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May 3, 2000

2 Min Read
Be true to your tool

That was the title of a paper that David G. Bank, account manager of rapid prototyper Papago Plastics, presented at the 10th international Molding 2000 conference and exhibition held Feb. 28 to March 1 in New Orleans, LA. In it, Bank says gas-assist injection molding is one of the best ways to build molds faster, and to make better molds and parts, even when dealing with OEM designers who lack molding experience.

He laments the near extinction of experienced plastics design engineers in the industry today, adding that molders and moldmakers have too many pressing demands on their time to educate the inexperienced CAD jockeys left.

"Today, we are seeing designs that are poorer in quality and content than in any time in recent memory," he notes. "The files we see have no draft, are without the proper wall thickness, or have wild excursions between thick and thin walls. With all that being said, what does the toolmaker or molder do?"

Bank believes that gas assist has tremendous untapped potential for making simpler molds and better parts faster and cheaper. Gas assist also allows even experienced designers to break almost all the rules of good plastic part design they’ve spent their whole lives trying to learn, he says.

Gas-assisted Simplification
Papago received an order to build an aluminum tool (Figure 1) and mold a few hundred underhood parts in glass-filled nylon for an automotive customer. A component in an engine cooling package, the part mounts to the backside of the radiator.

One side is a smooth surface. Its leading edge has a large radius that tapers wider as it falls away from the radiator surface. Bank says the other side was a study in all the traditional ways to core or thin out cross-sectional geometry (Figure 2).

Managing warpage in such a design would be challenging. So, Bank convinced the tooling engineer he was working with to help him redesign the part to take full advantage of gas assist. The V-shaped base was redesigned into a tubular gas channel, replacing the ribs (Figure 2). The results of the new design were impressive:

  • Design time savings from 160 hours for the original down to 40 hours.

  • Machining time reduction from 120 to 40 hours.

  • A 15 percent materials saving.

  • Cycle time reduction from 33 to 30 seconds.

  • Clamp tonnage reduction from 350 to 220 tons.

  • Zero warp.

  • Component cost from $1.54 down to $1.31.

Copies of all Molding 2000 presentations are available from Executive Conference Management Inc. (Plymouth, MI), phone: (734) 420-0507, fax: (734) 420-2280.

Contact information
Papago Plastics Inc.
  Div. of the Foster Group
Rochester, NY
David G. Bank
Phone: (716) 243-9298
Fax: (716) 254-4739
E-mail: [email protected]

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