Where Are Ejector Pin Typically Designed on Products?

In injection mold design, the ejector pin system is a critical component for ensuring the smooth demolding of formed products. Proper ejector pin layout directly affects product quality, production efficiency, and mold lifespan. This article explores the typical design locations of ejector pins, selection principles, and key considerations in engineering practice, providing practical technical guidance for mold design engineers.

Core Functions of Ejector Systems

The ejector system serves three primary functions:

• Demolding: Ejects cooled and solidified products from the mold cavity.
• Support: Prevents product deformation during injection.
• Venting: Some ejector pins can also function as venting channels.

Common Types of Mold Gates

Structural Reinforcement Areas

• Rib Roots: Preferred at junctions between ribs and main walls.
• Boss: Typically arranged evenly (3-4 pins) around the base of cylindrical features.
• Thick Sections: Prevents vacuum adhesion due to shrinkage.
• Industry Data: ~65% of ejector pins are placed in reinforced areas (Source: 2023 Journal of Mold Engineering).

Non-Cosmetic Surfaces

• Internal surfaces: Priority is given to non-visible interior surfaces.
• Flat bases: Large flat products usually require uniform pin distribution.
• Near parting lines: 5-10mm from the parting line.

 Pin Gate (Direct Gate)

• Location: Directly into the cavity.
• Advantages: Minimal pressure loss, good for thin walls.
• Disadvantages: Leaves a noticeable mark.
• Best for: Technical parts where appearance is secondary.

Functional Locations

• Slider mechanism sides: Coordinates with slider movement sequences.
• Around inserts: Prevents insert sticking.
• Curved transitions: Avoids deformation during ejection.

Engineering Principles for Ejector Layout

 Force Balance Principle

• Symmetrical distribution for even ejection force.
• “Radial pattern” for large products.
• Minimum 1 ejector pin per 100cm² product area.

Geometric Compatibility

Process Optimization

• Avoid pin marks in functional areas.
• Standardize pin diameters to reduce machining costs.
• Use specialty steels (e.g. H13) for high-temperature zones.

Common Design Mistakes & Solutions

Issue 1: Visible Pin Marks

• Cause: Insufficient contact surface area
• Solution: Use stepped pins or increase the contact area

Issue 2: Uneven Ejection

• Cause: Asymmetric layout
• Solution: Verify with mold flow analysis

Issue 3: Pin Jamming

• Cause: Improper fit tolerance
• Solution: Maintain H7/g6 clearance fit

Optimal ejector pin design requires balancing structural, cosmetic and production requirements. With advancements in CAE simulation, modern mold design can precisely analyze ejection processes—we recommend conducting ejection simulations during the design phase.