Die Casting Draft Angle and Parting Line

Draft angle is the taper applied to walls that run in the direction of die opening. It allows the casting to leave the die without dragging, scoring or cracking the part.

The amount of draft needed depends on wall depth, surface texture and the alloy. Deep walls and textured surfaces need more draft because the contact area and friction are higher.

• Draft allows clean ejection from the die
• Deep walls need more draft
• Textured surfaces need more draft
• Insufficient draft shows up as drag marks and tool wear

For many aluminum die casting features, 1° to 2° of draft is a practical starting point. Short features can sometimes use less, while deep bores, ribs and textured faces generally need more.

Zinc alloys often reproduce fine detail with slightly lower draft on short features, but the same principle applies: the deeper the feature, the more draft it needs.

• 1–2°: common starting range for aluminum
• 0.5°: possible on short, smooth features
• 3° or more: deep walls and heavy texture
• Confirm values feature by feature

The parting line decides where flash appears and which faces can be formed in one half of the tool. It should be placed on a surface where flash is acceptable or can be removed without damaging a cosmetic area.

If a feature cannot be formed in the direction of die opening, a slide or side core is required. That adds tooling cost and maintenance, so it should be a deliberate design decision.

• Place the parting line away from cosmetic faces
• Plan for flash removal
• Avoid unnecessary side cores
• Document the accepted parting line direction

Texture, anodizing, powder coating and polishing all interact with draft. A textured surface increases friction during ejection and may need an extra degree of draft or a change in texture depth.

Deep ribs, bosses and pockets should be reviewed together with draft and filling. A feature that is easy to draw may still be difficult to fill, vent or eject in volume production.

• Texture increases the required draft
• Review deep features for filling and venting
• Plan polishing and coating before tooling
• Lock the values into the controlled drawing