Injection Molding: It’s not just the energy savings…

First it was a novelty, then a niche, then a specialty product. Now electric molding has reached the mainstream. For some machinery manufacturers, all-electrics comprise over 50% of small- to medium-tonnage injection machine sales. Almost every machinery manufacturer offers all-electric injection molding machines now, acceding to demand for the unique capabilities and high performance of this technology.

“Electric press sales are, by far, the fastest growing segment of the market for injection molding equipment. At present, about one-third of the inquiries we receive at Battenfeld of America are for all-electric presses,” says president Thomas Lenz.

In Canada, Al Lemieux reports that sales of Nissei all-electrics are brisk. “We have sold all-electrics into all markets, not just cleanroom applications. We have some in automotive, and lots in packaging, where users love the speed of these machines.” Lemieux is president of En-plas Inc., which represents Nissei injection molding machines in Canada.

All-electric machines generally demonstrate faster cycle times, higher precision, more consistency and less maintenance than general purpose hydraulic machines.

And they’re not really priced out of reach, although the hype on this subject runs the gamut. A recent brochure produced by Boy Machines Inc. cites a payback period of 31 years for a 110-ton all-electric versus an 88-ton Boy hydraulic machine, but the study only looks at energy savings, not quality of product or other considerations. For an equal and opposite spin, a press release from Milacron cites a molder who expects payback of less than three years for the purchase of all-electric machines, considering all direct and indirect factors.

Generally, an all-electric machine costs only slightly more than a comparable hydraulic unit. The key word here is comparable. All-electrics can still cause sticker shocker compared with general-purpose hydraulic machines, but compared with hydraulic machines that can achieve similar levels of productivity and repeatability all-electrics become a more attractive option.

And then there’s the energy savings.

“All customers like the energy savings,” says Brad Hancock, national product specialist for Milacron’s Powerline machines, “but they buy their second and third all-electrics because of the higher productivity and lower per part cost.”

There are some things an all-electric doesn’t do well. Hancock notes that electric machines are generally not able to achieve fill times of less than 0.25 sec. Also, there appears to be little demand for electrics above the 1000-ton range.

Hybrid injection molding machines, which generally have one or more major functions converted to electric drives, can also achieve energy savings compared with traditional designs. They can even achieve some of the unique capabilities of electric molding, but they retain both the benefits and the drawbacks of hydraulic machines.

Servo presses like any other servo product

Do you like your servo robot? All the things to like about a servo robot also hold true for a servo-driven injection molding machine, says Hancock: the accuracy, the reliability and the consistency.

All-electric machines turn molding into a “predictable, robotic” operation, says Milacron literature. This facilitates lights-out molding, reduces overpacking and molded-in stress, and allows you to mold closer to the threshold of a short shot without falling below the threshold.

So even if your shop is churning out storage baskets for the dollar store market, if an all-electric molding machine can produce 48 g parts every time, rather than parts that vary from 47 g to 53 g, the resin and scrap savings add up quickly.

Another significant feature of electric machines is that they allow overlapping of functions, which contributes to faster cycles. Because each axis has its own drive, parallel movements are possible. For example, Nissei’s ultra high-speed electric machine, the ES200H, can produce parts such as connectors in less than 1 second. To achieve the fast cycles, the unit employs simultaneous operations, such as injection during mold clamping, mold pressure decompression while cooling, and mold opening/closing during metering.

To a molder with a longer cycle time, say 30 seconds, shaving a fraction of a second by overlapping functions may not seem like much benefit. “But the little things add up,” says Hancock. Perhaps you can save fractions of a second by pre-injection (injecting while the clamp is closing and building tonnage), he explains. Pre-injection may permit more venting of gasses before the mold closes, and that may reduce the tendency to warp. In turn, this may mean you can cut back on cooling time and possibly on packing pressure, since there’s less gas to pack out. In the end, that 30-second cycle time may be reduced by 5 or 10%, he explains.

To fully benefit from electric technology, the machine must be designed to capitalize on the possibilities presented by servo motors.

Battenfeld’s new EM Series of all-electrics is equipped with a belt-less drive with two synchronized servo motors. This contributes to “substantially higher nozzle contact force than anything available in the industry to date,” says Lenz. The design eliminates nozzle leakage, which is said to be a source of reduced yield due to inconsistent mold packing.

Sumitomo’s new SED Series all-electric machines have adopted synchronous direct-drive motors, eliminating the use of belts. The direct-drive design offers higher injection power and velocity, with injection speeds up to 500 mm/sec. In addition, velocity response is improved over belted motors.

Everyone’s in on the action

The list of those supplying all-electric machines grew tremendously at K ’01, as the European machinery manufacturers jumped aboard.

Arburg introduced its Allrounder Alldrive series (also known as the Allrounder A), which uses all servo drives for the main functions but leaves the option of having either electric drives or hydraulics for the auxiliary functions, such as core pulls. An auxiliary hydraulic motor allows the unit to run existing molds that are not designed for all-electrics. The first machine in this line is an 88-ton model.

Similarly, Demag’s Ergotech El-Exis E Series machines offers an auxiliary hydraulic unit.

Engel improved on its e-motion all-electric tiebarless machine with the addition of a high-speed option. This package effectively doubles standard injection rates. The e-motion machine also achieves extremely fast opening and closing of the clamp through the use of a five point toggle, servo motor and planetary gearbox. The gearbox is said to offer longer life and less maintenance than the ball screw mechanism used by most electric machines. E-motion units are available with clamp forces of 60, 110 and 165 tons.

Negri Bossi’s ELMA all-electric series achieves higher injection speed and pressure, as well as increased screw rotation speed and torque, compared with the company’s hydraulic machines. For example, injection speed on the 160 tonne machine has been increased 100% to 200 mm/s. System architecture continues to be built around the CANbus protocol.

Hybrids: Another high performance alternative

Arburg has designed a hydrid model of its Allrounder line called “Advance”. It incorporates electric screw drive and an energy-saving, frequency-regulated pump drive for its hydraulics. One contributor to high repeatability on the Advance machine is position regulation of the screw, achieved by a double-action cylinder that pressurizes the injection piston on both sides. This ensures that exact injection speed profiles or holding pressure profiles can be maintained.

In Husky Injection Molding Systems Ltd.’s hybrid Hylectric machines, an electric screw drive is coupled with a high-performance injection unit to achieve injection speeds up to 1500 mm/sec. The Hylectric line uses a small diameter stroke cylinder to provide fast platen motion and a low oil-volume clamp piston to apply tonnage. In a statement comparing hybrids and all-electrics, Husky concl
udes that a well-designed hydro-mechanical hybrid readily meets or exceeds the performance offered by all-electric machines.

It’s not just the energy savings

Admittedly, not all shops need high-performance injection molding machines. But the demand for all-electrics is rising, and so is the understanding of the nuances of electric molding.

As deregulation and pricing uncertainty become a factor in the Canadian electric marketplace, the energy savings of electric or hybrids do merit consideration, and energy costs alone may offset their higher purchase price. But the faster cycles, repeatability and more consistent parts could do more than cut costs; they could increase business.

Who Makes What

*Hybrid models may be available by special request from any supplier. The above list shows only those companies that actively promote hybrid product lines.