| Exjection® Process
Was developed by IB STEINER and Hybrid Composite Products GmbH in Spielberg, Austria which combines extrusion along with injection molding. The process can be used to produce long, thin-walled and structured components from materials including commodity plastics, engineering plastics and high performance materials. End caps and functional geometries can be formed with the profile. The process overcomes the difficulty of molding long profile parts by injection molding as the liquid resin has to flow through long sections of a cooled mold. As compared to conventional injection molding Exjection® involves moving the mould in tandem with the injection movement at perpendicular to the machine's longitudinal axis. This concept makes possible the geometry changes into a long profile while inducing low stress and employing relatively small injection machines. The same is not very easily achieved by extrusion. Moreover, Exjection makes it possible to have screw bosses, snap-fit hooks, closures, or ribs, molded on the profile as the mold moves in the direction normal to the hot-runner nozzle. Due to the continuous movement of the mold with the continuous filling of the cavity, the process results in short flow paths. As a result, the area where actual filling takes place is affected as against the entire part making it ideal for the molding of long, thin-walled parts along with caps and closures on machines having small clamping force particularly for applications including automotive, packaging and other sectors. Materials having high viscosity offer a wider process window for Exjection process. The movement speed of the cavity (thus the cycle time) depends on the type of material and wall thickness of the part.
In Exjection, a moving carriage functioned by an electric motor and ball screw houses the mold. The variotherm element is characterized by a supply zone (hot zone) on one side of the fixed nozzle which is set to 20 o C below the melt temperature of the material being employed. On the other side of the nozzle appears a calibration zone (cold zone) on the other side. Filling pressure of several hundred bar is generated at the nozzle which remains unchanged during filling irrespective of the length of the part. The speed of the moving carriage normally ranges between 50 and 100 mm/sec; however, anything which goes above or below this speed can have an impact on the part quality. Along with the uniform movement of the mold carriage, the cold supply zone of the nozzle side works like an extrusion die and is heated while the cool calibration zone of the nozzle side works like an extrusion calibration unit and is cooled.
The Exjection process is characterized by use of a mold that moves horizontally or vertically past the injection point and fills a small, continuously moving cross-section of the cavity. Given that only a small cross-section of the part at a time is filled at the injection stage, significantly less clamp force is needed and parts have low internal stress. This technology was first showcased by Engel at K 2007 where it molded strips on a 60-ton, all-electric e-motion 200/55 press. Later, it was Arburg's 55-ton Allrounder 375 V 500-290 vertical hydraulic machine which manufactured a rail of 640 mm length and 60 grams from ABS with a cycle time of 45 seconds, during the start of 2008. Without Exjection process, such a rail would otherwise demand an injection moulding machine with clamping force in the range of 300?500 tons.
The license fee for the Exjection process involves a one-time payment of €40,000 for a non-exclusive and non-transferable production license for a single production facility. However, license fee does not depend upon the product produced, the size of the production cell or the number of parts produced. An Exjection mould is not necessarily much more expensive than a conventional injection mould. If the geometry of the part is suitable for Exjection the additional investment for the movable carriage is balanced with the expenditure incurred for the often relatively complex hot runner system at a conventional injection mould. As a result, the costs for a mould used in Exjection process are considered to lie somewhere around the costs for a conventional mould. However, finally the actual part has to be considered. The benefits of Exjection process in comparison to conventional injection molding include usage of presses with lower clamp forces, short flow paths, low pressure levels, avoidance of weld lines, smooth and gentle processing of the melt, low level of internal stress on parts and high quality surfaces. Exjection allows the use of injection molding machine with 50 tons ? 150 tons clamping force range for production of a part which is 1 meter long. As a result, the relatively lower tonnage presses required in tandem with the above factors in Exjection drags the investments down by as much as 30-50% compared to conventional injection molded parts while trimming manufacturing costs by 10-70%.
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