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November 1, 2003

1 Min Read
Negative-coining system for lenses

Engel is cooperating with optical specialist Leica Projection GmbH (Braunschweig, Germany) on process technology for producing plastic lenses and optical components with microstructured surfaces. It makes use of a newly developed injection-compression unit that enables a negative-coining process—the cavity first expands during injection and then compresses during the holding pressure phase—operated by a moving core with the mold fully closed.

Hobs in the mold are connected to the clamp unit pressure pad. Prior to injection, these are moved into a position that leaves a cavity gap less than the final part thickness to ensure that the melt can be injected quickly and without jetting, while precisely reproducing the mold suface. After volumetric filling, the hobs are pushed back against an adjustable counterpressure. A hydraulic pressure transducer in the compression cylinder allows the determination of the melt pressure in the cavity without the need for a direct pressure transducer inside the cavity.

Alternating mold heating and cooling allows accurate mold surface reproduction while containing cycle times. Pressurized water at 120C is pumped through channels during injection and followed by cooled water. The mold temperature control system is from Robamat Automatisierungstechnik (Gmunden, Austria). Engel Austria GmbH, Ludwig-Engel-Strasse 1, A-4311 Schwertberg, Austria www.engel.at

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