Research On Sub-regional Processing Technology With Variable Feed Speeds For Contour With Rapidly Varied Curvature

Parts with curvature rapidly varied contour are widely applied in the fields of aerospace, energy power, and automobile, and are difficult to process because of the more special structure and the higher requirement of machining precision. NC machining is extensively used in processing parts with curvature rapidly varied contour for high production efficiency, good processing accuracy and stable quality. As the existence of rapidly varied geometric feature, the actual moving speed of the workbench of the NC machine tool cannot reach the excessive feed speed set in the NC program timely during the NC machining process of this kind of contours for the response lag of the servo system, and the actual machining route and the theoretical curve programmed cannot be ensured to be coincident due to the drive constraint of NC machine tool, while reducing the programmed feed may decrease processing efficiency. Therefore, employing the constant machining parameter results in poor processing quality and processing contour with rapidly varied curvature can even be unachievable. Thus, it is of practical significance to carry out research on processing method for contour with rapidly varied curvature concerning feed speed scheduling according to curvature division. In order to manufacture such parts with high quality, a sub-regional processing method with variable feed speeds is proposed. The concrete contents are as follows:(1) Aiming at the problem that the actual feed speed cannot reach the programmed feed speed in time or remain at the programmed value during NC machining process, velocity analysis of patterns with constant curvature is conducted, and the congruent relationship between curvature and stable feed speed is acquired, which helps predict the actual feed speed of curve with variable curvatures; taking an equiangular spiral for examples, the prediction model is verified, and the results demonstrate that the model can forecast the feed speed of contour with rapidly varied curvature accurately.(2) To process contours with rapidly varied curvature with high quality, the equiangular spiral is taken as an example; the generation mechanism of the dynamic contour error is studied, and its mathematical model is built with iteration method based on the predicted results of the actual feed speed; the change rule of the dynamic contour error influenced by the curvature and the NC programmed feed speed is found out, and a dynamic contour error measuring method is proposed by way of stripping the dynamic contour error from the contour error, which is applied in measuring the machining results of replication experiment; the results show that the established dynamic contour error model is of high veracity.(3) On the basis of the dynamic contour error model, the sub-regional processing method with variable feed speeds is proposed; taking the drive constraint and the machining error requirement into account, the relationship between the programmed feed speed and the curvature is established, and the corresponding programmed feed speeds to different curvatures are obtained; the geometrical feature of the equiangular spiral is divided into different regions and corresponding programmed feed speeds are assigned; the NC machining results illustrate that compared with the machining results with constant feed speed, the maximum dynamic contour error and the average value of the dynamic contour error of the sub-regional processing method with variable feed speeds are both decreased by a large margin, which improves the processing quality effectively.This paper provides a sub-regional processing method with variable feed speeds considering the drive constraint of the NC machine tool. The research results prove that the method distributing the programmed feed speeds based on the curvature variation can improve the machining precision and ensure processing efficiency, and provides an effective method to manufacture parts with curvature rapidly varied contour, which is of theoretical significance and application value for the actual production of parts with curvature rapidly varied contour.