ENGLISH
German injection moulding machine producer Arburg has launched a new add-on injection unit for production of micro-mouldings.
Rather than the screw and plunger combinations used by some of its rivals, the new Arburg micro-moulding module uses two screws. Initial plasticising is carried out using a three-zone plasticising screw while final metering and injection is carried out in a second servo-electric drive 8mm diameter screw with non-return valve.
The pre-plasticization screw has almost conventional flight design, and is mounted piggy-back style at 45°. It is used simply to melt the plastic material prior to delivery to the 8mm injection screw. The latter has purely a material transport function.
This technique is claimed to enable extremely small parts to be moulded with standard size granulates, making the use of specially prepared micro granulates unnecessary. Micro granulate is usually required on micro moulding machines with screw diameters below 15mm, says Arburg.
The use of a screw rather than a plunger also has a benefit in terms of quality, according to Arburg technical director Herbert Kraibühler , as the polymer material is injected on a FIFO (first-in-first-out basis). This means there is a reduced risk of contamination of mouldings due to extended melt residence times, which can lead black speck development, he says.
The company demonstrated the module running on a standard 35-tonne clamping force all-electric Arburg Allrounder 270A Alldrive injection moulding machine at the Arburg Technology Days open house event in Lossburg, Germany, last week.
An Arburg Multilift H robot was used to remove the 1.58mm diameter 0.001g micro gearwheels, while a special pneumatically driven gripper system applied pneumatic force to remove the parts from an 8-cavity mould from Stamm in Switzerland.
The mould and parts were the same as run on an Arburg 15-tonne hydraulic drive Allrounder 170S, equipped with a size 30 injection unit and 12mm diameter screw, at the 2009 Technology Days event. That machine was also running at the 2010 open house, this time producing micro “shift gates” weighing 0.0025g that were removed from the mould using a Multilift H robot system.
From:http://www.europeanplasticsnews.com
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