TAKING THE MEASURE OF THE MACHINES
This past year has seen the entrance of the first all-electric machines into the Canadian market (see CP, July 1998). Could this be a sign that more companies are shedding the typically Canadian wait-...
This past year has seen the entrance of the first all-electric machines into the Canadian market (see CP, July 1998). Could this be a sign that more companies are shedding the typically Canadian wait-and-see attitude toward newer technologies and are ready to embark on some major upgrades to their equipment?
It would appear so. As borne out by this magazine’s last molders’ survey, in which over 50 percent of the respondents said they intended to purchase injection molding machines in 1998, four plus years of strong growth in the Canadian plastics industry have given many molders the confidence and resources to make long-delayed investments in new equipment. Yet many of these companies, especially small- to medium-sized enterprises, will find the injection machine market vastly changed from the one in which they last purchased. New machine technologies offer increased customization and flexibility features. Understanding the comparative advantages afforded by both the newer and older machine technologies is a key first step in helping you make the choice of machine best suited for your operation.
TWO PLATEN, THREE PLATEN
The main advantage of a two-platen clamp design is a reduction in overall machine length and the resulting space savings. While there are presently at least a dozen worldwide suppliers of two-platen machines, Battenfeld of America has opted not to carry an off-the-shelf two-platen design in its line-up of presses. The company’s “hydraulic modular” or HM line of presses (51) comes with a standard three-platen design. According to Battenfeld president Wolfgang Meyer, the three-platen design gives minimal platen deflection, and more exact platen parallelism, in comparison to a two-platen system.
“In a two-platen machine the clamp force is not introduced in the center of the mold, but on each of the four tiebars,” says Meyer. “Suppliers of two-platen clamps have introduced various locking designs to offset the inherent disadvantage of having only two platens.”
The requirement for locking mechanisms on each tiebar of a two platen machine generally makes two platen machines wider than three platen machines, Meyer claims. The net result, says Meyer, is that the overall square footage saved with a two-platen clamp may not be as significant as it seems.
The three platen design, with optimized platen parallelism, is ideal for use with large and/or expensive molds, in which high accuracy of platen alignment reduces premature wear on molds, says Meyer.
Manufacturers of two-platen machines claim platen deflection can be built out or eliminated by particular designs of tiebar locking mechanisms and the arrangement in which the tiebars and platens move toward and away from one another.
Two platen machines can be built with tiebars mounted on the moving platen, or with tiebars mounted on the stationary platen. In general, two-platen machines with tiebars mounted on the moving platen provide better access to the mold area. To offer similar access, two-platen machines with tiebars mounted to the stationary platen require tiebar pullers. Machinery manufacturers, such as Husky Injection Molding Systems Ltd., which make two-platen machines with tiebars attached to the stationary platen, claim the design provides faster, smoother and more energy efficient movement by removing the need to move the masses of the tiebars with every cycle. Additionally, the tiebars of Husky’s E-Series line of two platen presses (52) extend through the moving platen, which Husky claims provides guidance and counters stationary platen tilting under mold weight.
Van Dorn Demag has addressed the issue of platen deflection in the design of its Caliber Series (53, Stephen Sales Group) of two-platen presses by benchmarking to a standard of deflection measured in standard three-platen hydraulic presses, says Scott Kroeger, product manager, large machine lines.
“First of all, no platen design, two or three, can claim absolute zero deflection,” says Kroeger. “There are a number of ways to combat the deflection and every manufacturer has a unique answer.”
Kroeger says that tests done at the company show the overall deflection rating of its Caliber-design platens to be around 0.0025 in. under full load with a specifically sized test block installed. This compares, notes Kroeger, with the overall deflection rating of its three-platen hydraulic machine platens of 0.003 in. Kroeger interprets this to mean that platen deflection in Van Dorn’s two-platen Caliber Series is designed to be equal to or sometimes less than the deflection found in its three-platen machines.
“We don’t see platen deflection as an overall issue,” says Kroeger. “The growth of interest in two-platen machines that started in Europe is translating into the North American market. More companies in Canada are changing over.”
