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June 7, 2001

7 Min Read
2001: The gas-assist odyssey continues

Editor's note: Molding 2001, which was held Jan. 29-30 in New Orleans, LA, included a forum on gas assist. Following are some of the details that emerged from presentations and subsequent discussions. To request copies of the complete Molding 2001 proceedings, contact Executive Conference Management Inc., Plymouth, MI; (734) 420-0507; fax (734) 420-2280. To find contact information for suppliers of gas-assist equipment, go to www.immalmanac.com and search by company, keyword, or product.

Just as the groundhog and his shadow are sure signs of the coming spring, so, too, is the seasonal state-of-the-market address on gas assist from Jack Avery of GE Plastics (Pittsfield, MA). Avery's message at Molding 2001 was that because technology license fees are now bundled into equipment costs, prior concerns over any extra investments that may have once been required for gas assist have been all but forgotten. 

License-bundled gas-assist systems that in the mid-1990s cost $90,000 to $100,000 today generally cost $30,000 to $50,000, according to Avery. This has allowed gas assist to become more readily accepted as a core injection molding process. 

Nevertheless, Avery says molders must recognize the fact that gas assist still involves extra investment, though of a somewhat different nature. Getting the most out of gas assist requires that significant changes be made in the way people think about material selection, processing, tooling, and part design. There is a lengthy learning curve for newcomers. In today's nonstop, time-to-market rush, few have any extra time or resources to spare. As a result, gas-assist growth has been relatively slow. 

Though concrete and more reliable numbers are difficult to come by, recent surveys suggest that there are about 2000 or so gas-assist molders in North America, and that their ranks are growing at less than 5 percent annually. The top users usually are larger shops doing $75 million or more in annual sales that can afford the R&D investment required. Newcomers face fierce competition from these houses with gas-assist experience, creating another major factor slowing growth. 

Confidence Index 
On top of all of this, growth has been slowed by what Avery calls the lack of a perceived level of stability among the ranks of the gas-assist suppliers. Skittishness over all the different levels of systems pricing and technological sophistication being offered is delaying more widespread acceptance of gas assist, especially among those facing a steep learning curve. 

Still, Avery is optimistic that the customer base will broaden as experienced gas-assist molders continue to open new market opportunities for all. He is encouraged by the success of molders who have recently produced a number of exciting new automotive, IT, industrial, and sporting goods applications while cashing in on the faster cycles and lower machine rates the process provides. 

Emerging developments—like all-electric gas-assist nozzles, plug-and-play gas-assist injection units, and process simulation software—may help speed growth. And Avery is confident that research into application-specific materials selection and processing parameters presently under way will help improve the industry's perception of gas assist. 

Water-assist Molding Update

Avery also had something to say about water-assist molding, quoting Battenfeld's Helmut Eckardt's opinion about the technology: "We're where we were with gas assist 10 to 13 years ago." Water-assist molding was developed by the IKV, a research institute based in Aachen, Germany. Avery says considerable development work still remains in the areas of process control and water supply management. Regarding the latter, the big question is, what do you do with the water you drain out of the part? Nevertheless, he believes water-assist molding holds promise, particularly for providing faster cooling of relatively thick-walled parts. Avery mentioned the 17-kg PP shopping cart that was water-assist molded by Sulo GmbH of Herford, Germany (see March 2001 IMM, p. 96). It was first displayed at Fakuma 2000 at a booth belonging to materials supplier A. Schulman GmbH (Sindorf, Germany). Using water assist, part weight was reduced 50 percent and cycle times by 70 percent.

For more information, contact the IKV at +49 (241) 803981; fax +49 (241) 8888262; www.rwth-aachen.de/ikv.

Gas Assist vs. Lost Core 
One of the highlights of the gas-assist session at Molding 2001 was a presentation from a next-door neighbor of Avery's in Pittsfield. Carl M. Olson is manager of sales and marketing for moldmaker/custom molder Hi-Tech Mold & Tool Inc. Olson detailed how Hi-Tech found gas-assist molding to be a more cost-effective process than lost-core molding for producing a complex PVC drainage part for a customer, HVAC systems supplier Hays Fluid Controls (Dallas, NC). 

