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2026年1月17日
Comprehensive Guide to Lifter Design in Injection Molding
As an essential component in complex injection mold design, the Lifter (Angled Ejector) serves a dual purpose: it handles the mechanical "core pulling" for internal undercuts and facilitates the eje
As an essential component in complex injection mold design, the Lifter (Angled Ejector) serves a dual purpose: it handles the mechanical "core pulling" for internal undercuts and facilitates the ejection of the plastic part. Below is a professional synthesis of design standards and best practices for high-quality mold manufacturing.
1. Primary Functions of a Lifter
- Internal Undercut Release: To demold features that cannot be pulled in the direction of the main draw.
- Ejection Support: Acting as a localized ejection surface to ensure balanced part removal.
2. General Technical Standards
Precision is key to the longevity of the mold. Adhere to the following parameters:
- Standard Angles: Typically ranges between 3° to 8°. A 1° angle is specifically reserved for deep rib ejection to prevent vacuum or friction drag.
- Dimensional Limits: The minimum cross-section for a lifter head should generally be 3mm x 3mm to ensure structural integrity.
- Stroke Length: Standard ejection stroke is usually between 20mm and 30mm.
- Material & Hardness: High-quality hot-work die steel (e.g., 8407 / H13) is preferred. Heat treatment should reach HRC 50-52.
- Surface Treatment: Nitriding is mandatory for the lifter surface to enhance wear resistance and prevent galling.
3. Common Lifter Structural Forms
A. T-Slot / Full-Hanging Style (Most Common)
This is the industry standard for small to medium lifters.
- Applicable Width: Ideal for lifter widths where $3\text{mm} < W \le 8\text{mm}$.
- Guidance: For "Half-Lifters" (short-stroke), a T-shaped "ear" guide on the main body is necessary for stability.
B. Design Optimization for Durability
- Safety Buffer (Straight Section): At the molding end, a straight section of at least 6mm must be incorporated. This provides a stable sealing surface and prevents the lifter from shifting under high injection pressure.
- Top Clearance: The lifter top should be designed 0.05mm - 0.10mm higher than the surrounding core surface. This prevents the lifter from "dragging" or scratching the part surface during the forward ejection stroke.
- Space-Saving Measures: If the lifter is excessively long or thin, utilize a shortened lifter assembly (stepped design) to increase rigidity and service life.
- Reinforcement: When space allows, thicken the lifter body toward the exterior of the part. This provides enough room for a robust B1 return device (mechanical reset).
4. Critical Assembly & Safety Notes
- Limit Blocks: Always install a limit block for the lifter travel. Use the formula $H3 = H1 + 0.5\text{mm}$ to ensure a safety margin.
- Wear Components: The horizontal slide pins and bushings at the base must be hardened (HRC 50-52) to withstand constant friction.
- Anti-Rotation: For non-cylindrical lifters, ensure the guide rod has a flat-side or "keyway" to prevent rotation, which would result in catastrophic tool damage.
Technical Summary Table for Quick Reference
Feature | Specification |
Material | 1.2344 / H13 / 8407 |
Hardness | HRC 50-52 (Nitrided) |
Draft Angle | 3° - 15° (Max recommended) |
Clearance | 0.05 - 0.10mm above part level |
Fit Tolerance | H7/g6 for guide shafts |
Pro-Tip for Export Molds:
When designing for European or US clients, always ensure that the lifter can be serviced without removing the entire core insert if possible. This "easy-maintenance" approach is a significant selling point for high-end mold shops.
Advanced Strategies for Lifter Design: Optimization and Best Practices
In high-end export mold manufacturing, the lifter mechanism (angled ejector) is critical for part quality and mold longevity. Beyond the basic standards, professional designers must implement advanced calculations and structural optimizations to ensure reliability.
1. Precise Calculation of Stroke and Angle
To guarantee a clean release of the undercut, the relationship between vertical ejection and horizontal travel must be mathematically verified.
- The Golden Formula: $$S = L \cdot \tan(\theta)$$
- Where $S$ is the Horizontal Release Distance, $L$ is the Vertical Ejection Stroke, and $\theta$ is the Lifter Angle.
- Safety Margin: The horizontal travel $S$ should always be 2.0mm to 3.0mm greater than the actual undercut depth to account for material shrinkage and mechanical play.
- Angle Constraints: Ideally, keep the lifter angle under 15°. Exceeding this limit significantly increases lateral force, leading to uneven stress on the ejector plates or potential bending of the lifter rod.
2. Structural Classification & Application
Selecting the right lifter type depends on the available space and the complexity of the undercut.
Type | Ideal Application | Key Features |
Integral Lifter | Ample space; Medium to large undercuts. | Maximum structural strength; simplified machining. |
Two-Piece (Split) | Restricted space; High-precision tools. | Head and rod are separate; allows for specialized head materials (e.g., Beryllium Copper). |
Round-Rod Lifter | Narrow or circular locations. | Easy to manufacture (Wire EDM + Lathe); requires a robust anti-rotation feature. |
3. Critical Details for High-Performance Lifters
Wear Plates and Guidance
- Friction Management: Where the lifter passes through the Core (B-Plate), it is highly recommended to install Wear Plates or machine oil grooves.
- Long-Stroke Support: For exceptionally long lifters, guide blocks must be installed on the bottom clamping plate to prevent tilting or "snaking" during ejection.
Thermal Management (Cooling)
Large lifters tend to trap heat, which causes sink marks or warping on the plastic part.
- Optimization: Whenever space permits, design internal water channels or use high-conductivity alloys like Beryllium Copper (BeCu) to accelerate cooling.
Precision Positioning
- Base Fitment: The clearance between the slide pin and the slider seat should be strictly controlled within $0.01\text{mm}$ to $0.03\text{mm}$.
- Anti-Rotation: For non-symmetrical lifter heads, a "D-shaped" or keyed flat must be machined on the rod to prevent rotation, which could damage the undercut or the mold core.
4. Troubleshooting & Design "Red Flags" (Pro-Checklist)
- Interference Check: Always perform a dynamic simulation in CAD to ensure the lifter does not collide with ribs, bosses, or adjacent ejector pins during the full ejection stroke.
- Flash Prevention (Relief): To prevent friction dust (galling) from entering the sealing area, apply a 0.5mm relief on non-sealing surfaces of the lifter.
- Reset Logic: While lifters are forced back by the ejector plate, adding a helper spring can assist in smooth movement—but ensure the spring's life cycle matches the mold's production rating.
Final Thought for Export Quality:
A great lifter design isn't just about moving an undercut; it's about maintenance accessibility. For export molds, always design lifter heads that can be replaced or adjusted without stripping the entire B-side of the mold.
As a mold designer with years of experience in export-standard tooling (DME/HASCO standards), we believe we can offer the perfect and suitable design layout for your molds. Let's talk more if you want to have some similar design for your projects by info@jstmould.com.