Designing Draft Angles That Do Not Fight the Die
What draft does
As a die-cast part solidifies it shrinks onto the male core and pulls away from the female cavity. Without draft, ejection drags the skin across the steel, causing galling, lubricant streaks and dimensional distortion. Draft converts sliding release into clean separation.
Typical practice is 1 to 2 degrees on most external walls and often more on internal cores, which shrink tightest. Deep features, ribs and bosses need proportionally more draft because friction accumulates along their length.
Why draft is not free but is cheap
Every degree of draft slightly changes wall thickness and assembly fit, so designers sometimes resist it. The alternatives, however, cost more: slide cores for undercuts, longer cycle times from slow ejection, or higher scrap from damaged skins. A planned draft almost always wins economically.
Where a true vertical face is functionally required, for example for a sealing face, it should be localized and the tooling planned around it rather than applying zero draft globally.
Design checklist
Review castings for: draft on all walls perpendicular to the parting line, extra draft inside deep cores, draft continuity where a feature crosses the parting line, and allowance for draft at texture or machined datums. Machining stock removes draft locally, so datum selection matters.
Our engineering team reviews customer 3D models for draft as part of standard DFM feedback, typically returning marked-up suggestions before tooling kickoff.
FAQ
How much draft should I add to my part?
Common starting points are 1–2 degrees on external walls and 2–3 degrees or more on internal cores and deep ribs. The exact values depend on depth, alloy and surface finish requirements.
Can die casting be done with zero draft?
Only with special measures such as slides, increased ejection systems and higher tooling cost, and still not truly zero in most geometries. Some draft is normally the economical answer.
Does draft affect machining datums?
Yes. Drafted faces are not parallel to the axis, so datums for machining should be chosen on drafted or cast features deliberately, and machining stock accounts for local draft removal.
Is draft direction ever ambiguous?
It can be. Where a wall could draft toward either die half, moving the feature or adding a slide changes the draft direction; this is exactly what DFM review resolves before tooling.
All figures above refer to standard product data sheets; final confirmation is subject to written quotation.