Analysis Of Synthesis Error For Numerical Control Machining

Nowadays, the application of the NC machine tools is more and moreextensive.The machining accuracy of CNC machine tools is the core issue, The keyissues to improve the level of processing is reducing processing errors. Generallybelieved that the processing error of CNC machine tools is mainly caused by thegeometric errors of machine tools, but with the continuous development of numericalcontrol technology, the accuracy of modern machine tool manufacturing isimproving,so the cutting force induced error that can be negligible in the past becomesimportant. The geometric error and the cutting force induced errors of CNC machinetools co-exist, they affected the quality of the workpiece.This dissertation studies thegeometric error and the cutting force induced errors of CNC machine tools.The main contributions of this dissertation are shown as follows:1. The error mechanisms of main components in NC machine tools,whichincluding link,prismatic joint and rotary joint,are analyzed in detail to derive thehomogeneous transformation.The21geometric error elements and35cutting forceinduced error elements of a3—axis CNC machine tools are identified. Based on theprinciple of homogeneous coordinate transformation, the mathematical model of theCNC machining error are deduced.The mapping relationships between the syntheticerror and the error components are proposed to trace error source.The Modelingmethods have universal and can be used in descibing the error of other3—axis NCmachine tools.2. Based on the measurement system of Heidenhain grid encoder, detect thecircular trajectory errors in different feed velocity and circular radius. According to thedata Obtained these: When radius is certain, the feed speed is proportional to thecircular trajectory error.When feed speed is certain, the radius is inversely proportionalto the circular trajectory error. The mapping relationships between the Radial error andgeometric error elements are found out.3. The finite element model of a vertical machining center CINCINNATI ARROW750was created by use of CATIA and ABAQUS,and the cutting forceinduced error was analyzed which resulted from the deformation of the machining-center’s components that caused by the cutting force. Then conclude that: X directionof the vertical machining center is the sensitive direction of the cutting force inducederror. And relatively its stiffness in the X, Y direction is weaker than Z direction.Finally, to reduce the effect of cutting force induced error on machiningaccuracy,propose improvement program of the spindle bearing configurations andcolumn structure.4. The cutting force induced error and the geometric error are the importantsource of error of CNC machine tools. This dissertation based on the finite elementanalysis of the transmission chain components, and obtain the cutting force inducederror. Through the experiment get the geometric error. On this basis, apply BP neuralnetwork technology to build a synthesis error prediction model, which is prepared forcompensation of error.