Most metal workpieces produce surface oxidation during forging heat treatment. This scale has serious damage to the chemical coating of parts, and needs to be shot cleaned. For the parts that need cutting, cleaning the oxide scale is the necessary condition to reduce tool wear, improve the service life of cutting tools, keep the accuracy of machine tools and control the size of forging billet to obtain the best cutting state. This is even more important for automatic machine tools. By means of shot peening after final heat treatment, the comprehensive effect of removing the oxide scale and strengthening the workpiece can be obtained. Almost all gears of automobiles, tractors and other vehicles should be treated by shot peening after heat treatment.