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Laser fusion cutting commonly applies a high-pressurized nitrogen gas jet to blow the molten material out of the cut kerf. However, theoretical considerations suggest that the use of a plasma jet may offer some advantages over this conventional approach. In this preliminary investigation, the characteristics of a non-transferred plasma jet for the application as auxiliary gas in laser beam cutting are analyzed using numerical CFD simulation. Based on this study, a first prototype of a plasma jet generator was manufactured and used in initial cutting experiments on 6 mm thick AISI 304 stainless steel. Two different cooling concepts for the plasma torch were considered and investigated in practice. Suitable values for the nozzle exit diameter, the distance between the electrodes of the plasma torch, the auxiliary gas flow rate and the electric current were identified both model-based and experimentally. The achieved cutting performance is considered a proof-of-principle of the suggested approach of a plasma-assisted laser beam cutting process.

In this work, the impact of laser cutting and a subsequent pre-deformation on the fatigue behavior of AISI 304 was investigated. This represents a typical process chain in steel sheet manufacturing. Laser cutting trials with variating process parameters were evaluated with regard to resulting dross formation and surface roughness. A subsequent deformation can influence the appearance of the laser cut edge. Fatigue tests up to 108 load cycles were carried out on specimens which were processed with selected parameter sets. It can be shown that dross attachment is the failure relevant feature which sets up a shape dependent, crack inducing notch effect. Furthermore, pre-deformation can detach melt droplets and therefore increase the fatigue strength.

Factorial Design-of-Experiment analyses were applied for conventional and beam oscillation fiber laser cutting of 10 mm thick AISI 304 stainless steel. Considered factors in case of the conventional process with a static beam involve both laser and cutting gas parameters, in particular the laser power, the focal plane position, the cutting gas pressure, the nozzle stand-off distance as well as the nozzle diameter. The conducted trials were evaluated with respect to the achievable cutting speed, the cut kerf geometry and the cut edge roughness. Noticeable correlations between cut edge roughness and cut kerf geometry stimulated the development of a corresponding Computational Fluid Dynamics (CFD) model of the cutting gas flow through the kerf. A specific approach of data synchronization revealed that the experimentally determined roughness values do well correlate with numerically computed values of the backward directed component of the gas-induced shear stress and that the cut kerf geometry as internal process-inherent boundary condition influences relevant cutting characteristics more than controllable external cutting gas parameters. Finally, effects of circular beam oscillation were investigated by an additional factorial analysis considering the laser power, the focal plane position, the oscillation frequency and the oscillation amplitude as factors. The results demonstrate the potential of beam oscillation techniques for quality improvements in laser cutting.

The industrial application of laser materials processing methods is still far ahead of research into the physical phenomena occurring during these processes. In particular, the effect of high temperatures on the energy coupling of laser irradiation of metals is poorly understood. However, most processes in laser materials treatment involve temperatures above the melting point or even cause evaporation. This study therefore evaluates the effect of high temperatures on the energy coupling efficiency of stainless steel experimentally for three typical laser wavelengths (515 nm, 1.07 µm, 10.6 µm). As a result, it is shown that the effect of temperature on the energy coupling efficiency depends on the wavelength. In this context the relevance of the X-point phenomenon known from the emissivity theory could be demonstrated for laser material processing. Further, the effect of a process-induced surface oxidation is analyzed. At temperatures above 650 °C the energy coupling efficiency dramatically increases to around 65% at melting point and stays at this high level even in the liquid phase.

To increase the capability to weld copper using laser radiation, Direct Laser Interference Patterning is used for producing different surface textures with increased optical absorptivity. Depending on the depth of the produced patterns, the absorptivity of copper for a laser wavelength of 1070 nm was almost trebled from 4%, corresponding to a polished flat reference surface, to 11.3%. The last value equals the absorptivity of liquid copper, which permitted to obtain a temporally homogenous temperature distribution during the welding process, independently of the material temperature as well as material phase. Corresponding welding trials showed an increased stability and a continuous weld seam cross section using fiber lasers in the infrared.

Fiber laser fusion cutting trials on AISI 304 stainless steel sheets of 10 mm thickness were performed with the aim to gain further insights into the striation formation process on cut edges. The study is based on a factorial Design-of-Experiment (DoE) approach with consideration of laser power, focal plane position, gas pressure, nozzle stand-off and nozzle diameter as control factors. Analyzed responses include the achievable cutting speed, the cut kerf geometry and the cut edge roughness. In addition, numerical simulations of the cutting gas flow were carried out for adapted kerf geometries and gas parameters. The evaluation of these results reveals strong correlations between experimental roughness values and the numerically computed rear-directed shear stress component within the transition zone between cutting front and cut edge surface. This finding supports the hypothesis that the particular characteristics of the boundary layer zone of the cutting gas flow affects the structure and roughness of cut edges.

