Determination of core pulling distance in die casting
The die-casting core pulling distance is the minimum distance the core needs to be pulled out. It is necessary to ensure that the core is completely separated from the side structure of the die-casting to provide sufficient space for demolding. Its determination needs to be combined with the product structure, mold layout and safety margin to avoid damage to the die-casting or inability to demold due to insufficient core pulling.
The basic core-pulling distance is based on the maximum depth of the die-casting’s side structure. The depth of the undercut or side hole is a key parameter. For example, if the die-casting’s undercut depth is 15mm, the minimum core-pulling distance must be ≥15mm. To prevent interference when the core and die-casting separate, a safety margin of 5-10mm should be added, with a practical value of 20-25mm. For stepped side holes, the calculation should be based on the deepest step depth. If the first step is 10mm deep and the second step is 22mm deep, use 22mm as the base, add an 8mm margin, and the core-pulling distance should be 30mm.
The core’s inherent structure increases the required core-pulling distance. If the core head has a protrusion or boss, the core-pulling distance must cover the height of the protrusion. For example, if the core end has a 5mm-high positioning boss and the die-casting side hole is 20mm deep, the core-pulling distance = 20 + 5 + safety margin = 25 + 8 = 33mm. If there is interference between the separation trajectory of the core and the die-casting, 3D simulation is required to determine the interference-free distance. For example, when pulling an L-shaped core, it is necessary to ensure that the corners are completely separated. In this case, the core-pulling distance may be 30% to 50% larger than the depth value alone.
The mold’s spatial layout constrains the core pulling distance. The core pulling mechanism must move within a limited space to avoid interference with components such as the ejector mechanism and guide pins. During the design process, a diagram of the core pulling stroke limits should be drawn to ensure a clearance of 10mm or more between the core and other mold components after core extraction. For multi-directional core pulling, the core pulling distances of each core must be coordinated. For example, if the horizontal core pulling distance is 30mm and the vertical core pulling distance is 25mm, ensure that there is no cross-interference between the two movement paths. If necessary, increase the core pulling distance in one direction by 10% to 15%.
The final determination of the core pulling distance requires verification through mold trials. This is accomplished by applying red lead to the core surface and then inspecting the die casting for contact marks after core pulling. If marks are only seen at the ends, the core pulling distance is sufficient; if contact is still present in the middle, increase it by 5-10mm. For threaded core pulling, the core pulling distance must satisfy the requirement of “thread length + 2-3 pitches.” For an M10×1.5 thread with a length of 30mm, the core pulling distance is 30 + 2 × 1.5 = 33mm, ensuring full thread extraction. During mass production, the core pulling distance must be regularly checked, as core wear may reduce the effective core pulling distance. If wear exceeds 0.5mm, stroke compensation adjustment is required.
