Direct laser fabrication of nickel alloy samples

Direct laser fabrication (DLF) is an advanced manufacturing technology which can build full density metal components directly from CAD files without using any modules or tools. An open-loop controlled hardware system and associated control software for the DLF process of nickel alloy samples was constructed in our work. The hardware system is consisted of a CO₂ laser, a 4-axis CNC table, a coaxial powder nozzle and a powder recycler. In order to achieve the maximum flexibility and extensibility for the fabrication of metal parts, path plug-ins was introduced into the control software. The effect of the specific energy on the cross-section shape of nickel alloy cladding was studied by a single-track cladding experiment with different laser processing parameters. The comprehensive effect of the optimized laser processing parameters was also studied by an orthogonal experiment. The experimental results showed that the specific energy for laser processing is the most important factor, which controls the component qualities. There is an appropriate range for the specific energy in which the nickel alloy samples can be fabricated layer by layer with a uniform height. If the specific energy is too low, the inner height of a sample is lower than its contour height. Banding structure can be observed in the microstructure of nickel alloy samples. The gain size in the light zones of the bandings is much smaller than those in the dark zones.     

激光金属制造薄壁零件z轴单层行程模型

为了提高激光金属直接制造薄壁零件的成形精度,制备出表面平整的薄壁零件,研究了z轴单层行程参数对成形薄壁试件表面精度的影响规律,提出并验证了z轴单层行程理论模型.结果表明,在一定简化条件下,根据质量守恒定律,推导出任意参数下的z轴单层行程模型,该模型显示z轴单层行程是单道熔覆层宽度与高度的函数,当z轴单层行程与模型计算值一致时,能够制造出表面平整的薄壁零件.     

Manufacturing of micro thin-walled metal parts by micro-droplet deposition

Metal micro-droplet deposition manufacturing technique is a novel direct metal rapid prototyping for building the miniaturized parts. In this paper, the novel direct metal rapid prototyping was proposed to fabricate micro thin-walled metal parts. A direct droplet fabrication experimental system was developed based on the forming principle of micro-droplet deposition manufacture. Several deposition experiments were conducted to investigate the influences of process parameters on the formed wall thickness and deposition accuracy of droplets. The experimental results show that the proper deposition distance Hs for obtaining high deposition accuracy of droplet ranges from 1 mm to 20 mm; the formed wall thickness W can be controlled by selecting different nozzle diameters D and formed angle of deposited droplet θ. According to the experiment results, a micro thin-walled structure with wall thickness of 400 μm was fabricated by adjusting the process parameters. The above research works show that it is feasible to fabricate the micro thin-walled metal parts by micro-droplet deposition manufacturing technique.     

激光熔覆载气式同轴送粉喷嘴关键参数的探究

以激光熔覆载气式同轴送粉喷嘴为研究对象,建立了三通道激光熔覆喷嘴的三维模型,运用计算流体动力学理论对激光熔覆送粉喷头关键参数进行了数值分析,基于商用计算流体力学(CFD)软件FLUENT对送粉通道不同倾角和送粉口不同直径条件下的粉末流场情况进行了数值模拟。分析与计算结果表明,在其他参数一定的条件下,选样送粉通道倾角角度70°和送粉口直径1.5 mm时,有利于改善激光熔覆效果,为CFD技术在流体机械分析中的应用提供了参考。     

阀芯端帽激光表面合金化工艺制定

对自动流量平衡阀阀芯端帽进行激光表面合金化,以改善其表面硬度、耐摩擦和耐腐蚀等性能。从合金化成分选配、合金粉末添加方式制定及合金化层质量控制等3个主要方面制定阀芯端帽激光表面合金化工艺,为薄壁圆筒形零件激光表面合金化工艺的制定提供参考。     

The significance of deposition point standoff variations in multiple-layer coaxial laser cladding (coaxial cladding standoff effects)

Direct laser deposition (DLD) is an additive manufacturing process that builds up a part layer-by-layer by fusing metal powder to a solid substrate. A coaxial laser and powder delivery head is commonly used, and here a critical process variable is the standoff distance between the nozzle and the material deposition point. This contribution investigates the role of this variable and the effect that it has on the final part geometry. The experimental results show that good layer consistency can, in fact, be obtained with no movement of the substrate between layers for more than 20 layers, or 10 mm under tested conditions, and that poorer results are obtained by regular movement of the substrate by a badly chosen constant amount. A theoretical analysis of the situation establishes a method to estimate melt pool size using an analytically calculated temperature near the heat source. Based on this, simple heat and mass flow models are established to allow some of the results to be explained.     

