FEM based simulation of the pulsed laser ablation process in nanosecond fields

For the pulsed laser ablation in nanosecond fields, the key physical phenomenon of the removing process is thermal evaporation. For the process optimization of the nano-second laser ablation, it is essential to set up effective simulation that can reflect material absorption coefficient, energy intensity of laser, laser pulse shape, and so forth. In this research, material ablation in nano-second region is simulated by using a finite element method (FEM) commercial package and its result has been compared with experiment results focused on the difference in the ablation depth and its shape occurred after each laser pulse hitting. Finally, the effect of the parameter variation on the ablation process has been verified.     

Theoretical and experimental investigation of pulsed laser grooving process

A theoretical model has been developed for simulating the laser grooving process. It takes into account the interaction among subsequent pulses, the required time for the melting temperature to be reached and the subsequent removal of a finite volume of material during each laser pulse. The model predicts the maximum groove depth that can be achieved for a specified set of process parameters, such as laser power, pulsing frequency, and scanning velocity. The theoretical predictions have been experimentally tested with a medium-power laser beam.     

A prototyping and microfabrication CAD/CAM tool for the excimer laser micromachining process

A CAD/CAM tool for prototyping and small-scale production of micro-electro-mechanical systems (MEMS) devices based on the excimer laser ablation process has been developed. The system’s algorithms use the 3D geometry of a microstructure, defined as an STL file exported from a CAD model, and parameters that influence the process (laser fluence, pulse repetition frequency, number of shots per area, wall angle, stitching errors) to automatically generate a precise NC part program for the excimer laser machine. The performance of the system has been verified by NC part program generation for several 3D microstructures and subsequent machining trials. An initial stitching error of 23.4±2.2-μm wide and 3.4±1.5-μm high was observed when the overlap size between adjacent volumes was zero, when ablating 100×100-μm features in polycarbonate (PC) at a fluence of 0.5 J/cm² using a workpiece-dragging technique. When the size of the overlap was optimised by a system based on optimal process parameters determined by the Taguchi design of experiment method (DOE), and incorporated in the mask design, the maximum stitching error was reduced to 13.4±2.2-μm wide and 1.4±0.9-μm high under the same conditions. By employing a hexagonal-shaped mask with incorporated size of the image overlap, reduced horizontal-stitching errors of 2.4±0.2-μm wide and 1.4±0.2-μm high were observed. The system simplifies part program creation and is useful for excimer laser operators who currently use a tedious trial and error process to create programs and complex masks to generate microstructure parts.     

Effect of process parameters and mathematical model for the prediction of bead geometry in pulsed GMA welding

Pulsed gas metal arc welding is one of the most widely used processes in the industry. It offers spray metal transfer at low average currents, high metal deposition rate, versatility, less distortion, and the ability to be used in automated robotic welding systems. The weld bead plays an important role in determining the mechanical properties of the weld. Its geometric parameters, viz., width, reinforcement height, and penetration, are decided according to the welding process parameters, such as wire feed rate, welding speed, pulse current magnitude, frequency (cycle time), etc. Therefore, to produce good weld bead geometry, it is important to set the proper welding process parameters. In the present paper, mathematical models that correlate welding process parameters to weld bead geometry are developed with experimental investigation. Taguchi methods are applied to plan the experiments. Five process parameters, viz., wire feed rate, plate thickness, pulse frequency, pulse current magnitude, and travel speed, are selected to develop the models using multiple regression analysis. The models developed were checked for their adequacy. Results of confirmation experiments show that the models can predict the bead geometry with reasonable accuracy.     

脉冲紫外激光和X射线辐照Al靶冲量耦合的异同性

为了探索不同脉冲束辐照热-力学效应的相似性关系,同时为实验室开展激光模拟x射线热力学效应研究提供参考,分析了脉冲紫外激光(0.308μm)和X射线辐照Al靶喷射冲量的异同性.首先,对二者辐照热一力学效应机理的异同性进行了比较;其次,理论和实验研究了两种脉冲束辐照Al靶引起的喷射冲量,对较低能注量(小于100 J/cm2...     

Effect of the process parameters on the three-dimensional shape of molten pool during full-penetration laser welding process

Slow tool servo (STS) turning is superior in machining precision and in complicated surface. However, STS turning is a complex process in which many variables can affect the desired results. This paper focuses on surface roughness prediction in lenses STS turning. An exponential model, based on the five main cutting parameters including tool nose radius, feed rate, depth of cut, C-axis speed, and discretization angle, for surface roughness prediction of lenses is developed by means of orthogonal experiment regression analysis. Meanwhile, a prediction model of surface roughness based on least squares support vector machines (LS-SVM) with radial basis function is constructed. Orthogonal experiment swatches are studied, and chaotic particle swarm optimization and leave-one-out cross-validation are applied to determine the model parameters. The comparison of LS-SVM model and exponential model is also carried out. Predictive LS-SVM model is found to be capable of better predictions for surface roughness and has absolute fraction of variance R² of 0.99887, the mean absolute percent error e_M of 8.96 %, and the root mean square error e_R of 10.68 %. The experimental results and prediction of LS-SVM model show that effects of tool nose radius and feed rate are more significant than that of depth of cut on surface roughness of lenses turning.     

