我国汽车、拖拉机等用的圆柱形和椭圆形活塞都用磨削加工。这种形状的活塞,由于受热膨胀不均匀,活塞与缸套的配合间隙不均匀,不但使活塞与缸套产生摩擦,影响使用寿命,而且还会产生严重的漏油、漏气现象,浪费能源,污染环境。一些先进国家的活塞,均已由圆柱形和椭圆形改变成中凸渐变椭圆形;其加工方法也由车削代替了磨削。中凸渐变椭圆形活塞的形状如图1如示。其椭圆度由裙部的上端至下端逐渐减小,这种活塞各部壁厚 China’s cars, tractors and other cylindrical and oval piston are used for grinding. This shape of the piston, due to uneven heating expansion, piston and cylinder liner with the uneven gap, not only the piston and cylinder liner friction, affecting the service life, but also have serious oil spill, leakage, waste of energy ,polluted environment. Pistons in some advanced countries have been changed from cylindrical and oval to convexly convex oval, and the machining method has also replaced the grinding by turning. Convex gradient oval piston shape as shown in Figure 1. The ovality of the skirt from the upper end to the lower end of the gradual decrease, each piston wall thickness