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.
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.
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.
There are two main types of undercuts:
Internal undercuts
Found inside the part
Examples: threaded holes, snap-fits
External undercuts
Found on the outer surface
Examples: clips, hooks, flanges
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.
Undercuts play a crucial role in injection molded parts. They offer several benefits that make them indispensable in modern manufacturing.
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.
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.
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.
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 |
Creating undercuts in injection molding requires specialized techniques. Let's explore the most common methods and their pros and cons.
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
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:
Hydraulic - powered by hydraulic pressure
Mechanical - driven by cams or linkages
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
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
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
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
Collapsible cores are mold components that collapse or retract during ejection. They allow the part to release from internal undercuts.
Types of collapsible cores:
Mechanical - driven by cams or linkages
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
When designing parts with undercuts, there are several key factors to keep in mind. Let's explore them in detail.
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.
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.
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.
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 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.
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.
DFM is a crucial aspect of successful undercut design. Let's dive into its principles and benefits.
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.
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.
Here are some key DFM tips for designing undercuts:
Minimize undercut depth and complexity
Use consistent wall thickness throughout the part
Provide adequate draft angles for easy ejection
Avoid sharp corners and edges
Consider the parting line location and its impact on the undercut
Use standard materials and tolerances whenever possible
Following these guidelines can help streamline the molding process.
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 |
Designing and molding undercuts comes with its fair share of challenges. Let's explore some common issues and their solutions.
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.
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.
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
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.
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.
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 |
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!
TEAM MFG is a rapid manufacturing company who specializes in ODM and OEM starts in 2015.