3D printing of multiple metallic materials via modified selective laser melting

Selective laser melting (SLM) is a powder bed layer-by-layer fusion technique mainly applied for additive manufacturing of 3D metallic components of complex geometry. However, the technology is currently limited to printing a single material across each layer. In many applications such as the manufacture of certain aero engine components, conformably cooled dies, medical implants and functional gradient structures, printing of multiple materials are desirable. This paper reports an investigation into the 3D printing of multiple metallic materials including 316L stainless steel, In718 nickel alloy and Cu10Sn copper alloy within a single build-up process using a specially designed multiple material SLM system combining powder-bed with point by point powder dispensing and selective material removal, for the first time. Material delivery system design, multiple material interactions, and component characteristics are described and the associated mechanisms are discussed.     

金刚石磨粒激光钎焊的试验研究

激光钎焊用于金刚石磨粒与基体的焊接,因激光具有高的功率密度,可实现快速加热和降温,有效控制金刚石磨粒的热损伤;由于热影响区小,可保证基体基本不变形。本文主要研究了金刚石磨粒的激光钎焊。重点讨论了激光功率、扫描速度及光斑直径等参数对连接界面的影响;讨论了其结合界面的微观形貌及热损伤、开裂等缺陷。研究结果表明,当ρ在25～30J／mm^3范围,可以实现激光钎焊金刚石颗粒与基体45钢的优良焊接。     

船舶钢板激光弯曲成形的实验研究

在对船舶钢板激光弯曲成形过程进行实验研究中，采用CO2激光器研究了激光功率、扫描速度、扫描次数以及钢板厚度对船舶钢板激光弯曲成形的影响规律。实验中实时测量了船舶钢板激光弯曲成形过程钢板弯曲角度和温度的变化。结果表明：钢板弯曲角度随激光功率的增加而增加，随激光束扫描速度的增加而减小，而且随着钢板厚度的增加，弯曲角度减小；激光工艺参数和钢板厚度都对钢板激光多次扫描成形产生影响，钢板的弯曲角度随着激光扫描次数的增加而增加。对于较薄的船舶钢板，钢板弯曲角度随扫描次数增加近似呈线性增加，而较厚的钢板，随扫描次数的增加，钢板弯曲角度的增加逐渐减小。     

激光熔覆-激光氮化复合法制取TiNi-TiN梯度材料

将激光熔覆与激光表面氮化技术相结合制取TiNi-TiN梯度材料。采用先进的六孔同轴送粉喷嘴系统,分别将纯Ti、Ni粉末按一定比例送入激光熔化区,在粉末熔化过程中发生Ti、Ni间高温合成反应,原位合成一定厚度的TiNi金属间化合物熔覆层,然后将原位合成的熔覆层在富氮气氛中进行激光氮化处理,表面形成一层金黄色的TiN。利用光学显微镜和扫描电镜观察了熔覆层组织,并测量了熔覆层及氮化层的厚度。对不同工艺参数获得的熔覆层用X射线衍射仪进行了物相鉴定,并对氮化试样的熔覆层进行了显微硬度分布测试,得出了较好的制取TiNi-TiN梯度材料的工艺参数为:激光功率600 W,扫描速度0.5 m/min,钛送粉量2.5 g/min;镍送粉量3.2 g/min。     

Experimental study of weld position detection based on keyhole infrared image during high power fiber laser welding

Keyhole is one of the important phenomena in high-power laser welding process. By studying the keyhole characteristic and detecting the seam offset during high-power fiber laser welding, an infrared sensitive high-speed camera arranged off-axis orientation of laser beam was applied to capture the dynamic thermal images of a molten pool. The 304 austenitic stainless steel plate butt joint welding experiment with laser power 10 kW was carried out. Through analyzing the keyhole infrared image, the weld position was calculated. Least squares method was used to determine the actual weld position. Image filtering technique was used to process the keyhole image, and the keyhole centroid coordinate were calculated. Also, least squares method was used to fit the keyhole centroid curve equation and establish a nonlinear continuous model which described the deviation between keyhole centroid and weld seam. The heat accumulation effect affected by the infrared radiation was analyzed to determine whether the laser beam focus spot deviated from the desired welding seam. Experimental results showed that the keyhole centroid has related to the seam offset, and can reflect the welding quality.     

Welding phenomena and in-process monitoring in high-power YAG laser welding of aluminium alloy

Laser welding of aluminium alloys is difficult because of their low laser coupling, easy formation of welding defects, etc. and thus the establishment of in process monitoring technique is expected in various industries to obtain highly reliable laser welds. In this study, therefore, both the reflected laser beam and radiation light from die molten pool were investigated as monitoring signals during YAG laser welding of A5052 and A5182 aluminium alloy to confirm validity and usefulness of these signals for monitoring. At the same time, laser-welding phenomena were observed through a high-speed video camera to better interpret the monitored signals. Two signals were detected by utilizing photo sensors and band pass or cut-off filters coaxially against a laser beam and from the above-back direction. In this paper, experimental setup, and monitoring and observation results were presented. The correlation between monitoring signals and welding phenomena was clarified when the welding defects such as underfilling and through holes were formed.     

