Ti6Al4V激光选区熔化成形悬垂结构的质量研究

为了减小成形误差,提高激光选区熔化成形复杂特征结构件的能力,实验采用Ti6Al4V金属粉末,设计了不同倾斜角度的悬垂结构模型,研究了倾斜角度、扫描策略对悬垂结构SLM成形质量的影响。结果表明：倾斜角度越小,悬垂面的边缘线宽度误差越大（>80μm）,表面粗糙度值越大（>20μm）,翘曲变形越严重;岛形随机扫描策略的整体成形质量要低于Z形正交扫描策略,但对不同角度的悬垂结构影响不同。结合QM-Meltpool监控系统,从熔池的角度分析了倾斜角度和扫描策略的影响,为悬垂结构SLM成形提供了参考依据。     

激光选区熔化技术及其在个性化医学中的应用

激光选区熔化是一种精密金属增材制造技术,可以成形任意复杂的功能零件。个性化医学用品需要具有个性化的几何外形和良好的生物性能,为了探究激光选区熔化在个性化医学用品中的应用,采用DiMetal系列激光选区熔化设备成形医用金属材料如316L不锈钢、CoCrMo合金、Ti6Al4V,并对医用金属材料成形致密度、成形力学性能和几何结构成形性进行了研究。通过个性化设计和DiMetal系列激光选区熔化设备,设计与制造了个性化牙冠、舌侧正畸托槽、手术模板、全膝置换股骨远端假体、股骨近端假体、颅骨修复体等医学用品。研究证明DiMetal系列激光选区熔化装备、工艺可用于个性化医学用品的快速制造,这为个性化医学用品的快速响应设计与制造提供了一种新的手段。     

双光子三维微结构快速制备技术

建立了一种利用双光子聚合技术快速制备三维微结构的方法,并对加工分辨率进行了研究。通过对高速扫描原理的研究,提出了采用二维振镜与一维压电微移动台相结合,利用跳跃和扫描协同的运动模式,以段段扫描方式进行三维微结构加工的系统来提高其加工速度。实验制备千里马和具有木堆结构的三维光子晶体结构说明,采用上述扫描方式可使其加工速度较点点扫描方式提高10倍至1 000倍。实验结果表明,使用一定的激光功率时,其加工分辨率随曝光时间减小而显著提高,实验得到了50 nm的线宽分辨率,超过文献报道的100 nm的最高值。研究还表明,上述加工方法可实现激光三维微结构的快速制备并具有高分辨率加工的特点。     

选区激光熔化快速成型扫描路径优化算法研究

本文针对选区激光熔化成型过程中所存在的翘曲变形、球化等现象及其成因进行了简要分析,并且结合相关文献,提出了重复扫描和分区扫描相结台的路径生成算法.分区避免了长线扫描,因而可以有效减小翘曲变形,一个层面上重复扫描可以减小层间的内应力,并且可以提高熔化层的表面质量,因而此种扫描路径生成算法可以有效地改善零件的成型质量.     

Laser-arc hybrid welding of wrought to selective laser molten stainless steel

Selective laser melting (SLM) is a successful tool-free powder additive technology. The success of this manufacturing process results from the possibility to create complex shape parts, with intrinsic engineered features and good mechanical properties. Joining SLM steel to similar or dissimilar steel can overcome some limitations of the product design like small dimension, undercut profile, and residual stress concentration. In this way, the range of applications of the SLM process can be broadened. In this paper, the hybrid laser welding of selective laser molten stainless steel was investigated. A high-power fiber laser was coupled to an electric arc and austenitic stainless steel wrought and SLM parts were welded together. The power and speed parameters were investigated. The joints were analyzed in terms of weld bead profile, microstructure, microhardness, and tensile test. The efficiency of the welding process was evaluated through the line energy input versus the weld molten area.     

选择性激光烧结方法加工仿生支架的工艺研究

在利用选择性激光烧结技术加工仿生支架过程中,加工参数(包括激光功率、扫描速度、扫描间距)是影响成形质量的重要因素,通过调整加工参数可以使成形零件内部保持一定的孔隙,从而产生支架内部微孔结构。正交试验方法可以科学地安排和分析多种因素的影响,从而优化加工参数,最终获得具有较高孔隙率的仿生支架。     

