New Concept for Multi-Shot Molds

Production of multi-color or multi-material articles on a conventional injection press without additional equipment is enabled by new tooling technology from German moldmaker Zahoransky Formenbau GmbH. Its newly patented Servo Cavity Positioning System (SCPS) differs from rotary-table, indexing-platen, or turning-stack approaches to molding multi-component articles. “Those approaches require platen enlargement or guide-pillar extensions. SCPS runs on a standard press rather than modified machinery, due to the space-saving cavity design of the SCPS mold, which allows its use on a smaller, lower-cost press”, says Michael Schmidt, sales director. He also says SCPS allows for higher productivity than alternative systems by fitting more cavities in the same space and/or operating faster between shots.

Zahoransky has supplied more than 1000 multi-component injection molds worldwide, and claims to be the first to have built a two-component injection mold for toothbrushes (1984). A four-component prototype SCPS mold will be shown for the first time in a dry-run demonstration at the Fakuma show in Germany this month.

 

VERTICAL CAVITY TRANSFER

SCPS relies on a “stacked” tooling design that lays out each step of the process vertically in the mold. Each injection unit serves a distinct molding area or section of the mold where a material is injected. Each injection zone or section has its own cavity geometry and hot-runner system.

The vertical or stack alignment of the injection stations in the tool is combined with a special cavity-indexing system that is the heart of SCPS technology. Movable cavity or core inserts shift outward from the mold base and then index up to the next zone of molding. The moveable inserts are actuated by an electric servo drive and spindle built into the mold. The spindle drive repositions the inserts from one molding station to the next. It can travel 1200 mm in 0.8 sec with highly accurate positioning, says Schmidt. The spindle drive not only transfers the inserts from station to station, but also moves the completed parts on the inserts to a demolding position outside and above the mold.

The movable inserts are divided into sets of cavities, one set for each shot. After parts removal, the set of empty cavity inserts at the demolding station above the mold are clasped by a second spindle drive system on the opposing mold half while detaching from the spindle drive in the first mold half. The second spindle transfers the set of inserts to the first molding station and reattaches them to the bottom end of the interlocking chain of cavity inserts.

The mold has its own controller to regulate spindle movements as well as core pulls and hot-runner valve gates. It can even control auxiliary injection units and hot-runner temperatures. The mold operates independent from the machine, which can be hydraulic or all-electric.