Arburg, a German-based machine builder, is applying lessons learned in the new defunct compact disc business to the thin film transistor (TFT) market.
A specially fitted hydraulic Allroudner S was shown at Chinaplas last month compression molding light-guide panels with a thickness of 0.5 mm and a flow/path wall thickness ratio
of 350:1 in a cycle time of 15 seconds. Lower pressure compression is required—with some special tricks—to meet the flow requirements for the part, which Arburg described in a press release as a light-guide panel with LED background to save energy in tablet devices.
In order to achieve a high luminous efficiency, the components must be as thin as possible and require a specific optical surface.
To achieve the thinness, a change in cavity volume is required during the injection and/or holding pressure phase. That means that the mold only closes completely once the melt is already in the cavity. In standard injection molding, the mold must be fully closed at the start of injection so that high pressures don’t squirt melt out of the tool cavity.
In the Arburg concept, there is ideally a constant level of pressure within the cavity during the process. In terms of the machine, it is necessary to move the injection unit and mold or mold components simultaneously. The mold, in turn, must be designed so that the cavity is sealed, even in the partially open state
This leads to greater molding precision, improved evenness and consequently higher part quality. Internal stresses are minimized and double refraction effects are reduced.
Special machine modifications include specially adapted mounting platens on the clamping side, as well as a special hydraulic system. On the injection side, the Allrounder 630 S is equipped with hydraulic accumulator technology, a position regulated screw as well as an electromechanical dosage drive.
Five devices from HB Therm are used for temperature control purposes.