When Engel introduced its tiebarless line of machines at the 1989 K Show, its aim was to eventually replace its tiebar machines in the small- to mid-size tonnage range with tiebarless machines only, says Franz Strohmaier, vice president, engineering, Engel Canada (54). Success of both the design concept and the strategy can be measured in over 10,000 tiebarless machines Engel has sold since then. In North America today Engel builds only tiebarless machines in the range of 28 to 85 tons of clamping force; both tiebarless and tiebar machines in the range of 100 to 250 ton, and tiebar machines only above 250 ton. At K’98 Engel introduced a 660 ton tiebarless machine, which it is currently selling only in Europe.
One of the major advantages to the tiebarless design is that it provides a larger mold-mounting area, says Strohmaier. This in turn allows a molder to run today’s larger, more complicated molds on smaller machines (Figure 1). Other benefits of tiebarless machines, according to Strohmaier, include:
* Freer access to clamping area (beneficial if your shop has ceiling height restrictions and lacks an overhead crane)
* Reduced floor space requirements
* Faster mold changes
* Simplified, more cost-effective automation
* Cycle time reduction related to faster robot movement in and out of the mold
Engel’s solution to the problem of applying clamp force without tiebars is a “C-frame” machine design coupled with its Flex Compensation Linkage clamping technology. The design allows the moving platen to “follow” the stationary platen during clamp-up, ensuring the parting line doesn’t see any unbalanced forces and preventing platen misalignment, says Strohmaier.
“The biggest barrier for molders to change to a tiebarless system–any tiebarless system–is to overcome the fear of insufficient platen alignment and non-uniform clamp force distribution. This has been designed out and eliminated,” says Strohmaier.
Other manufacturers of tiebarless machines include Cincinnati Milacron (55) and HPM (56, CNSMITH Plastics Machinery Sales). Also, Engel has become the first to combine tiebarless and all-electric features in one machine with a tiebarless, fully electric 100 ton machine, which was introduced at K’98 (57). The machine should be available in North America in about one year, according to Strohmaier.
At the 1997 NPE Cincinnati Milacron’s Barr Klaus predicted that 70 to 75 percent of all injection molding machines 800 tons and below sold in developed countries would be electric in 10 years. In Canada, at least eight all-electric Cincinnati Roboshot (58) machines were sold in 1998 and, as if others are coming around to Klaus’ view, the number of companies making all-electric or electric/hydraulic “hybrid” machines continues to grow. For example both Toshiba Machine Co., America (59 ) and UBE Machinery Inc. (60, Hamilton Avtec) recently launched new lines of all-electric machines. Toshiba’s initial machine line will be available in sizes ranging from 40 to 250 tons. UBE made its entry into the electric market an auspicious one, as the company delivered what it claims is the world’s largest all-electric press yet to be built, a 950-ton model, to Stanley Electric Company
in Ohio late last year.
Bob Kadykowski, vice president and general manager of specialty equipment business at Cincinnati Milacron, summarizes the main advantages of all-electric in comparison to hydraulic machines:
* Energy savings of up to 75% during operation
* Machine repeatability within +/- 0.0005 in.
* Low melt pressure variation
* Elimination of hydraulic oil (direct mechanical drive)
* Cleaner running/quieter
“One reason an all-electric gives better consistency is because the injection unit velocity and pressure are decoupled, whereas in a hydraulic, the two are tied together,” says Kadykowski. “Once you set the velocity on an electric, the machine will not exceed it.”
Kadykowski says applications for all-electric molding continue to grow: “Anything that can be molded on a hydraulic can be molded on an electric. We’ve seen everything from coat hangers to high-precision gears being molded on electrics.”
Kadykowski says the cost difference between an equally equipped electric and a hydraulic machine can be recouped in as little as one year. The return on investment for an all-electric is faster for higher tonnage presses.
Hydraulics still popular
Van Dorn Demag’s Kroeger says there are a number of good reasons that hydraulic machines have dominated in the tonnage class of 500 tons and above for the past 20 years.
“A hydraulic machine delivers power when you need power,” says Kreoger. “Molders like the direct hydraulic pressure feedback for tonnage control they get with the machines.”
Kroeger notes that boosting power on a hydraulic is easily accomplished by adding accumulators and upsizing pumps. Another reason for the continued popularity of hydraulic machines, he says, is the comfort level a lot of molders have with the machines.
“Most hydraulics have a simple design and are maintenance friendly,” notes Kroeger. “Many molders have cut their teeth on these machines and are extremely comfortable with them.”
