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An aluminum die casting draft angle is the taper built into a wall so the part can leave the die. It is easy to draw a vertical wall. However, that wall increases friction, scuffing and ejection damage. The useful question is not “What is the standard angle?” It is “What angle keeps this feature stable during filling, cooling and ejection?”
How the aluminum die casting draft angle changes with depth
A shallow feature has less contact area with the die than a deep pocket. As depth increases, the casting contracts onto cores and pulls against more of the die surface. A small angle that works for a 5 mm feature can be inadequate for a 50 mm wall.
Draft also creates clearance along the direction of movement. One degree per side creates a small offset at the opening. The same angle creates more clearance near the bottom of a deep pocket. The die designer must check this against alloy shrinkage and expected tool wear.
A practical aluminum die casting draft angle range
For many ordinary aluminum die-cast surfaces, a starting range of 1–3 degrees per side is common. This is a planning range, not a universal rule. A supplier may request less draft on a short outside wall. Deep cores, textured faces and difficult ejection areas often need more.
Use the aluminum die casting draft angle as a starting assumption in the CAD model. Confirm the final value during tooling review.
| Feature | Starting consideration | What to review |
|---|---|---|
| Short outside wall | Lower end of the range | Shrinkage, die polish and cosmetic finish |
| Deep pocket | Higher draft | Core depth, draft on both sides and knockout support |
| Textured surface | Additional draft | Texture depth, grain direction and die release |
| Inside core | Generous draft | Contraction onto the core and removal clearance |
Do not assign one angle to the entire model without checking the pull direction. A surface that is “vertical” in the CAD view may be an inside wall. It may also be an outside wall or a surface that moves relative to both die halves.
Dynacast provides related guidance in its article on design tips for improved die casting.
Texture and coating change the release condition
A textured aluminum casting has more surface contact than a polished one. The peaks and valleys can increase friction. The texture must be applied in a way that does not create an undercut. Deep decorative grain often requires more draft than a smooth engineering surface.
Surface treatments applied after casting usually do not change the required draft. They can change the final dimension and appearance. If the part will be anodized, powder coated or painted, the drawing should identify the finished surface. It should also show where a parting line or ejector witness is acceptable.
Where draft causes trouble in the CAD model
Draft operations can fail around small fillets, split faces or features that cross the parting line. Check the model after applying draft instead of assuming the software has produced a continuous surface. A local error can create a sharp vertical patch that is difficult to polish and likely to drag.
- Add draft before the final fillet and rib detail.
- Check that adjacent drafted faces do not create a knife edge.
- Keep the intended pull direction visible in the model or drawing notes.
- Do not draft a surface that is expected to be machined later unless the cast stock is controlled.
Draft is not a substitute for good rib design
Deep ribs can reduce material and improve stiffness. They also create narrow steel sections in the die and difficult conditions for alloy flow. Too little draft on a tall rib may produce drag marks. Too much draft can reduce the bearing area at the tip.
Review ribs as part of the whole section, not as isolated lines. A gradual root transition and a sensible tip radius help more than adding draft to weak geometry.
What the die caster needs for the draft angle decision
Provide the CAD model and a drawing with the pull direction. Add a clear statement of cosmetic requirements. Mark any surface where a draft or parting-line witness cannot be accepted. Explain whether the relevant dimension applies as cast, after machining or after coating.
If a feature is already fixed by an assembly, send the mating part or a section view. It is easier to redesign a small boss than to add a complex side action. A short design review can show whether the angle is truly necessary or whether the feature can be moved.
Inspection should match the function
Draft is usually checked through the resulting geometry. The angle does not need to be measured after every shot. Check the features that affect fit, wall thickness or pull direction. For a cosmetic wall, inspect for dragging and cold shuts under the agreed lighting.
The first article should confirm that the die and process produce the intended taper without flash or local deformation. If the result is marginal, changing the die is more expensive than changing the drawing before tooling starts.
Draft-angle checklist
- Identify each feature as inside, outside or cross-parting-line.
- Relate the angle to depth, texture and ejection direction.
- Use a supplier-approved value rather than a copied table.
- Confirm the drafted model is watertight and free of narrow slivers.
- Resolve cosmetic witness marks before die construction.
- Include the pull direction and surface requirements in the RFQ.
For the surrounding decisions, read our aluminum die casting design guide. If your model already has a tight assembly requirement, send the drawing and mating details for a review of the die opening, draft and machining route.