激光熔覆粉末粒径对熔覆层成形控制的影响

目的 揭示激光熔覆过程中TiC粉末粒径及工艺参数对复合材料熔覆形貌的影响规律,实现熔覆层成形控制。方法 采用响应面法中心复合设计模块分析扫描速度、激光功率、粉末粒径对复合材料熔覆形貌的影响,建立工艺参数及TiC粉末粒径与复合材料熔覆层面积、熔覆层高度、熔覆层宽度之间的数学模型,通过方差分析和模型检验验证模型的准确性。结果 激光功率对复合材料熔覆形貌的影响不显著,粉末粒径对熔覆面积影响最为显著,熔覆层面积随着扫描速度的减小和粉末粒径的增大而增大;粉末粒径对熔覆层高度影响最为显著,熔高随着粉末粒径的增大而增大,随着扫描速度的降低而减小;扫描速度对熔覆层宽度的影响最为显著,熔宽随着扫描速度的增大而下降,随着粉末粒径的增大而增大。结论 以熔覆面积最大及熔宽熔高最大为优化目标,对比预测值与实际值,熔覆层面积、熔覆层高度、熔覆层宽度的误差率分别为6.81%,3.9%,7.7%。该研究成果为提高复合材料熔覆形貌的预测与控制提供了理论依据。     

交变磁场对高硬熔覆层成型质量的影响

为改善激光熔覆高硬熔覆层的成型质量,外加辅助交变磁场是行之有效的方法。本工作设计了一种可调频、调幅的简易机械式类正弦交变电磁场发生装置,在激光熔覆过程中辅助施加了类正弦交变磁场,通过改变磁感应强度和交变频率,在Q235A表面制备了单道和多道高硬合金熔覆层,通过对熔覆层的宏、微观检测,研究了交变磁场对熔覆层几何特征、稀释率和微观组织的影响。研究结果表明,当磁场频率和磁感应强度变化时,熔覆层宽度波动范围很小,且平均值基本保持不变;熔覆层高度和接触角随着磁感应强度的增大而减小;稀释率的大小基本不受磁场参数变化的影响;在磁场作用下,熔覆层中气孔向熔覆层表面迁移,熔融金属对流加剧,粗大枝晶破断,熔覆层组织更加均匀致密。     

TC4零件激光快速修复加工参数带的选择

通过研究激光加工参数,包括激光功率、光束扫描速度以及送粉率对热输入效率η和熔覆层形状系数ζ的影响规律,并结合激光快速修复过程对热输入效率和熔覆层形状系数的要求,建立了TC4激光快速修复的加工参数带。采用文章所确定的加工参数带中的参数,有利于减小激光快速修复件的变形,得到的修复件无熔合不良缺陷。     

激光熔化沉积工艺参数对CoCrFeNiMn系高熵合金成形的影响

目的 用激光熔化沉积法制备Co Cr Fe Ni Mn系高熵合金,以得出最优成型方案。方法 通过正交试验方法,以沉积层的显微硬度为评价指标,分析激光功率、激光扫描速度和送粉速度对沉积层成型质量的影响程度,并得出激光增材制造的最佳工艺组合。结果 当激光功率超过2 000 W时,沉积层表面开始出现烧蚀现象,沉积层表面出现波纹,熔池宽度不均匀;当激光扫描速度为5、7 mm/s时,沉积层相对较均匀,表面平坦;当送粉速度为0.7 r/min时,送入金属粉末的量的增加使沉积层体积增大,宽度变均匀。结论 最佳工艺参数为：激光功率P=2 000 W、扫描速度V_g=7mm/s、送粉速度V_f=0.7r/min。多道沉积时,搭接率为50%其成型性最优,制备得到的材料抗拉强度为453.7 MPa,伸长率为27.5%。     

