-
采用自主研发的梯度材料零件SLM成型系统(见图 2)为成型设备,展开梯度材料成型实验,验证系统的性能。实验中采用尺寸为50mm×50mm×5mm的304不锈钢板作为基板。采用经磁选法反复分离提纯的4340钢粉末以及CuSn10青铜粉末作为原始材料,其中4340钢粉末中Fe,Cu,Sn,Ni,Si 4种元素含量(质量分数w)占比分别为0.9490,0.0008,0.0001,0.0171,0.0025,CuSn10青铜粉末中Fe,Cu,Sn,Ni,Si 4种元素含量(质量分数w)占比分别为0.0005,0.8650,0.1240,0.0006,0.0003[18]。两种原始材料分别装入两个漏斗中,粉末粒径均为15μm~53μm,球形,4340粉末呈银灰色,CuSn10粉末呈金黄色。实验成型过程中,保护气体采用体积分数为0.9998的氩气。
实验后,对照零件照片、并结合显微图像及X射线能谱成分分析(设备型号:蔡司EVO18,牛津OXFORD Inca250X-Max20mm2电制冷能谱仪),获得梯度材料零件成型的形貌及成分信息。
-
先成型了两个具有复杂外形结构的梯度材料零件,如图 3所示。可见具有复杂外形结构的梯度材料零件也可以打印出来。由图 3a可知,所成型的零件,在水平方向、垂直方向的材料颜色都可呈梯度变化,显示系统可按比例供给及混合两种原始粉末,并按零件模型各部分材料信息布置材料及成型,最终获得梯度材料零件。在图 3b中,是一个在垂直方向具有4个1.5mm厚的梯度材料区域的法兰零件,自下而上,各梯度材料区域内的4340钢/CuSn10青铜材料的预设体积比分别为4 ∶1,3 ∶2,2 ∶3和1 ∶4,由图 3b可知,其4个梯度区域内的颜色变化呈较好的缓慢渐变效果。
-
为进一步考察本梯度材料零件SLM成型系统的成型效果,设计了如图 4a所示的梯度材料零件3维模型。零件为10mm×10mm×4mm的方块,在垂直方向,依次设置有4340钢(厚1mm)、垂直梯度1(厚1mm)、垂直梯度2(厚1mm)、顶部材料块(厚1mm)等4个层次的材料过渡;自零件顶面向下1mm范围的厚度内,是顶部材料块,顶部材料块在水平方向上,设置有4340钢(长4mm×宽4mm)、水平梯度1(长4mm×宽1mm)、水平梯度2(长4mm×宽1mm)、CuSn10青铜(长4mm×宽4mm)4个层次的材料过渡。对水平梯度1的成型材料,采用4340钢粉与CuSn10青铜粉按体积比为1 ∶1混合而成;对垂直梯度1的成型材料,采用4340钢粉与CuSn10青铜粉按体积比为3 ∶2混合而成;对垂直梯度2或水平梯度2的材料,采用4340钢粉与CuSn10青铜粉按体积比为1 ∶3混合而成。因此,该模型可考察成型系统在水平方向以及垂直方向的成型效果。
图 4a所示模型每种颜色的块体都代表一种材料成分,可设计为一个单独的零件模型,总的梯度材料零件3维模型通过几种颜色的块体零件模型装配而成。按前面所述,由各个颜色块体零件模型生成扫描路径数据HPGL格式文件,并创建材料信息TXT格式文件后,即可获得整个梯度材料零件的增材数据[18]。
实验开始前,在梯度材料零件SLM成型系统中设置的相关实验参数如表 1所示。
Table 1. SLM experimental process parameters for producing the gradient material part
forming parameter seting value laser power 140W air mixing time 10s(for single layer)or 15n s(for continuous n layers) gas flow 10L/min times of powder cleaning 7 layer thickness 30μm laser scanning space 0.08mm scanning speed in 4340 material region 650mm/s scanning speed of gradient 1 region 550mm/s scanning speed of gradient 2 region 450mm/s scanning speed in CuSn10 bronze material region 400mm/s 成型件照片如图 4b所示,其材料分布基本与图 4a的模型图相一致:底部为深色的4340钢,然后过渡到垂直梯度1、垂直梯度2(颜色逐渐变淡);在顶部,分布着处于同一水平面的4340钢、水平梯度1、水平梯度2和CuSn10青铜几种材料区域,颜色同样逐渐变淡。
按图 4b所示的剖切位置示意点划线,对成型零件进行了剖切,制成金相试样并通过扫描电镜获得了图 5所示的一个带清晰水平梯度及垂直梯度形貌的扫描电镜照片。由该照片的颜色不同可知,在水平方向及垂直方向,材料的成分的确依次按梯度分布。
Figure 5. Asection micrograph of the part and position and direction of EDS line scanning (horizontal dotted line: horizontal line scanning; vertical dotted line: vertical line scanning; dotted line: color boundary)
为考察粉末混合的均匀性,在图 5剖面的水平梯度1区域内部(不靠近两种材料区域边界)、垂直梯度1区域内部(不靠近两种材料区域边界),各随机选取4个不重叠的160μm×160μm的微细区域,对每个区域内的主要元素平均质量分数作能谱仪(energy dispersive spectrometer, EDS)分析,以考察粉末混合效果,所得的数据如表 2及表 3所示。元素分布的离散程度可用变异系数体现[23-24],由表 2、表 3可知,采用10s~15s的单层平均混合时间混合后,8个微区内的主要元素变异系数最大不超过0.59,因此,各微区内的粉末元素平均质量分数离散程度小,达到较好的混合均匀性。
Table 2. Average mass fraction of main elements in selected micro zones in horizontal gradient region 1 of the Fig. 5