拉深模激光毛化工艺参数实验研究

为改善拉深模摩擦和润滑条件,提高其使用寿命,提出使用激光毛化技术对其表面进行造型强化。通过实验对影响激光毛化效果的主要工艺参数进行研究,得到拉深模激光毛化的合适工艺参数范围,为拉深模激光毛化表面摩擦性能研究及毛化点尺寸优化奠定基础。     

薄壁TC4钛合金激光焊缝成形试验研究

以TC4薄壁钛合金为研究对象,开展激光焊工艺研究及焊缝成形控制。主要研究了焊接过程保护方式、激光能量控制、离焦量和倾斜角度等焊接参数对焊缝成形的影响。研究结果表明,激光低速焊接TC4薄板钛合金工艺窗口较窄,需要进行精确的能量输入控制。采用高速激光焊接TC4薄板结构,有效地扩大工艺窗口。提高激光离焦量也可以提高熔化宽度,激光功率与离焦量比值为100～140 W/mm可得到良好的熔透效果。激光大角度斜向焊接会出现散射现象,提高能量输入可以良好地保证成形质量。     

Experimental investigation of melt pool behaviour during selective laser melting by high speed imaging

Melt pool behaviour and the characteristics of the surrounding metal powder during selective laser melting (SLM) are captured using high-speed imaging, and the influence of the substrate temperature and the line building sequence on the formation of the built structure and the generation of spatter particles is experimentally investigated. The results indicate that the substrate temperature has a measurable effect on the formation of droplets and the generation of spatter particles, while the volume specific energy density of the process was the principal factor affecting the built structure.     

Modeling of temperature field and pool formation during linear laser welding of DP1000 steel

A rotary-Gauss body heat source was employed in the study to model the laser welding of DP1000 steel. The condition of heat dissipation during the welding has a significant effect on the temperature field as well as the shape and size of the laser weld. A series of welding experiments were performed, and good agreement was observed between the calculated weld dimensions and the experimental results. The microhardness values across the welded joint were measured to determine the range of the soft zone in the heat affected zone (HAZ) and simultaneously the temperature range experienced in this region. The results indicated that the soft zone significantly affects the mechanical performance of the welded joint. The width of the soft zone and its distance from the weld center increase with increasing laser power, while the width of the soft zone and its distance from the weld center decrease with increasing welding speed.     

Experimental and numerical characterisation of heat flow during flame cutting of thick steel plates

Temperatures measurements during flame cutting of a thick steel plate and measurements of the extension of the fusion and heat affected zones and Vickers hardness after cutting have been performed. Additionally, a 3-D thermal model for simulation of flame-cutting has been developed. For the sake of simplicity, the model depends only on two parameters: (i) the heat density within the flame, and (ii) the heat transfer coefficient within the air gap that forms behind the cut. The results show that the model is able to properly reproduce the measured temperature curves and the heat affected zone with an input power in the same range of those reported in the literature. A process efficiency of 26.5% is found in the steady state regime of flame-cutting.     

激光功率对42CrMo钢激光熔覆层组织和摩擦磨损性能的影响

利用摩擦磨损试验探究不同激光功率下42CrMo钢激光熔覆层的耐磨性,采用SEM和OM观察了试样摩擦磨损前后的熔覆层组织形貌。结果表明:42CrMo钢基体的摩擦因数较大,且在该摩擦磨损后出现了严重的脆性剥落现象,激光熔覆层可以提升42CrMo钢的耐磨损性能;当激光功率为1600 W时,摩擦因数可降低至0.28,熔覆层表面SEM形貌较为光滑,耐磨性优异,熔覆层组织中的晶粒细化均匀,主要表现为细小的等轴晶,组织较为致密,从而提高了熔覆层的耐磨损性能。     

Simulation of cracking phenomena during laser brazing of ceramics and cemented carbide

To investigate the mechanism of the occurrence of the microcracks produced in laser brazing of silicon carbide and cemented carbide using a silver–copper–titanium alloy as the filler metal, a numerical simulation for thermal cycle and thermal stress was performed using the finite element method. The laser-irradiated area of the cemented carbide was heated selectively, and almost uniform temperature distribution in the filler metal was obtained. The tensile thermal stress in the silicon carbide appeared near the interface between the silicon carbide and the filler metal, and the maximum principle stress at about 400 K during the cooling process reached the fracture strength of the silicon carbide. This resulted in the formation of microcracks in the silicon carbide which was observed in the experiment.     

