Optimization Of Electrolytic Polishing Process For WC-12Co Coating And Polishing Equipment Development

Remanufacture is a new class in machinery industry, and by advanced repair methods like leaser cladding, thermal spraying and cold welding, etc., waste electromechanical products get upgraded and rebuilt. Electromechanical products obtained by remanufacturing are superior to new products in performance, and because of its energy conservation and material economization in manufacturing process, remanufacturing has attracted extensive attention worldwide. WC-12Co hot spray coating is widely used in fields of aerospace, metallurgy and machinery, etc. but with high hardness and high wear resistance, it brings many difficulties for simple machining, especially for complex surface polishing. Electrochemical polishing, however, is not restricted by part material hardness, and it doesn’t increase residual stress on part surface, the machining precision can also meet requirements. So conducting research on the application of electrochemical polishing in remanufacturing processing plays an important role in the development of remanufacture.In this paper, the compressor rotor basis material FV520B is the main study object. By repairing with spraying WC-12Co coating, using COMSOL simulation experiment, the influence regularity of pole distance, voltage, conductivity on electrochemical polishing quality was analyzed. It is found that in the concave, electric current density is greater, corrosion rate is faster, and pole distance is the biggest factor which influences electric current density and erosion rate. The 3 factors impact telectric current density change from big to small rank in:pole distance, voltage, conductivity; while for erosion rate:pole, conductivity, voltage.By analyzing electric polarization curve of WC-12Co coating in electrolyte with different properties, and combining the functional mechanism of electrochemical polishing, the electrolyte formula which fits WC-12Co coating was obtained. The electrolyte formula uses NaNO3 with quality fraction of 5% as base fluid, adding a tiny amount of NaOH solution, making the PH value range from 12 to 13, meanwhileaddinglg/L Na2H2PO4as organic complexing agent, promoting dissolution of Co.By designing orthogonal experiment using voltage, time, and pole distance as experimental parameters, the 3 technological parameters impacting surface roughness change form big to small rank in:time, pole distance, voltage; while for residual stress, the effect degree changes in turn:voltage, pole distance, time; and for the erosion rate: pole distance, time, voltage. By single factor test analysis of surface roughness, the most fitting electrochemical polishing parameter for WC-12Co coating was obtained: voltage=8V, pole distance=20mm, time=115s. With surface stain resistance analysis after polishing, found that electrochemical polishing could improve coating stain resistance, and by analyzing hardness change after polishing, it was found hardness reduces less than 10%.Based on machine tool’s structure rigidity, operating maintainability, processing stability, economical efficiency as well as many other factors, the electrochemical machining facility and its accessory have been developed. Spherical cathode head and corresponding fixture have also been designed and researched.