NURBS曲线曲面数控铣削球头刀刀具半径补偿原理

发布时间：2018-05-16 16:08

本文选题：NURBS + 球头刀刀具半径补偿算法　；参考：《兰州交通大学》2017年硕士论文

【摘要】：伴随着制造业的发展,以NURBS(Non-Uniform Rational B-Spline,非均匀有理B样条)为核心的自由曲线曲面造型技术得到了进一步的发展,进而推动了数控加工领域的进步。目前以FANUC为代表的数控系统厂商已开发出支持NURBS曲线插补功能的数控系统,但这一技术作为对我国禁用的关键技术之一,在国内进口机床是缺失了这一功能的。我国是制造业大国,拥有大量的传统数控机床,但是这些传统数控系统只具备直线插补、圆弧插补和抛物线插补,对于复杂曲线曲面的加工显得能力不足,那么如何在传统数控机床上实现NURBS曲线插补,使其具备自由曲线曲面的加工能力,同时克服CAM软件生成程序带来的刀位文件大、加工中引起机床振动而影响表面质量等问题,并获得高效率、高精度的加工就有了现实意义。本文基于一台FANUC 0i-MB系统的XK715D数控立式铣床,分析了NURBS曲线曲面加工中存在的过切现象,通过对NURBS曲线曲面插补点进行刀具半径补偿,实现了对NURBS曲线曲面无过切插补的加工功能。第一,根据刀具对NURBS曲线加工过程中存在的过切现象,研究了NURBS曲线插补过程中的球头刀刀具半径补偿算法,计算并比较了无球头刀刀具半径补偿算法和球头刀刀具半径补偿的计算结果,对插补结果采用VERICUT仿真和机床实际加工进行了验证。在此研究过程中,不考虑NURBS曲线曲率半径与刀具半径大小关系的影响。通过验证发现,球头刀刀具半径补偿算法通过使刀刃与曲线的插补点相切去切削,可以避免曲线的过切。第二,对于NURBS曲线曲率半径小于刀具半径的情况,由于在应用球头刀刀具半径补偿算法的过程中会造成过切,因此我们研究了过切预判算法,即在NURBS曲线插补计算过程中,首先通过比较NURBS曲线曲率半径和刀具半径的大小,提前判定是否存在过切来决定插补过程。通过研究发现,在此过程中,我们不仅可以判断是否存在过切并重新规划刀具路径,同时也可以得到最大允许刀具直径,最后通过VERICUT进行了仿真分析和验证。最后,论文研究了NURBS曲面球头刀刀具半径补偿算法,算法与NURBS曲线球头刀刀具半径补偿算法相似。首先通过等弧长插补算法计算插补点,然后对插补点进行球头刀刀具半径补偿,通过使刀刃与NURBS曲面插补点相切来控制刀具路径,实现NURBS曲面的切削。通过VERICUT仿真比较了无球头刀刀具半径补偿算法和球头刀刀具半径补偿算法的去除体积,验证了NURBS曲面球头刀刀具半径补偿算法的可行性,最后通过机床实际加工进行了验证。
[Abstract]:With the development of manufacturing industry, free-form curve and surface modeling technology with NURBS(Non-Uniform Rational B-Spline (non-uniform rational B-spline) as the core has been further developed, which has promoted the progress of NC machining field. At present, the CNC system manufacturer, represented by FANUC, has developed a CNC system that supports the interpolation function of NURBS curve, but as one of the key technologies that are forbidden to our country, the imported machine tools are missing this function in our country. China is a large manufacturing country with a large number of traditional CNC machine tools, but these traditional CNC systems only have linear interpolation, arc interpolation and parabola interpolation, which is insufficient for complex curve and surface machining. So how to realize the NURBS curve interpolation on the traditional NC machine tool, make it have the machining ability of the free curve and surface, at the same time, overcome the problem that the tool position file caused by the CAM software generation program is large, and the machining cause the machine tool vibration and affect the surface quality, etc. And to obtain high efficiency, high-precision processing has practical significance. In this paper, based on a XK715D vertical milling machine with FANUC 0i-MB system, the overcutting phenomenon in NURBS curve and surface machining is analyzed, and the tool radius is compensated by interpolation point of NURBS curve and surface. The machining function of NURBS curve and surface without overcutting interpolation is realized. Firstly, according to the over-cutting phenomenon in the machining process of NURBS curve, the radius compensation algorithm of the spherical cutter in the process of NURBS curve interpolation is studied. The algorithm of tool radius compensation without ball cutter and the calculation result of tool radius compensation of ball cutter are calculated and compared. The interpolation results are verified by VERICUT simulation and actual machining of machine tool. In this study, the relationship between the radius of curvature of NURBS curve and the radius of the cutter is not considered. It is found by verification that the cutter radius compensation algorithm can avoid the over-cutting of the curve by cutting the cutting edge and the interpolation point of the curve. Secondly, for the case that the curvature radius of NURBS curve is smaller than the radius of the tool, because of the overcut in the application of the tool radius compensation algorithm of the ball cutter, we study the prejudgment algorithm of over-tangent, that is, in the process of NURBS curve interpolation calculation. Firstly, by comparing the curvature radius of NURBS curve with the size of tool radius, the interpolation process is determined by determining whether there is overtangent in advance. It is found that in this process, we can not only judge whether there is overcut and reschedule the tool path, but also obtain the maximum allowable tool diameter. Finally, the simulation analysis and verification are carried out by VERICUT. Finally, this paper studies the algorithm of NURBS curved tool radius compensation, which is similar to NURBS curve tool radius compensation algorithm. Firstly, the interpolation point is calculated by the equal-arc length interpolation algorithm, then the cutter radius of the ball cutter is compensated for the interpolation point. The cutting path of the NURBS surface is controlled by tangent the cutting edge with the interpolation point of the NURBS surface. The removal volume of the tool radius compensation algorithm is compared by VERICUT simulation, which verifies the feasibility of the NURBS curved tool radius compensation algorithm. Finally, it is verified by the actual machining of the machine tool.
【学位授予单位】：兰州交通大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG547

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