扫描速度对激光沉积ER630丝材修复层力学性能与显微组织的影响

采用直接激光沉积法(DLD)在45钢基材上激光沉积ER630丝材,研究了扫描速度对ER630丝材修复层力学性能和组织的影响。结果表明,随着扫描速度的不断提高,ER630修复层中夹渣逐渐增多,且尺寸逐渐增大;扫描速度对ER630丝材修复层密度的影响可忽略不计。在30 mm/s扫描速度下,组织主要为板条柱状马氏体和少量圆胞状奥氏体,随着扫描速度的提高,板条柱状马氏体减少,圆胞状奥氏体逐渐增多。在30 mm/s扫描速度下,激光沉积丝材试样的力学性能与550 ℃时效处理的630不锈钢相当。随着扫描速度的提升,屈服强度与硬度均呈下降趋势,30 mm/s时屈服强度最大,为961.07 MPa,40 mm/s时硬度最大,为428.88 HV。拉伸断口形貌为韧窝断裂或准解理断裂,可见DLD工艺可实现优异的冶金结合;比较30 mm/s扫描速度下的强度,当沉积效率提高至2倍时,仍能得到较好的修复强度。     

扫描路径规划对激光弯曲成形影响的实验研究

在三维激光成形中,扫描步距、扫描的先后次序、扫描线距自由端的距离等扫描路径规划参数对最终变形量都有影响。实验表明：当扫描线距自由端的距离L′增加时,弯曲角度随之增大,但当L′继续增加时,板料的弯曲角度却减小,最后逐渐趋于平缓。当扫描步距太小,板料的总体弯曲效果并不好,而且由于重叠加热,使板料硬度降低。随着扫描步距的继续增大,板料的最终弯曲效果只是每次扫描的弯曲变形量的简单迭加。而且实验发现,先采用大的步距对板料进行扫描,然后在两条扫描线之间再插入扫描线,此时的弯曲效果比顺次加热的弯曲效果要好。     

Electrochemical investigation of the influence of laser surface melting on the microstructure and corrosion behaviour of ZE41 magnesium alloy – An EIS based study

Surface melting of a magnesium alloy, ZE41 (4%-Zn, 1%-RE) was performed to achieve electrochemical homogeneity at the surface by microstructure refinement. Large secondary precipitates are particularly known to cause severe pitting in magnesium alloys. The corrosion resistance of the laser treated and untreated alloy was investigated by potentiodynamic polarisation and electrochemical impedance spectroscopy. Contrary to the reported behaviour of other magnesium alloys (such as AZ series alloys), laser surface melting did not significantly improve the corrosion resistance of ZE41. This observation is attributed to the absence of beneficial alloying elements such as Al in ZE41 alloy.     

不同激光功率对Co基合金堆焊重熔层组织和性能的影响

研究了同一扫描速度（2mm/s）下，3种不同激光功率（1.5kW、2.0kW、2.5kW）对Co基合金堆焊层熔深、枝晶尺寸以及显微硬度和耐磨性的影响。试验结果表明，堆焊层经激光重熔后，组织较原始堆焊层明显细化，硬度明显提高。随着激光功率的加大，堆焊重熔层的熔深、枝晶尺寸均随之增大，表面硬度有所下降。但耐磨性并不随表面硬度下降而降低。硬度与耐磨性没有简单的对应关系。     

取向硅钢激光刻痕对绝缘层的影响及刻痕耐热性分析

研究了不同输入电流下激光刻痕对取向硅钢表面绝缘涂层的影响,分析了刻痕宽度、刻痕深度和磁性能随电流的变化规律及刻痕对绝缘涂层的破坏程度,并对刻痕后的取向硅钢样品进行退火,研究刻痕后磁畴粗化规律,对激光刻痕的耐热性进行分析。结果表明:随着电流的增大,刻痕的宽度和深度增大,刻痕对绝缘涂层的损伤严重。激光刻痕样品在500℃以上的温度下进行去应力退火,磁畴开始粗化,铁损较刻痕后升高。确定了磁畴粗化定量关系。随着退火温度升高,磁畴宽度增大,铁损升高的幅度增大。     

Stability analysis and time domain simulation of multiple diameter parts during infeed centerless grinding

Multiple diameter part applications cope a relevant percentage of infeed centerless grinding operations. Nevertheless, general stability analysis and process optimisation has been mainly investigated for mono-diameter parts. This paper presents a time domain simulation software developed for multiple diameter parts that allows the simulation of average and particular evolution of process forces, power, machine deflections, thermal behaviour, real part diameter and roughness. First, a work rotation stability analysis is carried out. Then, with the use of both the stability analysis and the infeed cycle simulation, optimized process parameters and cycles are defined in order to increase process productivity.     

激光熔覆钛基金属陶瓷复合涂层的组织与性能

为了提高TC4合金的耐磨减摩性,利用激光熔覆技术在TC4合金表面激光熔覆TC4+h-BN混合粉末制备钛基金属陶瓷复合涂层,利用X射线衍射仪(XRD)、扫描电镜(SEM)、能谱分析仪(EDS)等手段对熔覆层宏观形貌和微观组织进行观察,利用显微硬度计对熔覆层、热影响区、基体的硬度进行测试,通过摩擦磨损试验机对熔覆层和基体的摩擦因数进行测量,利用电子精密天平对熔覆层和基体的磨损量进行检测。结果表明:熔覆层主要由杆状相TiB、三元共晶组织(Ti-B-N)和基底α-Ti组成。熔覆层硬度分布在1000～1200 HV0.5之间,熔覆层磨损机理为轻微的磨粒磨损,TC4基体为严重的磨粒磨损。熔覆层摩擦因数较基体下降了0.04,磨损量较基体下降了7 mg,熔覆层的耐磨减摩性能较基体有所提高。