As it has over the years,gas-assist injection molding once again led the topics discussedat the 10th international Molding 2000 conference and exhibition,held Feb. 28 to March 1 in New Orleans, LA. New developments incoinjection and super-precision molding also were covered. Presentationson the latest advances in emerging technologies included one froma Swiss visitor-Hubert Lorenz of Mimotec SA, discussing his company'sintriguing UV LIGA technology for producing micromolds for thefirst time in the U.S. (see September1999 IMM, pp. 79-80 for an initial report). New developmentsin decorating and inmold finishing also were addressed.

Jack Avery of GE Plastics updated the SRO audience on the continuingemergence of gas assist as a global mainstream process. He admittedthat market research studies show that only three more moldershave licensed their way into gas assist since his Molding 1999presentation. However, he says that the use of the process byexisting licensees is dramatically increasing.

Leading the way are automotive companies, including GeneralMotors, Ford, DaimlerChrysler, Porsche, Audi, Volkswagen, Nissan,Mitsubishi, and Delphi. At this year's SPI Structural PlasticsDiv. Conference in Vancouver, BC, 20 percent of the New ProductDesign Competition entries used gas assist.

Xerox is representative of the nonautomotive molders increasingtheir use of the process. At the 1999 Structural Plastics Div.Conference Xerox entered a component it developed with rapid prototyperPapago Plastics. Among other benefits, gas assist reduced thepart's weight by 57 percent. (For more on Papago's use of gasassist, see p. 180.)

Gas-assistTechnologies
Avery's talk also covered the recent global alliances and technologicaldevelopments of gas-assist systems suppliers. For example, FerromatikMilacron North America has obtained patents on the full-shot AirpressIII gas-assist technology. Dennis Richmond of Milacron presenteda paper on Airpress III, in which gas and plastic are injectedseparately (see Figure 1).

The gas expands and fills the cavity completely along withthe melt, producing a void inside the part and allowing uniforminternal pressure to be exerted. Richmond sees particularly beneficialapplications of the technology when it is used with FerromatikMilacron's Mono-Sandwich coinjection molding systems. It lowerspart weight of thick-walled multimolded parts while improvingstiffness and aesthetics.

Avery also mentioned that following Incoe's agreement to provideNorth American sales and support of technology from Gas InjectionLtd. of the U.K., Incoe has developed a complete package of gas-assistproducts and services and has positioned itself as a full-servicesupplier.

AtMolding 2000, Incoe's John D. Blundy told attendees his companyalso has licensed rights to sell External Gas Molding (EGM) fromAsahi of Japan in both North and South America. EGM involves low-pressuregas injection through the core side of the mold, blanketing gasacross the entire sealed surface area or selected sealed areasof the molded part (see Figure 2).

EGM replaces the normal packing phase of the cycle and compensatesfor volumetric shrinkage and cooling. Blundy sees beneficial applicationof EGM in a number of molding applications, not the least of whichis inmold lamination, or backmolding. Battenfeld GmbH and GasInjection also license similar technology, according to Avery.

Water-assist Molding
In addition to several studies on applications of process simulationsoftware being conducted overseas, Avery also discussed work beingcarried out by the Institute for Plastics Processing (IKV) inAachen, Germany in developing what it calls water-assist injectionmolding technology. Following its anticipated commercializationin 2002, Avery believes, water assist will complement gas assistwhen it comes to coring out larger-diameter rod-like sectionsof parts such as automotive air ducts. Gas assist is more forcoring out flat parts, thin walls, and ribs.

Cold water is injected into the melt in IKV's water-assistprocess and remains in the liquid phase. It is held at 290 psiduring injection and 2176 psi during hold. The water can be drainedwhile the part is still in the mold, or after ejection. This isdifferent from Hettinga's Helga gas-assist process, which involvesuse of a proprietary liquid that vaporizes in the mold and formsgas channels. Drainage is unnecessary in Hettinga's process, Averysays.

In another gas-assist presentation at Molding 2000, Greg Crawfordof Epcon Gas Systems discussed work at his company on integratingan SPC program into its control systems to track critical weights,measurements, and temperatures. Online SPC-based control has beenfound by Epcon to be an excellent means of consistently controllingthe quality of traditionally short-shot gas-assist molded parts.

Editor's note: More information is available in a new bookfrom the IMM Book Club. Gas Assist Injection Molding by Paul Dierand Rick Goralski is available for $99. To order, contact ReneeLeatherman at (303) 321-2322 or visit our website at www.immbookclub.com.

 

 

Alternatives to gas assist

Gas assist and alternativesto the process popped up in a number of other Molding 2000 presentations.For example, two alternatives were discussed, each of which isquickly gaining in popularity: MuCell microcellular foaming technologywas discussed by David Pierick of Trexel, and Sequential ScrewLoading (SSL) by Simcha Kilim of Addmix. Pierick reminded theaudience that, unlike gas assist, MuCell foams the entire partwith microscopic cells without requiring injecting holes or voids.Part weight reduction, highlighted in Pierick's cost savings breakdownpictured to the right, is achieved without the need to addressgas bubble placement or size (see IMM, October1999, pp. 100-101 and January2000, p. 53 for more).

MuCell also is not limited by part complexity, and is suitable for thinner-wall molding than gas assist. Still, it provides many gas-assist benefits, including reductions in fill, pack, and hold pressure and a resultant reduction in clamp tonnage.

Use of blowing agents in the core material of coinjected partsto reduce part weight and improve properties is only one of thebenefits of the SSL process that Addmix's Kilim covered. As previouslydetailed (see July1998 IMM, pp. 78-80), the greatest benefit of SSL is thatit allows coinjection molding on existing, conventional, single-barrelpresses of any size.

Kilim also announced that Addmix has a new do-it-yourself SSLCD-ROM. It guides users through setting up their SSL systems forrepeatable production of high-quality multimolded parts, usingtheir own materials and their own machines. Find out more aboutit on the Web (see contact box), or pick one up from Addmix atNPE (Booth N8723).