With the development of new energy vehicle technology to this day, cast aluminum rotors have been widely used in squirrel cage induction motors. The cast aluminum rotor can make the induction motor lighter, increase the power/mass density, have a small moment of inertia, and release a greater starting torque. Due to the low melting point of aluminum, the manufacturing process of cast aluminum rotors is mature and the manufacturing cost is low, which is one of the reasons why it is widely used.
Cast aluminum rotor manufacturing process
The rotor of the squirrel cage induction motor has two structural types: copper row rotor and aluminum bar rotor. The aluminum bar rotor is made of cast aluminum. The guide bars in the slot and the end rings at both ends of the iron core, balance columns, and fan blades are cast out to make the rotor a solid whole.
There are five ways to cast aluminum for the rotor: vibration cast aluminum, gravity cast aluminum, centrifugal cast aluminum, pressure cast aluminum and low pressure cast aluminum.
Due to the vibrating cast aluminum and gravity cast aluminum rotors, it is not easy to be replenished with aluminum water when the lower end ring is solidified, and shrinkage holes are often generated, so it is generally rarely used. Low-pressure cast aluminum has not yet been widely used in professional motor manufacturers. Centrifugal cast aluminum and pressure cast aluminum have been adopted by most motor manufacturers.
The working principle and characteristics of two rotor casting aluminum methods
Working principle of die-cast aluminum:
Use pressure to inject molten aluminum into the cavity, and become a casting after cooling and solidification
The rotor pressure cast aluminum adopts a cold chamber die casting machine, which is divided into three types: full vertical, vertical and horizontal according to the position of the injection chamber. The main parameters of the rotor die-casting machine are: injection force (N), injection speed (m/s), forming force (N), injection specific pressure (Pa) and maximum pouring volume of aluminum (kg), etc. The die-casting machine is composed of a bed, an injection mechanism, a fitting mechanism, hydraulic and electrical control devices, etc. The injection mechanism is a key component to achieve injection, and its structure and correct use are the main factors that determine the quality of die castings. The injection mechanism generally adopts two-stage and three-stage injection systems, and most of the die-casting machines used in production currently use three-stage injection. Equipped with a quantitative pouring device and a workpiece loading and unloading mechanism on the die-casting machine, the die-casting production can be automated.
Features of die-cast aluminum:
(1) Pressure plays a major role throughout the die-casting process.
(2) During die-casting, during the high-speed filling process of molten metal, if the gas in the cavity is too late to be discharged, it will be involved in the metal, causing pores in the casting.
(3) Since the metal filling process is carried out under pressure, the rotor core can be die-cast in the cold state.
(4) High production efficiency, easy to realize mechanization and automation, which can reduce labor intensity and improve working conditions.
Working principle of centrifugal cast aluminum:
The molten aluminum is poured into the rotating cast aluminum mold to fill the cavity and solidify under the action of centrifugal force.
It is carried out on a dedicated centrifuge. There are two types of centrifuges: constant speed and variable speed, with variable speed centrifuges being the best. The process parameters include: centrifuge speed, aluminum temperature, rotor core preheating temperature, aluminum casting mold preheating temperature, casting speed, etc.
Features of centrifugal cast aluminum:
(1) Centrifugal force plays an important role in the forming of castings and the process of metal crystallization. It helps to discharge the gas and non-metallic impurities (lighter than metal) in the molten metal. More importantly, it affects the metal crystallization process and plays a role in strengthening feeding and crystal refinement.
(3) The equipment used for rotor centrifugal cast aluminum is relatively simple. However, there are many manual operations in the casting process, and the labor intensity is relatively high.