element element content of microzone 1 (mass fraction w) element content of microzone 2 (mass fraction w) element content of microzone 3 (mass fraction w) element content of microzone 4 (mass fraction w) average value (mass fraction w) variability coefficient Fe 0.5014 0.5073 0.4802 0.5304 0.5048 0.04 Cu 0.4540 0.4446 0.4721 0.4253 0.4490 0.04 Sn 0.0299 0.0309 0.0310 0.0277 0.0299 0.04 Ni 0.0097 0.0103 0.0097 0.0108 0.0101 0.05 Si 0.0050 0.0069 0.0070 0.0058 0.0062 0.13 Table 3. Average massfraction of main elements in selected micro zones in vertical gradient region 1 of the Fig. 5
element element content of microzone 1 (mass fraction w) element content of microzone 2 (mass fraction w) element content of microzone 3 (mass fraction w) element content of microzone 4 (mass fraction w) average value (mass fraction w) variability coefficient Fe 0.6347 0.6102 0.5945 0.6100 0.6123 0.02 Cu 0.3151 0.3276 0.3469 0.3349 0.3311 0.03 Sn 0.0387 0.0417 0.0409 0.0390 0.0401 0.03 Ni 0.0116 0.0150 0.0119 0.0116 0.0125 0.11 Si 0 0.0055 0.0059 0.0045 0.0040 0.59
实时混粉梯度材料SLM成型系统构建与实验
System construction and experiment for SLM of gradient materials based on real-time powder mixing methods
-
摘要: 为了在成型过程中,方便地在零件上按需获得梯度材料成分,采用了集成同步送粉碰撞混合、锥形聚集混合、气流混合等多重混粉动作的实时混粉方法,研制成梯度材料激光选区熔化增材制造系统,并展开了梯度材料成型实验验证,结合试样照片、显微图像及能谱仪检测,分析了成型效果。结果表明,系统可自由按需在水平及垂直方向添加成分渐变材料,可方便获得具有复杂外形结构的梯度材料零件;成型件梯度材料区域微区成分分析显示,各微区内元素平均质量分数离散程度小,成型过程中每层平均混粉时间10s~15s时,各微区主要元素变异系数不超0.59,达到了较好的混合均匀性。该研究为自由制造梯度材料零件提供了新途径。Abstract: In order to obtain the gradient material composition of parts easily in the part forming process, a selective laser melting additive manufacturing system for gradient materials was developed by using the real-time powder mixing method which integrates multiple powder mixing actions such as impact mixing after synchronous discharge powders, converging mixing through a conical cavity, and air flow mixing. With this system, the experimental verification of gradient material forming was carried out, and the forming effect was analyzed combined with the sample photos, microscopic images, and energy spectrometer detection. The result shows that the gradient materials can be freely added in the horizontal and vertical directions to produce gradient material parts with complex shape and structure in the system. The micro areas composition analysis of the gradient material zones of the gradient material part shows that the dispersion degree of the average mass content of elements in each micro zone is small. The variability coefficient of the main elements in each micro zone is not more than 0.59 when the average powder mixing time of each layer is 10s~15s during selective laser melting process, achieving good mixing uniformity.This research provides a new way for free manufacturing of gradient material parts.
