Droplet-targeting laser hybrid indirect arc for additive manufacturing technology-A preliminary study

The contradiction between manufacturing accuracy and manufacturing efficiency is discussed in this paper.In order to solve this problem,a novel droplet-targeting laser hybrid indirect arc for additive manufacturing technology is proposed in which a couple of wires are melted using the alternating current with interwire indirect arc to achieve high deposition rate.On the other hand,droplets actively target the laser beam and detach from wire tip under the recoil pressure subjected to pulsed laser irradiating at desired position and with controlled mass for a precise bead forming.The process of alternative droplet growing at desired position are mathematically analyzed and then preliminary verified by experiment.By precisely controlling the wire feed speed and current frequency,the melting process at desired position and mass of wire is successfully obtained which is the fundamental for next-step for the droplet actively targeting laser.

Modeling thermal and mechanical cancellation of residual stress from hybrid additive manufacturing by laser peening

Additive manufacturing(AM)of metals often results in parts with unfavorable mechanical properties.Laser peening(LP)is a high strain rate mechanical surface treatment that hammers a workpiece and induces favorable mechanical properties.Peening strain hardens a surface and imparts compressive residual stresses improving the mechanical properties of a material.This work investigates the role of LP on layer-by-layer processing of 3D printed metals using finite element analysis.The objective is to understand temporal and spatial residual stress development after thermal and mechanical cancellation caused by cyclically coupling printing and peening.Results indicate layer peening frequency is a critical process parameter affecting residual stress redistribution and highly interdependent on the heat generated by the printing process.Optimum hybrid process conditions were found to exists that favorably enhance mechanical properties.With this study,hybrid-AM has ushered in the next evolutionary step in AM and has the potential to profoundly change the way high value metal goods are manufactured.

Subsurface Defect Evaluation of Selective-Laser-Melted Inconel 738LC Alloy Using Eddy Current Testing for Additive/Subtractive Hybrid Manufacturing

New materials and manufacturing technologies require applicable non-destructive techniques for quality assurance so as to achieve better performance.This study comprehensively investigated the effect of influencing factors includ-ing excitation frequency,lift-off distance,defect depth and size,residual heat,and surface roughness on the defect EC signals of an Inconel 738LC alloy produced by selective laser melting(SLM).The experimental investigations recorded the impedance amplitude and phase angle of EC signals for each defect to explore the feasibility of detecting sub-surface defects by merely analyzing these two key indicators.Overall,this study revealed preliminary qualitative and roughly quantitative relationships between influencing factors and corresponding EC signals,which provided a prac-tical reference on how to quantitively inspect subsurface defects using eddy current testing(ECT)on SLMed parts,and also made solid progress toward on-line ECT in additive/subtractive hybrid manufacturing(ASHM)for fabricating SLMed parts with enhanced quality and better performance.

Determination of Surface Roughness in Wire and Arc Additive Manufacturing Based on Laser Vision Sensing

Wire and arc additive manufacturing(WAAM) shows a great promise for fabricating fully dense metal parts by means of melting materials in layers using a welding heat source. However, due to a large layer height produced in WAAM, an unsatisfactory surface roughness of parts processed by this technology has been a key issue. A methodology based on laser vision sensing is proposed to quantitatively calculate the surface roughness of parts deposited by WAAM.Calibrations for a camera and a laser plane of the optical system are presented. The reconstruction precision of the laser vision system is verified by a standard workpiece. Additionally, this determination approach is utilized to calculate the surface roughness of a multi-layer single-pass thin-walled part. The results indicate that the optical measurement approach based on the laser vision sensing is a simple and effective way to characterize the surface roughness of parts deposited by WAAM. The maximum absolute error is less than 0.15 mm. The proposed research provides the foundation for surface roughness optimization with different process parameters.

