Experimental Study Of Laser Milling Of Micro-fluidic Grooves

Micro-fluidic chip have broad application prospects and huge market demand in the DNA analysis, gene expression analysis, disease diagnosis, drug screening, determination of immunology and many other aspects. Micro-fluidic chip can be mass produced by using injection molding and hot pressing method, which can decrease its product cost. But manufacture of complex structure of micro-fluidic grooves limits application of micro-fluidic chip. There is lot of disadvantages such as complex processes, long production period, as so on in the traditional micro-fluidic grooves manufacturing method. In order to let batch manufacturing of micro-fluidic chip to be more cheap and flexible, we need to find an new processing method.Laser milling technology will be introduced into the process of mold forming field, which brought about the new solution to the batch manufacturing problems of micro-fluidic chip. Laser milling as a non-contact forming process, no cutting force, no tool wear, is an efficient and flexible forming method. This paper focused on experimental study of laser milling on pre-hard mirror plastic mold steel HPM75 and solved driving force problem of melt chip-removal, which is significant for promoting application of laser milling technology. The following contents have been done in this thesis:(1) According to the material surface melting, gasification model of laser milling, chip-removal model in the process of laser milling is established. A proper heat conduction equation is selected to calculate the power density threshold of laser milling. Meanwhile, the conversion formula between overlap coefficient and laser scanning speed is derived. Laser processing area status adjustment system is established. This part of work supplied foundation for choosing proper milling parameters and preparing devices.(2) The pre-hard mirror plastic mold steel HPM75 is chosen as experimental material. And the melt power density threshold of laser milling mould steel HPM75 is calculated 0.566×109W/m2. Analysis the relationship between overlap coefficient and the border and surface quality of milling grooves. By overlap coefficient choice tests, optimum overlap coefficient is determined. When the overlap coefficient is 0.8, it will gain continuum boundary and better surface quality of milling groove.(3) In the coaxial assisted blowing environment laser milling experiments study the law of different laser parameters (including laser output power, defocus distance, auxiliary gas pressure, gas type and scanning direction), groove width, depth and surface roughness. For the width of grooves, the main effect factors are the laser energy parameters, including laser output power, defocus distance, but for the depth and surface quality of the groove, the main effect factors are auxiliary gas pressure, gas type and scanning direction. Overlap coefficient is the key factor influencing the border of groove. Laser milling vacuum environmental experiments mainly studied the law of width and milling topography of groove influenced with laser output power, defocus, scanning direction. From the experiments, we can conclude the defocus distance play more important role than the laser output power and scanning direction in changing the width and milling effect of groove.(4) Combined with specific size of micro-fluidic chip die, the milling process has been analyzed. Using the optimized scanning path which scanning direction and chip-removal direction keep with the approximate direction, the coaxial air-assisted milling experiments have been done. Specific parameters are the laser output power of 1W, pulse-width 1ms, defocus distance of 0.5mm, overlap coefficient of 0.8, the scanning speed 80mm/min, auxiliary gas pressure 0.5MPa. Milling results meet the required groove width, depth and surface roughness value, which keep well consistent.The work supplies experimental and theoretical foundation for laser milling micro-fluidic grooves, which solves batch manufacturing problem of micro-fluidic chip. The study also presents a way for laser milling application.