Milling method for ternary impeller with large diameter

The invention relates to a manufacturing method for a ternary impeller of a compressor, in particular to a milling method for a ternary impeller with large diameter. The method comprises the following steps: generating a data file from the blade type and hub data of the calculated ternary impeller with large diameter, and inputting the data file into an operation platform; defining the rotating direction of blades, the quantity of the blades, a blade fillet and a blade round head manner; carrying out three-dimensional entity modeling by using the existing operation platform to generate an impeller ternary model file; clamping an impeller blank on a work table of a five-axle numerical control manufacturing center; linking three linear axles and fixing two rotating axles; firstly milling the welding line of the slot body of the short blade, and welding the short blade; after vacuum stress relieving, milling the welding line of the slot body of the long blade; and welding the welding line of the slot body of the