Efficient air flow control plays a crucial role for the reliability of remote laser beam welding applications. Local air flows are helpful to suppress unfavorable interactions between laser radiation and welding fumes as a result of absorption and/or scattering effects. On the other hand, local and additional global flows have to be applied for emission control to protect optical components and workpieces from contamination and to avoid harmful air pollution of the atmosphere. However, the appropriate design of complex air flow systems under the additional condition of preferably low overall gas consumption is still a challenging task because a high number of decisive factors and a multitude of possible interactions complicate the pure empirical selection and positioning of suitable flow components and the adjustment of the numerous control parameters. This paper presents the results of a combined and complementary approach of experimental and theoretical investigations to meet these challenges. The experimental work was focused on the aspects of interaction mechanisms between the laser beam and the welding fume. Besides the characterization of process emissions, some of the requirements of stable remote processing with maximum penetration depth are revealed. In contrast, the theoretical work describes a general methodology on how to support the optimization of the cabin air flow by means of Computational Fluid Dynamics (CFD) models in combination with Design-of-Experiment (DoE) approaches.Efficient air flow control plays a crucial role for the reliability of remote laser beam welding applications. Local air flows are helpful to suppress unfavorable interactions between laser radiation and welding fumes as a result of absorption and/or scattering effects. On the other hand, local and additional global flows have to be applied for emission control to protect optical components and workpieces from contamination and to avoid harmful air pollution of the atmosphere. However, the appropriate design of complex air flow systems under the additional condition of preferably low overall gas consumption is still a challenging task because a high number of decisive factors and a multitude of possible interactions complicate the pure empirical selection and positioning of suitable flow components and the adjustment of the numerous control parameters. This paper presents the results of a combined and complementary approach of experimental and theoretical investigations to meet these challenges. The exper...

A systematic experimental investigation of fiber laser cutting stainless steel in a wide range of material thicknesses is performed. The achievable maximum cutting speed, the resultant thermal efficiency of the process as well as the surface roughness of the cut edges were determined using different optical setups and beam geometries. In order to find out some reasons for characteristic features of the fiber laser cutting process also the cut kerf geometries were analyzed. The systematic investigation clarifies the most promising procedural possibilities for improvements of cutting performance and cut edge quality in fiber laser cutting of stainless steel.

The standard procedure for the calculation of the angle-dependent absorptivity consists of applying the well-known Fresnel formulas to the material property refractive index n and extinction coefficient k. However, the Fresnel formulas are only applicable for perfect smooth surfaces. Hitherto the effect of rough surfaces on absorptivity values and profiles are not thoroughly explored. Yet, this knowledge is vital for many kinds of theoretical consideration in computational models as they are applied in laser material processing, imaging and metrology. Therefore, we present experimental results on the angle-dependent absorptivity of stainless steel with five different surface finishes for fibre laser radiation with a 1.07 µm wavelength and for s- and p-polarisation separately. We can show that for probes which fulfil the modified Fraunhofer smoothness criterion at normal incidence (R z λ/32), the Fresnel formalism is applicable. For the tested probes with higher surface roughness, the real absorptivity differs considerably from this solution: the maximum of absorptivity at the pseudo Brewster angle is decreased and shifted towards lower inclinations. Furthermore, other effects are observed which are not explained by theoretical approaches like Fresnel or ray-tracing models.

Laser beam radiation and particularly its effects on irradiated materials are commonly specified in terms of intensity. However, laser beam radiation is also a carrier of considerable momentum as a result of high photon flow rates which give rise to a pressure acting at the surface of irradiated probes. Both characteristics, i.e. intensity and radiation pressure are directly related, and resultant effects cannot be easily distinguished from each other under real processing conditions. The current analysis presents theoretical estimations of the different pressure levels that are supposed to be involved in interactions with target surfaces in continuous wave and pulsed-wave laser applications. The results demonstrate that neglecting the radiation pressure seems not to be justified for an appropriate physical characterization and/or interpretation of effects in a number of established laser applications. It is concluded that there is a need to evaluate more profoundly the role of radiation pressure by appropriate experimental and theoretical studies.

