In mold design, the ejection system is not an afterthought—it directly determines demolding efficiency and part quality. A common rule of thumb is to provide 0.5–1.0 mm of ejection stroke per millimeter of part depth, but that number must be adjusted for material shrinkage, draft angle, and wall thickness. For example, a 100 mm deep ABS part with a 1.5° draft typically needs at least 60–80 mm of ejection travel to clear the core without dragging. Ejector pins should be positioned at high-stress areas such as ribs, bosses, and corners, with a minimum diameter of 2.5–3 mm to avoid punching through the part. When ejector sleeves or blades are used, clearance should be kept at 0.02–0.04 mm per side to prevent flash while allowing smooth movement.

The molding mechanism—including the core-pulling system, slider, and lifter—must work in sync with ejection. For undercuts, a slider with a 5–10° angle is common, but the actual angle depends on the undercut depth and the coefficient of friction. A typical design uses a 7° slider angle for a 2 mm undercut in PP, with a safety margin of 1–2 mm on the slide travel. Hydraulic core pullers are preferred when the undercut exceeds 5 mm or when the mold runs in a high-speed press above 300 cycles per hour. In addition, the ejection plate must be guided by at least four guide pins, and the return springs should be sized to overcome the ejection force plus a 20–30% safety factor. Ignoring this leads to plate binding, broken pins, and costly downtime.

From a quoting perspective, these details matter. A mold with a complex ejection and slider system can add 15–25% to the tooling cost compared to a simple two-plate mold, but it prevents field failures that would wipe out margins. Always review the ejection stroke, pin layout, and core-pulling sequence before finalizing the price. For more mold sourcing and design references, visit MoldWorld at www.moldw.com.