Parameters Including Laser Power Research Articles

Fiber laser cutting of CFRP laminates with single- and multi-pass strategy: A feasibility study

Experimental data is presented relating to hole quality and feasibility studies when using continuous wave (CW) fiber laser to cut CFRP laminates (6.0 mm diameter hole) with single- and multi-pass strategy. The effect of typical processing parameters including laser power and cutting speed on thermal defect was also investigated. The statistical significance of individual cutting parameters was determined using main effects plot together with ANOVA analysis. Three methods were proposed to characterize HAZ based on the feature of thermal defect. According to statistical analysis, both cutting speed and laser power were significant with respect to HAZ (recorded at hole exit). The minimal value of HAZ was recorded with laser power of 650 W and cutting speed of 1100 mm/min. Energy per unit length (El) should be set above 40 J/mm to ensure cutting through CFRP laminates using fiber laser in high efficient machining process. Multi-pass strategy was investigated without setting pause/break time between each pass in order to increase cutting efficiency. Results showed limited improvement in terms of the level of HAZ even with cutting speed up to 10,000 mm/min, while machining time was significantly reduced to cut 6.0 mm diameter hole compared with single-pass strategy. For machining small holes with diameter down to 2.0 mm, high power fiber laser was not preferred due to severe thermal defect observed at hole entry and exit.

Optimisation of process parameters and weld shape of high power Yb-fibre laser welded 2024-T3 aluminium alloy

A novel approach to welding crack sensitive 2024 aluminium alloy was made by using fibre laser. Bead on plate welding of 3 mm thick sheets of 2024-T3 was performed to determine the optimum sets of welding parameters including laser power, welding speed, power density and focal position, which meet the quality and specification requirements of aircraft structures. A correlation between these parameters and weld shape, microstructure, and defects was found. The weld quality was assessed in terms weld-seam geometry, root to width ratio, surface appearance, penetration depth, microstructure and defects. Microstructural analysis was performed using optical microscopy, scanning electron microscopy and energy dispersive spectroscopy. The parametric optimisation was conducted to obtain crack and porosity free full penetration welds with ideal sized face and root width or weld shape, and a minimal amount of undercut, underfill and reinforcement. While high-quality welds were produced, in some cases, micro-cracks less than 0.5 mm were observed in the weld metal as optimising the parameters only had a limited effect on completely shifting the crack sensitive composition. The addition of filler metal with a different chemistry was found to be also necessary to adjust the composition to a less crack sensitive range.

Analysis and modeling of melt pool morphology for high power diode laser cladding with a rectangle beam spot

Dynamic behavior of a melt pool reflects the internal heat transfer, convection and mass addition in laser cladding, and it is closely related to the complex geometry and quality of the cladding layer. A machine vision system was built to directly detect and measure the melt pool morphology in wide-track laser cladding by high power diode laser (HPDL) with a rectangle beam spot (RBS). The captured images were processed with image processing technology to obtain the geometry profile and the characteristic parameters of the melt pool such as width (Wm), length (Lm) and area (Am). A full factorial experiment with pre-placed powder method was conducted to obtain the correlation between the geometrical characteristics and the process parameters. The effect of the process parameters including laser power, powder thickness and scanning speed on the Wm, Lm and Am were analyzed in detail. A nonlinear fitting model was used to fit the relationship between the process parameters and the geometrical characteristics. And a mathematically defined curve was adopted to describe the melt pool geometry profile. The above model was confirmed by all the experiments. The results indicated that the Wm, Lm and Am will increase with increasing laser power, while increasing scanning speed will cause the decreasing of the melt pool size. Moreover, the Wm and Lm can be predicted by the process parameters, and the melt pool contour profile can be well described as the curve.

