Ever try to make a waffle with a balky waffle iron? Well, then, you know the Goldilocks problem with temperature: if the iron is too hot, you’ll have a char-broiled brick; too cool, and you’ll be left with a gooey, sticky mess. To produce a perfect, golden waffle, you need the “just right” temperature inside the waffle mold.
It’s the same with the manufacture of plastics parts using injection molding. Liquid plastic is injected into a metal mold which is heated just like a waffle iron. The objective is to make a perfect cast of the tool’s surface, which is in the concave shape of the part you’re producing. The ideal process will be nearly automatic, with no need for human interaction, such as cutting away excess plastic. It should also be energy efficient and cost-effective too.
The traditional process is to heat the entire forming tool to approximately 218 degrees Fahrenheit using a technique known as variothermic tempering. In order to extract the completed plastic part without damaging it, the mold must be cooled by around 70 degrees. Then the whole process can begin again, often within minutes, which uses a lot of energy.
Scientists are currently working to develop a new kind of tempering technique that, depending on the part to be produced, is up to 90 percent more energy efficient than other processes. The key is to avoid heating up the entire tool, which can weigh half a ton or even more. The only surface that has to be heated to the correct temperature is the area that actually comes into contact with the plastic melt. This is accomplished by coating the wall of the forming tool using a technique known as sputtering. The sputtered material is deposited onto the surface of the forming tool in layers only a few micrometers thick (1 micrometer equals one thousandth of a millimeter). This incredibly thin layer is all that’s needed to keep the rest of the tool cool, saving energy and money.
The research teams working to develop this new process are currently looking for industry partners to help finance their work.