基于激光选区熔化的免组装机构直接制造技术

采用数字化设计和组装并直接制造成形、无需实际组装工序的机构,称之为免组装机构。激光选区熔化能够直接制造冶金结合、组织致密、尺寸精度高和良好力学性能的功能零件,是直接制造免组装机构的理想技术。研究了激光选区熔化成形免组装机构的摆放方式、间隙特征的尺寸精度和表面粗糙度、间隙特征结构优化等关键技术。通过自由设计和DiMetal-100系列激光选区熔化成形设备成形了免组装的铜钱算盘和折叠算盘、平面连杆机构(曲柄滑块、曲柄摇杆、摇杆滑块)和万向节等免组装机构。研究证明,激光选区熔化不仅能够顺利成形形状很复杂的零件,也能够直接成形具有相对运动的免组装机构,为机电产品的数字化设计和一体化制造提供了一种可行的方法。     

Influence of process parameters on surface roughness of aluminum parts produced by DMLS

Direct metal laser sintering (DMLS) is an additive manufacturing technique for the fabrication of near net-shaped parts directly from computer-aided design data by melting together different layers with the help of a laser source. This paper presents an investigation of the surface roughness of aluminum samples produced by DMLS. A model based on an L₁₈ orthogonal array of Taguchi design was created to perform experimental planning. Some input parameters, namely laser power, scan speed, and hatching distance were selected for the investigation. The upper surfaces of the samples were analyzed before and after shot peening. The morphology was analyzed by means of field emission scanning electron microscope. Scan speed was found to have the greatest influence on the surface roughness. Further, shot peening can effectively reduce the surface roughness.     

45钢送丝激光熔覆成型基础工艺

45钢送丝激光熔覆成型工艺将通过单道及搭接熔覆实验进行研究.送丝方向和角度、送丝速度、激光扫描速度和功率对熔覆质量和效率的影响将首先得到研究.搭接实验旨在研究45钢的最佳搭接率.熔道微观硬度和微观组织的研究旨在证明基于送丝技术的激光熔覆成型可得到致密的金属组织,为后续激光熔覆修复和激光熔覆快速成型打下基础.     

选区激光熔化医用316L多孔结构的多目标工艺优化

为解决选区激光熔化技术成形医用多孔结构成形质量较差的问题,研究了工艺参数对316L成形样件致密度、孔隙率差值和表面粗糙度的影响,结合灰色关联分析方法建立了多元非线性预测模型。结果表明,预测模型的拟合度可达96.85%,最优工艺参数分别为激光功率250 W、扫描速度800 mm/s、扫描间距0.08 mm。优化后的灰色关联度达0.9195,得到样件的致密度为99.25%,孔隙率差值为0.60%,表面粗糙度均值为4.39 μm。致密度与激光功率正相关,随着致密度的增大,扫描速度和扫描间距呈现先增大再减小的趋势,孔隙率差值和表面粗糙度与激光功率、扫描速度、扫描间距均保持先减小再增大的趋势。结合激光体能量密度概念,揭示了工艺参数影响成形质量的原因,体能量密度为109.65～145.83 J/mm3时粉末的熔化状态最好。     

基于双模式超声换能器的选择性激光熔化316L制件弹性常数无损表征研究

选择性激光熔化技术(SLM)可以快速成型任意结构的金属零件,但其制件的内部组织和材料性能与传统制件有着显著区别。基于双模式超声换能器对SLM 316L不锈钢制件的不同方向弹性常数及其分布进行表征研究。首先通过设计并制备高性能双模式超声换能器,搭建超声弹性常数分布测量系统。对SLM制备的316L不锈钢试样依次进行纵波和两个正交横波声速测量,获得同位置处不同方向弹性模量和泊松比。通过不同成型方向的声速测量,发现SLM制件在堆积z方向熔化层内呈现显著区别,表现出明显的各向异性。而y-z平面内弹性常数分布表征表明,杨氏模量E_(13)大于E_(12),泊松比σ_(13)小于σ_(12),且制件各熔化层弹性常数分布规律相似。此外,还讨论了加工过程中扫描速度和扫描间距等工艺参数对弹性参数的影响。选择性激光熔化制件弹性常数的有效无损表征将为增材制件内部质量控制和工艺改善提供技术基础。     

