11 Common Die Casting Defects – Causes and Solutions

Die Casting Defects - Causes and Solutions

What are die-casting defects, and what can you do to prevent them? When casting parts, you want them to be error-free. That can only happen if you follow proper casting rules. Here, we take you through a list of these defects and their causes. We also discuss the steps to take to avoid them.

What are Die Casting Defects?

Die-casting defects are unwanted features that occur when die-casting parts using various metals or alloys. They may be internal and invisible to the naked eye or superficial and easily identifiable. They could also be dimensional, as explained below.

Surface Defects

Surface defects are external and easily visible. They can be of many types, from depressions to holes or flashes. Their presence may affect the functionality of your part. But they also make the part less appealing visually and cause it to appear to be of low quality.

Internal Defects

These occur internally and are difficult to visualize from the outside. They’re primarily voids from trapped gases or cracks resulting from shrinkage and other causes. You can only see them with X-rays and other imaging techniques like ultrasonic tests. Internal defects weaken your part.

Dimensional Defects

Dimensional imperfections are variations in measurements that affect the size and shape of the part. In addition to causing aesthetic issues, these defects make your part unusable in its intended application. So you want it within specified geometries.

Analyzing defects in casting
Analyzing defects in casting
Resource: https://www.youtube.com/watch?v=de9xgRg43eg

Die Casting Defects Causes

There are various causes of die-casting quality issues. They include trapped gases, wrong material composition, incorrect machine and casting parameters, and the use of low-quality agents to release parts.

Trapped Gases

Trapped gases cause voids in the finished part, weakening its structure internally or causing spots on the surface and opening in a machined surface. Some gases, such as hydrogen, may result from the decomposition of moisture or mold-release materials. The melt may also trap air.

Incorrect Alloy Composition

Some alloys cannot be die-casted. The metals must be high quality and contain no impurities when they can. Impurities cause problems, and so does inconsistency in the melt composition. The molten metal may not flow as intended, among other issues.

Die casting Machine Problems

Most casting quality issues are machine-related. You may be setting the machine to incorrect values, or the various components are worn out, deformed, or damaged in any other way. The different parts, particularly the mold or die, could be structurally poor, or you could be using surfaces containing impurities.

Low-Quality Release Agents

Mold-release materials have their share of problems, but only if you use low-quality types. They cause parts to come out with surface defects. Incorrect amounts of the release agents are also another cause of imperfections.

Casting surface defects

Types of Die Casting Defects

Die-casting defects occur in various ways, giving rise to unwanted features in the finished products. Below is a list of these casting defects, how to identify them, and their possible causes.

1. Porosities

These defects result from pockets of air trapped in the melt. They are usually small, round, or oval holes on the part surface. They can also be internal voids that you can only visualize using X-ray equipment, ultrasonic waves, and other means.

Main Causes:

  • Gases from mold-release materials
  • Hydrogen from the decomposition of moisture and mold greases
  • Turbulence in the melt that causes gases to get trapped

2. Cracks

These are surface defects that appear as openings. The openings are either hot or cold. Hot cracks have oxidized material, while the other types do not. Cracks make your part weak and low-quality looking.

Main Causes:

  • Wall thickness inconsistencies
  • Extended part-formation time
  • Excessive levels or too low amounts of an element in the alloy
  • Low die temperatures
  • Incorrect ejection

3. Soldering

The die casting soldering defect happens when a part of the melt attaches to the die surface. As a result, some sections of the casted part appear to have more or less material than others. Unlike internal imperfections, these irregularities are visible to the eyes and easily identified.

Main Causes:

4. Blisters

Blisters are raised parts on the surface of the die-casted part. They are surface errors and are identifiable by visually inspecting the part after ejection. They have various causes.

Main Causes:

  • Trapped gasses
  • Using excessive mold-release materials
  • Temperatures being too high

5. Flashes

Flashes are material excesses that look like thin sheets on the edges. They’re irregular and not part of a casted product. Flashes are also prominent imperfections you cannot miss when inspecting a part.

Main Causes:

  • Excess melt injection speeds
  • High filling temperatures
  • Worn or damaged parts of the die
  • Low clamping forces

6. Deformation

Deformation is said to occur if the dimensions of the finished part do not match those of its design or drawing. This irregularity type is confirmed by taking measurements of the finished part.

Main Causes:

  • Incorrect ejection system structure
  • Shrinkage caused incorrect mold design
  • Opening the mold too early
  • Contaminated parting components
  • Damaged casting machine hinges

7. Sinks

These are saucer-like depressions on the surface that are not part of the mold geometry. They’re typically seen on the thick-walled sections and are visible when inspecting your casted part.

Main Causes:

  • Partial heating of the die
  • Shrinkage from uneven wall thickness
  • Low injection pressure
  • Improper venting that results in compression
  • Insufficient holding time
  • Wrong gating position

8. Laminations

A die-casting lamination defect is a layered imperfection on a parting line. It indicates excessive material in the various parts of the casting machine, specifically the inserts and sliders.

Main Causes:

  • Die cavity contaminated with materials
  • Problems with mold structural strength
  • Incorrectly designed gating
  • Plunger movement problems

9. Inclusions

These are openings visible on the part surface or internally located holes that you can only see using X-rays. Inclusions affect the mechanical strength of the product.

Main Causes:

  • Contaminated casting equipment or melt
  • High levels of graphite in the release agent
  • A poor gating system

10. Flow Marks

Flow marks are directional (or non-directional) streaks occurring on the surface. When directional, they align with the melt flow. They also have a different color than the core alloy.

Main Causes:

  • Excessively low die and filling temperatures
  • Using excessive mold-release materials or lubricants
  • Splashing of the melt due to improper gating
  • Slow filling speed
  • Inadequate venting

11. Short Filling

These casting defects appear as areas with inadequate material. Short filings are visible on the part surface and can have various causes.

Main Causes:

  • Low part ejection pressures
  • Excessive use of release agents
  • Poor melt flow
  • Low filling temperatures
  • Involved gases
Defects on a casted part

How to Prevent Die Casting Defects

Defects that occur during casting have various causes. Their elimination, therefore, requires several steps. To prevent them, apply the following rules.

1. Adjust the casting machine to the correct values and optimize casting parameters. These include the injection and casting speed, pressure, temperature levels, and clamping force.

2. Use premium-quality materials with correct compositions. Test them before use. Ensure the ingots are clean to prevent material decomposition and gas formation that may lead to porosity.

3. Make sure the machine has no worn or damaged parts. Always clean its parts, such as the die cavity and ejection system.

4. Use high-quality mold-release agents and lubricants. Use them in their correct amount, too. If excessive, they cause irregularities such as

5. Employ strict quality control measures. Use effective monitoring systems for the entire process. Inspect and analyze finished parts to catch external and internal irregularities.

Conclusion

Different die-casting defects have specific causes. Understanding what they are and the reasons for their concurrence should help you avoid them. This guide has listed the most common irregularities, including their remedies. Use it to improve the quality of your products by making error-free parts.

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Willie

Willie is a professional metal processing and manufacturing writer with more than eight years of industry experience.

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