Automatic Melt Preparation Setup for Reciprocating Screw Injection Molding Machines
Alexander Bakharev, Russel Speight
Moldflow
Australia
Keywords: plastication, setup, injection
This paper presents an algorithm for the automatic setting of screw rotational speed, back pressure and barrel temperature profiles in a reciprocating screw injection molding machine. The algorithm is based on a computer simulation of polymer plastication process. It achieves maximal throughput and good quality of melting and mixing within the limits provided by the injection molding machine.
The plastication simulator is based on the Tadmor-Klein model for three distinctive process zones of plastication along the screw: solid transport, melting/compression, and melt transport. The screw is represented as a number of geometrical zones, each with individual start and end pitches, inner and outer diameters, flight widths, and numbers of threads. The position of the screw end relative to the hopper is used to calculate temperature boundary conditions and the actual working length of the screw.
The optimization algorithm modifies back pressure and rotational speed profiles and barrel temperature settings to achieve the following objective:
- Set quality of melting and mixing;
- Melt preparation time below set cooling time;
- Minimal energy consumption, wear and tear;
- Average temperature of the melt equal to the recommended for the polymer;
- Easy startup for injection molding process after a pause
The method was tested on a Battenfeld BKT 1500/400 injection molding machine and results have shown good agreement with actual process conditions. For all tested materials the algorithm provided good moldings, with the charge time matched to the cooling time of the injection molding process. The charge time predictions were within 20% margin of error.