Recently, laser assisted plasma arc welding applying a coaxial arrangement of both heat sources has been developed. This process is now utilised to investigate the impact of beam spot positioning in relation to the arc axis. Arc shapes, arc voltage signals and weld seam geometries for arrangements with a leading and trailing laser beam are compared. The analysis clearly demonstrates the crucial role of small variations in beam spot positioning on the characteristics and the performance of laser assisted plasma arc welding. The results provide new insights into the most efficient driving mechanisms for synergistic effects in laser arc processing.

First results of an experimental study on inert-gas fusion cutting stainless steel with different types of laser are presented. In particular, the cutting capabilities of a fiber and a CO2 laser beam with similar Rayleigh length have been compared as a function of material thickness with respect to achievable maximum cutting speed, cut edge surface roughness and cut kerf geometry. The most interesting finding achieved so far concerns the observation that the cut kerfs are nearly identical in size but differ qualitatively in shape for both laser teypes.

Plasma arc welding (PAW) is a modern welding technique for challenging joining tasks in a wide range of materials and plate thicknesses, A further improvement of the welding characteristics involving achievable welding speed, process stability and penetration depth is expected by an additional low energy laser beam with a maximum output power of 600 W, The paper presents an experimental and numerical analysis of the interaction between a plasma arc and a superimposed laser beam, The experiments are carried out with a non-concentric set-up of the plasma arc column and the laser beam, As results of bead-on-plate welding trials the cross-sectional weld areas were presented in order to demonstrate benefits of the combined process in comparison to separately conducted arc and laser welding, Fur thermore, high speed video images (1 kHz frame rate) with synchronized current and voltage recording (1 MHz frame rate) were used, The experimental results demonstrate a different behaviour for welding steel and aluminium, In case of welding aluminium, an arc guidance was observed whereas destabilization effects occur for welding ferrous alloys, A numerical magneto hydro dynamical (MHD) arc model with a concentric set-up of arc column and laser beam set-up was aimed to improve our understanding of relevant interaction phenomena between the plasma arc and the laser beam.

This work presents a new approach to the thermal modelling of direct laser interference patterning (DLIP). The spatial and temporal evolution of the temperature distribution within metallic substrates, which are irradiated by nanosecond pulses during the DLIP process, is computed by means of a smoothed particle hydrodynamics (SPH) method. The developed model considers the conversion of laser energy into heat within a very thin surface layer, heat conduction into the bulk material and the effect of latent heat during involved phase transformations. The importance of proper determination of characteristic SPH parameters and adequate spatial resolution of the computational domain on the accuracy of the numerical solution is discussed in detail. The computed temperature distributions are in good agreement with the results of a previously developed FEM model and correspond very well to simultaneously performed experimental investigations.

Laser cutting is still the most common industrial application of CO 2 laser systems but currently available high-power fibre lasers seem to be an attractive alternative to the established CO 2 laser sources for several cutting tasks. Practical experience has shown that fibre lasers enable significantly increased travel rates in the case of inert-gas fusion cutting. This advantage in achieving higher cutting speeds in comparison to CO 2 laser cutting is however a clear function of the sheet thickness to be cut. In the first part of this article, possible reasons for this experimental fact are derived from a thermodynamic analysis of the process with consideration of the specific beam absorption characteristics under cutting conditions. After that, in the second part, a quite new laser cutting variant, namely the gas-free remote cutting process that considerably benefits from the high beam quality of fibre laser systems, is presented.

A mathematical model for the simulation of characteristic weld pool phenomena during deep penetration laser beam welding based on a numerical solution of the conservation equations of energy, momentum and mass is presented. The modelling is carried out in dimensionless form and the various melt pool effects are investigated separately with regard to dependence on characteristic dimensionless groups. The developed three-dimensional simulation model allows numerical experiments in order to investigate the influence of the fluid dynamics in the fusion zone on the local temperature distribution. To assess the accuracy of the predicted weld pool shapes and sizes, the computed and experimentally determined seam widths of laser beam welded joints are compared for welds on different steels.

The development of a steady-state process model for a numerical study of transport phenomena in the fusion zone of deep penetration laser beam welded joints is described. Based on the conservation equations of energy, momentum, and mass in dimensionless form, the three-dimensional modeling considers viscous, buoyancy, and friction forces as well as surface tension gradients. The developed simulation program enables the prediction of the local temperature and velocity distribution in the molten material. Consequently, the resultant weld pool dimensions dependent on the characteristic dimensionless groups can be derived.

