Assistant Gas Research Articles

Evaluation of laser cutting process with auxiliary gas pressure by soft computing approach

Evaluation of the optimal laser cutting parameters is very important for the high cut quality. This is highly nonlinear process with different parameters which is the main challenge in the optimization process. Data mining methodology is one of most versatile method which can be used laser cutting process optimization. Support vector regression (SVR) procedure is implemented since it is a versatile and robust technique for very nonlinear data regression. The goal in this study was to determine the optimal laser cutting parameters to ensure robust condition for minimization of average surface roughness. Three cutting parameters, the cutting speed, the laser power, and the assist gas pressure, were used in the investigation. As a laser type TruLaser 1030 technological system was used. Nitrogen as an assisted gas was used in the laser cutting process. As the data mining method, support vector regression procedure was used. Data mining prediction accuracy was very high according the coefficient (R2) of determination and root mean square error (RMSE): R2 = 0.9975 and RMSE = 0.0337. Therefore the data mining approach could be used effectively for determination of the optimal conditions of the laser cutting process.

High fluence nanosecond laser machining of SiCp/AA2024 composite with high pressure assistant gas

This paper presents a feasibility study on machining SiCp/AA2024 composite using nanosecond fiber laser (λ = 1064 nm) with the rated average power of 20 W and the assistance of 1 MPa Ar gas. Ablation characteristics are investigated with variation of pulse repetition rate (f = 3 ∼ 10 kHz, τl = 200 ns) and pulse width (τl = 4, 13, 20, 30, 50, 100, 200 ns, f = 3 kHz). The ablation morphology measured by scanning electron microscopy (SEM) changed from “coated layer”, “partially coated layer” to “column array” appearance with decreasing pulse repetition rate. An effective ablation of the SiCp/AA2024 composite was demonstrated at 3 kHz repetition rate. By increasing pulse width with a fixed pulse repetition rate of 3 kHz, ablation depth and ablation rate linearly increased, meanwhile, both surface roughness and recast layer thickness saturated. The rate achieved was in the range from 27 nm to 157 nm per pulse, and the resultant roughness from 6.75 μm to 20.60 μm. Ablation mechanism was analyzed from the aspects of high pressure assistant gas, high pulse fluence and high beam overlap of 99.8%. Furthermore, the morphology formation mechanism was discussed considering the competition effect between the time for ablated material escaping from cavity and the pulse interval time of “Δτl=1/f” available for ablation.

Analysis of plasma oscillations by electrical detection in Nd:YAG laser welding

Plasma oscillations were investigated by electrical detection under different operating parameters during bead-on-plate welding of 304 stainless steel with a Nd:YAG laser. The varied parameters were the laser output power, welding speed, assistant gas type and assistant gas flow rate. The plasma electrical signals were detected by a passive electrical probe and analyzed in the frequency domain by power spectral density analysis. Combined with observation of the corresponding weld cross sections, the fluctuating characteristics of the plasma in different welding modes were obtained. A high-speed camera was employed to observe the plasma during experiments using different types and flow rates of side assistant gas. The features of plasma, including the plasma area and inclination angle, were extracted by the mathematical morphology method. By comparing the electrical signal of plasma with the extracted plasma features, the effects of the side assistant gas on the oscillations of plasma were discussed.

Thermal-Responsive Anisotropic Wetting Microstructures for Manipulation of Fluids in Microfluidics.

We show morphology-patterned stripes modified by thermal-responsive polymer for smartly guiding flow motion of fluid in chips. With a two-step modification process, we fabricated PNIPAAm-modified Si stripes on silicon slides, which were employed as substrates for fluid manipulation in microchannels. When the system temperature switches between above and below the lower critical solution temperature (LCST) of PNIPAAm, the wettability of the substrates also switches between strong anisotropy and weak anisotropy, which resulted in anisotropic (even unidirectional) flow and isotropic flow behavior of liquid in microchannels. The thermal-responsive flow motion of fluid in the chip is influenced by the applied pressure, the thickness of PNIPAAm, and dimension of the microchannels. Moreover, we measured the feasible applied pressure scopes under different structure factors. Because of the excellent reversibility and quick switching speed, the chip could be used as a thermal-responsive microvalve. Through tuning the system temperature and adding the assistant gas, we realized successive "valve" function. We believe that the practical and simple chip could be widely utilized in medical detection, immunodetection, protein analysis, and cell cultures.

