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Custom molders: take a shot at multi-component molding.

Multi-color or multi-material molding isn't just for captive molders anymore. Applications are multiplying far beyond keycaps and taillights, making investment in specialty machines thinkable for custom shops.

* Looking for a way to cut part costs or add value to your molded components? For more and more molders, the route to achieving both goals is multi-component molding. A collection of several different techniques, multi-component molding offers the ability to combine different materials or colors in a single one-shot or multi-shot process.

Multi-shot processes such as overmolding can drive down part costs by squeezing what would otherwise have been two distinct molding jobs plus an assembly operation into a single manufacturing step. The cost reduction can be as great as 25-50%. Overmolding can also add value by making the end product more attractive to consumers through the addition of splashy colors or soft-touch elastomeric materials. "In these cases, the satisfaction of the end-use customer, not manufacturing cost, is the number-one concern," says Tim Reis, industry manager at GW Plastics, a Bethel, Vt., custom molder that has two-shot capability.

Similar benefits of cost reduction and added functionality can be achieved with mono-sandwich molding and coinjection, two methods that combine different melt streams in a single shot. The most popular application of these single-shot methods is to "bury" regrind or less costly materials under an outer skin that must meet strict aesthetic or functional requirements. "The savings can be as much as 50%," says Bruce Kozak of Cincinnati Milacron. These single-shot methods can just as easily insert special functional layers under the outer skin - such as a foamed core underneath a solid skin or a coinjected barrier layer within a PET bottle preform.

Although these techniques have been around for decades, they have emerged into the limelight over the past year or so. "The multi-component field is evolving quickly right now," notes Michael Santa, v.p. of Krauss-Maffei. Though some new technology has come to light recently, most of the excitement is in new applications and new opportunities for custom molders to adopt these more tricky and expensive technologies.

Multi-component applications are spreading among automotive, consumer, packaging, and medical products. Favorable manufacturing economics are one factor encouraging this growth. Another is product designers' growing awareness of what the processes can do. Also important is resin suppliers' eagerness to develop new grades that allow a wider range of compatible material pairings - especially the soft/hard combinations described in our June issue (p. 45).

Not just for captive molders

A sure sign that multi-material molding is hot now is that several suppliers report accelerated sales of multi-barreled injection machines. "We've seen a serious upswing in the last 12 months," says Jim Moran, sales manager for Engel Machinery. Likewise, Krauss-Maffei reports that its North American sales of such machines in the first half of 1998 far exceeded those for all of 1997. Other machine builders cite similar increases.

The same goes for toolmakers that build multi-component molds. "A lot of molders are attempting to get into the market right now," notes Brian Hartlmeier, v.p. of Mold Makers Inc.

Conventional wisdom holds that only captive molding operations making long runs of a proprietary product can justify the up-front costs of a multi-component molding cell. The press itself can cost from about 1.3 to three times as much as a standard machine, owing to the extra injection units, rotary platens, extended tiebars, and extra pumps and accumulators.

Tooling also can cost up to twice as much as usual. Overmolding, in particular, requires a tool with a second set of cavities. Such molds also require extra engineering work, complex internal actions, and two hot-runner systems. "There's more of everything," says Hartlmeier.

Another drawback for custom molders is the non-standard layout of the multiple injection units. That limits the ability to run conventional one-component molds if there isn't enough multi-component work to keep the press busy. "In some machine configurations, you can't run regular molds due to the sprue bushing location," notes Robert Hare, general manager of Ferromatik Milacron. For this reason, he says, custom molders like to configure multi-component machines with one standard horizontal injection unit and a vertical parting-line injector. Such a machine layout is more compatible with standard tools.

Custom molders historically have had a tough time justifying the upfront investment unless they had firm, high-volume orders to keep such expensive hardware occupied. In the past, the few custom molders that did have multi-shot and coinjection machines tended to be large automotive molders running mostly high-tonnage presses for jobs like taillight lenses.

But now, custom molders outside the automotive world have started to view multi-component technology as a way to develop a competitive edge. Suppliers of machinery and tooling say their recent quoting activity indicates that custom molders are taking a serious look at multi-component molding. "There's no question that multi-component molding is growing for both custom and captive molders, but the custom molding segment is growing faster," says Rick Shaffer, product manager for Van Dom Demag. New multi-component applications have prompted sales of more small- and medium-tonnage machines. "There has been some action in the 50- to 80-ton range as custom molders leave the prototype stage and start pilot projects," Shaffer reports.

Nowadays, a few custom molders are even willing to risk a multi-component system purchase before they land a large-volume order. "In order to get the work, you have to have the machinery," says Krauss-Maffei's Santa. He sees more custom molders willing to believe that "if you build it, they will come."

