Hill and Griffith
The Days of Using Die Casting Lubricants to Control Die Temperature is Over
NADCA Video News Update: Engineering Die Casting Dies: Dimensional Repeatability
The material presented in this video are some highlights from NADCA’s online webinar - Engineering Die Casting Dies: Dimensional Repeatability. This looks at defining what the customer wants and gives a standard approach to what the process can normally achieve, with such things as dimensional tolerances and flatness. It covers defining what your plant can achieve on a day-by-day basis using a small amount of math.
(A transcript from the promotional video excerpt.)
"Things can change that can change dimensions. Cooling time, the time the casting is in the die. The steel die is very, very strong aluminum or zinc, or whatever is not, so the longer you hold it in the die, the more the casting will have the dimensions of the die. There is a limit because if you go too long, the casting will crack, but the closer you want to dimensional tolerance, the longer your cooling time usually is, not always, but usually is. Steel guides are very, very strong. Metal temperature, as you increase your metal temperature or decrease your metal temperature, the amount of heat going into the die changes, so you are now getting castings that are different in dimensions. Die temperature across the insert - if you have the left side of your die is hotter than the right side, then the casting coming out will usually be hotter on the left side than on the right. As it starts to cool, the left side has to cool more, so it will shrink more, so the casting will warp. You start to get dimensional changes, difference from left to right. That's why cooling of the die is so important. Internal cooling is critical to controlling dimensional accuracy. We have produced castings with extreme flatness, extreme dimensions, and it all comes down to, or part of it comes down to controlling the die temperature and making it consistent. Spray time, the days of spraying the die to control die temperature, in many plants, is over. The spray is to add the lubricant and to cool certain sections, which you cannot cool internally. For example, the fins on an air cooled motor. It's very hard because there are a number of cores in there, but most of the time, die spray is down to a minimum. We are consistently using die sprays on 2,500-ton machines where the die spray time is a second or .8 of a second to get accuracy. Die spray pattern, again, the same thing. You change your die spray pattern, you will change your dimensions of your casting. Pre-heating of dies, if you use a blue flame, a strong gas torch, then you are heating the dies in certain spots. When the aluminum or zinc, or magnesium, or brass starts going into it, it changes the profile, so there is a difference between the first few shots coming out and the last, the shots during production when the die has become stable. People say, "How many die pre-heats should I do?" There are many ways of finding out, measuring die temperature, measuring the quality of the part, measuring the accuracy, but it's worthwhile doing it. There is no magic rule that says make three castings; everything will be fine. It depends on your plant. It depends on how you design your dies. Die flash, that's an obvious one. You flash the die; you slowly build up metal on the joining faces. The die splits, and then your dimensions across the die are changing. The die flash builds up until it gets to a certain level, and then either an operator removes it, or the die spray blow blows it away. That gives you changing dimensions. In the modern plant, die flashing is something that is attacked very, very definitely to make sure that it does not happen. There are a number of plants internationally, which do not have die flashing. Soldering, or soldering, that's where metal sticks to the die. It chemically attacks to the die, so you can have, in one section of the die you get soldering, as the casting's ejected, it sticks on that spot. It's more difficult to eject, so the casting bends. You can get it on cores, and as it slowly builds up, you are losing dimensional accuracy. The diameter is increasing. If you're using coatings, if you're using jet cooling, if you're using a number of things, you can postpone soldering a lot. Very difficult to get rid of it, but you can postpone it coming. "There are many, many other things that can change." 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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