Laser Brazing Characteristics of Al to Brass with Zn-Based Filler

Laser brazing of Al to brass in lap configuration with Zn-based filler was performed in this work. The process parameters including laser power, defocused distance were found to have a significant influence on appearance, microstructure and mechanical properties. The process parameters were optimized to be laser power of 2700 W and defocusing distance of + 40 mm from brass surface. In addition, preheating exerted great influence on wetting and spreading ability of Zn filler on brass surface. The microstructure observation showed the thickness of reaction layer (CuZn phase) at the interface of the brass side would grow with the increase in laser power and the decrease in the laser defocusing distance. Moreover, preheating could increase the spreading area of the filler metal and induced the growth of the reaction layer. The highest tensile–shear load of the joint could reach 2100 N, which was 80% of that of Al alloy base metal. All the joints fractured along the CuZn reaction layer and brass interface. The fracture morphology displayed the characteristics of the cleavage fracture when without preheating before welding, while it displayed the characteristics of the quasi-cleavage fracture with preheating before welding.

Experimental study on the picosecond pulsed laser cutting of carbon fiber-reinforced plastics

An experimental investigation of carbon fiber-reinforced plastics cutting with an Nd:YVO4 picosecond pulsed system was presented. One-factor experimental design was used in order to explain the influence of cutting parameters including laser power, hatch distance and cutting speed on the pulsed laser–material interaction. The process parameters were optimized by using central composite design of response surface methodology. The results in kerf width, taper angle, material removal rate, and heat-affected zones were discussed through the micrographs observed with optical microscope. Specimens were cut with three different tools: picosecond pulsed laser, nanosecond pulsed laser, and conventional cutting, and the tensile strength and bending strength tests were conducted. Furthermore, the effect of the heat-affected zones on the static strength was also analyzed.

Fabrication of Polyethylene Terephthalate Microfluidic Chip Using CO2 Laser System

Abstract CO2 laser machining technology is a wide and low-cost method for fabrication of microfluidic chips on polyethylene terephthalate (PET). In this paper, the influence of CO2 laser parameters including laser power and laser moving velocity on the depth and width of PET microchannel are studied. Laser power is set from 4 W to 20 W and laser moving velocity is set from 5 mm/s to 25 mm/s in the experiment. Compared with experimental results, some rules for the depth and width on laser parameters are obtained. The depth and width of the microchannel increase with the increase of laser power at the same laser moving velocity. However, the depth and width of the microchannel first increase and then decrease with the increase of laser moving velocity at the same laser power. The PET microfluidic chip is fabricated by a hot bonding machine.

TSV by 355 UV laser for 4G component packaging with micro-electroforming

Nickel micro-electroforming was integrated with 355-nm wavelength ultraviolet laser process to fabricate the through silicon via (TSV) for 4G communication device packaging. This technology was applied to package the high-frequency solidly mounted resonator (SMR). Different parameters including laser power, focus length, frequency, and termination diameter were explored to characterize the quality of TSV for laser drilling. The thickness of silicon sample of 550μm was drilled. The diameter of the silicon by laser drilling was 100–110μm, where the taper was about 1.6° and the aspect ratio was about 5. The relationship between micro-electroforming deposition thickness and time were obtained. The deposition thickness was carried out by various current densities under 0.5Amps per square decimeter (ASD), 1ASD, 2ASD, and 4ASD, respectively, to analyze the electroplating quality. In addition, nanoindenter, energy dispersive spectrometer (EDS), and X-ray diffraction (XRD) were used to analyze the material characteristics of micro-electroforming samples. Laser drilling and micro-electroforming were integrated to package the high-frequency SMR. The result shows that the S11 parameter was −3.5dB under the frequency of 2.5GHz. This TSV with micro-electroforming process shows potential use for 4G packaging application.

Effects of laser processing parameters on the mechanical properties, topology, and microstructure of additively manufactured porous metallic biomaterials: A vector-based approach

