1. A turning and milling method, comprising:positioning a workpiece on a work station of a rotary table, and causing a to-be-machined surface of the workpiece to protrude from the rotary table, wherein the workpiece has a top surface, a lower surface, corners connecting the top and lower surfaces, and edges connecting the top and lower surfaces, the edges also interconnecting the corners;
establishing a three-dimensional coordinate system O-XYZ, wherein axis Z is a vertical axis passing through a geometric center O of a machining area of the workpiece, axis X and axis Y are horizontal axes perpendicular to each other;
inputting parameters of a model workpiece into a control terminal, calculating axis Z coordinate values corresponding to the top surface and to curved surfaces at the edges of the workpiece according to the inputted parameters, then obtaining machining depths of a cutter at different positions along the axis Z; and
setting a variation rate of a machining radius of the cutter that is a distance between the cutter and the geometric center O of the machining area and setting a rotation frequency of the rotary table, and driving the cutter to perform machining, wherein the machining successively includes machining of the corners of the workpiece, turning and milling of the top surface, and machining of the curved surfaces at the edges of the workpiece;
during the machining of the corners of the workpiece: a second drive mechanism is controlled to drive the cutter to move to a first machining position of one of the corners of the workpiece, and the second drive mechanism is also controlled to drive the cutter to move vertically according to machining depths on the axis Z corresponding to different machining positions of the corners of the workpiece, and when a first drive mechanism is controlled to drive the rotary table to cause the workpiece to rotate about the vertical axis of the workpiece, the second drive mechanism drives the cutter to gradually reduce the machining radius until the machining of the corners of the workpiece is completed.