Most Japanese injection press makers are moving toward all-electric power, especially on small-tonnage presses, but one - Sodick Plustech Co. Ltd. - is taking a hybrid approach on its Eclipse, which incorporates both electric and hydraulics.
Better known in metalworking machinery circles, Sodick is not yet a household name in the U.S. plastics industry. Last year, after several failed attempts to crack the U.S. market, Sodick linked up with Yamazen Inc., a major Japanese machine tool distributor in Schaumburg, Ill. Yamazen hired Michael Santa, executive vice president of Krauss-Maffei Corp., to run its new plastics division.
``We have a servo-driven machine with hydraulic elements to it,'' Santa said.
The Eclipse, available in clamping forces of 20-385 tons, and 40 and 110 tons for a vertical-clamp version, are designed for close-tolerance parts that require highly accurate molding and a high degree of mold protection, such as lenses and medical parts.
Sodick combines servo-electric technology with hydraulic accumulators on both the clamping end and the injection unit of the Eclipse. An electric servomotor drives a ball screw that moves the clamp back and forth. Servomotors also move the ejectors and rotate the screw. Hydraulic power builds up the clamping force, drives injection and handles nozzle pressure and carriage movement.
In two key design features, the Eclipse eschews the toggle clamp, commonly used on all-electrics, and a reciprocating screw. Instead of a toggle, the press uses a direct-pressure hydraulic clamp. Once the electric motor brings the mold halves together, known as the ``kiss point,'' a pneumatic locking mechanism kicks in, and then tonnage is built up by a hydraulic pump assisted by an accumulator.
Instead of a reciprocating screw, Sodick presses have a V-style plasticizing unit that separates the functions of melting and injection. An electric-driven plasticizing screw, mounted at an angle atop the injection barrel, feeds the melt into the injection chamber. Once an encoder determines when the screw has retracted to its predetermined shot size, a hydraulic cylinder pushes the screw forward to seal off the system, eliminating backflow. Hydraulic power also moves the plunger, for injection.
Santa said the V-style eliminates the need for a check-ring, which can cause material shear and shot inconsistencies.
Benefits of the hybrid design include high injection pressures and speed - 500 millimeters per second, thanks to the accumulators.
Hydraulic core-pull also is easier than on an all-electric press, because hydraulics are built into the machine; all-electric presses need add-on units.
Santa said the direct-pressure clamp is better than a toggle clamp, which has more parts to wear out.
The technology is not cheap. Eclipse machines sell for 8-12 percent more than similar-size all-electrics. Santa admits Eclipses are not for everybody.
Given the slow economy, selling any type of injection press is a challenge, let alone a premium-priced machine. But Santa thinks a specialization trend means molders will give Sodick a look.
``The custom molding market is establishing itself as being more specialized. In the past, a custom molder wanted to be everything to everybody. ... Well, in the age of specialization ... custom molders are being forced to determine what markets they want to serve,'' he said.
Santa said Eclipse presses do use more energy than an all-electric. However, he added: ``We're very, very close. But by not being as efficient, it allows us to increase our performance capability, and we're saying the additional performance that you get is more than justified in terms of the energy increase.''
Compared with conventional hydraulic presses, the Eclipse cuts energy use by 40 percent, Santa said. The press uses just 10 gallons of oil on an 88-ton model, compared with 70 gallons of oil used by the same-size hydraulic clamp machines, said Sodick.
Sodick is based Yokohama, Japan.