Micro Hole Machining Of Metal Materials By Femtosecond Laser Pulses

With the development of science,technology and production,the micro-hole broad applications in micro-porous surface,micro / nano structure,micro-fluidic devices,micro sensors,aerospace,aviation,automotive,medical,biological and other fields,what's more,the devices with micro-holes play a more and more important role in modern science and technology.Due to the improvement of product performance,the micro-hole requires increasingly high accuracy and the materials for fabrication are more and more variable,such as difficult-cutting materials including cemented carbide,diamond and so on,besides,in the field of precision manufacturing,the fabrication of air film cooling holes on the turbine blade of aircraft engine is a challenge for our country.Therefore,on the one hand,our researchers improve and perfect the traditional micro-hole drilling technology,on the other hand,they attempt to explore a number of new micro-hole drilling methods.Different from the traditional micro-hole fabrication processing,the femtosecond laser has the characteristics of fast,high energy density and nonlinear,and femtosecond laser drilling belongs to non-contact fabrication.The characteristics above make femtosecond laser fabrication present features such as ablating almost all materials,small heat affected zone,high precision,high quality,wide application range,and show great potential micro-hole fabrication.In this paper,based on the background above and the current status at home and abroad,an extensive study of large diameters,high-quality vertical micro-holes drilling was conducted.In order to find out the impact regulation and the mechanization of multitudinous parameters,this paper observe the influence of multi-parameters in femtosecond laser large-hole drilling innovatively.On the basis of the understanding of the mechanization in the micro-hole drilling process,we presented the fabrication process to drilling large diameters,small hole-taper and high-quality vertical microholes with controllability.The main innovative work of this paper includes the following aspects:1,on the foundations of traditional laser fabrication,femtosecond laser pulse sequence means that a laser pulse can be divided into two sub-pulses by the beam splitter and the double-pulse delay can be controlled in several femtoseconds.Regulating the excitation state of energy transmission can control the phase transition process of metal materials.It is an effective method to reduce the thermal effect in the process,and then improve the quality of micro-holes.2,On the basis of the experimental conditions in the laboratory,we present a systematic study on the percussion drilling of micro-holes fabrication on the metal material using femtosecond laser.By charactering and analysing the drilling results of micro-holes,we could find out the interaction rules and the mechanism of numerous parameters.In other words,it is to explore the influence of main parameters(femtosecond laser energy and defocus,pulse number,double-pulse delay)for the interaction between femtosecond laser and materials on the ablation area and the holetaper.Compare to traditional laser pulse micro-hole drilling,femtosecond laser pulse sequence can get the micro-hole diameters smaller and reduce the micro-hole taper with the same energy.What's more,the micro-hole diameters and the micro-hole taper reduce with fluctuation as double-pulse delay increasing.3,As far as we know,the diameters of micro-holes are main based on the laser energy,so there are some limitations on micro-hole diameters.What's more,the microhole taper is another drawback for laser irradiating material surface vertically.Based on femtosecond laser percussion drilling,for micro-holes with larger diameters,we draw support from the helical scanning function of six-dimensional platform to make the material produce a circular motion to the laser focus.We can achieve micro-holes with any diameters by changing the scanning radius.Decreasing the scanning speed can accumulate more pulses on the same position of the material and multitudinous pulse can reduce the ablation threshold.Smaller interval depth can keep laser focus staying in the micro-hole for more time to ablate more material.And these experiments can ensure to get micro-holes with hole-taper below 5°.We get micro-holes with diameter of 170?m and hole-taper of 3.93° when the laser energy is 30 mW,the scanning radius is 40?m,the scanning speed is 10?m/s and the interval depth is 10?m.4,The complex drilling environment is an important factor affecting the quality of micro-holes.We divide the femtosecond laser helical scanning micro-hole drilling into three phase innovatively.In pilot-hole drilling and enhancement,we attempt to increase the exit diameter of the micro-hole,and these experiment processes can make the drilling environment of micro-holes better which lays the foundation for the finishing phase.Combined with femtosecond laser pulses sequence,helical scanning micro-hole drilling can improve the quality of micro-holes and reduce the taper in a certain extent.We get micro-holes with diameter of 270?m and hole-taper of 3.48° when the laser energy is 100 mW,the scanning radius is 100?m,the scanning speed is 20?m/s and the interval depth is 10?m.