Effect of process parameters on ferrite number in cladding of 317L stainless steel by pulsed MIG welding

Journal of Mechanical Science and Technology - In the current scenario cladding process are used in many engineering industries to enhance the corrosion resistance surface and wear resistance of...     

Investigation of laser and process parameters for Selective Laser Erosion

The process of Selective Laser Erosion (SLE) was investigated to study the effects of different process and laser parameters on the process outputs such as surface quality and erosion rate. The SLE process is a direct method to remove material in a layer-by-layer fashion due to high energy densities provided by the laser beam. In addition to its direct use as a subtractive manufacturing method, SLE may be used in combination with layer-additive techniques such as Selective Laser Melting (SLM). Such combination mainly makes sense when both processes can be performed with the same laser. However, one of the major problems involved in SLE process is the high number of the laser and process parameters (laser power, pulse frequency, scan speed, scan spacing, ambient atmosphere, etc.) and the complexity of the relations between them which has not yet been investigated completely.This paper presents an overview of the laser erosion process with nano-second Nd:YAG laser pulses and the results of several single-factor experiments that were carried out to determine the influence of the major parameters on the depth of erosion per layer and surface roughness. Additionally, the relations between the parameters are studied to investigate the interactions between them. The results from single-factor experiments showed that some relations were highly governed by the power intensity of the laser beam and also that cross interactions between the parameters play an important role on the output characteristics. The paper explains how multiple parameters (spot size, pulse frequency, scan speed, scan spacing) can be combined to define two indirectly controlled geometrical parameters, namely the scan and pulse overlap factors. Those two parameters allow calculating the number of hits of the laser beam on a same location on the workpiece possible which is the first step in physical modeling the topography of the surface left behind.     

微槽激光电解组合微加工研究

微槽结构作为微型结构的基本单元,具有增加散热面积、存储润滑剂和减少阻力等功能,多用于大热流密度器件的散热或表面润滑,但其存在加工尺寸小、精度要求高以及加工难度大等问题。为了实现微槽的高效高精度加工,提出了一种激光电解组合微加工方法,并搭建了纳秒激光加工装置和数控微细电解加工装置;利用激光烧蚀快速加工出微槽结构的基本形貌,再通过微细电解的方式去除其表面再铸层及飞溅颗粒,提高其表面精度和表面性能。通过理论研究以及优化加工参数试验,加工出长度为400μm,宽度为220μm,深度为120μm的微槽结构。激光电解组合微加工微槽的表面粗糙度由激光加工后的Ra 5.36μm降低至Ra 1.23μm;激光电解组合微加工的加工效率是微细电解加工的4.26倍。     

工艺参数对H13热作模具钢激光重熔-火焰喷涂复合涂层性能的影响

研究了工艺参数对激光重熔-火焰喷涂复合涂层后H13热作模具钢的高温耐磨损性能、高温力学性能、抗高温氧化性能和热疲劳性能的影响规律。结果表明,单一增大激光功率或喷枪移送速度,激光重熔-火焰喷涂H13热作模具钢的高温耐磨损性能、高温力学性能、抗高温氧化性能和热疲劳性能均先提高后降低。与未经喷涂处理的H13钢相比,激光重熔-火焰喷涂复合涂层H13钢在500℃下的磨损体积减小91%、抗拉强度增加151%、屈服强度增加182%、500℃高温氧化72h后的单位面积质量增重减小90%、热疲劳裂纹级别从11级变为2级。     

An innovative method to build support structures with a pulsed laser in the selective laser melting process

In selective laser melting machines, continuous laser are usually used to melt the powder. The support structures, which are inevitable when dealing with elaborated pieces, necessitate a complex design by CAD in order to be easily removed. This paper propose an innovative laser manufacturing method by combining pulsed and continuous modes of radiation. Continuous radiations are used for the object-to-build itself, in order to guarantee the requested mechanical properties. Pulsed radiations are used to build the support structures. The resulting support structures have sufficient mechanical properties to withstand the deposition system and to evacuate heat, and are easy to remove from the denser parts. This building method reduces drastically time to market since the same laser can be used in two modes and because pulsed radiation allows very high scanning speed with high power during the building of support structures.     

纳秒级激光脉冲展宽系统的分析及应用

建立了一种纳秒级多腔式激光脉冲扩展系统.通过激光脉冲展宽,该系统可以有效降低脉冲激光的峰值功率,从而在激光燃烧诊断实验中避免激光诱导等离子体的产生,减少背景干扰,有效提高信噪比.建立了理论模型,对影响脉冲展宽的分束比、腔长以及光学腔个数等几个主要参数进行了分析,并通过数值计算实现了各参数的优化.利用建立的多腔串联式激光...     

