Die-cast holes and slots
Die-cast holes and slots are common structural elements in die-cast parts and are widely used in scenarios such as component assembly, positioning, weight reduction, and heat dissipation. Die-cast holes include through holes, blind holes, and stepped holes, while die-cast slots come in various forms, including rectangular slots, arc slots, and T-slots. Reasonable design of the structure, size, and position of die-cast holes and slots can not only meet the functional requirements of die-cast parts, but also improve the stability of the die-casting process and reduce the occurrence of defects. In the design of die-cast holes and slots, the characteristics of the die-casting process, such as the fluidity of the molten metal, the difficulty of mold forming, and the ease of demolding, must be fully considered to ensure the quality of die-cast parts and production efficiency.
The design of die-casting holes requires a focus on aperture size, depth, and distance from other structures. An overly small aperture can result in the mold core being too thin, making it susceptible to bending or breaking during the die-casting process. Furthermore, it can be difficult for the molten metal to fully fill the bottom of the hole, leading to under-casting defects. Generally speaking, the minimum diameter of a die-casting hole should be determined based on the hole’s depth. For through holes, the minimum diameter should not be less than 0.8mm, and the hole depth should not exceed five times the diameter. For blind holes, the minimum diameter should be larger, typically no less than 1mm, and the depth should not exceed three times the diameter to ensure core strength and molten metal filling. Furthermore, the distance between the hole and the edge of the die-casting or other holes should not be too small, generally greater than 1.5 times the aperture diameter. Otherwise, insufficient molten metal filling or shrinkage in that area can occur, impacting the strength of the die-casting.
The design of the die-casting groove needs to consider the groove width, depth and corner form. If the groove width is too small, it will increase the difficulty of mold forming, and the flow resistance of the molten metal in the groove will increase, which will easily cause cold shuts or flow marks. If the groove width is too large, the molten metal in this area may be too thin, affecting the overall strength of the die-casting. Generally, the minimum width of the die-casting groove should not be less than 1mm. For grooves with greater depth, the width needs to be increased accordingly to ensure that the molten metal can be filled smoothly. The corners of the groove should be designed to be rounded, and right angles or sharp corners should be avoided. Right angles will cause the molten metal to flow poorly, generate eddies and air entanglement, and also cause stress concentration, reducing the fatigue strength of the die-casting. The fillet radius should generally not be less than 0.5mm. For groove structures with greater stress, the fillet radius needs to be appropriately increased.
The placement of die-casting holes and slots must also adhere to certain principles. Holes and slots should be avoided where the die-casting wall thickness changes suddenly or where stress concentrations occur, as this can exacerbate defects in these areas. For example, creating a larger hole or slot in a thinner wall further weakens the strength of that area, potentially causing the die-casting to break during use. The axis of the holes and slots should be aligned with the die-casting direction whenever possible to simplify the mold structure and facilitate core placement and demolding. If the holes and slots are oriented perpendicular to or at an angle to the die-casting direction, a core-pulling mechanism will be required, increasing the complexity and cost of the mold. Friction during the core-pulling process may also affect the dimensional accuracy of the holes and slots. Therefore, while meeting functional requirements, hole and slot configurations aligned with the die-casting direction should be preferred.
The mold structure and die-casting process have a significant impact on the quality of die-cast holes and slots. For die-cast parts with complex holes and slots, the mold needs to adopt a mosaic structure or a core-pulling mechanism to facilitate the installation and demolding of the core. The core-pulling mechanism must be designed to ensure smooth movement and accurate positioning to avoid dimensional deviations or surface damage to the holes and slots due to poor core pulling. In terms of die-casting process parameters, the injection speed and injection pressure need to be appropriately increased to ensure that the molten metal can fully fill the small areas of the holes and slots. At the same time, the mold temperature needs to be controlled within a reasonable range to avoid premature solidification of the molten metal in the hole and slot areas due to excessively low temperatures. In addition, for deeper holes and slots, exhaust slots can be installed in the corresponding parts of the mold to promptly exhaust the gas in the cavity and reduce the occurrence of defects such as pores and shrinkage.
Post-processing also plays a significant role in improving the precision of die-cast holes and slots. Due to the limitations of the die-casting process, the dimensional accuracy and surface roughness of die-cast holes and slots often fail to meet the requirements of high-precision assembly, necessitating subsequent machining processes such as drilling, reaming, and slot milling. During post-processing, care must be taken to avoid deformation of the die-cast part due to excessive machining stress. Thin-walled parts, in particular, should be machined with low stock removal and high speeds. Furthermore, the machined holes and slots require deburring to ensure safe and smooth assembly. For holes and slots requiring high sealing performance, surface treatments such as electroplating and anodizing are also required to improve corrosion resistance and sealing. Appropriate post-processing can compensate for the shortcomings of the die-casting process, ensuring that the performance of the holes and slots fully meets the requirements of use.
