INNOVATION | OPTICAL MOULDING
The aim of a development by Engel was to obtain a high optical quality in complex light guide shapes. The fine structures on the top of the demonstration parts (right) serve for
outcoupling of the light
require a greater degree of engineering,” says Flowers. “We envisage a lot of R&D in micro- moulding as well as LSR. Rapid development of various micro technologies, including micro-optics, nanotechnologies and microfluidics, mainly in Western Europe, is expected to increase demand for micro-injection polymer moulding globally.” Optical moulding applications play a vital role in
important global markets such as the automotive industry or entertainment and communication systems, says Engel. “Injection moulding technol- ogy allows the production of optical components that exhibit complex free-form geometries that are difficult or even impossible to produce using other methods,” says Thomas Leng, Vice-President, Global Application Engineering. “Key arguments for the application of polymeric materials are the significant lightweight potential and the possibility to integrate electrical, mechanical or decorative elements into the optical component.” He says in optical moulding, key applications are light guides and head-up displays (HUDs). “We
30 INJECTION WORLD | July/August 2021
provide know-how and expertise in the field of injection-compression moulding, a technology essential for areal parts with the highest demands on surface quality and low internal stresses.” According to Leng, there are two main forces driving technical developments in optical mould- ing. Firstly, there are improvements in quality and increased complexity of light sources. More sophisticated light sources put higher requirements on the optical elements like lenses, for example pixel LED technology. Secondly, improvements in sensors, in smartphones and digital cameras for example, allow for higher resolution. More precise, defect-free, high-quality optical elements are required to provide images free of defects. Engel says that it is continuously working on improving melt quality, both from a hardware – screw design for example – and a software perspective. Engel has introduced a number of develop- ments in optical moulding recently. These include the process optimisation and application of special process technologies for the improvement of optical properties of light guides. A good light guide transmits the light from a given source over long distances without noticeably decreasing its intensity or changing its colour. This requires a smooth surface over the entire transmission distance to ensure total internal reflection of the light. The light can only escape at particular points, which are equipped with prism-like structures for this purpose. As a result, the injection moulding process is required to provide high-precision reproduction of the part surface and high homoge- neity and purity of the plastic melt. The solution involves a combination of high-
precision Engel E-motion machinery with ancillary equipment for numerous improvements in the processing chain. A newly developed plasticising process employs starve feeding in combination with an optimised process guide, which allows long and complex-shaped light guides to be produced in very high optical quality. This is continually assessed with a high-resolution imaging colourim- eter for automatic qualification of the optical properties of the light guide. Feedback is provided to the machine for the disposal of rejects. A further development involves multi-layer
lenses. Automotive headlamps often use large and thick lenses. In a single-step process, these lenses require cooling times of more than ten minutes, making profitable production difficult. Engel has developed a special process to manufacture these lenses in a multi-step process. The production of a first base layer is followed by intermediate cooling and overmoulding with outer cover layers. A big
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IMAGE: ENGEL
IMAGE: ENGEL
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