The box is the basic part of all kinds of machines. It connects the shaft sleeve, gear and other relevant parts in the machine and components into a whole and keeps them in the correct position to transfer torque or change speed to complete the specified movement.

The structure of box parts is generally complex, with thin and uneven wall thickness. There are many processing parts, including one or more datum planes and some bearing surfaces, and one or more pairs of bearing support holes with great processing difficulty.