真空环境下TC4激光熔丝增材制造工艺实验研究

目的 针对TC4金属增材制造制备的零件质量差的问题,研究真空环境下不同工艺参数对TC4激光熔丝增材制造的影响规律。方法 通过单因素单道工艺实验,研究激光功率、扫描速度、送丝比等工艺参数对单道沉积层形貌、宽度和高度的影响。结果 当激光功率小于230 W时,得到的单道表面形貌较为良好,熔覆层与基板区域结合较好,而当激光功率大于230 W时,则会在初始段产生鱼鳞状缺陷。随着激光功率从150 W增大到230 W,单道截面宽度从0.582 mm增大到1.123 mm,增大了93.0%。单道截面高度从0.443 mm降低到0.351 mm,降低了20.8%。当扫描速度小于1.5 mm/s时,单道表面也出现了“鱼鳞”状结构,导致质量下降;当扫描速度从1 mm/s增大到5 mm/s时,单道横截面宽度从1.003 mm降低至0.887 mm,降低了11.6%,而单道横截面高度则从0.332 mm增大至0.353 mm,只增大了6.32%。在不同送丝比情况下,单道表面形貌都较为良好,且随着送丝比从1增大至3,单道沉积层的高度从0.308 mm增大至0.465 mm,增大了51.0%。结论 激光功率是影响单道沉积层表面形貌和横截面宽度的重要因素,而扫描速度对横截面宽度和高度的影响幅度都很小,其影响程度远不如激光功率显著,送丝比只对单道沉积层的高度影响显著。     

结构材料喷射成形技术与雾化沉积高温合金

喷射成形是利用快速凝固方法直接制备金属材料坯料或半成品的先进材料制造技术 ,喷射沉积高温结构材料的冶金性能好、生产效率高、成本低 ,因而在近几年得到了迅速发展 .本项研究的主要目的是要通过喷射成形工艺参数的调整、最大限度地直接减少喷射成形坯中的孔隙度 ,进而得到优质坯料 .利用优化的雾化喷射沉积技术制备了多种高温合金沉积坯 ,沉积坯整体致密、晶粒细小、组织均匀、无宏观偏析、含气量低、力学性能提高 .还简要地比较了喷射成形高温合金与用常规铸锭冶金工艺和粉末冶金工艺制备高温合金的异同 ;总结了航空材料研究院喷射成形高温材料近年来的研究状况 ,包括专用高温材料喷射成形装置和技术及其应用 .     

基于回归方法和神经网络的电弧增材制造单道成形形貌预测

目的 针对电弧增材制造技术实际应用中工艺参数选取困难和成形结果难预测的问题,确定高效、准确的电弧增材制造单道成形形貌预测的数学方法,以快速、方便地选取丝材电弧增材制造工艺参数并指导成形质量控制。方法 在单道单层丝材电弧增材制造实验的基础上,采用多种回归方法和神经网络方法分别建立焊接电流、电压和焊枪移动速度等多个工艺参数与增材层宽度、增材层高度及熔池深度等成形形貌参数之间的数学关系模型。结果 电弧增材制造单道成形形貌与焊接电流、电压和焊枪移动速度显著相关,且各参数间存在非线性交互作用;采用多元线性回归法可较准确地预测单道增材层宽度,但对于增材层高度和熔深的预测效果较差;神经网络可良好地处理各工艺参数间复杂的非线性关系,其对增材层宽度、增材层高度和熔深的预测平均误差率分别为4.17%、6.60%和7.01%,显著优于多元线性回归法。结论 采用神经网络法可以准确预测电弧增材制造单道成形的形貌参数,进而指导增材制造工艺参数的选取和成形质量的控制。     

Rapid prototyping with high power fiber lasers

Laser rapid prototyping technologies comprise a set of technologies used in a wide range of materials to produce prototypes or small batches of complex shaped components. This paper presents a research work on rapid prototyping technology with laser additive manufacture of wire based alloy Ti-6Al-4V with an 8 kW fiber laser for the production of components with cylindrical geometry. For this, an engineering system was developed, a demonstration part produced and the deposition process was characterized. Two processing parameters were investigated: and these were the relative position between the wire feeding system and the substrate and the laser beam to wire width ratio. The former affects the molten metal transfer mode and the pressure exerted by the wire tip on the molten pool, while the laser beam to wire width ratio affects the process efficiency, since this is a compromise of process stability and process speed. Both parameters control surface finishing and the smoothness of the part. The melting efficiency of the process is low when compared to alternative processes involving powder pre deposition, but the density of the part is improved with homogeneous structural characteristics.     

