Close-up look at a lost-core manufacturing cell.
What Siemens describes as the first complete lost-core molding cell in North America is surprisingly compact, measuring only 60 x 60 ft. The 75,000-sq-ft Windsor plant has room for eight such cells and will probably get another one by spring of this year. The cell was supplied as a turnkey system by Klocknet Ferromatik Desma of Germany. (Now called Klockner Desma, with U.S. offices of the same name in Erlanger, Ky., the firm remains in the lost-core equipment business despite its recent exit from all other aspects of thermoplastic injection molding.)
The fully automated process, starts with the core-casting machine. It's a horizontal Klockner Windsor 30-ton press, which molds two 76-lb tin-bismuth cores per cycle, using a German-built stack mold. The cores are demolded by a pair of Klockner Remak servo-electric gantry robots and placed on a cooling conveyor. The cores are cast at 340 F and the centers are still molten when the parts are placed on the conveyor. By the time they reach the thermoplastic injection machine, the cores have cooled to 80 F.
The cores are overmolded with nylon in a 650-ton Klockner vertical press with a turntable. Another Remak servo gantry robot loads the cores into the mold and unloads the finished parts, cutting off a short sprue as well. The German-built hot-runner mold has two lower mold halves and one upper half so that loading/unloading and molding can take place simultaneously.
Molded manifolds with cores travel on fixtures on a vertical conveyor into the melt-out tank. The unusually compact melt-out system (from FTF in Germany) contains a four-level carousel with 60 stations and a hot bath of glycol (Lutron HF3 from BASF Corp., Parsippany, N.J.). The bath is heated above the melting point of the tin-bismuth alloy, 320 F, well below the 491 F melting point of the plastic. The molten ahoy sinks to the bottom of the tank and is gravity-fed to a heated storage tank.
Another robot then transfers the empty manifolds into a four-stage hotwater washer to rinse off all traces of glycol. The rinse water is subsequently vacuum distilled so that the glycol (which costs $6/gal) can be recycled.
A conveyor takes the clean parts to a series of manual finishing stations where operators install brass inserts, which would be plated over with core alloy if they were molded in. Operators also ultrasonically weld a plastic cap over a hole in the plenum (used to locate the cores securely in the injection mold), and leak test the part.
All the automated stages of production are timed to coordinate with the 60-sec injection molding cycle. Thus, two cores are cast in 120 sec, and 60 parts are in transit through the 1-hr melt-out stage.
The complete cell, which costs well over $5 million, operates 24 hours, five days a week, producing around 315,000 parts a year. Finished manifolds are shipped to Chrysler's assembly plant in Trenton, N.J.
The Neon manifold is Siemens Automotive's first lost-core project. The decision to go ahead with lost-core molding was made on October 1, 1992. The first crates of equipment came in the door at Windsor on March 28, 1993. The system took four weeks to erect, and the first approval parts were submitted to Chrysler on July 1. In September, the manifolds went into full production.
Putting the lost-core system into production was rife with difficulties, says engineering director Alan R. Taylor. "There were no easy parts," he jokes, but integrating the robotic transfers between all the time-coordinated stages was one of the two biggest challenges. General manager Jim J. Riordan puts his finger on the other one: "Tooling, tooling, tooling." Getting the time-temperature cycle right on the core-casting tool was critical. "If you cool too fast, the cores crystallize and become brittle," Riordan notes. "Cool too slowly and you get 'bleeders'--molten metal intrusion into the overmolded plastic."
The injection tooling involved even trickier considerations, Riordan says. "For instance, what will the core do during molding?" And there's also the fact that the plastic undergoes stress relief and shrinkage during the melt-out stage. The key is to anticipate those post-molding dimensional changes and build them into the tool design. On a tool where some dimensions had a total tolerance of only 0.5 mm, it's no surprise that the molds required some dimensional adjustments after they were built. What's more, the injection tools had to be sent out for ion nitriding to protect them from wear by the glass-filled nylon--but that couldn't be done until all adjustments were final. Taylor considers the system "99% bug-free now, but we still want to optimize uptime." He says the current uptime performance is 93-94% but he expects to do even better.
BULLISH ON LOST-CORE
"These plastic manifolds are coming in very aggressively," says director of business development David G. Geran. "All the Big Three car makers are interested in plastic manifolds. And the Asian transplants have shown a sharp increase in interest in the last six months."In Europe, where it all started, he sees an evolution beyond a single plastic component, such as a manifold, to more complex integrated systems--e.g., a manifold with integrated fuel rails, throttle bottle, and air-cleaner housing. "We're already working on designs for the 1997-98 model year. The industry could go 80% to plastic manifolds in 10 years."
Because Siemens Automotive has chosen to focus on the more complex designs, its strategy is based on lost-core processing. However, Riordan adds that Siemens is keeping an open mind toward alternative approaches such as welded plastic assemblies and two-shell overmolding, which he sees as more appropriate for simple and moderately complex designs, respectively. Whatever the design, he expects plastic to beat aluminum on cost, except in low-volume applications. In the future, Siemens may consider other thermoplastics besides nylon 66. Nylon 46 could be useful if higher heat resistance is required, says Siemens manufacturing engineer Rick Weckerle, though it is also more expensive. Likewise, PPS could be considered for methanol resistance.
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|Date:||Feb 1, 1994|
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