Hybrid Molding Machine Bridges Electric-Hydraulic Divide

Originally Published MPMN March 2002

EQUIPMENT NEWS: Molding Equipment

Hybrid Molding Machine Bridges Electric-Hydraulic Divide

Unit combines accuracy of electric machines and power of hydraulic molders

As the electric-versus-hydraulic debate rages on, one firm hopes to achieve a consensus opinion with the introduction of a new generation of machines equipped with electromechanical and hydraulic axes. The company launched the first machine in its new series at a recent European plastics and rubber show. The machine, which has 800-kN clamping force, was shown using a 72-cavity hot-runner mold to produce needle clamps.

Hybrid electric and hydraulic molding machines, such as the Allrounder A introduced by Arburg Inc., provide electromechanical accuracy and repeatability along with economic energy consumption. They represent a sensible solution in many cases, according to company spokeswoman Susanne Wurst. "All-electric machines drive up capital equipment costs, and they simply are not necessary for many applications," says Wurst. "If clamping force is what matters to you, then an all-electric machine is not required." But if you do want an electric molder, Arburg offers the best of both worlds with its hybrid Alldrive series machines, she adds.

Blending electrically driven main axes and combinable hydraulic and servoelectric auxiliary axes provides sufficient hydraulic force and ensures electromechanical accuracy, according to Arburg. The systems' flexibility allows the user to optimize cost-benefit ratios while adapting to changing production requirements.

The Allrounder A on display at the exhibition operates with a 35-series cylinder module and is equipped with a new electrically driven five-point toggle joint to enhance positioning accuracy. A high-power spindle is integrated into the shaft motor to save space in the clamping unit. The ejector has a 150-mm stroke and the nozzle contact force is generated hydraulically. A two-stage spur gear transmits torque between the servomotor and the plasticizing screw. A spindle unit adapted to the feed force converts the rotational movement into a translation movement, permitting the full injection force over the entire injection stroke.

Currently, the 800-kN unit is the only model available in the Alldrive series. "We wanted to start with a mid-range clamping force," says Wurst, "but as needs arise and we receive customer requests, we will develop other sizes."

The machine is distributed worldwide from the company's headquarters in Lossburg, Germany.

Electrohydrostatic drives reduce energy consumption

Like the Allrounder A, the El-Exis E features a combination of electric and hydraulic technologies in the independent electrohydrostatic drives for its clamp and injection units. Offered by Demag Ergotech USA, the machine is available in clamp forces ranging from 60 to 350 t. According to the company, tests have shown the machine consumes approximately 50% less energy than traditional hydraulic machines without compromising performance. It can achieve a 0.5-millisecond processing speed and a 0.0004-in. accuracy for all linear movements. A single servomotor drives both injection and screw rotation. The clamping unit includes a servomotor that acts through a hydrostatic transmission to reduce conversion loss from rotary movement. The mold is guarded by a sensitive protection system that will stop the clamp in a fraction of a second at any sign of resistance.

The electrohydrostatic drive has been designed to provide accurate and repeatable back-pressure control. Standard parallel functions include on-the-fly ejection and core movement, and screw rotation while the clamp is moving. The machine offers a choice of three injection units, each with three quick-change screws and barrels.

The El-Exis E is suitable for cleanroom applications because of its drive system, which offers clean operation, and an optional laminar-flow system. Pressure control during the holding phase of injection provides the precision required for medical devices. Sales manager John Ward sums up the machine's features, citing "high precision through control of pressure and velocity during the injection phase, efficient cycle sequences due to parallel-operating drive units, energy savings, cleanliness, and low noise."

