Ways To Achieve Injection Molding Undercuts

Have you ever wondered how complex plastic parts with intricate details are made? The answer lies in a clever technique called injection molding undercuts. But what exactly are undercuts, and why are they so important?

Undercuts are features that prevent the easy removal of a part from its mold. They're crucial for creating parts with enhanced functionality, improved assembly, and reduced need for secondary operations. However, designing and molding undercuts comes with its own set of challenges.

In this post, you'll learn what undercuts are, why they are important, and how to manage their complexities effectively.

What are Injection Molding Undercuts?

Injection molding undercuts are features that prevent a part from being easily ejected from its mold. They're like hooks or overhangs that "lock" the part in place. Let's explore them in detail.

Detailed Explanation of Undercuts

Undercuts are typically formed when a part has:

• Protrusions

• Holes

• Cavities

• Recessed areas

These features aren't perpendicular to the mold's parting line. This makes it challenging to remove the part without damaging it.

Types of Undercuts

There are two main types of undercuts:

1. Internal undercuts

• Found inside the part

• Examples: threaded holes, snap-fits

2. External undercuts

• Found on the outer surface

• Examples: clips, hooks, flanges

Common Applications

Undercuts are used in various industries for:

• Consumer electronics

• Button slots

• Battery compartments

• Medical devices

• Luer locks

• Snap-fit assemblies

• Automotive components

• Clips and fasteners

• Fluid channels

Industry	Application	Benefit
Electronics	Button slots	Easy access
Medical	Luer locks	Secure connection
Automotive	Clips	Quick assembly

Undercuts add functionality and simplify assembly. They're a key aspect of injection molding design.

Importance of Undercuts in Injection Molded Parts

Undercuts play a crucial role in injection molded parts. They offer several benefits that make them indispensable in modern manufacturing.

Enhanced Functionality and Design Complexity

Undercuts allow designers to create parts with:

• Intricate geometries

• Interlocking features

• Snap-fits and hinges

These elements enhance the functionality of the part. They also enable more complex designs that would be impossible without undercuts.

Improved Assembly and Disassembly

Undercuts facilitate easy assembly and disassembly of parts. They allow for:

• Quick snap-fit connections

• Reduced need for screws or adhesives

• Easy replacement of worn or damaged components

This streamlines the assembly process and makes maintenance a breeze.

Reduced Need for Secondary Operations

By incorporating undercuts directly into the molded part, you can:

• Eliminate the need for post-molding drilling or machining

• Reduce the number of assembly steps

• Minimize the risk of human error

This saves time, effort, and resources in the manufacturing process.

Cost-Effectiveness in Mass Production

Undercuts contribute to cost-effectiveness, especially in high-volume production runs. They enable:

• Faster cycle times

• Reduced material waste

• Lower assembly costs

Over time, these savings add up, making undercuts an economical choice for mass production.

Benefit	Impact
Enhanced functionality	Enables complex designs
Improved assembly	Streamlines production
Reduced secondary ops	Saves time and resources
Cost-effectiveness	Lowers overall expenses

Techniques for Achieving Injection Molding Undercuts

Creating undercuts in injection molding requires specialized techniques. Let's explore the most common methods and their pros and cons.

1. Parting Line Adjustment

Parting line placement is crucial for undercut design. It involves:

• Aligning the parting line with the undercut feature

• Splitting the undercut into two halves

This allows the part to be ejected without interference.

Advantages:

• Simple and cost-effective

• Minimal mold complexity

Limitations:

• Limited to certain part geometries

• May require additional draft angles

Tips for optimizing parting line design:

• Consider part functionality and aesthetics

• Minimize the number of parting lines

• Ensure proper venting and cooling

2. Side-Actions

Side-actions are movable mold components that create undercuts. They work by:

• Retracting or rotating out of the way during ejection

• Allowing the part to release freely

Types of side-actions:

1. Hydraulic - powered by hydraulic pressure

2. Mechanical - driven by cams or linkages

3. Pneumatic - actuated by compressed air

Design considerations:

• Ensure proper clearance and alignment

• Plan for adequate cooling and venting

• Consider the force required to operate the side-action

Benefits:

• Enables complex undercuts

• Provides design flexibility

Drawbacks:

• Increases mold cost and complexity

• May increase cycle time

3. Bump-Offs

Bump-offs are raised sections on the mold that compress during ejection. They allow the part to flex and release from the undercut.

