High Power CO2 Laser Research Articles

瞬变电磁场辐照下液晶显示模块的电磁兼容预测

The Liquid Crystal Display (LCD) module in a high power TEA CO2 laser is easy to couple with electromagnetic interference, so as to affect the normal work of the laser. Therefore, this paper explores the prediction method of Electromagnetic Compatibility (EMC) for the LCD module under transient irradiation in an electromagnetic field. The coupling mechanism of electromagnetic interference received by the LCD module integrated in the laser system was analyzed. On the basis of the coupling of field and line, the field line electromagnetic interference of the LCD module was analyzed and calculated by using the BLT equation in the Taylor form, then, the prediction results were verified by several experimentally. The experimental results show that the interference voltage produced by connect cables coupled with electromagnetic fields on the data lines of LCD display module is 1 V, and exceeds the noise margin of the circuit. So the EMC control measures must be taken to ensure the performance of the LCD module. Moreover, the verification experiments indicate that prediction results for the EMC has correctly reflected the actual EMC performance of LCD module. The method has a guiding significance for prediction and design of EMC of electrical equipment in high-power TEA CO2 lasers.

Crack separation mechanism in CO2 laser machining of thick polycrystalline cubic boron nitride tool blanks

An improved method for cutting thick polycrystalline cubic boron nitride (PCBN) tool blanks is explored because current methods of pulsed Nd:YAG laser cutting and wire electrical discharge machining (EDM) are constrained by low speed and low precision. We present a CO2 laser/waterjet (LWJ) process to cut 4.8-mm-thick PCBN tool inserts by a crack separation mechanism. In LWJ, the PCBN blank is locally heated using a high-power continuous wave CO2 laser to cause phase transition from cubic to hexagonal followed by water quenching to generate thermal stresses and form boron oxide leading to increased brittleness, subsequent cracking, and material separation. A 23 fractional design of experiment (DOE) approach was employed to determine the factors of laser power, cutting speed, and waterjet pressure on the responses of phase transformation depth, taper, and surface roughness. A numerical heat flow model, based on Green’s function, was used to calculate the temperature distributions along the depth. Surface profilometer, scanning electron microscopy, and Raman spectroscopy were utilized to analyze the phase transformation and crack zones. Results from LWJ compared with pulsed Nd:YAG laser and laser microjet™ methods indicate LWJ cuts 30 times faster; this was attributed to a nonconventional material removal (crack separation) mechanism. When LWJ was compared against nitrogen-assisted CO2 laser cutting, improved cut quality (less taper and smaller heat-affected zone) was observed due to a greater control on phase transformation and crack propagation. DOE analysis revealed laser power and waterjet pressure, and the interactions among them are more significant factors than others.

A study on an efficient prediction of welding deformation for T-joint laser welding of sandwich panel PART I : Proposal of a heat source model

The use of I-Core sandwich panel has increased in cruise ship deck structure since it can provide similar bending strength with conventional stiffened plate while keeping lighter weight and lower web height. However, due to its thin plate thickness, i.e. about 4~6 mm at most, it is assembled by high power CO2 laser welding to minimize the welding deformation. This research proposes a volumetric heat source model for T-joint of the I-Core sandwich panel and a method to use shell element model for a thermal elasto-plastic analysis to predict welding deformation. This paper, Part I, focuses on the heat source model. A circular cone type heat source model is newly suggested in heat transfer analysis to realize similar melting zone with that observed in experiment. An additional suggestion is made to consider negative defocus, which is commonly applied in T-joint laser welding since it can provide deeper penetration than zero defocus. The proposed heat source is also verified through 3D thermal elasto-plastic analysis to compare welding deformation with experimental results. A parametric study for different welding speeds, defocus values, and welding powers is performed to investigate the effect on the melting zone and welding deformation. In Part II, focuses on the proposed method to employ shell element model to predict welding deformation in thermal elasto-plastic analysis instead of solid element model.

Numerical and experimental study of the effect of groove on plasma plume during high power laser welding

The influence of groove on the static feature and dynamic behavior of plasma plume during high power CO2 laser welding process was studied using a hydrodynamic three-dimensional model and corresponding experiments. The temperature, composition, and velocity of plasma plume along the incident path of laser beam were computed. The static morphology of plasma plume was analyzed through both models and comparative experiments. The difference of dynamic behavior of plasma plume between inside groove and on-plate was studied based on plume images taken by high-speed camera. The results showed that the groove could significantly affect the characteristics of plasma plume including static morphology, dynamic behavior, the coupling of laser energy, and resultant weld penetration. Modeling results concerning the influence of groove on plasma characteristics were reasonably consistent with experiment results.

