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NADCA Video: Using die casting lubricants to prevent shrink porosity

Posted by Hill and Griffith Company on Jan 31, 2018 4:35:47 PM

NADCA Video News Update: including using die casting lubricants to cool die and prevent shrink porosity

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The material presented in this video are some highlights from NADCA’s online webinar - Defects in Die Casting: Porosity Defects and their Causes. Porosity is the biggest problem for die casters and is the most common cause of rejecting a part. This first webinar covers the various types of porosity and how to identify them. It is important to realize that porosity can have a combination of causes rather than just one “magic bullet” solution.

For information on purchasing a downloadable copy of this webinar in its entirety, please visit: diecasting.org/store/detail.aspx?id=WEB227

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"Shrinkage Porosity, you can end up with shrinkage pores and here they are. They look ragged and long. So shrink porosity is always thermal. If it's hot, cool it. If it's cold, warm it. So you have a section of casting that is hot, and the surrounding air is cooler, you'll end up with shrink porosity.

So if you look at this casting here, here is a runner coming in gate, heres a part, as the metal is freezing from both sides, you'll end up with shrink porosity in the middle. Since the location of shrink porosity is also the hottest spot in that section of the casting, it is usually in the center of a heavy section.

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Two options: feed the shrinkage or move it with metal temperature. Die cooling is the tool we use to indirectly affect metal temperature. That is the main one nowadays. And even casting temperature will cause the porosity to spread out. And to be roughly on the center line. The last point of freeze.

Shrink porosity and core pins, this is an important part. Core pins are surrounded by molten metal. So you have a quarter inch core pin that is an inch long. The heat can only get out from that core pin through the quarter inch that's connected to the die. As the molten metal comes in, the core pin is surrounded by molten aluminum, or zinc, or magnesium. They can reach the temperature of the molten metal so core pins can easily get up to a temperature of the molten metal.

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The core pin cannot lose heat cause its only got a small base. And hence the surrounding area is often the last place to freeze. Hence, shrink porosity is often around core pins. And if you look at a core pin, this is often what we see. Here's the core pin, and you have shrinkage porosity around the core pin. So then when you machine it and decide to thread it, you suddenly strike porosity, which occurs and then disappears. And it depends on where that shrinkage porosity is.

The answer is, either use fountains or jet cooling to cool that pin and then the shrinkage defects disappear. So things like engine blocks, where we have very long cores, we use jet cooling to cool those cores.

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To purchase access to this course, visit the NADCA marketplace at www.diecasting.org/store. Purchasing a course through the online education system grants you one year of access to the recording, presentation, support material and test when applicable."

About the North American Die Casting Association

Headquartered in Arlington Heights, IL, the North American Die Casting Association (NADCA) represents the voice of the die casting industry, representing more than 3,100 individual and some 300 corporate members in the United States, Canada and Mexico. NADCA is committed to promoting industry awareness, domestic growth in the global marketplace and member exposure.


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