Research On High Peak Power Quasi-continuous Wave Laser Cleaning Technology And The Key Technology Of Fiber Transmission

Laser cleaning is an advanced and environment-friendly cleaning technology.The main mechanism is the absorption of instantaneous?psⁿs?high energy?mJ^J?laser on the surface of the object.After that,the pollutant is vaporized and volatilized and expanded instantaneously,so as to overcome the adsorptive force from the surface of the object.Compared with chemical cleaning,the laser cleaning does not need chemical reagents.Compared with the method of grinding,the laser cleaning is non-contact and no stress,so the damage to the surface of the substrates is very small and even zero.In addition,the laser source can be delivered by a flexible fiber,the area that is not easy to be cleaned can be cleaned and the scope of application also is expanded.The applicable object is also more widely,to remove rust and dirt,paint,in addition to the wafer surface treatment;high cleanliness,and can remove the nano particles.Rust removal?the oxide layer of hot-rolled sheet steel?and paint removal by laser are two important directions of laser cleaning in industrial applications.The high peak power quasi-continuous wave laser?kHz,¹00ns,×10mJ?is the preferred laser source for laser cleaning.The reasons can be listed as follows:because of¹00ns laser pulse so that the temperature of the paint can be continuously heated by the laser pulses.The absorption of laser energy by the paint from the high repetition rate pulses can bring the paint to the ablation threshold rapidly,and the ablation capacity and efficiency can be increased when a higher repetition rate of laser is used.Because of the high pulse energy,when the laser is used for cleaning the paint,a large focus spot is usually used;the large beam spot is beneficial for preventing damages to the substrates due to the high power density and reducing the difficulty in controlling the processing parameters.In addition,flexible transmission by fiber is an important core technology of laser cleaning,and the high peak power quasi-continuous wave laser can carry out long-distance flexible transmission through fiber,which greatly improves its application scope.Therefore,this paper focuses on the oxide layer of hot-rolled sheet steel removal and paint on the surface of the aluminum substrate removal by high peak power quasi-continuous wave laser.The main research contents and the results are as follows:?1?Using flat-flat resonant cavity strcture,double acousto-optic Q switches vertical and orthogonal placed.By a single oscillation and amplified?MOPA?,900W high peak power quasi-continuous wave laser is realized.The two-dimensional laser cleaningsystemis realized by rapid scanning in the X-direction using a galvanometer and translationalmotionin the Y-direction using a translational stageto achieve the full coverage of the samples.The spot distribution of two dimensional laser scanning laser cleaning system was studied,and the pattern of spot distribution of two dimensional scanning laser cleaning system was obtained.The overlap rate of the spot in Y-direction is low in the middle,which will result in the uneven laser cleaning.A method for calculating the overlap ratio of pulse laser in X direction and Y direction is established.It is proposed that the unit scale pulse number density method to describe the calculation method of high frequency pulse laser acting on the surface of the.?2?Based on the CO₂ laser ring optical field,the fiber end-cap large gradient fusion system is developed.The temperature field variation of fiber end-cap large gradient fusion process was simulated by finite element method;Based on the analysis and simulation results,the time sequence diagram of the fiber end-cap large gradient fusion is set up.The high quality,large gradient and heteromorphic bonding between the end-caps and the fiber are realized.The TracePro software is used to simulate the mode stripping principle of the cladding laser.It is proved that changing the refractive index and incidence angle can achieve cladding laser stripping,and based on surface etching that change the laser angle of incidence of cladding.The effective removal of destructive laser cladding remains in the process of laser transmission.In the process of laser transmission by the fiber,the effective stripping of the destructive laser in the cladding is achieved.?3?Based on the result of large gradient fusion between fiber and end-cap,a water-cooled optical cable with standard QB interface structure has been developed.The transmission of 900W,20 kHz,100ns high peak power quasi continuous wave laser is realized by using the optical fiber cable with end-cap structure.?4?Based on the Fourier heat conduction equation and the law of conservation of energy,a one-dimensional linear laser cleaning heat conduction equation for the material temperature rise under the action of Gauss energy distribution pulse laser is constructed.The cleaning process of pulse laser ablation mechanism based on gasification were analyzed,in using pulsed laser ablation material removal,part of pulsed laser acting on the surface of the first heating to high temperature ablation threshold,subsequent pulses for material removal.Therefore,the process of pollutant cleaning by pulsed laser can be divided into two processes.The study of the nanosecond pulsed laser ablation process can be described by the Fourier heat conduction equation.?5?By high frequency Nd:YAG¹00ns pulse laser,using different process parameters,established two cleaning process schemes for the oxide layer of hot-rolled sheet steel by laser cleaning.Through 3 low speed,high power scanning and 1 high speed,low power scanning,the best cleaning process for the surface oxidation layer of the oxide layer of hot-rolled sheet steel was realized.This process can not only effectively remove the oxide layer on the surface of the Q235 hot-rolled sheet,but also avoid the new surface oxidation layer caused by the heating.High repetition rate¹00ns pulse laser cleaning of oxide layer of hot-rolled sheet steel was simulated,the simulation results agree well with the experimental results,which can provide effective guidance for the removal of oxide layer high quality and efficient by laser.?6?The high repetition rate¹00ns pulse laser for resin-base paint ablation process is simulated,ablation depth and temperature rising process of resin-base paint under the action of laser was obtained.A formula for estimating the depth of total ablation of resin-base paint is established.Based on the estimation formula of the total ablation depth,the layer by layer removal experiment of the 3 layers structure on the surface of the aluminum substrate has been completed.