Study On The Technology Of Slotting Using EDM And ECM Composite Method

Sand production in oil well is a key issue hindering the exploition of heavy oil reservoirs and unconsolidated sandstone reservoirs.As an effective tool of sand control,slotted liners with the advantages of large diameter,low flow resistance and high reutilization rate are widely used.There are two methods of mechanical cutting and laser cutting are commonly used to machine the slotted liners at home and abroad.However,the liners slotted by mechanical cutting have poor surface quality and accuracy and those processed by laser cutting are not only costly but also prone to have defects such as explosion hole,hook head and internal dross.To solve the above problems,this paper proposes a new approach of EDM and ECM composite machining to study the slotting technology,so that the sand control operation can be both economical and effective.To be able to achieve the desired slot width with high processing efficiency,the influences of electrical parameters(machining polarity,pulse width,pulse interval)and non-electrical parameters(electrode rotation speed,liquid velocity)on the composite machining are studied and then the optimal parameters combination is determined.The results show that: the machining efficiency by negative polarity is higher than the positive polarity machining efficiency,while the slot width of positive polarity machining is superior to that of the negative polarity machining.With the increase of pulse width,the slot width always increases while the efficiency firstly increases and then decreases.Too large or too small pulse gap will both reduce the machining efficiency.The pulse gap has little effect on the slot width.The optimal machining parameters under the experimental conditions are as follows: pulse width 38 us,pulse interval 10 us,electrode rotation speed 400r/min,the liquid velocity 200L/min.In order to further improve the processing efficiency and improved surface quality,the impact of powder particles on the discharge channel is analysed theoretically and the influence of powder type and concentration on the composite machining are studied.The results show that: the addition of powder particles will cause the electric field distortion and increase the discharge gap,which makes the discharge breakdown easier to occur.The effect of Si powders is better than that of Al powders.The Si powder makes the possibility of small pulse energy discharge breakdown greatly increased so that the machining efficiency could be higher.While it also enables the discharge energy to disperse uniformly and therefore the surface roughness is better.When 16g/L of Si powders is added,the composite machining will have high efficiency and better surface quality.The influences of the pulse width,the additive powder and its concentration on the surface microstructure,microhardness and the surface modification layer are also studied.Meantime,the formation processes of surface microcracks and pores are analyzed.The results show that: the bigger the pulse width is,the larger size the discharge pit will have and the worse the surface roughness will be.Surface protrusions are formed because the molten metals re-solidify and cover each other and the molten particles with high-speed crash onto the electrode surface.The completion of solidification of the outer layer limits the volume change of the inner molten metal during the solidification,which results in internal stress and causes microcracks.The bigger the pulse width is,the more microcracks there will be.When an appropriate concentration of Si powder particles are added into the working fluid,the surface quality can be improved and the surface hardness can be increased.Meanwhile,the generation of cracks will be effectively reduced.