A senior mold engineer summarizes: advantages of double/single mounting platforms, guide vanes, foolproof design, round rod Lifter systems, and three solutions for mold sticking, helping you completely overcome pain points of lifter design.

 

Common connection types for bottom of sloping roofs:
1) Double-sided mounting brackets sliding on lifter base.
2) Single-sided mounting brackets sliding on lifter base. When lifter size is very small and double-sided mounting brackets cannot be designed, a single-sided mounting bracket connection can be used.

In lifter structure design, bottom connection method directly determines stability and lifespan of movement. Common methods are double-sided mounting platform connections and single-sided mounting platform connections, both relying on sliding of lifter seat to achieve lateral core pulling.
1. Double-sided Mounting Platform Connection – First Choice for Conventional Structures
Suitable for standard-sized Lifters, mounting platform height ≥ 3mm, corner radius R0.5 to relieve stress, mounting platform width 5~10mm, thickness 2~5mm. During machining, a step is formed by two cuts; mating surfaces must be tightly fitted, with a 0.5mm clearance at the top to reduce friction. For long-term operation, pay attention to steel wear; lubrication maintenance is recommended.
2. Single-sided Mounted Connection – A Solution for Small Lifters

 

When width of lifter is less than 5mm and a double-sided mounted connection cannot be designed, a single-sided mounted connection is used. Side is fixed in place, with a 0.2~0.5mm clearance on non-mounted side. Shear stress must be verified to ensure a minimum thickness ≥2mm to avoid uneven stress leading to breakage. Single-sided structure is suitable for extremely limited space, but its strength and wear resistance are inferior to double-sided structure.

Selection of lifter sliding pair directly affects stability of mold mass production and maintenance costs.

 

Advantages of Mounted Connection (Steel to Steel): Simple structure, low processing cost, easy fixing (ejector plate screw fixing). Disadvantages: Poor lubrication; direct friction between steel materials easily creates gaps of 0.2mm or more; after wear, the entire lifter seat needs to be replaced; not suitable for large-angle lifters exceeding 8°, prone to jamming.
Advantages of Guide Plate Type (Bronze + Graphite): Bronze guide plates have a friction coefficient only 1/3 that of steel, self-lubricating grooves, and a maximum adaptable angle of 15°; after wear, only guide plate needs to be replaced, with maintenance costs approximately 1/5 of the overall cost; particularly suitable for high-life, high-load molds. It is recommended to prioritize guide plate structure when conditions permit.

Regardless of structure, non-load-bearing surfaces should have a 0.2~0.5mm clearance, and contact surfaces should have a zero-clearance fit; single-sided mounting platforms require shear resistance checks; during mold opening stage, it is essential to simulate relative sliding trajectory of ejector pin and base to check for interference; a 0.1mm wear compensation allowance should be reserved in design, and regular inspection requirements should be noted on drawings to significantly extend mold life.

 

When ejector pin has a specific slope, incorrect installation direction can lead to reverse motion (e.g., it should be downward but is upward), causing mold collision. Core of foolproof design is asymmetrical chamfering: While using a standard four-corner chamfered design, one corner is left uncut to create a clear directional marker; combined with tilted feature of ejector plate, this physically prevents reverse installation. Reputable companies include this in their design specifications to effectively reduce risk of errors.

 

�� Foolproofing illustration: Lifter retains one uncut corner feature, preventing reverse installation → eliminating assembly accidents

Design optimization often requires adjusting length of lifter to avoid insufficient strength or interference. An excessively long lifter is like a "long chopstick that easily breaks." Lifting lifter and shortening its overhang can significantly enhance rigidity.
Lifting Method and Travel Avoidance: Duplicate lifter and its assembly, move lifter upwards by a specified distance (e.g., 30mm), cut and reconnect, maintaining angle. Simultaneously adjust guide block position to ensure sufficient ejection distance (e.g., if ejection requires 40mm, move guide block upwards by 25mm, leaving a 5mm margin), and maintain a clearance of ≥2mm between all moving parts.
Interference Handling and Parametric Modification Techniques: When using "Move Surface" command, all associated surfaces (including chamfers) must be selected. Complex structures can be reconstructed. Create blocks in interference area and calculate difference, chamfering edges to ensure guide block steps are flat. After modification, ejection stroke and mold closing sequence must be re-verified.

Maximum allowable angle for an lifter is typically 12°. Exceeding this value requires structural changes (such as universal joints or float structures). If undercut is large, ejection distance can be increased to increase demolding amount—achieved by increasing height of square block, but attention must be paid to the overall mold height limit. For large-angle lifters (45°~60°) in automotive molds, a dedicated universal joint structure can perfectly solve problem.
�� Core Angle Design Principle: Slope of back of lifter head must be 1~2° larger than slope of rod; otherwise, assembly is impossible, and interference with B-plate is likely.

