Injection Molding Machine
A servo-hydraulic injection molding machine drives the hydraulic pump with a servo motor instead of a fixed-speed asynchronous motor. The pump turns only when movement is needed and only as much as needed; in the waiting and cooling phases it almost stops. As a result it provides 30–60% energy savings compared with a conventional hydraulic machine; compared with an all-electric machine its investment cost is lower and its hydraulic force density higher.
In a conventional hydraulic machine the pump turns continuously throughout the cycle, and the surplus oil returns through the relief valve and turns into heat. A servo drive eliminates this relief loss: because the cooling phase makes up more than half of the cycle, the gain is large.
As an intermediate class, "hybrid" machines make the injection unit electric and the clamping unit hydraulic; this is a sensible balance if the precision and speed requirements are on the injection side.
The number of shifts and the part precision decide. In single-shift general production a servo-hydraulic investment pays back faster; in medical, optical and clean room applications the repeatability and oil-free operation of an all-electric machine come to the fore.