Study On The Ultrasonic Extrusion-Based Surface Finishing Technology For Parts

The principle of finishing technology based on the ultrasonic extrusion is thatthe high frequency energy of16KHz~80KHz is used to directly impact the surfaceof the sample. As the impact tool head touches the workpiece in a short time(usually10-5~3×10-5seconds) and the high-speed impact energy enables thematerial surface to have slight plastic deformation, the residual stress will generatefor a long time. Under the action of impact, the microcosmic contour peak on themachined surface generated by conventional tooling is flattened, the surfacestructure of parts becomes finer and the roughness increases substantially. As theresidual stress field generated by ultrasonic impact has the depth of up to1~2mm,the residual stress can effectively suppress the expansion of surface cracks.Therefore, such technology can effectively improve the fatigue resistance ofmaterials.In this paper, on the basis of analyzing the theory of ultrasonic extrusionfinishing technology, a new amplitude transformer with better shape factors andlarger amplification coefficient is designed through the use of large-scale generalfinite element analysis software. Specifically, through taking the cubic spline curveas the initial bus shape of the axial cross section of the amplitude transformer andusing the two-dimensional axial symmetry to establish the initial model, theresearchers design this amplitude transformer according to the the kinetic analysis.After the design, some factors of influencing the inherent frequency are identifiedthrough theoretical verification, correction, tests and experiments. Meanwhile, thenew amplitude transformer is used in the ultrasonic processing device, and theextrusion tool is improved in design. In this way, the tool can make the flexibilityadjustment with the change of surface shape to avoid the problem of pooruniformity of surface roughness. Finally, the comparative experimental study isconducted for typical materials in the aerospace industry. Through the morphologyanalysis, tensile test, metallurgical analysis, surface residual stress analysis andfatigue test for the specimen, it can be proved that the ultrasonic extrusion finishingmachining is superior to the conventional mechanical processing, able to replace thetraditional finishing machining.