Wolfgang Kienzl has an unorthodox but effective way of describing foam injection molding.
At some point in our lives, we’ve all been on the receiving end of a bottle of Coke or Pepsi that, intentionally or not, was shaken up before being opened. “Immediately, foam shoots out of it and spreads generously in the vicinity,” writes Kienzl, who works in the Development Technologies department of injection molding machine maker Engel. “In principle, foam injection molding works in exactly the same way,” he explains in a blog post. “A propellant is added to the material — in the case of Coke, this is the carbonic acid — which dissolves evenly in the material due to high pressure and high temperature — corresponding to the shaking of the bottle. If the pressurized polymer gas solution is injected into the mold cavity (or if the Coke bottle is opened), this causes a sudden drop in pressure in the material, the mixture becomes supersaturated, and the dissolved gas escapes to form foam.” Where the analogy drifts apart, he adds, are the controlled conditions under which foam injection molding takes place. “After all, we want a functioning component at the end, not a mess,” writes Kienzl.
The embedded video, provided by Engel’s partner company Trexel, illustrates the foam injection molding process. For a more technical explanation of the technology and its benefits, notably in terms of lightweighting, read Kienzl’s article here.