激光加热辅助切削技术及研究进展

激光加热辅助切削技术将激光作为热源来提高切削区的温度,达到降低切削力、延长刀具寿命、提高表面质量及加工效率的目的.介绍了激光加热辅助切削技术的特点、加工方式及加工机理,从仿真研究与试验研究两方面,对激光加热辅助切削技术的研究现状进行了分析和总结,讨论了其研究的发展方向.     

Effect of intermediate heat treatment temperature on microstructure and notch sensitivity of laser solid formed Inconel 718 superalloy

Inconel 718 superalloys deposited by laser solid forming (LSF) were heat treated with solution treatment,intermediate heat treatment (IHT) and two-stage aging treatment in sequence (SITA heat treatment).The effect of IHT temperature on microstructure,tensile property and notch sensitivity of LSFed Inconel 718 superalloy at 500 ℃ were investigated.As-deposited columnar grains have transformed to equiaxed grains and the grains were refined due to the recrystallization during the SITA heat treatment.It is found that the size and amount of δ phase dispersed at grain boundaries decreased with the increasing of IHT temperature,and δ phase disappeared when the IHT temperature reached 1 020 ℃.The ultimate tensile strength (UTS) and yield strength (YS) of smooth samples increased to a maximum when the IHT temperature reached 980 ℃ and then decreased slightly to a minimum when the IHT temperature was 1 000 ℃,and followed by slight increasing again till the IHT temperature reached 1 020 ℃,resulted from the competition of precipitation strengthening effect of γ″ and γ’ phase and the grain boundary weakening effect caused by the gradual disappearance of δ phase with increasing the IHT temperature.The notch sensitivity factor (qe) decreased but still greater than 1 as the IHT temperature increased,which is attributed to the decrease of the size and amount of δ precipitation.     

Microstructure of Selective Laser Sintered Polyamide

1　IntroductionSelectivelasersintering (SLS)isanadvancedrapidprototypingtechnologythatcanshortenthedesignandmanufacturingcycle ,hencereducetheproductioncostandincreasethecompetitivenessofnewproducts[1] .SLSisathermalprocess ,creatinglayersbyascanninginfraredla serbeammeltingpowder[2 -4] .Eachlayerisdrawnonthepartcylinderusingthelasertosinterthematerial.Thenthepartbedisloweredandpowder feedingcartridgeraised .Anewcoveringofpowderisnextspreadbyaroll er.Thesinteredmaterialformsthepartwhiletheu…     

陶瓷材料激光加热辅助切削温度场分析

对激光加热辅助切削时的温度场进行了分析研究。在建立激光加热及切削温度场数学模型的基础上,利用有限元数值分析的方法,对激光加热辅助切削时的 温度场进行了分析计算。计算的结果表明,激光加热辅助切削时,由于激光加热温度场和刀具切削温度场的叠加作用,使切削区的温度很高,其高低的程度和激光加热点到刀具的距离以及切削速度有关,另外还与被加工材料的热物理性能有关。     

6061铝合金表面激光熔覆温度场的仿真模拟

利用连续波Nd:YAG固体激光在6061铝合金表面激光熔覆SiC陶瓷粉末，采用ANSYS有限元软件对6061铝合金激光熔覆过程中热量传递及温度场分布进行模拟，在分析过程中采用三维单元，并考虑了材料热物性的非线性及对流和辐射的边界条件，建立了有限元模型，得出了熔覆过程中试样表面的温度分布模拟图.结果表明，温度场模拟等温线呈椭圆形，在移动热源的前方等温线密集，温度梯度较大，热源后方的等温线稀疏，温度梯度较小，熔池内最高温度与激光扫描速度、光斑半径均成反比，与激光功率成正比.模拟结果为陶瓷金属基复合材料激光熔覆工艺参数的优化提供了理论依据.     

