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New technique builds molds that outrun the competition.

* A new moldmaking method reportedly produces tools that give much faster cycle times than conventional injection molds and better parts, as well. Molds made with this technique typically provide 15-30% shorter cycle times and sometimes raise output by more than 50%, says Tom McDonald, president of ExpressTool Inc., Warwick, R.I., which developed the process.

ExpressTool uses a proprietary electroforming process to "grow" core, cavity, and slide inserts that fit into conventional mold bases. "We build up the inserts gradually around a model of the part," explains McDonald. His firm uses CNC machining to create the part model from a proprietary conductive material that accepts electroplating. The finished mold inserts consist of a 1-2 mm thick shell of nickel backed up by 3-4 mm of copper and a backing support of a proprietary composite. Similar coefficients of thermal expansion keep the three layers from coming apart, McDonald says.

Faster cooling wins out

ExpressTool's short cycle times are due to improved cooling capacity. Technology v.p. Dr. Paul Jacobs says nickel and copper together have an effective conductivity six to seven times greater than tool steel.

ExpressTool also achieves faster cooling through "conformal" cooling channels that follow the part's contours in three dimensions. "We're not constrained to straight lines," says McDonald. Conformal channels can be made by encapsulating bent copper tubing within the copper backing just behind the nickel-shell surface.

Better speed and accuracy

While ExpressTool guarantees at least 15% reduction in cycle time, early tools have performed even better. McDonald cites the example of an automotive retainer clip that was molded in 21 sec in a standard P-20 steel mold. Cycle time dropped to 12 sec in an ExpressTool mold. In the case of a HIPS cap for a small jar, cycle time was 15 sec in a conventional mold but only 9 sec in the ExpressTool mold.

Conformal cooling also improves part quality, Jacobs claims. He says conformal cooling drastically reduces hot spots in the mold, thus promoting more uniform shrinkage. "We don't have any hard data yet, but every indication is that the parts show less distortion," he says.

McDonald says ExpressTool's moldmaking tolerances are as tight as traditional production methods. "We have the same precision as molds made with EDM electrodes." Jacobs adds, "We're down into the tenths of thousandths of an inch on critical dimensions."

As good as tool steel

With less than a year of production experience, ExpressTool lacks long-term data on tool life. Current tools have surpassed 250,000 shots of nylon with no sign of wear, says Jacobs. Even if the inserts prove less durable than tool steel, he says their higher productivity could pay for more than one set of inserts.

ExpressTool inserts can withstand injection pressure over 20,000 psi, melt temperature up to 800 F, and mold temperature of 350 F.

ExpressTool makes inserts up to 20 x 20 in., but McDonald says the process can go as large as 3 x 3 x 6 ft.

An entire mold can be built in about eight weeks. Inserts alone take five weeks. McDonald expects tool cost to be comparable to conventional molds. "It looks like we'll be more cost effective with complex shapes and less so with simple shapes," he says.

Early customers using or evaluating ExpressTool molds include United Technologies, Chesebrough Ponds, Hasbro, and a Detroit car company. GE Plastics plans to test the tools at its development center in Pittsfield, Mass.
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Title Annotation:ExpressTool Inc.'s moldmaking technique
Author:Ogando, Joseph
Publication:Plastics Technology
Date:Oct 1, 1998
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