Achievable benefits in hybrid laser-arc welding are closely related to suitable parameter settings. Basic optimizations consequently need a profound understanding of the relevance of involved interaction mechanisms. These are however differently evaluated and discussed in literature. This paper gives an over-view on the most popular hypotheses in the field of laser-arc processing. The importance of direct interactions between laser radiation and arc plasma as well as the role of metal evaporation are particularly considered by own experimental and numerical investigations. The results of this analysis suggest that these phenomena cannot be regarded as main driving mechanisms for synergistic achievements in hybrid laser-arc welding with respect to process stability and performance.Achievable benefits in hybrid laser-arc welding are closely related to suitable parameter settings. Basic optimizations consequently need a profound understanding of the relevance of involved interaction mechanisms. These are however differently evaluated and discussed in literature. This paper gives an over-view on the most popular hypotheses in the field of laser-arc processing. The importance of direct interactions between laser radiation and arc plasma as well as the role of metal evaporation are particularly considered by own experimental and numerical investigations. The results of this analysis suggest that these phenomena cannot be regarded as main driving mechanisms for synergistic achievements in hybrid laser-arc welding with respect to process stability and performance.

The high power laser market has been remarkably influenced by the introduction of high-brightness lasers, i.e., laser sources offering a high optical output power in combination with a high beam quality or a low beam parameter product, respectively. These features are primarily exhibited by fiber and disk laser systems, but diode lasers are also increasingly available with improved beam quality and higher output levels. The development of new processes that make use of the advantages of high- brightness lasers was intensively pursued in recent years and some examples of innovative solutions were given in this paper.

Results of an experimental study are presented in which the impact of a low power laser beam on the stability behaviour of plasma arcs was investigated. Both heat sources were arranged in a recently developed coaxial set-up. Bead on plate welding trials on AISI 304 stainless steel sheets demonstrated that the additional laser beam is capable of extending existing limitations of low current plasma arc welding processes with respect to realisable welding speeds. In particular, an effective stabilisation of the anodic arc attachment under conditions of direct current electrode negative plasma arc welding was achieved by use of a laser beam with only 100 W output power. As a result of a performed stability analysis, the particular conditions for arc stabilisation are specified and co nclusions about the most probable physical reasons for the stabilising action of the laser beam are drawn.

A plasma arc and a low-power/high beam quality laser beam were coaxially combined into one process in order to obtain a more efficient and stable arc for thin sheet welding applications. Theoretical discussion of interaction mechanisms between the laser beam and the plasma arc and results of bead-on-plate welding trials carried out on AISI 304 stainless steel will be presented. Measurements were made of electrical and geometrical arc properties with and without assistance from the laser beam. Additionally, the impact of the laser beam on the weld seam geometry was evaluated. The results showed that the use of the additional low-power laser beam is capable of producing significant process improvements in comparison to the individual plasma arc process alone with respect to arc stability and welding performance.

The development of appropriate processes aims to shorten the cycle time of the production of parts, based on fiber reinforced polymers. Here, the laser can be a tool for the future, because the wear- and tool free processing expands the area of treatment processes. But laser processing is a challenging process due to the strong differing thermo-optical properties of fiber- and matrix material. The present paper shows a solution to take these limitations into account. An experimental setup is applied to combine radiation with 1 and 10 μm. Thereby, the parameter and application window is expanded by the mixing ratio of radiation with both wavelengths. The present paper will show optimized parameters for different kind of materials as a result of this novel type of processing.

Details and results of experimental investigations of a laser-supported plasma arc welding process are presented. The particular feature of the realized experimental set-up is the coaxial arrangement of a single-mode fibre laser beam through a hollow tungsten electrode in combination with a modified plasma welding torch. The analysis of the welding capabilities of the combined laser-arc source comprises high-speed video recordings of the arc shape and size, corresponding simultaneous measurements of the arc voltage as well as an evaluation of the resultant weld seam geometries. Results of welding trials on different types of steel and aluminum alloys are discussed. The corresponding investigations reveal that a fibre laser beam with a wavelength of 1.07 microns can have a crucial impact on the arc and welding characteristics for both categories of materials even at very low laser power output levels. Beneficial effects are especially observed with high welding speeds. In that particular case the arc root and therefore arc column can be substantially stabilized and guided by the laser-induced hot spot.

