A basic principle of injection mold design is that the molded part should be able to leave the mold in the defined opening direction. However, side holes, hooks, clips, channels or other protrusions can prevent direct ejection.
What Is an Undercut?
An undercut is a geometric feature that prevents the part from being removed directly in the main mold-opening direction. In such cases, a fixed cavity and core alone may not be sufficient.
Why Do Undercuts Make Mold Design More Complex?
In a standard mold, the mold opens and the ejector system releases the part from the core. With an undercut, the mold feature holding the part must first move away. This can require additional moving components, machining, assembly and maintenance points.
What Is a Slide?
A slide is a mold mechanism that moves in a direction different from the main mold-opening direction to form side features. A side hole, groove or clip can, for example, be created with a slide.
What Is a Moving Core Used For?
Depending on part geometry, core systems moving in different directions may be required. A moving core creates features that cannot be formed and released using the standard opening direction alone.
Why Do Undercuts Affect Mold Cost?
Additional moving mechanisms increase mold complexity. More components must be machined accurately and work together. Slide and core surfaces can wear over time, so maintenance must also be considered.
Can Undercuts Affect Cycle Time?
They can. Moving mechanisms must operate safely during mold opening and closing. The actual effect depends on the mold mechanism and the part rather than a fixed allowance that applies to every tool.
Does Every Undercut Require a Slide?
No. Some features can be eliminated with small design changes. A hole direction can be changed, a clip redesigned or geometry adapted to the main pull direction.
Why Early Review Helps
If undercuts are identified during the CAD stage, the solution is usually easier. If they are discovered after mold design or manufacturing, major revisions may be required.
Project Evaluation at İdeal Plastik
At İdeal Plastik, undercuts, pull direction, parting line, moving mechanisms and series-production requirements are evaluated together.
Conclusion
A small side hole or clip can become a major mold-design decision. Undercuts may require slides or moving cores and can affect mold cost, maintenance and structure.
Review DFM and mold design together with tooling investment. To evaluate slides or moving cores for your part, share your CAD file or sample with İdeal Plastik.