Looking for a Measure of Demoldability? Here’s a New Approach

If you’ve ever had trouble ejecting parts from a difficult mold—I should have said when, not if—you may have experimented with different mold finishes or even coatings to overcome sticking.

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You may have found something that worked, but it may have taken time-consuming and expensive trial and error. A German research institute may have found a better way.

At the recent annual Technology Days expo hosted by Arburg in Lossburg, Germany (details here), one machine exhibit showcased a four-year development effort by KIMW Forschungs-GmbH, a venture of Kunststoff Institut Ludenscheid. As explained by KIMW managing director Frank Mumme, this work is directed at helping molders determine the best mold finish or coating to achieve desired release of parts from injection molds.

KIMW has developed a test apparatus with disc-shaped inserts that replicate the mold surface. Any desired coating can be applied to the insert. The test mold produces a disk of 35 mm diam. and 2 mm thick. The disk has a series of raised “teeth” arranged radially around the sprue on the back side (photos). These teeth engage with a mechanism that rotates the disc and senses the force required to cause the disc to start to turn against the cavity insert. That force serves as a proxy for the force required to release the part. If the user wants to simulate a situation in which the part has shrunk onto a core, a controlled force is applied to press the part against the cavity before the rotational force is applied. KIMW began by investigating release of soft TPEs but is now testing hard thermoplastics.

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