Additively manufactured (AM) porous structures are a new class of biomaterials with many advantages as compared to conventionally produced biomaterials. The goal of this study was to find out how the laser processing parameters including laser power and exposure time affect the mechanical properties, topology, and microstructure of porous biomaterials AM using a novel vector-based approach. Several cylindrical porous specimens were additively manufactured using a wide range of exposure time and laser power. The effects of those parameters on the surface roughness, strut diameter, relative density, hardness, elastic modulus, yield stress, first maximum stress, and plateau stress of the porous structures were studied. The results showed that the rate of change in mechanical and topological properties with respect to exposure time was non-linear while it was linear with respect to the laser power. The results also showed that the effects of laser power and exposure time on the mechanical properties and topology of AM porous structures could be decoupled from each other, enabling derivation of predictive emperical relationships. The emperical and experimental curves showed very good agreement, which further validates the validity of the separation method used for obtaining the emperical relationships. The analytical relationships for elastic modulus and yield stress that we had obtained in a previous study could predict the elastic modulus and yield stress of the porous strucutres when the energy input was high enough (i.e. exposure times≥450μs), because the local mechanical properties of the matrix material decreased for the lower levels of energy input. The change in the mechanical properties of the bulk material due to change in laser processing parameters should thus be taken into account.

Investigation of Carbon Fiber Reinforced Plastics Machining Using 355 nm Picosecond Pulsed Laser

Carbon fiber reinforced plastics (CFRP) has been widely used in the aircraft industry and automobile industry owing to its superior properties. In this paper, a Nd:YVO4 picosecond pulsed system emitting at 355 nm has been used for CFRP machining experiments to determine optimum milling conditions. Milling parameters including laser power, milling speed and hatch distance were optimized by using box-behnken design of response surface methodology (RSM). Material removal rate was influenced by laser beam overlap ratio which affects mechanical denudation. The results in heat affected zones (HAZ) and milling quality were discussed through the machined surface observed with scanning electron microscope. A re-focusing technique based on the experiment with different focal planes was proposed and milling mechanism was also analyzed in details.

Metallurgical and geometrical characterisation of the 316L stainless steel clad deposited on a mild steel substrate

In this study, the characteristics of the clad of 316L stainless steel deposited onto the mild steel substrate was investigated, in terms of dimensional and metallurgical variation across the length of the tracks. Significant variation in the clad thickness, depth of penetration of the melt pool, and depth of the heat affected zone (HAZ) was observed and correlated with the process parameters including laser power, scan speed, dilution, and specific energy of the laser beam. A significant variation in the clad thickness was observed across the entire length of the tracks. Based on this observation, three zones were identified and their characteristics discussed. Microstructural variation in the clad as well as the HAZ has been presented in detail. Moreover, hardness values ranging between 400–450HV and 320–380HV was measured in the deposited tracks with clad thicknesses of 0.5 and 1mm, respectively. This was attributed to the presence of fine austenitic grains of the size 4–8μm. Apart from the minute porosities observed in the clads, micro-cracking on the top surface of the tracks due to residual thermal stresses has also been reported. Lastly, “end-of-track” cracking was noticed in the deposited tracks and the possible mechanisms of crack formation are discussed.

Geometry modeling of single track cladding deposited by high power diode laser with rectangular beam spot

This paper presents an investigation on the relationship between the process parameters and geometrical characteristics of the sectional profile for the single track cladding (STC) deposited by High Power Diode Laser (HPDL) with rectangle beam spot (RBS). To obtain the geometry parameters, namely cladding width Wc and height Hc of the sectional profile, a full factorial design (FFD) of experiment was used to conduct the experiments with a total of 27. The pre-placed powder technique has been employed during laser cladding. The influence of the process parameters including laser power, powder thickness and scanning speed on the Wc and Hc was analyzed in detail. A nonlinear fitting model was used to fit the relationship between the process parameters and geometry parameters. And a circular arc was adopted to describe the geometry profile of the cross-section of STC. The above models were confirmed by all the experiments. The results indicated that the geometrical characteristics of the sectional profile of STC can be described as the circular arc, and the other geometry parameters of the sectional profile can be calculated only using Wc and Hc. Meanwhile, the Wc and Hc can be predicted through the process parameters.

