Both gasoline and diesel engines widely use aluminum alloy pistons; cast iron or heat-resistant steel pistons are only used in a few engines. Due to the special processing characteristics of pistons, it is difficult to meet the high-precision requirements of pistons with ordinary machine tools. Therefore, machine tool manufacturers must increase the intensity of technological transformation and provide numerically controlled, clean, and flexible piston special machines suitable for the performance requirements of pistons. The piston is the heart of an automobile engine, bearing alternating mechanical and thermal loads, and is one of the most severely operating key components in the engine.

With the increasingly stringent requirements for engine power, economy, environmental protection, and reliability, the piston has developed into a high-tech product integrating lightweight and high-strength new materials, shaped cylindrical composite surfaces, and shaped pin holes, etc., to ensure the piston's heat resistance, wear resistance, stable guidance, and good sealing performance, reducing engine friction power loss, fuel consumption, noise, and emissions. The piston's main surface dimensions and the precision requirements between the surfaces are high; after processing, it is also required to ensure the uniform wall thickness of the skirt and the top of the piston. The above characteristics and requirements have brought difficulties to the processing of piston special machines, and its processing characteristics mainly include the following aspects: 1、 The piston wall is thin, and the radial stiffness is poor. If the piston is processed as a general rotating part, it is easy to deform under the action of clamping force and cutting force, thus affecting the processing accuracy. Therefore, when formulating the processing technology and selecting the processing equipment, attention should be paid to the position of the clamping points and the selection of the piston clamping method. 2、 The piston has many processing surfaces, and the processing is complex. It not only requires the dimensional accuracy of each processing surface but also the mutual positional accuracy of each processing surface. Therefore, when carrying out processing technology, the positioning datum should be correctly selected to reduce the processing errors caused by improper selection or conversion of the positioning datum. At the same time, when selecting processing equipment, multi-tool or multi-station machine tools should be selected as much as possible to reduce the number of clamping times and the processing errors caused by the clamping process. 3、 The size and shape accuracy of the hole are very high, and the roughness is low. 4、 Thin and poor rigidity. If the cutting force is too large, it will cause the piston to deform, affecting the processing accuracy. Therefore, when processing piston special machines, a smaller feed rate and a higher speed should be selected. ， At the same time, the fine machining of important processing surfaces such as the piston top surface, skirt outer circle, and piston pin hole should be carried out last.

Piston special machine processing from 20 century 70 years of grinding, 80 years of three-dimensional shaping to 90 years of numerical control shaping has been developed and applied, bringing the production efficiency and processing accuracy to a new level. Production efficiency has increased from three-dimensional shaping spindle 800 rotation / minutes to numerical control shaping 2000 rotation / minutes. Due to the elimination of the shaping distortion factors in the traditional three-dimensional shaping by the piston special machine processing, the processing accuracy has been greatly improved. Due to this breakthrough progress in processing technology, 20 century 90 years, automobiles developed and designed have adopted low-friction pistons with shaped cylindrical composite surfaces.