R. Soto

CO2 laser cutting of slate

Slate is a natural stone which has the characteristic that shows a well-developed defoliation plane, allowing to easily split it in plates parallel to that plane which are particularly used as tiles for roof building. At present, the manufacturing of slate is mostly manual, being noisy, powdery and unsafe for the worker. Thus, there is a need to introduce new processing methods in order to improve both the working conditions and the quality of the products made of slate. Following the previous work focused on the drilling and cutting of slate tiles using a Nd : YAG laser, we present in this paper the results of the work carried out to explore the possibilities to cut slate plates by using a CO2 laser. A 1.5 kW CO2 laser was used to perform different experiments in which, the influence of some processing parameters (average power, assist gas pressure) on the geometry and quality of the cut was studied. The results obtained show that the CO2 laser is a feasible tool for a successful cutting of slate. r 2001 Elsevier Science Ltd. All rights reserved.

Carbon nitride films prepared by excimer laser ablation

The preparation of carbon nitride films by laser ablation of graphite in ammonia atmosphere is reported. Experiments were performed at room temperature under different NH3 total pressures using an ArF excimer laser (193 nm). The films were deposited on silicon and metal substrates from the ablated carbon radicals and the species generated by the ammonia photodissociation under the laser VUV photons. Profilometry and ellipsometry show an evolution of the growth rate and refractive index. Energy dispersive X-ray and Fourier transform infrared spectroscopies reveal a gradual incorporation of nitrogen in the films for increasing ammonia concentration. Furthermore, infrared spectra show the presence of CN and C–N groups and the incorporation of hydrogen bonded to carbon and nitrogen. These observations were corroborated by Raman spectroscopy and hydrogen effusion.

Theoretical analysis of material removal mechanisms in pulsed laser fusion cutting of ceramics

It is well known that the efficiency of material removal mechanisms has a crucial influence on the performance and quality of the laser cutting process. However, they are very difficult to study since the physical processes and parameters which govern them are quite complicated to observe and measure experimentally. For this reason, the development of theoretical models to analyse the material removal mechanisms is very important for understanding the characteristics and influence of these processes.In this paper, a theoretical model of the pulsed laser fusion cutting of ceramics is presented. The material removal mechanisms from the cutting front are modelled under the assumption that the ceramic material may be, simultaneously, melted and evaporated by the laser radiation. Therefore, three ejection mechanisms are investigated together: ejection of molten material by the assist gas, evaporation of the liquid and ejection of molten material due to the recoil pressure generated by the evaporation from the cutting front.The temporal evolution of the material removal mechanisms and the thickness of the molten layer are solved for several laser pulse modes. Theoretical results are compared with experimental observations to validate the conclusions regarding the influence of frequency and pulse length on the cutting process.

Comparative study of the influence of the gas injection system on the Nd:yttrium-aluminum-garnet laser cutting of advanced oxide ceramics

Cutting of advanced oxide ceramics is still a difficult task. In this work, the possibility to effectively cut them using a Nd:YAG laser guided by an optical fiber is demonstrated. The key points are the aerodynamic interactions of the assist gas jet in the fusion laser cutting of ceramics. A comprehensive study of the influence of these aerodynamic interactions on the laser cutting of advanced oxide ceramics has been carried out. The characteristics of the heat affected zone (HAZ) were studied related to the efficiency of the assist gas to eject the molten material. It has been demonstrated that the HAZ can be avoided with a suitable design of the gas injection system combined with an appropriate selection of the values of the processing parameters. With the aim of improving the efficiency of the assist gas injection system, a new cutting head with an off-axis supersonic nozzle was developed. Furthermore, a comparison between the utilization of a conventional coaxial conical nozzle to inject the assist gas and the new system is presented. The results obtained give clear proof that the use of the new gas injection system leads to a great improvement on the cut quality by means of a more efficient removing of the molten material out of the cutting front. This result is of special interest in the laser fusion cutting of thick ceramic plates at high processing rates.