单道激光熔覆Inconel 625熔覆层尺寸预测

目的 准确预测激光熔覆Inconel 625熔覆层尺寸。方法 以送粉速率、扫描速度和激光功率为试验变量,以熔覆层的宽度和高度为评价指标,结合中心复合试验设计方法进行试验设计,开展单道激光熔覆试验,探究工艺参数对单道熔覆层尺寸的影响规律,并建立以工艺参数为输入、熔覆层尺寸为输出的BP神经网络模型,利用粒子群算法对BP神经网络模型进行优化,对比分析优化前后模型的预测效果。结果 激光功率对熔覆层宽度的影响最显著,其次是扫描速度,最后是送粉速率;扫描速度对熔覆层高度的影响最显著,其次是激光功率,最后是送粉速率;粒子群算法优化BP神经网络预测模型对熔覆层尺寸的预测精度较高,熔覆层宽度和高度的测量值和预测值之间的平均相对误差分别为4.238%和2.910%。结论 研究成果可以为激光熔覆Inconel 625熔覆层尺寸的调控和预测提供参考。     

Numerical and experimental study of molten pool behaviour and defect formation in multi-material and functionally graded materials laser powder bed fusion

Laser powder bed fusion (LPBF) of multi-material and functionally graded materials (FGM) has attracted significant research interest due to its ability to fabricate components with superior performance compared with those manufactured with single powder material. However, the forming mechanisms of various defects remain unknown. In this paper, a DEM-CFD model was first established to obtain an in-depth understanding of this process. It was discovered that the defects including partially melted and un-melted Invar36 powder were embedded in the lower level of the powder layer; this was attributed to the low laser absorptivity, low melting point and high thermal conductivity of the Cu10Sn powder. Inter-layer defects were more likely to occur with an increased powder layer thickness. In addition, the scanned track width was found related to an equilibrium achieved among the thermal properties of the powder mixture. Process parameters were optimised to obtain FGM structures without defects in both horizontal and vertical directions. Invar36/Cu10Sn samples were fabricated with a multi-material LPBF system using different mixed powder contents and laser volumetric energy densities (VEDs). By increasing the VED, fewer defects were observed between the interface of two processed powder layers, which had a good agreement with the modelling results.     

Bulk synthesis of amorphous and nano‐crystalline materials by spray forming

Bulk amorphous and nano‐crystalline metallic materials have been observed to possess excellent mechanical and physical properties. The conventional process routes, to synthesize such materials, are restricted by their ability to achieve rapid solidification, which limits the dimensions of the materials produced. In the last 10–12 years, spray forming has been employed to avoid these limitations by using its capability of layer by layer deposition of undercooled droplets. The current literature indicates that the opportunities provided by this process can be effectively utilized to produce bulk materials in a single step. In this paper, an attempt has been made to bring out the developments in the synthesis of bulk amorphous and/or nano‐crystalline materials by spray forming. The effect of process parameters, droplet size distribution in the atomized spray, the thermal conditions of droplets prior to deposition and the deposition surface conditions have been discussed. It has been demonstrate that a layer by layer deposition of undercooled droplets of glass forming alloys on a relatively cold deposition surface is the suitable condition to achieve bulk amorphous/nano‐crystalline materials.     

Feasibility of underwater laser forming of laminated metal composites

Laminated metal composites are of great interest in various industries. Previous studies demonstrate undesired mechanical or microstructural changes in these composites during the laser forming process due to rapid temperature gradient. In this research, underwater laser forming is proposed to minimize this effect. This process could also be an effective method for on-site forming or repairing of large metal/composite sheets used in underwater applications, such as marine equipment, ships, and lake/sea-based offshore oil platforms. The underwater laser forming process is performed experimentally on a three-layered stainless steel/copper/stainless steel composite and compared with the results of in-air tests. Total forming time, bending rate, and microstructural changes are compared for both underwater and in-air conditions. The effects of forming parameters, such as the number of irradiations, laser beam velocity, diameter, and power, are also compared and discussed. It is shown that the bending angle per irradiation in underwater forming is significantly lower in comparison with in-air condition, but the production time is less due to the elimination of cooling time. Also, the microstructure of stainless steel at heat-affected zone was unchanged, and the hardness of upper layer experienced smaller changes when formed under water. The underwater laser forming process is demonstrated to be feasible and can be applied for underwater applications with a high degree of reliability.     

