One of the most significant and highly publicized trends in injection molding of the last two decades has been toward all-servo-driven electric injection presses. Energy savings, quietness, cleanliness and increased precision of these oil-less machines have grown to around 30% of new machine sales in the U.S. and 70% in Japan, despite price tags higher by 20% to 40%. U.S. molders have shown a tendency to believe that buying an electric machine demonstrates a company’s willingness to invest in the latest technology.
All-electric injection presses were first introduced in the 1960s by Battenfeld but never gained market traction and were discontinued. Husky also started out using electric screw drive in 1961 before it switched to hydraulics. (Battenfeld reintroduced small all-electric machines in 1998, and Husky revived electric screw drive in 2000.)
The benefits of electric drives were not realized until two decades later, when at a 1984 plastics fair in Japan, Nissei Plastic Industrial Co. created a buzz with the introduction of a line of electric machines, its MM series, in sizes of 5 and 10 metric tons. These machines used a single electric servo motor to power plasticating, clamping, and injection functions. It also allowed for immediate start-up without warm-up, a wide range of speed control, and ability to overlap functions.
Niigata Engineering showed a 10-ton all-electric prototype at the same 1984 show. All-electric machines from Niigata, Toyo, and a joint-development effort between Fanuc and Cincinnati Milacron came out about two years later. The Nissei and Toyo machines used a system of ballscrews, gears, clutches, and brakes to transmit power from one central AC servo motor to the injection and clamping functions. the Milacron/Fanuc ACT line featured four servomotors, one each for screw rotation, injection stroke, clamp, and ejector, all coordinated by a CNC controller. The machines could hold clamp-position repeatability to within 0.001 in., and could attain a standard deviation in part weight over 50 cycles of only 0.00693%. The low operating noise level of 58 to 75 dBA and lack of oil suited it to cleanroom applications.
Machine sizes rose to around 300 tons in 1985 on the heels of increases in available servo-motor sizes. Since then, maximum press size has grown to 3300 tons with the latest model from Ube. Over the last 15 years at least 11 OEMs entered the market with some form of an electric press.
Very few readers of this issue can remember, or even imagine, what it was like when an injection mol...