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Injecting New Life into Plastics Processing Equipment


Posted in Manufacturing Equipment by mddiadmin on April 1, 1999

An MD&DI April 1999 Column

Although room-sized systems still exist, equipment is becoming smaller, transportable, and capable of handling jobs of various demands.

Although many injection molding and plastics processing equipment companies will be the first to admit that, as an industry, they've lagged a bit behind those working with metals, change is definitely in the air. New machines are increasing the ease with which small or uneven-surfaced parts are produced, single machines can perform more functions than ever before, and technology is shifting from hydraulics to electric systems, as well as from analog to digital.

Realizing that the specific dimensions of whatever part is being molded is what determines the best setup in an injection molding machine, some manufacturers have gone overboard to provide options. Autojectors (Avilla, IN) has more than 30 different machines, which virtually guarantees that one of them will meet a customer's specfications. Just one of many options, the HCS-40 is ideal for molding inserts with long leads. Its horizontal two-station shuttle table is operated by a hydraulic cylinder and adjustable stops, and the shuttle system allows inserts to be loaded at one end of the table while parts are molded at the opposite end.

MINIATURIZATION ISSUES

Led by the surge into microelectronics a few years ago, the trend toward miniaturization is a hot topic in injection molding. Everything seems to be preceded with micro—microsensors, micropumps, even microsurgical instruments. On the road to shrinking parts, however, technical problems need to be resolved. Cycle times are usually longer than necessary for such small parts because the sprue and runner sizes aren't always proportionately reduced to minimize material residence times and melt degradation. Longer cooling and heating cycles, meant for larger part sizes, also increase energy consumption. Standard machine ejector mechanisms can damage minute structures, develop electrostatic charges during the part ejection process, and fail quality standards because of the large sprue-to-part ratio.

The Microsystem's seven modules can mold parts weighing less than 0.1 g (Battenfeld; Meinerzhagen, Germany).

Battenfeld (Meinerzhagen, Germany) has introduced a new injection molding manufacturing cell designed to counteract these problems. The Microsystem 50/2 SE's plunger injection system has a diameter of 5 mm, and each of the seven modules is operated by the company's new Unilog B4 control system. The Microsystem can mold parts weighing less than 0.1 g while avoiding the typical problems outlined above. A rotary table clamp system, with one station for injection molding and a second for part ejection, has reduced cycle times by more than 50%. The two-axis handling system removes parts using suction cups that also help separate and orient them for optical quality control and packaging. Parts that do not fit the specifications are automatically discarded by the handling system.

OUT WITH THE OLD, IN WITH THE NEW

Some machines don't get a complete technical overhaul, but are improvements nonetheless. Such is the case with the new Omega III ultrasonic welding series from Forward Technology Industries (Minneapolis), which is replacing the Omega II line. The three models, with varying degrees of complexity, are geared toward the fast, reliable assembly of thermoplastic parts. The MCA is the company's basic unit, and the MCS intermediate model now offers features that were previously available only on the most advanced model. The MCX offers extensive control and optimum adjustment for complex applications. The new modular design for all three welders allows the generator and controller to be placed in a number of locations on or around the welder.

"The new line will considerably increase the general capacity and flexibility of the machine," says Bryan Schaupp, ultrasonic product manager. Among the new performance features is an improved reactive welding system (RWS) exclusive to Forward Technology products. RWS provides the precise amount of ultrasonic energy necessary to complete the weld, regardless of the dimensional variations or irregularities of the part.

Husky Injection Molding Systems (Bolton, ON, Canada), in its new S-Series, has introduced a line of small-tonnage (60–160 tn) units that are well suited for high-end medical applications. The machines incorporate a number of features from the company's current E- and G-Series that have helped to simplify unit design, reduce maintenance, and decrease the incidence of part contamination.

New models don't always have entirely new technology but offer improved features, such as simplified programming and machine adjustment, a larger working area, a back-lit display screen, improved amplitude control, optical encoders, a power clamp, a foot-operated material hopper, and other features that reduce operator fatigue or simplify integration into an assembly line.

CLEANROOM CONSIDERATIONS

For some manufacturers, the ability to meet cleanroom specifications is of utmost importance. The Newbury Vertical injection molding machine by Van Dorn Demag Corp. (Strongsville, OH) offers a three-year, no-fluid-leak guarantee. Toggle clamps reduce the amount of oil in the processing environment, and a breather cap at the oil tank cap provides additional assurance of cleanroom compliance. The company's Ergotech 60 system reduces particle emissions by having only two dynamic seals and featuring a permanent lubrication system with a lubrication interval of three months.

Krauss-Maffei Corp. (Florence, KY) offers a line of machines for liquid injection molding, multicomponents, and thermoset processing. Its KM80 injection molding/cleanroom system features a clamp end that remains in the cleanroom during processing, sealing off the cleanroom during operation and maintenance with two additional metal plates. Casters supporting the hardwall cleanroom allow the unit to be rolled away from the clamp for mold change and maintenance.

The two-platen C-design offers speed, superior precision capability, and excellent repeatability, according to the company. The cantilevered clamping unit results in full accessibility, reduced footprint, and reduced energy consumption. The MC4F process control system is mounted on the machine and swivels for operation either inside or outside the cleanroom.

