摘要
活塞是内燃发动机的关键部件之一，工作于高温高压的特殊环境中，并由此产生热变形和受力变形。现代的发动机活塞裙部被设计为中凸变椭圆型面(即纵截面为中凸形，横截面为椭圆形状，且椭圆度沿裙高方向逐渐变化)，可以抵消发动机工作时产生的变形，提高活塞的对中性，使活塞承载均匀，减小冲击，降低发动机运行时的噪声，改善润滑，减少零件的磨损，提高活塞的工作性能和使用寿命。所以，活塞的加工和装配精度是影响内燃机性能的一个至关重要的因素，研制一种可用于中凸变椭圆活塞加工的数控系统，对于提高发动机性能、推动我国汽车、航空工业的发展具有重要意义。
本论文的提出了一种新型的非圆数控加工系统，用于横截面为非圆形状的轴类零件加工，内燃机的活塞裙部的中凸变椭圆型面是其最典型和常见的应用实例。
我们在一台现有的精密车床上进行革命性改造，将它作为实验机床。先用数学软件Matlab进行控制算法的图形仿真以验证其可行性，然后进行软件编制和调试。
改造后的机床是本系统里面至关重要的部分，它打破了传统车床和卧式铣床的界限，同时结合了硬靠模的结构特点，成为一种独特的新型机床。正是由于它的独特结构设计使得本系统具备国内外许多非圆车削加工机床所不具备的优点：切削力大，柔性好，加工精度高。
与目前现有的非圆轴数控加工方式比较，本论文所提出的系统采用了基于凸轮的机械式的微进给机构，比通常采用的(基于直线电机或者电磁吸铁方式)微进给伺服机构能产生更大的切削力，刚性更好。
本文阐述的机床系统除了主轴可回转之外，圆盘形刀具也可绕自身轴线高速旋转。而且，刀具可以根据需要更换，既可铣削，又可磨削，如果关闭负责微进给的U轴，还可以进行普通两轴的数控车削，体现了良好的加工柔性。
在独特的机械结构基础上，本论文创造性地提出了回转坐标和往复平动
电子科技大学机械电于工程学院硕士学位论文
坐标之间的曲线式插补方法，以一种简单凸轮作为硬靠模却可实现儿乎任意
非圆横截面的加工成形；提出了变截面加工成形的控制算法；软件设计上，
集成了自动编程和数控插补功能，使曲线逼近和插补运算一次完成，更加方
便用户的使用。
As one of the most important part of the internal-combustion engine, piston would be distorted in the special working condition by the heat and force acted on. In order to compensate this distortion, modern pistons with convex contour and vari-elliptical cross-section are designed, which can decrease wear and tear, depress working noises, prolong piston longevity and enhance engine performance. Therefore, machining precision and assembly precision of pistons influence engine
performance greatly. It is valuable to develop a new kind of CNC (Computer Numerical Control) System for automobile industry and airline industry, which can
machine pistons with convex contour and vari-elliptical cross-section.
In this paper, a new kind of CNC system to machine shaft with non-circular cross-section is proposed. Pistons with convex contour and vari-elliptical cross-section are most representative examples of non-circular shaft workpieces.
A universal precision lathe is rebuilt creatively as the experiment machine. Before software programming and debugging, the control algorithm is simulated with graphic in order to validate its' feasibility.
The rebuilt machine, in which characteristic of lathe, feature of milling machine and advantage of explorator are integrated, is a key unit of the system. Unique mechanics designs made this system have larger cutting force, excellent flexibility and nice precision.
On compare with other similar NC system, micro-feed mechanism based on a simple cam explorator proposed in this paper, which can offer greater cutting force and more dynamic rigidity than the fine feed servo mechanism based on linear motion actuator or electromagnetic actuator.
Besides an rotatable principal axis, this system has a special cutter like a disc which can rotate around its' own axis at high speed. The CNC system proposed in this paper can machine workpiece by turning, milling and grinding, if proper tools are replaced, which shows excellent flexibility.
Ill
On the basis of special mechanical structure, a new interpolation method between a turning coordinate axis and an linear coordinate axis is proposed firstly. A simple cam outline under affine transformation can fit multiple non-circular carves of revolution. A control method to form vari-section surface is also proposed in this paper. In order to make manipulators use the system software easily, the function of auto-programming is integrated with interpolation module.
引文
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[2] 李峻等．活塞裙部中凸变椭圆异型面车削加工．制造技术与机床，1999年第12期：31～33
[3] 何培杰等．数控非圆车削中的三种微进给刀架．上海机床，2000年第一期：20～23
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[7] 何培杰等．中凸变椭圆活塞加工机床的五个实例．上海机床，1997年第三期：49～51
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