Looking for better performance and lighter weight without sacrificing strength? Consider magnesium injection molding, which combines the best of plastic injection molding with die casting. One example is a prize-winning center housing of a hot new fishing reel.
Once avoided as an unpredictable process, magnesium molding showed its merits on the reel frame produced by Phillips Plastics for Marsh Technologies, Inc. (St. Charles, MO). The one-piece magnesium frame offers better rigidity than bolted metal frames sometimes used in bait casting. A new product, the mag frame replaced plastic or aluminum used in previous designs. Weighing 31 grams, the reel offered lighter weight compared to aluminum and provided part density and surface quality that could not be achieved with a plastic molding. It won one of the top awards in the 2005 International Die Casting Competition held by the North American Die Casting Association. Judges noted that the magnesium molding process could create complex geometry with varying wall thickness, while maintaining tight tolerances of bores and surfaces for mating components. The complex geometry, including undercuts, was made possible through three hydraulically actuated slides included in tooling design and produced on a tight production schedule. Good venting on a mag tool requires engineering that is as much art as science. Production of the parts takes place in specially made injection molding machines, starting with the melting of magnesium chips. Magnesium molded parts are cooled at lower temperatures (by 50-100F) than plastics. The process yields net shape parts, although post-machining is typical. The smallest part size achieved in the Phillips shop is 21 grams versus the common industry standard minimum shot size of 65 grams. Maximum part weight is 1816 grams in an 850 metric ton press. The bigger parts are aimed at electronic enclosure or automotive applications. “Our forte is precision molding with tight tolerances, good surface finish and action in the tool,” comments Dave Coon, senior project engineer at Phillips Plastics, Menomonie, WI. Phillips commits to NADCA precision tolerances in its molding processes, which recently re-located to a dedicated facility.