Study On Electrochemical Discharge Machining Of Carbon Fiber Reinforced Composites

Carbon fiber reinforced composite material(hereinafter referred to as CFRP)has the characteristics of light weight,high strength,wear resistance and corrosion resistance,and has been gradually applied to micro-electromechanical systems as the main structural components.In the actual application of CFRP,they usually need to process micro-holes and micro-grooves to meet assembly needs.However,due to the unique material characteristics of CFRP,the traditional machining methods are difficult to effectively realize the micro-level processing,and special processing methods such as electric spark and laser also have shortcomings.Electrochemical discharge machining(ECDM for short),as a special processing method for difficult-to-conductive materials,has its unique advantages in the field of micromachining and can realize the microfabrication of CFRP.But ECDM still has problems such as unstable processing and low processing precision.In response to the above problems,the author has carried out ECDM processing stability and cathode loss research and analysis,and on this basis,has carried out CFRP micro processing,thereby improving the processing quality.Based on the research and summary of ECDM processing mechanism and process technology,firstly this thesis analyzes and discusses the processing mechanism of ECDM.Secondly,collects the voltage and current signals of the ECDM process through an oscilloscope and analyzes the process parameters.The influence of the average current and gas film of ECDM processing.After that,the influence of processing parameters on the loss of tool electrode was studied through single factor experiment,and the morphology of it was analyzed by scanning electron microscope.Finally,combined with the previous research,the CFRP micro-hole and micro-groove processing experiment was carried out,and the influence of different process parameters on the CFRP aperture,groove width and groove roughness value.And using a reasonable combination of processing parameters to effectively improve the processing quality of holes and slots.The research results for the processing stability of ECDM show that:the increase of the pulse voltage increases the discharge density and effectively reduces the gas film formation time during the ECDM process,but it will eventually stabilize,and the average current will usually show "Increase-decrease-increase" phenomenon,and reach a stable discharge state in the interval of "decrease-increase"(40 V-50V).The increase of the power supply frequency and the duty cycle can reduce the gas film formation rate and the average current size,and a larger discharge density will be produced at a high frequency.The increase of electrolyte concentration helps to improve the gas film quality and reduce the average current and gas film formation time.The tool electrode rotation speed has no significant effect on the gas film formation time and average current.The research results of cathode loss show that:the loss of tool electrode(tungsten carbide spiral microelectrode)in ECDM is mainly related to processing heat energy,and its loss morphology is mainly manifested by the melting and shedding of spherical cobalt particles.And the loss occurs preferentially in the areas where the discharge is concentrated,such as the electrode ends,edges and bumps.As the main influencing factor,the increase of pulse voltage aggravated the loss of the tungsten carbide electrode.After 44 V,the quality of the tool electrode began to lose,and after 58V,the length loss occurred.The increase in power frequency and duty cycle and electrolyte concentration all have an impact on tool wear,but it is not significant compared with voltage.The tool electrode speed has no significant effect on tool electrode wear.Compared with before tool wear,the gas film formation time will be reduced after wear,and the average spark discharge current will only decrease during the tool length loss stage.The experimental research results of ECDM process show that:the processing quality of CFRP micro-holes and micro-grooves is affected by many factors.When the pulse voltage is low(below 44V),the material removal effect is poor,resulting in defects such as fiber tow exposure and incomplete processing.Compared with low voltage,increasing the pulse voltage can improve the material removal effect,but the CFRP processing surface will have thermal effects Zone,over-cutting and resin melt accumulation phenomenon.Increasing the pulse power frequency can effectively reduce the aperture and groove width and reduce the roughness value.Too high power frequency(>5000Hz)will lead to unstable spark discharge,which is not conducive to the improvement of processing quality.The increase in speed promotes the circulation of electrolyte,improves the uniformity of spark discharge,increases the frequency of side discharge,and increases the aperture.Increasing the feed speed while ensuring the material removal effect can reduce the processing time,thereby reducing the aperture and the groove width and the thermal influence of the material,and reducing the roughness of the micro groove.