Understanding Shrinkage Porosity Casting Defects and remedies and Simulation Insights with Gravity die casting simulation software – ADSTEFAN

Gravity die casting is a widely used manufacturing process known for producing high-quality metal parts. However, one of the persistent challenges in this method is the formation of shrinkage porosity defects. These voids can compromise the integrity of the casting, leading to decreased mechanical properties and surface quality. In this blog, we will explore the Shrinkage Porosity Casting Defects and remedies and how Gravity die casting simulation software – ADSTEFAN simulation software can help shrinkage porosity prediction and manage these defects effectively.

What is Shrinkage Porosity?

Shrinkage porosity is a type of casting defect characterized by the presence of small voids or cavities within the casting material. These voids occur due to insufficient feeding of molten metal during solidification, resulting in localized shrinkage and the formation of pores within the casting.

Density of a casting alloy in the molten state is less than its density in the solid state. So, alloy changes phase from the molten state to the solid state and it always shrinks in size. This shrinkage takes place when the casting is solidifying inside a die and shrinkage can end up as many small voids known as ‘Shrinkage Porosity’.

Causes of Shrinkage Porosity in Gravity Die Casting

1. Inadequate Feeding:
   • As the metal solidifies, it shrinks. If there isn’t enough molten metal available to fill the voids created by this shrinkage, porosity will result. This often occurs in thick or complex sections.
2. Cooling Rate:
   • Rapid cooling can lead to uneven solidification, where certain areas cool and solidify faster than others. This can create hotspots increasing the likelihood of porosity.
3. Poor Gating design:
   • Poor Gating design can lead to inefficient metal flow and inadequate feeding systems. Complex geometries or poorly placed risers leads to shrinkage porosity casting defect.
4. Alloy Selection:
   • Different alloys have varying solidification behaviors. Alloys with high shrinkage rates are more susceptible to forming porosity if not properly managed.

Remedies for Shrinkage Porosity

1. Optimize Methoding/Gating Design:
   • Incorporate risers and feeders strategically to ensure that molten metal can compensate for shrinkage. Proper gating systems should facilitate smooth metal flow.
2. Control Pouring Temperature:
   • Increasing the pouring temperature can enhance fluidity, allowing the molten metal to fill the mold more effectively and reduce the risk of shrinkage porosity.
3. Adjust Cooling Rates:
   • Implementing techniques to control cooling rates can promote directional solidification. This may include using insulating materials or optimizing cooling channels and utilization of chills for directional solidification.
4. Material Selection:
   • Choosing alloys with lower shrinkage rates can help reduce the likelihood of porosity. Conduct thorough research on the properties of different materials before selection.

Predicting Shrinkage Porosity with ADSTEFAN

ADSTEFAN is a powerful casting defect prediction software that aids in predicting and addressing shrinkage porosity in gravity die casting. Here’s how it can be beneficial:

1. Comprehensive Simulation:
   • ADSTEFAN simulates fluid flow, solidification and thermal analysis during the casting process, allowing users to visualize how molten metal behaves in the die during filling, solidification stage and identify potential areas for porosity.
2. Gating optimization:
   • The software enables users to experiment with different die designs and gating systems to find the most effective configuration for minimizing porosity.
3. Material Property Analysis:
   • Users can input various material properties to see how different alloys might behave under specific casting conditions, helping to select the best materials for the application.
4. Cost Efficiency:
   • By predicting potential defects before production, ADSTEFAN reduces the need for costly trial-and-error approaches, saving time and resources.

Case study for shrinkage porosity using GDC simulation software – ADSTEFAN

Above figure demonstrates defect mapping of shrinkage porosity casting defect for Gravity Die casting process with ADSTEFAN simulation shrinkage porosity prediction results. Root cause of defect is identified as isolation during solidification are observed in casting in ADSTEFAN results. Due to this isolation during solidification is observed in cavity which leads Shrinkage porosity in casting and same phenomenon is observed in shop floor trails.

Preventive action taken on component by modifying gating design to provide proper gating design and optimized feeders and thus shrinkage defect is controlled. This gating optimization is carried out in ADSTEFAN and best gating design are considered in shop floor trails thus leading to elimination of shrinkage porosity defect in shopfloor. By performing corrective actions using ADSTEFAN casting defect simulation, we are able to reduce shop floor trails, production, and development time of component.