All-electric presses break new ground.

Two new all-electric press series from Cincinnati Milacron's Plastics Machinery Div., Batavia, Ohio, together cover the broadest spectrum yet of molding applications--from general-purpose to high-precision. With their introduction at NPE '94 last month, Milacron is wagering that over the long term there will be market shift from hydraulic to electric servo drives as there has been in machine tools and robotics.

Milacron aims to make the cleanliness, quietness, precision, and energy efficiency of all-electrics accessible to a wider spectrum of molders through the introduction of its new Elektra series, which is being positioned to match the Vista series of hydraulic presses in price and performance. The first U.S.-built all-electric machines, the Elektra series is being manufactured both in Batavia, Ohio, and Malterdingen, Germany. Although this series borrows the name of a 110-ton servo-electric injection press introduced by Klockner Ferromatik Desma before Milacron's acquisition of Ferromatik last year, the new line was designed from scratch in the U.S. It incorporates Milacron's proprietary ball-screw drive (developed for its machine tools), Milacron's patented d-c brushless "Variable Power" servo drive, Vista Toggle clamp technology, and new Milacron controls. (The original Elektra press, though more expensive, is still available from Ferromatik Milacron for high-speed applications.)

Milacron's new Elektra series is now available from 85 to 300 tons. Units from 500 to 700 tons will be added later this year and larger presses up to 1500 tons will be offered next year.

The liquid-cooled d-c servo motors (supplied by Powertec Industrial Corp., Rocky Hill, S.C.) are said to offer high torque at all speeds, matching the cycle times of hydraulic toggle machines. Digital signal processing on the servo provides closed-loop speed, position, and torque control. Initial tests show that the brushless d-c motors use up to 63% less energy than a comparable-size hydraulic machine, according to national sales manager Paul Rudzinski. They also operate at a power factor of 0.98--well above the efficiency of hydraulic toggle machines that typically run from 0.3 to 0.8 power factor. Elektra machines also reportedly operate at noise levels well below 70 dbA.

As on Vista machines, the base is of rigid I-beam construction and provides three-way part removal. Elektra's totally enclosed design eliminates exposed hoses and wires, and the electrical cabinet is mounted flush with the base.

Elektra machines are equipped with new PC-based CAMAC 486 (monochrome) and 486 Plus (color) 32-bit controllers, which are also now standard on Vista hydraulic machines and share common screen layouts and commands. Its flat-screen display is mounted by the safety gate.

Price of a "fully loaded" 85-ton Elektra press starts in the low $90,000 range, about the cost of a similarly equipped Vista toggle press, according to a Milacron source. He adds that many options on the Vista come standard on the new Elektra.

NEW HIGH-PRECISION LINE

In addition, Milacron introduced a successor to its ACT line of a-c servo-electric machines produced by Fanuc Ltd. of Japan. The new Roboshot "fourth-generation" Fanuc-built machine is positioned as an "Ultimate Precision" line. It is aimed at such jobs as molding contact-lens casting cups. Roboshot is more expensive than the Elektra series but is as much as 15% less costly than the preceding ACT line.

Available in 33 to 300 tons, Roboshot features a new, compact digital control for faster response and better accuracy. The operator panel is now mounted directly on the machine, and the a-c servo drives have been shortened, both factors reducing the machines' footprint. Higher motor acceleration and improved toggle design are said to contribute to 22% faster dry-cycle times. Other new standard features include a longer gate, separate purge gate, and base design that accommodates auxiliary equipment or tridirectional part removal.

Also, the Roboshot machine introduces the use of artificial intelligence for real-time melt-pressure (RTM) tracing capability. Described as a completely new method of injection control, RTM eliminates the conventional boost-to-hold transition. Instead, multi-stage closed-loop melt-pressure control is exercised throughout the cycle by means of a strain-gauge sensor located behind the screw.

To set up the initial injection-pressure profile, the operator selects the starting and ending points and the type of curve ramping, and the controller plots the profile. Now that the controller "knows" what injection profile is desired, it can exercise "anticipatory" or "feed-forward" control. This is different from conventional "reactive" feedback control. Milacron compares feed-forward control to a racing-car driver who circles the racetrack in advance to learn the curves and know how to adjust his speed before he hits them during the race. The use of real-time melt-pressure control is said to compensate instantly for variation in checkring sealing and to provide unprecedented repeatability of part weights and dimensions in high-speed, high-pressure molding. Shot-to-shot repeatability of [+ or -]0.0005 in. is claimed.