-
Key words:
- laser technique /
- gradient materials /
- selective laser melting /
- metal part /
- additive manufacturing
-
Figure 3. Two verification parts of gradient material (main molding parameters: laser power of 170W; powder cleaning times of 5 times; scanning distance of 0.08mm; layer thickness of 30μm; scanning speed of 250mm/s ~450mm/s)
a—gradient material part of steel copper nozzle b— gradient material part of steel copper flange
Table 1. SLM experimental process parameters for producing the gradient material part
forming parameter seting value laser power 140W air mixing time 10s(for single layer)or 15n s(for continuous n layers) gas flow 10L/min times of powder cleaning 7 layer thickness 30μm laser scanning space 0.08mm scanning speed in 4340 material region 650mm/s scanning speed of gradient 1 region 550mm/s scanning speed of gradient 2 region 450mm/s scanning speed in CuSn10 bronze material region 400mm/s Table 2. Average mass fraction of main elements in selected micro zones in horizontal gradient region 1 of the Fig. 5
element element content of microzone 1 (mass fraction w) element content of microzone 2 (mass fraction w) element content of microzone 3 (mass fraction w) element content of microzone 4 (mass fraction w) average value (mass fraction w) variability coefficient Fe 0.5014 0.5073 0.4802 0.5304 0.5048 0.04 Cu 0.4540 0.4446 0.4721 0.4253 0.4490 0.04 Sn 0.0299 0.0309 0.0310 0.0277 0.0299 0.04 Ni 0.0097 0.0103 0.0097 0.0108 0.0101 0.05 Si 0.0050 0.0069 0.0070 0.0058 0.0062 0.13 Table 3. Average massfraction of main elements in selected micro zones in vertical gradient region 1 of the Fig. 5
element element content of microzone 1 (mass fraction w) element content of microzone 2 (mass fraction w) element content of microzone 3 (mass fraction w) element content of microzone 4 (mass fraction w) average value (mass fraction w) variability coefficient Fe 0.6347 0.6102 0.5945 0.6100 0.6123 0.02 Cu 0.3151 0.3276 0.3469 0.3349 0.3311 0.03 Sn 0.0387 0.0417 0.0409 0.0390 0.0401 0.03 Ni 0.0116 0.0150 0.0119 0.0116 0.0125 0.11 Si 0 0.0055 0.0059 0.0045 0.0040 0.59 -
[1] LI Y. Research progress on gradient metallic materials[J]. Materials China, 2016, 35(9): 658-665(in Chinese). [2] XIA X G, DUAN G L. Advances and prospects of additive manufacturing technology of functionally graded material[J/OL]. (2021-07-30)[2021-08-10]. http://kns.cnki.net/kcms/detail/50.1078.TB.20210730.1014.004.html (in Chinese). [3] LIU Zh S, XUE D Q, HAN Sh H, et al. Microstructure and mechanical properties of double metal arc additive forming part based on CMT welding[J]. Hot Working Technology, 2017, 46(17): 184-186(in Chinese). [4] ONUIKE B, HEER B, BANDYOPADHYAY A. Additive manufacturing of Inconel 718—Copper alloy bimetallic structure using laser engineered net shaping (LENSTM)[J]. Additive Manufacturing, 2018, 21: 133-140. doi: 10.1016/j.addma.2018.02.007 [5] WANG P, LAO C S, CHEN Z W, et al. Microstructure and mechanical properties of Al-12Si and Al-3.5Cu-1.5Mg-1Si bimetal fabricated by selective laser melting[J]. Journal of Materials Science & Techno-logy, 2020, 36: 18-26. [6] GUO Y F. Experimental research on multilayer structure of high nitrogen steel-316L made by robot CMT additive manufacturing[D]. Nanjing : Nanjing University of Science and Technology, 2018: 9-15(in Chinese). [7] LIU M N, WEI K W, DENG J F, et al. Study on selective laser melting rapid forming technology of aluminum liquid cold plate[J/OL]. (2021-01-06)[2021-07-26]. https://kns.cnki.net/kcms/detail/31.1690.TN.20210105.1351.013.html (in Chinese). [8] ZHANG Ch