Influence and application of laser parameters on unit of H13 steel by laser remelting process

The International Journal of Advanced Manufacturing Technology - Die service life improvement is an important problem in high-pressure die casting industry. Former studies show that biomimetic...     

An investigation of accuracy,repeatability and reproducibility of laser micromachining systems

Component technologies of laser micro machining systems are key factors affecting their overall performance. The effects of these technologies on accuracy, repeatability and reproducibility (ARR) in different implementations of such systems have to be investigated to quantify their contributions to the overall processing uncertainty, especially those with the highest impact on beam delivery sub-systems. The aim of this research was to evaluate the capabilities of state-of-the-art machining platforms that were specially designed and implemented for laser micro structuring and texturing. An empirical comparative study was conducted to quantify the effects of key component technologies on ARR of four state-of-the-art systems. In particular, the capabilities of the optical and mechanical axes were investigated when they were utilised separately or in combination for precision laser machining. Conclusions are made about the positional accuracy of the mechanical and optical axes and the importance of their proper calibration on the systems’ overall performance is discussed. It is shown that the laser machining platforms can achieve repeatability and reproducibility better than 2 μm and 6 μm, respectively.     

结合核岭回归与多目标粒子群优化算法的激光焊接工艺参数预测

工艺参数选择是动力电池焊接行业面临的困难,为提升动力电池焊接效率并满足多项目标,采用核岭回归与多目标粒子群优化算法相结合的方法辅助优化工艺参数选择.构造了工艺参数对应的焊接下限,继而利用基于高斯核函数的核岭回归模型进行拟合;多目标粒子群的每个粒子代表一组工艺参数,通过群体进化与变异、引导者选取与优化、解集维护3种操作,并结合回归模型,有效获取了指定焊接目标下的最优解集.该方法还借鉴K近邻算法思想设计评价标准,以度量每个解的可靠性,进一步筛选更优质的解,保证所选工艺参数有更高的容错性.所提方法解决了电池焊接行业目前面临的问题,具有极其重要的应用价值.     

Ultrashort pulse laser micromachined microchannels and their application in an optical switch

The capability of direct writing makes ultrashort pulse laser significant in the microfabrication of MEMS devices based on polymer and glass. In particular, nanosecond and femtosecond lasers are able to transfer the adequate energy in femtosecond intervals for the removal of the materials. Because of its advantages, just like the small feature size, smooth finishing surface, flexible structuring and the minimum thermal effect, ultrashort pulse lasers have become a convincing technique with the high peak power. This paper presents the femtosecond laser machining results of the polycarbonate, aluminosilicate glasses and nanosecond laser machining of aluminosilicate glasses. The microchannels with the critical micron-scale dimensions and the sub-micron scale surface roughness were achieved by the optimized operating parameters of the laser. The major influence factors such as cutting speed, power energy, and power stability were analyzed to obtain the optimized parameters for the fabrication of the microchannels for a bubble switch. The ultrashort pulse laser micromachining was applied in the prototype of a bubble optical switch. By miniaturization of the structure of the microchannel, the switch speed can be promisingly improved.     

Elastic contact between rough surfaces: Effect of roughness at large and small wavelengths

The area and pressure distribution in elastic contacts between frictionless, nonadhesive surfaces is studied as a function of load and surface geometry using finite element calculations. Surfaces that follow self-affine scaling on all resolved scales are compared to surfaces with cutoffs at small and large length scales, and experimental surfaces that are not self-affine. In all cases the true area of contact is proportional to load and inversely proportional to elastic modulus and the mean slope of the surface. The constant of proportionality κ is nearly constant and lies between analytic predictions. Large wavelength cutoffs lead to a small increase in κ, a homogeneous distribution of contacts at large scales, and limit the size of the largest connected regions. Small wavelength cutoffs lead to local redistributions in pressure that decrease the probability of low and high local pressures.     

Effect of laser beam incidence angle on cladding morphology in laser cladding process

The change of angle θ between laser cladding powder plane and substrate plane will lead to changes in cladding layer's geometric morphology. Therefore, we established a quantitative numerical prediction model for cladding layer geometry. In this model, we consider the variation of θ, the laser energy attenuation rate and the temperature rise of the powder particles. At the same time, the simulation results were verified by experiments. The results show that when θ is in the range of 50°~90°, the initial temperature is 298 K, the scanning speed is 3.75 mm/s, and the laser spot diameter is 4.5 mm, the Fe#1 powder cladding can achieve better forming effect on Q235. In general, with the decrease of θ, the height of the cladding layer decreases and the width of the layer increases. However, when θ is less than 50°, the quality of the formed morphology significantly deteriorated. The experimental results are in good agreement with the simulation results, which verifies the validity and reliability of the model. This work provides a theoretical reference for further understanding the relationship between the laser cladding morphology and the incident angle.