Today's KNOWLEDGE Share : The Importance of Draft Angle in Die Casting

Today's KNOWLEDGE Share

The Importance of Draft Angle in Die Casting – Guidelines and Failure Examples

Draft angle is one of the simplest yet most important elements in die casting design. It ensures that the part can be ejected smoothly from the mold without damage, sticking, or deformation . Even a perfect casting can fail if the draft angle is neglected during design.

What Is Draft Angle?

A **draft angle** is a slight taper applied to vertical surfaces so the casting can be removed from the die without dragging or locking.

Without sufficient draft:

* Parts scratch during ejection

* Surface finish deteriorates

* Dimensional accuracy changes

* Mold life is reduced

* Cycle time increases

📐 Recommended Draft Angle Guidelines

✔ For Zinc Die Casting

* Typical draft: **0.5° – 1°**

* Polished surfaces can go down to **0.25°**

* Textured surfaces should have **1° – 3°** depending on texture depth

✔ For Aluminum / Magnesium

Due to higher shrinkage and less fluidity:

* Typical draft: **1° – 2° minimum**

* Textured: **up to 4° or more**

✔ Internal Features

Core pins or deep internal cavities require:

* **More draft** because metal contracts inward

* Sometimes **progressive draft** that increases with depth

⚙ Real Failure Examples

❌ Failure Case 1 – No Draft, Surface Dragging

A telecom connector housing had:

* 0° draft on side walls

* Polished cavity

* Multi-cavity tooling

As casting cooled, it clamped tightly to the cavity walls. The result:

* Scratches on internal surfaces

* Mold showed early wear

* Ejection force increased

* Rejection rate rose over 12%

After adding **1° draft**, parts released cleanly and damage disappeared.

❌ Failure Case 2 – Deep Boss with Insufficient Draft

A deep mounting boss with only **0.3° draft** caused:

* Core pin friction

* Part deformation around pin exit

* Visible “drag lines”

Solution:

* Increased draft to **1.5°**

* Added surface polishing in the boss

* Result: **100% production stability**

🏭 Example from GuangWei Communication Technology

For die cast housings used in AI and telecom equipment:

* All vertical faces follow **DFM draft rules before tooling**

* CAE simulation predicts cooling and shrink behavior

* Mold lines are validated for opening and extraction angle

* Multi-cavity layouts ensure consistent release

A small design update provides:

✔ Lower tool wear

✔ Shorter cycle time (faster ejection)

✔ Better surface quality

✔ Longer mold life

In many cases, adding draft is the simplest and most cost-effective improvement in die casting design.

source : GuangWei Communication Technology.

#DieCasting #DraftAngle