选区激光熔化工艺参数对Ti-6Al-4V成形质量的影响

选区激光熔化是一种利用高能束选择性熔化金属粉末进而直接制造复杂几何形状产品的增材制造技术。采用选区激光熔化成形Ti-6Al-4V样品,分析影响选区激光熔化成形质量的主要因素,采用体式显微镜、金相显微镜、扫描电子显微镜(SEM)、显微硬度计系统研究了不同工艺参数对Ti-6Al-4V合金选区激光熔化成形样品的表面形貌、致密度、组织、显微硬度的影响规律。研究得出Ti-6Al-4V合金选区激光熔化成形的优选工艺参数为:扫描功率450W,扫描速度2 500mm/s,扫描间距0.07mm,该工艺参数下打印出的样品具有较为优良的成形质量,致密度高达97.8%,显微硬度平均值为446HV。     

Parametric studies of multi-material laser densification

Fabrication of multi-material components via a laser-assisted layer-by-layer fabrication process has been numerically simulated and analyzed using a three-dimensional thermo-mechanical model. Effects of the chamber preheating temperature, laser scanning rate, initial porosity and thickness of each powder layer on the out-of-plane warping and residual thermal stresses of a nickel/porcelain workpiece have been investigated. It is found that warping and residual thermal stresses of the laser-densified multi-material workpiece are more sensitive to the chamber preheating temperature and the thickness of each powder layer than to the laser scanning rate and the initial porosity of the powder layer. The major mechanism responsible for these phenomena is identified to be related to the change of the temperature gradient induced by these laser processing parameters.     

Selective laser sintering of barium titanate–polymer composite films

A selective laser sintering process has been used to consolidate electro-ceramic thin films on silicon substrates. Methods of forming pre-positioned layers of barium titanate were investigated by spin-coating the feedstock powder mixed with a commercial polymer photo-resist. The ceramic–polymer composite was deposited directly onto a nickel film which was evaporated onto a silicon substrate, pre-oxidised to form an electrically insulating layer. A range of laser processing parameters was identified in which consolidated barium titanate layers could be formed. The laser power was found to be more influential in forming sintered microstructures than laser exposure time. The microstructure of barium titanate films is sensitive to the SLS laser-processing conditions, with the optimum laser powers for the processing of the BaTiO₃–polymer found to be in the range 17–20 W. This article highlights the possibility of using ‘direct write’ techniques to produce piezoelectric materials upon silicon substrates.     

Spray forming

Spray forming is a relatively new manufacturing process for near net shape preforms in a wide variety of alloys. Spray formed materials have a characteristic equiaxed microstructure with small grain sizes, low levels of solute partitioning, and inhibited coarsening of secondary phases. After consolidation to full density, spray formed materials have consistently shown properties superior to conventionally cast materials, and comparable to powder metallurgy equivalents. The reduction of processing steps for spray forming in comparison with powder metallurgy and conventional cast/forge routes offers potential economic advantages. However, serious economic barriers to the widespread commercialisation of spray forming remain. These include the high cost of inert gases for atomization, significant losses from overspray, bounce-off and machining, poor process reproducibility and problems of implementing robust on-line control for metallurgical quality. Extensive model experiments with process monitoring and numerical simulation have been used to understand the underlying process physics and the development of preform shape and microstructure in an effort to enable full process control and so reduce losses. However, despite considerable progress, the cost of spray forming has not yet reduced significantly to compete broadly with existing technologies.     