Die Casting Mold Repair by Hybrid Manufacturing

This paper describes the process of repairing a damaged die for injection molding using a 5-axis Hybrid Milling Machine equipped with a Direct Laser Deposition(DLD)tool.A software developed by the authors—DUOADD—is adopted to detect the location of missing material and to create a solid model of the damaged spot.The resulting CAD file is used to calculate the paths of the DLD nozzle for filling the damage spot with new material.Finally,to restore the original shape of the mold,the surplus of added material is removed by a milling operation.The paper describes every step of the repair process:from 3D scanning of the damaged component to the finishing operation.This repair method can be applied to extend the life of a costly component and to restore the original shape of valuable objects—e.g.historical or artistic artifacts.The material used for the mold repair is stainless steel 316L,while the mold is made of hot-die-steel.In this paper the functionality of the repair process has been investigated by checking whether all the damaged spots are properly filled with new material.Moreover,this work investigates how to perform the milling operations that allow restoring the original shape of the object,minimizing mismatches between the machined surface and the original one.

Microstructure and properties of hybrid additive manufacturing 316L component by directed energy deposition and laser remelting

Arc additive manufacturing is a high-productivity and low-cost technology for directly fabricating fully dense metallic components.However,this technology with high deposit rate would cause degradation of dimensional accuracy and surface quality of the metallic component.A novel hybrid additive manufacturing technology by combining the benefit of directed energy deposition and laser remelting is developed.This hybrid technology is successfully utilized to fabricate 316L component with excellent surface quality.Results show that laser remelting can largely increase the amount ofδphases and eliminateσphases in additive manufacturing 316L component surface due to the rapid cooling.This leads to the formation of remelting layer with higher microhardness and excellent corrosion resistance when compared to the steel made by directed energy deposition only.Increasing laser remelting power can improve surface quality as well as corrosion resistance,but degrade microhardness of remelting layer owing to the decrease inδphases.

电弧熔丝增材制造控形技术研究现状与展望

金属增材制造是制造强国战略下推动我国高端装备制造业转型升级的重点发展方向。电弧增材制造以其高沉积效率、低成本、可进行复杂结构直接成形等优势受到了广泛的关注。但增材过程中涉及的物理过程复杂,成形质量与精度面临很大挑战。针对电弧增材制造技术短流程、长周期的制造特征,讨论如何从热源上降低成形偏差、从过程上降低制造误差、从结果上改善成形精度,介绍了一系列创新的热源调制、过程控制与结果优化的方法策略,总结了现有技术存在的问题与面临的挑战,为如何进一步提升电弧增材过程的成形控制效果提出了几点思考。

金属增材制造质量控制及复合制造技术研究现状

相比传统制造工艺,增材制造能够实现复杂结构金属部件的近净成形。然而,增材制造具有冷却速度快、热梯度大、非平衡凝固与往复热循环历史等特点,容易存在孔洞、残余拉应力、各向异性等缺陷,极大限制增材制造的进一步应用。复合增材制造技术是将传统制造方法与增材制造有机结合,充分发挥传统制造工艺在性能调控与尺寸精度等方面的优势,抑制单纯增材制造引起的各类缺陷,获得高质量、无缺陷的增材制造部件。本文首先揭示增材制造工艺缺陷的形成机理,明确工艺参数优化方法在缺陷改善方面的局限性,进而阐明复合增材制造的内涵,综述近年来增材制造与轧制、激光冲击强化、热等静压、热处理等复合制造技术的研究现状与工艺原理,探讨复合增材制造技术对不同缺陷的适用性,并对增材制造未来发展方向进行了展望。

激光-电弧复合增材制造Al-Cu合金T型结构微观组织演变与熔池流动行为分析

在T型结构增材制造过程中,交叉节点处易出现冶金结合不良及重熔缺陷等问题,制约该结构性能的提升。采用激光-电弧复合增材制造技术制备了Al-Cu合金T型结构,对交叉节点处的组织形貌进行了表征,并通过数值模拟分析了节点处熔池内的温度分布以及流动特征。结果表明,在T型结构节点处能够观察到重熔作用所导致的弧形条纹特征,该区域的模拟形貌与实际结果具有良好的一致性;熔池边界处等温线分布较为密集,内部Marangoni对流导致逆时针涡流的形成,最高流速可达0.16 m/s。依据顶层晶粒形态差异,分为顶层节点重熔区(RZI)和顶层热影响区(HAZ)。其中RZI内主要为细小的树枝晶,平均晶粒尺寸相比于HAZ降低了20.8%,内部析出相主要为与α-Al基体呈非共格界面的大尺寸θ(Al_(2)Cu)相;平均显微硬度可达(98.4±6.4)HV_(0.1),相比于未重熔区最高提升约14.0%。

