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Common Pressure Die Casting Defects (Porosity, Cold Shuts, Warpage, Short‑Shot) – Root Causes & Practical Fixes

Created on 05.21

Meta Description: Learn the root causes of common pressure die casting defects (porosity, cold shuts, warpage, short-shot) and practical, factory-proven fixes to reduce scrap rates and improve production stability. #die casting defects #porosity in die casting #cold shuts die casting

Pressure die casting is a high-speed, high-pressure process—even small deviations in design, mold, or process parameters can lead to defects. For OEM manufacturers and customers, common defects like porosity, cold shuts, warpage, and short-shot are major pain points: they increase scrap rates (often 10-20% without optimization), cause rework, delay deliveries, and even lead to customer complaints. Especially for new energy battery shells and automotive structural parts, strict air tightness and dimensional requirements make defect control critical. As an experienced pressure die casting OEM, we’ve summarized the root causes and practical fixes for these common defects, helping you achieve stable mass production.

4 Common Pressure Die Casting Defects: Root Causes & Fixes

Below are the most frequent defects in pressure die casting, their root causes (from design, mold, material, and process), and actionable fixes that can be directly implemented in the factory.

1. Porosity (Most Common Defect)

Symptom: Small holes (visible or internal) in the part, affecting air tightness, mechanical strength, and surface treatment (anodizing will bubble). Most common in aluminum alloy die castings.

Root Causes:
Poor venting design: Trapped air cannot escape during high-speed filling, forming air pockets in the part.
Insufficient material degassing: Moisture or gas (H₂, O₂) in the alloy melt is trapped in the part during solidification—aluminum alloy is particularly sensitive to hydrogen, which is the main cause of internal porosity.
Uneven wall thickness: Thick areas cool slowly, leading to gas entrapment and shrinkage porosity.
Excessive injection speed: Air is trapped in the mold cavity due to too fast filling, and the melt cannot fully discharge the air.
Inadequate holding pressure: Insufficient pressure to squeeze out trapped gas and compensate for shrinkage.

Practical Fixes: Optimize venting: Add venting slots (0.03-0.06mm thick) and overflow grooves at the end of the flow path; for large parts or parts with complex cavities, add additional venting pins. Degas the alloy melt: Use a degassing device (nitrogen or argon) to remove moisture and gas—aluminum alloy should be degassed for 5-8 minutes at 680-720℃, and the hydrogen content should be controlled below 0.2ml/100g; zinc alloy can be degassed at 410-430℃ for 3-5 minutes. Adjust wall thickness: Ensure uniform wall thickness and avoid overly thick areas (aluminum alloy ≤5mm, zinc alloy ≤3mm, magnesium alloy ≤4mm). Adjust injection speed: Adopt a segmented speed control—reduce initial injection speed (30-50mm/s) to allow air to escape, then increase speed (80-120mm/s) for full filling; avoid constant high-speed filling. Increase holding pressure: Maintain holding pressure at 80-120MPa (1.2-1.5 times the injection pressure) and extend holding time (5-10 seconds) to squeeze out trapped gas. #porosity solution die casting

2. Cold Shuts

Symptom: A linear or irregular seam on the part surface, caused by two streams of molten alloy meeting without full fusion. Reduces mechanical strength and affects appearance.

Root Causes:
Low alloy temperature: Molten alloy cools too quickly before filling the mold, and the surface solidifies, resulting in incomplete fusion when two streams meet.
Insufficient injection speed/pressure: Alloy streams cannot fuse completely due to insufficient kinetic energy.
Poor gate design: Multiple gates lead to uneven flow, causing alloy streams to meet at different temperatures and speeds.
Excessively low mold temperature: Mold is too cold, causing the alloy surface to solidify quickly, forming a cold layer that prevents fusion.
Long flow path: The alloy loses too much heat during filling, leading to temperature drop and incomplete fusion.

