Description High-frequency Heating Shaft Sleeve Press-Mounting device Technical Field The invention relates to a high-frequency heating shaft sleeve press-mounting device which belongs to the technical field of production and manufacturing equipment of motors. Background of the Invention In the prior art, a shaft sleeve is mostly mounted on a shaft in the knocking way through a wooden mallet and other soft hammers, the mounting way is not only lower in working efficiency, but also easy to cause damages to the shaft sleeve and even the shaft; furthermore, the consistency of assembly quality of the shaft sleeve and the shaft is poorer. Summary of the Invention The invention aims at providing a high-frequency heating shaft sleeve press-mounting device which can improve working efficiency, avoid causing damages to a shaft sleeve and a shaft, enable consistency of assembly quality of the shaft sleeve and the shaft to be better and solve the problems of lower working efficiency, easiness in causing damages to 1 the shaft sleeve and even the shaft, poorer consistency of the assembly quality of the shaft sleeve and the shaft, and the like in the prior art. The above technical purpose of the invention is mainly solved through the following technical scheme: the device comprises a base, a vertical frame is fixedly arranged on the base, a positioning structure for a motor shaft in the vertical direction is arranged on the vertical frame at a certain distance from the base, a compression cylinder which can compress the motor shaft in the up-and-down direction is arranged at the upper end of the vertical frame, the compression cylinder comprises a pressure head, a liftable high-frequency heating shaft sleeve supporting table is arranged on the base below the positioning structure for the motor shaft, and the high-frequency heating shaft sleeve supporting table is connected on a piston rod of a lifting cylinder. Wherein, the pressure head of the compression cylinder can move up and down under the drive of the compression cylinder, when in assembly, the motor shaft is arranged on the positioning structure for the motor shaft and compressed in the up-and-down direction through the compression cylinder, and the shaft sleeve is placed on the shaft sleeve supporting table; then high-frequency heating is performed on the shaft sleeve for a certain time till the shaft sleeve is thermal-expanded, the lifting cylinder can lift the shaft sleeve supporting table, press-mount the shaft sleeve in a predetermined position of the motor shaft and then retract, and the shaft sleeve is arranged on the 2 motor shaft by close fit after being cooled, thereby having no need of performing artificial knocking, greatly improving the assembly efficiency of the shaft sleeve and the shaft, avoiding damaging the shaft sleeve and the shaft, and enabling the consistency of the assembly quality of the shaft sleeve and the shaft to be better. Preferably, the positioning structure for the motor shaft comprises an upper positioning plate and a lower positioning plate, which are arranged in parallel, and an upper arc-shaped gap and a lower arc-shaped gap are respectively formed on the upper positioning plate and the lower positioning plate, wherein the diameters of the upper arc-shaped gap and the lower arc-shaped gap are larger than the diameter of the motor shaft which needs to assemble the shaft sleeve and smaller than the outer diameter of a housing of a motor. Preferably, an open hole for accommodating the shaft sleeve is formed at the upper end of the high-frequency heating shaft sleeve supporting table, and the open hole allows the motor shaft to insert. Therefore, the invention has the characteristics of improving the working efficiency, avoiding damaging the shaft sleeve and the shaft, enabling the consistency of the assembly quality of the shaft sleeve and the shaft to be better and the like. Brief Description of the Drawings 3 Figure 1 is a schematic diagram of structure of the invention. Detailed Description of the Invention In combination of the figures, the technical scheme of the invention is further specifically described through the following embodiment. Embodiment 1: as shown in Figure 1, a vertical frame 2 is fixedly arranged on a base 1, a positioning structure for a motor shaft in the vertical direction is arranged on the vertical frame 2 at a certain distance from the base 1, the positioning structure for the motor shaft comprises an upper positioning plate 3 and a lower positioning plate 4, which are arranged in parallel, an upper arc-shaped gap 5 and a lower arc-shaped gap 6 are respectively formed on the upper positioning plate 3 and the lower positioning plate 4, a compression cylinder 7 which can compress the motor shaft in the up-and-down direction is arranged at the upper end of the vertical frame 2, the compression cylinder 7 comprises a pressure head 8, the pressure head 8 can move up and down under the drive of the compression cylinder, a liftable high-frequency heating shaft sleeve supporting table 9 is arranged on the base of the lower positioning plate 4, the high-frequency heating shaft sleeve supporting table 9 is connected on a piston rod of a lifting cylinder 10, an open hole 11 for accommodating a shaft sleeve is formed at the upper end of the high-frequency heating shaft sleeve supporting table 9, and the open hole 11 allows the motor 4 shaft to insert. When in assembly, as shown in Figure 1, the motor shaft 12 is fitted in the upper arc-shaped gap 5 and the lower arc-shaped gap 6 of the upper positioning plate 3 and the lower positioning plate 4 and compressed in the up-and-down direction through the compression cylinder 7, and the shaft sleeve is placed on the shaft sleeve supporting table; then high-frequency heating is performed on the shaft sleeve for a certain time till the shaft sleeve is thermal-expanded, the lifting cylinder can lift the shaft sleeve supporting table, press-mount the shaft sleeve in a predetermined position of the motor shaft and then retract, and the shaft sleeve is arranged on the motor shaft by close fit after being cooled, thereby having no need of performing artificial knocking, greatly improving the assembly efficiency of the shaft sleeve and the shaft, avoiding damaging the shaft sleeve and the shaft, and enabling the consistency of the assembly quality of the shaft sleeve and the shaft to be better. 5