In die-casting mold design, gate location determines 90% of final yield rate, including porosity, cold shuts, and poor filling. Especially for long, rectangular die-casting shells with bosses, should gate be placed on long side or narrow side? Should it be a flat gate or a ramp gate?

 

Many mold makers rely on experience to make decisions, resulting in batches of porosity, air blockage, and incomplete filling at the end after mass production, leading to repeated mold modifications that are time-consuming and costly.
Today, we'll use a full mold flow comparison of three gate schemes for a long, rectangular cap, combined with ADC12 die-casting industry standard, to explain everything clearly in one go:
How to select, place, and judge quality of gates for long, rectangular die-casting parts. After reading, you can directly apply this to your mold design.

Product analyzed: Long, bulging top cover
Material: ADC12 aluminum alloy (the most commonly used alloy in die casting, prone to oxidation, air entrapment, and extremely sensitive to gate flow patterns)
Dimensions: 100mm * 50mm, with a long, hollowed-out section in the middle and mounting platforms at both ends; a typical long, bulging shell die casting part.
Core Risks: Hollowed-out structure easily causes flow turbulence; air trapping at cavity ends; and air entrapment due to backflow on sidewalls.
Following three completely different gate schemes all use fan-shaped gates, with injection from long side, narrow side flat, and narrow side sloping, respectively. Mold flow parameters are unified: pouring temperature 620℃, grid 0.3mm, ingate velocity 40m/s, for a fair comparison of flow patterns and venting effects.

Scheme Structure: Long, rectangular gate with a fan-shaped flat gate. Injection is along long side, with the gate at a 90° angle to product. Molten metal impacts product wall directly after passing through gate, spreading out in a fan shape towards top for filling.

 

Simulation Conclusions: Simulated flow pattern is similar to prediction; flow pattern is a wraparound filling pattern, with filling end at keyway rear end. Gas content results indicate a higher risk at this location, as some gas is trapped and cannot escape.
Industry Pain Point Analysis (Benchmarking GB/T 11350-2019 Die Casting Structural Design Specification)
1. 90° direct-impact gating is a design taboo in die casting: ADC12 high-speed molten metal directly impacts sidewalls, easily generating turbulence, air entrapment, and oxide inclusions.
2. This product uses long-side gating under long conditions, resulting in an excessively long filling path. Keyway at the end of cavity becomes final filling area, preventing gas from overflowing through parting surface and creating high-pressure trapped air.
3. Enveloping flow pattern traps air inside cavity within material flow, leading to a surge in end-hole porosity, pinholes, and airtightness leaks after mass production. This is core reason for scrapping of many long shell molds.
Mass Production Forecast: Solution 1 can only achieve complete filling, with a mass production yield of less than 60%. End-hole porosity defects cannot be eliminated through process optimization, making it an unqualified gating solution.

Scheme Structure: Long, rectangular cap, fan-shaped sloping gate, narrow-side feed. Molten metal flows directly towards top of product according to gate's guidance, then diffuses to side walls, simultaneously filling rear.

 

Simulation Conclusion: Simulated flow pattern differs from prediction; molten metal directly fills rear through top surface, and side walls are filled by reflux of molten metal from rear, resulting in the end point appearing on both sides of gate's side walls; this gate design is unsuitable.
Industry Pain Points Analysis
1. Ramp gate design has excessively strong directional force, causing molten metal to rush directly to the top surface. Sidewall areas can only be filled by molten metal recirculation, inevitably leading to air entrapment and slag buildup during recirculation process.
2. Sidewalls of gate become final filling area, causing trapped air to concentrate around gate, directly forming porosity and pitting on product's surface.
3. Recirculation filling process has extremely poor interface integration, easily resulting in cold shuts and weld lines. Shell structure is also highly susceptible to cracking under stress.
Mass Production Forecast: Scheme 2 has the highest degree of flow turbulence, with a mass production yield of less than 50%. It exceeds standards for both external and internal defects, making it a completely unqualified gate design.

Scheme Structure: Long, rectangular cap; fan-shaped flat gate; narrow-edge feed; gate angle 90° with product; molten metal impacts product wall directly after passing through gate, spreading out in a fan shape towards top and rapidly filling both sides along curved surface.

 

Simulation Conclusions: Simulated flow pattern is close to prediction; metal at the top surface flows faster than through side walls, and flow ends precisely at parting surface, making overflow system arrangement more efficient.
Industry Advantages Analysis
1. Narrow-edge gating matching long-condition filling logic, fan-shaped flat gating gate forms an orderly laminar flow, with no obvious backflow or severe turbulence, significantly reducing risk of gas entrapment;
2. Filling end precisely lands on parting surface, allowing gas to be directly discharged from cavity through overflow grooves and venting grooves, perfectly conforming to die-casting "end-entry and venting" design principle;
3. Arc surface guides material flow to spread evenly, ensuring good synchronization of filling on both sides of hollowed-out area, controllable weld line position, dual protection of appearance and internal density.
Mass Production Forecast: Scheme 3 is the only qualified scheme among three schemes. After optimizing overflow system, mass production yield can stably reach over 90%, with a significant reduction in porosity and cold shut defects, making it preferred gating form for long, bulging shell-type die-casting parts.

Based on comparison of three schemes and design guidelines for ADC12 aluminum alloy die casting, here are three ironclad rules for our peers:
1. For long, narrow shells, prioritize narrow-side gating; be cautious with long-side gating.
Long-side gating results in an excessively long filling path, making it prone to air trapping at the end. Narrow-side gating offers more controllable flow and makes it easier to guide end to parting surface.
2. Use ramped gates with caution; flat gating is more versatile.
Mounted gates have excessive directional force, easily causing backflow and are only suitable for simple flat parts. For bulging shells, prioritize flat-side fan-shaped gating for more uniform material flow.
3. Ultimate goal of gating design: ensure filling end lands on parting surface.
80% of all porosity problems in die casting are caused by air trapping at the end. If end lands on parting surface, 80% of defects can be solved by using venting channels.