Laser Cladding Functionally Graded Composition of Molybdenum Disilicide and Co-Based Alloy

An approach for fabricating functionally graded specimens of Co-based alloy and molybdenum disilicide (MoSi2) compositions via Selective Laser Cladding (SLD) is presented. The focus aimed at using the functionally graded material (FGM) concept to gradually grade powdered compositions of MoSi2 within a base material of Co-based alloy. A high power CO2 laser was used to process the material compositions to a high density with gradual but discrete changes between layered compositions. The graded specimens initially consisted of 100% Co-based alloy with subsequent layers containing increased volume compositions of MoSi2 (0-80wt.%). Specimens were examined for porosity, phase composition and microstructure. It was found that crack sensitivity of layer can be reduced by adding Co-based alloy into the pure MoSi2 powder.

Comparative research of multichannel slab and discharge tube CO2lasers

The laser power and beam quality of the high-power CO(2) laser are very important for laser applications. The multichannel slab discharge CO(2) laser (MSDL) and the multichannel discharge tube CO(2) laser (MDTL) are two main lasers, which have different functions. Two lasers and laser beams are compared and studied quantitatively from the following factors: intensity distribution, M(2) factor, phase locking, misalignment, and output power. It is shown that MSDL could obtain the laser beam with high power when the misaligned angle is small, but the beam quality is poor in comparison with that of MDTL. MSDL is more sensitive to the misaligned angle than MDTL.

Final Manufacturing Process of Front Side Metallisation on Silicon Solar Cells Using Conventional and Unconventional Techniques

The paper presents the results of the investigation of the front electrode manufactured using two silver pastes (PV 145 manufactured by Du Pont and another based on nanopowder experimentally prepared) on monocrystalline silicon solar cells in order to reduce contact resistance. The aim of the paper was a comparison between a conventional and an unconventional method to improve the quality of forming electrodes of silicon solar cells. The Screen Printing (SP) method is the most widely used contact formation technique for commercial silicon solar cells. Selective Laser Sintering (SLS) is a modern manufacturing technique, which uses a high power CO2 laser to melt or sinter metal powder particles into a mass that has the desired three-dimensional shape, in precisely defined areas. The whole process is controlled by a program that is used for micro-processing. An innovative aspect of this method is the application of a nano silver paste to create the seed layer of the front electrode using the SLS method. The topography of both co-fired in the infrared belt furnace and melted/sintered in the Eosint M250 Xtended device equipped with CO2 laser were studied. Contacts were investigated using confocal laser scanning microscope (CLSM 5) and a scanning electron microscope (SEM) with an energy dispersive X-ray (EDS) spectrometer for microchemical analysis. Both surface topography and a cross section of the front electrodes were studied using SEM microscope. Phase composition analyses of the chosen front electrodes were done using the XRD method delineated in this paper. Front electrodes were formed on the surface with a different morphology from the solar cells. The median size of the pyramids was measured using the atomic force microscope (AFM). Resistance of the front electrodes was measured using the Transmission Line Model (TLM).

IR Spectroscopy of b4 Fragment Ions of Protonated Pentapeptides in the X–H (X = C, N, O) Region

The structure of peptide fragments was studied using "action" IR spectroscopy. We report on room temperature IR spectra of b4 fragments of protonated GGGGG, AAAAA, and YGGFL in the X-H (X = C, N, O) stretching region. Experiments were performed with a tandem mass spectrometer combined with a table top tunable laser, and the multiple photon absorption process was assisted using an auxiliary high-power CO2 laser. These experiments provided well-resolved spectra with relatively narrow peaks in the X-H (X = C, N, O) stretching region for the b4 fragments of protonated GGGGG, AAAAA, and YGGFL. The 3200-3700 cm(-1) range of the first two of these spectra are rather similar, and the corresponding peaks can be assigned on the basis of the classical b ion structure that has a linear backbone terminated by the oxazolone ring at the C-terminus and ionizing proton residing on the oxazolone ring nitrogen. The spectrum of the b4 of YGGFL, on the other hand, is different from the two others and is characterized by a band observed near 3238 cm(-1). Similar band positions have recently been reported for one of the four isomers of the b4 of YGGFL studied using double resonance IR/UV technique. As proposed in this study, the IR spectrum of this ion at room temperature can also be assigned to a linear N-terminal amine protonated oxazolone structure. However, an alternative assignment could be proposed because our room temperature IR spectrum of the b4 of YGGFL nicely matches with the predicted IR absorption spectrum of a macrocyclic structure. Because not all experimental IR features are unambiguously assigned on the basis of the available literature structures, further theoretical studies will be required to fully exploit the benefits offered by IR spectroscopy in the X-H (X = C, N, O) stretching region.

