Die-cast teeth and threads
Die-cast teeth and threads are crucial structures in die-cast parts that enable transmission and connection functions, and are widely used in components such as gears, nuts, and connectors. Compared to traditional machining, directly forming teeth and threads through die-casting significantly improves production efficiency, reduces production costs, and minimizes material waste. However, the quality of die-cast teeth and threads is affected by a variety of factors, including mold precision, die-casting process parameters, and alloy material properties. The design and production process is complex, requiring meticulous parameter control and structural optimization to ensure dimensional accuracy and performance.
The design of die-cast teeth requires key consideration of parameters such as tooth profile, module, and tooth direction. Common die-cast tooth profiles include involute teeth, rectangular teeth, and trapezoidal teeth. Involute teeth are widely used due to their smooth transmission and strong load-bearing capacity. The module of die-cast teeth should not be too small, otherwise it will make the mold tooth profile processing difficult. At the same time, the molten metal will not be able to fill the gaps between the teeth, which can easily lead to incomplete tooth profile or dimensional deviation. Generally speaking, the minimum module of die-cast teeth is 0.5mm. For gears with higher precision requirements, the module should be no less than 1mm. The tooth direction design should be consistent with the die-casting direction as much as possible to simplify the mold structure and facilitate demolding. If there is an angle between the tooth direction and the die-casting direction, a spiral core pulling mechanism will be required, which will increase the complexity and cost of the mold. In addition, the tooth top and tooth root should be designed with appropriate fillets to avoid sharp corners to reduce stress concentration and improve the fatigue strength of the gear.
The design of die-cast threads requires attention to thread type, pitch, and precision grade. Common die-cast threads include triangular threads and pipe threads, among which triangular threads are widely used due to their ease of processing and reliable connection. The pitch of die-cast threads should not be too small. Too small a pitch will make it difficult to process the mold thread core. At the same time, the molten metal will not fill the space between the thread teeth, which can easily lead to defects such as incomplete teeth or random buckling. Generally speaking, the minimum pitch of die-cast threads is 0.75mm. For threads with smaller diameters, the pitch needs to be increased accordingly. The precision grade of die-cast threads is usually low, generally grade 6-8. If higher precision is required, thread processing such as tapping or threading is required after die-casting. In addition, the starting and ending ends of the threads should be designed with transition fillets or chamfers to avoid stress concentration at the root of the thread and facilitate assembly.
Mold precision is key to ensuring the quality of die-cast teeth and threads. The mold’s tooth profile and thread cores must be manufactured using high-precision processing equipment, such as CNC grinders and EDM machines, to ensure dimensional accuracy and surface roughness. The accuracy of the tooth core should be 1-2 grades higher than the die-casting tooth profile, and the accuracy of the thread core should be no less than grade 6 to ensure the molding quality of the die-casting teeth and threads. The mold core material must be selected from high-strength, high-wear-resistant alloy steels, such as Cr12MoV and H13, and undergo appropriate heat treatment to improve its hardness and service life. In addition, the installation and positioning of the mold core must be accurate and reliable to avoid excessive coaxiality or positional tolerances of the teeth and threads due to installation deviations.
Die-casting process parameters have a significant impact on the molding quality of die-cast teeth and threads. The injection speed and injection pressure need to be appropriately increased to ensure that the molten metal can fully fill the small areas between the teeth and the thread profile. An injection speed that is too low will result in insufficient filling, while an injection speed that is too high may generate eddy currents and air entrainment, affecting the density of the teeth and threads. The mold temperature must be controlled at a high level to extend the flow time of the molten metal and ensure the complete molding of the tooth profile and thread. If the mold temperature is too low, the molten metal will solidify rapidly during the filling process, resulting in missing material at the tooth top or thread top. The pouring temperature also needs to be properly controlled. Excessively high pouring temperatures will increase the oxidation and gas absorption tendency of the molten metal, while too low a pouring temperature will reduce the fluidity of the molten metal. Therefore, the die-casting process parameters need to be optimized according to the structural characteristics of the teeth and threads and the alloy type to obtain high-quality die-cast teeth and threads.
Post-processing and inspection are crucial to ensuring the performance of die-cast teeth and threads. For die-cast teeth with high precision requirements, tooth surface grinding or honing is required to improve tooth profile accuracy and surface roughness, reducing transmission noise and wear. For die-cast threads, if the accuracy does not meet the requirements, tapping or threading is required to correct the thread size and accuracy. Inspection requires specialized testing tools, such as gear testers and thread gauges, to verify parameters such as the pitch, tooth profile, and tooth direction of the die-cast teeth, as well as the pitch, pitch diameter, and tooth profile of the threads, to ensure they meet design requirements. Furthermore, mechanical testing, such as hardness and tensile testing, is required to ensure that their strength and wear resistance meet operational requirements. Rigorous post-processing and inspection ensure the quality of die-cast teeth and threads, ensuring safe and reliable operation during transmission and connection.
