Porosity in die-cast components is one of the primary concerns of purchasers and designers. In die casting, porosity refers to pockets of air, small voids or holes found within a metal part. Too much porosity in a part can be dangerous, as it can harm the component’s structural integrity. Porosity can also cause leakage in certain parts, which can reduce how effective a part is and lead to other problems.
To reduce porosity in your materials, you can establish processing parameters and part design standards. Learn more about the sources of porosity in die casting and how you can reduce it in your materials with this post.
Sources of Porosity in Die Casting
To understand the sources of porosity in die casting, you must know about the die casting process first. At the beginning of creating a cast part, you close the mold and inject molten metal at high pressure into a die-cast machine. After doing this, the die-cast machine and the mold hold the molten metal until it solidifies due to pressure. Water is run through waterlines to help with casting at the optimal rate and cooling the metal.
While this process is fast and cost-effective, injecting molten metal into the die can cause porosity. The two most common sources of porosity in die casting are:
- Solidification shrinkage: Solidification shrinkage occurs when the material goes from a liquid to a solid. This volumetric shrink can cause some pores to open up in the material.
- Gas impurities: Gas can come from various sources and cause impurities in the material. Additionally, gas can get entrapped in the material and lead to higher material porosity.
How to Control Porosity With Die Casting Processing Parameters
Processing parameters are measurements that monitor a process to see if it’s hitting its goals or if there’s something wrong that needs to be adjusted. When you create die casting processing parameters, you can continuously measure the porosity of parts and make sure they’re at an acceptable level.
Learn about some of the primary casting processing parameters you can utilize to reduce porosity:
- Mold design: The design of cast and mold parts will often affect the overall porosity of your final product. For example, a mold with sharp corners and edges can affect porosity. You can establish processing parameters to ensure the mold is designed properly and has the appropriate hardness.
- Pouring speed: Your pouring shot speed and machine speed can affect the porosity of your final product. Putting high-pressure die casting process parameters in place can ensure your pouring speed and pressure are consistent. These parameters can also help your machines pour at the most optimal speed and pressure for reduced porosity.
- Pouring temperature: Your pouring temperature can affect the porosity of your parts and components. For example, low metal temperatures can result in greater porosity.
- Cleanliness of alloy: Your alloy’s cleanliness can affect the porosity of the part. Contaminants on an alloy can lead to more porosity and harm your part. Good processing parameters will ensure the alloy stays as clean as possible, keeping potential contaminants away from it.
- Solidification time: The time it takes for the material to go from a liquid to a solid can affect its porosity. Controlling the solidification time and setting parameters can help the material solidify at the best rate for reduced porosity.
Part Design to Reduce Porosity in Die Casting
When you want to reduce porosity in die casting, you need to start with your part design. A part design that doesn’t consider the die casting porosity standards or aim to address them will likely have greater porosity than one that does. To reduce porosity, start by working with an engineering team that’s well-versed in die casting and can give you designs for manufacturing insight. You should preferably do this step at the beginning of the project.
A company can also simulate the die casting process with software to optimize it. To prevent porosity and protect the part, engineers regularly employ overflows, vents, cooling channels, waterlines and runner gates in key locations.
Additionally, when a part needs extra assistance in the injection process, engineers will sometimes use vacuum assists to improve the casting’s porosity. Since the high-speed injection of molten alloy will meet resistance and pressure from the die cavity’s air, it’s common for porosity to occur. By including vacuum vents, the air in the die cavity can be pulled out faster. As a result, there’s less porosity in the part after the molten alloy has been injected.
Vacuum casting can also reduce the amount of die lubrication and other residue materials before the metal is injected into the cavity. This ability to reduce residue material helps prevent excess gas porosity from generating during the solidification process.
Another way you can design your part to reduce porosity in die casting is to ensure there’s uniform wall thickness throughout the part. Thinner walls tend to have less porosity, while thicker walls usually will have more shrink porosity. Ensuring your part is designed with uniform walls can help the metal flow to fill in more of the part and better prevent porosity than if you have a mix of thin and thick walls.
How to Predict and Measure Porosity
Having processing parameters to control porosity can help you better predict your porosity, as you’ll have a greater handle on the entire die casting process. With die casting porosity standards in place, it’s much easier to predict a lower porosity level. Additionally, you can use software to simulate the die casting process, which can help you better predict your part’s porosity and address factors that lead to higher porosity before you begin die casting.
You can use a few different methods to measure porosity in your materials. One common and easy way to test for excessive porosity in a part is to conduct a density or weight measurement. If the part is lighter than it should be, too much porosity has likely occurred.
For a more advanced test, you can measure the porosity with deconstruction testing or a 3D X-ray machine. These methods can give you more information about where porosity has occurred in the parts, as well as more accurate measurements about the porosity of the part or material being tested. If you want to verify the casting’s pressure tightness, you can also use leak testing by utilizing special purpose-built fixtures.
Contact Premier Die Casting for Die Casting Services
When you want to control porosity in your parts, you’ll want to turn to the experts. At Premier Die Casting, we know how to reduce porosity with the proper processing parameters. As a result, we can deliver high-quality parts and components to your business at an affordable cost. With over 70 years of experience in the industry, we’re ready to quickly create aluminum parts backed by our quality assurance measures.