Engel’s Strohmaier says hydraulic machines still offer advantages in certain applications, such as thin-wall molding where injection pressures can be as high as 30,000 psi. A hydraulic machine can provide these ultra-high injection pressures in a much more cost effective manner than electric machine can, Strohmaier claims.
Kroeger thinks the predicted dominance of the all-electric machine in the market is not as sure a thing as some people believe. “If I was trying to decide between an electric and a hydraulic, I would want to cost justify both machines and see the return on investment in the long term for my particular application.”
Hybrids-the best of both worlds?
Strohmaier traces the growth of interest in hybrid hydraulic/electric machines to the desire of molders to have the best features of both machine types at the most economical cost: “We’re seeing more interest in hybrids and the main reason is that the molder has a machine in which the mold clamp is still hydraulic, which can be used for core pulls, while keeping all the advantages of an electric injection unit. The other reason is that the cost is cheaper than a full electric.”
Engel has built hybrid machines to order, mostly in the 200 to 300 ton range. Other recent additions to the line of hybrid machines available to North American processors include Sandretto USA, Inc.’s MEGA TE machine, available with clamping forces of 610, 820 and 1100 tons, as well as upgraded models (61, Ontario Heater), Van Dorn Demag’s new Ergotech elexis with clamping forces ranging from 50 to 300 tons (62, Stephen Sales Group), and HPM’s Next Wave machine, introduced at K’98, and currently available with 600 tons of clamping force (63, CNSMITH Plastics Machinery Sales).
The HPM two-platen, Next Wave machine is the latest extension of the company’s Pail Master Series of machines. It comes with a hybrid injection unit design which utilizes an electric motor to drive screw rotation, while injection transfer is accomplished with a traditional hydraulic arrangement.
According to HPM product manager, Michael McKee, the hybrid design provides significant energy savings in comparison to all-hydraulic machines.
“The primary energy consumer in an injection molding machine is plastication,” says McKee. “An electric drive uses far less energy than a hydraulic to turn the screw.” McKee also points out that the electric motor’s ability to provide variable speed control of screw drive eliminates the need for proportional hydraulic valve control, thereby reducing the size and complexity of the hydraulic system.
On the other hand, McKee notes, the hybrid design preserves the most desirable attributes of the hydraulic machine–the clamping mechanism.
Says McKee: “The hydraulic clamp allows us to design the Next Wave with a compact size and retractable tiebars, as well as with hydraulic ejectors, core pulls and other conventional hydraulically actuated devices. Additionally, electric clamps are traditionally toggle mechanisms which have more moving parts than hydraulic clamps and have hinges which may be susceptible to wear and misalignment if not properly lubricated and maintained.”
Commenting on the comparative advantages of an all-electric vs. a hybrid machine, David Bernardi, director marketing and sales, Elektron Technologies, Cincinnati Milacron, says energy savings is not the only reason to consider using an all-electric machine. Bernardi says that by adding electric servos to a hydraulic machine, you may save some energy and run a little quieter, but that you still basically have a hydraulic machine; one that lacks the superior processing capability of an all-electric. Further, Bernardi claims, by the time a processor adds a servo drive on the pump and the extruder of a hydraulic machine, it’s probably close in cost to an all-electric.
While the debate will go on over which type of machine–electric, hybrid or other styles–provide the ultimate advantage, processors are the ones who stand to gain from the explosion of new machine technology. While the sheer number of machine choices for a molder to consider can seem intimidating, knowledge and experience with the new technologies will, in the long run, help the processor choose the best machine for their particular operation. Perhaps the wisest rule of thumb for the processor to live by is this one–don’t assume anything. CPL
For more information circle reader service number in parenthesis. Company inside parenthesis is Canadian representative. Reader Service card is located on p.40
THIS ARTICLE’S SCOPE
This article is not intended to be a machine vs. machine comparison of the pro’s and con’s of individual injection molding technologies offered by each OEM equipment manufacturer. It is acknowledged that certain proprietary technologies involved in the design of, for instance, tiebarless or two-platen machines, are diverse enough to make such comparisons difficult, if not virtually meaningless, in the absence of a molder’s specific operational requirements. Rather, the article is intended to give the reader a feel for the strengths and limitations of different categories of machine types.