Why molders love all-electric machines.

All-electric injection presses carry higher price tags, but molders who use them don't seem to care. They say price pales in comparison to the valuable molding advantages they get with electric machines. These first-hand accounts tell why the 'go-electric' movement is spreading.

A growing number of injection molders have encountered the sticker shock of all-electric molding machines - and bought them anyway. Did they get the machine of their dreams or an over-priced, over-hyped status symbol? To find out, PLASTICS TECHNOLOGY asked a group of all-electric users, from both custom and captive shops, what it's really like to work with these machines shift after shift.

To hear these molders tell it, all-electric presses have few, if any, drawbacks once you learn how to set them up. "It's pretty hard to find anything bad to say about these machines," says Ed Christensen, president and CEO of Aspen Engineered Products, a custom molder of medical and electronics parts in Poway, Calif. Christensen, whose plant operates two hydraulic presses and five Fanuc Roboshot all-electrics (supplied by Milacron), has had what he calls "a long love affair with electrics" lasting nearly a decade.

With prices ranging from 15% more than a precision hydraulic press to as much as 40% more than a general-purpose model, electric machines had better be good. For molders without the financial resources or inclination to consider long-term costs, this price barrier may remain insurmountable. It's a different story for a growing class of molders who make close-tolerance, high-quality parts and who care more about payback than price tag. "Ten years ago, when we were a new company, electric machines seemed more expensive. Now, their price is overshadowed by other factors," says Ralph Healy, a Roboshot user and president of Mill Valley Molding, which custom molds medical, telecommunications, and electronics parts in West Hatfield, Mass. For Healy and others who have embraced all-electrics, three interrelated factors have tilted the scales in favor of electric machines: superior performance, lower operating costs, and a better molding environment.

Price for performance

One of the first things that emerges from molders' experiences is that energy savings may be easiest to justify to accountants, but it's molding accuracy and repeatability that really draws molders to all-electric machines.

"You set up the machine to do something, and it does it - over and over again," says Bob Arrighi, president of Union Tool & Mold Co., which runs four Roboshot electrics and three hydraulic machines in Maplewood, N.J. The need to hold tight tolerances on a difficult job propelled Union into all-electric molding five years ago. Arrighi recalls that the company was having trouble filling a nylon telecommunications connector. The part's interior had deep, 0.018-in.thick ribs with a [+ or -]0.001 in. tolerance. Union tried to run the part on a variety of hydraulic machines without any success. "If we filled the part too fast. it would burn. If we filled it too slow, it would short-shot," recalls Arrighi. Of all machines Union tried, only a 165-ton Roboshot proved capable of consistently staying within the narrow processing window for that part, Arrighi says.

Don Rochelo, president of Apex Engineering Inc., a custom molder in Pittsfield, Mass., says his company got into electric machines for a similar reason the desire to improve the quality of an insert-molded slide assembly for a camera. "There was a very narrow processing window to operate in." Rochelo says. Otherwise. the overmolded component wouldn't maintain the dimensional tolerances and release properties it needed for the slide to work. Using the same tool. Apex performed a comparison of a 50-ton hydraulic machine against a 55-ton Niigata all-electric. With the hydraulic press, 25 parts had to be sampled every hour to maintain the customer's quality specifications. "With the same tool on the electric, we only have to check one part every three or four hours," Rochelo says.

With hydraulic machines so vastly outnumbering all-electrics, the performance edge of electric machines remains a matter of debate. But those who have used electrics argue that they have two characteristics that boost machine performance.

First, electric machines have more efficient drive systems. according to Ed Kalis, a manufacturing engineer who has studied an Ube/Niigata all-electric machine for Visteon Automotive Systems in Sandusky. Ohio. "Electric machines have the advantage of a mechanical linkage of the ram with the drive motor. So that when the controller gives a signal to the motor for a specific speed, as long as the motor is not overloaded, that speed will be achieved," he explains.

Second, the elimination of hydraulic fluid variations seem to play a large role. "Hydraulic fluid changes across time and temperatures. It varies within a single day. It doesn't allow the added precision that equates with better part quality," claims Ricardo Rodriguez, process engineer for Cutler-Hammer's molding operation in Arecibo, Puerto Rico. Mill Valley's Healy agrees: "When you have hydraulics, there's a certain amount of give. The oil can be sluggish. There can be valve problems. All of that's gone with the direct drive of an all-electric."

Quality improvement pays for itself. Rodriguez explains that the precision of the all-electric machines turns out more acceptable parts per hour. Cutler-Hammer's circuit-breaker division brought in its first all-electric in 1997, adding it to its line-up of seven hydraulic machines. Since then it has added seven more electrics from 55 to 165 tons. "With the electric machine, we saw an immediate increase in productivity of 115%. That's with the same tools, which were not in top shape," says Rodriguez. As the company gained experience with the machines, the plant gained another 40% in productivity, he reports.

