INNOVATION | OPTICAL MOULDING
Right: The iQ weight control intelligent assistance system
compensates for fluctuations in the raw material and ambient conditions before rejects are produced
Below:
Sumitomo (SHI) Demag’s Intelect S machines have the precision and repeatability necessary for LSR moulding
Like the established thermoplas- tic lens materials PMMA and polycarbonate, silicone offers significant weight savings compared to glass. However, LSR is superior to organic polymers in terms of thermal and chemical resistance. Highly transparent grades for optical applications have a lower yellowing index than 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. In terms of the geometry, there are almost no limits when processing LSR in injection moulding. Engel demonstrated the procedure by process- ing Dowsil MS-1002 Moldable Silicone from Dow Silicones, a material developed specifically for use on injection moulding machines. The curing speed has been optimised to obtain a smooth and hard surface similar to thermoplastic. The high light transmission ensures a good luminous efficiency. In addition, the high thermal stability enables an outstanding transparency. The surface, with its extremely filigree structure, is moulded with highest reproducibility. The LED lenses leaving the production cell are ready for installation. “The prerequisites for economically producing geometrically demanding products from liquid silicone are automated, rework-free processes as well as high precision and stability of the injection moulding process,” says Gero Willmeroth, the President East Asia and Oceania at Engel. “Thanks to its tie-bar-less clamping unit, the E-victory machine with an electric injection unit is predes- tined for this.” According to the company, tie-bar-less injection moulding machines offer a number of advantages for processing LSR. The fact that the robot can reach the cavities directly from the side without having to circumvent any obstacles reduces the handling time, and therefore the mould opening time. On top of
PHOTO: ENGEL
this, the tie-bar-less technology allows for particu- larly compact production cells. Because there are no tie bars in the way, the mould mounting platens can be fully used up to their very edges. This means that the high-volume lens mould necessi- tated by the complex component structure fits on a comparatively small 120 tonne injection moulding machine.
Engel adds that one of the reasons for the
accurate reproduction of surface detail is the good parallelism of the mould mounting platens. The patented force divider ensures that the moving mould mounting platen follows the mould precise- ly while clamping force is building up and that the force introduced is evenly distributed across the platen surface. When multi-cavity moulds are used, the parting lines of all cavities experience the same surface pressure. This prevents flash when process- ing very low-viscosity silicones, and avoids rework- ing of the injection moulded parts.
Engel has equipped the E-victory with iQ weight
control for the manufacture of the LED lenses to ensure the required precision during injection throughout the entire manufacturing process. The intelligent assistance system from Engel’s Inject 4.0 program analyses the pressure profile during injection of the polymer melt, compares the measured values with a reference cycle and adjusts the injection profile, the change-over point and holding pressure shot by shot to the current conditions. Fluctuations in the raw material and ambient conditions are automatically compensated
before even a single reject moulding is produced. The camera system integrated in the process checks and documents the quality of the parts. An Engel Viper 40 linear robot is used for parts handling.
Sumitomo (SHI) Demag Europe agrees
that LSR is probably where the most significant developments are happening in automotive injection moulding right now. “Utilised for Ad- vanced Driver Assistance systems, LSR is being used for safety critical applications,” says Henrik
PHOTO: SUMITOMO (SHI) DEMAG 20 INJECTION WORLD | September 2019
www.injectionworld.com
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