Diffraction-limited high power lasers represent a new generation of lasers for materials processing, characteristic traits of which are: smaller, cost-effective and processing "on the fly". Of utmost importance is the high beam quality of fiber lasers which enables us to reduce the size of the focusing head incl. scanning mirrors. The excellent beam quality of the fiber laser offers a lot of new applications. In the field of remote cutting and welding the beam quality is the key parameter. By reducing the size of the focusing head including the scanning mirrors we can reach scanning frequencies up to 1.5 kHz and in special configurations up to 4 kHz. By using these frequencies very thin and deep welding seams can be generated experienced so far with electron beam welding only. The excellent beam quality of the fiber laser offers a high potential for developing new applications from deep penetration welding to high speed cutting. Highly dynamic cutting systems with maximum speeds up to 300 m/min and accelerations up to 4 g reduce the cutting time for cutting complex 2D parts. However, due to the inertia of such systems the effective cutting speed is reduced in real applications. This is especially true if complex shapes or contours are cut. With the introduction of scanner-based remote cutting systems in the kilowatt range, the effective cutting speed on the contour can be dramatically increased. The presentation explains remote cutting of metal foils and sheets using high brightness single mode fiber lasers. The presentation will also show the effect of optical feedback during cutting and welding with the fiber laser, how those feedbacks could be reduced and how they have to be used to optimize the cutting or welding process.

Results of experimental investigations on disk and CO 2 laser beam fusion cutting cold-work tool steel 90MnCrV8 are presented. The study was performed with the aim to detect features of the cut front geometry and differences in the corresponding absorptivity behavior as a function of the laser wavelength. Longitudinal sections of the cut front were prepared for different sheet thicknesses, focal plane positions, and cutting speeds. The digitalization of the geometrical cut front data enabled the determination of local inclination angles and the calculation of corresponding Fresnel absorptivity values. The analysis revealed that particular areas of the cut front geometry are preferably inclined to values close to the Brewster angle which offer the theoretical maximum absorptivity for both l aser types.

A new welding heat source consisting of a plasma arc and a coaxially superimposed low-power laser beam was developed. For this purpose, a single-mode fiber laser beam was guided through the hollow tungsten electrode of a commercial plasma welding torch. The capabilities of the corresponding welding process were experimentally analyzed for bead-on-plate welding trials on steels and aluminum alloys. Besides the evaluation of the resultant seam geometries also the behavior of the arc under the action of the additional laser beam was studied by means of arc voltage measurements and high-speed camera observations. The results of this study demonstrate so far beneficial improvements of the combined process in comparison to the single welding techniques. First, the melting efficiency can be significantly increased for particular parameter constellations. Secondly, the additional laser beam is very capable of stabilizing the arc attachment under conditions of low arc currents and/or high welding speeds. The experimental results also provided some new insights into possible physical reasons of the observed laser-arc interactions.A new welding heat source consisting of a plasma arc and a coaxially superimposed low-power laser beam was developed. For this purpose, a single-mode fiber laser beam was guided through the hollow tungsten electrode of a commercial plasma welding torch. The capabilities of the corresponding welding process were experimentally analyzed for bead-on-plate welding trials on steels and aluminum alloys. Besides the evaluation of the resultant seam geometries also the behavior of the arc under the action of the additional laser beam was studied by means of arc voltage measurements and high-speed camera observations. The results of this study demonstrate so far beneficial improvements of the combined process in comparison to the single welding techniques. First, the melting efficiency can be significantly increased for particular parameter constellations. Secondly, the additional laser beam is very capable of stabilizing the arc attachment under conditions of low arc currents and/or high welding speeds. The exper...

A few years ago, the introduction of high-brightness lasers remarkably influenced the high-power laser market. Among others, performance increases in different application areas could be achieved and completely new processes were developed by use of the capabilities of these new sources. On the other hand, the available high intensities of high-brightness lasers required innovative solutions for mastering related issues. Both aspects are considered in this paper. In the first part, novel approaches for the prevention of optical feedbacks as well as the measurement and suppression of the focal shift are introduced. The second part presents diverse application examples. Remote cutting with highest processing speeds and welding with high-frequent beam oscillations will demonstrate the enhanced use of high-brightness lasers in combination with recent scanner technology. Another application demonstrates how the low divergence of a single-mode fiber laser can be used to enhance a plasma arc welding process. The direct laser interference patterning (DLIP) with high brightness pulsed systems is presented as an efficient method for patterning different structures onto the surface of a workpiece, which opens a variety of new application possibilities in tribology, bio and medical technology and optical design. Finally, innovative solutions for laser cladding processes with improved efficiency are discussed.

