Tool making

Quelle: Fraunhofer IPT
Werkzeugsatz Linsenarray
The tool mold inserts that deform the glass and are therefore in continuous contact with it must satisfy a complex requirement profile. Due to the high reactivity of technical glasses in this temperature range and the often high surface pressures, materials must be corrosion-resistant, heat-resistant, hard, and wear-resistant. They must also be extremely leak-proof and capable of being machined at optical surface quality. These requirements are met by binder-poor hard metals based on tungsten carbide, as well as certain high-performance ceramics.

Next, the form inserts are fabricated by ultra-precision grinding with point contact kinematics and polished by hand. The key to success here lies in tool making due to the imaging character of molding technology. Molding tools are subject to the same requirements with regards to shape and surface as the glass optics themselves ‚ but with materials that are much more difficult to machine. Every micro-defect, the slightest shape deviation, is replicated onto the surface of the glass and will make unwanted rework on the glass optics necessary.

Since none of the materials listed is fully inert during molding, additional optical coating systems are applied to the tool surface that represent a diffusion barrier between the glass and the mold. These coating systems are applied using CVD or PVD sputter technologies and are based on noble metals or ceramics, based on the application. In addition to inertness, the essential requirement of the coating system is to maintain high surface quality and outstanding adhesion to the basic material. The coats must also be extremely thin (submicrometer range) and homogeneous in order to retain the high dimensional accuracy of the basic shape.
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