Suitable materials for bump-offs:

• Elastic polymers like TPE and TPU

• Flexible materials with good compression set

Design guidelines:

• Ensure sufficient draft angles

• Use smooth, rounded surfaces

• Consider the material's compression limits

Advantages:

• Simple and cost-effective

• Ideal for flexible parts

Disadvantages:

• Limited to certain materials and geometries

• May cause visible witness marks on the part

4. Hand-Loaded Inserts

Hand-loaded inserts are manually placed in the mold before each cycle. They create undercuts by:

• Blocking off certain areas of the mold cavity

• Being removed after the part is ejected

When to use hand-loaded inserts:

• For complex undercuts that can't be achieved with other methods

• In low-volume production runs

Design and material considerations:

• Ensure proper fit and alignment of the insert

• Choose materials with good wear resistance

Pros:

• Enables intricate undercut geometries

• Provides flexibility for design changes

Cons:

• Increases labor costs and cycle times

• May introduce variability in part quality

5. Sliding Shutoffs (Telescoping Shutoffs)

Sliding shutoffs are mold components that move parallel to the ejection direction. They create undercuts by:

• Sliding into position before injection

• Retracting during ejection to release the part

Applications:

• Threading and snap-fits

• Hollow or recessed features

Design tips:

• Ensure proper alignment and clearance

• Use wear-resistant materials for the shutoff surfaces

• Plan for adequate cooling and venting

Advantages:

• Enables complex undercut geometries

• Provides good surface finish and part quality

Limitations:

• Increases mold cost and complexity

• May require additional maintenance

6. Collapsible Cores

Collapsible cores are mold components that collapse or retract during ejection. They allow the part to release from internal undercuts.

Types of collapsible cores:

1. Mechanical - driven by cams or linkages

2. Hydraulic - actuated by hydraulic pressure

Design considerations:

• Ensure proper alignment and timing of the core movement

• Plan for adequate cooling and venting

• Consider the force required to collapse the core

Benefits:

• Enables deep, internal undercuts

• Provides good part quality and surface finish

Drawbacks:

• Increases mold cost and complexity

• May require additional maintenance and setup time

Choosing the right technique depends on factors like:

• Part geometry and complexity

• Material properties

• Production volume and cost constraints

Design Considerations for Undercuts

When designing parts with undercuts, there are several key factors to keep in mind. Let's explore them in detail.

Draft Angles

Importance of Draft Angles

Draft angles are crucial for undercut design. They help ensure:

• Easy part ejection from the mold

• Minimal friction and wear on mold surfaces

Without proper draft, parts can stick or deform during ejection.

Recommended Draft Angles

The optimal draft angle depends on the specific design. However, here are some general guidelines:

Feature Type	Recommended Draft
External walls	1-2 degrees
Internal walls	2-3 degrees
Ribs and bosses	0.5-1 degree per side

Increasing draft angles can improve part release but may affect aesthetics.

Wall Thickness

Maintaining Uniform Wall Thickness

Consistent wall thickness is essential for undercut design. It ensures:

• Even cooling and shrinkage of the part

• Reduced risk of warping or sink marks

Always follow the resin manufacturer's guidelines for wall thickness.

Impact on Part Integrity

Variations in wall thickness can lead to:

• Weak spots or stress concentrations

• Uneven material flow and packing

• Visible defects on the part surface

Maintain a uniform thickness throughout the part for optimal results.

Ribs and Radiuses

Supporting Structures in Molded Parts

Ribs are thin, wall-like features that provide structural support. They help:

• Reinforce large, flat surfaces

• Prevent sink marks and warping

• Improve part rigidity and strength

Use ribs strategically to enhance the performance of undercut parts.

Radiusing Internal Corners

Sharp internal corners are prone to stress concentrations. To mitigate this:

• Add a radius to the corner

• Ensure a smooth transition between surfaces

Radiused corners distribute stress more evenly, improving part durability.

Designing for Manufacturability (DFM) in Undercut Injection Molding

DFM is a crucial aspect of successful undercut design. Let's dive into its principles and benefits.