侧吹气体对奥氏体不锈钢激光焊缝组织和耐腐蚀性能的影响

侧吹气体对奥氏体不锈钢激光焊缝组织和耐腐蚀性能的影响

Considerations on Assist Gas Jet Optimization in Laser Cutting with Direct Diode Laser

The emergence of new generations of laser sources for cutting of metal sheets results in the reopening of research topics that were long closed for established technologies such as CO2 lasers. After the success of the fiber/disk generation, we now see a third generation of Direct Diode Lasers (DDLs) taking their chance. As the diode laser technology matures and the process boundaries are shifted to meet metal sheet laser cutting requirements, new challenges arise. This paper deals with gas jet optimization in laser cutting with a linearly polarized DDL setup with an output power of 750W. Different concepts were investigated for improving the nitrogen assist gas jet when processing 3mm thick 304 L stainless steel sheets. After performing a set of tests with conventional conical nozzles, several efforts were made in order to test possible improvements in cutting performance. This included accelerated gas jets designed for an exit Mach number of 2 (both a linearized version of the Laval nozzle and a Minimum length nozzle were tested) and non-axis symmetric nozzle configurations, such as laser to nozzle center offset or nozzles with obround exit shapes. A general discussion on the design methods and procedures for these nozzle shapes is also given. Results of this exercise show the importance of well-designed nozzles for cutting with DDL's and specifically the need to take the beam shape and laser quality constraints into consideration.

Flow Analysis of Assist Gas in Laser Cutting Slot

Flow Analysis of Assist Gas in Laser Cutting Slot

Catalytic oxidation removal of gaseous elemental mercury in flue gas over niobium‐loaded catalyst

Nb‐Co‐Ce/Al2O3 catalysts prepared by impregnation, sol‐gel method, and co‐precipitation were examined for elemental mercury (Hg0) oxidation in a simulated coal combustion flue gas. The catalysts were characterized by SEM‐EDS, BET, XRD, FTIR, and XPS techniques. The performances of different niobium‐loaded catalysts on Hg0 oxidation efficiency with regard to preparation method, assistant, reaction temperature, and typical individual flue gas were investigated. The results showed that the Hg0 oxidation efficiency performed at the highest value for niobium‐loaded catalysts at 523 K. SO2 was observed to have a negative effect on Hg0 oxidation. The niobium‐loaded catalysts prepared by the sol‐gel method and co‐precipitation exhibited higher Hg0 oxidation efficiency than that prepared by impregnation, due to higher specific surface area and more exposure of active sites. However, it also results in these catalysts being affected by SO2 more easily. An enhancing effect of O2 was observed and an addition of HCl would promote the Hg0 oxidation further. Results also indicated that synergistic effects between NbOx, CoOx, and CeOx could promote the sustainable capacity of Hg0 oxidation for Nb‐Co‐Ce/Al2O3 catalysts. Hg0 oxidation over Nb‐Co‐Ce/Al2O3 catalysts is thought to follow a Mars‐Maessen mechanism in which lattice oxygen derived from NbOx would react with absorbed Hg0.

Ti Surface Laser Polishing: Effect of Laser Path and Assist Gas

Laser polishing is a process by which the surface roughness of machined parts can be reduced avoiding ablation phenomena. In this process the laser spot irradiates the sample surface with short laser pulses at a power density that causes a surface melting of the order of few nanometers. Compared to conventional polishing process (as grinding) it ensures the possibility of avoiding any surface orientation, no tool wear, no abrasive or liquids, no debris and less machining time; moreover coupled with a galvo system it results to be more suitable in case of 3D complex workpieces.Nowadays, on this process, several authors are focusing their attention on the wavelength and pulse length effect but a lack of knowledge concerning the effect of other process parameters still exists.In this work the effects of laser path and assist gas were tested by the authors. Nd:YVO4 laser source, characterized by a wavelength equal to 532nm, was used in the experiments and Ti grade 2 samples were selected. A full experimental plan was designed to investigate the influence of process parameters in terms of average roughness reduction achieved.

Definition of Mathematical Models of High-alloyed Steel 1.4828 in CO2 Laser Cutting

This paper defines mathematical models of value changes for surface roughness (Ra, μm) and heat affected zone width (HAZ, mm) during high-alloyed steel 1.4828 laser cutting using oxygen as an assistance gas. For the definition of appropriate mathematical models, multiple linear regression analysis is used, with four independent variables that were varied at five levels. Following parameters are varied: cutting speed (V), assist gas pressure (p), focus position (fs) and stand-off (Nd). In comparison between the model and the experimental results, it can be concluded that the effects of specified parameters on cut quality, productivity and thus the legitimacy of this technology for cutting high-alloyed steels are well described by the obtained mathematical models.