Numerical Simulation of Transport Phenomena for Laser Full Penetration Welding

In laser full penetration welding process, full penetration hole(FPH) is formed as a result of force balance between the vapor pressure and the surface tension of the surrounding molten metal. In this work, a three-dimensional numerical model based on a conserved-mass level-set method is developed to simulate the transport phenomena during laser full penetration welding process, including full penetration keyhole dynamics. Ray trancing model is applied to simulate multi-reflection phenomena in the keyhole wall. The ghost fluid method and continuum method are used to deal with liquid/vapor interface and solid/liquid interface. The effects of processing parameters including laser power and scanning speed on the resultant full penetration hole diameter, laser energy distribution and energy absorption efficiency are studied. The model is validated against experimental results. The diameter of full penetration hole calculated by the simulation model agrees well with the coaxial images captured during laser welding of thin stainless steel plates. Numerical simulation results show that increase of laser power and decrease of welding speed can enlarge the full penetration hole, which decreases laser energy efficiency.

An effective method for fabricating microchannels on the polycarbonate (PC) substrate with CO2 laser

This paper proposes an effective processing method for fabricating microchannels on the polycarbonate (PC) substrate with CO2 laser. The width of microchannel has close relationship with CO2 laser parameters including laser power, laser moving velocity, and length of microchannel. In order to optimize the width of the microchannel, the orthogonal experiment method is successfully applied in this experiment with L9(33) orthogonal test table. Then, the optimal machining parameters are obtained and a verified experiment is confirmed. Finally, the optimal microcahnnels on the PC can be obtained with the presented process parameters.

SURFACE ROUGHNESS STUDY ON MICROCHANNELS OF CO2 LASER FABRICATING PMMA-BASED MICROFLUIDIC CHIP

A novel method named soak sacrificial layer ultrasonic method (SSLUM) has been presented for optimizing the surface roughness of the microchannels of polymethyl methacrylate (PMMA)-based microfluidic chips. CO2 laser was used for ablative microchannels on the PMMA sheet, and the effects of key parameters including laser power, laser ablation speed and solution concentration on the surface roughness of microchannels were estimated and optimized by SSLUM. The experimental observation demonstrates that the surface roughness results mainly from the residues on the channel wall, which are produced by the bubbles movement and bursting. The research results show that the surface roughness can be improved effectively by using SSLUM. In our experiment, the best value was Ra [Formula: see text] 110[Formula: see text]nm with laser power 12[Formula: see text]W, laser ablation speed 10[Formula: see text]mm/s, the solution concentration 75%, and the time of ultrasonic vibration 25[Formula: see text]min. SSLUM is proven to be an effective, simple and rapid method for optimizing the surface roughness of microchannels of microfluidic chips.

Research on Process and Property of H13 Die Steel Directly Manufactured by Selective Laser Melting

The process of selective laser melting direct manufacturing based on H13 Die Steel is studied to explore the optimized process of H13 mold products. Laser linear energy and two critical process parameters including laser power and scanning space are carried out process validation and analysis, test the mechanical performance of samples manufactured, analyze the surface morphology and microstructure of the representative samples. The result shows that with the laser power of 180W, scanning speed of 450 mm/s, laser linear energy of 0.40 J/mm, the sample manufactured directly by selective laser melting with 57 HRC surface hardness which is higher than the coasting standard. The internal structure of the sample is homogeneous, and the defects such as pore and spherify are less.

Progress in the Understanding of the Microstructure Evolution of Direct Laser Fabricated TiAl

With the introduction of TiAl in aircraft jet engines, there is an increasing demand for the evaluation of novel processing routes for gamma titanium aluminides such as additive manufacturing (AM). A Ti-47Al-2Cr-2Nb powder material has been used as feedstock for laser fabrication of 3D samples by means of “Selective Laser Melting” (SLM) and “Direct Metal Deposition” (DMD). A number of processing parameters including laser power, laser scan rate, powder feed rate, have been varied to evaluate their effects on the material soundness. Optimised conditions can significantly reduce the crack sensitivity for this relatively low ductility material. In particular, crack-free experimental conditions have been identified by using additional heating strategies, thus limiting built-up residual stresses during fast cooling. The different samples have been examined using optical and scanning electron microscopy in the as-built condition. The non-equilibrium cooling conditions generate ultra-fine and metastable structures exhibiting high microhardness values. A range of post-heat treatments have been performed to relieve the residual stresses and to tailor more uniform microstructures. Conventional heat treatments in the α+γ two-phase domain or in the α single phase domain have been successfully used to fully restore homogeneous microstructures either duplex or fully lamellar. A comparison is made with microstructures of both laser treated materials and of conventionally processed materials.

