You have designed an innovative part with tight tolerances. Your design looks perfect in your initial drawings. However, there is one invisible challenge that can compromise even the best designs: porosity in zinc die casting.
Zinc die casting porosity is air trapped within a die-cast part in an unwanted location. This air weakens structural integrity and creates visual defects. Every high-pressure die casting process traps some amount of air because of shot speed.
The goal is straightforward: design parts that minimize and control trapped air with minimal impact on performance.
You need to understand die casting porosity. At Deco Products, our engineers manage porosity in castings to ensure high-quality castings that meet industry standards.
Ways to Reduce Die Casting Porosity
In high-pressure die casting, it is impossible to completely eliminate entrapped air. The molten metal is injected under such high pressure that the liquid metal could risk shooting out of channels made for the air to escape. As such, some amount of air will always be trapped in any casting. However, the right designs and features can minimize the amount of air trapped, and try to make sure the air is trapped in locations that won’t create problems for the product application.
Make the Casting Design Better
The best way to improve a part is by optimizing the die-cast part design itself. Adding features that help molten metal flow reduces the amount of porosity in critical areas. Our engineering team reviews your drawings and identifies potential porosity issues in your design.
Our engineers make recommendations for designs, features, and revisions to wall thickness based on the anticipated flow in critical sections of the part. Features like sharp corners, perfect circles, and dead ends can all have impacts on the amount and location of porosity. The features can create pockets of turbulence that hold and trap air.
Design effective runners
Product design is only part of the story. We can also significantly impact the amount and location of the product through runner design. The “runner” is the channel that the molten metal flows through as the zinc is injected from the plunger-chamber into the actual part cavity in the tool. Runners design can improve material flow through the die cast part without changing part features directly.
The key is to develop a clean path for zinc to flow through the part without creating excessive turbulence. By changing the angle, position, width, and symmetry of the runner systems, we can influence the speed and turbulence of the molten zinc, allowing us to try to make sure material flow is smooth in key areas and the turbulence is contained to less critical areas. These changes are powerful as they allow us to improve porosity without any changes to the part.
Eliminate Dead Ends with Vents and Overflows
Vents and overflows are two other ways we can improve porosity.
When molten metal hits a “dead end”, air is trapped in place with no escape. Vents and overflows can help resolve those problems.
A vent is an open-ended feature in the tool which allows air to escape without letting zinc escape. Essentially, these are specially shaped channels that have many ridges to slow down the molten zinc before it can escape the tool. These channels allow most of the air to escape but prevent the molten zinc from spraying out of the machine. These vents require thoughtful design, as they can present dangers to machine operators.
An overflow is a close-ended feature intended to push molten zinc and air into the overflow feature to allow the molten metal to better flow and fill the desired part. Overflows are more commonly a solution to “poor fill”, but can also be used as a place to try to push entrapped air.
In both cases, these solutions create small appendages on the part that need to be removed after the casting has cooled.
Methods to detect porosity in castings
Porosity in zinc die casting sometimes appears visible at the product surface, but frequently remains hidden beneath the casting skin.
Visual inspection for surface porosity
The most common and effective method for detecting superficial porosity is visual inspection. A thorough visual examination of the die cast part surface reveals visible defects or imperfections related to die casting porosity.
Advanced detection for internal porosity
Detecting porosity beneath the surface is more complex. In some cases, x-raying parts detects where air trapped is located. This approach is more common in high quality operations such as aerospace or automotive applications where die cast parts serve safety-critical functions.
A simpler method involves cutting open a casting where suspected air entrapment occurs. When coupled with mold flow analysis, this ensures good correlation with earlier tool design analyses and helps identify both gas porosity and shrinkage porosity patterns.
Deco Products optimizes your design for success
All high pressure castings will have some amount of air trapped inside the casting. If there is too much trapped air or it is in the wrong place, the porostiy can negatively affect quality, strength, appearance, and structural integrity of the final product. Careful design and production techniques can minimize and manage porosity in castings to deliver reliable high-quality castings.
Our design engineers have significant experience in pressure die casting and are prepared to help you optimize your design. At Deco Products, we utilize Flow-3D Cast simulation software and an experienced team of Engineers to support the manufacturability of your design before any tooling is produced.Getting porosity management right saves time, reduces scrap, and improves tooling life.
Contact us today to learn if we are the right zinc die cast partner for your next casting project. If you found this article helpful, you may be interested in learning more about our Design and Engineering Team.