Investigations On Pulsed Laser Processing Technology And Wettability To Micro Flow Channels In The Composite Of Resin And Graphite

The composite of Resin and Graphite is a new type of fuel cell electrode material prepared by vacuum molding of graphite powder and epoxy resin.Due to its excellent properties such as small specific gravity,good electrical conductivity and outstanding corrosion resistance,it has important engineering application value and scientific research value as electrode material in hydrogen fuel cell field.The gas flow channel on the electrode plate of hydrogen fuel cell is the most important factor affecting its performance.The reaction gas(hydrogen and oxygen)enters into the cell through the gas flow channel,generates water and is discharged through the gas flow channel.The dense flow channel with high aspect ratio is the key to improve the current density of hydrogen fuel cell,which is difficult to be achieved by the existing molding method,and the pulse laser processing method is an important way to solve this problem.It is of great significance to study the laser ablated graphite composites and the dense flow channel with high aspect ratio.Therefore,finite element simulation and experiment were used to study the short pulse laser ablation resin/graphite composites,and on this basis,the process of preparing high aspect ratio dense channel by pulse laser was further explored.The main research parts and relevant conclusions are as follows:(1)Study on the interaction between short pulse laser and resin/graphite composites.Based on the properties of resin/graphite composites,the interaction process between short pulse laser and graphite composites was studied,and the removal of thermal effect and non-thermal effect in short pulse laser processing was introduced.Based on the short pulse laser processing system composed of motion control system and optical system,the interaction between single pulse and multiple pulses was analyzed,the material removal mechanism of short pulse laser was clarified,and the processing parameters of short pulse laser were determined with pulse width of 60 ns and repetition rate of 100 k Hz.(2)Finite element simulation analysis of graphite composites ablated by short pulse laser.On the basis of the mechanism of short pulse laser ablation of graphite composites,in COMSOL simulation software environment,in turn,has established the geometric model of graphite composite materials,time and space on the energy density distribution is gaussian pulse laser light source model and transient heat conduction model of two-dimensional cartesian rectangular coordinate system,is analyzed under different input pulse number,Change law of threshold value of ablation material by pulsed laser.Based on the single-pulse and multi-pulse laser ablation process,the changes of aperture and hole depth were observed,and combined with the extrapolation method,the fitting data were used to calculate the threshold of laser ablation material under different incident pulse number.Based on the finite element simulation results and the experimental results,the change rule of ablation threshold under multiple pulses was summarized.Based on the results,the incubation effect of pulsed laser ablation on graphite composites was analyzed,and the incubation factor of experimental materials was determined as low as 0.35.(3)Experimental study on gas channel machining by short pulse laser.Through the single factor variable experimental design,the gas flow channel experiment of short pulse laser processing on resin/graphite composite was carried out.The experiment content is divided into the following parts:Firstly,the influence of laser processing parameters(including processing times and pulse overlap rate)on material removal efficiency was studied.It was determined that when the number of scanning times was 50,pulse overlap rate OV_x was50%and OV_y was 50%,the material removal efficiency of short pulse laser was the highest.Secondly,the effects of pulse overlap rate(OV_x and OV_y)on the flow channel size and surface roughness were studied.The variation of flow channel width and depth with pulse overlap rate and the change of flow channel bottom surface roughness with pulse overlap rate were determined.On this basis,the wettability of flow channel bottom surface was further studied.Finally,combined with the research basis of the first two parts of the experiment,the preparation of dense flow channel with high aspect ratio was realized,and the conditions of superhydrophobic performance of the bottom surface of the flow channel were determined.