高强铝合金电弧增材制造的研究进展

高强铝合金因具有高强度、低密度、优异的延展性和抗腐蚀性,成为了航空航天和汽车应用零件最常用的金属材料之一。电弧增材制造技术具有快速原位成形制造复杂结构零部件的能力,非常适用于中型或大型高强铝合金铝部件的制造。本文综合分析了高强铝合金电弧增材制造工艺和设备研发现状、高强铝合金电弧增材的固有属性和缺陷以及主要的性能优化手段,讨论了组织和性能的固有特征和复合增材制造技术对组织和性能的影响。针对电弧增材制造高强铝合金不可忽略的本质冶金缺陷、特征性能需求和多种优化工艺的优劣等问题,提出了电弧增材制造高强铝合金综合评价体系、成分设计和丝材开发、专用热处理制度和复合增材制造技术的协同性等发展方向,以期为电弧增材制造高强铝合金的性能提升和应用推广提供重要参考。

镁基复合材料增材制造技术研究进展

镁基复合材料通过基体与增强体的协同配合,克服了传统镁合金绝对强度和刚度较低、承载能力较差的难题,而增材制造技术的强成形能力、高制备精度、短制备周期为定制复杂结构且组织均匀的镁基复合材料提供可能。因此,本文从镁基复合材料的组成出发,简单介绍传统制备方式后,归纳梳理了镁基复合材料增材制造技术的研究进展,总结不同制造过程中工艺参数对成形件组织和性能的影响规律,最后在分析所存在的问题和挑战的基础上,对镁基复合材料增材制造技术未来的研究方向进行聚焦和展望。

采用增减材复合制造技术的模具修复工艺研究

激光金属沉积增减材复合制造技术是实现模具等高附加值部件修复与再制造的理想候选工艺之一。为了提高模具修复的效率和精度,本文将增减材复合制造技术应用于模具修复领域,并且对修复工艺进行研究。首先根据具体使用工况和材料性能要求,确定了最佳模具修复参数,随后讨论了该模具修复工艺的应用条件和应用范围。实验结果表明:利用本文提出工艺方案进行模具修复时可以实现修复区域无拼接痕迹,并且修复区域硬度提升7.4 HRC,能够有效提升模具的使用性能。

增材制造金属结构件残余应力的研究进展

增材制造技术近年来取得了重大进展,金属增材制造可以三维成型精度高的复杂形状零件,在各行业的应用中具有独特优势。然而,增材制造金属零件成形时由于高温度梯度会引起复杂残余应力。简要分析了增材制造技术的特点,重点总结了激光选区熔化和电弧增材制造的工艺原理。在此基础上,详细综述了增材制造过程中残余应力的产生机制及测量方法,其中,温度梯度机制是解释残余应力产生机制最常用的方法。针对残余应力的测量,分别从无损检测和破坏性检测两方面进行归纳,最常用的破坏性检测残余应力的方法是轮廓法和钻孔法,而无损检测的方法是X射线衍射法。并且总结了残余应力的调控方法,包括工艺参数调控、预热缓冷及重熔调控、结构设计调控、辅助外场调控、后处理调控。最后简要总结增材制造金属结构件残余应力研究中亟待解决的问题,并展望了金属增材制造的发展方向。

