The real highlight of the ENGEL X-MELT technology is the outstanding repeatability of the process cycle. That results from the exact to position, electromechanic screw drive. Variations of the locking behavior of the non return are eliminated by an adaptive software.
The residual pressure after melt pressure relaxation works like the post pressure as with the conventional moulding process.
The x-melt concept
ENGEL X-MELT is an unconventional process for the high-speed injection moulding of small and/or thinsection parts. Conventional high-speed injection moulding is based on a machine technology which utilizes a high drive output for the injection of the melt, involving high acceleration and deceleration of the screw as it performs its forward movement. X-MELT, on the other hand, utilizes the energy stored in the highly compressed melt in the space in front of the screw. Injection is effected simply by opening the needle valve nozzle, allowing the melt to expand and fill the mould cavity. No additional means of generating injection pressure are necessary.
Process stage 1: Plasticizing
The plasticizing unit of the machine or, preferably, the hot runner system of the injection mould (see illustration above) is equipped with a needle shut-off mechanism. The nozzle is closed when in its starting position. The plasticizing screw rotates and plasticizes a defined amount of material.
Process stage 2: Compression of the melt
Upon completion of the plasticizing process, and with the shut-off nozzle still in its closed position, the screw then serves as a plunger to compress the melt. Depending both on the application and on the material, the compression pressure ranges from 2,000 to 2,500 bar. At this pressure, the metered volume of melt is reduced by approximately 10 %. The state of compression is maintained for a short time in order to ensure a uniform temperature throughout the melt.
Process stage 3: Filling the mould
The shut-off mechanism is now opened. The melt "explodes" abruptly and fills the mould cavities in only fractions of a second. The residual pressure acts as holding pressure to compensate shrinkage. During the mould filling operation, the screw is kept in exactly the same position, thus ensuring perfect reproducibility of the process.