Deep ribs and excessive clamping force causing product sticking to anchor pins are common defects. Three mechanical anti-sticking solutions are reliable and effective:
1. Circular Positioning (Ejector Pin Positioning Ring): Add a 1mm high annular step to ejector pin, with a wall thickness of 0.5~0.8mm, ensuring complete contact between top surface and product surface. When anchor pin moves backward, arc surface holds product, forcing it to remain on ejector pin side and preventing it from moving backward. Positioning depth 1mm, interference 0.3~0.5mm, surface roughness Ra below 0.8, must be integrally machined with ejector pin. Suitable for small to medium-sized undercuts (depth < 15mm).
2. Straight Ejector Mechanism: Uses a square straight ejector pin with 90° vertical movement, firmly blocking product surface and preventing anchor pin from carrying material. Suitable for areas where lower ejector pins are not allowed, providing the most thorough effect. Design must completely incorporate rounded corners, and blocking coverage area must be confirmed through transparent inspection to avoid sharp corners.
3. Lifter with Spring-loaded Pin: A spring-loaded pin and spring are installed inside lifter. During lifter's movement, spring-loaded pin maintains resistance, and disengages after lifter has retracted a certain distance. In practice, it is often used in combination with a straight ejector to form a double safety mechanism. It is especially suitable for deep-cavity products with complex structures and extremely high clamping force.
�� Expert Tip: For each additional rib side, clamping force increases by approximately 15%. With multiple clamping points, demolding resistance can reach over 90%, necessitating use of locating rings or straight ejectors for early intervention.

For large molds of 1-2 meters, round rod lifters, machined through deep hole drilling, offer significant advantages. Components: Lifter head (plastic contact, back slope greater than rod), lifter rod (φ12/16/20/25mm standard), self-lubricating guide sleeve (bronze + graphite, used in pairs), and universal head (360° rotation). Undercut depth can reach 10-20mm, guide sleeve has low friction, and movement is smooth.
Key design considerations for lifter heads: Copper or aluminum inlays should be used at contact points with glue to prevent screw exposure; material should be wear-resistant to ensure molding quality.

Multi-Lifter molds require material assembly via wire cutting. Basic principles: Align lifter from its initial tilt to ensure all pin holes are concentric; when assembling lifters of same structure, maintain a 0.5mm gap (for molybdenum wire passage); adjust all dimensions to integers, adding a 0.5mm allowance to beveled surface; thin-walled areas can be thickened by 5mm to prevent deformation. C-corners should be cut at reference angle or "D" should be engraved to mark processing direction.
Standardized Engraving of Parts: Lifters are numbered using "L" series (L1, L2…), ejector seats use "6" series (601, 602), and guide blocks use "7" series (701, 702). Engravings should be placed in a prominent position on the front of part, arranged according to assembly sequence for easy assembly and maintenance traceability.

Support head should be positioned to support B-plate and base plate, close to lifter but without damaging structure, maintaining a clearance of ≥0.5mm from lifter. Limiting post must be at least 5mm higher than lifter (5-10mm recommended) to ensure that limiting post contacts B-plate first during ejection; otherwise, lifter hitting B-plate will cause functional failure. When guide block interferes with ejector pin, difference can be directly calculated, with a 1mm clearance at contact surface; offset screw positions or asymmetrical layouts can resolve spatial conflicts.

Straight plane at the rear end of lifter pin acts as a delay: during mold opening, lifter head moves upward, pin blocks product through straight plane, and only begins to retract after backward movement exceeds length of straight plane, at which point spring returns to its original position. This mechanism, in conjunction with positioning ring or straight ejector, achieves orderly demolding and avoids product damage. Length of straight plane (usually 3-5mm) must be precisely controlled during design to ensure product is completely detached from core before pin retracts.
Key Parameter Quick Reference Table (Design Practice Reference)

Conclusion: Although ejector pin is small, details determine success or failure
As core component of mold's side core pulling mechanism, ejector pin mechanism affects mass production stability and maintenance costs at every step, from selection of mounting platform, lubrication method, foolproof design to product anti-sticking solution. This article systematically reviews more than ten practical knowledge points, covering double/single side mounting platforms, advantages of guide vanes, round rod systems, mold sticking countermeasures, and processing assembly specifications. Designers are advised to flexibly select appropriate model based on specific mold type (standard size, automotive mold, high lifespan mold) and strictly adhere to principles of clearance avoidance and wear compensation.