Laser Scribing of Grain Oriented Electrical Steel Under the Aspect of Industrial Utilization using High Power Laser Beam Sources

Abstract The core loss of grain oriented electrical steel can be improved by an additional treatment process. For the industrial utilization, the CO2 or Nd:YAG lasers are most widely used for laser scribing with typical core loss improvements of about 10%. In this work, a high power CO2 laser and fiber laser up to 4 kW laser power are investigated under the aspect of industrial utilization. It was found that a specific parameter range for both laser beam sources was necessary to improve the core losses for the applied parameter range. Furthermore, an increase of the core loss improvement of 0.3 mm HiB (High-Permeability) electrical steel was investigated by using the fiber laser compared to the CO2 laser.

高功率光纤激光和CO2激光焊接熔化效率对比

高功率光纤激光和CO2激光焊接熔化效率对比

Spatial analysis of the back reflected laser light during CO2-laser cutting of metal sheets

During laser material processing such as laser welding or cutting, it is known that the whole laser power is not only absorbed in or transmitted through the interaction zone, but a significant percentage is also reflected back to the laser source. Some publications analyzing the laser welding process showed a clear correlation between the reflected laser power and the result of the process. In this report, the authors analyze the information content of back reflected laser light during the high-power CO2-laser cutting of metal sheets. For this purpose, laser reflections are detected coaxially via a scraper-mirror online during laser cutting with a high time resolution. For different materials (mild steel, stainless steel, aluminum) and thicknesses (1 and 3 mm), a detailed spatial analysis on where the laser beam is reflected from (cutting front or workpiece surface) will be given. The spatial analysis of the reflected laser light shows that only 10% is reflected from the cutting front in the kerf. The main part (>90%) is reflected from the overlap zone of the laser beam with the workpiece surface outside the cutting kerf. Therefore, the signal strongly depends on the surface roughness of the treated material. It will be shown that, as expected, reflective surfaces with little roughness show higher CO2-laser reflections than rough surfaces with a higher level of roughness. Furthermore, the fraction of back reflected laser light increases with higher cutting feed rate which can be explained with a larger overlapping zone of the CO2-laser beam with the workpiece surface in front of the cutting kerf. In addition, the back reflection signal also strongly depends on the position of the focal plane with respect to the workpiece surface. This relationship can be used to measure the absolute position of the focal plane in-process as well as detecting an undesired focus shift during laser cutting.

Mechanical and Microstructural Characterization of 8 mm Thick Samples of SS 316L by CO<sub>2</sub> Laser Welding

Laser beam welding offers various advantages over the other conventional weld processes. In fusion reactor, some critical components with high weld quality are proposed to be fabricated with Laser beam welding. The present paper reports the mechanical properties and micro structural characterization of 8 mm thick SS 316L samples fabricated with high power CO2 Laser welding system. The process parameters of 3.5 kW and speed of 600 mm/min with Argon shielding gas are used. The Laser welded samples are subjected to non destructive testing with X-ray radiography and ultrasonic tests. The welded samples tested have indicated good quality joints with full penetration and no significant porosity and cracks. Further, the samples are subjected to standard mechanical tests namely tensile properties test (UTS), bend test and Impact Fracture test. The Laser weld joints produced better tensile properties as compared to the base metal. In addition, Vickers hardness tests and optical microstructure are studied for the base metal (BM), Heat Affected Zone (HAZ) and weld zone(WZ).