工艺参数对304不锈钢表面激光熔覆Ni基合金涂层的组织、耐磨性及耐腐蚀性的影响

研究了不同工艺参数对304不锈钢表面激光熔覆Ni基合金后熔覆层微观组织及硬度、耐磨、耐蚀性能的影响,并寻求最佳激光工艺参数,以期获得冶金结合较好,耐磨、耐蚀性能良好的熔覆层。根据组织与性能的综合分析可知,最优激光工艺参数为激光功率2.5kW、扫描速度4mm/s、送粉速率300mg/s。利用优化工艺参数熔覆后的熔覆层宏观形貌平整、光滑,熔覆层宽度为14.36mm,高度为1.612mm,熔池深度为0.248mm,稀释率为13.33,硬度较高,平均显微硬度为646.4HV,并且耐磨损性能较好,磨损量较低。此外,熔覆层的耐腐蚀性能也较好,自腐蚀电位为-286.77mV。在一定的激光工艺参数下,组织从结合区至熔覆层表层依次为平面晶、胞状晶、柱状晶、树枝晶、等轴晶。激光功率、扫描速度、送粉速率不同,熔覆层中组织粗细变化呈现一定的规律性:随着激光功率的增大,组织由细小逐渐变的粗大;随着扫描速度的增大,组织先变细小,然后变粗大;随着送粉速率的增大,组织逐渐变细小。合金的耐磨性与耐蚀性不仅与组织大小有关,而且与组织物相组成密切相关。     

激光技术在过滤器壳体制造中的研究与应用

目的 研究火箭发动机关键部件过滤器壳体的改良加工方案,以替代传统的化学铣切、手工氩弧焊等工艺,提高产品尺寸精度和生产效率。方法 改良加工方案采用激光切割、激光焊接等技术,利用激光切割精度高、成形快的优点,实现镂空区域的一次成形,避免化铣周期长、易于产生飞边且打磨困难的问题;利用激光焊接热输入量低、焊接变形少的特点,使镂空状态下单边宽度3.5 mm的筋条焊接成为可能。结果 通过设置合理的工艺参数,可以有效保证产品尺寸精度并控制焊接变形,提高生产效率。结论 使用该工艺方法已成功制备了产品,并经过了发动机试车考核。     

5556铝合金CMT增材单道成形质量及尺寸预测模型研究

目的 研究不同参数下5556铝合金CMT增材单道成形质量及尺寸预测模型。方法 利用游标卡尺和钢直尺,对增材试样截面的余高、熔宽、成形高度及成形宽度进行测量,并且使用SPSS、Excel及Origin等软件进行尺寸预测模型的建立及验证。结果 对于单层单道增材试样,随着焊接电流从60 A增至140 A,其余高、熔宽均整体呈上升趋势,并且余高的增长速度远小于熔宽的增长速度;随着焊接速度从300 mm/min增至1 100 mm/min,其熔宽、余高均呈下降趋势,但当焊接速度超过700 mm/min时,熔宽的变化较小;随着气体流量从10L/min增至25L/min,余高的变化幅度较小,但熔宽的变化幅度较大。对于多层单道增材试样,随着焊接速度从400 mm/min变为800 mm/min,其成形高度和宽度均变小;随着焊接电流从90 A变为130 A以及层间停留时间从1 min变为5 min,其成形高度和宽度均变大。通过多层单道增材实验和尺寸预测模型可知,焊接电流与增材试样的宽度呈正相关,焊接速度与增材试样的高度和宽度皆呈负相关。结论 单层单道增材试样的熔宽主要受焊接电流的影响,而余高主要受焊接速...     

基于PSO–BP–GA混合算法的激光熔覆工艺多目标优化

目的 为了提高镍基高温合金熔覆涂层的综合质量,提出了一种基于PSO–BP–GA混合算法的激光熔覆工艺优化方法。方法 选取工艺参数（激光功率、扫描速度、送粉速率）为优化变量、熔覆层质量（稀释率、显微硬度、热影响区深度）为优化目标,根据正交试验结果建立PSO–BP神经网络预测模型,采用线性加权法和层次分析法建立熔覆层质量的综合评价体系,结合GA算法探寻综合质量最优的工艺参数组合。结果 PSO–BP神经网络模型预测值与试验值之间的相对误差不超过6%,最优工艺参数组合如下：激光功率为2 158 W、扫描速度为10.4 mm/s、送粉速率为2.9 r/min,其熔覆层稀释率降低了70.4%、显微硬度增大了25.4%、热影响区深度减少了41.8%。结论 该算法为制备出高性能镍基高温合金熔覆涂层提供了一定的参考与借鉴。