Nd:YAG激光器金属零件激光快速成型工艺研究

利用Nd:YAG1.1kW激光器和同轴送粉方式进行了金属零件激光快速成型工艺实验研究。叙述了激光快速成型制造系统的基本组成和实验方法;分析了主要工艺参数如:激光功率、扫描速度、送粉量以及Z轴增量对成型质量和形貌的影响。给出了在最佳工艺参数下得到的激光成型实例。     

A2219高强铝合金的激光粉末焊接

采用一种较常用的A2219高强铝合金,在(Slab)CO2激光器上进行了粉末焊接试验.通过是否填充合金粉末的比较试验,研究了填充合金粉对铝合金激光焊接的影响以及各种工艺参数对送粉时焊接过程和粉末利用率的影响.结合高速摄像仪和光束光斑诊断仪的观察数据对试验现象和结果进行了合理的分析,并给出优化的工艺参数区间.试验表明,合金粉末的加入可以提高焊接过程中激光能量的有效利用率和焊接过程的稳定性;只有当粉束作用在熔池的恰当区域,粉束才能有效地进入熔池;当送粉量一定时,需要相应的功率、功率密度和焊接速度匹配,粉束才能被有效利用.最后通过优化工艺参数,成功地获得了具有理想余高、成形良好、焊接过程稳定的焊缝.     

Numerical simulation and experimental investigation of gas–powder flow from radially symmetrical nozzles in laser-based direct metal deposition

Laser-based direct metal deposition (DMD) is a solid freeform fabrication process capable of fabricating fully dense and metallurgically sound parts. The process has been greatly enhanced toward multi-directional deposition by the use of discontinuous radially symmetrical powder nozzles to supply the build material. Since many operational parameters depend on the gas–powder stream characteristics between the nozzles and the deposition point, an extensive understanding of the gas–powder flow is necessary. Three-dimensional (3D) multi-phase gas–powder flow structures of radially symmetrical nozzles are modeled using computational fluid dynamics methods. The obtained results are in good agreement with the experimental ones, and they provide a good insight into the process phenomena.     

等离子熔覆技术的研究现状及展望

等离子熔覆技术是一种高效且应用广泛的表面处理技术,具有与基体结合良好、设备成本低、工作环境无污染及操作简单等优点。从等离子熔覆工艺参数研究、等离子熔覆合金涂层、等离子熔覆颗粒增强金属基复合涂层、等离子熔覆层质量调控方法、等离子熔覆技术应用等五个方面,介绍了等离子熔覆技术当前的发展概况。其中,关于等离子熔覆工艺参数研究方面,阐述了熔覆电流、离子气体流量、送粉气体流量、粉末送粉量、焊枪摆动幅度、焊接速度、喷嘴与工件之间的高度及多道搭接时搭接率等参数对涂层组织性能的影响;在等离子熔覆合金涂层方面,介绍了等离子熔覆用合金粉末及其引入方式的研究进展;在等离子熔覆颗粒增强金属基复合涂层方面,叙述了增强颗粒及其添加方式的最新研究成果;在等离子熔覆层质量调控方法部分,阐述了预热缓冷、热处理、外加磁场、机械振动、超声波辅助、加入变质剂及添加稀土元素等手段对熔覆层的质量调控作用;在等离子熔覆技术应用方面,介绍了等离子熔覆技术在矿山机械、汽车零部件再制造以及阀门修复等领域的应用。最后对等离子熔覆技术的应用前景及发展趋势做出了展望。     

Comparison of coaxial and off-axis nozzle configurations in one step process laser cladding on aluminum substrate

Laser cladding of aluminum bronze alloy has been studied in order to increase the wear resistance of aluminum parts. Aiming a more productive and controlled process, this study analyzes the blown powder process, with two possibilities of blowing configurations that are off-axis and coaxial nozzle, and process parameters, such as axial motion speed, mass flow and power modulation. Dilution, catchment efficiency and hardness were analyzed for the used process parameters and nozzle configurations.     

激光烧结工艺参数对Fe-16%Ni合金致密度的影响

采用激光烧结成形技术研究了不同工艺参数对Fe-16%Ni金属粉末选区激光烧结成型件微观结构和致密性的影响。结果表明,随着脉冲宽度、扫描速度和铺粉厚度的增加,烧结后试样的密度先增加然后减少,随着扫描间距的增加,烧结后试样的密度减小。当脉冲宽度0.7 ms,扫描速度1000 mm/min,铺粉厚度0.15 mm,扫描间距0.15 mm时,烧结成型件成型质量较好。     

选择性激光烧结成形温度场的研究进展

选择性激光烧结技术与传统铸造工艺相结合,为快速制造某些难以用传统方法获得的铸件提供了有利途径.对于各种粉末材料在选择性激光烧结成形过程中温度场的模拟与预测,是合理选择其烧结工艺参数的基础.本文中综述了聚合物粉末、聚合物覆膜金属/陶瓷粉末和金属粉末在选择性激光烧结过程中的热物性参数变化规律及其相应的成形温度场分布,以利于激光选择性烧结各类粉末材料而精确成形零部件.     

