WHO NEEDS TIEBARS?
Although some critics contend that these machines pose platen-parallelism risks, tiebarless machine suppliers say their prime justification is the wide-open molding area that permits mounting extra-wide tools, aids tools changes, and readily accommodates parts-removal automation. The marketplace seems to be accepting those benefits: Engel has sold more than 4000 tiebarless machines worldwide since their introduction at K'89. More than 400 have been sold in North America alone. So it's no wonder that this year's show brought a bumper crop of tiebarless machines, including the following brand-new entries:
* Engel introduced the Optima 220-ton hybrid electric version. It uses electric drives on the injection unit and hydraulic drives on the clamp.
* Arburg showed its first fully electric tiebarless machine, the All-rounder E, although its commercial availability is at least three years off. Two servo-driven columns on a C-frame open and close the clamp.
* Hemscheidt, which introduced its first tiebarless machine of 165-tons in 1994, extended the range with 220-and 352-ton machines. The company also introduced a new "intelligent frame" with a computer-optimized cut-away design of its inner corners that allows the frame to flex during clamping to keep the platens parallel.
* Germany's Sachsische Kunststofftechnik (SK) GmbH brought along its new tiebarless design with an H-shaped frame. Available in 80 and 250 tons, the machine uses two short-stroke cylinders to dynamically compensate for the clamping force by providing an "equal and opposite" force on the frame.
* Oima of Italy showed a 77-ton prototype of a tiebarless machine that will ship by the middle of next year.
* Billion of France displayed a semi-tiebarless machine in which the top two tiebars have been removed to provide greater access to the molding area while the bottom two have been retained for the sake of platen parallelism. A toggle mechanism performs opening and closing movements, but a hydraulic cylinder provides the clamping force. The press will be available in 90 to 320 tons.
Of all these new models, only the Engel and Hemscheidt machines are easily available to North American molders right now. And be aware that some suppliers of these machines are involved in legal disputes over tiebar-less patents.
THE AGE OF ELECTRICS?
All-electric machines have grown beefier with the introduction of a 725-ton Elektra model from Cincinnati Milacron. This machine has more than doubled the clamp force of the company's previous big gun, a 300-tonner. The Elektra 725's injection unit comes in an 80-mm size with shot capacities from 3.75 to 4.8 lb. A 100-mm version is also available. The company plans to introduce a 550-ton model, thereby completing the Elektra range that starts at 85 tons. All are controlled by Milacron's Camac 486 controller.
New hybrid machines are on the scene as well. These typically combine an electric servo motor on the injection unit with hydraulic clamping. The makers claim energy savings up to 20%.
Hybrids also make it easy to provide screw plastication concurrent with clamp holding pressure. Suppliers say the result can be less recovery-time limitation and the potential for downsizing both plasticating units and machine cost.
The newest hybrids at the show were the Engel tiebarless machine and models from Van Dorn Demag and Krauss-Maffei. Van Dorn Demag's new hybrids come in sizes of 125-330 tons, with 420-800 ton models to follow next year.
The injection unit doesn't use a ball-screw drive, but something more like a timing chain driven by gears. "We're reaching accumulator injection rates with an electric machine," says product manager Rick Shafer, citing an 80-millisec fill rate for an eight-cavity mold for 1.1-mm jewel boxes. Price of the machine will be less than or equal to a conventional machine, says Shafer.
Krauss-Maffei's new 165-ton KM 150 CZ carries an injection-rate spec of up to 39.4 in./sec. Unlike the Van Dorn Demag hybrid machine, it also uses an electric drive on the ejector assembly. The hydraulic clamp and accumulator resemble those of the C-Series machines, and can handle speeds up to 15.6 in./sec. Price of the machine, which won't be commercial until next year, is expected to be about 40% higher than a conventional machine.
GETTING MORE FROM LESS
Other "next-generation" machines at the show have embraced modularity and compactness in an effort to get more productivity from machines that use up less energy and floorspace. Machine "footprint" and energy consumption are already big concerns in Europe and seem to be of increasing importance in North America. In the U.S. the push for floorspace conservation is being driven by the use of more beside-the-press automation. "Smaller machines mean less beam length for robots," points out Barry Potter, president of Netstal's U.S. operation. Some molders have even started to calculate "productivity per square foot" when specifying machines, adds Schafer of Van Dorn Demag.
In the compact category, Netstal showed its new Synergy line, which replaces the earlier HP machines. Synergy upgrades platen dimensions and tiebar spacing to the equivalent of the next larger press size while reducing the footprint by roughly 10%. For energy savings, its new hydraulic system uses dual pumps - one variable- and one fixed-volume type - cutting energy consumption by 10-20%, says Potter. Noise reduction is provided by encasing the drive motor and positioning the pump so it protrudes into the tank. The machine also has a brand-new injection unit that uses a sliding rotary piston to reduce its inertial mass. The new unit reaches top injection speed more quickly than the HP, and Netstal's controller now profiles injection times in 0.3-sec intervals. Synergy also has standard quick-change and clean-room features that were optional on past machines. The Synergy range currently includes presses from 66 to 385 tons.
Battenfeld's new HM Series of modular machines in the 550-to 1430-ton range employs a new hydromechanical clamp design with wider platens and a lower profile than the BA-T Series it replaces. Injection units maintain a 22:1 L/D on all screw sizes to promote a homogeneous melt and higher plastication rates. In place of a standard accumulator, the HM's new hydraulic system uses a multiple pump arrangement: Each motor drives two pumps, one of fixed and one of variable displacement. This arrangement shaves about 10-15% off the cost of the machine - though an accumulator is still available when there's a need for speed. Finally, Battenfeld replaced the gearbox assembly on the injection unit with a low-speed hydraulic motor, cutting the machine's length by several feet.
The new "Short 1600" from Sandretto cuts 13 ft off the length of the company's 1760-ton machine while leaving press height unchanged. And a new 820-ton wide-platen machine designed for the U.S. market has platens 8 in. wider without any change in floorspace. At the show, this machine produced a garden chair, an application that would normally go in a 1000-ton or bigger press.
So-called two-platen machines are another space-saving design, examples of which were shown by Engel and Krauss-Maffei. Another is in development by Husky (see PT, Nov. '95, p. 11).
Hemscheidt showed off its retractable-tiebar machine, which also uses a two-platen concept, in a new larger 1600-ton version.
Another two-platen design on the new SGA 420 SCR high-speed 464-tonner from Fahr Bucher (sold here by Bucher Inc.) was shown with an integrated clean-room environment around the clamp end. This arrangement is made possible by the free-hanging Superlock clamp design that uses hydraulic pistons built into the tiebars to pull the mold shut, leaving no hydraulic components to project into the clean room.
CONTROLS & CIM NETWORKS
One of the most interesting developments in controls at the show was Barber-Colman's new "Impact" auto-tuned controller with an expert system to optimize boost/hold transfer (PT, Nov. '95, p. 11). Dong Shin of Korea (sold in the U.S. by Promax) is one of the first OEMs to implement the Impact control. Dong Shin also showed a new molding-machine network based on a customized version of Barber-Colman's Maco 4000 control and a new graphic interface.
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|Title Annotation:||K'95; injection molding machinery exhibition|
|Date:||Dec 1, 1995|
|Previous Article:||New plant is world-class from day one.|