By Matthew H. Naitove, Executive Editor

From: Plastics Technology
Issue: August 2011

The combined MD&M East and Plastec East shows in N.Y.C. in June presented intriguing developments for medical injection molders.

 

POWDER-METAL CAVITIES

In multi-cavity tooling programs for medical and other precision molding applications, key goals are exact uniformity and minimal cost in replicating cavities. Both goals reportedly can be satisfied by powdered-metal technology (PMT), in which the cavities are injection molded from a master cavity, using a mixture of metal powder and a small amount of plastic binder. Then, cavities are slowly “debinded” over a period of three to five weeks to obtain tight dimensional tolerances. Cavities can be machined after debinding.

 

Polyshot Corp., W. Henrietta, N.Y. (polyshot.com), is offering PMT tooling made by Israeli sister company Plasel Mold, said to be the largest moldmaker in the Middle East. PMT cavities are typically made of H-13 steel (though others are available on request) with feature tolerances down to 15 microns and cavity-to-cavity repeatability of less than 5 microns. Max. size is 70 x 30 x 25 mm. Cooling is typically through contact with a water-cooled mold base.

 

Advantages of PMT are said to include easy production of fine details and sharp corners, unique shapes that would be difficult or impossible by any other metalworking process, and short lead times to produce duplicates or spares.

Together with Plasel, Polyshot is offering uniquely designed pipette tip molds with PMT cavities. These tools have 32 cavities arranged in four blocks, each block having eight cavities in a circular cluster. The 110-mm center distance within each cluster is the smallest in the world, according to Polyshot president Doug Hepler. Overall mold size is 300 x 386 x 305-355 mm, depending on tip length. Tooling is modular, so different tip lengths can be produced.

 

The cooling capacity in this mold is also said to be the highest in the world. The PMT cavities are inserted into precisely fitting cooling sleeves with spiral water channels milled on a multi-axis CNC lathe that rotates the part while it mills the grooves. The sleeves are in two halves and can be disassembled for cleaning. Thermal pins (heat pipes) are inserted into the core pins for internal cooling without risk of plugged circuits. Polyshot has a demonstration pipette-tip mold at its plant.

 

In addition, Polyshot has a new hot-runner nozzle (pinpoint or valve gate) suited to medical applications. Its latest Accutrak nozzle is designed to flush the insulating well completely on each cycle, eliminating stagnant melt and resulting burn marks at the gate, which can occur with materials like PC and acetal.

 

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