激光选区熔化单道扫描与搭接数值模拟及试验

激光选区熔化（Selective laser melting,SLM）单道扫描的数值模拟,在数值建模时多采用规则实体模拟铺设的粉末层,通过等效定义材料热物理属性模拟铺设粉末层中粉末与气体共存的情况,难以模拟粉末颗粒的随机性而带来的扫描结果的随机性,且难以分析熔池形貌、内部缺陷的微观衍变过程。针对SLM成形过程中激光功率和单道搭接率对扫描单道和单道搭接质量的影响,以316L不锈钢材料为例,建立SLM首层单道扫描与单道搭接数值模拟模型。SLM的铺粉过程在基于离散单元法的EDEM中建立,并得到数值化的粉床几何模型。SLM的单道扫描与搭接的模拟基于有限体积法,在FLUENT中实现,采用两相流模型与熔化/凝固模型捕捉熔池形貌变化过程,得到不同激光功率和扫描搭接率下成形单道与单道搭接的数值模型。最后结合试验表明了在100~300 W激光功率下成形单道表面形貌与缺陷的形成,当激光功率为100~150 W时,单道形貌不规则,且容易形成局部缺陷;在200~300 W功率下,激光功率越大,保证搭接质量的最低搭接率越小,当激光功率为250 W时,应保证单道填充间距不大于0.1 mm。研究成果对SLM工艺参数的调整与优化具有重要的参考价值。     

Build orientation determination of multi-feature mechanical parts in selective laser melting via multi-objective decision making

Selective laser melting (SLM) is a unique additive manufacturing (AM) category that can be used to manufacture mechanical parts. It has been widely used in aerospace and automotive using metal or alloy powder. The build orientation is crucial in AM because it affects the as-built part, including its part accuracy, surface roughness, support structure, and build time and cost. A mechanical part is usually composed of multiple surface features. The surface features carry the production and design knowledge, which can be utilized in SLM fabrication. This study proposes a method to determine the build orientation of multi-feature mechanical parts (MFMPs) in SLM. First, the surface features of an MFMP are recognized and grouped for formulating the particular optimization objectives. Second, the estimation models of involved optimization objectives are established, and a set of alternative build orientations (ABOs) is further obtained by many-objective optimization. Lastly, a multi-objective decision making method integrated by the technique for order of preference by similarity to the ideal solution and cosine similarity measure is presented to select an optimal build orientation from those ABOs. The weights of the feature groups and considered objectives are achieved by a fuzzy analytical hierarchy process. Two case studies are reported to validate the proposed method with numerical results, and the effectiveness comparison is presented. Physical manufacturing is conducted to prove the performance of the proposed method. The measured average sampling surface roughness of the most crucial feature of the bracket in the original orientation and the orientations obtained by the weighted sum model and the proposed method are 15.82, 10.84, and 10.62 μm, respectively. The numerical and physical validation results demonstrate that the proposed method is desirable to determine the build orientations of MFMPs with competitive results in SLM.     

选区激光熔化工艺参数对Ti6Al4V粉末成型性的影响

以Ti6Al4V钛合金粉末为研究对象,在单层扫描和单道扫描实验的基础上,研究SLM工艺参数对Ti6Al4V合金材料成型性的影响,并进行了块体成型实验,通过设计正交试验及观察试样的形貌和致密度分析,最终得到Ti6Al4V合金粉末SLM块体成型的最佳工艺参数为:激光功率400W、搭接率1、扫描速度750mm/min,其致密度可以达到96.17％.     

Effect of Trace Addition of Ceramic on Microstructure Development and Mechanical Properties of Selective Laser Melted AlSi10Mg Alloy

Selective laser melting(SLM) is an emerging additive manufacturing technology for fabricating aluminum alloys and aluminum matrix composites. Nevertheless, it remains unclear how to improve the properties of laser manufactured aluminum alloy by adding ceramic reinforcing particles. Here the effect of trace addition of TiB_2 ceramic(1% weight fraction) on microstructural and mechanical properties of SLM-produced AlSi10Mg composite parts was investigated. The densification level increased with increasing laser power and decreasing scan speed. A near fully dense composite part(99.37%) with smooth surface morphology and elevated inter-layer bonding was successfully obtained. A decrease of lattice plane distance was identified by X-ray di raction with the laser scan speed decreased, which implied that the crystal lattices were distorted due to the dissolution of Si and TiB_2 particles. A homogeneous composite microstructure with the distribution of surface-smoothened TiB_2 particles was present, and a small amount of Si particles precipitated at the interface between reinforcing particles and matrix. In contrast to the Al Si10 Mg alloy, the composites showed a stabilized microhardness distribution. A higher ultimate tensile strength of 380.0 MPa, yield strength of 250.4 MPa and elongation of 3.43% were obtained even with a trace amount of ceramic addition. The improvement of tensile properties can be attributed to multiple mechanisms including solid solution strengthening, load-bearing strengthening and dispersion strengthening. This research provides a theoretical basis for ceramic reinforced aluminum matrix composites by additive manufacturing.     

