钛合金激光填粉焊接粉末烧损研究

发布时间：2018-01-01 04:21

本文关键词：钛合金激光填粉焊接粉末烧损研究　出处：《湖南大学》2015年硕士论文　论文类型：学位论文

【摘要】：钛合金以其优良的机械性能,广泛地应用于飞机蒙皮中。但在钛合金激光焊接中因焊接装配间隙过大或者高能激光束对焊缝金属的辐射汽化,易出现焊缝塌陷现象。焊缝塌陷对飞机蒙皮隐身涂层涂装及整体的隐身性能具有直接影响。而激光填粉焊接技术可以有效抑制焊缝塌陷,同时可以提高焊缝力学性能。在焊接过程中,激光束与粉末束的能量耦合作用对于作为激光填粉焊接的核心技术之一的粉末有效输送具有直接影响。因此,本文采用模拟与试验分析相结合的方法研究了激光束与粉末束的能量耦合作用以及粉末填充对于钛合金焊缝塌陷的补偿作用。首先,以传热学、概率学理论为基础,本文通过对粉末颗粒空间密度分布与单位传输距离粉末颗粒数的求解,建立了粉末束与激光束能量耦合的数学模型,并将通过模型计算出的单位传输距离上粉末吸收的激光功率与粉末汽化潜热的比值转化为粉末烧损摩尔量。该模型考虑了粉末颗粒直径,粉末颗粒速度,激光功率密度分布,送粉量等主要因素。其次,本文搭建了粉末束与激光束能量耦合试验观测平台,拍摄了在激光辐照作用下粉末束灰度图。依据图像灰度与粉末质量的相关函数以及所建数学模型,对比有无激光辐照作用的粉末质量分布,测量得到了粉末在激光功率为1000W、2000W时的吸收率。并讨论了各参数对于粉末束中粉末颗粒烧损的影响。结果表明:粉末质量峰值随着激光功率的增加而减小;随着载粉气流量的增加,粉末烧损率呈先下降再上升的趋势,并且在6L/min时烧损率达到最小值15.10%;在相同激光功率下,直径较大的粉末颗粒的烧损量较小。最后,依据上述粉末烧损规律,计算了钛合金填粉焊接中纯钛粉末颗粒的填充量,并使用激光填粉焊接工艺对TC4钛合金进行了焊接试验。试验结果显示:填充粉末的钛合金激光焊接焊缝无明显塌陷,与普通激光焊接相比,组织、力学性能基本相同,延伸率略有增加。光粉耦合粉末颗粒烧损量的研究探讨了以激光填粉焊接技术为代表的激光增材制造技术中激光束能量在粉末束上的分布关系,为焊缝高度和元素组织的调控提供了设计理论依据。
[Abstract]:Titanium alloys are widely used in aircraft skin because of their excellent mechanical properties, but in laser welding of titanium alloys, the welding gap is too large or the radiation vaporization of weld metal by high energy laser beam. Welding seam collapse is easy to occur. The seam collapse has a direct impact on the coating of aircraft skin stealth coating and the overall stealth performance. Laser powder filling welding technology can effectively suppress the seam collapse. At the same time, the mechanical properties of welding seam can be improved. In the process of welding, the coupling of laser beam and powder beam has a direct impact on the effective transportation of powder as one of the core technology of laser powder filling welding. In this paper, the energy coupling between laser beam and powder beam and the compensation effect of powder filling on weld collapse of titanium alloy are studied by means of simulation and experimental analysis. Firstly, heat transfer is used to study the effect of laser beam and powder beam on the weld collapse of titanium alloy. Based on the theory of probability, the mathematical model of energy coupling of powder beam and laser beam is established by solving the spatial density distribution of powder particles and the number of powder particles per unit transmission distance. The ratio of the laser power absorbed by the powder to the latent heat of vaporization is converted to the molar amount of the powder burning in the unit transmission distance calculated by the model. The model takes into account the particle diameter and particle velocity. The main factors such as laser power density distribution, powder feeding amount and so on. Secondly, the experimental observation platform of energy coupling of powder beam and laser beam is built in this paper. According to the correlation function between image grayscale and powder mass and the established mathematical model, the powder mass distribution with or without laser irradiation was compared. The laser power of the powder is 1000W. The absorptivity of 2000W and the influence of various parameters on the burning loss of powder particles in the powder beam are discussed. The results show that the peak value of powder mass decreases with the increase of laser power. With the increase of the flow rate of the carrier gas, the burning loss rate of the powder decreased first and then increased, and the burning rate reached the minimum value of 15.10 at 6L / min. At the same laser power, the amount of burning loss of the larger diameter powder particles is smaller. Finally, according to the law of the above powder burning, the filling amount of pure titanium powder particles in titanium alloy powder filling welding is calculated. The welding test of TC4 titanium alloy was carried out by using laser powder filling welding technology. The results showed that there was no obvious collapse in the welding seam of titanium alloy filled with powder, and the microstructure was compared with that of conventional laser welding. The mechanical properties are basically the same. The research on the burning loss of photo-powder coupling powder particle has discussed the distribution of laser beam energy on powder beam in laser material augmentation manufacturing technology represented by laser powder filling welding technology. It provides a theoretical basis for the control of weld height and element structure.
【学位授予单位】：湖南大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TG456.7

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