CHICAGO — There's no turning back. Two-platen injection molding presses are here to stay, especially in larger-tonnage machines, according to machinery executives at NPE 1997, held June 16-20 in Chicago.
The idea of injection presses with two platens, instead of the traditional three, has been around for years. But that third platen, also called the end platen, wasn't just there for show — it transmits clamping force to the tie bars and the moving platens. Eliminating it reduced manufacturing costs and made the machines much smaller, a big advantage in very large machines. But first, machine suppliers had to solve problems with platen deflection, or the tendency for the platen, a large plate of steel, to flex under clamping force.
Although the basic technology has been around for years, the flood of two-platen machines started at the K'95 show in Dusseldorf, Germany. They proliferated last month at NPE, when at least five companies showed their first-ever two-platen models: Husky Injection Molding Systems Ltd., Cincinnati Milacron Inc., HPM Corp., Van Dorn Demag Corp. and LG International (America) Inc., which makes Goldstar-brand presses.
This year's NPE generated some heat, in the form of a patent lawsuit HPM filed against Husky June 12, just a few days before the Chicago show. HPM sued Husky in a court in Dusseldorf over a 1980 patent held by Hemscheidt Maschinentechnik Schwerin GmbH & Co. HPM owns Hemscheidt.
According to HPM, the German suit covers the locking mechanism, among other areas.
At NPE, Husky officials denied their machine, the E-Series, violates the Hemscheidt patent.
In Chicago, two-platen advocates were bullish.
Krauss-Maffei AG showed its first two-platen machine in Dusseldorf at K'95. Just two years later, at NPE, Cletus von Pichler, chairman of the German firm's managing board, predicted two-platen technology will be ``the only machine to survive.''
``Anyone who does not go for two-platen will be outdated,'' von Pichler said.
Husky President Robert Schad said: ``I think two-platen machines will gradually replace the three-platen machines, because they're less-expensive to build. You see it all over now. Every show you see more of them.''
Available in clamping forces from 1,000-4,400 tons, Husky's E-Series machine has replaced its old three-platen D machines. Husky manufactures the two-platen E-Series press in Pittsfield, Mass., and in Europe at Dudelange, Luxembourg. Husky is based in Bolton, Ontario.
Husky, by cutting the number of parts by 30 percent, has been able to reduce prices by about 10-20 percent, said Bill Baillie, Husky's general manager of large-tonnage machines in Pittsfield. Plus reliability improves with fewer parts, he said.
Cincinnati Milacron Inc. sold its NPE show machine, a 1,760-ton Vista Maxima, to custom molder Bloom Industries, a division of Pacal Molded Plastics of Warren, Ohio. Cari Vota, Milacron engineering product supervisor, said the press is just the second Milacron has built. The first has been running since February in Batavia, Ohio, at Milacron's Plastics Machinery Group headquarters.
The firm will continue to make three-platen machines, but Vota thinks the trend will keep moving to two platens.
``Absolutely, this is definitely the way to go,'' she said.
Van Dorn Demag Corp., which also introduced its first two-platen model, called the Caliber, also will keep making traditional three-platen presses, said Scott Kroeger, Caliber product manager. But he said two-platens should keep growing in popularity.
``It's definitely a trend that needs to be recognized,'' he said. ``It shouldn't be taken lightly.''
Kroeger, a former sales engineer with Engel, said North American processors now recognize the importance of two-platen presses' smaller footprints.
``North American molders are seeing the trends a lot faster than they were before, through international partnerships and through shows like the K show and NPE,'' he said.
But not everybody in Chicago was doing back flips over two platens. Officials of Battenfeld GmbH, based in Meinerzhagen, Germany, said they plan to stick with three platens on their larger machines.
``There's no need, from our viewpoint, to change over immediately to a two-platen machine,'' said Lutz Weisbecker, a Battenfeld managing director who plans technology.
