Die casting molds ensure the precision requirements of die castings
Die-casting molds play a central role in ensuring the precision of die-cast parts. The precision of their design and manufacturing directly determines whether the die-casting can meet the preset dimensional tolerances, form and position tolerances, and surface quality requirements. The precision of die-castings not only affects the product’s assembly performance but also its functionality and service life. Therefore, comprehensive consideration of all factors affecting precision is crucial during the mold design phase. Critical factors in determining die-casting accuracy include the dimensional accuracy of the mold cavity, the fit of the parting surface, and the positioning accuracy of the guide mechanism. Deviations in any of these steps can result in substandard die-casting precision.
The dimensional design of the mold cavity is fundamental to ensuring the accuracy of die-cast parts. Because the molten metal shrinks during the cooling process, the size of the mold cavity must be precisely calculated and adjusted based on the shrinkage rate of the die-casting material to ensure that the die-casting meets the designed dimensional requirements after cooling and forming. For example, for aluminum alloy die-castings, the shrinkage rate is typically between 0.8% and 1.2%. The size of the mold cavity needs to be increased based on this, while also considering the shrinkage differences in different parts and making targeted adjustments to areas with uneven wall thickness. In addition, the surface roughness of the cavity can also affect the surface accuracy of the die-casting. A smooth cavity surface can reduce resistance to the flow of molten metal, avoid defects such as scratches and bruises on the casting surface, and improve the surface finish.
The accuracy of the parting surface’s fit significantly impacts the dimensional and positional accuracy of die-cast parts. If the parting surface isn’t tightly fitted, flashing can easily occur during the die-casting process, leading to flash on the die-cast part, which in turn affects its thickness accuracy and flatness. To ensure the fit of the parting surface, the mold must maintain a flatness error within 0.01mm/100mm during processing. At the same time, a reasonable clamping force must be set to ensure a tight fit between the movable and fixed molds during die-casting. Parting surfaces with complex curves require high-precision machining and testing to ensure the parting surface’s shape is consistent with the design and to avoid shape deviations in the die-cast part due to parting surface misalignment.
The positioning accuracy of the guide mechanism is crucial for ensuring accurate cavity positioning during mold opening and closing. The guide mechanism typically consists of a guide pin and a guide sleeve. The clearance between the guide pin and the guide sleeve should be kept within a reasonable range, typically 0.01mm to 0.03mm, to ensure precise alignment of the movable and fixed molds during mold opening and closing, preventing cavity shifting. Excessive clearance in the guide mechanism can cause the mold to wobble during the die-casting process, potentially exceeding form and position tolerances for coaxiality, perpendicularity, and other aspects of the die-casting. Furthermore, the guide mechanism must exhibit excellent wear resistance and rigidity to ensure stable positioning accuracy over long-term use and minimize degradation of die-casting precision due to guide wear.
Mold temperature control also has a significant impact on the precision and stability of die-casting parts. During the die-casting process, mold temperature uniformity directly affects the cooling rate and shrinkage uniformity of the molten metal. If the mold temperature is too high in a certain area, the molten metal in that area will cool more slowly and shrink more, resulting in defects such as warping and deformation in the die-casting. If the temperature is too low in a certain area, the molten metal may solidify prematurely, affecting the filling effect and, in turn, dimensional accuracy. Therefore, the mold needs to be equipped with a reasonable cooling system. Through evenly distributed cooling water channels, the mold temperature can be precisely controlled to keep the temperature of each part of the cavity within the set range, reducing the precision fluctuations of the die-casting caused by uneven temperature.
Finally, the mold’s assembly accuracy and maintenance during use will also affect the precision and stability of die-casting parts. During mold assembly, the relative positions of all components must be accurate, especially moving parts such as the core pulling mechanism and ejection mechanism. Their movement accuracy must be strictly controlled to avoid dimensional deviations or shape defects in the die-casting parts due to assembly errors. During use, the mold must also be regularly inspected and maintained, promptly replacing worn guides, cleaning debris from the parting surface, and repairing damage to the cavity surface to ensure that the mold is always in good working condition and provide continuous protection for the accuracy of the die-casting parts. Only by strictly controlling every link from design, manufacturing, assembly to maintenance can the die-casting mold truly play its role in ensuring the accuracy of the die-casting parts.