选区激光熔化快速成形系统的关键技术

研究激光、铺粉、扫描三个重要选区激光熔化子系统的技术要点。通过计算成形过程所需激光能量,确定激光器的选用。研究表明成形升降台的连续下降精度、铺粉辊的回转偏心量及径向跳动量都对实现最小铺粉厚度控制有着重要影响。结合扫描速度对比试验,分析扫描系统的扫描特征,认为采用快的扫描速度是选区激光熔化工艺的一个重要特点,此外应采用合适的扫描策略克服热变形。在上述研究基础上,采用铜基合金粉末进行三维金属实体成形试验,试验分析表明,成形实体是一个由等轴晶和枝晶组成,相对密度达95%,具有冶金结合组织的金属实体,尺寸精度为±0.5 mm。所获得的成形实体多层断面构造、铺粉、扫描特征等信息可证实部分技术要点分析。     

激光熔覆工艺参数对铁基双层涂层组织和残余应力的影响

针对激光熔覆过程中剧烈的温度场变化伴随着应力、应变演化,进而导致零件具有高裂纹敏感性的问题,对不同激光扫描路径及工艺参数下残余应力演变规律进行研究。采用激光熔覆在Q345钢上制备了Fe基双层多道涂层,并以X射线衍射法结合电化学腐蚀剥层法测量沿涂层深度方向的残余应力分布,探究激光扫描路径、功率以及扫描速度对涂层显微组织和应力分布的影响。结果表明：涂层表面和内部为残余压应力,在涂层基体熔合线处残余应力发生突变,热影响区表现为残余拉应力;激光熔覆工艺对涂层残余应力的大小和分布规律有显著影响,当激光扫描路径为轮廓偏置式、激光功率为1.8 kW、扫描速度为0.02 m/s时,涂层具有最优的残余应力分布和成形质量;残余应力的产生主要与激光束对熔池的冲击作用以及熔覆层的非平衡凝固特性有关。     

Research on the forming process of three-dimensional metal parts fabricated by laser direct metal forming

To improve the forming quality of parts fabricated by laser direct metal forming (LDMF), the forming process of three-dimensional parts under open-loop LDMF system was studied in this paper. The influencing rule of scanning space on the forming quality was studied, and the optimal scanning space was derived. The software of control system about scanning style is also optimized, and thus, the forming quality of parts is improved. During fabricating three-dimensional parts, uneven heat distribution caused by multi-overlapping is one of the main factors affecting the sidewall forming quality. To solve the uneven heat distribution, the strategy of changing scanning speed was put forward. The influence of the standoff distance on the height of single-trace cladding layer was studied, and it was suggested that uneven surface of parts was caused by instability of process parameters, which could be compensated automatically in the condition of suitable standoff distance in the process of LDMF. Thus a so-called self-regulation effect is reached. Typical multi-overlapped parts with good forming quality are fabricated using the above-mentioned methods.     

Differences in microstructure and properties between selective laser melting and traditional manufacturing for fabrication of metal parts: A review

Selective laser melting (SLM), as one of the additive manufacturing technologies, is widely investigated to fabricate metal parts. In SLM, parts are manufactured directly from powders in a layer-by-layer fashion; SLM also provides several advantages, such as production of complex parts with high three-dimensional accuracy, compared with other additive manufacturing technologies. Therefore, SLM can be applied in aeronautics, astronautics, medicine, and die and mould industry. However, this technique differs from traditional methods, such as casting and forging; for instance, the former greatly differs in terms of microstructure and properties of products. This paper summarizes relevant studies on metal material fabrication through SLM. Based on a work completed in Huazhong Univ. Sci Tech., Rapid Manuf. Center (HUST-RMC) and compared with characteristics described in other reported studies, microstructure, properties, dimensional accuracy, and application of SLM are presented.     

Select laser melting of W–Ni–Fe powders: simulation and experimental study

Using W, Ni, and Fe powders as raw materials, selective laser melting (SLM) technology was considered for fabrication of 90W–7Ni–3Fe parts in one step. The investigation into simulation of temperature field of SLM W–Ni–Fe powder system was highlighted. Effects of processing parameters of scan velocity, laser power, scan interval, and preheating process on temperature field distribution were studied through establishing a 3D model based on finite element analysis theory. The simulation results show that a lower thickness, narrower scan interval, and a slower scan velocity tend to improve the temperature in powder bed. Moreover, the parameter range in which the maximum temperature in powder bed could reach up to the melting point of W (about 3,420°C) was obtained. Experiments on different processing parameters were carried out, and a good agreement with the simulation results could be found.