Mitsubishi Corp. has taken the opposite approach. After originally licensing two-platen technology from Natco Inc., which went out of business in 1990, the Japanese company showed a two-platen back at NPE '91, said David May, national sales manager for its U.S. operation, Mitsubishi Heavy Industries Injection Molding Machinery Inc. of Wood Dale, Ill. At NPE 1997, the company showed two models, a 1,450-ton press and a 610-tonner, both MMIII machines.
In addition to space savings, May said the modern two-platen machines boast better control of clamping pressure near the outside perimeter of the mold, which is important on large parts.
``Automotive's telling us these parts are going to get bigger and bigger, with deeper draws,'' he said.
Peter Neumann, managing director of Austrian press maker Engel Vertriebsgesellschaft mbH, thinks two-platen machines will completely replace machines with three platens in the near future. Neumann, at NPE, said the two-platen concept is more than 10 years old, but improved sensors and control technology are making the machines more popular.
``It's very important to have a very precise control of the locking mechanism,'' Neumann said. The locking mechanism must fit snugly, but not wear against the other parts, he added.
Duo-brand two-platen machines now account for 80 percent of Engel presses with 1,000 tons of clamping force and larger. Engel North America has operations in Guelph, Ontario, and York, Pa.
Ube Machinery Inc., a Japanese press manufacturer which last year began assembling machines in Ann Arbor, Mich., still sells mostly three-platen machines in the United States. But Taku Tawarada, marketing and sales manager, said Ube in Japan makes a form of two-platen hydromechanical presses, for Japan and Southeast Asia, where factory space is tight. The press is 20 percent shorter than the company's three-platen machine.
The two-platen actually has two platens and one end plate, which helps maintain alignment and structural integrity.
Tawarada thinks floor space is not a huge priority at most U.S. molders. Anyway, Ube's toggle clamp is shorter than the same size machine with a hydraulic clamp, he said.
Here is a two-platen wrap-up of machines that debuted at NPE.
Van Dorn Demag of Strongsville, Ohio, showed a 1,760-ton Caliber press molding an automotive door part. The hydromechanical clamp machine comes in clamping forces of 1,100-4,400 tons. The machine builds tonnage from the moving platen through four cylinders mounted on the tie bars. When the mold closes, calipers move in place into notches in the tie bars; the cylinders release when the mold opens. The tie bars are fixed to the moving platen.
A large yoke, resting on bushings that nearly encircle the guide rods, supports the moving platen and the mold.
Milacron's Maxima press is initially available in four sizes, of 1,500, 1,760, 2,200 and 3,000 tons, with shot sizes from 179-540 ounces. Eventually the line will run from 500-4,000 tons. Instead of building tonnage with cylinders on the tie bars, as many competitors have done, Milacron engineers devised a single, large pancake-shaped ram, which is mounted on the stationary platen behind the die plate. The ram distributes clamping force evenly and limits deflection, the company said. The ram is as big as the platen. It moves just 1.37 inches. Large skates support the moving platen.
HPM of Mount Gilead, Ohio, claims it has eliminated deflection through a parabolic design. A two-piece platen allows for flexibility between the platen and its carrier, connected together by a patented proprietary design. HPM said the hydromechanical Next Wave press comes in clamping forces of 360-5,000 tons and shot sizes of 14-1,325 ounces.
Husky uses a patented Reflex design on both the platens to maintain parallel alignment, transmitting clamping forces from the tie bars into the molding areas to compress the platens, instead of deflecting them. Tie bars are mounted in the fixed platen, instead of the moving platen, to reduce the amount of mass the machine has to move and to eliminate added weight from the tie bars.
LG International of Englewood Cliffs, N.J., showed its first two-platen Goldstar machine, the LGH 500 M. Initially it will be available in just one size, of 500 tons; at the LG booth, LG was showing the first one ever made. Hee-Seok Park, team manager in charge of exports, said LG plans to add a 950-ton model. A two-platen design reduced the size of the press by 15 percent, according to Kyung-Chung Kim, chief research engineer for LG Cable & Machinery Ltd., the company's Korean parent.