Production of polyamide-12 membranes for microfiltration through selective laser sintering

This study investigates the feasibility of manufacturing polyamide-12 microfiltration membranes through selective laser sintering (SLS). This process is different from traditional solvent casting methods, which have limited control over the membrane structure. The SLS technique also eliminates the usage of solvent, which lowers the production cost and avoids environmental issues. In this study, different processing parameters including laser power, hatch spacing and laser scan count are used to optimize the membrane performance. The laser energy density is shown to be directly linked with pure water flux and rejection. A laser energy density of 0.1J/mm2 results in membranes with the highest rejection and relatively high pure water flux. This work offers an alternative approach for fabrication of membranes for microfiltration. The findings in this exploratory study offer a perspective for optimization of membrane performance in future work.

Laser ignition of elastomer-modified cast double-base (EMCDB) propellant using a diode laser

An experimental study was conducted to investigate laser ignition using a diode laser for elastomer-modified cast double-base (EMCDB) propellant in order to develop more liable and greener laser ignitors for direct initiation of the propellant. Samples of the propellant were ignited using a 974nm near-infrared diode laser. Laser beam parameters including laser power, beam width and pulse width were investigated to determine their effects on the ignition performance in terms of delay time, rise time and burn time of the propellant which was arranged in several different configurations. The results have shown that the smaller beam widths, longer pulse widths and higher laser powers resulted in shorter ignition delay times and overall burn times, however, there came a point at which increasing the amount of laser energy transferred to the material resulted in no significant reduction in either delay time or overall burn time. The propellant tested responded well to laser ignition, a discovery which supports continued research into the development of laser-based propellant ignitors.

Influence of scan strategy and process parameters on microstructure and its optimization in additively manufactured nickel alloy 625 via laser powder bed fusion.

Laser powder bed fusion (L-PBF) as an additive manufacturing process produces nearly fully dense nickel alloy 625 (IN625) parts with complex features. L-PBF generates surfaces and microstructure through directional solidification that can be controlled by scan strategies and selection of process parameters. This study provides experimental investigations on microstructure formation including sizes of cellular grains and growth directions of columnar grains on the nickel alloy 625 test coupons. The effects of process parameters including laser power, scan velocity, hatch distance, and scan strategy that produce various solidification cooling rates and thermal gradients during the process, which also contribute to resultant microstructure, have been analyzed. Optimization studies are conducted on several objectives to improve the productivity while controlling the process effects on the resultant microstructure using response surface regression, desirability functions, and multi-objective genetic algorithm optimization.

Simulation and experimental investigation for the 2D and 3D laser direct structuring process

The molded interconnected devices (MID) technology is vastly growing as an important innovative technology in the field of electronics production. The laser direct structuring (LDS) method is one of the most common available technologies for building up MID’s products. The current existing knowledge in industry and in research about the standards in the respective manufacturing processes and process parameters is up to now not fully comprehensive in terms of mutual influencing and dependencies on each other. This is particularly the case for the three-dimensional applications and micro products. In the present contribution, a new simulation procedures based on a three-dimensional finite element model (FEM) has been developed. The effect of each of latent heat of fusion and temperature on the material properties as well as the 3D Gaussian heat source for the laser beam has been considered in this work. The used material was a polymer plate poly ether ether ketone (PEEK). The effect of the process parameters including laser power, speed, frequency, hatching percent or overlap between the laser lines, the laser incident angle, and the focal length have been investigated in experiments and simulations. The present simulation can be used to predict, temperature distribution, maximum temperature, groove dimensions, and groove profile at different process parameters setup. The theoretical and the experimental results can show a good accordance. It can be concluded that the FEM simulation can be used efficiently for predicating, analyzing, and optimizing the 2D/3D laser parameters for the LDS process.