增材制造铜/钢双金属材料研究进展

铜/钢双金属材料具有力学强度高、物理化学性能优良等优势,在交通运输、电力能源和建筑工业等领域应用前景广阔。然而,传统熔铸工艺在制造铜/钢双金属材料时,容易在铜/钢界面处产生偏析现象,在一定程度上限制了铜/钢双金属材料的发展。与传统工艺相比,增材制造技术不仅能实现复杂加工零件的快速制造,而且在成形过程中较短的保温时间能缓和或消除异种金属材料界面产生的冶金缺陷,进而增强铜/钢双金属材料的力学性能。由于双金属材料是近年来的研究热点,有关增材制造铜/钢双金属材料的综述性文章较少,故综述了近年来激光、电子束及电弧增材制造技术制造铜/钢双金属材料的研究发展现状,分析了各技术的优缺点,并从制备方法、工艺参数及界面合金元素等角度,分析了影响材料界面组织性能变化的关键因素。发现在增材制造铜/钢双金属材料方面,目前激光增材制造技术主要应用于精度要求较高的小尺寸零部件,电子束增材制造技术适用于某些具有特殊性能的合金,如钛合金,而电弧增材制造技术适用于精度要求较低的大型复杂零部件。在铜/钢双金属材料增材制造过程中,界面处易形成显微组织分布不均匀、界面晶粒尺寸差异较大等现象,导致界面处产生应力集中,从而造成材料断裂失效。为解决上述难题,学者们已深入研究第二相形成机理,并采用优化界面处Cu-Fe比例和控制脆相金属间化合物等方式提高铜/钢双金属材料的性能。最后,对目前增材制造铜/钢双金属材料的研究发展现状进行了总结与展望,未来在冶金学和热力学方向上对铜/钢双金属材料仍需进行系统性理论研究,对双金属材料而言需要建立相关模拟数据库,以期为相关从业人员提供精细化指导建议。新型增材制造技术或复合增材制造技术的开发与应用都将成为未来增材制造铜/钢双金属材料研究的重点发展方向。

基于DMG MORI LASERTEC 65 3D加工中心的不锈钢粉末激光沉积增/减材复合制造

采用国内首台增/减材复合加工中心——DMG MORI LASERTEC 65 3D,完成不锈钢粉末的增/减材复合制造,通过研究激光直接金属沉积成形的激光功率、扫描速度及送粉速度等増材工艺参数对不锈钢沉积层截面形状尺寸与表面粗糙度的影响,优化沉积工艺参数,测定沉积件的力学性能,并初步探究DMG MORI LASERTEC 653D复合加工中心对于不锈钢异型涡轮增压壳体的增材与减材复合制造的能力水平和应用空间。结果表明:最佳沉积工艺参数为:激光功率为2 400 W,扫描速度为1 000 mm/min,送粉速率为14 g/min,粉末沉积件获得理想的等轴晶组织,其抗拉强度和伸长率分别达到632 MPa和46.9%,与同材料的锻件相当。用DMG MORI LASERTEC65 3D复合加工中心,可完成不锈钢异型涡轮增压壳体的粉末激光直接金属沉积成形和5轴铣削的复合加工制造,在保证工件精度的前提下,能较好地实现如法兰钻孔、接头生产等难加工部件的一次性成形,较传统加工方式效率提高5~8倍。

Development of Micro Selective Laser Melting:The State of the Art and Future Perspectives

Additive manufacturing(AM)is gaining traction in the manufacturing industry for the fabrication of components with complex geometries using a variety of materials.Selective laser melting(SLM)is a common AM technique that is based on powder-bed fusion(PBF)to process metals;however,it is currently focused only on the fabrication of macroscale and mesoscale components.This paper reviews the state of the art of the SLM of metallic materials at the microscale level.In comparison with the direct writing techniques that are commonly used for micro AM,micro SLM is attractive due to a number of factors,including a faster cycle time,process simplicity,and material versatility.A comprehensive evaluation of various research works and commercial systems for the fabrication of microscale parts using SLM and selective laser sintering(SLS)is conducted.In addition to identifying existing issues with SLM at the microscale,which include powder recoating,laser optics,and powder particle size,this paper details potential future directions.A detailed review of existing recoating methods in powder-bed techniques is conducted,along with a description of emerging efforts to implement dry powder dispensing methods in the AM domain.A number of secondary finishing techniques for AM components are reviewed,with a focus on implementation for microscale features and integration with micro SLM systems.

