Advantech Plastics is always researching the latest advances in plastic injection molding. That’s why we are interested in the M3 High Volume Micro Molding Machine will make its first public appearance later this month at the K 2013 exhibition in Düsseldorf, Germany. This is the first complete molding system offered by MHS-Mold Hotrunner Solutions, Georgetown, Ont., a supplier of hot-runner systems. It is aimed at part weights below 50 mg and part volumes up to and exceeding 150 million parts/yr.
The machine is operated with a combination of electric servo motors and pneumatics. It is compact, measuring 1907 x 717 mm x 2300 mm high.
NOVEL TWO-STAGE INJECTION
The fundamental principle behind the design of this machine is minimizing melt residence time in order to preserve material quality, says Harald Schmidt, president of MHS. To that end, the M3 system is designed both for minimal melt inventory and also for the lowest practical melt temperature.
The injection system starts with a stationary (non-reciprocating) screw of 18 mm diam., the smallest that can accept standard pellets. (Larger screws could be supplied, if needed.) The screw operates on an intermittent basis, supplying melt to eight micro-plungers. These injectors are independently controlled and capable of up to 15,000 psi injection pressure. Each injector feeds directly into an MHS hot-runner valve-gate nozzle for direct gating into the mold cavity. These nozzles have 0.028-in., pneumatically actuated pins. Accumulation of the melt for each shot so very close to the gate avoids variations in shot volume that can arise from melt compressibility, Schmidt says.
Another unusual feature of this system, he points out, is that the plasticating screw delivers melt to the plunger injectors at a temperature below that normally required for filling a mold. That temperature is increased somewhat in the plunger, and increased further to final injection temperature in the hot-runner nozzle. This step-wise increase in melt temperature is the gentlest possible way of handling the melt so as to preserve maximum material properties while achieving good processability, Schmidt states.
The 4-ton clamp is perhaps the first to involve no pushing mechanism to force the platens together. Rather, the platens are pulled together by four electromagnets mounted in the corners. A linear electric motor accomplishes mold opening and closing. There are no tiebars, and the platens ride on rails. The ejector mechanism is built into the platens. Schmidt also notes that this clamp system allows for a large daylight opening of 18 in. and ample access from all sides to allow for in-cavity parts inspection and maintenance access.