Undercuts in Die Casting: When They’re Necessary and How to Handle Them

In die casting, an undercut is any feature that prevents the part from being ejected straight out of the mold. They add complexity and cost—but sometimes, they’re unavoidable due to part function.

Understanding when undercuts are justified (and how to manage them) helps strike the right balance between design freedom and tooling practicality.

🔄 What Creates an Undercut?

• Side holes or slots

• Snap-fit features

• Overhanging flanges or lips

• Internal clips or dovetail features

🧠 Why Avoid Undercuts If Possible?

1. Require Sliders or Lifters

   These are mechanical components in the die that move sideways to release the undercut—adding cost, machining time, and wear.

2. Increase Tooling Lead Time

   More moving parts = more complexity during tool fabrication and setup.

3. Higher Maintenance

   Sliders and lifters require frequent cleaning, lubrication, and calibration to avoid flash or misalignment.

4. Cycle Time Impact

   Tool opening and closing sequences take longer when extra components must move in and out.

✅ When Undercuts Are Acceptable

• Functional necessity (e.g. locking mechanisms, mating clips)

• Low-volume production where manual trimming or inserts are viable

• Complex part consolidation that reduces total BOM or assembly steps

At LVIO Precision, we assess every undercut with our DFM checklist—determining whether it’s worth the added tooling complexity or if a design workaround (like split parts or removable inserts) can achieve the same function more efficiently.