Since 1983, Hi-Tech's niche has been in manufacturing some of the most technically demanding parts anyone has ever seen, but even Hi-Tech had never seen anything like the Hays P-Trap. It is a tube that first makes a full 90° bend to the right, then a 180° bend left, and then a final 90° bend right. 

"The best that retractable cores can do is to form a single 90° bend, and then only by butting together in a straight section," Olson says. The continuously hollow Hays P-Trap requires smooth bends for proper fluid flow. 

Hays tried lost-core thermoforming of extruded tubing, using a core of processed clay, but that posed many problems. For one thing, the core materials acted as a heat sink and an air flow restrictor, lengthening cycle times. Removing the clay and the residual dust also proved troublesome and costly. Hi-Tech just got into gas assist last year, but it was no newcomer to challenging parts. It knew it needed help when called on by Hays to use gas to core out the part. 

Hi-Tech retained the services of gas-assist specialist Mike Caropreso of Caropreso Assoc. (Becket, MA), and later called in consultant David G. Bank of David Bank Assoc. (Geneseo, NY), a specialist in gas assist and in quick-cooling aluminum tooling. Though Olson admits that further work must be done to reduce manufacturing costs and cycle times, Hi-Tech has proven to Hays that gas assist is the most viable option. 

P-Traps weighing 114g are being molded at 128-second cycles on a 200-ton Niigata at Hi-Tech, with gas-assist systems from Gain Technologies and a Sterlco two-zone mold heater. 

Packing With Gas

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Sink marks are readily visible in this 10 1/2-by-9 1/2-by-5/16-inch PC scanner cover used in tests by Incoe. Shot without packing with 38 tons of clamping force, it weighed 252g.

John Blundy, vp of business development at Incoe Corp. (Troy, MI), updated the Molding 2001 audience on External Gas Molding (EGM) technology. He announced Incoe's intent to license and market EGM at Molding 2000 (see May 2000 IMM, p. 216). Unlike traditional gas assist, in which gas is injected into the melt, EGM uses a low-pressure blanket of gas to pressurize an entire part, or specific sections of a part, in a sealed cavity. 

In so doing, Blundy says EGM brings the uniform clamping pressure distribution benefits of compression molding to the injection molding process. "You need tonnage only for filling," Blundy says. Gas packs the part, significantly reducing clamp tonnage requirements—reportedly up to 70 percent—though Blundy reminded all that a big press with ample projected area is still required for molding big parts with EGM. Still, though it offers no appreciable cycle time savings, EGM comes through in a number of other value-added ways. 

Uniform gas pressure in the sealed cavity reduces stress cracking. It fully packs sink-free ribs and bosses under flat Class A surfaces without using gas channels (see comparison photos). Because packing pressure is remote from the material's injection point, inmold decoration becomes a more practical option. The gas also can be used to eject parts, eliminating witness marks. 

Blundy says Incoe has emerged as a full-service gas-assist technology supplier since Molding 2000, especially when it comes to engineering parting line sealing solutions for its licensees, a proprietary key to the process. EGM mold-owner licenses cost $5000 to $15,000, based on part projected area. 

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Even after packing, sink marks are still visible—under 125 tons of clamping force, the part weighed 271g.

Using Incoe's EGM process with 800 psi gas pressure and the identical clamping force as used in the unpacked part test, the scanner cover weighed in once again at 252g and was sink free.



Contact information
GE Plastics
Pittsfield, MA
Jack Avery
Phone: (413) 448-4816
Fax: (413) 448-7567
Web: www.geplastics.com
E-mail: [email protected]

Incoe Corp.
Troy, MI
John Blundy
Phone: (248) 616-0220
Fax: (248) 616-0225
Web: www.incoe.com

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