激光切割筛管中的温度场与热影响区研究

在求解温度场的数学模型时,采用了更接近实际状况的变物性非线性热传导方程.应用有限元法,数值求解了激光切割这种高能流密度、移动点热源所形成的非稳态温度场,得到了激光切割石油筛管过程的传热规律.结果表明:激光切割石油筛管的过程是在热源附近形成一个准稳定高温区,即对于以热源中心为原点的移动坐标系,该温度区内的温度不随时间而变化,并且不同输出功率的热影响区不同.     

IR Spectra Analysis of SiO2-TiO2-GeO2 Gel Glass of CO2 Laser Transmitting Hollow Waveguide

Both titanium and germanium were introduced into silicon dioxide system by sol-gel method to move its region of anomalous dispersion caused by IR resonance absorption towards the wavelength of CO₂ laser. It is indicated by IR absorption spectra that as the content of SiO₂ decreases in this glass system TiO₂ and GeO₂ tends to exist in their own phases. As for the gel glass with a composition of 40 SiO₂·30TiO₂·30GeO₂, when the temperature is below 600°C, germanium atoms exist mainly in Ge−O−Ge bonds. With the temperature increasing from 800°C to 1000°C, titanium atoms in Si−O−Ti bonds abmost transform into Ti−O−Ti bonds. Furthermore, a large number of Si−O−Ti and Si−O−Ge bonds formed when the temperature approaches 800°C, which makes a notable IR absorption band round the wavelength of CO₂ laser. Therefore, sol-gel based SiO₂−TiO₂−GeO₂ gel glass is a candidate material for CO₂ laser hollow waveguide. JING Cheng-bin: Born in 1974. This work was partly financially supported by the Foundation of Key Teachers of Ministry of Education, China.     

双脉冲输出激光器设计

激光器作为一种重要的辅助光源已被广泛应用于用于材料加工、激光加工、精密测量和精密加工等工业环境中。文章设计了一种双脉冲输出光器,对其进行了理论及实验装置结构设计,并对设计进行了可行性验证试验,结果表明:在LD泵浦源的激励下,产生了最高功率达到0.57 W的双脉冲绿色激光;随着泵浦源电流的增大,得到的绿色激光的光功率越大,直到其达到峰值;通过光电转换,采用高速示波器进行双脉冲的光信号采集,检测出激光脉冲的周期和脉宽均为20μs。     

Preparation and Properties of IrO2 Thin Films Grown by Pulsed Laser Deposition Technique

Highly conductive IrO2 thin films were prepared on Si （100） substrates by means of pulsed laser deposition technique from an iridium metal target in an oxygen ambient atmosphere. Emphasis was put on the effect of oxygen pressure and substrate temperature on the structure, morphology and resistivity of IrO2 films. It was found that the above properties were strongly dependent on the oxygen pressure and substrate temperature. At 20 Pa oxygen ambient pressure, pure polycrystalline IrO2 thin films were obtained at substrate temperature in the 300-500℃ range with the preferential growth orientation of IrO2 films changed with the substrate temperature. IrO2 films exhibited a uniform and densely packed granular morphology with an average feature size increasing with the substrate temperature. The room-temperature resistivity variations of IrO2 films correlated well with the corresponding film morphology changes. IrO2 films with the minimum resistivity of （42 ±6）μΩ·cm was obtained at 500℃.     

Radiometric Calibration Chain Design Based on Uniform Collimated Laser Source

A uniform collimated laser source,composed of the integrating sphere source and the off-axis parabolic,is designed.The calibration process is analyzed theoretically,and Monte Carlo ray tracing method is used to simulate and analyze the design model.The results show that when the calibration source is composed of an 8 cm diameter integral sphere,10 mm diameter exit port,and 1 000 mm focal length,and an off-axis angle 60°parabolic mirror,the maximum divergence angle is 7.5 mrad and the uniformity of irradiance is 99.31%.Finally,the uncertainty of radiometric calibration process is analyzed,and the calibration accuracy of 0.335%for imaging spectrometer can be achieved by using the radiation calibration laser source.     

