Sophisticated LED lenses made of LSR

Liquid silicone rubber (LSR) can be processed efficiently in injection moulding and also scores with excellent material resistance. Without doubt, LSR has become the material of choice for a wide range of complex products. It has also become increasingly important as a material for optical lenses. 

 

At Fakuma 2018, from October 16 to 20 in Friedrichshafen, Germany, system partners ENGEL, ACH-Solution and Dow Silicones present for the first time in Europe, an integrated solution for cost-effective production of LED lenses with a highly demanding geometry. ENGEL has been actively innovating in LSR injection moulding with machine models specifically serving the needs of this niche sector. 

 

At the Dow Silicones stand, lenses for LED headlamps will be produced on a tie-bar-less ENGEL e-victory 310/120 injection moulding machine, with an integrated ENGEL viper 40 linear robot, in a two-cavity cold runner mould by ACH-Solution (Fischlham, Austria). The lenses are representative of a wide range of applications. Apart from the automotive industry, LSR is becoming increasingly important for building and street lighting. The reason for this is the material characteristics. Highly transparent grades for optical applications have a lower yellowing index than conventional thermoplastic lens materials. They are extremely resistant to environmental influences such as UV radiation and can be used over a wide temperature range from 40 to +200 °C. In addition, they allow particularly flexible design. DOWSIL MS-1002 Moldable Silicone will be processed at Fakuma; it creates smooth and very hard surfaces much like thermoplastics. The headlamp lenses, with their extremely filigree structure, are moulded with highest reproducibility. The lenses leaving the production cell are ready for installation. 

 

 

Compact and high-precision

Not only by the complex part geometry, the production of LED lenses places high demands on the processing technology. In general, to be profitable in the production of high-tech products made of LSR, the process must be automated and the product must be rework-free. Injection moulding machines with tie-bar-less clamping units already provide the optimum design for this. Free access to the mould area enables particularly efficient automation concepts and compact production cells. Since the mould mounting platens can be fully utilised right up to the edge, the high-volume lens mould fits on a comparatively small 120-ton injection moulding machine. 

 

One of the reasons for the tie-bar-less e-victory's accurate reproduction of surface detail is the outstanding parallelism of the mould mounting platens. The patented force divider ensures that the moving platen follows the mould precisely while clamping force is building up and that the force is evenly distributed across the platen face. When multi-cavity moulds are used, all cavities within the parting line experience the same surface pressure, which prevents flash even when processing very low-viscosity silicones.

 

The ENGEL victory line of injection moulding machines offers a flexible modular system, making it the machine of choice for producing many different technically complex parts or for running an extensive selection of process technologies. With its tie-bar-less design, the ENGEL victory provides absolute freedom for complex mould design, rapid mould change and unobstructed robot movements. This innovative machine also allows the selection of a machine size based specifically on clamp force requirements –not mould dimensions -- thereby using less production space and reducing investment costs.

 

To guarantee the required precision during injection of LSR, the e-victory machine is equipped with an electric injection unit. In addition, iQ weight control improves process stability. This intelligent assistance system from ENGEL's inject 4.0 product programme is able to detect fluctuations in the ambient conditions and raw material, and to compensate for them automatically during the shot. The electric valve gates in the mould are also automatically self-regulating. The Servoshot system by ACH-Solution makes it possible to control each electric valve gate individually.

 

As a system supplier, ENGEL integrates all of the production cell components with the injection moulding machine's CC300 control unit; the entire process, including the MaxiMix G2 type LSR metering equipment by ACH-Solution, can therefore be set up and controlled in an uncomplicated way. Control integration reduces complexity and enhances ease of use.