A Study on Prediction of Weld Geometry in Laser Overlap Welding of Low Carbon Galvanized Steel Using ANN-Based Models

Predictive modelling for quality analysis becomes one of the most critical requirements for a continuous improvement of reliability, efficiency and safety of laser welding process. Accurate and effective model to perform non-destructive quality estimation is an essential part of this assessment. This paper presents a structured approach developed to design an effective artificial neural network based model for predicting the weld bead dimensional characteristic in laser overlap welding of low carbon galvanized steel. The modelling approach is based on the analysis of direct and interaction effects of laser welding parameters such as laser power, welding speed, laser beam diameter and gap on weld bead dimensional characteristics such as depth of penetration, width at top surface and width at interface. The data used in this analysis was derived from structured experimental investigations according to Taguchi method and exhaustive FEM based 3D modelling and simulation efforts. Using a factorial design, different neural network based prediction models were developed, implemented and evaluated. The models were trained and tested using experimental data, supported with the data generated by the 3D simulation. Hold-out test and k-fold cross validation combined to various statistical tools were used to evaluate the influence of the laser welding parameters on the performances of the models. The results demonstrated that the proposed approach resulted successfully in a consistent model providing accurate and reliable predictions of weld bead dimensional characteristics under variable welding conditions. The best model presents prediction errors lower than 7% for the three weld quality characteristics.

A Three-Dimensional Numerical Model for Predicting the Weld Bead Geometry Characteristics in Laser Overlap Welding of Low Carbon Galvanized Steel

Laser welding (LW) becomes one of the most economical high quality joining processes. LW offers the advantage of very controlled heat input resulting in low distortion and the ability to weld heat sensitive components. To exploit efficiently the benefits presented by LW, it is necessary to develop an integrated approach to identify and control the welding process variables in order to produce the desired weld characteristics without being forced to use the traditional and fastidious trial and error procedures. The paper presents a study of weld bead geometry characteristics prediction for laser overlap welding of low carbon galvanized steel using 3D numerical modelling and experimental validation. The temperature dependent material properties, metallurgical transformations and enthalpy method constitute the foundation of the proposed modelling approach. An adaptive 3D heat source is adopted to simulate both keyhole and conduction mode of the LW process. The simulations are performed using 3D finite element model on commercial software. The model is used to estimate the weld bead geometry characteristics for various LW parameters, such as laser power, welding speed and laser beam diameter. The calibration and validation of the 3D numerical model are based on experimental data achieved using a 3 kW Nd:Yag laser system, a structured experimental design and confirmed statistical analysis tools. The results reveal that the modelling approach can provide not only a consistent and accurate prediction of the weld characteristics under variable welding parameters and conditions but also a comprehensive and quantitative analysis of process parameters effects on the weld quality. The results show great concordance between predicted and measured values for weld bead geometry characteristics, such as depth of penetration, bead width at the top surface and bead width at the interface between sheets, with an average accuracy greater than 95%.

FEM SIMULATION OF RESIDUAL STRESSES INDUCED BY LASER SHOCK WITH OVERLAPPING LASER SPOTS

The finite element method is presented to attain the numerical simulation of the residual stresses field in the material treated by laser shock processing. The distribution of residual stresses generated by a single laser shock with square and round laser spot is predicted and validated by experimental results. With the Finite Element Method （FEM） model, effects of different overlapping rates and impact sequences on the distribution of residual stresses are simulated. The results indicate that： （1） Overlapping laser shock can increase the compressive residual stresses. However, it is not effective on the growth of plastically affected depth; （2） Overlapping rate should be optimized and selected carefully for the large area treatment. Appropriate overlapping rate is beneficial to obtain a homogeneous residual stress field; （3） The impact sequence has a great effect on the residual stress field. It can greatly attenuate the phenomenon of the “residual stress hole” to obtain a homogeneous residual stress field.

EFFECT OF OVERLAPPING TREATMENT ON MICROSTRUCTURE OF LASER-CLAD WC/Ni60A COMPOSITE COATING

The effect of overlapping treatment on microstructure of laser clad WC/Ni60A composite coating was studied with XRD, SEM, TEM and SAED etc. The results show that during the overlapping treatment the existence of the residual heat and edge angle effect on the substrate has changed the composition and microstructure of the coating by raising the fusion temperature and increasing the dilution degree of the coating.

