Having preached the gospel of all-electric injection molding machines for more than a decade, we are always surprised to find people still discovering the energy efficiency of these machines, as explained in your Sept. 25 story about tests by Southern California Edison (``Tests show efficiency of all-electric press," Page 21).
Yes, the savings are big, and they´re going to get bigger as the shock of utility deregulation rolls across the country. Molders who have enjoyed low-rates from state-subsidized utilities will see their bottom lines under pressure in the new free-market of supply/demand-driven rates.
A couple of comments in the article need to be clarified. Near the end of story, the SCE engineer seems to question whether servomotors can handle cycle fluctuations for 15 years. In 15-plus years of supporting thousands of all-electric presses, Milacron has replaced approximately 2 percent of the servomotors it has sent to the field.
The engineer also says changing of an electric motor "may turn out to be just the same as changing a valve or actuator in a hydraulic machine." Fortunately, it´s not. The change-out of an electric motor is pretty much a plug-and-play operation, plus there´s no hydraulic oil to deal with.
Energy savings are a big and important part of the story, but the story that goes untold is that most molders don´t buy these machines for energy savings. The principal driver is closer to a molder´s heart: more good parts, for a lower cost, at the end of the day. It´s one of the few ways molders can re-capture some of the profit lost in cost give-backs being demanded by original equipment manufactures in many industries, especially automotive.
How do you get more good parts? Here´s just one reason: the electric machine´s precision injection control eliminates wasteful overpacking. This means:
* Better parts can be molded on smaller machines. Flash-prone molds are often run in machines larger than really needed because higher clamp tonnage is the only way to stop the flash that occurs when a hydraulic machine overpacks a mold to counteract screw drift. The need to control flash with higher clamp tonnage is eliminated, allowing the mold to run in a smaller machine.
* Profit lost because of overpacking — "giving away" excess material in the part — are recovered. The smallest acceptable shot weight for a part can be delivered consistently and repeatably, allowing a molder to run up to the threshold of a short shot, without crossing the threshold. Again, material savings go straight to the molder´s bottom line.
* Optical parts — sensitive to the molded-in stress caused by overpacking — run better on electric machines, and usually a smaller machine, too.
There´s much more to electric machines than energy savings, but the rate increases of the deregulated utility environment will, no doubt, make this a primary issue for the foreseeable future.