Healy adds that electric machines have let his company optimize press utilization and put off some machine purchases. "If you turn out more parts at a higher quality, it's like adding machine capacity," he says.

The power of energy savings

As Healy puts the case for all-electrics, "My biggest concern is molding a quality product, but I'll take the energy savings, too. At one point, we had 11 hydraulic machines and our power bill was $13,000 per month. Now with 16 machines, six of them electric, we run for more hours per day, and our bill is just $8000 month."

Visteon Automotive monitored the energy usage of a 385-ton Ube/Niigata electric press and comparable hydraulic machines during a year-long production trial. Kalis says energy cost for the all-electric was only 10-16% as high as for the hydraulic machines (see sidebar for details).

And at Apex, Rochelo compared energy requirements on one job by pitting its 55-ton Niigata against a hydraulic machine of the same size. He found the peak energy usage for that job dropped by nearly a factor of four.

Union's Arrighi adds an important point: "Don't forget about the energy savings from the chiller." He can run his entire seven-machine shop on a single 10-ton chiller, half of whose capacity is used to cool the hydraulic oil of one 300-ton hydraulic press. "We could probably get by with a much smaller chiller if we only had electric machines," he says.

Cheaper to run

In an area with high power costs, energy savings alone might justify the purchase of an all-electric machine. "If you do the math," says Rochelo, "you'll see that the payback is there." But energy savings are only a small part of the operating-cost picture.

Another byproduct of the all-electric machine's precise control can be faster cycle times - even though electric machines are not necessarily the fastest machines on the market. "It's not always how fast you can move but how consistently you can move fast," Healy explains. For example, he reports 25% cycle-time reduction on some jobs through more precise mold protection. If you have to slow down to avoid banging the mold, you lose cycle time, he explains. Also, when cycle time is limited by screw recovery, the simultaneous clamping and plasticating functions of an electric machine can also contribute to lower cycle times.

On top of productivity advantages, molders report that their electric machines need little maintenance and suffer from less downtime then hydraulic machines. "I can't overemphasize the fact that these machines do no break. In 10 years I can count on two hands the number of times the service guy has been in here," says Apen's Christensen, whose machine problems have amounted to only a broken tiebar and two motor replacements.

ALL-ELECTRIC MACHINE CAPABILITY
(VISTEON TEST RESULTS)

Injection-Speed Linearity(a)

Injection Speed.                Fill-Time
mm/sec                          Difference. %

160                                 17
120                                 11.5
80                                   6.0
40                                   2.4
20                                   1.6
10                                   1.4
5                                    1.4

Load Sensitivity(b)                  2.42%
Transfer Response, sec(c)            0.15

a Percent difference between actual and expected fill times al a
given speed. b Per cent difference between fill times under normal
and low-pressure filling conditions (zero is ideal). c Time to
complete transfer from pock to hold.

Union Tool molding manager Ed Melka adds that it takes longer to troubleshoot and maintain the company's hydraulic machines. "There's more that can go wrong. On the electrics, we grease the ball screws. That's it."

Melka and the other molders interviewed all noted that electric machines have no hydraulic fluid to buy, filter, or dispose of. While oil-related costs are not the largest factor in the payback equation, "they add up," says Healy.

When Christensen tallies up all the day-to-day cost savings from his electric machines, he arrives at a payback of three to five years. "Price is very much an issue for us, but electrics have a clear advantage over hydraulics in the long haul. They're a good investment," he says.

Less tangible assets

The molders quoted here make parts for medical, electronics; and other markets where cleanliness really counts. All of them cite the cleanliness of all-electric machines as one bonus - and quieter operation as another.

Melka argues that the cleanliness and quiet contribute to better morale on the shop floor. "Workers have a better outlook in an all-electric environment. It's not like being in a factory," he says.

While cleanliness is imperative in producing medical and electronic parts, an oil-free environment can be advantageous even in making auto lighting components, says Visteon's Kalis. He notes that stray oil droplets can interfere with secondary coating processes - a problem that could be eliminated with all-electrics.

Short learning curve

Molders report that it doesn't take long to get used to running electric machines. "People from a hydraulics background have to learn to think in terms of true position values rather than percent of pump capacity. But that's not that big a deal," says Christensen.

Cutler-Hammer's Rodriguez estimates that all-electric operator training can be accomplished in a week of classroom instruction or a month of on-the-job training. "The biggest thing is the transition to molding by position. Electric machines work from position instead of hydraulic pressure. The only pressure involved is the plastic pressure," he says.