Experimental Investigation of Laser Welding Process in Overlap Joint Configuration

This paper presents an experimental investigation of laser overlap welding of low carbon galvanized steel. Based on a structured experimental design using the Taguchi method, the investigation is focused on the evaluation of various laser welding parameters effects on the welds quality. Welding experiments are conducted using a 3 kW Nd:YAG laser source. The selected laser welding parameters (laser power, welding speed, laser fiber diameter, gap between sheets and sheets thickness) are combined and used to evaluate the variation of three geometrical characteristics of the weld (penetration depth, bead width at the surface and bead width at the interface). Various improved statistical tools are used to analyze the effects of welding parameters on the variation of the weld quality and to identify the possible relationship between these parameters and the geometrical characteristics of the weld. The results reveal that the reached hardness values are similar for all the experimental tests and all welding parameters are relevant to the weld quality with a relative predominance of laser power and welding speed. The effect of the gap is relatively limited. The investigation results reveal also that there are many options to consider for building an efficient welds quality prediction model. Results achieved using an artificial neural network based simplified model provide an indication of the prediction model performances.

异质金属熔覆搭接率对Ni60A熔覆层显微组织影响

利用半导体激光器在45钢基体上熔覆Ni60A材料来制作镍基合金涂层的实验方法,研究了熔覆层内部显微组织、物相成分及显微硬度随着搭接率的变化规律,根据实验结果选择合适的搭接率以满足性能要求.结果表明,在搭接率为20%、30%、40%及50%时,随着搭接率的增大,熔覆层搭接区底部组织晶粒逐渐增大,中上部组织晶粒逐渐减小;熔覆层主要物相为γ-Ni固溶体相,还有大量的铬硼化物、碳化物等硬质强化相,并且当搭接率从20%逐渐增大到30%时,主要物相成分逐渐增多,搭接率从30%增大到50%时主要物相成分有所减少;熔覆层的显微硬度变化规律大致与物相成分变化规律相同,同样是在搭接率从20%增大到30%时逐渐增大,在搭接率为20%时显微硬度最低,在搭接率为30%时显微硬度最大,为700 HV,随后当搭接率增大到50%时显微硬度降低至665 HV.根据熔覆层的性能要求,显微硬度要高,组织晶粒要细小均匀,在仅考虑搭接率的变化时,综合分析显微组织、物相成分及性能,选择30%搭接率为最佳.

DP1180和S700MC异种高强钢激光焊接接头的组织和性能

采用激光搭接焊对DP1180和S700MC异种高强钢进行焊接,研究了焊接接头的微观组织和力学性能,并与DP1180同种钢焊接接头进行了对比。结果表明:DP1180和S700MC异种钢焊缝的横截面呈Y形,而DP1180同种钢焊缝的横截面呈V形;异种钢搭接焊接头的DP1180钢侧热影响区分别出现了软化和硬化现象,而S700MC钢侧热影响区只出现了较为严重的硬化现象,并没有明显的软化现象;在相同的熔宽条件下,DP1180和S700MC异种钢接头的拉剪力明显小于DP1180同种钢接头,但仍高于S700MC钢母材;所有接头的拉伸性能稳定,力学性能良好,并且同种钢和异种钢焊接均可通过增加焊长来提升焊接接头的承载性能。

光斑搭接率对激光清洗铝合金阳极氧化膜表面质量及耐磨性能的影响

目的研究激光清洗铝合金表面阳极氧化膜后,光斑搭接率对基材表面质量及磨损性能的影响规律。方法采用纳秒脉冲激光器清洗7075铝合金表面的阳极氧化膜,分析不同激光光斑搭接率(20%~60%)对材料表面形貌、元素含量、表面粗糙度、显微硬度、残余应力和耐磨性的影响,通过研究激光清洗后7075铝合金的表面特征,探究激光光斑搭接率对铝合金表面耐磨性的影响规律。结果随着光斑搭接率的减小,被清洗表面的显微硬度、粗糙度均呈现先减少后增大的趋势,残余应力呈现下降趋势。当光斑搭接率为46.7%~60%时,试样表面存在烧蚀形成的凹坑,导致粗糙度增大。当光斑搭接率为20%时,氧元素的含量较高,氧化膜去除不完整,达不到清洗要求。当激光光斑搭接率为33.3%时,激光清洗能够有效去除7075铝合金表面的阳极氧化膜,并会形成粗糙度较小、显微硬度较大的熔融热氧化层。结论经不同光斑搭接率清洗后,清洗表面磨损机制主要以磨粒磨损和剥层磨损为主,在光斑搭接率为33.3%时,表面清洗效果较好,同时清洗后的表面生成的熔融热氧化层可以提高耐磨性,此时样件表面磨损量达到最低值,这为铝合金清洗后重新使用提供了可行性。

