IMECH-IR  > 先进制造工艺力学重点实验室
DIN18CrNi18合金钢毫秒激光打孔孔型研究
SAAD NAWAZ
Thesis Advisor虞钢
2017
Degree Grantor中国科学院大学
Place of Conferral北京
Subtype博士
Degree Discipline一般力学与力学基础
Keyword激光打 ,离焦量 锥角 纵剖面 重铸层 Laser drilling defocusing length Tapper angle longitudinal profile recast layer
Abstract

在现代制造领域中,相对于其他打孔技术而言,例如电火花线切割加工、切削、CNC、传统钻孔等,激光打孔是一项精确可控的打孔技术。与其他传统打孔技术相比,激光打孔技术具有尺寸精度高、孔型精确和加工效率高等优点,使其具有明显优势。由于电子、计算机、汽车零部件加工、重型机械、航空航天和通信等行业的快速增长,激光打孔技术在工业上得到了广泛应用。本实验研究了离焦量和其他工艺参数的影响、Nd:YAG毫秒脉冲激光打孔工艺的优化、工艺参数对进/出口孔型的影响、热影响现象以及辅助气体的影响。从实验上探索了18CrNi8激光打孔过程中的关键工艺参数,如不同离焦平面的脉冲频率、脉宽和气压等。实验结果表明,随着离焦量的增加,孔入口直径增加,然而当离焦量低于焦点时,孔径增加速度减小,并讨论了实验上观察到的不同进/出口直径增大和减小的趋势。激光束从垂直到锥形盲孔入口的离焦变化,可以获得最佳孔型(入口和出口)。锥角对孔型的影响体现在改变孔内的流体流动。本文研究了Nd:YAG毫秒脉冲激光打孔的工艺参数优化及其对进/出口孔型的影响。所使用的材料是应用于磨损和高温环境的材料,如涡轮叶片和燃料喷射喷嘴等。本文研究提高了圆锥角测量精度,并将测量结果与理论计算值进行比较。不同离焦平面下从直孔到盲孔的大量实验结果表明,可在入口和出口处获得最佳孔型。本文还获得了较低热效应的最佳参数组合,提高了工作效率。从热影响区、材料沉积、再铸层和碎屑形成等方面讨论了激光束的温度效应,并得到了获得低热效应、高质量孔的最佳参数的合。本文研究了直径为毫米级音速气流的不同气体的影响和行为。早期的研究表明,使用这种气体辅助射流有利于提高孔的圆度,但也降低了钻孔速度并增加了孔入口直径。本文从热影响区、氧化反应、在入口/出口的重铸层和出口处熔池喷溅等方面,研究了氩气、氮气和氧气的性能。辅助气体氧气的使用可以通过入射气体射流与熔融材料之间的放热氧化反应来提高打孔性能。

Other Abstract

Laser drilling process is an adequate controlled drilling process in modern manufacturing worldcompared to other alternate techniques, like wire EDM, broaching, CNC, conventional drilling or other famous destructive hole drilling processes. Accurate dimensional results, precise hole geometry and rapid material removal rate make it superior while comparing with other conventional hole drilling techniques such as EDM, broaching, drilling with tool bit or other destructive processes. The Present experimental study accounts defocusing impact along with other technical parameters and optimization of Nd:YAG millisecond pulsed laser drilling; and finally their influence on the entrance and exit holes geometry/topology, Heat affected phenomena and assisting gases influence . The key technical parameters such as pulse frequency, pulse width and air pressure with respect to different defocused focal plane were explored experimentally for the percussion laser drilling of high grade steel 18CrNi8. An imperial impression was revealed that there is an increment in hole entrance diameter with the increase in defocusing distance; however, the rate of increasing diameter remains slow, as long as defocusing was below the focal point.Different observed trends of increasing and decreasing diameters at entrance and exits were recorded and discussed with existing knowledge. The defocusing variation of laser beam at the entrance from straight to tapered blind holes leads to conclusive results for obtaining optimal hole profile (at entrance and exit). Tapper angle has enough sufficient influence on the shape of the hole to alter the requirement of the flowing fluid from these holes. The study also focused on operating parameters optimization in Nd:YAG millisecond pulsed laser drilling and their impact on the entrance and exit holes geometry. The material used is one of the preferred candidates for conductive materials for wear and heating applications such as turbine blades and fuel injection nozzles etc. The novel technique was developed here to increase the measurement accuracy of tapper angle and the results were compared with theoretically calculated values. The results evaluation from straight to blind hole under empirical influence of defocused plane was investigated at different levels. The extensive experimentation leads to conclusive results for obtaining optimal hole profile at entrance and exit. The optimum parametric combinations for attaining lower heat treatment effects were also discussed for superior process efficiency. High temperature treatment of laser beam is also discussed in terms of heat affected zones, Material deposition, recast layer and debris formation. Empirical Probe leads to evaluate the optimal combination of parameters which resulted in less heat treatment for high quality holes. Different gasses via sonic gas jets with diameters of the order of millimeters are employed in present study to investigate their effects and behaviors. Earlier Studies show that using such gas assist jets have the benefit of increasing the roundness of the holes, but it also reduces the drilling rate and increases thehole entrance diameter. The performance of argon, nitrogen and oxygen was investigated in terms of heat affected zones, oxidations, recast layer at entrance and exit and splashes from molten pool at entrance. The use of oxygen assist-gas can enhance drilling performance through the exothermic oxidation reaction between the impinging gas jet and the molten material.

Call NumberPhd2017-037
Language中文
Document Type学位论文
Identifierhttp://dspace.imech.ac.cn/handle/311007/78623
Collection先进制造工艺力学重点实验室
Recommended Citation
GB/T 7714
SAAD NAWAZ. DIN18CrNi18合金钢毫秒激光打孔孔型研究[D]. 北京. 中国科学院大学,2017.
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