五轴联动加工中进给速度的控制算法

目的研究刀具进给速度平稳性对五轴联动加工中复杂自由曲面表面粗糙度、轮廓精度的影响。方法首先对五轴联动机床运动过程中的空间线性插补原理进行了分析,推导出插补周期内各轴的分解速度数学模型。根据数控系统中不同的速度指令方式以及刀具在空间的实际运动距离,分端铣和侧铣两种情况,分别建立了刀具空间运动的实际速度计算模型,然后根据机床各轴的最高速度及加速度约束条件,对各轴分速度、分加速度进行校核处理,最终求得刀具实际的合成速度。最后,基于后置处理技术,用开发的专用后置处理软件进行刀位源代码后置处理,采用某叶轮试件进行了验证,并对实验结果进行了分析。结果在复杂曲面加工中,稳定的表面进给速度会获得较高的表面质量及轮廓精度,曲面曲率变化越大,速度变化对加工质量的影响越大。在同等条件下切削,刀具采用恒表面速度与采用恒进给速度相比,获得的叶片进出汽边轮廓误差值由0.1 mm减小为0.04 mm。结论在五轴联动加工中,越稳定的表面进给速度,越能获得较高的表面质量和轮廓精度,对于曲率变化较大的复杂曲面,需要严格控制刀具的进给速度,尽量获得稳定的表面速度以减少过切值,从而提高零件表面质量。

Control Algorithm of Feed Rate in Five-axis Linkage Machining

The work aims to study influence of tool feed rate smoothness on surface roughness and contour accuracy of complex freeform surfaces in five-axis machining. Firstly, the principle of spatial linear interpolation in operation of five axis machine tool was analyzed, and mathematical model was derived for velocity component of each axis in the interpolation period. According to different modes of velocity instruction and actual movement distance of the tool in the numerical control system, actual velocity calculation model was built for spatial movement of tool in terms of end milling and side milling. Then speed and acceleration component of each axis were checked and processed according to the maximum speed and acceleration constraints of each axis on the machine tool, and actual synthetic speed of the tool was finally obtained. Finally, based on post-processing technology, special post-processing software as-developed was used for source code post processing of cutter location, and an impeller test piece was used for verification, and experimental results were analyzed. In the process of complex surface machining, high surface quality and contour precision were obtained at stable surface feed rate. Changes in feed rate had great effects on machining quality if surface curvature changed greatly. Under the same cutting conditions, contour error of blade leading and trailing edge was reduced from 0.1 mm (at constant feed rate) to 0.04 mm (at constant surface speed). In five-axis machining, the more stable the surface feed rate is, the higher the surface quality and the contour precision are. For the complex surface exhibiting great curvature change, it is necessary to strictly control feed rate of tool and obtain stable surface speed as far as possible, so as to reduce overcut value and improve surface quality of parts.