选区激光熔化430不锈钢成形工艺优化

研究了选区激光熔化(SLM)430不锈钢线-面-体的成形质量与工艺参数之间的关系。设计了单熔道、多道搭接以及块体成形试验,分析了SLM过程中缺陷形成的原因,以致密度为评价指标,确定SLM430不锈钢的最佳成形参数。结果表明:高功率低扫描速度有利于获得连续均匀的单熔道形貌,当激光功率为200 W、扫描速度为800 mm/s时,熔道宽度分布均匀。多道搭接的结果显示表面粗糙度随扫描间距的增加先降低后升高,扫描间距为0.08 mm时粗糙度最小,为3.88μm,表面成形质量最佳。通过正交试验分析,发现3种因素对块体成形件相对致密度影响的显著性排序为:扫描速度>激光功率>扫描间距;相对致密度随扫描速度的增大而减小;随着激光功率和扫描间距的增加,相对致密度呈现先升高后降低的趋势;最终确定SLM 430不锈钢的最佳成形工艺参数组合为激光功率200 W、扫描速度600 mm/s、扫描间距0.08 mm,该参数下成形件相对致密度达99.56%。

无人机激光扫描测绘系统误差的模型检校技术及实验研究

该文提出一种检验和校正无人机激光扫描测绘系统误差的技术,并设计实验对该技术的误差检校效果进行验证。该技术的实现方法是根据系统主要误差构建基于航带平差的差异分析模型。无人机航测获得扫描数据后,使用迭代最近点(ICP)算法对采集到的数据进行航带点云配准,得到航带平差。将平差参数输入到差异分析模型中解算出系统误差,利用解算结果补偿系统、消除误差,从而达到系统校正的效果。从实验结果来看,使用系统误差模型校验技术后,初始点云图和校准后的新点云图在不同方向的航带点云颜色深浅一致,说明高程误差被消除。

随机重频激光制导雷达抗高重频干扰技术

为了能有效对抗高重频干扰,在分析高重频干扰破坏激光制导雷达信号处理机理的基础上,采用了随机重频照射激光波形,并利用激光目标指示器、目标和探测器的先验距离、速度特征,提出了基于自适应交叠波门的高重频干扰信号排查和鉴别方法,有效控制了重频干扰对目标捕获环节的影响,形成一套从波形设计到信号处理、目标捕获的端到端的抗高重频干扰解决方案,并进行了理论分析和实验验证。结果表明,在不同干扰场景下,有效捕获目标的时间均低于0.2 s,捕获时间在亚秒量级,与无干扰背景下目标典型捕获时间相当。此技术可有效对抗数十赫兹到250 kHz的固定/随机重频干扰,有利于提高制导武器对抗重频干扰的能力。

Global Calibration Method of Multi-sensor Vision System Using Skew Laser Lines

Multi-sensor vision system plays an important role in the 3D measurement of large objects.However,due to the widely distribution of sensors,the problem of lacking common fields of view（FOV） arises frequently,which makes the global calibration of the vision system quite difficult.The primary existing solution relies on large-scale surveying equipments,which is ponderous and inconvenient for field calibrations.In this paper,a global calibration method of multi-sensor vision system is proposed and investigated.The proposed method utilizes pairs of skew laser lines,which are generated by a group of laser pointers,as the calibration objects.Each pair of skew laser lines provides a unique coordinate system in space which can be reconstructed in certain vision sensor＇s coordinates by using a planar pattern.Then the geometries of sensors are computed under rigid transformation constrains by taking coordinates of each skew lines pair as the intermediary.The method is applied on both visual cameras with synthetic data and a real two-camera vision system;results show the validity and good performance.The prime contribution of this paper is taking skew laser lines as the global calibration objects,which makes the method simple and flexible.The method need no expensive equipments and can be used in large-scale calibration.

激光熔覆316L涂层晶粒生长取向与形貌对其耐蚀性能的影响

目的表征316L激光熔覆层的晶粒取向、形貌与其耐蚀性之间的关系,阐明晶粒形态对316L熔覆层耐蚀性能的影响原理。方法在Q235钢板上激光熔覆制备搭接率为20%、35%、50%的316L不锈钢熔覆层,获得具有不同取向与含量柱状晶的熔覆层。采用光学显微镜、扫描电子显微镜、能谱仪、X射线衍射仪、电化学工作站对熔覆层的显微组织、元素分布、物相组成及耐蚀性能进行表征。结果熔覆层的晶粒形态和耐蚀性能受到搭接率影响。熔覆层因搭接发生部分重熔和回火,产生了横向柱状晶,随着搭接率从20%增大至50%,横向柱状晶含量从25%提升到41%。搭接率不影响熔覆层物相组成,熔覆层主要物相均为γ相。横向柱状晶含量在38%和41%时的熔覆层自腐蚀电流密度较25%含量的熔覆层下降1个数量级,分别为3.73、1.34μA·cm^(-2),熔覆层耐蚀性能随横向柱状晶含量的增加而提升。结论熔覆层物相与搭接率无关,但搭接率会导致熔覆层晶粒生长取向与形貌发生变化:随着搭接率的增大,晶粒由等轴晶转变为横向柱状晶。横向柱状晶降低了腐蚀性介质的传输效率,导致熔覆层耐蚀性大幅度提升。

