Andreas Wetzig

A comparative study of cut front profiles and absorptivity behavior for disk and CO2 laser beam inert gas fusion cutting

Results of experimental investigations on disk and CO2 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 laser types.

A comparative study on fusion cutting with disk and CO2 lasers

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.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 mech...

Localized investigation of magnetic bulk property deterioration of electrical steel: Analysing magnetic property drop thorough mechanical and laser cutting of electrical steel laminations using neutron grating interferometry

The knowledge of manufacturing related magnetic property degeneration in electrical steel laminations is essential for selecting correct obstructing material grades and designing efficient electrical machines. Until now these effects stay undiscovered due to the lack of adequate investigation methods that reveal local information on troubling lamination areas. Here we show how the use of a non-destructive testing method based on a neutron grating interferometry setup provides spatially-resolved information about the local bulk domain wall density. Different representative manufacturing techniques are compared in terms of magnetic flux density deterioration such as punching, mechanically cutting by guillotine as well as laser fusion cutting applying industrial high power laser beam sources.

Combining remote ablation cutting and remote welding: opportunities and application areas

Remote Ablation Cutting (RAC) is a most promising process for cutting thin metal sheets in the automotive, medical and consumer industry. Characteristically for the RAC are high cutting velocities for metal foils as well as material processing of box structures without spatter contamination at the inner surface. Furthermore, the system technology for RAC can also be used for other processes, like welding and marking. Thereby, the flexibility of a production unit is increased, compared to a conventional cutting system. Despite several advantages, the RAC is not yet state of the art in industrial production. Reasons for that are lacking knowledge in the area of process itself and in possible application areas. In this paper a conceptual model of the ablation and the ejection mechanism is presented. It consists of the laser beam absorption within the processing zone, the melt ejection from the kerf and the resulting spatter formation above the part surface. Besides the model, the process boundaries and limitations are identified using empirical data. Addressing possible applications, the following samples of different industrial areas are introduced to show the potential of the process: Cutting of heat exchanger plates, cylinder head seals, and cathode/anode material for Li-Ion-Batteries. Furthermore, a concept and first results of the combined processing of remote cutting and welding with one laser and one scanner optics are presented.

Energetic efficiency of remote cutting in comparison to conventional fusion cutting

The remote cutting technique provides an enormous potential in terms of cutting speeds when working on thin sheets. Even on contour cutting speeds about 100 m/min are realizable. Working without any cutting gas, the material of the cutting kerf must be vaporized partially. It is evident that the energy input must be higher than for pure melting of the cutting kerf’s material. In order to characterize laser cutting processes in terms of energetic efficiency, the severance energy can be used. This parameter depends on the necessary laser power to cut a defined sheet thickness at a certain cutting speed. Hitherto, it was used to compare different laser cutting processes using different laser beam sources when cutting straight lines. In order to characterize different processes for cutting real contours, the geometry of the part to be cut is also important. The complexity of a part can be characterized by the agility. The target of this paper is to combine the severance energy and the agility in order to comp...

Experimental investigation on the cut front geometry in the inert gas laser fusion cutting with disk and CO2 lasers

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...

Laser welding with long focal length optics

Industrial lasers have gained acceptance as effective and reliable production tools. However, up until recent years either power or beam quality limitations have constrained welding focus optics to relatively short focal lengths. Since the advent of CO2 lasers with excellent beam quality (M2 up to 1.2) a few years ago, now both relatively high power and near perfect beam quality are available in the same laser. This has allowed the use of extremely long focal lengths for laser welding, even for keyhole welding, which (for extremely long focal lengths) was something unheard of just a few years ago.The unusually long focal length, combined with the extraordinarily long depth of focus, has demonstrated equally extraordinary welding results. By comparing the welding results with conventional systems using relatively short focal lengths, some surprising observations have been noted. This topic has been investigated with the use of the remote welding system (RWS), which is a system utilizing an extremely long f...

Direct laser interference patterning of planar and non-planar steels and their microstructural characterization

The direct laser interference patterning method was used to fabricate periodic structures on flat and cylindrical specimens of austenitic stainless steel (X5CrNi18-10) and martensitic bearing steel (100Cr6). In such laser processing the characterization of materials is a central issue. Therefore, this paper places special emphasis on the chemical, metallurgical and mechanical characterization of the laser processed metals. During the patterning process of 100Cr6, the carbides in the martensitic structure appear as elongated needles and become aligned to the direction of melt flow. The chemical composition analysis before and after laser interference patterning did not reveal any significant changes to either material. However, the surface hardness of 100Cr6 decreased when energy densities above 2.0 J/cm2 were applied. For cylindrical specimens, the grating period changes with position along the circumference. The observed difference, however, is less than ∼6.4% for rotation angles smaller than 20°.

Opportunities to enlarge the application area of remote-cutting

Remote-Cutting is an alternative method to conventional laser cutting processes when working on thin sheets. Working without any cutting gas the inertia can be reduced significantly. Deflected by two mirrors the laser beam becomes more flexible in the working envelope of the scanner. Depending on the sheet thickness cutting speeds of about 100 m/min in contours are possible [1], [2], [3].The target of this paper is to give some opportunities to enlarge the application area of remote-cutting. It will be shown how the maximum separable thickness can be increased. Furthermore, possibilities to widen the working area are shown. Investigations were done to determine the parameters, which have effect on the cutting quality. Obtained qualities and quantities are compared with those of conventional technologies.Moreover, investigations were done in order to determine the possibility to cut various materials. For example, the selective cutting of material compounds is described. This technology is also known as “Kiss-Cutting”. Using “Kiss-Cutting” improves the handling of thin metal foils and thus the productivity.Remote-Cutting is an alternative method to conventional laser cutting processes when working on thin sheets. Working without any cutting gas the inertia can be reduced significantly. Deflected by two mirrors the laser beam becomes more flexible in the working envelope of the scanner. Depending on the sheet thickness cutting speeds of about 100 m/min in contours are possible [1], [2], [3].The target of this paper is to give some opportunities to enlarge the application area of remote-cutting. It will be shown how the maximum separable thickness can be increased. Furthermore, possibilities to widen the working area are shown. Investigations were done to determine the parameters, which have effect on the cutting quality. Obtained qualities and quantities are compared with those of conventional technologies.Moreover, investigations were done in order to determine the possibility to cut various materials. For example, the selective cutting of material compounds is described. This technology is also known as “K...

Large area direct fabrication of periodic arrays using interference patterning

Periodic patterned surfaces do not merely provide unique properties, but act as intelligent surfaces capable of selectively influencing multiple functionalities. One of the most recent technologies allowing fabrication of periodic arrays within the micro- and submicrometer scales is Direct Laser Interference Patterning (DLIP). The method permits the direct treatment of the materials surface based on locally induced photothermal or photochemical processes. Furthermore, DLIP is particularly suited to fabricate periodic patterns on planar and non-planar surfaces offering a route to large-scale production. In this paper, the fabrication of spatially ordered structures on different materials such as polymers, metals and diamond like carbon films is discussed. Several application examples as function of the processed material are introduced, including bio functional surfaces for cell guidance on polymers, wear resistant properties for structured diamond carbon like coatings and metals, as well as micro-patterned flexible polymers with controlled optical properties.