Overview of DFM Principles

DFM is a design approach that focuses on ease of manufacturing. Its key principles include:

• Simplifying part geometry

• Minimizing the number of components

• Designing for efficient assembly

• Considering material properties and limitations

By applying DFM, designers can create parts that are easier and cheaper to produce.

Importance of DFM in Undercut Design

Undercuts add complexity to the injection molding process. DFM helps manage this complexity by:

• Identifying potential manufacturing issues early in the design phase

• Optimizing part geometry for specific molding techniques

• Ensuring the design is compatible with the chosen material

• Reducing the risk of defects and production delays

Incorporating DFM is essential for successful undercut design.

Common DFM Guidelines for Undercuts

Here are some key DFM tips for designing undercuts:

1. Minimize undercut depth and complexity

2. Use consistent wall thickness throughout the part

3. Provide adequate draft angles for easy ejection

4. Avoid sharp corners and edges

5. Consider the parting line location and its impact on the undercut

6. Use standard materials and tolerances whenever possible

Following these guidelines can help streamline the molding process.

Benefits of Incorporating DFM

Implementing DFM in undercut design offers several advantages:

• Reduced production costs and lead times

• Improved part quality and consistency

• Enhanced collaboration between design and manufacturing teams

• Faster time-to-market for new products

• Increased overall manufacturing efficiency

DFM Benefit	Impact
Lower costs	More competitive pricing
Faster production	Shorter lead times
Better quality	Higher customer satisfaction
Enhanced efficiency	Increased profitability

Challenges and Solutions

Designing and molding undercuts comes with its fair share of challenges. Let's explore some common issues and their solutions.

Material and Design Challenges

Managing Rigid Materials and Complex Geometries

Rigid materials like polycarbonate and ABS can be challenging for undercut design. They:

• Require higher draft angles for proper ejection

• Are more prone to stress and deformation during molding

Complex geometries with deep or narrow undercuts further complicate the process.

Solutions to Common Design Issues

To overcome these challenges, designers can:

• Use more flexible materials like TPE or nylon

• Optimize wall thickness and draft angles

• Incorporate side-actions or collapsible cores for complex features

Collaboration between designers and molders is key to finding effective solutions.

Aesthetic and Functional Considerations

Dealing with Visible Parting Lines

Parting lines are often visible on parts with undercuts. They can:

• Affect the aesthetics of the final product

• Create weak points or stress concentrations

To minimize their impact, consider:

• Adjusting the parting line location

• Using texture or color to hide the lines

• Employing sliding shutoffs for a seamless appearance

Ensuring Functional Integrity

Undercuts can also affect the functional performance of the part. To maintain integrity:

• Conduct thorough design reviews and simulations

• Test prototypes under real-world conditions

• Make necessary design adjustments based on feedback

Finding the right balance between functionality and manufacturability is crucial.

Cost Implications

Balancing Complexity and Production Costs

More complex undercuts generally mean higher production costs. This is due to:

• Increased mold complexity and maintenance

• Longer cycle times and higher material usage

• Additional labor for hand-loaded inserts or secondary operations

Designers must weigh the benefits of undercuts against their cost impact.

Long-Term Impacts on Investment

The upfront investment in a complex mold with undercuts can be significant. However, it's important to consider:

• The long-term savings in assembly and secondary operations

• The potential for increased product functionality and market appeal

A well-designed undercut can pay off in the long run, despite initial costs.

Challenge	Solution
Rigid materials	Use flexible alternatives
Visible parting lines	Adjust location or use texture
Functional integrity	Conduct thorough testing
Production costs	Balance complexity and benefits

Summary

In summary, achieving injection molding undercuts involves several key techniques. We explored parting lines, side-actions, bumpoffs, hand-loaded inserts, and telescoping shutoffs. Selecting the right technique is crucial for success. Material choice and Design for Manufacturability (DFM) are also vital in undercut molding. Collaborating with experts ensures the best results. Effective undercut design requires both knowledge and precision.

Have a complex undercut design? Team Mfg has the expertise to bring it to life. Submit your CAD files today at https://www.team-mfg.com for a fast, free quote. Our experts are ready to assist you. Get started now!