Consider the experience of GW Plastics. It brought in its first two-shot press, a Nissei 120-tonner, well in advance of the company's first large order. "To make sure we didn't get our first production job and then fumble it, we spent a year and a half developing our expertise," says Tim Reis. That foresight paid-off when GW won a high-volume consumer-product order that went into production this month. The company has since added a 200-ton multi-component press to keep pace with that order and to support additional ones in medical, automotive, and consumer products.

While new custom molders weigh entering the multi-component business, those who are already in it are adding capacity. Take Armin Molding in South Elgin, Ill.: It has run multicomponent jobs on three 350-ton Newbury presses since 1982. In the past few months, the company has bought four Krauss-Maffei machines - two 175-ton models with rotating platens and two 80-tonners with stationary platens.

Getting started

Multi-component molding is not for everyone. Its dependence on high-volume jobs will lock out some custom molders. And the complexity of the technology itself may deter others. "You don't just plunk down one of these machines on the floor and say here I am," cautions Ferromatik's Hare.

"Your average shoot-and-ship molder would be overwhelmed by this technology," agrees Haans Petruschke, development engineer at Endura Plastics in Kirtland, Ohio. This molder of precision automotive parts recently began overmolding a small high-volume part for a power accessory drive using a 50-ton Demag press. The machine has stationary platens, so the tooling employs a built-in rotary action.

Recounting some of the challenges Endura faced in launching its first two-shot project, Petruschke says the materials caused some difficulties: The part consists of glass-filled nylon overmolded with a type 6T modified nylon that Petruschke says is tough to mold to tight tolerances even in a single shot. But the firm's general lack of experience with two-shot tooling and machinery - especially the sequencing - presented the biggest hurdle. "It was like trying to get two machines and two molds started up at the same time and to work in conjunction with one another," says Petruschke. Even with all the engineering resources available to an automotive molder like Endura, it took three months of full-time work to get the tool and machine into production.

But now that the job is up and running, Endura is pursuing more multi-component business. "Our challenge is to apply what we've learned to other jobs," says Petruschke.

Get the tooling right

As applications grow, molders are apt to discover that tooling expertise can make or break a multi-component project, according to Harry Webster, sales engineer at Delta Tech Mold. One of the key toolmaking challenges is to precisely align the first and second shots once the cores have rotated into position for overmolding. The margin for error is often less than 0.005 in. "It must be a seamless interface, and that takes engineering experience," says John Thirlwell, v.p. of Caco Pacific. Factors such as accurate shrinkage compensation, draft-angle calculation, and machining tolerances all become more critical than in ordinary single-shot molds, agrees Rick Scheidt, molding manager at Accede Mold and Tool.

Because of the growing strength of the multi-component market and the sometimes lengthy debugging effort required for these complex jobs, some toolmakers have recently installed their own two-component machines for prototyping and mold tryout. Accede, for example, recently added a Demag 80-ton press. Delta Tech Mold has a 300-tonner from Krauss-Maffei with parting-line injection and a rotary table. Meanwhile, Armin Tool & Mfg., a leader in this field, runs its own multi-component molding operation.

Among the new tooling technology for multi-component molding is a horizontal rotary mechanism in which the center platen swivels 180 [degrees] to bring the primary shot into overmolding position. Developed by Ferromatik Milacron, this "stack-mold" configuration enables full platen utilization. Thus, two-component jobs can run on smaller presses than would be required if using a vertical rotary platen that must accommodate both cavity sets of a two-shot mold. Hare says the first North American application of this technology allowed a 32+32 cavity mold to fit on a 350-ton press, rather than the 700-ton model that it would otherwise demand. Hare notes the center platen could index the cores by only 90 [degrees] per cycle to permit secondary operations to be performed atop the machine.

Hot-runner systems are the norm in multi-material molding. Recent developments in this area include the introduction of sequential valve-gate systems for coinjection by Incoe Corp. and by Dynisco's Hot Runner Group (formerly Kona). Both companies have supplied sequential valve gates to Visteon Automotive Systems, Milan, Mich., which bas coinjected a bumper fascia that contains 20% painted scrap. Incoe sales director Jack Steele says valve-gated coinjection has also been used for pump housings and lawnmower parts.

Valve gates have also been used with the new Multi-Gate Coinjection technology from Kortec, Inc. This technique uses parallel hot-runner systems within a special manifold to feed two separate melts to proprietary coinjection nozzles at the gates. This approach can be used with any type of multi-barreled machine and is said to give highly selective control over skin thickness on both sides of the part. The same system can also be used for overmolding or one-component injection.

RELATED ARTICLE: Multi-Component Applications Multiply

Many of the newest multi-component products have yet to come to market - particularly those for the medical field - so molders tend to be tight lipped about them. But some of the promising applications include the following:

* Consumer Products. A walk down the aisles of your local pharmacy reveals ample opportunities for hard/soft material combinations. Arrays of multi-colored toothbrushes with swirls and stripes greet you on one side. On the other are Schick disposable razors with a slip" grip. You'll also find Gillette's new Mach 3 razor, which has two-component moldings on the handle and blade. It's molded on equipment from Ferromatik.