铝合金薄壁筒滚珠旋压成形分析

作为一种连续局部塑性成形工艺,滚珠旋压被应用于制造铝合金薄壁筒形件。介绍了滚珠旋压的基本原理,以塑性力学为基础,分析力学参数对旋压件成形性的影响。实验中通过采用LF2和LY12两种铝合金筒坯,获得金属材料的塑性和屈服强度对旋压件可旋性影响的一般规律。最后研究咬入角对金属材料稳定流动的影响,并通过实验获得了合理的咬入角值。     

The influence of powder apparent density on the density in direct laser-sintered metallic parts

In direct laser sintering, the density is expected as high as possible for the industrial application. Since the density not only determines the industrial acceptance, but also limits the accuracy of the parts. This paper reports on the influence of the powder apparent density on final density of the sintered part's in direct laser sintering of Cu-based metal powder. The relative densities of the sintered parts with the different apparent densities using different process parameters have been investigated. The result shows that the apparent density has the most significant effect on final density of the sintered part. The final density increases with the increase of the apparent density. It is easy to get a higher final density in direct laser sintering process if a higher apparent density is used. However, the final density seems to have an upper limit for a given metal powder system.     

高强铝合金激光粉末焊接过程

采用CO2激光(slab)系统进行了高强铝合金的激光填粉焊接,分析了激光与粉末相互作用的5个阶段过程;研究了填充合金粉对CO2激光焊接功率阈值、焊缝成形和焊接过程稳定性的影响.试验表明,合金粉末可以提高焊接过程中激光能量的有效利用率;激光深熔焊接时的临界功率密度明显降低,粉末束流只有作用在光致等离子体的恰当区域才能有效地进入熔池;在一定送粉量下,匹配适当的功率密度和热输入,才能保证得到理想的焊缝.高速摄像图片显示了激光支持的燃烧波及焊接中的过程孔洞,并且合金粉末还可以减弱等离子体的膨胀跳动,有利于获得较为稳定的焊接过程和理想的焊缝成形.     

Characteristics of laser aided direct metal/material deposition process for tool steel

Laser aided direct metal/material deposition (DMD) process builds metallic parts layer-by-layer directly from the CAD representation. In general, the process uses powdered metal/materials fed into a melt-pool, creating fully dense parts. Success of this technology in the die and tool industry depends on the parts quality to be achieved. To obtain designed geometric dimensions and material properties, delicate control of the parameters such as laser power, spot diameter, traverse speed and powder mass flow rate is critical. In this paper, the dimensional and material characteristics of directed deposited H13 tool steel by CO₂ laser are investigated for the DMD process with a feedback height control system. The relationships between DMD process variables and the product characteristics are analyzed using statistical techniques. The performance of the DMD process is examined with the material characteristics of hardness, porosity, microstructure, and composition.     

Preparation and selective laser sintering of nylon-12 coated metal powders and post processing

A dissolution–precipitation process was successfully developed to prepare nylon-12 coated carbon steel powders. The SEM and laser diffraction particle size analysis results show that the metal particles are well coated by nylon-12 resin; therefore, an effective method for preparing nylon-12 coated metal powders is provided. Green parts were formed from the coated powders by selective laser sintering (SLS) process, and when the nylon-12 content in the coated powder was 1.0 wt% and the applied laser energy density was 0.06 J/mm², the SLS green parts had sufficient strengths for features as small as 0.1 mm to be built and post-processed, and relatively high dimensional accuracy. The SLS green parts were post-processed by binder decomposition and epoxy resin infiltration, and the obtained epoxy-infiltrated parts have the dimensional errors in the X, Y and Z directions of −0.30, −0.32 and −0.25% respectively, and the bend strength, bend modulus, tensile strength and impact strength of 93.4 MPa, 14.7 GPa, 70.3 MPa and 12.4 MPa respectively.     

激光微区烧结微成形技术研究

目前微小零部件的制造方法很多,激光微成形即为其中一种。介绍了在激光选区烧结技术的基础上,结合微成形特点开发的激光微区烧结成形技术。该技术可对金属粉末进行直接微区烧结成形,所成形的金属微型零件强度高,不需后续处理,大大节省了从原材料到最终实体的时间,并具有环境污染小、材料利用率高、成形速度快和效率高的特点。