Effect of Laser Polarization on Cutting Properties in Assist Gas Free Laser Cutting

The new cutting process, Assist Gas Free laser cutting (AGF laser cutting), was developed and the cutting properties were investigated in our laboratory. In a previous study of AGF laser cutting by using circular polarized CO2 laser, basic properties have been investigated. On the other hand, when cutting of metallic materials with a linear polarized laser is performed, it is known that the cutting kerf might slant and critical cutting speed can be accelerated. These phenomena have been also observed in AGF laser cutting. However, more detailed research about the properties by using a linear polarized laser in AGF laser cutting is needed. In the present study, the effect of laser polarization on cutting properties in AGF laser cutting by using linear polarized laser was investigated. The cutting speed and direction were varied in order to study the influence of these parameters on the critical cutting speed and kerf shapes such as slant angle, width, and removed area of kerf. The study showed that when the cutting direction and the polarized direction were parallel, the kerf slant was depressed. In addition, the critical cutting speed could be the fastest in any other cutting direction.

Application of Mixed-Level Orthogonal Design in Determination of Heavy Metals in Soil, for Example Pb

In order to precisely determinate absorbance of all kinds of heavy metals in soil,7- important factors were optimized by mixed-level orthogonal design.For example Pb,discuss the factors influence degree on digestion and determination of Pb.Pb-absorbance trends within the area is expressed by the change of two-dimensional planar contour.Pb-absorbance distribution was drawn by 3D visualization technology.In order to optimize the orthogonal design,taking the optimal value of decentralized points in orthogonal test convert into taking the optimal value on a continuous plane. Using Minitab16 software analyzed the experimental results.The results showed that affecting Pb digestion Primary and secondary order is B(HF)> C(HNO3)> A(HClO4)> I(Acetylene flow rate)>D(HCL)>G (Assistant combustion gas)>H(Lamp current)>F(Burner height),that was adding 9 mlHNO3, 3mLHF, 3 mlHClO4 in soil samples, after microwave digestion, got the optimal Pb-absorbance value 0.304 under the the working conditions of atomic absorption spectrophotometer for Pb 217.0nm, slit width 1.3nm, burner height 4nm, assistant combustion gas 2.4 L/min, the lamp current 4.0mA, propane flow rate 4.0 L/min.

CO2 Laser Cutting of Alloy Steels Using N2 Assist Gas

Laser beam machining (LBM) is one of the most widely used thermal energy based non-contact type advance machining process which can be applied for almost whole range of materials. This paper defines mathematical models for surface roughness prediction (Ra, μm) and width of heat affected zone (HAZ, mm) during laser cutting of alloy steels 1.4571 and 1.4828 with nitrogen as assist gas. For defining appropriate mathematical models multiple regression analysis is used with four independent variables. Following parameters are varied: cutting speed, focus position, nitrogen assist gas pressure and stand-off. Obtained mathematical models describe dependence of Ra and HAZ from varied process parameters.

Experimental Comparison of Laser Cutting of Steel with Fiber and CO2 Lasers on the Basis of Minimal Roughness

The fiber and CO2 laser were compared from the viewpoint of two laser-cutting methods: the oxygen-assisted cutting of low-carbon steel and fusion cutting of stainless steel with a neutral assistant gas. The absorbed laser energy was measured in respect to the unit of the removed material volume at the cutting parameters correlating to the minimal roughness of the cut surface. This value equals to 11..13 J/mm3 both for the fiber and CO2 lasers. During the fiber-laser cutting, the minimal roughness is reached at the Peclet number 0.35..0.4, at the CO2-laser cutting – at 0.45..0.55. At the fusion cutting of stainless steel, the minimal roughness is reached at the maximal cutting speed. The maximal cutting speed has the higher value in the fiber-laser case at the same laser power. The paper discusses the potentiality of the method of absorbed laser energy measurement by the value difference at the cut channel inlet and outlet.

Cutting Properties of Austenitic Stainless Steel by Using Laser Cutting Process without Assist Gas

Recently, laser cutting is used in many industries. Generally, in laser cutting of metallic materials, suitable assist gas and its nozzle are needed to remove the molten metal. However, because of the gas nozzle should be set closer to the surface of a workpiece, existence of the nozzle seems to prevent laser cutting from being used flexible. Therefore, the new cutting process, Assist Gas Free laser cutting or AGF laser cutting, has been developed. In this process, the pressure at the bottom side of a workpiece is reduced by a vacuum pump, and the molten metal can be removed by the air flow caused by the pressure difference between both sides of the specimen. In this study, cutting properties of austenitic stainless steel by using AGF laser cutting with 2 kW CO2 laser were investigated. Laser power and cutting speed were varied in order to study the effect of these parameters on cutting properties. As a result, austenitic stainless steel could be cut with dross-free by AGF laser cutting. When laser power was 2.0 kW, cutting speed could be increased up to 100 mm/s, and kerf width at specimen surface was 0.28 mm.

