The entire industrial spectrum relating to Allrounder injection molding machines and the freeformer for additive manufacturing was on display, with, as always, a major focus on production efficiency. Under the heading "Efficiency from product design to the individual part," the company demonstrated how to incorporate Industry 4.0 technologies into a production process by combining injection molding and additive manufacturing. Also, an eight-station production process, which included complete traceability for quality assurance purposes, had been set up in the Efficiency Arena to illustrate the optimization potential for efficient plastic parts production throughout the entire value-added chain.
A completely new development that was being showcased for the first time by Arburg was an innovative foaming solution, called Profoam, which has not yet been commercialized. Profoam is a physical foaming process that reportedly saves material and reduces cooling time, while yielding a foam similar to that produced using the well-known MuCell process, developed by Trexel.
Conventional foaming processes tend to produce parts with an inferior surface due to problems such as silver streaks and displaced melt. Also, foaming is always accompanied by a reduction in the absolute mechanical properties of a part. The MuCell process dispenses with these problems, but requires a special plasticizing unit.
Developed in collaboration with the Institute for Plastics Processing (IKV), with an aim to improve the mechanical properties of foamed parts, the new Profoam process requires no additional peripherals and is suitable for conventional injection molding machines. The system can be retrofitted on almost any molding machine. The injection unit features a normal screw geometry; however, the screw must be fitted with a seal at the back to prevent the gas from escaping.
During the Profoam process, the plastic granules are mixed with liquid propellant in a granulate lock upstream, rather than downstream of the injection unit. In other words, the gas—carbon dioxide or nitrogen—goes into the hopper. The airlock chamber is sealed and the gas is diffused. "There are no mixing elements that can damage the fibers when using reinforced materials," said Heinz Gaub, Arburg's Managing Director, Technology & Engineering.
The result is a lightweight, stable part with low distortion and a homogeneous foam structure. Other advantages of the Profoam process include easy control and a melt temperature that does not damage the material. "We've also found that, while the Profoam process affects fiber length, it does so less than conventional injection molding techniques," said Gaub. "Moreover, the mechanical properties are on par with those seen in conventionally molded products."
At the Technology Days, an electric Allrounder 820 A equipped with a two-cavity mold was producing airbag housings made from fiber-reinforced PP in a cycle time of around 70 seconds. As Gaub pointed out: "It's a product that needs to be light and very stable—an airbag reacts directionally. And this we managed. In this case, stability is provided by the fibers, while foaming the part makes it lightweight."
In fact, the thick-walled, lightweight part measuring 280 millimeters in length weighed just 272 grams, around 18% less than conventional compact injection molding.
Gaub: "The Profoam process therefore makes it possible to produce mechanically loaded parts that weigh less, while eliminating the drawbacks of conventional processes."