选区激光熔化交叠熔融扫描方法研究

选区激光熔化(selective laser melting,SLM)的成型质量主要与扫描激光参数、扫描路径策略有关。为降低SLM成型工件的位移偏差、内部等效应力以及成型表面的粗糙度,首先通过ANSYS Additive软件进行热应变仿真,研究在水平排列熔融和上下层交叠熔融两种情况下零件的应力分布和几何尺寸位移。结果表明,通过上下层交叠熔融的尺寸位移变形和内部应力均有所减小。然后在热应变仿真分析的基础上,采用一种小区域上下层二次交叠熔融的扫描策略,在SLM机器上采用316L不锈钢粉末进行小区域样件成型实验,结果表明能获得满足要求的成型质量。

多光束激光选区熔化拼接区域熔池动力学行为数值模拟

目的 针对多光束激光选区熔化加工拼接重叠区域的质量控制难题,研究拼接重叠区域的缺陷形成机理与控制手段。方法 通过建立激光选区熔化介观尺度高保真数值模型,基于流体体积法和射线追踪热源,还原粉末熔化凝固的加工过程,研究不同加工参数下拼接重叠区域熔池动力学和激光反射吸收行为,并对比分析拼接重叠区域和非拼接重叠区域激光-材料能量耦合机制。结果 在拼接重叠区域大小不同的情况下,重叠区域长度分别为160、200、240μm时,其拼接重叠区域熔道宽度宽于非拼接重叠区域,拼接重叠区域与非拼接重叠区域存在高度差,且重叠区域的全局激光吸收率要高于非重叠区域,其中重叠区域皆有孔隙缺陷,重叠区域240μm长度方案下的全局平均吸收率达到最高(0.417 56)。在拼接重叠区域长度为240μm、扫描速度为0.9 m/s和1.2 m/s时,由于获得的能量低于扫描速度为0.6 m/s时的能量,其重叠区域不存在孔隙缺陷。结论 拼接重叠区域的表面形貌和孔隙缺陷与熔池动力学和激光反射吸收行为密切相关,合适的加工参数可以改善拼接重叠区域的成形质量。

超高速线光斑激光熔覆不锈钢涂层显微结构及性能研究

目的设计超高速线光斑激光熔覆送粉喷嘴,在极高的熔覆效率和极低的搭接率下制备不锈钢熔覆涂层,对比研究圆光斑及线光斑下的熔覆涂层的微观组织结构及性能。方法基于送粉喷嘴流场及粉末粒子运动轨迹的模拟研究,设计超高速线光斑激光熔覆专用送粉喷嘴。在此基础上,以27Si Mn为基体,采用1mm×10 mm线光斑,在10%搭接率、熔覆效率4.5 m^(2)/h下,采用超高速线光斑激光熔覆FeCr合金薄涂层;作为对比,采用超高速圆形光斑(2 mm)激光在0.2 m^(2)/h熔覆效率下熔覆FeCr合金涂层。采用SEM、XRD对比分析线光斑/圆光斑涂层微观组织结构与涂层显微硬度。结果通收束角度为25°~27°的单流道送粉喷嘴可得到分布均匀、飞行速度适中的粉末束流。对比研究超高速线光斑及圆光斑激光熔覆涂层可知,相同扫描速度下2种光斑制备的涂层均较为致密,无裂纹与气孔,由熔覆层底部到熔覆层表面均呈现出平面晶—柱状晶—等轴晶的变化趋势,线光斑和圆光斑涂层硬度在700~800HV,线光斑下的熔覆层硬度分布更加均匀,表面粗糙度Ra可低至<4μm,搭接率可低至10%,熔覆效率可达4.5 m^(2)/h,远高于圆光斑激光下的熔覆效率。结论2种光斑模式下的涂层微观组织、相组成及硬度相当,但超高速线光斑激光熔覆层表面光洁度更高,表面粗糙度更低,熔覆效率可达圆光斑的20倍。

