Italian molder SOLE is the first company to make commercial use of the Dolphin multi-component, hard/soft molding technology from Engel Austria (U.S. office in York, Pa.). SOLE started using the process last fall to mold cockpit covers for the new Mercedes Benz Actros truck. Dolphin is a one-step process to producing auto interior parts with a pleasing tactile surface.
The process uses physical foaming with the MuCell microcellular process from Trexel Inc., Wilmington, Mass., together with a core-back process that Engel calls “reverse compression.” Molded on an Engel combi M machine with a horizontal rotary platen and opposing injection units, the process starts with molding the rigid substrate, such as PC/ABS. After cooling, the part is transferred to the second injection station by rotating the center mold stack. Then a copolyester TPE from SO.F.TER of Italy is injected to form the soft covering. The overmolding thickness is at first held to around 2 mm to prevent the gas (nitrogen or CO2) from foaming. After a short cooling phase to form a solid skin that replicates the grained surface of the cavity, the clamp is opened slightly by a defined amount—the reverse of injection-compression molding—to allow foaming to occur.
Since the next substrate is already being molded on the other side of the tool, the clamp force must not decrease during the precise opening stroke. Also, the mold requires a spring-loaded frame to seal the mold halves so that neither foam nor gas escapes during the opening stroke. The Dophin process is not only simpler than other methods of producing soft-surface interior parts, but it also allows for complex geometries and undercuts