* Cameras. Last year, Eastman Kodak began producing a one-time-use camera body in a two-component process. The case has a hard housing of clear polystyrene overmolded with a rubbery outer cover, which serves as a "grippable" exterior and forms a waterproof seal. Kodak molds the Fun Saver Sport camera on a Ferromatik 220-ton multi-component machine running a 2x2 mold that turns out two finished camera bodies per cycle.

* Airbag covers. With the proliferation of airbags for passenger and side-impact protection, airbag covers are an "immediate opportunity" for multi-component molding says Jim Moran, sales manager for Engel Machinery. Engel recently delivered an 825-ton machine for molding these large parts (4-6 lb) from two polyester TPE grades with different hardnesses. (Moran and other suppliers note that established multi-component applications, such as overmolded taillights and coinjected bumper fascias, remain strong as well.)

* Cosmetics packaging. According to Ferromatik's Hare, multi-component molding has long been popular in the high-end European cosmetics market, which favors visually striking packages. The fashion now appears to be crossing the Atlantic, notes Keith Ruby, v.p. of Motor City Plastics in Livonia, Mich. His firm, which specializes in cosmetics packaging, recently started overmolding a high-production compact case on a 300-ton press from Husky. The system robotically transfers parts from the first-shot to second-shot cavities. It turns out 12 compacts at a time in a 14-sec cycle.

* Molded-in gaskets. Sealing gaskets that were once applied in a secondary molding process or pressed in by hand are increasingly being considered as candidates for overmolding. While much of the interest revolves around automotive parts, tool suppliers report activity in closures and containers as well. Master Precision Molds, Greenville, Mich., recently built a tool for a food-container cap in which the hard component of the cap is fully encapsulated by a soft component that serves as both a gasket and as a soft-touch exterior.

One gasket application that's poised to take off combines thermoset liquid silicone rubber (LSR) and a thermoplastic in a single machine. Most of these parts go under the hood, such as automotive connectors with a built-in gasket. Van Dorn Demag recently delivered a 165-ton LSR/thermoplastic machine to GE Plastics in Pittsfield, Mass. The LSR enters from the side of the press. The biggest processing challenge has to do with the tooling, which must heat the LSR and cool the thermoplastic, says Demag technical sales specialist Christian Renners. Other machine vendors - including Ferromatik, Krauss-Maffei, Engel, and Battenfeld - report selling similar machines or other thermoplastic/thermoset systems in Europe.

* Gas assist. Multi-component molding combined with gas assist is a promising opportunity, according to machine suppliers. "You'll start to see more marriages of multi-component with different technologies," Hare predicts. At this month's K'98 show in Germany, Ferromatik will demonstrate gas assist with the company's mono-sandwich technology, in which two different melts can be injected in sequence from a single injection barrel. Together, these two technologies will produce a windshield-wiper arm in which the inner structural component is a glass-filled PBT and the outer, visible component is unfilled PBT.

RELATED ARTICLE: Try Sandwich Molding With a Single Barrel

Who says you need special machinery to perform multi-component molding? Not Milko Guergov of M&C Advanced Processes. He came up with a way to use a standard single-barrel molding machine to produce sandwich parts from carefully selected material combinations.

With the right resins, says Guergov, you can blend the two kinds of pellets in one hopper, then plasticate and inject them together in the same barrel, and finally achieve complete encapsulation of one material by the other in the mold, just as with coinjection.

The key is to pick two materials that are "chemically compatible and have moduli at least 150,000 psi apart," Guergov says. Material separation depends on the relationship between modulus and temperature. When the melt hits the cavity wall and begins to cool, the two materials quickly separate "like water separating from oil." The one with the higher modulus forms the core because it freezes first and begins to shrink, squeezing out the lower modulus material, which forms the skin.

Unlike coinjection, the two materials do not form totally separate layers. "There is a partial physical infiltration of the skin into the core," Guergov notes, resulting in a stronger bond between the layers.

Guergov's technology requires a constant melt pressure during injection. The latter is achieved with M&C's proprietary gas counterpressure control technique. It is said to provide real-time dynamic control of melt pressure by shooting into a cavity filled with pressurized gas and instrumented with transducers.

Guergov says his approach works with combinations of nylon 66 and high-impact nylon 66, as well as with PP and thermoplastic vulcanizate (TPV) elastomer. Guergov says one customer has used his method to mold a bumper with a virgin PC/PET skin over a core of PC/PET painted regrind. "The paint's adhesive acts as a filler, which increases the modulus difference between the two materials," he explains. He also says a liquid paint skin can be formed around a thermoplastic core in the mold.
COPYRIGHT 1998 Gardner Publications, Inc.
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Copyright 1998, Gale Group. All rights reserved. Gale Group is a Thomson Corporation Company.

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Title Annotation:includes related articles
Author:Ogando, Joseph
Publication:Plastics Technology
Date:Oct 1, 1998
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