Preparation of hydrophobic surface on titanium by micro-rolling and laser diffusion carbonitriding

The application of rolling for fabricating grate on titanium stripe has been explored in this paper. Then the mechanically robust Ti(C,N) diffusion layer was synthetized directly on the grates by laser carbonitriding in the mixture gas of nitrogen and methane. The results shows that the carbonitriding process is accelerated by temperature enhancement with decreasing scanning speed. The Ti(C,N) diffusion layer is kept at 2 μm in thickness, when the scanning speed is smaller than 4 mm/s. The contact angle increases from 20° to 143.6° by designing an appropriate grate size and surface roughness. Meanwhile, the relationship between hydrophobicity, hardness performance and scanning speed is also discussed. The hardness of diffusion layer increases with decreasing laser scanning speed, and is up to 11.2 GPa. The surface structure and hydrophobic state are maintained after three cycles of sandpaper abrasion, which has improved the robustness of surface grate.     

激光相位噪声对相干光纤通信系统性能的影响

研究了激光相位噪声对相干光纤通信系统调制格式选择、参数优化和载波相位估计性能等的影响,仿真研究表明:对于16-QAM相干光纤通信系统,star型星座图中星点位置关系可以依据系统噪声特性优化,具有比square型星座图更大的激光相位噪声容限;经典的Viterbi-Viterbi载波相位估计方法用于相干光纤通信系统时,算法中对符号序列平均的最佳长度与激光相位噪声成反比;对于一定的目标误比特率,相干光接收机中A/D有效位数的大小与系统调制格式阶数和星座图特征基本无关。     

冷硬铸铁激光加热辅助切削实验研究

冷硬铸铁具有很高的硬度、强度和很好的耐磨性，但其切削加工性能很差。激光加热辅助切削是加工冷硬铸铁这种高硬材料的有效方法。进行了常规切削和激光加热辅助切削对比性实验研究，检测了切削力随切削深度和切削速度的变化规律，实验结果表明，激光加热辅助切削冷硬铸铁时切削力下降非常明显，接近50％；进行刀具磨损实验，加热辅助切削明显减轻了刀具的磨损，磨损量降低了24％，提高了刀具的寿命。     

FV520(B)钢叶片激光再制造动态形变规律及试验优化

针对体积损伤压缩机叶片的激光再制造成形形变控制难题,采用有限单元"生死"控制方法,模拟脉冲激光优化工艺下成形过程,获取成形形变动态历程及规律,优化了脉冲激光成形工艺并采用IPG光纤激光再制造系统开展了叶轮激光再制造成形试验.采用Power Scan II型蓝光三维反求测量仪精确测量了再制造成形形变尺寸,验证了有限元分析结论的正确性.试验结果表明:增加首末两成形层之间时间间隔,可控制整体形变在1 mm以内,热影响区形变控制在0.280.50 mm以内,经机械加工后尺寸误差精度不超过0.02 mm,角度误差精度不超过0.03°,验证了脉冲激光工艺的优化性,为叶片类部件再制造成形提供工艺参考.     

直接金属选区激光多道烧结温度场有限元模拟

局部输入的集中移动激光热源势必造成直接金属选区激光烧结过程中温度场分布不均匀、不稳定。研究多道激光烧结对掌握烧结过程中温度场动态分布及不同烧结道的相互影响规律具有重要意义。在考虑随温度变化而变化的热传导、比热容等热物性参数的作用下，建立直接金属多道烧结的三维温度场有限元模型。采用ANSYS参数化设计语言模拟多道烧结的热源移动，用焓处理相变潜热的影响。模拟结果显示：随着烧结过程的进行，随后的烧结道具有越来越大的热影响区域，且热影响区域的不均衡性越来越明显；极大的温度梯度发生在激光束扫描方向改变时的烧结件边沿区域。模拟结果的最高温度、平均温度与先前的实验结果一致。     

