Top 5 Die Casting Defects and How to Avoid Them

Die casting is a widely used manufacturing process that enables the production of complex metal parts with high precision and efficiency. What is casting in the manufacturing process? Casting is a manufacturing method where molten metal is poured into a mould cavity to solidify and form the desired shape. In the case of die casting, a reusable mould called a die is used, which allows for the production of multiple parts with consistent quality.

However, like any manufacturing process, die casting is susceptible to various defects that can compromise the quality and functionality of the final products. Understanding die casting defects and taking proactive measures to address them is vital for successful operations.

This blog discusses the top 5 die casting defects and some effective techniques to avoid them. By understanding these defects and implementing preventive measures, manufacturers can enhance the quality of their die casting processes, reduce production costs, and deliver superior products to their customers.

Five Common Die Casting Defects & their Solutions

1. Cold Shut

Cold shut is a common type of casting defect where two or more streams of molten metal fail to fuse properly, resulting in incomplete casting formation. This defect occurs due to several reasons, such as inadequate molten metal temperature, improper gating or runner design, or fast injection speed. When the molten metal does not merge completely, it leads to visible lines or gaps on the surface of the casting, affecting its structural integrity and aesthetics.

How to Prevent?

1. a)Maintain proper molten metal temperature for proper flow and fusion during the filling of the die cavity.
2. b)Optimise gating and runner design like gate size, location, and shape for smooth and even flow of molten metal into the die cavity.
3. c)Employ a controlled injection speed for better filling and fusion within the die cavity.
4. d)Ensure proper venting in the die design for the escape of air and gases during the filling process.
5. e)Consult with material suppliers and select suitable alloys with higher fluidity and better fusion characteristics for reduced defects.

 

2. Porosity

 

Porosity is a common defect in die casting characterised by the presence of small voids or air pockets within the casting material. These voids can range in size and distribution, and they can significantly impact the mechanical properties and structural integrity of the casting.

Porosity occurs due to various factors, including:

• Gas entrapment
• Non-Uniform Cooling or Shrinkage
• High melt temperature
• Improper gating and venting

How to Prevent?

1. a)Implement metal degassing techniques, like vacuum or inert gas degassing to help remove dissolved gases from the molten metal.
2. b)Proper temperature control ensures the optimal balance between fluidity and gas content.
3. c)Well-designed gating systems promote proper metal flow and minimise turbulence, reducing the chances of gas entrapment during casting.
4. d)Preheat the die mould before casting to help minimise thermal gradients and ensure uniform cooling.
5. e)Consult with material suppliers and select alloys with lower gas absorption tendencies to mitigate porosity issues.

3. Shrinkage

Shrinkage is a common type of casting defect characterised by the presence of voids or discontinuities in the casting due to inadequate material flow and solidification. It occurs when the molten metal undergoes a reduction in volume during the cooling and solidification process.

Shrinkage defects can occur for various reasons, including:

• Insufficient feed metal
• Improper cooling rate
• Alloy composition

How to Prevent?

1. a) Design an effective gating and runner system for sufficient feed metal flow to compensate for shrinkage.
2. b) Use cooling channels in the die mould, as well as control mould temperature for uniform cooling and solidification.
3. c) Place properly designed risers for additional material to flow into the casting as it shrinks.
4. d) Collaborate with material suppliers and consider alloy properties with  lower shrinkage rates or wider solidification ranges.

 

4. Flash

Flash is a common defect in die casting characterised by the occurrence of thin, excess metal projections or fins on the surface of the casting. It happens when molten metal escapes from the mould cavity through small gaps or spaces between the mould halves or other mating surfaces.

Flash defects in casting process can occur due to several reasons, including:

• Improper mould closure
• High injection pressure
• Poor mould maintenance

How to Prevent?

1. a) Ensure precise alignment of the mould halves and apply sufficient clamping force. Conduct regular maintenance and inspection of the mould to identify any misalignments or worn-out components.
2. b) Control the injection pressure and velocity to set the injection parameters within the recommended range for the specific casting and mould design.
3. c) Regular cleaning, lubrication, and repair of the mould surfaces maintains their integrity.
4. d) Utilise well-designed gating and venting systems for controlled metal distribution and the escape of trapped air or gases.
5. e) Implement regular monitoring and inspection protocols during the casting process to identify any deviations or potential flash issues in real-time.

5. Gas Porosity

Gas porosity is a common defect in die casting characterised by the presence of gas-filled voids or bubbles within the casting material. These voids can vary in size and distribution, and they can negatively impact the mechanical properties and structural integrity of the casting.

Gas porosity occurs due to several factors, including:

• Entrapped air
• Dissolved gases
• Moisture content

How to Prevent?

1. a) Implement degassing techniques like vacuum or inert gas degassing to remove dissolved gases from the molten metal.
   b) Ensure adequate venting in the die mould for the escape of air and gases during the filling process.
   c) Optimise gating and runner systems to promote smooth and controlled metal flow, reducing turbulence and the likelihood of gas entrapment.
   d) Preheat the die mould before casting to reduce the chances of moisture or steam vaporisation during the filling process.
   e) Consult with material suppliers and select alloys with low gas solubility.

 

To summarise, understanding and addressing common die casting defects is essential for producing high-quality castings with optimal aesthetics and functional properties. Manufacturers can significantly reduce the occurrence of casting defects and remedies can turn out helpful in enhancing overall casting quality.