In recent years, several studies on laser beam fusion cutting demonstrated significant differences in the characteristics of the well-established CO2 laser cutting and cutting with solid-state disk and fibre lasers. The absorptivity behaviour of metals shows essential quantitative differences for the corresponding wavelengths of both laser sources as a function of the inclination angle between the laser beam and the material to be irradiated. In order to further the understanding of the involved phenomena, a series of cutting experiments with CO2 and disk lasers was carried out. Similar geometry of CO2 and disk laser beam in terms of focus diameter and Rayleigh length was used. In this work, the two dimensional stationary geometric shape of the cutting front is acquired by the longitudinal sections of the cut specimen. The cutting front geometry and the corresponding local inclination angle are related with the absorptivity calculated in each point of the cutting front. The effects of various laser processing parameters, as focal position and cutting speed, on the geometric shape of the cutting front have been analyzed systematically on steel sheet 5 and 8 mm thick.In recent years, several studies on laser beam fusion cutting demonstrated significant differences in the characteristics of the well-established CO2 laser cutting and cutting with solid-state disk and fibre lasers. The absorptivity behaviour of metals shows essential quantitative differences for the corresponding wavelengths of both laser sources as a function of the inclination angle between the laser beam and the material to be irradiated. In order to further the understanding of the involved phenomena, a series of cutting experiments with CO2 and disk lasers was carried out. Similar geometry of CO2 and disk laser beam in terms of focus diameter and Rayleigh length was used. In this work, the two dimensional stationary geometric shape of the cutting front is acquired by the longitudinal sections of the cut specimen. The cutting front geometry and the corresponding local inclination angle are related with the absorptivity calculated in each point of the cutting front. The effects of various laser proces...

In heat conduction mode laser beam processes on steel materials only a fraction of the beam energy induces heat in the irradiated material. If the laser emits radiation with a wavelength of λ=1070 nm, 35 % of the beam energy is absorbed. The percentage of the beam energy, which is used for the melting process, is even smaller. A significant amount of this energy is transported into the material by heat conduction and convection without melting the material. With optimized beam spot geometries, optimized intensity distributions respectively, improved energy efficiencies can be achieved. For a heat conduction mode laser beam welding (HCMLB) process it is shown in this paper, that the intensity distribution has an impact on the energy transport mechanisms. Hereby, the welding depth and the overall energy efficiency were enhanced. Single and twin beam spots with Gaussian distributed intensities were used in experiments on stainless steels. The results have been compared for their energy efficiencies and seam geometries. Finite difference (FD) simulations based on experimental conditions were conducted for single beam spots to identify the physical mechanisms, which are responsible for the observed changes of the welding process. For modeling the energy transport phenomena heat conduction, radiation, thermal and Marangoni convection have been taken into account. In addition, non-linear behavior of the surface-tension influencing the Marangoni convection was respected in the FD simulation. The melt pool geometry, flow and the surface-temperature were calculated. Results of the FD simulation have been compared with the experimental data.In heat conduction mode laser beam processes on steel materials only a fraction of the beam energy induces heat in the irradiated material. If the laser emits radiation with a wavelength of λ=1070 nm, 35 % of the beam energy is absorbed. The percentage of the beam energy, which is used for the melting process, is even smaller. A significant amount of this energy is transported into the material by heat conduction and convection without melting the material. With optimized beam spot geometries, optimized intensity distributions respectively, improved energy efficiencies can be achieved. For a heat conduction mode laser beam welding (HCMLB) process it is shown in this paper, that the intensity distribution has an impact on the energy transport mechanisms. Hereby, the welding depth and the overall energy efficiency were enhanced. Single and twin beam spots with Gaussian distributed intensities were used in experiments on stainless steels. The results have been compared for their energy efficiencies and seam ...

In recent years, several studies on laser beam fusion cutting demonstrated significant differences in the characteristics of the well-established CO2 laser cutting and cutting with solid-state disk and fiber lasers. The reasons for the observed differences in cutting efficiency and cut edge quality are still the subject of the current research and not finally clarified. In order to further the understanding of the involved phenomena, a series of cutting experiments with CO2 and disk lasers was carried out using a Design of Experiment (DoE) approach. The particular feature of the applied experimental setup was the similar geometry of both the CO2 and the disk laser beam with comparable values of the focus diameter and the Rayleigh length. Cutting trials on cold work steel test specimens with different sheet thicknesses were performed. The extensions of the generated cut kerf and of the heat-affected zone as well as the recast layer were analyzed in order to reach a better understanding of the physical mechanisms which take part in the cutting process. The experimental evaluation of transmitted and reflected energy losses throughout the kerf was realized by means of PMMA (Polymethylmethacrylate) blocks placed under the sheet during the cutting process.