Лазерная сварка сталей больших толщин с применением мощных оптоволоконных и СО2-лазеров

Лазерная сварка сталей больших толщин с применением мощных оптоволоконных и СО2-лазеров

Investigations on laser welding of magnesium alloys

AbstractThe welding processes of three different magnesium alloys ZK60, AZ31, and Mg-rare earth alloy NZ30K were studied using a high-power CO2 laser. The microstructure and tensile strength of welded joints were tested and analyzed. With increasing welding speed the tensile strength and total elongation of welded joints of ZK60 alloy are improved. The ultimate tensile strength of the welded joint of ZK60 is 211.18 MPa, 90% of the base metal. The tensile strengths of welded joints of AZ31 and NZ30K are better than those of the base metal. The expansion of the plasma of laser-welded ZK60 is the strongest with the highest temperature.

Arc-discharge monitoring system of a high-power repetitively-pulsed TEA CO2 laser

High-power repetitively-pulsed TEA CO2 lasers are excited by a glow discharge, and it turns out to be the arc discharge under some conditions. The arc-discharge is a disadvantageous condition and must be avoided. According to the Faraday electromagnetism induction principle, the arc-discharge monitoring system with a magnetic-field probe is designed for high-power repetitively-pulsed TEA CO2 lasers. The magnetic-field variation induced by the discharge current can be tested, and the discharge state can be distinguished according to the output induction voltage. Experimental results show that the magnetic-field induction voltages generated by a glow discharge and an arc discharge are very different ones. The maximum induction voltage of the glow discharge is 2.0 V, while the minimum induction voltage of the arc discharge is 2.5–4 V. Three alarm levels are set by measuring the arc-discharge intensities. At the first level, automatic filling–exhausting equipment starts to refresh the gas media, at the second level, the laser repetition rate is reduced, and at the third level the laser operation stops immediately. As a result, the working reliability of a high-power repetitively-pulsed TEA CO2 laser system can be improved significantly by using the arc-discharge monitoring system.

Beam quality of array beam from axisymmetric folded-combined CO2 laser

There are the small distances between the axes of the parallel array beams from axisymmetric folded-combined (ASFC) CO2 laser and each other due to the compact structure. Three methods are used for describing the combined array beams quality, such as, the size of focal spot, M2-factor and power in the bucket (PIB). The combined beam radius is calculated by using the second order moment. It is shown that the high quality beam can be obtained by the ASFC high power CO2 laser, and M2-factor and PIB will be influenced by the spherical aberration. The numerical examples are given to illustrate our calculated results.

Effects of Heat Input on Microstructure and Mechanical Properties of Laser-Welded Mg-Rare Earth Alloy

The effects of heat input on the quality of laser-welded Mg-rare earth alloy NZ30K were studied. Using a 15-kW high-power CO2 laser, the microstructure and mechanical properties of welded joints under different heat inputs had been analyzed and tested. It is found that the welding heat input plays an important role in laser welding of NZ30K. Good welded joint without macroscopic defects can be obtained using the proper heat input. With the increasing heat input, welding penetration gets deeper, the width of the heat-affected-zone becomes larger, and the distribution of precipitates changes concentration. Tensile tests display that the ultimate tensile strength (UTS) of the welded joint tends to increase at first with the increasing heat input. After the welded joint gets full penetration, the UTS remains almost the same, although the heat input is increased.

Initiation of ignition of a combustible gas mixture in a closed volume by the radiation of a high-power pulsed CO2 laser

The results of experiments on initiating the ignition of a CH4 — O2 — SF6 triple gas mixture in a closed volume by the radiation of a high-power CO2 laser are presented. It is shown that spatially nonuniform (in the direction of the laser beam) gas heating by the laser radiation leads to formation of a fast combustion wave, propagating along the chamber axis and giving rise to 'instantaneous' ignition. At the threshold value 16.5 J of the laser radiation energy the fast combustion wave is transformed into a detonation wave, which causes an explosion and destruction of the reaction chamber

大功率CO2激光器倍频晶体综述

大功率CO₂激光器倍频晶体综述

High-speed analog fiber-optic link for electromagnetic interference suppression in infrared power measurement

Electromagnetic interference (EMI) is a common problem in a high-power pulsed infrared laser measurement. In order to eliminate susceptibility to radiated EMI, we developed, tested and implemented an infrared power measurement system using a high-speed analog fiber-optic link. Key components are commercially available parts designed for high-speed digital data transmission, but can be operated in analog mode. We successfully utilized the system for time-resolved measurements of high-power transversely-excited atmospheric-pressure CO(2) lasers in amplifier and oscillator configurations. This paper presents experimental setup, testing results, and the details of the laser power measurements results.