Carbon nitride films prepared by guanazole laser ablation in ammonia atmosphere

Abstract Carbon nitride thin films were deposited using an ArF excimer laser to ablate a target of 3,5 diamino 1,2,4 triazole (guanazole) in a reactive atmosphere of ammonia. Films were obtained at room temperature onto crystalline silicon and aluminium substrates. The dependence of the film properties on the ammonia pressure is reported. Films were characterized systematically by profilometry, Fourier Transform infrared and energy dispersive X-ray (EDX) spectroscopies. Infrared spectra are dominated by a broad absorption band from 1300 to 1650 cm −1 , and a peak located at 2165 cm −1 indicating that nitrogen is bonded to carbon in different configurations. The broad band at high wavenumbers (3100–3500 cm −1 ) is attributed to NH x stretching modes revealing the presence of hydrogen in the films. Additional X-ray photoelectron spectroscopy measurements corroborate the presence of carbon bonded to nitrogen. Composition estimated by EDX shows that as the ammonia pressure is increased, higher concentration of nitrogen is incorporated into the films, reaching values up to 53 at% for NH 3 pressures > 1 Torr. Post-deposition thermal treatments up to 500 °C induce structural changes and promote the CN bond formation. Simultaneous analyses of the effused gases from the film during the thermal annealing are also reported.

Pulsed laser deposition of a-CNx :H films : the role of target-to-substrate distance and laser fluence

The effect of the mean free path of the ablated species to the target-to-substrate distance ratio on chemical composition and growth rate of carbon nitride films is reported. The composition of the films deposited at room temperature by ablating a glassy carbon target with an ArF excimer laser (193 nm) in 0.3 Torr ammonia was determined by Fourier transform infrared spectroscopy. At fixed pulse energy, the nitrogen content of the films decreases while the hydrogen content remains practically constant with increasing target-to-substrate distance. When the deposition geometry is fixed, increasing pulse energy results in an increase in the nitrogen content.

Laser surface texturing of bioactive materials

Surface topography and chemical composition are two factors affecting the osseointegration of an implant, extremely relevant to satisfy all the requirements needed for bio-implant applications. Nevertheless, some of the materials used for implants do not satisfy properties such as biocompatibility and osteointegration. In this sense, lasers are adequate tools to produce macro-and micro-structures on metallic alloys or polymer surfaces in order to improve their biological response. In view of this, the process of laser surface texturing of two common materials used in implants, such as titanium and PEEK (polyetheretherketone) is investigated in the present work, both from a theoretical and experimental point of view. In order to perform this process, influence of different laser wavelengths has also been studied (λ = 10600, 1064, 532, and 355 nm).Surface topography and chemical composition are two factors affecting the osseointegration of an implant, extremely relevant to satisfy all the requirements needed for bio-implant applications. Nevertheless, some of the materials used for implants do not satisfy properties such as biocompatibility and osteointegration. In this sense, lasers are adequate tools to produce macro-and micro-structures on metallic alloys or polymer surfaces in order to improve their biological response. In view of this, the process of laser surface texturing of two common materials used in implants, such as titanium and PEEK (polyetheretherketone) is investigated in the present work, both from a theoretical and experimental point of view. In order to perform this process, influence of different laser wavelengths has also been studied (λ = 10600, 1064, 532, and 355 nm).

