Contents
Introduction
You designed a perfect part. The dimensions are exact. The geometry is complex. But when you try to remove it from the die, it sticks. You pull harder. The part bends. The die surface gets scratched. Now you have scrap parts and lost time.
This happens when draft angle is overlooked.
In die casting, draft angle is a small taper on vertical surfaces. It usually measures between 0.5 and 3 degrees. Its job is simple: let parts come out of the die without damage.
Think of a baking pan. If the sides were straight up, your cake would never come out. The slight slope in the pan lets it release cleanly. Die casting works the same way.
This guide explains why draft angle matters. You will learn how to choose the right angle for your material and part shape. You will see real examples of what happens when angles are wrong. And you will get practical rules you can use today.
What Exactly Is Draft Angle?
The Simple Definition
Draft angle is the slope added to vertical walls of a die casting part. It creates a slight taper from the parting line to the deepest point of the cavity.
Without this slope, the part would have parallel walls. When the metal cools and shrinks, it grips the die tightly. Removing it requires force. That force can:
- Scratch the die surface
- Distort the part shape
- Crack thin sections
- Wear out ejection pins
With the right draft, the part slides out smoothly. The friction drops. The die lasts longer. Your rejection rate falls.
How Draft Angle Works
When you add draft, you create a gap. As the ejector pins push the part, one side releases first. The part tilts slightly, breaking the vacuum and reducing contact area.
Here is a simple comparison:
| Without Draft | With Draft |
|---|---|
| Full surface contact | Reduced contact area |
| High friction force | Low friction force |
| Risk of sticking | Smooth ejection |
| Potential part damage | Clean part release |
What Happens When You Get Draft Angle Wrong?
The Sticking Problem
A manufacturer made aluminum housings with zero draft on a 50 mm deep wall. Every cycle, the part stuck. Operators increased ejector pin force. The pins broke. Then the die surface scratched.
They added 1.5 degrees of draft. The sticking stopped. Ejector pin life increased by 300%. Scrap rate dropped from 8% to under 1%.
When your part sticks, you lose more than time. You lose die life, tooling reliability, and production consistency.
The Dimensional Failure
Draft affects dimensions. If you design without considering it, your finished part may not fit assembly.
Real example: An automotive supplier made a steering knuckle with 0.5 degrees of draft on a critical mounting surface. The mating part required a flat surface. The draft caused a gap. Assemblies failed.
They had to recut the die at a cost of $15,000 and lost 3 weeks of production.
Draft must be planned from the start. Adding it later is expensive.
The Surface Damage
Too little draft creates drag marks. As the part slides out, sharp edges of the die scrape the surface. This is visible on cosmetic parts.
A consumer electronics company made handheld device housings. With 0.5 degrees of draft, they saw visible drag lines. Increasing to 1 degree eliminated the marks. They saved $2 per part in secondary finishing.