Near-infrared vision system protects molds and reduces cycle times

An injection molding control system offers camera adjustment and image viewing from its touch screen. Xtreem from Milacron Inc. does not require separate controller hardware, minimizes costs, and simplifies installation and training. According to Milacron, the Xtreem system is the first PC-based controller designed for plastic injection molding that allows drop-in integration of Avalon Vision Solutions's MoldWatcher II vision system. Using near-infrared technology, MoldWatcher's camera is unaffected by changes in ambient lighting. The system's light source is invisible to the human eye, thus increasing operator comfort. The integrated vision and control system "eliminate the need for a separate controller and monitor that would add clutter and cables to the molding cell," says manager of controls development Ron Sparer. A dual-processor configuration allows Xtreem to run the vision system's 50-millisecond algorithm without degradation of speed or performance.

Xtreem is available in two models: Xtreem St, the standard model that has PC control and is Internet- and intranet-ready, and Xtreem NT, the Windows NT–compatible model that comes standard with Internet Explorer. The system features a 10.4-in., full-color, backlit LCD and allows users to access the boards and control panels through a side panel. Its data-processing capabilities include process documentation, troubleshooting via the Internet, and a variety of networking options.

MoldWatcher II increases uptime and overall production of good parts by protecting expensive molds and detecting part defects. With its camera mounted on the A half of the mold, it can detect stuck parts or runners, frozen ejector pins, broken cores, cam and slide misalignments, flash, short shots, and problems with inserts on vertical machines. In a horizontal setup, MoldWatcher verifies the presence of good parts on the B side, allowing the mold to close only after confirmation of acceptable part quality, complete part drop, and proper tool alignment.

Compact hydraulic molding press is self-contained

A 30-tn compression molding system integrates the press, power unit, and controls into a compact unit. Its small size and modular packaging allow the press to be moved quickly and easily with minimal expense and production downtime. Built-in lift-truck tubes facilitate placement and relocation. Supplied by The French Oil Mill Machinery Co., the column-style press has an adjustable clamping force of 3–30 tn, and features a 15 x 15-in. pressing surface, a 6-in. stroke, and 6–12-in. adjustable daylight. Electrically heated platens include provisions for water cooling and T-slots for mounting tooling. The machine's design can be adapted to a range of materials and applications in both laboratory and production settings. The molder "delivers superior-quality products, with fewer rejected and scrap parts," says chairman of the board and president Daniel P. French. "In medical device manufacturing, where close tolerances and high quality standards are critical, this can translate to improved productivity and profit margins."

Clamping system results in small footprint

Two injection molders feature a two-platen clamping system that uses four tie bars as clamping cylinders, resulting in a smaller overall footprint than traditional machines with a three-platen design. Available from Boy Machines Inc., the Model 55 and Model 90 have 60.6- and 99.2-tn capacities, respectively. Triple-layered tie bars develop the clamp tonnage in the direction of the fixed platen, permitting the cantilevered clamping system to be open on all sides and fully accessible. Other advantages include uniform distribution of the clamping force on each corner of the platen, which reduces deflection across the platen face. It also enables the use of asymmetrical molds, which would typically require larger machines. The injection unit swivels horizontally with minimal effort, making it easy to change nozzles, screws, and barrels. Both models offer energy efficiency, low noise levels, high accuracy, and repeatability thanks to an electronically regulated variable displacement pump. Precise and consistent part molding is achieved by an electronically programmable and regulated oil temperature control.

Plastic-injection machine suitable for cleanroom applications

A plastic-injection machine is suitable for a range of applications from R&D projects to production runs. Supplied by Laservall North America LLC, the AB 200 combines safety with production capabilities. The all-pneumatic device does not use lubricants, making it suitable for cleanroom applications. An adjustable mold stop comes with an automatic ejector, and an adjustable mold clamp accommodates different mold thicknesses. The injection chamber and piston are made of stainless steel to resist corrosion. A transparent safety guard and heat shield protect the working area. Other features include a digital temperature controller, adjustable sequencing and injection cycles that range from 5 to 99 seconds, and a built-in resettable production counter.
Katherine Sweeny and Norbert Sparrow

Copyright ©2002 Medical Product Manufacturing News