Research On Vibration Characteristics Of Slender Shaft In Three-knife Turning Process

Slender shaft is a class of axis that is usually defined as the ratio of length and diameter greater than 20.These shafts parts are often applied to aerospace,mechanical engineering equipment and other important fields,such as spiral,screw,bull rod,crank-shaft and so on.It leads to the work-piece with poor rigidity and weak flexural capacity because of large ratio of length and diameter,and it is also easy to produce vibration and bending deformation under external force,thereby reducing the machining precision.It is easy to make knives relieving in the machining process of slender shaft,the work-piece produces straightly by cutting with several times.For some important shaft parts of high machining accuracy requirement,follow-rest is often used to auxiliary machining in turning process.However,the progress of choosing follow-rest is relatively trouble,for example,revising supporting pawl,adjusting the contact of supporting pawl and work-piece that is not too loose nor too tight.Considering current commonly used two-claw follow-rest,putting forward turning method that used three knives with 120 degree distribution on the some axis to shorten the production cycle and guarantee machining quality is feasible from theory perspective.This article focuses on the research of bending deformation caused by the vibration produced by radial component force of tool force in the three-knife turning process of slender shaft.According to the force condition of work-piece on turning cylindrical axis,establishing the mechanic model of slender shaft and vibration model of radial bending,deducing mode shape functions,natural frequency and bending vibration response equation combining with boundary conditions of Euler Bernoulli Beam.Conducting numerical analysis to the bending vibration response equation used by software MATLAB and obtaining the influence rule caused by cutting parameters on the response of bending vibration.Then by using ANSYS Workbench simulation software to carry out modal analysis of three-knife turning and single tool turning on slender shaft,comparing and getting the relations of frequency and deformation on the radial component force of tool force loading on the fourth,half and three-fourths of the shaft.Finally,the thesis proceeds the harmonic analysis for two kinds of cutting ways,obtaining the displacement change curve and the node amplitude frequency curve in half of the shaft,and finding that displacement change and peak of three-knife turning of slender shaft would be smaller,verifying the feasibility of three-knife turning of slender shaft.Therefore,it has certain engineering application value to analyze machining process and guide production of slender shaft.