Die casting mold parting surface design
The design of the parting surface of a die-casting mold is a key step in the structural design of the mold. It is the contact interface between the fixed mold and the movable mold, and directly affects the demolding effect, dimensional accuracy, and mold processing difficulty of the casting. The rational selection of the parting surface requires comprehensive consideration of the shape, size, complexity, and production process requirements of the casting. Its core goal is to ensure that the casting can be smoothly removed from the mold while reducing the occurrence of defects such as flash and burrs. For example, for die-castings with deep cavities or undercut structures, if the parting surface is not properly selected, it may cause the casting to get stuck or deform during demolding. Therefore, it is necessary to cleverly design the parting surface to decompose the complex structure into both the fixed mold and the movable mold to make the demolding process smoother.
The location of the parting surface must follow certain principles. First, the casting should remain on the movable mold side. This is because the movable mold is usually equipped with an ejection mechanism to facilitate demolding. To achieve this goal, the parting surface should be set as close to the largest cross-section of the casting as possible, so that the casting can be firmly attached to the movable mold after solidification. For example, for cylindrical castings, the parting surface can be set at the maximum diameter in the middle of the cylinder to ensure that the casting moves with the movable mold when the mold is opened and is then ejected by the ejection mechanism. Secondly, the parting surface should simplify the mold structure as much as possible, avoiding complex curved parting surfaces or multiple parting surfaces to reduce mold processing costs and assembly difficulty. For symmetrical castings, symmetrical parting surfaces can be used to simplify the processing of the fixed and movable molds while ensuring mold closing accuracy.
Parting surfaces come in a variety of forms, including flat, beveled, stepped, and curved surfaces. Different types of parting surfaces are suitable for different casting structures. Flat parting surfaces are the most commonly used and are suitable for castings with simple shapes and flat contours, such as flat die castings. They are easy to machine, provide good sealing during mold closing, and effectively reduce flash. Beveled parting surfaces are suitable for castings with inclined structures, such as tapered or wedge-shaped parts. The combination of the bevels ensures uniform force distribution during parting, preventing deformation. Stepped parting surfaces are often used for castings with complex shapes and multiple steps. They ensure that each step is properly parted, ensuring dimensional accuracy across all parts of the casting. Curved parting surfaces are suitable for castings with curved contours, such as automotive die castings. Precise surface machining is required to ensure the fit of the parting surface and prevent metal leakage.
The design of the parting surface also needs to consider the exhaust and overflow effects to ensure that the gas and cold material in the cavity can be discharged smoothly. Exhaust grooves can be set at appropriate locations on the parting surface, usually used in conjunction with overflow grooves to guide the gas and cold material into the overflow groove. For example, on the parting surface corresponding to the last filling part of the casting, an exhaust groove with a width of 0.1-0.2mm and a depth of 0.05-0.1mm can be opened to allow the gas to be discharged in time during the molten metal filling process, thereby reducing porosity defects. At the same time, the fitting clearance of the parting surface must also be strictly controlled, generally 0.02-0.03mm. Too large a clearance can easily cause the molten metal to overflow and form flash. Too small a clearance may affect the smoothness of the mold opening and closing and increase mold wear.
After the parting surface design is completed, feasibility verification is required. Through 3D modeling and simulation analysis, the motion trajectory of the casting during the mold opening and demolding process is checked to ensure that there is no interference with other parts of the mold. For complex castings, a simple model can be made for demolding tests to observe the actual effect of the parting surface. In addition, the design of the parting surface must also take into account the convenience of subsequent processing technologies, such as electrospark machining and grinding, to ensure that the mold parts can be accurately machined into place. For example, when a company was designing an aluminum alloy die-casting mold with multiple undercuts, it initially used a flat parting surface, which made demolding difficult. Later, it changed to a stepped parting surface and set a core-pulling mechanism at the undercut part. This not only solved the demolding problem, but also improved the dimensional accuracy of the casting by 15% and reduced the scrap rate by 20%. It can be seen that a reasonable parting surface design is an important prerequisite for ensuring the smooth progress of die-casting production and the quality of castings.
