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Lost-core molding: don't count it out yet.

In car engine after car engine, aluminum alloys have already yielded to the onslaught of thermoplastics for air-intake manifolds. And the trend shows no sign of flowing, with Tier One automotive suppliers and resin companies predicting that 75% of the world's engine manifolds will be made from glass-reinforced thermoplastic composites by 2003.

Until recently, the manufacturing process that enabled this shift away from aluminum was lost-core injection molding. Thanks to its ability to produce one-piece hollow parts with complex internal geometries, lost-core molding seemed tailor-made for manifolds. Yet the process has a significant down side, too: "At $7 million per molding cell, lost-core is very capital intensive," explains Eric Sattler, senior engineer for automotive applications at BASF Corp. "And it's a very finicky, complex process," he adds. For these two reasons, manifold makers throughout the world have increasingly embraced "shell molding," a process that uses vibration welding to assemble manifolds from two or more conventionally injection molded parts.

In North America, this new generation of vibration-welded manifolds won't hit the streets in large numbers until 1999. After that time, they will take over a bigger and bigger chunk of the plastic manifold market as cheaper, simpler shell molding becomes the process of first choice, even for manifold suppliers who offer both processes. "It's certain that more than 50% of composite manifolds will ultimately be vibration welded," says David Geran, director of new business development for Siemens Automotive, which offers both lost-core and shell molding at its Windsor, Ont., plant. Pete Hradowy, sales and marketing director for Mann+Hummel Automotive in Southfield Mich., is even more upbeat about shell molding. In his view, as many as 75% of the composite manifolds worldwide will be vibration welded by 2003. "If a job can be done with welding technology, it will be," Hradowy asserts. His firm performs both molding processes in Europe.

With shell molding gaining ground so quickly, you might think that lost-core is coming to the end of its road. But think again. Ongoing engine programs keep North America's lost-core capacity - which is distributed among just four molders - humming right along. And shell molding does have some design limitations right now. Finally, the growing interest in more complex manifold designs with integrated air-fuel modules continues to ensure a role for lost-core molding and has even resulted in "hybrid" jobs that combine lost-core with shell molding. "There will always be a place for lost-core," says Siemens' Geran.


So far, cost has been the main strike against lost-core molding. First, there's the big capital investment in a molding cell that includes not just a large injection machine but also metal-casting machinery for the cores, robot handling devices, and a melt-out station. Mark Battista, operations manager at CoreTech Associates, a lost-core equipment supplier and engineering consultancy, estimates that shell-molding cells cost 10-15% less than a typical lost-core cell.

BASF's Sattler adds that lost-core also incurs significant operating expenses, chiefly the cost of the core alloy and of casting but also other costs related to the sophisticated processing knowledge required for lost-core molding. "Our customers tell us that vibration-welded manifolds cost 30-40% less than lost-core manifolds," says Sattler. At Mann+Hummel, Hradowy cites a more conservative role of thumb governing manifold costs: "Going from aluminum alloy to lost-core saves between 10% and 20%. Going to welding from lost-core saves an additional 10% to 15%."

In a recent job, for example, Mann+Hummel recently began production in Sonnenberg, Germany, of Honda's first composite (glass-filled nylon 6) manifold. Destined for the 1.6/1.8L Civic engine, the manifold cost 15-20% less than the aluminum manifold it replaced, according to Hradowy.

Shell molding's cost advantages give it a fair shot at replacing some existing lost-core manifolds, according to Jay Pyper, business manager for manifolds at AlliedSignal Engineering Plastics. Likewise, Hradowy reports that Mann+Hummel is actively considering replacement of more than one lost-core design with shell molding.


If cost is driving some applications away from lost-core, current manifold design requirements provide inertia that will keep some jobs in lost-core for a while to come.

For one thing, space is at a premium under the hood. Lost-core molding can produce a tighter manifold package than welding because the welding flange (about 8 mm wide) between the manifold's interior passages, or "runners," takes up extra space, Geran points out. "Multiply that space by four runners, and it adds up," he says. With lost-core molding, the runner walls are all that separates the runners, resulting in a more compact package.

Lost-core molding reportedly also does a better job of dealing with manifold runner routings as they are commonly laid out today. Vibration welding has trouble with sharp runner angles and runners that cross or touch, says Geran. On a manifold produced last year for Jaguar in Europe, complex runner routings are reportedly one reason the job went to lost-core rather than vibration welding.

Finally, as the number of parts to be welded into an assembly climbs, lost-core becomes more competitive. "Whenever you get to five or more parts, you may have to look at the cost benefit of lost-core," says Hradowy. However, Volkswagen still decided to go with a five-piece, shell-molded manifold that's part of an integrated air-intake system.


Finally, the growing trend toward integrated air-and-fuel handling systems may also keep some jobs in lost-core. An example is a new air-and-fuel handling module that Siemens Automotive will soon supply to Volkswagen.

The module employs three different molding processes to create the air-handling system. Lost-core makes the flange that seats the manifold on the cylinder head. Shell molding is used for the manifold itself. And die-slide molding, a tooling-based method for molding hollow parts, produces the remaining air-intake components.

RELATED ARTICLE: There's Life Beyond Automotive

Despite the inroads shell molding is poised to make in engine-manifold applications, there's a whole world of non-automotive jobs still open to lost-core. "The future for lost-core injection molding is very bright," says Mark Battista, operations manager at CoreTech Associates, which supplies metal-core casting technology and also integratES lost-core molding cells. Battista cites aerospace, marine, industrial and recreational parts that utilize lost-core molding. For example, Gould Pumps Inc. replaced a metal pump housing with a lost-core-molded glass-filled nylon. And Epic Industries in Auburn Hills, Mich., has molded bicycle and wheelchair wheels using the lost-core process.

CoreTech just opened a lost-core custom-molding facility - mostly for non-automotive parts. "We've set up a facility to make parts for customers whose volumes don't justify the cost of a molding cell," says Battista. CoreTech has two cells built around 300-ton presses for parts smaller than engine manifolds, which tend to run on machines of at least 650 tons.
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Author:Ogando, Joseph
Publication:Plastics Technology
Date:Sep 1, 1997
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