Inert-gas laser beam fusion cutting is an established thermal cutting technology for stainless and other high-alloyed steels. At the present time, CO2 lasers are particularly applied for corresponding cutting applications but the nowadays available solid-state disk and fiber lasers seem to be an attractive alternative as efficient cutting heat sources due to their advantages in power efficiency, beam guidance and beam quality. It is consequently anticipated that disk and fiber lasers possess a great potential to change the limits of the cutting performance.However, comparative experimental studies have also shown some distinct differences in the process behavior of CO2, disk and fiber lasers cutting which are not easy to understand at the first sight. Consequently, the available cutting data were thermodynamically analyzed. The theoretical investigations revealed some possible reasons for the detected quantitative and qualitative differences between the cutting results with different laser sources and the achieved deeper understanding of the relevant interactions between the beam properties and the cutting efficiency can be useful for the further establishment of disk and fiber laser cutting.Inert-gas laser beam fusion cutting is an established thermal cutting technology for stainless and other high-alloyed steels. At the present time, CO2 lasers are particularly applied for corresponding cutting applications but the nowadays available solid-state disk and fiber lasers seem to be an attractive alternative as efficient cutting heat sources due to their advantages in power efficiency, beam guidance and beam quality. It is consequently anticipated that disk and fiber lasers possess a great potential to change the limits of the cutting performance.However, comparative experimental studies have also shown some distinct differences in the process behavior of CO2, disk and fiber lasers cutting which are not easy to understand at the first sight. Consequently, the available cutting data were thermodynamically analyzed. The theoretical investigations revealed some possible reasons for the detected quantitative and qualitative differences between the cutting results with different laser sources and the...

Fiber lasers offer distinct advantages over established laser technology with respect to power efficiency, beam guidance and beam quality. Consequently, the potential of these new laser beam sources will be increasingly exploited for laser cutting applications that are conventionally carried out with CO2 lasers.However, theoretical estimates of the effective absorptivity at the cut front suggest that the shorter wavelength of the fiber laser in combination with its high focusability seems to be advantageous for thin sheet metal cutting only whereas the CO2 laser is still capable of cutting thicker materials more efficiently. This surprising result is a consequence of the absorptivity behavior of metals that shows essential quantitative differences for the corresponding wavelengths of both laser sources as a function of the angle of incidence between the laser beam and the material to be irradiated. In evaluation of the revealed dependencies, solution strategies were proposed and experimentally verified that could be useful to increase the efficiency of fiber laser cutting processes of thicker metal sheets.Fiber lasers offer distinct advantages over established laser technology with respect to power efficiency, beam guidance and beam quality. Consequently, the potential of these new laser beam sources will be increasingly exploited for laser cutting applications that are conventionally carried out with CO2 lasers.However, theoretical estimates of the effective absorptivity at the cut front suggest that the shorter wavelength of the fiber laser in combination with its high focusability seems to be advantageous for thin sheet metal cutting only whereas the CO2 laser is still capable of cutting thicker materials more efficiently. This surprising result is a consequence of the absorptivity behavior of metals that shows essential quantitative differences for the corresponding wavelengths of both laser sources as a function of the angle of incidence between the laser beam and the material to be irradiated. In evaluation of the revealed dependencies, solution strategies were proposed and experimentally verified th...

Heat and mass transfer in arc and beam welding is considered. The main objectives are analysis of the heat transfer in the weld pool and the workpiece and to demonstrate how computer simulation can be used as a tool to predict the temperature distribution as the determining element of the heat effects of welding. Simulation results of two particular welding processes are compared and validated with measurements.

Conduction-limited laser beam welding processes are characterized by moderate laser intensities below the threshold intensity necessary for evaporation and key-hole formation. The absorbed energy at the surface of the weld specimen is transferred into the material by heat conduction and convection. These processes are relatively slow. Consequently, the penetration depth of the fusion zone and/or the possible welding speeds are limited to considerably lower values than in deep penetration laser beam welding. Successful strategies for increasing the achievable weld depths bases on a control of the weld pool mass flow because the resultant convective heat transfer is the dominant heat transfer mechanism within the molten zone of many metallic materials. The melt pool flow is in turn dominated by the Marangoni effect, i.e. the development of a mass flow caused by surface tension gradients at the free surface of a viscous or liquid material. The strength and direction of this mass flow can be controlled either by the concentration of surface-active agents that change the temperature-dependence of the surface tension or by a control of the temperature distribution at the weld pool surface. A theoretical investigation of such optimization strategies requires a three-dimensional simulation of the melt pool formation during heat conduction mode laser beam seam welding.Conduction-limited laser beam welding processes are characterized by moderate laser intensities below the threshold intensity necessary for evaporation and key-hole formation. The absorbed energy at the surface of the weld specimen is transferred into the material by heat conduction and convection. These processes are relatively slow. Consequently, the penetration depth of the fusion zone and/or the possible welding speeds are limited to considerably lower values than in deep penetration laser beam welding. Successful strategies for increasing the achievable weld depths bases on a control of the weld pool mass flow because the resultant convective heat transfer is the dominant heat transfer mechanism within the molten zone of many metallic materials. The melt pool flow is in turn dominated by the Marangoni effect, i.e. the development of a mass flow caused by surface tension gradients at the free surface of a viscous or liquid material. The strength and direction of this mass flow can be controlled either...

