Therefore, the flange in the figure is marked with thickness 4, which can be considered as the thickness of the shell. Then the outer diameter of the workpiece cylinder should be 30+4+4=38.

If you choose a solid cylindrical blank with an outer diameter slightly less than 38, you can use the cold extrusion molding process, and you can use the molding process by increasing the equipment model and adjusting the die size.

The reason why the material with an outer diameter of 36 is selected may be that the size of 36 is within the standard series of outer diameter materials, and its formability is superior to other materials with outer diameters.