roughness and perpendicularity, kerf width, 90° inner corner cut edge sharpness and burr height. When applicable, the comparison was carried out according to the quality standard for thermal cutting.