New injection machines at IPF '94.

There was plenty of injection molding news at January's International Plastic Fair in Tokyo, which far exceeded the JP '93 Tokyo show of two months before in number of major machinery exhibitors. If IPF '94 is a barometer of what Japanese OEMs will exhibit at NPE '94 in Chicago this June, molders will see more all-electric presses, low-pressure/high-speed molding, new clamp designs, and innovations in mold degating and filling of thin-wall parts. Here is a brief overview of a few major highlights in injection molding. A more thorough account of injection molding news, as well as developments in extrusion, blow molding, and auxiliary equipment, will follow next month.

FAST-CYCLING ELECTRICS

A fast-cycling, electrically driven press that has been available in Japan since 1990 from Sumitomo Plastics Machinery is ready for introduction in the U.S. SHI (Sumitomo) Plastics Machinery Inc. of America, Norcross, Ga., plans to introduce the SE series at NPE. All machine movements are electric except clamp-tonnage build-up, in which small hydraulic cylinders built into the tiebars behind the tiebar nuts develop just enough pressure to stretch the tiebars. Hydraulic pressure is controlled by a closed-loop feedback circuit to a proportional valve in order to maintain uniform clamping force.

These machines reportedly combine the high accuracy of electric servos with high speed and pressure. At the Tokyo exhibit, a 200-ton model showed off its fast-cycling capability by molding thin-wall containers in a 7-sec cycle. It was demonstrated with a "Simpac" in mold labeling system, jointly developed by Yushin and Sumitomo and first shown at the JP '92 fair in Osaka (see PT, June '92, p. 15). According to Jerry Boggs, v.p. of SHI Plastics Machinery, a 200-ton SE press has a dry-cycle time of 1.5 sec and is capable of 40,000 psi injection pressure and 12 in./sec injection speed.

Niigata Engineering Co., Elk Grove Village, Ill., demonstrated a 75-ton servo-electric press. Its MD series of 50, 75, and 100 tons is not yet ready for the U.S.

SUPER-TIGHT TOLERANCES

For extremely tight-tolerance molding of stress-free parts without sinks, shorts, flash, or burning, Sumitomo showed its "Ultra" option to control clamp force during injection. It was demonstrated on an SH 75 hydraulic press that was molding an 0.025-in.-thick acrylic light guide for LCD panels to a tolerance of 1 micron (|+ or -~0.04 mils) in an eight-cavity mold. Sumitomo also demonstrated its "Press Alpha" system that reportedly enhances flow in thin wall sections and hard-to-fill areas (such as around baffles) and also eliminates sink marks and weld lines. The system involves modifications to both the press and the mold. Pins placed at critical spots in the mold oscillate at around 10 Hz during the filling and holding stages. After filling, gates are removed with an in-mold degating system.

LOW PRESSURE/HIGH SPEED

A new 605-ton M8 press from Toyo Machinery and Metal Co. (rep. by Maruka U.S.A., Pine Brook, N.J.) is said to eliminate stresses and flashing in molding large parts. The injection unit includes two sizes of hydraulic pistons and a differential-pressure hydraulic circuit. By selecting different combinations of pistons, eight modes of injection can be obtained, from low pressure/high speed to high pressure/low speed. (A similar concept was shown at the Philadelphia Plastics Fair last spring by Toshiba Machine Co. America, Elk Grove Village, Ill. See PT, July '93, p. 21.)

What's more, the clamp design of this model TC-550M8 eliminates the back platen and puts the clamping cylinders on the tierods--a trend that is becoming more common lately among injection machine suppliers. Unlike other designs, this machine extends the tierods back alongside the injection unit, where the clamp cylinders are located. With wide tiebar clearance of nearly 42 in., the 605-ton press is said to have the same molding capability as a conventional 935-tonner.

Space savings were also cited for Toshiba's new IS-G series. These machines are available in two clamp options. The GS clamp (308-605 tons) is said to be 15% shorter than its conventional counterpart and can employ a pre-fill valve for faster cycles and a special clamp hydraulic circuit for increased energy savings. The GT clamp type (715-935 tons) is said to be 20% shorter and to require only 10% as much oil chamber capacity as conventional clamps. It's said to decrease hydraulic oil usage by half.