Laser cutting plays a huge role in the field of laser materials processing. An excellent beam quality, a great laser power and a high absorption rate are the most important ones in order to reach high cutting speeds in combination with high cutting edge qualities. Providing the mentioned characteristics, the fibre laser has the biggest potential. Studies at Fraunhofer IWS have shown, that cutting with fibre lasers is promising in order to reach high cutting rates and cutting edge qualities [1][2][3].Beam qualities below 2.5 mm mrad at a wavelength of about 1 µm and a laser power in the area of several kW enable new possibilities in laser processing. With such characteristics it is possible to cut thin sheets with very high cutting rates. However, these cutting speeds cannot be achieved with linear drives, especially in the case of cutting contours. Thus the cutting speeds are currently limited by the dynamic of the used handling system. Cutting speeds limited by the ability of the laser are much higher. A solution to minimize this gap is described in the presented research paper.This paper describes a smart solution using the advantages of high brightness lasers – the remote cutting. Firstly a short introduction of the process is given and the experimental equipment will be explained. Disclaiming any cutting gas a nozzle is no longer necessary. Thereby the working distance does no longer depend on the distance between the nozzle and the work piece. In combination with a 2D-Scanner the laser beam is flexible in the working field of the scanner. Afterwards a thermodynamic characterization of the remote cutting process is carried out. The investigations show a process, which is completely different from conventional laser cutting. The cutting kerf is generated by a layer by layer ablation process. However, an example shows that contour cutting speeds of about 100 m/min are possible.Laser cutting plays a huge role in the field of laser materials processing. An excellent beam quality, a great laser power and a high absorption rate are the most important ones in order to reach high cutting speeds in combination with high cutting edge qualities. Providing the mentioned characteristics, the fibre laser has the biggest potential. Studies at Fraunhofer IWS have shown, that cutting with fibre lasers is promising in order to reach high cutting rates and cutting edge qualities [1][2][3].Beam qualities below 2.5 mm mrad at a wavelength of about 1 µm and a laser power in the area of several kW enable new possibilities in laser processing. With such characteristics it is possible to cut thin sheets with very high cutting rates. However, these cutting speeds cannot be achieved with linear drives, especially in the case of cutting contours. Thus the cutting speeds are currently limited by the dynamic of the used handling system. Cutting speeds limited by the ability of the laser are much higher. A...

In recent years, some promising results about laser beam welding with forced beam oscillation were published. Characteristic feature of this technology is the purposeful beam manipulation by an oscillatory beam deflection in superposition to the commonly uniform and rectilinear feed rate of a conventional laser beam welding process. Due to the increased number of welding variables, the application of oscillation techniques offers manifold possibilities to influence the energy deposition in dependence on the chosen oscillation regime. In such a way, the process behavior as well as the resultant properties of the weld can be favorably changed.An appropriate understanding of the interaction among the relevant welding and oscillation parameters was achieved through the modeling of the underlying physical relationships and the simulation of the transient energy deposition during beam oscillation procedures. Different deflection methods and various one-and two-dimensional oscillation patterns have been allowed for. By derivation of suitable dimensionless quantities, the developed model facilitates the distinction and characterization of different process regimes as well as the determination of appropriate oscillation parameters as function of the chosen welding variables.In recent years, some promising results about laser beam welding with forced beam oscillation were published. Characteristic feature of this technology is the purposeful beam manipulation by an oscillatory beam deflection in superposition to the commonly uniform and rectilinear feed rate of a conventional laser beam welding process. Due to the increased number of welding variables, the application of oscillation techniques offers manifold possibilities to influence the energy deposition in dependence on the chosen oscillation regime. In such a way, the process behavior as well as the resultant properties of the weld can be favorably changed.An appropriate understanding of the interaction among the relevant welding and oscillation parameters was achieved through the modeling of the underlying physical relationships and the simulation of the transient energy deposition during beam oscillation procedures. Different deflection methods and various one-and two-dimensional oscillation patterns have been allowed ...