IMECH-IR  > 先进制造工艺力学实验室
Thesis Advisor虞钢
Degree Grantor中国科学院大学
Place of Conferral北京
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


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
Document Type学位论文
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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