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Although the topic was ostensibly the implementation of plastic materials under the hood as replacements for metals—and with there being some significant reasons for doing so, as in “Weight savings vary from 20 to 50%, depending on the component. Cost savings are generally in the 20 to 30% range”—Mike Day, North American Development Director for DuPont Automotive (dupont.com/Automotive/en_US), makes an observation about a development project that is an absolute winner when it comes to the subject of doing fast physical prototypes of products.
It was an application in automatic transmissions. Inside the transmission there are (1) moving components, including gears and drive mechanisms and (2) transmission fluid. The issue that arises is that as the moving components do what they are supposed to do, they agitate the fluid such that there is aeration; the fluid becomes full of bubbles. Which makes it less effective. So the means by which this is ordinarily addressed is to create baffles that help ameliorate this bubbling. It is ordinarily steel. It is ordinarily an assembly.
(It is worth noting in the context of the aforementioned cost savings: Day explains that this is generally predicated on the fact that plastic allows the consolidation of parts—as in using a two-step molding process that permits the molding of a cylinder head cover and the elastomer gasket right in the same tool, which has all manner of associated savings, ranging from the reduction in required tooling—realize that if the cover is made out of metal, there still needs to be a gasket—to the reduction in costs associated with inventory (i.e., tracking one part rather than two separate ones).)
So when they were developing the transmission baffle, they selected Hytrel, a thermoplastic polyester elastomer. When doing prototype tooling, you’re not necessarily going to be crossing the proverbial T’s and dotting the associated I’s. So in this case, as in many, flash forms around the edge of the part where the prototype mold opens and closes. As this is just a prototype, that’s just something that is taken into account and usually designed out when the production tooling is produced.
But when they were testing out the performance of the baffle with the flash in place, they discovered that there was actually a benefit in terms of improved flow control. So the flash is now designed in as a flap for the finished part.
Day points out, of course, that they have an approach in place for part development that they call “rapid proof of concept.” There is molding and design analysis performed via computer modeling before there is any actual polymer put into play. But, Day says, “The real success comes when you actually take a concept for a plastic component and fabricate it, make a physical part and do testing. There are interesting things that you can learn when you do that, which helps the iteration process in a way that you can’t get in a virtual environment.”
There is still something to be said for reality.
The Hytrel baffle, by the way, is in production and is used in a number of transmissions produced by General Motors and Ford. Several million have been produced so far.—GSV