Practical Fixes:
Increase alloy temperature: Aluminum alloy (680-720℃; ADC12: 680-700℃, A380: 690-710℃), zinc alloy (410-430℃), magnesium alloy (650-680℃); avoid overheating (aluminum alloy >730℃ will cause oxidation and grain coarsening).
Increase injection speed (80-130mm/s) and pressure (100-150MPa) to ensure full fusion of alloy streams; for long flow paths, increase speed by 10-20%.
Optimize gate design: Reduce the number of gates or adjust gate position to ensure uniform flow and consistent temperature of alloy streams when meeting.
Adjust mold temperature: Aluminum alloy mold (180-220℃), zinc alloy mold (120-150℃), magnesium alloy mold (150-180℃); ensure uniform mold temperature distribution.
Shorten the flow path: Optimize the pouring system to reduce heat loss during filling. #cold shuts solution die casting

3. Warpage

Symptom: Part deformation after demolding, affecting assembly accuracy. Common in thin-walled parts and parts with asymmetric design.

Root Causes:
Uneven cooling: Mold cooling channels are unevenly distributed, leading to uneven shrinkage of the part during solidification.
Asymmetric part design: Uneven stress distribution during solidification, resulting in deformation after demolding.
Insufficient holding pressure: Incomplete compensation for shrinkage, leading to uneven stress and warpage.
Excessive mold release agent: Uneven application causes uneven cooling and stress concentration.
Incorrect ejection method: Uneven ejection force causes part deformation.

Practical Fixes:
Optimize mold cooling: Ensure cooling channels are evenly distributed (spacing 20-30mm) and add cooling channels in thick-walled areas; use temperature control equipment to maintain uniform mold temperature.
Adjust part design: Make the part as symmetric as possible and add ribs to distribute stress; avoid asymmetric structures and sudden thickness changes.
Increase holding pressure (120-160MPa) and extend holding time (5-10 seconds) to compensate for shrinkage; adopt segmented holding pressure control for complex parts.
Use a uniform amount of mold release agent (dilute to 5-10% concentration) and apply it evenly; avoid excessive application.
Optimize ejection system: Use multiple ejection pins with uniform distribution to ensure even ejection force.
#warpage solution die casting

4. Short-Shot

Symptom: Mold cavity is not fully filled, resulting in incomplete part shape. Common in complex-shaped parts or thin-walled parts.

Root Causes:
Insufficient injection speed/pressure: Alloy cannot fill the entire mold cavity due to insufficient kinetic energy.
Too thin wall thickness: Aluminum alloy ≤1.2mm, zinc alloy ≤0.6mm, magnesium alloy ≤1.0mm, leading to poor flow and incomplete filling.
Blocked gate or runner: Molten alloy cannot flow smoothly due to slag inclusion or mold wear.
Insufficient alloy supply: Not enough molten alloy to fill the mold cavity.
Low alloy flowability: Improper alloy selection or excessive temperature drop during filling.

Practical Fixes:
Increase injection speed (100-150mm/s) and pressure (120-180MPa) to improve filling capacity; for thin-walled parts, increase speed to 130-180mm/s.
Adjust wall thickness: Ensure minimum wall thickness (aluminum alloy ≥1.5mm, zinc alloy ≥0.8mm, magnesium alloy ≥1.2mm); for parts requiring thin walls, select high-flowability alloys (e.g., A380, Zamak-3).
Clean gate and runner regularly to avoid blockages; optimize gate and runner size (gate width should be 1.5-2.0x the wall thickness).
Increase alloy supply and adjust the pouring system to ensure sufficient molten alloy; control the alloy temperature to maintain good flowability.
Optimize the flow path: Shorten the flow path and reduce flow resistance. #short-shot solution die casting

By addressing these root causes and implementing the fixes above, you can reduce scrap rates to below 5% and achieve stable mass production. Our engineering team can help you diagnose defect causes and provide personalized optimization solutions. Contact us for professional support. #die casting defect solutions