Debating All-Electrics

The use of all-electric injection molding (I/M) machinery is at an all time high, and should make up almost half of all shipments of injection units in North America in 2006, according to the Society of Plastics Engineers.

Such figures have led to speculation whether all-electric machinery can and will replace hydraulic and hybrid devices. “There’s no ifs, ands or buts — all-electric is the wave of the future,” Michael Werner, technical sales manager, North America, at Toshiba Machine Co. America, in Elk Grove, Ill., said.

But other injection machine manufacturers disagree, pointing to situations where hydraulic and hybrid machines outperform all-electric models, and areas where hybrid machines are narrowing the performance gap.

ALL-ELECTRIC ENERGY ADVANTAGE

There is near universal agreement that all-electric machinery holds the advantage when it comes to energy consumption.

“Depending on the process and product, you can save 60 to 80 per cent of energy by using an all-electric machine,” David Bernardi, senior sales and marketing manager at Ube Machinery Inc., in Ann Arbor, Mich., said. “With all-electrics, the servo motors on each drive allows you to call for only the energy you need to perform a specific task, whereas on a hydraulic machine the motor runs continuously.”

According to the Strongsville, Ohio-based Demag Plastics Group, for example, its IntElect Series of all-electric machines use this principle to cut power consumption by 60 per cent over comparable hydraulic machines.

ACCURATE INJECTION

Another widely recognized strength of the all-electric machine is its accuracy and repeatability. “Servo motors give a more accurate injection,” Ube’s Bernardi said. “Once you have set your process to the correct parameters, you are going to repeat much more tightly.”

Florence, Ky.-based Krauss-Maffei Corp.’s all-electric EX Series, for example, has two direct drives controlling plasticizing and injection, translating into consistent shot weights and a highly stable production process, the company said.

And the new all-electric Allrounder Golden Edition Series from Arburg Inc., in Newington, Conn., meanwhile, uses a direct servo-drive to control the screw movement to achieve consistent reproducibility.

SPEEDING UP

All-electrics are also getting faster. “They apply torque immediately due to the servo motor capability, giving you rapid acceleration of clamp motion,” Ube’s Bernardi said. “For example, Ube’s all-electric machines are now into the 20 second (s) range for bumper fascias that used to be made in 70 s.”

Other all-electric vendors are following suit. Batavia, Ohio-based Milacron Inc.’s all-electric Roboshot S2000i-B Series, for example, provides a zero to 300 millimetres per second (mm/s) injection acceleration; Nissei Plastic Industrial Co. has improved the standard injection velocity of its Elject NEX Series to 500 mm/sec; and from Sumitomo Plastics Machinery, in Norcross, Ga., the new high-speed SE-HS Series is capable of achieving 800 mm/s injection speeds.

REACHING THE LIMITS

But not everyone is convinced that all-electric machines are ultimately a better investment than modern hydraulic or hybrid units.

“[All-electrics] are limited in specification, especially in nozzle force, ejector force and hold times in comparison with hydraulics,” Steve Elliot, manager, machine sales at Engel Canada Inc., in Guelph, Ont., said.

Plus, Robert Koch, president of Boy Machines Inc., in Exton, Pa., questioned the real value of the vaunted energy savings of the all-electric units. “[They] typically consume less energy, but not nearly enough to justify the significant cost difference,” he said.

SIZE MATTERS

The expense of all-electrics is indeed an issue. “The grey area for cost starts at about 500 tons,” Glenn Frohring, vice-president of sales and marketing at Worcester, Mass.-based Absolute Haitian Corp., said. “The price of an all-electric machine above that tonnage can get prohibitive because the drive motors become expensive.”

And economics currently limit the size of all-electric machines, Ube’s Bernardi noted. “If you needed a 4,400-ton this afternoon, you’d have to buy a hydraulic machine,” he said.

The size limitations, however, are likely to be overcome, as both Ube and Mitsubishi are developing all-electric models in the range of 3,000 tons.

APPEARANCES DECEIVE

Some of the secondary advantages of all-electric machines, such as cleanliness and quiet operation, may be more apparent than real, also.

“The oil or grease lubrication used on the linkages of a toggle machine is difficult to contain, especially at high speeds,” Jim Stewart, sales manager, Hylectric machines, at Bolton, Ont.-based Husky Injection Molding Systems Ltd., said.

“And both [hydraulic and all-electric] machines create noise,” Boy’s Robert Koch said. “Neither is the noisiest equipment in a typical injection molding environment.”

THE MIDDLE GROUND

Husky’s Stewart and others point to hybrid machines as a way of giving customers that buy large machines some of the advantages offered by all-electrics.

Hybrid technology is certainly not new, and industry insiders suggest the term itself is a misnomer, since hydraulic machines have always relied on electricity.

A working description of many of today’s hybrid machines is simply a reverse of the equation. “Our version of a hybrid machine is an all-electric with some form of hydraulics integrated in,” Toshiba’s Werner said.

All-electrics aren’t suitable for certain applications, and that’s where hybrids can shine. For example, Demag kept the packaging industry in mind when it designed the El-Exis S Series, which is targeted towards thin-walled applications; the models combine a servo drive with hydraulic accumulators, and are available in 3,600-, 7,000- and 10,500-ton ranges.

Additionally, hybrids are considered energy-efficient and clean. Husky’s Hylectric Series of hybrid machines approach the energy efficiency of comparable all-electric machines, the company said; on a 30-ton Hylectric, for example, only four litres of oil are necessary for the full clamp cycle.

With all of these considerations, it seems almost certain that, despite the all-electric’s growing popularity, hydraulic and hybrid machines won’t face extinction any time soon.