Common Defects of Die-Cast Parts and Solutions: Prevention and Handling Techniques for Gas Holes, Shrinkage Cavities, and Deformation

Common Defects of Die-Cast Parts and Solutions: Prevention and Handling Techniques for Gas Holes, Shrinkage Cavities, and Deformation

In the production of die-cast parts, gas holes, shrinkage cavities, and deformation are high-frequency defects. They not only affect the appearance but also weaken the product performance, so targeted prevention and handling plans must be formulated.

Gas holes are mostly manifested as holes inside or on the surface of castings, mainly caused by gas entrainment in the molten metal and poor gas venting of the mold. Prevention requires a two-pronged approach: on the one hand, optimize the mold's venting system by adding vent grooves or vent pins to ensure timely discharge of gas in the mold cavity; on the other hand, control the die-casting process by reducing the peak injection speed to avoid splashing and gas entrainment of the molten metal. At the same time, preheat the mold to a reasonable temperature to reduce gas precipitation caused by the temperature difference between the molten metal and the mold. If small gas holes have been generated, they can be sealed through the vacuum impregnation process without affecting the product's sealing; for severe gas holes, the casting must be scrapped and recast.

Shrinkage cavities often occur in areas with uneven wall thickness of castings, resulting from slow local cooling and insufficient feeding of molten metal. The key to prevention lies in optimizing the casting structure to avoid sudden changes in wall thickness, and setting reasonable risers and chills to guide the directional solidification of the molten metal. During die-casting, increase the holding pressure and holding time to ensure sufficient molten metal is available to compensate for shrinkage during the solidification process. Minor shrinkage cavities can be addressed by removing the surface defect layer through CNC machining; for deeper shrinkage cavities, welding repair is required, but it is necessary to control the welding temperature to avoid secondary deformation.

Deformation is mostly caused by uneven cooling of the mold or stress relief. Prevention involves improving the mold's cooling system by arranging cooling water channels evenly according to the casting shape to ensure consistent cooling rates across all parts. Additionally, conduct timely aging treatment after die-casting to eliminate internal stress. If the casting has already deformed, cold pressing correction can be performed using a correction tooling. For castings with good plasticity such as aluminum alloys, local heating correction can also be adopted, but it is essential to strictly control the heating temperature and time to prevent the casting from cracking.