激光电弧复合增材制造钛合金的组织和性能研究

为研究热输入对墙体宏观形貌、显微组织及力学性能的影响,用激光-MIG电弧复合热源对TC11钛合金丝材进行增材制造。结果表明:墙体柱状晶内组织都以条状α集束和α+β集束组织为主,存在明显的β相界,但堆积速度小的柱状晶中马氏体α′相尺寸较大;在堆积层重熔区中不同区域的初生α相和α+β网篮组织尺寸差异显著,堆积速度较大时的组织更细密;在墙体边界,堆积速度大时存在一定针状马氏体α′相,而堆积速度小时针状马氏体相对较少;热输入大的墙体抗拉强度比热输入小的提高2%,伸长率和断面伸缩率相近,且水平方向上墙体硬度更高,塑性更好。

基于自适应轮廓骨架分区的电弧增材制造成形路径优化方法

传统轮廓偏置路径规划方法具有较高几何还原度,适合电弧增材制造中等尺寸的复杂零件,但轮廓连续偏置过程中的退化现象易形成欠填充区域,进而导致缺陷,形成待优化区.针对上述问题,提出了基于布尔运算的待优化区域精确识别方法.将原始多边形与经过正反两次等距偏置的回溯多边形进行布尔差运算,可获得需要优化的缺陷区域,将待优化区域过滤与合并,重新构建为骨架填充区.结合最小矩形框确定每个骨架填充区的最优填充方向并生成往复直线路径,最后将轮廓偏置路径重新分类分区连接为连续成形路径,并按照骨架填充区成形路径优先打印原则输出为机器代码.后续成形试验采用机器人电弧增材制造系统打印了螺旋桨零件,结果表明,零件成形尺寸达到预期,且表面不存在传统轮廓偏置法中的成形缺陷,证明文中方法具有较高的可行性与适用性.创新点:(1)提出了一种骨架填充方法来准确识别和过滤传统轮廓偏置法中的待优化区域.(2)基于布尔运算的待优化区域精确识别方法,既保留了传统方法的优点,又减少了起熄弧次数.

ZL114A铝合金电弧-激光微铸锻复合增材制造组织与力学性能研究

对ZL114A铝合金进行电弧-激光自由熔积和电弧-激光微铸锻复合增材成形实验,探究工艺条件对该铝合金的冶金缺陷、显微组织、力学性能和断口SEM形貌的影响机理。结果表明:电弧-激光微铸锻增材成形工艺能明显抑制成形过程中气孔的产生,显微组织更加细小、均匀,共晶硅在晶间弥散分布;与电弧-激光自由熔积工艺相比,熔积扫描方向、熔积增高方向的拉伸强度、塑性、布氏硬度均提高;两种工艺的试样拉伸断口形貌均为细小的等轴韧窝,但电弧-激光微铸锻工艺的拉伸断面微型气孔缺陷更少。

激光冲击MAG复合增材工艺与组织性能研究

为了研究激光冲击熔化极活性气体保护焊(Metal Active-Gas welding,MAG)复合增材工艺规律,通过构建复合热源模型,对比研究激光加入前后电弧及熔池的变化,并通过改变激光功率参数,分别分析其对增材成形件宏观形貌、微观组织和力学性能的影响。结果表明,在激光的冲击作用下,电弧产生吸引和压缩现象,可提高电弧的稳定性和热源利用率、增加熔池内气体逃逸时间、细化成形件晶粒尺寸,以及提高成形件的力学性能。激光功率900 W为最佳工艺参数,此时增材成形件表面较为光滑、晶粒尺寸最小范围为5~16μm,平均显微硬度为(182.5±8.7)HV,抗拉强度为566 MPa,断后伸长率为10.35%,气孔率为0.74%。对比单电弧增材成形件,平均显微硬度、抗拉强度和断后伸长率分别提高了9.3%、13.4%、37.5%,气孔率减少了43.1%。