When designing parts for die casting, several key DFM guidelines should be emphasized to ensure manufacturability, quality, and cost-effectiveness:

1. Wall Thickness Optimization

Maintain uniform wall thickness throughout the part, typically 1.5-3.0 mm for aluminum alloys and 0.75-2.5 mm for zinc alloys. Avoid sudden thickness changes greater than 1.5× between adjacent zones, as uneven sections cause turbulence in metal flow, leading to porosity and irregular shrinkage. Increasing wall thickness from 2.5 mm to 5 mm can increase cycle time by 15-25% due to slower cooling.

2. Draft Angles

Apply draft angles to all surfaces parallel to the ejection direction. External walls should have at least 1° draft, while internal cavities require minimum 2° draft. For deep features (50 mm depth), use 3-4° draft. The general rule is to add 1° of draft per 25 mm of cavity depth. Textured surfaces require additional draft - add 1° per 0.1 mm of texture depth. Zero draft angles can increase reject rates by 25-35% due to sticking and ejection marks.

3. Fillets and Radii

Eliminate sharp corners completely. Use minimum internal radii of 0.75 mm or 0.5× wall thickness + 0.25 mm, and external radii of at least 1.0 mm. Sharp corners increase local stress by 2-3 times and can reduce tool life by up to 30%. Always use compound fillets at rib-to-wall junctions (1.0-1.5 mm) to avoid cold shuts and improve metal flow.

4. Rib and Boss Design

Ribs should be 0.5-0.7× the adjacent wall thickness to avoid sink marks. Rib height should be ≤ 2.5× rib thickness, with spacing ≥ 3× rib thickness to prevent heat buildup. Bosses should be hollow with fillets ≥ 0.5 mm and height ≤ 4× wall height to prevent voids and sink marks. Always add draft angles to ribs and bosses (≥1°).

5. Parting Line and Ejector Pins

Keep the parting line as straight or flat as possible. Design ejector pin locations carefully to minimize visible marks. The parting line should be perpendicular or parallel to the main axis of the part to reduce mold machining difficulty and improve part accuracy.

6. Undercuts and Slides

Avoid holes and undercuts parallel to the parting line whenever possible. Sliders (side cores) are costly and increase tooling complexity. If undercuts are necessary, work with the die caster to simplify the design and minimize the number of slides required.

7. Material Selection

Choose alloys based on wall thickness requirements and application needs. Aluminum A380 is most common for general applications, while zinc alloys (Zamak 3) offer superior fluidity for thin-walled parts. Magnesium alloys (AZ91D) are ideal for ultra-lightweight applications but require coating for corrosion protection.

8. Surface Finish Considerations

Die cast parts typically achieve surface roughness of 16-64 microinches (Ra). Highly polished tooling surfaces result in better part finishes. Raised logos and identification marks are easier to produce than recessed ones.

By following these DFM guidelines, you can significantly reduce reject rates, improve tool life, and optimize production costs. A practical example shows that redesigning an ECU housing with proper fillets (≥2 mm) and uniform wall thickness reduced reject rates from 18% to below 4% while doubling tooling maintenance intervals.