DON'T UNPLUG THIS CONCEPT

Molders who have tired of cleaning oil spills; replacing oil, water, and filters; and figuring out how to safely dispose of oil and water to meet environmental standards can make the move to fully electrical injection molding machines. Toshiba Machine Co.'s (Elk Grove Village, IL) initial machines, ranging from 45 to 250 tn, are billed as energy savers because the motors shut themselves off when a function is complete or the system is between cycles. Since each function is run by a separate motor, energy savings will vary depending on the process, but is expected to be more than 50% compared with traditional units. Ube Machinery Inc. (Ann Arbor, MI), which has produced electric machines for more than 10 years and has produced its third generation, believes that its servomotors save as much as 60 to 80% electrical use.

Barr Klaus, technical director of Cincinnati Milacron Inc. (Batavia, OH), says that although his company is already introducing their fourth generation of electrical machines, most users are just beginning to appreciate their advantages. "Our years of investment in this technology are paying off with increasing sales and enhanced market share in what we believe is the future direction of injection molding machinery," he explains. "The injection molding industry is just beginning the changeover from hydraulic to electric power that has already occurred in both machine tools and robots. Now we're being validated by both market acceptance and by competitors who are rushing out first designs."

Milacron's all-electric Roboshot injection molding machine makes liquid injection molded medical-grade parts. It features a water-cooled jacketed barrel and shot-off nozzle, as well as integrated mold-temperature control.

Last year, Cincinnati Milacron debuted the first electrically activated rotary mold on an all-electric machine. Klaus says that while there is an initial cost premium in this and other electric molders, operational cost savings quickly pay for the difference.

According to Toshiba and Ube, electric machine operation is more consistent than that of its traditional counterparts, and its part repeatability results in fewer rejected parts and less material scrap. The lack of hydraulic oil, and the water to cool it, provides a cleaner environment and eliminates leakage and the concern over oil recycling. Thus, maintenance and repairs are minimal. The elimination of hydraulic pumps reduces noise by 25%. Toshiba vice president Tim Glassburn says, "Our new line of electric machines will give our customers and 'not-yet customers' a whole new set of options from which to choose."

Boy Machines Inc. (Exton, PA) is also offering its customers the option of an electrical ejector system in its cleanroom machines to replace the standard hydraulic ejector. The electrical system increases the cleanliness of the operation and allows the machine to remain in operation during the clamping unit's movements.

The cleanroom features are met by installing a laminar-flow system on the hood of the clamping unit; stricter standards require that the freely overhanging clamping unit be segregated with its own enclosure and laminar-flow system. The rest of the machine remains outside of the cleanroom unit. The pump drive motor used for cleanroom applications is cooled by water instead of air, preventing air-turbulence contamination.

With Battenfeld's Microsystem, parts contamination is controlled by the cleanroom conditions inside the system enclosure. The servoelectric drive used in all machine functions is well suited for this environment, and its use allows a resolution 40 times that of conventional stroke-measuring devices used in hydraulic machines, leading to a better-controlled molding process. A final module places the parts in the proper orientation within blister packaging, protecting them from soiling and transport damage. If the parts are needed for another assembly process, they are already separated.

The ES Elject series from Nissei America Inc. (Anaheim, CA), ranging from 22 to 397 tn, is another line of electric injection molders. According to the company, the lack of hydraulic oil reduces each model's floor space by up to 15%. Also, the electrically driven actuators for injection, metering, mold opening and closing, and ejection can operate either individually or simultaneously, thus eliminating standby time.

Some owners of hydraulic injection molding systems have tried to upgrade to a partially electric system to avoid the cost of purchasing a new all-electric system. However, adding electric servos may decrease noise levels and save a bit of energy, but not improve process capability. Further changes won't do much to change the characteristics of the hydraulic system but can cost nearly as much as a new all-electric machine, so it's best not to scrimp when upgrading.

In fact, whereas many people are initially attracted to electrical systems because they hope to reduce energy costs and eliminate the hassles of recycling hydraulic oil, they are often pleased to discover that the best reason to turn to electrical systems is the increased quality and production they offer. Also, much less operator monitoring and system adjusting are needed.

FROM ANALOG TO DIGITAL

At Herrmann Ultrasonics (Schaumburg, IL), welding technology development has focused on process improvement, both in terms of consistency and capability. The solution: switching their signal generators and controllers from analog to digital circuitry. According to Jim Meggesin, the operating performance of analog components is affected by variations in factors including temperature, humidity, aging, and manufacturing tolerances. "A good analog circuit design can minimize the impact of these variations," says Meggesin, "but a digital design can eliminate them altogether. Better data resolution provides more-precise and faster control for improved system performance. And fewer components means greater system reliability."

A side benefit to the digital in-process data is its availability for uses other than system control loops. Meggesin explains that the computers monitor the actual weld parameters in real time and can identify violations of the process control window and the corresponding bad parts. The data are available for export to SQA software where statistical data can automatically be obtained.

"The data are invaluable for both process development and quality assurance of production processes," says Meggesin. He adds that although the capability isn't new, the upgraded computers now operate in a Windows environment to make data collection easier. The precise data allows the computer to identify individual product stacks by acoustic signatures and automatically set the appropriate weld parameter. The plug-and-play utility reduces setup time and eliminates human error.

CONCLUSION

As with any other major purchase, it's necessary for companies to examine the many molding or assembly machines available before deciding what best meets current needs. It's also important to learn about what kind of support the manufacturer can offer in terms of maintenance, repair, and the ability to provide additional services as needs grow. However, with the many new options available, it certainly seems like now is a good time to start shopping.

Jennifer M. Sakurai is managing editor of MD&DI.

Several of the units described in this article will be exhibited at the Injection Molding & Plastics Processing Pavilion at MD&M East 99, to be held May 25–27 in New York City.

 


Copyright ©1999 Medical Device & Diagnostic Industry

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