Design of Die Casting Die for Electric Motor
The design of die-casting molds for electric motors is a critical step in the motor manufacturing process, directly impacting their performance, reliability, and production efficiency. Electric motor die-castings primarily consist of components such as the housing, end caps, rotor, and stator. These components require a compact structure, high dimensional accuracy, and excellent heat dissipation, posing unique challenges for mold design. Initially, the design requires a thorough analysis of the motor’s operating principle and the die-casting’s operating environment to clearly define the performance requirements. For example, the housing must provide excellent sealing and heat dissipation, and the end caps must ensure a precise fit with the bearings. Furthermore, factors such as the motor’s power rating and mounting method must be considered to ensure the mold design meets the production requirements of different motor types. For example, die-castings for small motors have a relatively simple structure but demand high dimensional accuracy. Large motor die-castings, on the other hand, are larger and have thicker walls. Therefore, mold design must prioritize the filling and solidification processes of the molten metal to avoid defects such as shrinkage cavities and porosity.
The structural design of motor die-casting molds must fully consider the structural characteristics of the die-casting and the die-casting process requirements. Casing die-castings are typically cylindrical in shape, with flanges and mounting holes. The mold design should utilize either vertical or horizontal parting to ensure smooth demolding. The core and cavity design must ensure dimensional accuracy, including the inner and outer diameters and height of the casing. Molding cores are positioned at the mounting holes on the flanges. These cores must possess sufficient strength and rigidity to withstand the pressure of the die-casting process. End cap die-castings are often disc-shaped, with a central bearing chamber. The mold design emphasizes dimensional accuracy and surface finish of the bearing chamber. A mosaic core is typically used for ease of machining and replacement. For die-castings with complex slots, such as rotors and stators, the mold cavity design must precisely replicate the slot structure to ensure the die-casting meets the electromagnetic performance requirements of the motor. Furthermore, the runner and venting system must be properly designed to ensure uniform metal filling of each slot and avoid underfilling.
The choice of mold material is crucial to the service life and molding quality of electric motor die-casting molds. Electric motor die-castings are often made of materials such as aluminum alloys and zinc alloys. During the die-casting process, the mold cavity must withstand the high temperatures and high pressures of the molten metal. Therefore, the mold material must possess excellent heat resistance, wear resistance, and fatigue resistance. For mass-produced electric motor die-casting molds, H13 hot-work die steel is typically used. After quenching and tempering, this material exhibits high hardness and strength, meeting the demands of long-term production. For small, precision electric motor die-casting molds, cold-work die steels such as Cr12MoV can be used to ensure dimensional accuracy and surface quality. Furthermore, mold cavity surface treatment is crucial. Nitriding can improve mold surface hardness and wear resistance, reducing wear and extending mold service life. For molds with higher requirements, PVD coating can further enhance the mold’s anti-sticking and wear resistance, improving the surface quality of the die-casting.
Electric motor die-castings require high dimensional accuracy and form/position tolerances, necessitating exceptionally stringent mold design precision. Mold machining precision must be maintained at a high level. For example, the bearing housing’s dimensional tolerance is typically IT6-IT7, while the corresponding mold components’ tolerances must be controlled below IT5. During the design process, the shrinkage of the molten metal must be fully considered. This shrinkage must be accurately calculated based on the alloy material and die-casting structure to ensure that the die-casting will meet the required design dimensions after cooling. The mold’s guide mechanism utilizes high-precision guide pins and bushings, with clearances controlled within 0.01-0.02mm to ensure precise alignment between the fixed and movable dies and prevent misalignment that could compromise the die-casting’s accuracy. For die-castings with multiple mounting holes, the mold cores must maintain precise relative positioning. Typically, a monolithic template or locating pins are used to maintain a positional tolerance of within 0.02mm between the cores. In addition, the parting surface of the mold needs to be flat and smooth, and the flatness error of the parting surface should be controlled within 0.01mm/100mm to avoid defects such as flash and burrs in the die casting.
As electric motors develop towards higher efficiency, energy conservation, and miniaturization, the performance and quality requirements for electric motor die-castings continue to increase, driving innovation in electric motor die-casting mold design technology. CAE simulation technology is increasingly being used in mold design. Through numerical simulation of the die-casting process, parameters such as molten metal filling time, temperature distribution, and pressure changes can be analyzed to optimize the design of runners and exhaust systems, predict potential defects in die-castings, and thus improve mold design reliability. Mold cooling system design is also becoming increasingly sophisticated. The use of conformal cooling channels can achieve more uniform temperature distribution in the mold cavity, shorten the solidification time of die-castings, improve production efficiency, and reduce internal stress and deformation caused by temperature variations. Furthermore, modular and standardized designs are being promoted in electric motor die-casting molds. By standardizing common mold components such as guide pins, guide bushings, and ejector pins, mold design and manufacturing cycles can be shortened, reducing production costs. Furthermore, the application of 3D printing technology has provided a new method for manufacturing complex cavity molds, enabling the rapid creation of complex structures that are difficult to achieve with traditional machining. This improves mold design freedom and manufacturing precision, providing a strong guarantee for the high-quality production of electric motor die-castings.
