An integrated approach by combining finite-element analysis (FEA), Kriging model, and nondominated sorting genetic algorithm-II (NSGA-II) is utilized to realize modeling and optimization in mask-assisted laser transmission microjoining thermoplastic urethane and polyamide 6 (PA6). First, a three-dimensional FEA model is developed for obtaining the simulation data of the temperature field distribution that can determine the molten pool geometry. Then based on the initial training points generated by the optimal Latin hypercube sampling, the relationships between input parameters (laser power P, scanning speed V, and clamping force F) and weld quality [weld width (WW) and shear strength (SS)] are approximated through the Kriging model. Meanwhile, the main effects and contribution rates of various input parameters on the joint performance are discussed. Finally, the optimal weld quality is characterized as maximum SS and WW with a desired value, the NSGA-II is carried out to solve the multiobjective optimization problem for searching the Pareto-optimal front. The results of validation experiments under the optimal parameters indicate that the corresponding welding joint quality is significantly superior to that under other parameters.
According to different purpose, some high or low friction coefficient of the material surface is required. In this study, micro-dent texture was fabricated on cast iron specimens by a set of laser shock peening (LSP) experiments under different laser energy, with different patterns of micro dimples in terms of the depth over diameter. The mechanism of LSP was discussed and surface morphology of the micro dimples were investigated by utilizing a Keyence KS-1100 3D optical surface profilometer. The tests under the conditions of dry and lubricating sliding friction were accomplished on the UMT-2 apparatus. The performance of treated samples during friction and wear tests were characterized and analyzed. Based on theoretical analysis and experimental study, friction performance of textured and untextured samples were studied and compared. Morphological characteristics were observed by scanning electron microscope (SEM) and compared after friction tests under dry condition. The results showed that friction coefficient of textured samples were obvious changed than smooth samples. It can be seen that LSP is an effective way to improve the friction performance of cast iron by fabricating high quality micro dimples on its surface, no matter what kind of engineering application mentioned in this paper.
The wet ball-milling preparation of metal matrix micro-nanometer powder using nanosuspension as the precursor can well solve the agglomeration of nanoscale component, but the micro-nanometer powder prepared by the method can hardly meet the requirement of powder feeding in laser cladding process and its composite effect is still not desirable enough. Aiming at the problem, the ball-milling composite process of metal matrix micro-nanometer powder using nanosuspension as the precursor was analyzed. It has been found that the morphological diversity of original micron powder is the main influencing factor of the deliverability and the composite effect of micro-nanometer powder. In addition, the deposition of the compounding powder in the bottom of ball-milling tank also has some negative influences on the composite effect. Accordingly, two improving measures namely the micron powder pretreatment with Ball Mill Reshaping + Screening and the additional stirring during ball-milling process are proposed and experimented. Results show that the micron powder pretreatment could significantly improve the composite effect and the deliverability of micro-nanometer powder, and the additional stirring could further improve the composite effect of micro-nanometer powder.
Laser shot peening forming is a novel technique, which employes intense laser to induce residual stress distributed unevenly along the thickness to shape the metal plate. Theoretical analysis and experimental investigation reveal that laser peening forming is a mechanical, not a thermal process. The specimen was peened by laser along the centerline of the specimen, the shape of deformation of specimen is a bulge V-shape, that the plastic deformation centralizes on the narrow laser peening zone, and that other parts of specimen remain at original state but turn around the axis. The stress on both surfaces of deformed plate is compressive residual stress, which indicates that laser peening forming combines plastic deformation with surface improving treatment, and that the workpiece formed by laser peening has longer fatigue life.
The technology of laser shock wave is used to not only surface modification but also metal forming. It can be divided into three parts: laser shock processing, laser shock forming (LSF) and laser peenforming(LPF). Laser shock processing as a surface treatment to metals can make engineering components have a residual compressive stress so that it obviously improves their fatigue strength and stress corrosion performances, while laser shock forming (LSF) is a novel technique that is used in plastic deformation of sheet metal recently and Laser peen forming (LPF) is another new sheet metal forming process presented in recent years. They all can be carried out by a high-power and repetition pulse Nd:Glass laser device made by Jiangsu University. Laser shock technology has characterized of ultrahigh pressure and high strain rate (106 - 107s-1). Now, for different materials, we are able to form different metals to contours and shapes and simultaneity leave their surfaces in crack-resistant compressive stress state. The results show that the technology of laser shock wave can strengthen surface property and prolong fatigue life and especially can deform metals to shapes that could not be adequately made using conventional methods. With the development of the technology of laser shock wave, the applied fields of laser will become greater and greater.
As the rapid market need of micro-electro-mechanical systems engineering gives it the wide development and application ranging from mobile phones to medical apparatus, the need of metal micro-parts is increasing gradually. Microforming technology challenges the plastic processing technology. The findings have shown that if the grain size of the specimen remains constant, the flow stress changes with the increasing miniaturization, and also the necking elongation and the uniform elongation etc. It is impossible to get the specimen material properties in conventional tensile test machine, especially in the high precision demand. Therefore, one new measurement method for getting the specimen material-mechanical property with high precision is initiated. With this method, coupled with the high speed of Charge Coupled Device (CCD) camera and high precision of Coordinate Measuring Machine (CMM), the elongation and tensile strain in the gauge length are obtained. The elongation, yield stress and other mechanical properties can be calculated from the relationship between the images and CCD camera movement. This measuring method can be extended into other experiments, such as the alignment of the tool and specimen, micro-drawing process.