Spectrum of temperature pulsations of the melt in gas-assisted cutting with fiber laser

Measurements of the temperature behavior in the zone of action of the laser-radiation on the molten metal have been performed using multichannel pyrometer. Measurements were carried out for test cutting of a 3-mm mild-steel plate with several values of cutting speed and pressure of assist gas (oxygen), using an 1800-watt Ytterbium fiber laser. It is shown that fluctuations of temperature are related to local melt's surface deformations due to unequal radiation absorption; thus the noise spectrum of temperature fluctuations reflects turbulent surface deformation caused by gas jet and capillary waves. The maximum density of turbulent energy dissipation ε depends on cutting conditions: its value rises with increasing cutting velocity and oxygen pressure in a described range of parameters. The maximum of ε is localized near depth of (1.2...1.5) mm along the cutting front. We can distinguish the specific radiation pulsation spectrum of laser cutting from other processes of radiation affection to the sample, including unwanted degrading of the quality of technological operations. The spectrum of capillary waves on the melt's surface is formed under the effect of assisted gas jet and has a function of ω −3 , ω is cycle frequency. The results of this investigation can be useful for the development of monitoring and quality-control systems for the laser-cutting process.

Research on Removal Characteristic of the Optical Quartz with Atmospheric Pressure Plasma Jet

The Atmospheric Pressure Plasma Jet (APPJ) is an innovative technology in advanced optics manufacturing; it is a non-contact precision machining method based on the chemical reaction between a reactive neutral radical generated by the plasma and substrate surface atoms for atom-scale material removal. The APPJ involves a complicated process; therefore, the controllability of the technical process was investigated to describe the accuracy of machining efficiency that is the uniformity and repeatability for machining systems, the linearity relation between the removal rates and dwell time. Moreover, the experimental result of the fused quartz removal function variation trend with different processing parameters was discussed. The results of experimentation indicate that the APPJ method has good repeatability within a short dwell time, the removal depth increases with the dwell time and a linearity relation seems appropriate, and the radio frequency (RF) power and the flux of assistant gas oxygen have a great influence on removal efficiency. However, the removal rate remains stable under small perturbation of flux of plasma gas He and reactive gas SF6. And the surface roughness is improved from Ra 9.3nm to Ra 3.7nm.

Cutting Properties of Austenitic Stainless Steel by Using Linear Polarized CO<sub>2</sub> Laser without Assist Gas

Recently, laser cutting is used in many industries. Generally, in laser cutting of metallic materials, assist gas and its nozzle are needed to remove the molten metal. However, because of the gas nozzle should be moved closer to the position about 1 mm from the surface of a workpiece, it is thought that existence of the nozzle causes lack of flexibility of laser cutting. Therefore, the new cutting process, Assist Gas Free laser cutting (hereafter, called as AGF laser cutting), has been developed and investigated about cutting properties in our laboratory. In this process, the pressure at the bottom side of a workpiece is reduced by a vacuum pump, and the molten metal can be removed by the air flow caused by the pressure difference between both sides of the specimen. On the other hand, when cutting of metallic materials with a linear polarized laser is performed, it is known that the cutting kerf might slant. This phenomenon is also observed in AGF laser cutting. In the present study, cutting properties of austenitic stainless steel by using liner polarized CO2 laser in AGF laser cutting was investigated. Cutting speed and direction were varied in order to study the effect of these parameters on cutting properties. As a result, when the angle formed by the cutting direction and the polarized direction of laser was parallel, the kerf slant could be depressed, and the critical cutting speed could be the fastest in any other cutting direction.

The Role of the Assist Gas Nature in Laser Cutting of Aluminum Alloys

Laser cutting is a standard industrial process for cutting sheet metals. The process relies on the removal of the melted material with the aid of a pressurized assist gas. Among the main variables controlling the process, the assist gas type is an essential factor. This gas is normally chosen taking into account the material to be processed and the required cut quality. While the effect of the utilization of different assist gas is perfectly studied in cutting steels, the influence of the assist gas type during laser cutting of aluminum alloys is not well studied. This work presents a study on the influence of different assist gases (argon, nitrogen, oxygen and air) on the edge quality and its surface chemistry during laser cutting of a typical Al-Cu alloy.

Experiment Study on Nd: YAG Pulsed Laser Cutting Carbon Fibers Composites

Nd:YAG pulsed laser cutting carbon fibers reinforced epoxy resins composites was studied. HAZ and kerf width was made as evaluation index, as well as laser pulse energy, cutting speed, pulse duration and assistant gas pressure was made as controlled parameters. Ideal quality of cutting can be achieved by adjusting those parameters. The effect of each parameter was analyzed.