Rodriguez likes it this way. "Working from plastic pressure can be an advantage for the processing people because it's a direct indication of what the process is doing." This characteristic makes it easier to transfer tools from one machine to another, he notes. Setting up another machine to repeat processing conditions becomes much simpler. "Once you have the right plastic pressure, you're done. With hydraulic machines, there are still a lot of calculations to make."

'Less forgiving'

Because of the all-electric machine's reliance on absolute position and its overall precision, molders report that the machines can be overly sensitive to poor set-up or bad tooling. "You can't be abusive with an electric machine. The set-up technician must be good," says Union's Melka. For example, electric machines are not very forgiving of incorrect clamp-position settings. "You can ask a hydraulic clamp to go too far, but not an electric," says Melka, who notes that the electric machine will throw off alarms when incorrect position settings cause the motors to overload. Healy agrees, describing the machines as "less forgiving."

The same goes for ejection. "If you set a position past the point where the plate bottoms out, the machine will stop and sound an alarm," Rodriguez says. "With a hydraulic, the plate will keep going - bang!"

All-electric machines also are less tolerant of tooling problems. "Your tooling has to be in good shape. If you have a parting-line problem, for example, you can't 'overtoggle' or slam it away," says Arrighi.

"The machines are very sensitive," agrees Rodriguez. "The tool must be perfectly installed or the machine won't work." He has seen occasions where a dragging ejector plate has set off a machine alarm. "A hydraulic machine can force the plate, and the tool will work. That won't happen on an electric," he says.

On the positive side, once you set up the proper position settings, the sensitivity of the all-electric press can help protect your molds.

"Electric machines are mold savers," says Rodriguez. "With electrics, you never have to bang the tool. That's the beauty of these machines." Healy adds, "They definitely minimize mold wear and damage. You can open fast, eject quickly and smoothly, and close fast."

Electric machines may also alert molders to otherwise invisible tooling, set-up, or maintenance problems, according to Healy. He views the sensitivity of his all-electric machines as a "safeguard." He recalls an instance in which one of his electric machines wouldn't hold a consistent cushion. "It turned out to be a tiny chip in the check ring. You wouldn't notice it in the part right away, but it threw off an alarm."

Repeat buyers

When an all-electric machine wins a convert, they stay converted. Asked about future machine purchase plans, all the molders interviewed said they would stick with all-electrics. Christensen, for instance, won't buy any more hydraulic machines and would like to get rid of the ones he has. "If someone makes me a good offer on them, they can have them."

RELATED ARTICLE: Put All-Electric to the Test

Last year, Visteon Automotive Systems recently put an Ube/Niigata all-electric molding machine through its paces in a year-long molding trial in Sandusky, Ohio. The trial, carried out by a team of Visteon manufacturing engineers led by Edward Kalis and Ronald Polley, pitted a 385-ton electric press against a 350-ton hydraulic machine and a 300-ton toggle machine.

The trial consisted of extended production runs of automotive lighting components in ABS, acrylic, and polycarbonate. Visteon monitored the machines' energy consumption. On the electric machine. it also connected a "Dartscanner" process monitor from RJG Technologies to gather machine-capability data. Here's what Visteon learned about all-electric molding:

* Lite energy appetite. "The energy savings were impressive," says Kalis. The slightly larger all-electric machine consumed 84% less energy than the 300-ton toggle machine and 90% less than the 350-ton hydraulic press (see p. 56). Those results were better than Visteon anticipated at the start of the trial. "Ube told us to expect between 60% and 70% savings," Polley recalls.

* Better injection control. Using process-monitoring data, Visteon tested the all-electrics for injection-speed accuracy or linearity, load sensitivity (i.e., of injection speed to filling pressure), and speed of transfer response (see table). Summing up the results. Kalis says, "Injection speed linearity showed a deviation at high injection speeds. The load sensitivity and transfer response show a very robust machine that is capable of precise processing."

* Superb repeatability. Visteon also measured the "ram-velocity injection-forward integral" - that is, the area under the velocity curve from the start of injection to the end of injection forward. According to Kalis, the all-electric machine did particularly well on this measure of injection-speed repeatability. Over a series of more than 5000 shots, the velocity-integral variability was 0.18% - an order of magnitude better than for Visteon's hydraulic machines. "You typically get more variability with hydraulics," notes Polley.

* Consistent throughout the cycle. Kalis adds that the machine achieved "near perfect" stability of hold pressure (see above). Because the electric machine must maintain hold pressure through continuous control of the injection-forward motor, Kalis says, "Constant hold pressure is a good indication of the speed and stability of the feedback control of the controller/machine system."