Views: 0 Author: Site Editor Publish Time: 2025-12-05 Origin: Site
If you're designing a plastic part with an internal undercut—like a snap-fit hook inside a case or a rib in a deep pocket—you've hit a classic molding dilemma. You can't eject the part with straight pins, and a side-action slider seems like overkill. Enter the unsung hero of mold design: the Lifter Angle Pin, often referred to simply as a "Lifter" or "Angle Pin."
This ingenious mechanism is the key to molding complex internal features efficiently and reliably.
It is a specialized internal side-action ejection system. It's a core-cavity component that performs two synchronized movements during ejection:
Vertical Ejection: It pushes the part off the core.
Lateral Retraction: It simultaneously moves sideways to clear the internal undercut.
Simplified: It's an ejector pin that moves at an angle.
The system typically consists of:
Lifter Body: The angled pin or block itself. Its head forms part of the cavity surface.
Guide/Wear Plate: A hardened steel block with a precision-machined angled hole that guides the lifter's motion.
Mounting Block: Connects the lifter to the ejector plate.
The beauty lies in its forced kinematic motion:
Mold Opens: The part remains on the core (moving half).
Ejection Starts: The machine's ejector rod pushes the ejector plate forward in a straight line.
Compound Motion: The lifter, fixed to the plate, is forced to follow the path defined by the angled guide. The plate's straight-line push (Force Fv) is resolved into two components:
Vertical Ejection Force (Fv): Lifts the part off the core.
Horizontal Retraction Force (Fh): Pulls the lifter head away from the undercut.
Part Release: By the end of the stroke, the part is fully ejected, and the lifter has completely disengaged from the undercut.
Key Formula:Horizontal Travel (S) = Ejection Stroke (L) x tan(Angle α)
Getting a lifter design right is crucial for mold longevity and part quality.
Typical Range: 5° to 12°. This is the single most important parameter.
Too Small (<5°): Insufficient lateral travel. The lifter won't clear the undercut.
Too Large (>15°):
Excessive bending stress, leading to breakage.
Requires a very long ejection stroke.
High friction and rapid wear.
Pro Tip: Calculate the required lateral travel first, then use the formula above to determine the minimum angle for your machine's available stroke.
Fit: A sliding fit (H7/f7 or similar) between the lifter body and the guide block is essential.
Material: The guide block must be made of hardened tool steel (e.g., H13, hardened to 48-52 HRC). The lifter body is often a different, tough steel to prevent galling.
Lubrication: Incorporate grease grooves or use self-lubricating coatings.
The lifter head must perfectly match the part's undercut geometry.
Anti-Rotation is a MUST: The head cannot be allowed to twist. This is achieved by:
A flat side on the lifter body.
A key in the guide block.
A dedicated anti-rotation pin.
Head Polish: The forming surface should be polished to the same standard as the surrounding cavity to ensure a good finish and easy release.
Lifters act as cantilevers under high injection pressure.
Ensure adequate cross-sectional area. A common failure is a lifter that is too thin.
For long or tall lifters, use a "Kicker" or "Support Block" under the lifter to prevent it from deflecting during injection.
Ample clearance must be machined around the lifter body in non-sliding areas to prevent binding.
Pay close attention to the clearance between the lifter head and the surrounding core steel during retraction.
| Feature | Lifter (Angle Pin) | Side Core (Slider) |
|---|---|---|
| Drive Source | Ejection System (Ejector Plate). | Mold Opening (Angled Pin, Hydraulic Cylinder). |
| Actuation Timing | After mold opening, during ejection phase. | During mold opening, before ejection. |
| Location | Almost always in the moving half (core side). | Can be in moving or fixed half. |
| Best For | Internal, relatively small undercuts. | External or large undercuts. |
| Complexity & Cost | Lower. Integrated into ejection. | Higher. Separate actuation system. |
Rule of Thumb: If the undercut is on the inside of the part and you can access it from the B-side (ejector side), a lifter is usually the most economical and robust solution.
Consumer Electronics: Internal snap-fits in phone cases, battery covers.
Automotive: Undercuts on connectors, interior trim clips.
Household Goods: Internal threads, living hinges, container latch features.
Any part where an internal feature would lock it onto the core with straight ejection.
Lifter Breaks: Check angle (too steep), cross-section (too thin), or material/heat treatment.
Gallig/Scoring: Check lubrication, hardness mismatch between lifter and guide, or insufficient clearance.
Part Sticks to Lifter Head: Improve polish, add draft, or incorporate a slight undercut on the lifter head (for PP/PE).
Witness Marks on Part: Ensure the lifter head is properly seated during injection; check for wear.
The Lifter Angle Pin system is a testament to clever mechanical design in injection molding. It transforms a simple linear motion into the precise compound movement needed to form and release complex internal geometries. By mastering its design rules—respecting the angle, ensuring robust guidance, and preventing rotation—you unlock the ability to design more functional, integrated plastic parts without compromising manufacturability.