Thermal fatigue behavior of 441 ferritic stainless steel in air and synthetic automotive exhaust gas

The thermal fatigue behavior of 441 ferritic stainless steel was investigated in air and synthetic automotive exhaust gas by the cyclic tests under 100°C–800°C and 900°C conditions. After the fracture failure, the microstructure, oxide film, and precipitated phases were analyzed using optical microscopy, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. In both atmospheres, increasing the maximum temperature from 800°C to 900°C results in lower strength and fatigue life and higher elongation and grain size. At the same maximum temperature, the thermal fatigue life of the specimen is lower in the synthetic exhaust gas than in the air. Both the higher maximum temperature and the synthetic exhaust gas facilitate fatigue failure. The failure mechanism is discussed according to the grain size, thermal stress, high-temperature oxidation rate, and the precipitation of secondary phases. Some precipitated carbides play an important role in the rapid fatigue failure of specimens in the synthetic exhaust gas.

     

基于灰度相似性的激光点云与全景影像配准

针对传感器参数未知、环境结构特征不明显、影像数据较少等情况，提出基于灰度相似性的车载3D激光点云与全景影像自动化配准方法. 基于全景拼接算法和柱面投影原理，分别将多张单幅图片拼接为全景影像，并将3D激光点云转换为2D深度图. 基于灰度相似性原理，将全景影像和2D深度图在水平方向和垂直方向等间隔细分成区域对，沿水平方向和垂直方向移动全景影像，计算每次移动后各细分区域对之间像素灰度值之和的比值，并求解其均方差，将均方差最小时的区域移动值作为最终匹配偏移量. 根据偏移量计算得到全景影像相对3D激光点云的水平旋转角度和垂直平移距离. 实测结果表明，本研究所提算法对场景的适应性较好，平均配准误差为2个像素，而对比方法无法实现有效配准.     

激光熔覆Co基合金应力场的数值模拟

为了分析co基合金熔覆过程的应力场,建立了激光熔覆预置co基合金粉末过程的三维模型,考虑温度变化对热物理参数的影响以及表面对流换热和辐射散热等影响因素,使用SYSWELD软件分析了激光熔覆过程中的应力场,并进行了试验验证。结果表明：通过比较分析扫描速度为5mm／s的涂层获得良好的冶金结合;工件残余应力均为拉应力,且最大值出现在z向距表面约2mm处,最大变形量出现在工件的边缘位置;随扫描速度的增加,工件的残余应力和变形均明显减小,这说明在其它工艺参数一定的前提下,适当降低扫描速度,能有效减小熔覆层的应力集中,获得质量优异的涂层。模拟结果为激光熔覆过程的工业化提供了理论依据。     

Analytical solution and experimental verification for pulsed laser heating process with convective boundary condition

Duetothecomplexityandthetransientfeatureoflaserprocessingprocess,realtimequalitycontrolviaexactmodellingandmulti-fieldcouplinganalysisbecomeaNomenclatured,absorptioncoefficient1/m;a,thermaldiffusivitym2/s;Cp,specificheatJ/kgK;r,densitykg/m3;k,thermalconductivityW/mK;I0,laserpeakpowerdensityW/m2;rf,reflectioncoefficient;h,convectivecoefficientW/m2K;Bi,Biotnumber,namelyhkd;s,Laplacevariable;T1,ambienttemperatureK;T0,initialmaterialtemperatureK;Te,materialtemperatureattimetK;m,dynamicviscos…     

LD泵浦Nd:YVO4自拉曼1 176 nm激光器

采用激光二极管端面泵浦Nd:YVO4晶体和声光调Q技术,获得1 064 nm脉冲激光.利用激光晶体基质材料YVO4的拉曼频移效应,将1 064 nm激光转变为1 176 nm拉曼激光,获得最大平均输出功率980 mW,相应的光-光转换效率为6.125%,输出最短单脉冲宽度为17.6 ns,最高峰值功率为1.94 kW.