INNOVATION | OPTICAL MOULDING
Right: Arburg participated in the OptiLight research project for the energy-effi- cient produc- tion of hybrid lenses for LED street lighting
able to provide individual production cells includ- ing complete cleanroom cells,” he says. “The electric Allrounder injection moulding machines are particularly suitable for the production of high-precision optical parts. However, this is a field in which innovations are driven primarily by mould construction and new materials. Arburg provides customers with positive support by providing an injection compression moulding process tailored to the material and mould. The compression moulding sequences can be freely programmed on the central Selogica control system without the need for any additional programs.” The company adds that its injection compres- sion moulding software is continuously being refined. “As a process, injection compression moulding makes it possible to produce low-stress, thick-walled components without sink holes and with a high degree of contour accuracy,” says Inna Meder from Arburg’s application engineering consulting team. “This complex process sequence can be used to realise innovative applications, including precise free-form surfaces. Injection compression moulding is a variation of the injec- tion moulding process. It is characterised by a change in cavity volume during the ongoing injection and/or holding pressure phase. In injection compression moulding, the mould is usually not yet completely closed during injection. Only after the melt has been introduced into the cavity, will the mould be closed completely. This means that less pressure has to be applied to fill the cavity, reducing the pressure gradient during the filling phase. When the mould closes, uniform compression is then applied to the complete cavity surface of the shrinking component. The mould must therefore be designed in such a way that the cavity is sealed even if the mould is not completely closed. This enables the production of low-stress, thick-walled components without sink holes and with a high degree of contour accuracy.”
Arburg adds that it uses hydraulic and electric injection moulding machines for injection com- pression moulding. The hydraulic Allrounder S models are characterised by long compression paths and large compression forces, whereas the electric Alldrive series ensures positioning accuracy in the range of 1/1,000 mm. Arburg was involved with the OptiLight research
Light conductors play a crucial role in focusing and conducting the light from 40 LEDs in a car headlight. With an Allrounder 520 A, these precision parts made of liquid silicone are produced by Wilhelm Weber from Esslingen, Germany, for its customer Hella. They are used in cars such as the Audi A8
16 INJECTION WORLD | September 2019
project for the energy-efficient production of innovative hybrid lenses for LED street lighting. Using injection compression moulding, precise free-form surfaces are produced which direct the light into a rectangular illumination profile. The energy-efficient LED lenses are manufactured using an equally energy-efficient electric Allrounder A injection moulding machine with a clamping force of 600 kN. The servo-electric toggle-type clamping unit stands out for its reproducible, dynamic injection process. A hydraulic ejector enables long compression processes with high forces. The production cell is equipped with a vertical entry Multilift V for gentle removal of the lenses. The project is funded by the German Federal Ministry of Education and Research (BMBF) and supervised by the Project Management Agency Karlsruhe (PTKA). The goal is an efficient production chain for high-volume production of microstructured, thick-walled polymer hybrid lenses. Arburg cites another example in ophthalmic lenses for spectacles, where the thickness of the component can be adjusted by means of the compression path. The compression time for a lens of 10 mm thickness is 90 s, using a hydraulic injection moulding machine with multi-pump technology. The electric Allrounder injection moulding machines are also ideal for high-precision optical applications, such as automatic production of optical waveguides made from polycarbonate, says the company. Due to the microstructures measur-
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PHOTO: ARBURG
PHOTO: ARBURG
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