Function: The function of the piston is to withstand the gas pressure and transmit it to the connecting rod through the piston pin to drive the crankshaft to rotate. The top of the piston is also an integral part of the combustion chamber. Working conditions: The piston works under the conditions of high temperature, high pressure, high speed and poor lubrication. The piston is in direct contact with the high temperature gas, and the instantaneous temperature can reach more than 2500K. Therefore, the heating is serious and the heat dissipation conditions are very poor. Therefore, the temperature of the piston is very high during operation, the top is as high as 600-700K, and the temperature distribution is very uneven; the top of the piston bears The gas pressure is very high, especially when the work stroke pressure is the highest, the gasoline engine is as high as 3～5MPa, and the diesel engine is as high as 6～9MPa. This makes the piston produce impact and bear the effect of side pressure; the piston moves at a very high speed in the cylinder (8 ~12m/s) reciprocating motion, and the speed is constantly changing, which produces a large inertial force, which makes the piston subject to a large additional load. Pistons working under such harsh conditions will deform and accelerate wear, as well as additional load and thermal stress, as well as being chemically corroded by the gas.