The Research Of Contour Error Control Technology For Five-Axis Machining Of Complex Parts

In modern industry, five-axis machining technology is widely adopted. It plays an important role in many aspects, such as aviation, automotive, shipbuilding industry. Machining contour accuracy is a key to estimate whether the machined part is qualified or not. Currently, how to improve the technology for five-axis machining contour error control is a hotspot in machining system and CAD/CAM field. It involves many aspects, such as the control of machine tool servo motion accuracy, the measurement and compensateion of machine tool geometric precision, tool path designing, NC programining, interpolation method, machining parameters and so on. Although many scholars have finished many of theoretical and practical researches, and obtained relevant achievements, there are still some problems to be solved or improved.This paper takes five-axis machining kinematic constraint model as theoretical basis. From the aspects of improving machining condition, interpolating stabilization and the geometric error measurement, some methods are proposed to reduce contour error of five-axis machining. The main works are as follows:(1) The kinematic constraint modeling method for five-axis machiningThe five-axis machine multi-body model (taking worktable as inertial body) is proposed. It could unify the movement direction of the machine part and NC command, and the structure description of different five-axis machine tools according to topology series. By the kinematics solution, the velocity of five-axis machine tool path and the limitations of axes speed are expressed. On this basis, the dynamic machining model of five-axis machine tool is finished to research the relationship between tool path kinematic constraint and feeding performance, and to obtain the five-axis machining kinematic constraints based on machining characteristic.(2) The method of improving machining stability for contour waviness controlWaviness control method is proposed to improve machining states and restrain the low-frequency vibration of machining system. Through the average cutting force-sweep area model, the feedrate might be optimized to keep the cutting force stable. In addition, the unstable rotation states are defined. By decomposing the unstable rotation to micro continuous rotation, the machining stability could be improved. For micro non-monotonic uncontinuous and reciprocating rotation, the interpolation of the cutter location point is discussed. For micro monotonic uncontinuous rotation, the adjustment of vector under the constraint of machining tolerances is proposed.(3) The method of improving interpolation stability for contour error controlFive-axis spline interpolation algorithm is improved based on the enhancment of kinematic stability. The pre-interpolation is restrained by the instruction velocity of cutter location point, scallop error and Adams recursive method. The feeding velocity would change along with the trajectory curvature. The relationship among cutter velocity, spline parameters and corresponding accelerate/decelerate period would be stored as look-ahead information. Then, the ranges of accelerate/decelerate are adjusted according to the cosine acceleration strategy and kinematic constraint conditions. It could ensure the cutter point trajectory to be 3-order and reduce the contour error caused by the feeding impact.(4) The geometric error measurment theory and method for five-axis machine toolsWith the kinematic model that takes worktable as inertial body, the geometric error model based on worktable is established. The error measurement theory for rotary axis is improved. With bar-ball and RTCP/RPCP function and by measuring position error of different points relative to the reference point, the 12 kinematic errors about rotation axes could be identified. On this basis, the measuring methods for different table/tool structural rotation axes are explaned in detail. In addition, how to eliminate the error introduced is researched to improve the measurement accuracy.Based on the above researches, a set of technology for contour error control is formed, including improving cutting condition, interpolation stabilization and geometric error measurement for five-axis complex parts machining. In addition, a series of comparison experimentes show that the technolog is correct and feasible.