液压支架立柱基材27SiMn钢激光熔覆搭接工艺实验探究

根据矿用液压支架立柱在井下轴向和切向受力及易磨损的工作特点,对矿用液压支架立柱基材27SiMn钢的硬度和耐磨性进行实验探究分析,并利用激光熔覆技术对27SiMn钢表面改性。激光熔覆搭接实验在单道熔覆基础上,熔覆搭接第二道时,基材温度升高,实验条件与单道实验不同。在液压支架立柱基材27SiMn钢表面进行一系列激光单道熔覆实验,对比单道熔覆层厚度、摩擦磨损实验及硬度等检测结果,找到液压支架立柱基材表面搭接实验的合适参数。搭接处硬度高于基材3倍以上,搭接后熔覆层比基材更耐磨,实验结果满足实际加工工序需要,并为激光熔覆在液压支架立柱表面熔覆后加工处理奠定有效实验理论基础。

能量耦合模型的飞秒激光烧蚀面齿轮形貌研究

飞秒激光精微加工面齿轮材料18Cr2Ni4WA是去除材料的先进制造方法。本文依据烧蚀凹坑的深度与宽度和激光能量密度的关系得到材料的烧蚀阈值和影响重叠率的因素。考虑齿轮材料成分间互温感应效应与多脉冲激光累积效应,建立材料的能量复耦合模型。通过改变激光能量密度和脉冲数,研究飞秒激光烧蚀凹坑及齿面形貌表面的变化规律,得出脉冲数对烧蚀效果影响小,激光能量密度为1.730 J/cm2激光功率为1.9 W脉冲数N=3000进行烧蚀效果最好可得到最优的实际烧蚀面深度为17.604μm。

激光冲击光整对2024铝合金铣削平面表面质量的影响

目的减小铝合金铣削平面的表面粗糙度,满足工程应用中对构件高质量表面的需求。方法通过铣削加工获得3种具有不同初始表面粗糙度的平面试样,试样的Ra分别为1.439、0.614、0.220μm。采用短脉冲、高功率密度激光对表面进行光整处理,利用激光共聚焦显微镜观察光整后试样的表面形貌,采用粗糙度仪检测试样的表面轮廓和表面粗糙度,分析光斑搭接率和激光能量对铝合金铣削平面表面质量的作用规律。结果在脉冲宽度为12 ns、波长为1064 nm、工作频率为1 Hz、光斑直径为2 mm的平顶光束作用下,试样的表面形貌发生重塑。当光斑搭接率为30%、50%、70%时,对于Ra=1.439μm的试样,在冲击后其表面轮廓变化幅值分别为6.88、6.71、6.20μm,表面粗糙度变化率分别为−70.8%、−72.9%、−73.2%;对于Ra=0.614μm的试样,在冲击后其表面粗糙度变化率分别为−58.0%、−58.8%、−66.1%。当激光能量为1.5、2.5、3.5、4.5 J时,对于Ra=1.439μm的试样,在冲击后其表面轮廓变化幅值分别为6.92、6.71、5.22、6.18μm,表面粗糙度变化率分别为−68.1%、−72.9%、−74.6%、−73.8%;对于Ra=0.614μm的试样,在冲击后其表面粗糙度变化率分别为−49.2%、−58.8%、−54.4%、−58.1%。结论合理增大光斑搭接率和增强激光能量,能够有效去除铣削刀痕,改善试样表面形貌的均匀性。光斑搭接率和激光能量对表面粗糙度的影响与试样的初始表面粗糙度有关。对于Ra=1.439μm和Ra=0.614μm的试样,增大光斑搭接率和增强激光能量均能显著降低其表面粗糙度;对于Ra=0.220μm的试样,在文中的激光冲击参数范围内均不能有效提高其表面质量。

激光诱导击穿光谱的Gold去卷积算法自动寻峰

为提高激光诱导击穿光谱(LIBS)寻峰中重叠谱的分辨能力并抑制随机噪声的干扰,提出用Gold去卷积算法结合平滑处理的自动寻峰方法。对于标准样品NIST 1256b和NIST 1762的LIBS光谱,先进行平滑处理,然后采用高斯形系统函数去卷积,最后用五点法对去卷积结果进行自动寻峰。实验研究了平滑处理结合不同半峰全宽(FWHM)的系统函数对重叠峰分辨能力和抗随机噪声干扰能力的影响。结果表明,采用0.140 nm(比弱峰的FWHM稍大)作为Gold去卷积系统函数的FWHM,结合平滑处理能取得高达0.039 nm的重叠谱分辨能力,且寻峰峰位、峰值、曲线拟合与NIST数据库的数据都能较好地吻合。研究初步表明基于Gold去卷积算法的自动寻峰可应用于LIBS数据处理。