Introduction

In injection molding, undercuts are features that prevent the straightforward removal of the molded part from the mold due to their geometry.

These challenging design elements are common in modern plastic parts, from consumer electronics to automotive components, and require specialized solutions to ensure successful production.

As a professional injection molding manufacturer with over 15 years of experience, we’ve helped hundreds of clients overcome undercut challenges while optimizing cost, lead time, and precision.

Injection Molding Undercuts Design

Solution 1: Sliders (Slide Cores)

How It Works

Sliders are movable mold components that travel laterally to form undercut features before the mold opens. They help maintain the distance between the slide and core, ensuring the normal operation of the press and its precision.
This mechanism allows for complex side actions that would be impossible with standard two-plate molds.

Case Study: Automotive Air Vent Grille

Client: European automotive Tier-1 supplier
Challenge: Complex grille with 8 side undercuts requiring precise alignment
Solution: Dual-action slider system with hardened steel inserts

Results:

• Mold cost: $28,000 USD
• Lead time: 6 weeks
• Precision: ±0.05mm dimensional tolerance
• Production volume: 250,000 parts/year

Solution 2: Lifters (Inclined Pins)

How It Works

Lifters, also known as angled pins or inclined pins, are ejector pins that move at an angle during the ejection process to release internal undercuts.
Unlike sliders that move horizontally, lifters utilize vertical ejection force combined with angled movement to free complex internal features. This solution is particularly effective for shallow undercuts in tight spaces where sliders cannot fit.

Case Study: Medical Device Housing

Client: US-based medical device manufacturer
Challenge: Internal locking mechanism with 1.2mm undercut depth
Solution: 4-position lifter system with precision-ground guide pins

Results:

• Mold cost: $15,500 USD
• Lead time: 4 weeks
• Precision: ±0.03mm on critical dimensions
• Cycle time: 22 seconds per part

Solution 3: Gas-Assisted Injection Molding

How It Works

Gas-assisted injection molding uses inert gas (typically nitrogen) injected into the molten plastic to create hollow sections, effectively eliminating the need for mechanical undercut solutions in certain applications.
This technique not only solves undercut problems but also reduces material usage, cycle time, and part warpage while maintaining structural integrity.

Case Study: Power Tool Handle

Client: Global power tool manufacturer
Challenge: Ergonomic handle with internal channels and external grip textures
Solution: Gas-assisted molding with sequential gas injection control

Results:

• Mold cost: $35,000 USD (higher initial tooling cost)
• Lead time: 8 weeks
• Material savings: 28% reduction in plastic usage
• Weight reduction: 32% lighter than solid design
• Surface finish: Eliminated sink marks on thick sections

Comprehensive Comparison Table

Advanced Design Tips

For Sliders

• Draft Angle: Minimum 1° per side on slider faces to prevent binding
• Locking Mechanism: Always use positive locking to prevent slider movement during injection
• Cooling Channels: Integrate cooling lines directly into slider blocks for faster cycle times

For Lifters

• Angle Selection: 5°-15° is optimal for most applications; steeper angles increase stress
• Guidance System: Use double guidance (top and bottom) for lifters longer than 50mm
• Material Choice: Hardened tool steel (H13 or better) for lifter pins in high-volume production

For Gas-Assisted

• Wall Thickness: Minimum 2.5mm wall thickness for effective gas penetration
• Gate Location: Place gates at end of gas channel for optimal flow control
• Gas Pressure: Typically 50-150 bar; higher pressures for thicker sections

Undercut Best Practices

It is crucial to adhere to this principle: Simplify designs as much as possible—eliminate chamfers. When unavoidable, at least control their impact through thoughtful design. Striking a balance between design requirements and manufacturing realities will yield the most cost-effective solution for any injection molding challenge involving chamfers.

Below are three common chamfer structures and their elimination or minimization strategies.

Note: Certain chamfers may be unavoidable depending on part function or geometry.

Undercut Clip

Injection Molding Undercut Clip Solution

Undercut Hole

Injection Molding Undercut Hole Solution

Undercut Window

Injection Molding Undercut Window Solution

Placement of Part Lines

Repositioning the parting line to bisect an undercut often eliminates the need for additional mold actions, reduce mold costs and improve efficiency.

Conclusion

Sliders and lifters expand the possibilities of injection molding by enabling complex part geometries that would otherwise require costly secondary operations.
Understanding the cost, lead time, and precision trade-offs between these three solutions (sliders, lifters, and gas-assisted molding) is crucial for product designers and engineers working with injection molding partners.

By choosing the right undercut solution for your application, you can achieve significant cost savings, faster time-to-market, and superior product quality. Our factory specializes in complex undercut solutions with competitive pricing and fast turnaround times.

Contact Ulite Team for Your Next Project

As an experienced injection molding manufacturer, we consistently offer optimal mold design solutions, incorporating lifters and sliders for complex geometries.

Our engineering team specializes in undercut challenges and provides:

✅ Free DFM Analysis – We review your designs before quoting to identify undercut risks and opportunities

✅ In-house Tooling – Complete mold manufacturing from design to production under one roof

✅ Advanced Simulation – Mold flow analysis to predict and prevent undercut-related defects

✅ Rapid Prototyping – 3D printed molds for undercut validation before full production

Request your FREE undercut design analysis today!

📧 Email: inquiry@ulitemech.com
🌐 Visit: https://ulitemech.com/

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