Research On The Process And Mechanism Of Helical Drilling Based On Picosecond Laser

With the rapid development of science and technology,miniaturization of products with high precision is a general trend in many fields of industry.Among them,the demand for micro hole processing is particularly increasing,as micro holes are found in oil pump nozzle of automobile and diesel engine,micro integrated circuit board,optical fiber nozzle,gas film hole of turbine engine blade,etc.Traditional micro-hole machining methods mainly include mechanical drilling,EDM and long pulse laser machining.However,these existing processing methods have technical constraints on the efficiency and accuracy of micro hole forming,especially for the micro hole processing with large aspect ratio(depth/diameter).Therefore,it is urgent to explore the hole making process with higher accuracy,higher efficiency and greater depth/diameter ratio.In view of the above problems,this thesis intends to use both a helical drilling processing method and a ultrafast picosecond pulse laser to fabricate micro-holes in metal materials with expectation to achieve a high quality,high aspect ratio of micro-hole forming process.Based on the analysis on the physical processes of picosecond pulse laser drilling and the theoretical mechanism of picosecond pulse laser ablation of metal,and through the experimental method of controlling variables,the influence of laser processing parameters on the drilling results was explored.The main research contents include the following areas.(1)Based on the discussion on the application requirements of micro holes,this thesis will first describe in detail the advantages of laser drilling technology,and review the research status of laser drilling(especially picosecond pulse laser drilling)both domestically and worldwide.In the development of laser drilling technology,the technical characteristics of several main laser drilling methods,including single pulse drilling,percusion drilling,trepanning drilling and helical drilling)were reviewed and compared.The physical process of the interaction between laser and metal materials was analyzed,and the mechanism and temperature change model of picosecond pulse laser ablation of metal were introduced.The composition and function of each module(picosecond pulse laser module,rotating optical module,helical drilling head module)in picosecond laser rotary cutting equipment were analyzed.The sample materials used in the experiment and the processing methods of sample materials and measuring instruments after the experiment were introduced.(2)The principle of picosecond laser drilling was mainly described,analyzes the control principle of aperture and taper of the helical cutting from the optical system,and simulates the evolution process of machining aperture and taper through the beam tracking method.A series of basic experiments were carried out on 304 stainless steel plates with a variety of thickness to verify the accuracy of hole diameter simulation.(3)The micro-hole forming of 304 stainless steel with different thickness was explored on the helical drilling experimental platform.The control variable method was used to explore the influence of laser pulse energy,repetition rate,laser rotation speed,focus position,processing time and other parameters on the quality of micro holes.The best experimental parameters were obtained,and the high-quality micro holes with diameter range of 80 ? 300? m,maximum diameter depth ratio of 1:15 and controllable taper were prepared on the stainless steel sample.(4)Experiments were carried out on stainless steel samples with different thickness(0.8mm,1.5 mm,2 mm).The experimental results have shown that micro holes with controllable aperture size and taper can be processed stably as long as the thickness of the material is less than 1 mm,When the thickness of the material is more than 1.5 mm,the taper of micro holes is difficult to be controlled.Furthermore,it is difficult to complete the processing of a through hole once the thickness is more than 2 mm.