Leonardo Daniele Scintilla

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.

Experimental Investigation on Fiber Laser Cutting of Ti6Al4V Thin Sheet

The high strength to weight ratio and good corrosion resistance of titanium alloys, have led to an increasing use of these materials, particularly in the aerospace industry. The laser cutting technique may be a promising tool in machining titanium alloy parts like those with subsequent welding requirement: in this case, surface quality of the kerf edges is of great importance. The low thermal conductivity and the high chemical activity of titanium alloys lead, in fact, to alterations of the surface properties of the machined zone. This paper presents the results of titanium alloy laser cutting using a 2 kW fiber laser. The cutting process was performed in continuous wave mode and using Argon as shear gas. Laser cuts were realized on titanium alloy Ti6Al4V sheets 1mm thick. Image analysis and microscopy, were carried out to examine the cutting edge quality features including thickness of the recast layer and heat-affected zone.

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...

Fusion cutting of aluminum, magnesium, and titanium alloys using high-power fiber laser

Abstract. The effects of cutting speed and assist gas pressure on laser cutting of 1-mm thick Al 1050, AZ31, and Ti6Al4V lightweight alloys are experimentally investigated. Fiber laser cutting of these materials is not broadly investigated and the acquisition of a new level of knowledge is of fundamental importance for applications like sheet metal trimming in automotive industry. The main process outputs are in depth compared with results reported in literature and obtained by cutting with CO2 and Nd∶YAG lasers. The good cut quality, the high productivity, and the easy delivery of the beam obtained at the same time, corroborate the advantage of using fiber lasers for thin sheets lightweight alloys cutting.

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...

Continuous-wave fiber laser cutting of aluminum thin sheets: effect of process parameters and optimization

Abstract. One-millimeter-thick Al 1050 sheets were cut using a 2-kW fiber laser operating in continuous-wave (CW) mode. An experimental approach that consisted of fitting the regression models by means of response surface methodology was adopted. The effects of cutting speed, assist gas pressure, and focal position on roughness arithmetic mean value were investigated. The desirability function was applied for the simultaneous optimization of cut quality and operating costs. The full potential of the CW mode high processing speeds and of the better absorptivity of 1-μm laser radiation for highly reflective materials are employed at the same time. Cutting aluminum with fiber laser increases the cutting speed and gives a cut quality comparable with results obtained with CO2 and Nd:YAG lasers that represent the most established laser sources for this application.

Numerical and experimental evaluation of Nd:YAG laser welding efficiency in AZ31 magnesium alloy butt joints

In this paper, energy aspects related to the efficiency of laser welding process using a 2 kW Nd:YAG laser were investigated and reported. AZ31B magnesium alloy sheets 3.3 mm thick were butt-welded without filler using Helium and Argon as shielding gases. A three-dimensional and semi-stationary finite element model was developed to evaluate the effect of laser power and welding speed on the absorption coefficient, the melting and welding efficiencies. The modeled volumetric heat source took into account a scale factor, and the shape factors given by the attenuation of the beam within the workpiece and the beam intensity distribution. The numerical model was calibrated using experimental data on the basis of morphological parameters of the weld bead. Results revealed a good correspondence between experiment and simulation analysis of the energy aspects of welding. Considering results of mechanical characterization of butt joints previously obtained, the optimization of welding condition in terms of mechanical properties and energy parameters was performed. The best condition is represented by the lower laser power and higher welding speed that corresponds to the lower heat input given to the joint.

T-joints of Ti alloys with hybrid laser-MIG welding: macro-graphic and micro-hardness analyses

Titanium alloys are characterized by high mechanical properties and elevated corrosion resistance. The combination of laser welding with MIG/GMAW has proven to improve beneficial effects of both processes (keyhole, gap-bridging ability) while limiting their drawbacks (high thermal gradient, low mechanical resistance) In this paper, the hybrid Laser-GMAW welding of Ti-6Al-4V 3-mm thick sheets is investigated using a specific designed trailing shield. The joint geometry was the double fillet welded T-joint. Bead morphologies, microstructures and mechanical properties (micro-hardness) of welds were evaluated and compared to those achieved for the base metals.

Influence of fiber laser cutting parameters on the subsequent laser welding of Ti6Al4V sheets

One approach to reduce the titanium alloy machining costs and extensive material usage is to join pieces obtained by Laser Beam Cutting (LBC) process. Cutting with fibre laser sources represents a promising tool in machining titanium alloy parts with subsequent welding requirements. Fibre lasers offer a great potential in improving the productivity of cutting phase with an acceptable edge quality, in particular when thin sheets are concerned. The paper investigates the effect of laser cutting parameters on the mechanical behavior of laser butt welded joints whose edges were obtained by laser cutting. In the first part of the experimental activity, investigation on the effect of cutting speed and assist gas pressure on Ti6Al4V 1mm thick sheets cut with fibre laser was carried out. At the same time laser welding process using a Nd:YAG laser was performed on sheets with cut edges generated by machining. Once the optimal welding condition was determined, the mechanical characterization of Ti6Al4V sheets cut with fibre laser and then laser joined was performed. Tensile tests revealed that the shear gas pressure is the main parameter affecting the ultimate tensile strength because it is directly correlated to the quality of the cutting edge.One approach to reduce the titanium alloy machining costs and extensive material usage is to join pieces obtained by Laser Beam Cutting (LBC) process. Cutting with fibre laser sources represents a promising tool in machining titanium alloy parts with subsequent welding requirements. Fibre lasers offer a great potential in improving the productivity of cutting phase with an acceptable edge quality, in particular when thin sheets are concerned. The paper investigates the effect of laser cutting parameters on the mechanical behavior of laser butt welded joints whose edges were obtained by laser cutting. In the first part of the experimental activity, investigation on the effect of cutting speed and assist gas pressure on Ti6Al4V 1mm thick sheets cut with fibre laser was carried out. At the same time laser welding process using a Nd:YAG laser was performed on sheets with cut edges generated by machining. Once the optimal welding condition was determined, the mechanical characterization of Ti6Al4V sheets cut w...

A Thermal Model for Laser Hardening Simulation

Laser hardening is a very flexible and useful process for surface treatment of medium carbon steels, capable of processing varied and complex geometries. In order to enlarge the range of industrial applications to which this process can be applied, a suitable model is necessary in order to reduce the setup time requested for the optimization of new components. The process model presented is based on the Arrhenius-like equation for estimation of the thermally induced process reaction time for microstructural transformations. By means of experiments, all unknown parameters in the equations have been determined, highlighting the accuracy and low computation time of the simulator.Copyright