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玻璃基板为40mm×40mm×0.7mm的康宁EAGLE XG型硼硅酸盐玻璃,具有高透光率、高表面质量以及热稳定性等。玻璃料为一种低温涂敷浆料(BASS),玻璃料中的粒子平均尺寸在1.42μm,50%的粒子尺寸小于1.30μm,固体物质质量分数为0.641,使用Brookfield DV2测得粘度为101Pa·s(25℃)。玻璃基板与玻璃料的物理参数如表 1所示。
Table 1. Thermal properties of material used in the study
material transition temperature/℃ softening point/℃ coefficient of thermal expansion/ (10-7 ℃-1) glass substrate 722 971 31.7 glass frit 343 428 48 -
玻璃基板以蒸馏水与清洁剂的混合液进行超声波清洗,清洗后进行干燥处理,以去除玻璃表面存在的灰尘、氧化物等污染物。玻璃浆料以400目丝印网版(钢网厚度18μm,膜厚10μm)印在玻璃基板上。丝印图案为直线,长度30mm,宽度0.8mm。
试件置于加热炉中去除杂质。加热曲线如图 1所示。加热步骤分为两步: 加热台在空气中将涂敷涂层的玻璃基板直接加热至150℃,去除有机溶剂;再加热至300℃,去除粘接剂;最终加热至峰值温度,实现玻璃料的预烧结。试件在进行烧结前先在室温下平放10min。在加热炉中烧结过程的加热速率保持在5℃/min,降温过程中不控制降温速度。
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在丝印玻璃料的玻璃基板上方盖上另一块玻璃基板,使用激光进行焊接,玻璃料吸收激光能量温度升高产生熔融,熔融的玻璃料在夹具压力的作用发生扩散,直到激光能量消失,玻璃料熔融部分冷却凝固实现了两块玻璃的连接。玻璃激光焊接过程示意图如图 2所示。各组焊接参数如表 2所示。
Table 2. Bonding parameters
number laser power P/W welding speed v/ (m·min-1) defocusing amount D/mm 1 37 0.1 -15 2 40 0.1 -15 3 45 0.1 -15 4 50 0.1 -15 5 55 0.1 -15 6 60 0.1 -15 为实现空气和真空条件下玻璃激光焊接,设计大气条件下的夹具及真空夹具。大气条件下的夹具如图 3所示使用,利用压紧的弹簧提供预紧力Fs,通过调节螺母的位置,改变弹簧长度,调节Fs大小,压板压在焊缝两侧,通过弹簧传递过来的力压在焊缝两侧,玻璃板受到的直接压力为Fb。激光通过两块压板之间的间隙,作用在玻璃料上。真空夹具如图 4所示。采用玻璃板、底座及密封圈构成密闭空间,通过吸气口吸收空间中的气体实现真空环境。在抽真空的过程中,密封圈由于真空腔与大气条件下的气压差发生变形,被压扁,玻璃板压在试件上,提供预紧力Fg。激光透过夹具中的玻璃盖板,作用在玻璃料上。为减少真空夹具因透过夹具玻璃板引起的激光反射及吸收造成玻璃料吸收的激光能量减少对对比实验的影响,在大气夹具上也添加一块玻璃板。
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焊接平台如图 5所示。采用RFL-DDL-100型半导体激光器,激光器最大输出功率为100W,光束辐射波长为915nm; 激光头的焦距为150mm,焦点处光斑直径为300μm。使用同轴拍摄系统对激光焊接过程进行直接拍摄。滤波片为窄带滤波片,透光范围在450nm~490nm之间,避开激光加热玻璃料产生黑体发射出的500nm~2000nm之间的杂波。选用照明光源为蓝光光源。热烧结后的试件,置于运动平台上,进行玻璃激光焊接试验。焊缝观测分别采用金相显微镜PrimotechMAT,适用于材料分析,具稳定的色温和节能型发光二极管(light-emithing diode, LED)光源;基恩士超景深显微镜VHX-6000,能进行彩色图像拍摄还原焊缝原色。
大气及真空条件下玻璃激光焊接对比
Laser-assisted glass frit bonding in air and vacuum
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摘要: 为了验证真空环境对玻璃激光焊接气孔形成的影响,采用在大气及真空条件下进行玻璃激光焊接对比试验的方法,对两种条件下气孔率随激光功率的变化及玻璃料向两端扩展的程度进行了理论分析和实验验证。结果表明,气孔的成因不仅是玻璃料中残存的气体,功率提高至45W后,不稳定成分的升华与分解产生了更多气体,进一步提高了气孔率; 真空条件对焊缝扩展影响较小,无明显差异;而真空条件下的气孔率要显著大于在大气条件下的气孔率; 真空条件下气孔面积更大,但增大的气孔面积并不能扩大玻璃料的扩展宽度。该研究结果进一步地揭示了玻璃激光焊接下气孔的形成机制。Abstract: In order to verify the effect of vacuum environment on the formation of pores in glass laser welding, the comparative test of glass laser welding under atmospheric and vacuum conditions was adopted.Theoretically analyze and experimentally verify of the change of porosity with laser power and the extent of expansion of glass frit to both ends under the two conditions was then carried out. The results show that, the cause of the porosity is not only the residual gas in the glass frit, but also the sublimation and decomposition of unstable components to produce more gas after the power is increased to 45W, which further improves the pores. It is found that the vacuum condition has little effect on the bonding expansion, and there is no obvious difference. The porosity under vacuum condition is significantly greater than that under atmospheric condition. The porosity is larger under vacuum condition, but the enlargement of porosity can't enlarge the expansion width of glass frit. The results further reveal the formation mechanism of pores under laser-assisted glass frit bonding.
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Key words:
- laser technique /
- pores /
- laser bonding /
- vacuum /
- glass
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Table 1. Thermal properties of material used in the study
material transition temperature/℃ softening point/℃ coefficient of thermal expansion/ (10-7 ℃-1) glass substrate 722 971 31.7 glass frit 343 428 48 Table 2. Bonding parameters
number laser power P/W welding speed v/ (m·min-1) defocusing amount D/mm 1 37 0.1 -15 2 40 0.1 -15 3 45 0.1 -15 4 50 0.1 -15 5 55 0.1 -15 6 60 0.1 -15 -
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