Y, CHEN X Sh, SUN X T. The development situation of metal 3-D printing manufacturing technology[J]. Laser Technology, 2020, 44(3): 393-398(in Chinese). [9] CHEN J T, GUO Z Y, WANG Ch Y, et al. Research status of Ti-6Al-4V manufactured by selective laser melting for medical device applications[J]. Laser Technology, 2020, 44(3): 288-298(in Chinese). [10] WANG D, DENG G W, YANG Y Q, et al. Research progress in additive manufacturing of metal heterogeneous materials[J]. Chinese Journal of Mechanical Engineering, 2021, 57(1): 186-198(in Chinese). doi: 10.3901/JME.2021.01.186 [11] CHIVEL Y. New approach to multimaterial processing in selective laser melting[J]. Physics Procedia, 2016, 83: 891-898. doi: 10.1016/j.phpro.2016.08.093 [12] CHEN J, YANG Y, SONG C, et al. Interfacial microstructure and mechanical properties of 316L/CuSn10 multi-material bimetallic structure fabricated by selective laser melting[J]. Materials Science and Engineering, 2019, A752: 75-85. [13] LIU Z H, ZHANG D Q, SING S L, et al. Interfacial characterization of SLM parts in multi-material processing: Metallurgical diffusion between 316L stainless steel and C18400 copper alloy[J]. Materials Characterization, 2014, 94: 116-125. doi: 10.1016/j.matchar.2014.05.001 [14] MA Sh Y, SHI X Zh, TAN T H. Powder spreading and powder recovery device for selective laser melting of heterogeneous materials: China, 2014102203104[P]. 2014-08-13(in Chinese). [15] TAN T H. Molding process simulation of heterogeneous material molding for selective laser melting and its equipment stucture design[D]. Beijing: Beijing Institute of Technology, 2015: 17-75(in Ch-inese). [16] WEI C, LI L, ZHANG X, et al. 3D printing of multiple metallic materials via modified selective laser melting[J]. Cirp Annals-Manufacturing Technology, 2018, 67(1): 245-248. doi: 10.1016/j.cirp.2018.04.096 [17] WEI C, GU H, SUN Z, et al. Ultrasonic material dispensing-based selective laser melting for 3-D printing of metallic components and the effect of powder compression[J]. Additive Manufacturing, 2019, 29: 100818. doi: 10.1016/j.addma.2019.100818 [18] WU W H, YANG Y Q, MAO G Sh, et al. Selective laser melting free fabrication of heterogeneous material parts[J]. Optics and Precision Engineering, 2019, 27 (3): 517-526(in Chinese). doi: 10.3788/OPE.20192703.0517 [19] WEI C, SUN Z, CHEN Q, et al. Additive manufacturing of horizontal and 3-D functionally graded 316L/Cu10Sn components via multiple material selective laser melting[J]. Journal of Manufacturing Science and Engineering, 2019, 141(8): 081014. doi: 10.1115/1.4043983 [20] DEMIR A G, PREVITALI B. Multi-material selective laser melting of Fe/Al-12Si components[J]. Manufacturing Letters, 2017, 11: 8-11. doi: 10.1016/j.mfglet.2017.01.002 [21] LIU F, WU W H, YANG Y Q, et al. Manufacture of composition gradient material part by selective laser melting[J]. Optics and Precision Engineering, 2020, 28(7): 1510-1518(in Chinese). doi: 10.37188/OPE.20202807.1510 [22] WU W H, YANG Y Q, MAO G Sh, et al. Design and implementation of selective laser melting system for producing heterogeneous material parts[J]. Manufacturing Technology & Machine Tool, 2019 (10): 32-37(in Chinese). [23] FENG R, ZHAI D Ch, YUAN Y Sh. Research on air and surface water quality evaluation method incorporated with the coefficient of variation[J]. Journal of Environmental Engineering Technology, 2021, 11(4): 814-822(in Chinese). [24] HUANG Ch X, WU X Ch, CHEN Q H. Study of mixing effect of solid powder in horizontal plant-size twin-shaft paddle mixer[J]. Food & Machinery, 2017, 33(3): 80-83 (in Chinese).