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optical moulding | Technology

World for more on multi-layer optical moulding techniques Earlier this year, German injection machinery maker

Arburg demonstrated a fully automated overmoulding system for production of high precision thick-walled LED lenses at its factory in Lossburg. The LED lens parts were produced in a V920T optical grade of PMMA supplied by Altuglas using a 4+4 cavity 120˚ rotary mould with unloading station manufactured by German mouldmaker Kronacher and fi tted with a Ewikon hot runner system. Incorporation of the unloading station into the process

Above: Inside view of a Carclo Technical Plastics production facility

Centre right: A 20mm diameter

Carclo bubble optic for wide angle


a certain gate position, the geometry around the gate, and the differential wall thicknesses around the part,” says Grassi. “As a designer, I’m going to design a part to be as good as possible optically, but sometimes we have to make sacrifi ces for the sake of manufacturability. A lot of what goes on manufacturing-wise has been built on years of experience here – we have been making optical mouldings for the better part of 35 years so we have a very large toolbox we can draw upon,” he says.

The challenge of validation Validation is also much more challenging in the optical market place than in most technical moulding areas, according to Grassi. “You can’t really approve an LED optical part just by taking a few mechanical measure- ments and dimensions. LED lighting fi xtures go through a lot of testing, including measuring their light distribu- tion, and there is a lot of equipment required. We have two optical labs with over $100,000 invested just in optical test equipment.” Cycle times in the optical sector are lengthy due to

Lower right: Free form optics such as this Carclo

product are used in street and interior lighting

applications 20

the combination of thick sections, large variation in wall section, and the need to maintain very low levels of moulded-in stress. Grassi says some of Carclo Technical Plastics’ optical components have wall thicknesses of more than 35mm and cycle times for such parts can be as long as 10 minutes. Novel moulding techniques such as injection compression are used to help reduce cycle times to the minimum. Multi-layer injection moulding is seen by some as a technol- ogy that can better satisfy the confl icting demands of high optical quality and low manufacturing cost (see this article in the October 2012 edition of Injection

INJECTION WORLD | September 2013

allows the parts to be automatically unloaded from the front side of the machine while the mould is closed. This maximises the productivity advantages gained by using the over-moulding technique, according to Arburg, allowing four complete lenses to be produced every 40s. The production system was built around a full

electric Allrounder 520A moulding machine with a 150 tonne clamp fi tted with two injection units – a horizontal size 400 unit and vertical 70. All process sequences, including the servo-motor rotation of the mould and control of the six axis robot, were controlled from the

moulding machine using Arburg’s Selogica controller. The six-axis robot, which was integrated into the

production system by FPT Robotik, carried each 4.3g lens to an optical inspection system for 100% quality checking before placing them onto a cooling conveyor prior to packaging.

Procesing restrictions According to Arburg, two-component overmoulding technology results in very low internal stresses and highly precise surface contours while simultaneously cutting lens cycle times. However, the company warns that use of overmoulding technology is not unrestricted in this area; German multi-component injection moulding specialist Wilhelm Weber holds a patent covering some key aspects of the process it demonstrated. Austrian injection

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