Laser cutting of 2024-T3 aeronautic aluminium alloy

Since the beginning of the aeronautic industry aluminum alloys have played a crucial role in its development. Nowadays different aluminum alloy families are the base material of many pieces of aerospace vehicles. In this work, a novel approach of processing aluminium alloys is explored. Our efforts are aimed to cut 2024-T3 plates by a CO2 laser. To accomplish this objective we used a novel laser cutting head assisted by a gas jet working in supersonic regime. This supersonic nozzle and the intrinsic geometry of the cutting head allow carrying out the processing of these alloys more efficiently than conventional cutting heads. The microstructural characterization, grain morphology, kerfs’ dimensions and surface finish of the cuts have been analyzed. The cut edges are free of heat affected zone, dross and cracks. These successful results confirm laser cutting processing assisted by a supersonic assisting gas jet as a hopeful technique in the aerospace field.Since the beginning of the aeronautic industry aluminum alloys have played a crucial role in its development. Nowadays different aluminum alloy families are the base material of many pieces of aerospace vehicles. In this work, a novel approach of processing aluminium alloys is explored. Our efforts are aimed to cut 2024-T3 plates by a CO2 laser. To accomplish this objective we used a novel laser cutting head assisted by a gas jet working in supersonic regime. This supersonic nozzle and the intrinsic geometry of the cutting head allow carrying out the processing of these alloys more efficiently than conventional cutting heads. The microstructural characterization, grain morphology, kerfs’ dimensions and surface finish of the cuts have been analyzed. The cut edges are free of heat affected zone, dross and cracks. These successful results confirm laser cutting processing assisted by a supersonic assisting gas jet as a hopeful technique in the aerospace field.

Optimization of laser drilling of slate tiles

Slate is a natural rock with good mechanical properties and nice aesthetic appearance. Its utilization in residential constructions confers an elegant rustic external appearance, while keeping an excellent impermeability and robustness. Therefore, this rock is widely used in building construction, decoration, fireplaces and even handcrafted objects, particularly in regions owning natural slate quarries.The modern building construction is nowadays asking for improved manufacturing processes for its roofing materials since market requirements are continuously increasing. However, there is currently a lack of a reliable drilling process for slate. Making drills on a slate tile is still a difficult task because of its high hardness and its particular structure with parallel layers. A significant number of slate tiles are broken due to mechanical stress caused by traditional drilling tools. In this sense, lasers have already been demonstrated as a reliable tool for generate holes on a wide variety of materials and, particularly, in some stones. Due to its high precision, energy density, and its availability to be automated a great number of small holes can be produce in a short period of time.In this work, an experimental analysis on the CO2 laser drilling process of slate tiles is presented. We have used a systematic approach to determine the most adequate processing conditions to produce submillimeter holes in 5 mm thick slate tiles with good quality as well as in a minimum processing time.Slate is a natural rock with good mechanical properties and nice aesthetic appearance. Its utilization in residential constructions confers an elegant rustic external appearance, while keeping an excellent impermeability and robustness. Therefore, this rock is widely used in building construction, decoration, fireplaces and even handcrafted objects, particularly in regions owning natural slate quarries.The modern building construction is nowadays asking for improved manufacturing processes for its roofing materials since market requirements are continuously increasing. However, there is currently a lack of a reliable drilling process for slate. Making drills on a slate tile is still a difficult task because of its high hardness and its particular structure with parallel layers. A significant number of slate tiles are broken due to mechanical stress caused by traditional drilling tools. In this sense, lasers have already been demonstrated as a reliable tool for generate holes on a wide variety of materials...

Laser cutting of natural stone slabs

Natural stones are considered to be one of the best materials in all type of constructions, due to its durability, easy maintenance and aesthetics. There are different varieties of natural stones, like granite marble, sandstone or slate. These kinds of material are difficult to machine by conventional methods; moreover noise and powder are produced during its cutting. In this work, we present the results of a series of experiments carried out to cut natural stone slabs of Black South Africa granite using a CO2 laser assisted by a supersonic nozzle. The influence of the different parameters involved in the process, such as, average power, pulse frequency and nozzle position have been studied to characterize the cut geometry. Results from the tests show that it is possible to obtain sound cuts free of fractures in this type of natural stone.Natural stones are considered to be one of the best materials in all type of constructions, due to its durability, easy maintenance and aesthetics. There are different varieties of natural stones, like granite marble, sandstone or slate. These kinds of material are difficult to machine by conventional methods; moreover noise and powder are produced during its cutting. In this work, we present the results of a series of experiments carried out to cut natural stone slabs of Black South Africa granite using a CO2 laser assisted by a supersonic nozzle. The influence of the different parameters involved in the process, such as, average power, pulse frequency and nozzle position have been studied to characterize the cut geometry. Results from the tests show that it is possible to obtain sound cuts free of fractures in this type of natural stone.