Dolphin Process Allows Undercuts, Complex Design

Engel says it is negotiating with OEMs to extend application of its unique Dolphin process, which allows design engineers to achieve complex geometries and undercuts in a time- and labor-saving process.

Daimler supplier SOLE (Oderzo/Italy) is using the Dolphin system to produce cockpit covers for the new Mercedes Benz Actros at the Daimler facility in Wörth, Germany.

The Dolphin process combines two-component injection molding with MuCell physical foaming and a reverse compression process. A thermoplastic substrate is molded in the first injection station using a valve gated hot-runner system. The substrate is transferred to the second injection station by rotating the center mold stack following cooling.

The substrate is then overmolded with thermoplastic elastomer (TPE), holding the wall thickness to a defined dimension (usually 2 mm) to prevent the gas from foaming.  Inert gas (nitrogen or carbon dioxide) is introduced during recovery, in a supercritical state, to create a gas-saturated melt.  An injection unit with MuCell is mounted on the moving platen of am Engel combi M machine.

The melt solidifies on the mold wall and forms a skin layer, which duplicates the grained surface of the cavity. The clamping unit is then opened by a defined reverse compression stroke, allowing the dissolved gas to expand. Fine and uniform foam cells form since the pressure within the cavity decreases with a gradient equal across the cavity. That’s a requirement for a highly uniform and good cell structure within the part and a uniform density throughout the part.  The cavity is held in the extended position until the TPE has cooled completely and crystallized.

The next substrate is already being produced on the other side of the mold. A blocking system on the second mold side makes sure that the clamping force does not decrease during the precise opening movement required to create the foam layer. A surrounding spring loaded frame seals the mold halves during the opening stroke so that neither melt nor foam can escape.

The Dolphin process requires stable and high-precision molds. The mold maker for the Daimler project is Georg Kaufmann, Busslingen, Switzerland The tolerance in the temperature-controlled and movable elements is 0.001 inch. Cooling is also difficult because the mold halves are kept at different temperatures. The substrate requires a temperature that is 95 °F higher than the TPE overmolding.

The raw-material supplier for the Actros is SO.F.TER Tecnopolimeri, Forlì, Italy.

 

Th Dolphin process is used for interior cockpit components.

 

Undercuts are a big benefit

About Doug Smock

Former Chief Editor at Plastics World and Senior Technical Editor Design News
Automotive, Design, Europe, Foam, Foam molding, Injection compression

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