In two-component microinection molding, the runners usually cannot be longer than 4 to 12 mm in order that the relationship between runner and part weight remains balanced. Since the dimensions involved do not permit use of hot-runner systems or extended machine nozzles, the machine nozzle approach the cavity very closely.
Klöckner Desma Schuhmaschinen GmbH is now offering its new formicaPlast with parallel injection units for microinjection molding. After the mold opens, the mold inserts lift out of the mold base and rotate 180° into the new position. A pivoting arm built into the mold ensures high precision of this rotary motion. The system offers a wide range of variants and a high degree of design freedom as well as short cycle times, since the preshot and finished part are molded simultaneously. In addition, the mold cavities are arranged symmetrically around the long axis of the injection assembly, so that the forces tending to open the mold are distributed evenly.
The solution with two parallel injection units described here is made possible by the miniature assemblies used in the formicaPlast. The molding machine operates with two-stage plunger injection units: a 6-mm plunger- for preplastication and a 3-mm plunger for precise injection. The servoelectric drive used for the injection stroke generates injection pressures of over 2500 bar and injection velocities up to 500 mm/s.
As an example of potential applications, a fiber-optic assembly with 3-way distribution was produced. The shot weight of the transparent polycarbonate component is 9 mg, the surrounding ABS component weighs 10 mg. This total shot weight of 19 mg probably represents one of the smallest 2-component parts produced to date.
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