People’s expectations for the safety and appearance of die-casting parts are always rising as science and technology develop. The quality of the parts is evaluated differently depending on the application. The primary issue for manufacturers is how to improve the quality and output value of die-casting.

Surface Defects

Aluminum castings are vulnerable to defects such as internal looseness, shrinkage, and porosity throughout the casting process. The surface dense layer parts of these castings with defects are removed after machining, but defects in the internal tissue are still noticeable.

In this article, we’ll go through the different kinds of die case defects, their causes, solutions, and prevention strategies. Let’s begin straight away!

Porosity

In the die-casting process, porosity is a major challenge. The development of pores, holes, air pockets, or indentations on the surface or inside a die-cast object is known as porosity. It is a conditioning phenomenon that weakens a die cast’s structural integrity and causes leaks or corrosion in some areas.

Die castings with pores may experience component failure. As a result, these castings are inappropriate for applications requiring strong structural integrity. There are three primary types of casting porosity.

Cold Shut

These are irregular linear lines on the cast’s surface here. The lines are thin and narrow, with smooth edges that may widen in response to outside pressures. When two liquid metal fronts in the die cavity are improperly fused, cold shut faults in pressure die casting result.

Some of the reasons for cold shut include low molten temperature, slow injection speed, an inefficient gating system, and poor alloy fluidity. Visual examinations will assist you in identifying this defect. Increasing the temperatures of the mold and the molten metal is an effective approach to preventing cold shuts.

Gas Porosity:

This is caused by the creation of bubbles in the cast after it has cooled. Gas porosities are smooth, bright white or yellow surfaces with round or oval structures that are visible on the bodies of die-cast parts. 

Liquid metals can contain a lot of dissolved gas, although most solid metals cannot. As a result, as the solid metal cools, the gas inside it condenses as voids or bubbles inside the cast. You might see some holes in the cast as a result of this happening frequently throughout the solidification process. Gas porosity can result in additional defects and higher scrap rates, depending on how severe it is.

Causes:

• Molten metal alloys released hydrogen.
• Gases used in the filling process for metal alloys.
• Mold-releasing agent gases.

Solutions:

• Make sure the metal alloy ingot is dry and clean.
• Use distinct features, such as injection rate.

Shrinkage Porosity

Metal alloys shrink as they cool, and shrinkage porosity is created during the cooling and solidification stages of casting. As a result, without taking enough security measures, there is a substantial chance that this defect could appear.

Causes:

• An irrational cooling system design.
• An early mold opening.
• Pouring at a very high temperature.

Solutions:

• Improve the casting structure overall.
• Add ribs, cooling coils, or internal chills to better dissipate heat.
• Reduce total volume deficits by adjusting the casting temperature.

Dimensional Defects

Shrinkage

The process of solidification results in shrinkage defects. Open shrinkage defects are observed on the surface of castings, while closed shrinkage defects appear within the casting when isolated pools of liquid are permitted to form within the solidified metal.

Causes

• The distribution of the mold gradient is irrational, and the pouring temperature is too high.
• Both the boost pressure and the injection ratio are too low.
• The area is too small, and the inner gate is thin.

Solution

• Reduce shrinkage and lower the pouring temperature.
• Improve compactness by increasing injection and boosting pressure.
• Accelerate the cooling of thick parts.

Warping

Warping is an unwanted casting defect that can develop over time and change the final product’s dimensions. It may take place either before or after solidification. Aluminum casting may need straightening of the quench and aging operations.

Misruns and Cold Flows

A cold shut is a form of surface imperfection. The surface of the casting will have a line or crack with a circular edge. This defect appears to the naked eye and frequently leads to the cast being rejected since it leaves a weak point. Increasing the fluidity of the molten metal is the most effective approach to stopping cold closures.

Misruns happen when the liquid metal is too cold to flow to the mold cavity’s edges before it freezes and solidifies.

The causes of early solidification and cold shut are linked. Check these if you have a misrun:

• Mold design
• Gating system design
• Fluidity of molten metal

Distortion

Distortion in castings usually comes from stress, such as shrinkage restrictions in the mold. The stresses are enough to distort the components if they are released during mold removal. These stresses could cause cracks if the casting is removed at higher temperatures.

Mechanical Property Defects

Hot Tears

As the molten metal cools, the residual stress in the material causes the casting to fail since the metal is weak when it is hot. The casting failure in this instance appears as cracks and is referred to as hot tears or hot cracking.

Causes

• Ineffective mold design.

Solution

• These casting defects can be easily avoided with proper mold design.
• The removal of residual stress from the casting’s substance.

Cracks

Cracks happen when the material breaks due to internal and external stress. They arise as uneven or linear patterns on die-casting surfaces. The very first crack appears during the cooling and solidification process.

This defect can be avoided by enhancing the component’s structure and ensuring uniform wall thickness. Another effective remedy for this casting defect is balanced die-casting part ejection.

Inclusions

These are asymmetrical holes on the casting’s surface or inside. Inclusions are undesirable sand, material, dross, or deoxidation products that are present in metal casting.

Causes:

• Metal impurities brought on by defective purification or pollution from waste.
• Poor purity in the furnace charge.
• Excessive graphite content in mold release agents.

Solutions:

• Verify the purity of the furnace charge.
• Proper metal liquid purification, including complete slag removal.
• Carefully clean the ladles and die cavity.

Aluminum die casting is a manufacturing method that delivers perfectly shaped, textured, and smooth metal parts. A casting defect is a flaw in the metal casting process. Certain defects can be tolerated, while others must be fixed or removed. They can be divided into five basic groups: metallurgical defects, gas porosity, shrinkage defects, mold material defects, and pouring metal defects.