Colleagues designing and adjusting die-casting molds have likely encountered these pitfalls: Insufficient slider stroke results in core still obstructing casting's projection area after mold opening, causing product to jam on slider, damaging core and scratching product during ejection; Insufficient stroke lengthens slider body and enlarges mold base, drastically increasing mold costs, weakening force on angled pins and hydraulic cylinders, causing unstable slider movement, and accelerating wear.
Many newcomers design sliders by simply adding a few millimeters to product depth as a safety margin. However, core-pulling distance is not as simple as product depth. Calculation logic is completely different for circular parts and multi-lobed sliders.

Definition: The total stroke slider needs to move from forming position to outside die-casting's projection area without interfering with ejection is core-pulling distance.
⚠️Key Point: It's not enough to simply remove core from hole; it must be pulled out beyond projected outline of casting. Otherwise, ejected casting will collide with core.
Core pulling distance = Depth product needs to be ejected + Safety margin k. This safety value k is an essential part of die-casting molds, preventing jamming caused by slight deformation or flash in casting.

 

Typical example of calculating core-pulling distance
① Ordinary Single-Sided Core Pulling (Figure a, most commonly used)
Suitable for ordinary side holes, side concave, and side convex structures: S=h+k
- S: Core pulling distance (mm); - h: Depth of side hole/side concave/side convex forming; - k: Safety value, obtained from a table
This formula is used for most simple sliders. A common mistake many designers make: directly using S=h without adding safety k. If casting has flash or slight deformation, it will scrape core, causing jamming during ejection.
② Bisection Circular Slider Core Pulling (Figure b)
Outer circle of circular casting is entirely formed by two semi-slider blocks. Stroke cannot be calculated directly based on wall thickness; it must be calculated using Pythagorean theorem:

 

R: Maximum outer radius of the casting; T: Minimum inner radius preventing demolding.
Important: Core-pulling distance between two semi-circular sliders is not equal to R-r. If stroke is simply assigned based on radius difference, slider will still hook onto outer circle of casting after it has retracted to its final position, preventing demolding. This is a common design flaw in circular sliders.
③ Multi-Part Slider Core Pulling (Figure 3c)
Three-lobed, four-lobed, and other multi-lobed mold closing sliders, such as annular lobed mold closing sliders:

 

β: Slider closing angle; A: Half chord length of slider's sharp corner.
For multi-part sliders, radial dimension cannot be simply considered; included angle directly affects required extraction stroke.
Table: Core Pulling Safety Value k Reference (Manual Standard)