Laser Shock Forming (LSF) is a new forming method for sheet metal, and a settle of LSF equipment carry out technics and forming process, which are made up of high power pulse laser, 5-axis coordinated movement worktable, Industrial Personal Computer, SERCOS field bus and control software etc. In order to satisfy request to adjust the work surface which needs forming to be perpendicular to laser beam, put forward a kind of new B-spline interpolation arithmetic for 5-axis movement, and according to emulation by MATLAB, it testified that maximum error when interpolated a dimensional curve was not more than one micron if instruction speed is 600 millimeters per second.
The criterions for determining the minimum number of arrayed waveguides are presented using the design theory of arrayed waveguide gratings (AWGs) and Fraunhofer diffraction principle for the optimal design of AWGs. In addition, some parameters such as the cross section of waveguides and the waveguide separation between adjacent waveguides are chosen to optimize the AWG structure to satisfy the performance specifications and to match the fabrication conditions in our laboratory. As an example to demonstrate the effectiveness of the proposed method, the simulated results of the designed 16 16 AWGs with silica-based sol-gel material were provided using the beam propagation method (BPM). And the effectiveness of optimal parameters, especially to the selection of the minimum number of arrayed waveguides on the performance of the AWG, has been perfectly verified by comparing the transmission spectra of the designed AWGs. The design methodology can serve as a simple and useful tool for the optimal design of AWG multiplexers/demultiplexers.
Mechanism of laser shock forming(LSF) is introduced, and cause of laser shock wave is explained. As shortage of R. Fabbro's laser shockwave model and of pressure estimate, both a mathematical model and the estimated formula of shockwave pressure are put forward, the formula shows clearly the relation between the peak value of shockwave and the overlay, energy absorbed layer, sheet metal properties and the laser parameters. Based on the formula and the tensile yield strength of sheet metal, minimum laser energy of deformation is estimated. To discuss the relationship between laser energy and sheet metal deformation the experiment is done, the results show that minimum energy computation accords with critical value of deformation, and that the deformation increases with the increase of laser energy in a nonlinear way. These provide a theory foundation to exactly control and predict deformation of sheet metal.
Laser shock forming(LSF) is a new forming technique of sheet metal by applying a compressive shock wave on the surface of metal sheet. The plastic deformation of TA2 titanium metal sheet is performed under single laser shocking perpendicularly with Nd:Glass laser developed in Jiangsu University. The residual stress state in the horizontal and diagonal direction of the foursquare specimen, as well as the residual stress state in the radial direction of the circular specimen, was investigated with X-ray stress analyzer. The residual stress state of laser shock forming specimen is unique to some extent by contrast with traditional punch forming, which is influenced by the specimen shape and the deformation rate. The experiment results show that residual stresses value of TA2 Titanium Sheet Metal in laser shock area are up to 100MPa.Square specimen is more difficult to be formed than circular specimen, and the press value of cave is the larger than the one of convex.
Sheet metal forming is a widely applied industrial process that can be found in the fields of aerospace and automobile panel’s production, the conventional forming of sheet metal is realized by the Die and Mold, this method usually give rise to high cost, long production periods and little flexibility. In this paper, a flexible forming technique of sheet metal based on laser shock peening is presented and some preliminary experiments were carried out with Nd:Glass laser of a pulse of 20 nanoseconds long and 1.064μm wavelength, an energy per pulse of 10 to 30 joules. The mathematical modeling of sheet metal bulging based on laser shock peening was established, and a finite-element analysis method based on the ABAQUS software is applied to simulate the sheet bulging process. The numerical simulation indicates that the results agree well with the experiments under one laser shock peening. The investigation revealed that the combination of numerical simulation and experiments is a useful method to obtain the optimized laser parameters, and to better understand the sheet deformation characteristics under laser shock loading.
A new technique about evaluation of the adhesion strength of the film on the metallic substrate is presented in this article and the mechanism ofdynamic decohesion induced by the directed pulsed laser irradition forming is investigated elementarily from the theory. The procedure of laser-induced decohesion of TiN layers on SUS3O4 stainless steel has been investigated by means of in-situ laser interference ultrasonic measurements. The experiments were carried out by using a ?=532nm, ?=8ns (FWHM ) laser pulses irradiating the TiN film on the metallic substrate with a series of energy densities. The damage degree and dynamical procedure have been studied as a function of the energy density of laser pulses. The results demonstrate that interferometer measurements are a suitable non- invasive in-situ diagnostics tool for the assessment of the damage of the films that additionally provide valuable information conceming the process dynamics. Such results indicate that the dynamic decohesion procedure of the films is the most likely mechanism responsible for the laser-induced spallation process. At last the adhesion of the films on the metallic substrate are evaluated quantitatively.
Finite element simulation of measuring the film-matrix interface strength was the most concern of this paper. Instead of in previously reported measurements the experimentally measured free surface velocity, enegry and pessure of laser pulse in the present article allowed definition of the loading conditions in the numerical model. On the basis of theory for laser hypervelocity impact dynamics, experiment was predigested into two relative but non-coupling processes, transient thermal analysis and transient dynamics analysis. In the former, the procedure employed for the solution of thermal equation was the generalized trapezoidal rule. In the latter, the Crank-Nicholson difference time integration method was employed for the solution of wave equation. Based on the experiments, a model for laser-induced film spallation was proposed to study the propagation of stress wave and to evaluate the spall resistance of sputtered films. The analyzed result showed the dynamic adhesive strength of the TiN coating on the 304 stainless steel substrates is 183.64Mpa. It is theoretically proved that the interface stress triggering the film pry-offs was not single superimposition of pressure pulse and reflected tensile pulse, but multi-superimposition of pressure and tensile pulses.
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