Extrusion & Injection Moulding CombinedExtrusion & Injection Moulding Combined
Up till now, injection moulding of longer, thin-walled, profile-type plastic parts of defined lengths has always been restricted by the flow qualities of the material involved. Extrusion does not provide the flexibility customers need to produce parts of defined lengths, or with structural and geometric elements at right angles to the extrusion direction. A worldwide technological novelty, known as Exjection retains the advantages of the legacy technologies of extrusion and injection moulding while avoiding their disadvantages, thus supporting the production of profile-type plastic parts using injection moulding technology. ENGEL has been actively involved in the development of Exjection, a process that supports cost-effective production of long profiles with integrated fitting, closure, reinforcing and decor elements via a single injection point, and more or less in a single production cycle. The major difference between Exjection and legacy injection moulding is that the mould with the image of, say, a profile, moves at right angles to the longitudinal axis of the machine in sync with the injection of molten material. To achieve proper cavity filling, it is necessary to precisely adjust the screw advance speed, and thus the flow of molten material, to match the speed of the moving mould. The motion of the mould creates a continuous free cavity volume that is continually filled by molten material flowing into it. To achieve a defined compression of the molten material, and thus a post-injection pressure function for demoulding structures or avoiding sink marks, the molten material is pressurised in the vicinity of the injection point — in other words, the mould moves slightly slower than the theoretical speed dictated by the flow of molten material for more-or-less pressureless filling. These conditions are most closely met by a fully-electric injection moulding machine from Engel’s E-motion range. The mould is propelled by a servomotor, and a recirculating ball screw. Synchronisation of injection and movement is thus given throughout a great range of speeds. Excellent platen parallelism and uniform distribution of compression over a given area, as provided by the E-motion clamping units in the mould area, avoid the burrs on the one hand, and ensure that very little force is required to move the mould when clamping force has been built up. ENGEL will be demonstrating the Exjection method at K 2007 in Hall 15/C58 on a fully-electric ENGEL E-motion 200/55 injection moulding machine (clamping force 550 kN) with a mould for producing 930 mm thin-wall profiles with a wall thickness of 1.2 mm.
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